<%BANNER%>

Processable Variable Band Gap Conjugated Polymers for Optoelectronic Devices

HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Experimental
 Wide band gap bis-heterocycle-phenylene...
 Narrow band-gap cyanovinylene...
 Polypropylenedioxythiophene...
 Summary
 Appendix A: Crystallographic information...
 Appendix B: Gel permeation chromatograms...
 References
 Biographical sketch
 

PAGE 1

1 PROCESSABLE VARIABLE BAND GA P CONJUGATED POLYMERS FOR OPTOELECTRONIC DEVICES By EMILIE M. GALAND A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2006

PAGE 2

2 Copyright 2006 by Emilie M. Galand

PAGE 3

3 ACKNOWLEDGMENTS Going away from home for such a long time to pursue my Ph.D. studies was the most difficult decision I ever had to make, and I w ould never have been able to go through this adventure without my parents’ support. I was also lucky to share every step of this experience with Thomas Joncheray, who carried out his Ph .D. in polymer chemistry at the same time. Of course this learning experi ence would not have been so ri ch without the guidance of my research advisor Prof. John R. Reynolds. He handled the research group as a businessman, educating us very well for our fu ture industrial careers. I am very grateful for the time he put in reviewing my publications, oral presentations, career launch, and disserta tion, and also for his consideration for my well being. I would like also to acknowledge all the people I collaborated with, and who helped enrich the work presented in this dissertation: Dr. Kh alil Abboud for solving X -ray crystal structures, Dr. Tracy McCarley for performing MALDI analys es, Dr. Jeremiah Mwaura for his work on light-emitting diodes, Dr. Young-Gi Kim for his work on solar cells, Dr. Avni Argun for his studies on charge transport, and Prof. Yang Yang and Dr. Vish al Shrotriya from UCLA for performing comparative photovoltaic studies. Thanks go also to the administrative staff, Sara Klossner, Tasha Simmons, Lorraine Williams a nd Gena Borrero, and to the members of my committee: Prof. Kenneth B. Wagener, Prof. Randolph S. Duran, Prof. Paul H. Holloway and Prof. Ronald K. Castellano. A special thank you goes to my labmates Dr. Barry Thompson, Dr. John Sworen, Dr. Florence Courchay, James Leonard, Dr. Christia n Nielsen, Trish Hooper, Kate Opper, Nihan Cetinbas, and Pingjie Shi for making our lab such a nice place to work. I specifically want to express my gratitude to Barry and John who taught me a lot about labora tory techniques. John made me crazy with his music but I forgive him because his dancing moves always cheered me

PAGE 4

4 up! Thanks go also to my hood neighbors Flo and James for being my coffee break companions and for making me feel less lonely in front of my columns. A lot of people spent a couple of hours of their precious time to train me on certain techniques. For that I would like to show my appreciation to Ga rett Oakley and Genay Jones for helping me with the GPC measurements, Erik Be rda and Piotr Matloka for training me on the differential scanning calorimetry and thermo grav imetric analysis instruments, James Leonard for familiarizing me with the unf riendly X-ray software, and Chri stophe Grenier for helping me with the stubborn computers and printers. The Butler laboratory was the best environment for living a truly “team experience.” I want to th ank all the members for their contribution to scientific discussions, for being so helpful, and for making this experience so enjoyable. Thanks go also to the French mafia, R oxane Fabre, Thomas Joncheray, Florence Courchay, Sophie Bernard, Rachid Matmour, Chri stophe Grenier, Benoit Lauly, Sophie Klein, for their friendship and the get-togethers, wh ich always helped me feel close to home. Thanks go finally to my Florida tennis team who helped me stay in shape and healthy during that tough time!

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................3 LIST OF TABLES................................................................................................................. ..........8 LIST OF FIGURES................................................................................................................ .........9 ABSTRACT....................................................................................................................... ............14 CHAPTER 1 INTRODUCTION................................................................................................................. .16 1.1 Conjugated Polymers........................................................................................................ 16 1.1.1 Brief History...........................................................................................................1 6 1.1.2 Conjugated Polymers Electronic Properties...........................................................17 1.2 Band Gap Engineering......................................................................................................2 0 1.3 Polymerization of Thiophene Based Molecules...............................................................24 1.3.1 Oxidative Polymerizations.....................................................................................24 1.3.2 Metal Mediated Polymerizations............................................................................26 1.3.3 Solid State Polymerization.....................................................................................27 1.3.4 Knoevenagel Polymerization..................................................................................29 1.4 3,4-Alkylenedioxythiophene Based Polymers from Thiophene to EDOT to ProDOT...30 1.5 Applications............................................................................................................... .......33 1.6 Study Overview............................................................................................................. ...36 2 EXPERIMENTAL................................................................................................................. .39 2.1 General Synthetic Methods...............................................................................................39 2.2 Electrochemical Methods.................................................................................................41 2.2.1 Introduction............................................................................................................4 1 2.2.2 Electrochemical Set-Up..........................................................................................41 2.2.3 CV/DPV.................................................................................................................42 2.3 Optical and Spectroscopic Methods.................................................................................45 2.3.1 Absorption Spectra and Molar Absorptivities........................................................45 2.3.2 Solvatochromism/Thermochromism......................................................................46 2.3.3 Photoluminescence Spectra and Fl uorescence Quantum Efficiencies...................47 2.3.4 Spectroelectrochemistry.........................................................................................49 2.3.5 Colorimetry.............................................................................................................4 9 3 WIDE BAND GAP BIS-HETER OCYCLE-PHENYLENE POLYMERS............................52 3.1 Introduction............................................................................................................... ........52 3.2 Monomer Syntheses and Characterizations......................................................................54 3.2.1 Bis-thiophene-dialkoxybenzenes............................................................................55

PAGE 6

6 3.2.2 Bis-EDOT-dialkoxybenzenes.................................................................................57 3.2.3 Bis-ProDOT-dialkoxybenzenes..............................................................................60 3.3 Polymer Syntheses and Characterizations........................................................................62 3.3.1 Polymerization Attempts via GriM........................................................................62 3.3.2 Polymerization via Yamamoto Coupling...............................................................67 3.3.2.1 Poly(bis-thiophene-dialkoxybenzene)s........................................................67 3.3.2.2 Poly(bis-alkylenedioxythi ophene-dialkoxybenzene)s..................................70 3.3.3 Solid State Polymerization Attempts......................................................................71 3.3.4 Electropolymerization............................................................................................73 3.3.5 Oxidative Polymerization via Ferric Chloride.......................................................74 3.4 Polymer Electrochemistry and Spectroelectrochemistry..................................................78 3.4.1 PBT-B(OR)2...........................................................................................................78 3.4.2 PBProDOT-R2-B(OC12H25)2..................................................................................80 3.5 Colorimetry................................................................................................................ .......86 3.5.1 PBT-B(OR)2...........................................................................................................86 3.5.2 PBProDOT-R2-B(OC12H25)2..................................................................................87 3.6 Solvatochromism, Thermochromism, and Ionochromism...............................................88 3.7 Application to Devices..................................................................................................... 90 3.7.1 Photovoltaic Devices..............................................................................................90 3.7.1.1 PBT-B(OR)2.................................................................................................90 3.7.1.2 PBProDOT-Hex2-B(OC12H25)2....................................................................92 3.7.2 LEDs..................................................................................................................... ..93 3.8 Conclusions and Perspective............................................................................................95 3.9 Experimental............................................................................................................... ......97 4 NARROW BAND-GAP CY ANOVINYLENE POLYMERS.............................................111 4.1 Introduction............................................................................................................... ......111 4.2 Monomer and Polymer Synthesis and Characterization.................................................114 4.3 Ordering Properties........................................................................................................ .122 4.4 Polymer Electrochemistry and Spectroelectrochemistry................................................126 4.5 Colorimetry................................................................................................................ .....132 4.6 Application in Devices...................................................................................................13 3 4.6.1 Polymer Light-Emitting Diodes...........................................................................133 4.6.2 Photovoltaic Devices............................................................................................134 4.7 Summary and Perspective...............................................................................................137 4.8 Experimental............................................................................................................... ....138 5 POLYPROPYLENEDIOXYTHIOP HENE POLYELECTROLYTES................................150 5.1 Introduction............................................................................................................... ......150 5.2 Monomer Synthesis and Characterization......................................................................152 5.3 Polymer Synthesis and Characterization........................................................................153 5.4 Polymer Spectroelectrochemistry and Electrochemistry................................................161 5.6 Quaternization of the Amino-substituted PProDOTs.....................................................165 5.7 Summary and Perspective...............................................................................................168 5.8 Experimental............................................................................................................... ....170

PAGE 7

7 6 SUMMARY...................................................................................................................... ....174 APPENDIX A CRYSTALLOGRAPHIC INFORM ATION FOR COMPOUNDS.....................................177 B GEL PERMEATION CHROMA TOGRAMS OF POLYMERS.........................................183 LIST OF REFERENCES............................................................................................................. 186 BIOGRAPHICAL SKETCH.......................................................................................................196

PAGE 8

8 LIST OF TABLES Table page 3-1 GPC estimated molecular weights of the PBT-B(OR)2 polymers (polystyrene standards, THF as mobile phase, 40C).............................................................................68 3-2 Electrochemical results for BProDOT-R2-B(OC12H25)2 monomers and polymers...........82 3-3 Summarized photovoltaic ch aracteristics of PBT-B(OR)2/PCBM based solar cells.........92 4-1 GPC estimated molecular weights of the ProDOT:cyanovinylene polymers (polystyrene standards, TH F as mobile phase) and yi elds of the Knoevenagel polymerizations................................................................................................................ 116 4-2 Summary of thin-film polymer electroch emistry, and HOMO and LUMO energies of the ProDOT:cyanovinylene polymers derive d from the electrochemical results............128 4-3 Colorimetric results for the neutral and oxidized ProDOT:cyanovinylene polymers.....132 4-4 Summarized characteristics of Pro DOT:cyanovinylene polymer/PCBM based solar cells.......................................................................................................................... ........137 5-1 Solubility of ionic amino-substitute d PProDOTs in various solvents at room temperature.................................................................................................................... ..166 A-1 Crystal data and stru cture refinement for Br2-BT-B(OC7H15)2.......................................177 A-2 Crystal data and stru cture refinement for Br2-BEDOT-B(OC7H15)2...............................178 A-3 Crystal data and stru cture refinement for Br2-BEDOT-B(OC12H25)2..............................180 A-4 Crystal data and structur e refinement for BProDOT-Me2-B(OC12H25)2.........................181

PAGE 9

9 LIST OF FIGURES Figure page 1-1 Energetic representations of polyacetylene and poly( para -phenylene).............................18 1-2 Positively charged defects on poly( para -phenylene)........................................................19 1-3 Poly( para -phenylene) and evolution of energy levels with p-doping...............................19 1-4 Illustration of the formation of two charged solitons on a chain of trans polyacetylene.................................................................................................................. ...20 1-5 Aromatic and quinoid stat es of polyisonaphthalene..........................................................22 1-6 Illustration of the donor (D) acceptor (A) concept..........................................................22 1-7 Polymer band structures and optical ba nd gaps of the dioxythiophene-cyanovinylene polymer family................................................................................................................. ..23 1-8 GriM polymerization of disubstituted PProDOTs.............................................................26 1-9 Mechanism of aryl (Ar) polymerization via Yamamoto coupling and of the polymer chain degradation/termination oc curring during the polymerization.................................28 1-10 Mechanism of the solid stat e polymerization of DBEDOT...............................................28 1-11 Illustration of the Knoe venagel condensation steps...........................................................29 1-12 Effect of increasing donor strength in a donor-acceptor-donor configuration..................31 1-13 Synthesis of poly(3,4-propylen edioxythiophene-dihexyl)-cyanop phenylenevinylene.............................................................................................................3 3 2-1 Charge transport by hopping in pol ymer adsorbed to the electrode..................................43 2-2 Differential pulse waveform..............................................................................................44 2-3 Example of the procedure used to main tain a constant polymer concentration in flasks containing varying amount s of good and poor solvents..........................................48 2-4 CIE 1931 xy chromaticity diagram....................................................................................51 3-1 Targeted thienylene-phenylene polymers..........................................................................55 3-2 Bis-thiophene-dialkoxybe nzene monomer synthesis.........................................................56 3-3 Single crystals X-ray analysis of Br2-BT-B(OC7H13)2......................................................57

PAGE 10

10 3-4 Bis-EDOT-dialkoxybenzene monomer synthesis..............................................................59 3-5 Single crystals X-ray analysis of Br2-BEDOT-B(OC7H13)2..............................................62 3-6 Single crystals X-ray analysis of Br2-BEDOT-B(OC12H25)2.............................................63 3-7 Synthesis of methylan d hexyl-substituted ProDOTs.......................................................64 3-8 Synthesis of BProDOT-R2-dialkoxyphenylene and Br2-BProDOT-R2dialkoxyphenylene monomers...........................................................................................64 3-9 Single crystals X-ray analysis of BProDOT-Me2-B(OC12H25)2........................................65 3-10 Structure of LPEB......................................................................................................... .....65 3-11 GriM route for the polymerization of th e dibromo-thienylene-phenylene monomers......66 3-12 Polymerization of Br2-BT-B(OR)2 monomers via Yamamoto coupling...........................67 3-13 MALDI-MS of BT-B(OR)2 polymers...............................................................................69 3-14 Solution UV-Vis absorbance of Br2-BT-B(OR)2 monomers, and PBT-B(OR)2 polymers in toluene............................................................................................................ 69 3-15 DSC thermograms (second scans) of PBT-B(OR)2 polymers...........................................71 3-16 Thermogravimetric analysis of the PBT-B(OR)2 polymers...............................................72 3-17 Attempt in the solid state polymerization of Br2-BEDOT-B(OC7H15)2.............................73 3-18 Crystal packing of Br2-BEDOT-B(OC7H15)2 illustrating the inte rmolecular distances between bromine atoms.....................................................................................................73 3-19 Repeated potential scanning el ectropolymerization of BProDOT-R2-B(OC12H25)2 monomers....................................................................................................................... ....75 3-20 1H-NMR spectra.................................................................................................................7 7 3-21 Absorption spectra for molecular weight fractions of PBProDOT-Hex2-B(OC12H25)2.....78 3-22 Thermogravimetric analysis of the PBProDOT-Hex2-B(OC12H25)2 in a nitrogen atmosphere..................................................................................................................... ....78 3-23 PBT-B(OR)2 cyclic voltammetry.......................................................................................79 3-24 Spectroelectrochemical analysis of PBT-B(OC7H15)2 spray-cast onto ITO coated glass.......................................................................................................................... ..........82

PAGE 11

11 3-25 Spectroelectrochemical analysis of PBT-B(OC12H25)2 spray-cast onto ITO coated glass.......................................................................................................................... ..........83 3-26 PBProDOT-R2-B(OC12H25)2 cyclic voltammograms........................................................83 3-27 Cyclic voltammograms of PBProDOT-Hex2-B(OC12H25)2 as function of scan rate.........84 3-28 Spectroelectrochemical analysis of PBProDOT-Hex2-B(OC12H25)2 spray-cast onto ITO coated glass............................................................................................................... .85 3-29 Spectroelectrochemical analysis of PBProDOT-Me2-B(OC12H25)2 electropolymerized on ITO coated glass...........................................................................................................8 6 3-30 CIE 1931 xy chromaticity diagrams of PBT-B(OR)2 polymers.........................................87 3-31 CIE 1931 xy chromaticity diagram of a thin-film of PBProDOT-Hex2-B(OC12H25)2.......89 3-32 Thermochromic changes observed for a 0.1 M TBAP in CH2Cl2/ACN solution of the BProDOT-Me2-B(OC12H25)2 monomers...........................................................................89 3-33 UV-vis absorption sp ectra of PBProDOT-Hex2-B(OC12H25)2 in toluene/methanol mixtures....................................................................................................................... .......91 3-34 Photovoltaic results of solar cells ma de of a 1/4 blend (w/w) of PBT-B(OR)2/PCBM.....92 3-35 Current voltage characteristic of a so lar cell made of a 1/4 blend (w/w) of PBProDOT-Hex2-B(OC12H25)2 /PCBM under AM1.5 conditions (100 mW cm-2)...........93 3-36 Photoluminescence emission spectrum of PBProDOT-Hex2-B(OC12H25)2 in toluene solution and in thin-film (bold line) superimposed with electroluminescence spectrum of an EL device with the following configuration: ITO/PEDOTPSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al.......................................................................94 3-37 LED properties of an ITO/PEDOT-PSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al device......................................................................................................................... ........95 4-1 Family of ProDOT:cyanovinylene poly mers synthesized via the Knoevenagel methodology.................................................................................................................... 113 4-2 Synthesis of the phenylene-dia cetonitrile acceptor monomers........................................115 4-3 Synthesis of the ProDOT-dialdehyde monomers............................................................115 4-4 Synthesis of the ProDOT:cyanovinylene family of polymers via Knoevenagel polymerization................................................................................................................. 116 4-5 IR spectra of ProDOT:cyanovinylene polymers..............................................................117 4-6 MALDI-MS of ProDOT:cyanovinylene polymers..........................................................118

PAGE 12

12 4-7 Absorption spectra for molecular wei ght fractions of the ProDOT:cyanovinylene polymers....................................................................................................................... ....120 4-8 Thermogravimetric analysis of the ProDOT:cyanovinylene polymers...........................121 4-9 Solution UV-Vis absorbance and photol uminescence of ProDOT:cyanovinylene polymers in toluene..........................................................................................................12 3 4-10 Thermochromic behavior of PProDOT-OHex2:CNPV-DDO in 1,2-dichlorobenzene....123 4-11 DSC curves of ProDOT:cyanovinylene polymers...........................................................125 4-12 Cyclic voltammetry of ProDOT-cyanovinylene polymers..............................................127 4-13 Differential pulse voltammetry of ProDOT-cyanovinylene polymers............................128 4-14 Oxidative spectroelectrochemistry of ProDOT:cyanovinylene polymers.......................130 4-15 Reductive spectroelectrochemistry of ProDOT:cyanovinylene polymers.......................131 4-16 Relative luminance (%) as a function of applied potential for every ProDOT:cyanovinylene polymer.....................................................................................133 4-17 Normalized photoluminescence em ission spectrum of PProDOT-OHex2:CNPVMEH in thin-film (solid line) superimposed with normalized electroluminescence spectrum and accompanying photograph of an ITO/PEDOT-PSS/PProDOTOHex2:CNPV-MEH/Ca/Al device (dotted line)..............................................................134 4-18 LED properties of an ITO/PEDOT-PSS/PProDOT-OHex2:CNPV-MEH/Ca/Al device......................................................................................................................... ......135 4-19 Photovoltaic results for a device ma de of a 1/4 blend (w/w) of PProDOTOHex2:CNPV-MEH/PCBM............................................................................................136 5-1 Structures of investigated amino-functionalized PProDOTs...........................................152 5-2 Synthesis of amino-substituted ProDOT monomers and polymers.................................153 5-3 1H-NMR spectra...............................................................................................................155 5-4 MALDI-MS of PProDOT-NMe2.....................................................................................158 5-5 MALDI MS of PProDOT-NIsop2....................................................................................158 5-7 Thermogravimetric analysis of the am ino-functionalized PProDOTs in a nitrogen atmosphere..................................................................................................................... ..159 5-8 UV-vis absorption and photoluminescence spectra of neutral amino-functionalized PProDOTs....................................................................................................................... .160

PAGE 13

13 5-9 Spectroelectrochemisty of thin-films of the neutral amino-functionalized PProDOTs...163 5-10 Differential pulse voltammetry of amino-substituted PProDOTs...................................163 5-11 Relative luminance (%) versus applied pot ential for amino-substituted PProDOTs......164 5-12 CIE 1931 xy chromaticity diagram of amino-substituted PProDOTs..............................165 5-13 Quaternization of amino-s ubstituted PProDOTs using MeI............................................166 5-14 Solution spectroscopy for PProDOT-NMe3 +...................................................................168 5-15 Solution spectroscopy for PProDOT-NMe(Isop)2 +.........................................................169 A-1 Numbering system for Br2-BT-B(OC7H15)2 crystal structure..........................................177 A-2 Numbering system for Br2-BEDOT-B(OC7H15)2 crystal structure..................................178 A-3 Numbering system for Br2-BEDOT-B(OC12H25)2 crystal structure................................179 A-4 Numbering system for BProDOT-Me2-B(OC12H25)2 crystal structure............................181 B-1 Gel permeation chromatogram of PBProDOT-Hex2-B(OC12H25)2.................................183

PAGE 14

14 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PROCESSABLE VARIABLE BAND GA P CONJUGATED POLYMERS FOR OPTOELECTRONIC DEVICES By Emilie M. Galand December 2006 Chair: John. R. Reynolds Major Department: Chemistry Solution processable variable band gap thienylene-based conj ugated polymers were designed for application in vari ous optoelectronic devices. Th e synthesis of wide band gap regiosymmetric thiophene-dialkoxybenzene and 3,4-ethylenedioxyth ienyl-dialkoxybenzene polymers was investigated, and organo-solubl e isoregic poly(1,4-bi s(2-thienyl)-2,5-dialkoxybenzenes) (PBT-B(OR)2) were successfully synthesized via Yamamoto coupling, with estimated number average molecular weights ranging from 3,000 to 5,000 g mol-1, and a solubility of about 7 mg mL-1 in toluene. 1,4-Bis[2-(3,3-dialkyl -(3,4-propylenedi oxy)thienyl]-2,5didodecyloxybenzene derivatives, [BProDOT-R2-B(OC12H25)2)], were prepared by Negishi coupling of the ProDOT and didodecyloxybenzene units in ca. 40% yields. They were efficiently electropolymerized to form electroactive films e xhibiting redox switching at fairly low potentials ( +0.1 V vs. Fc/Fc+). BProDOT-Hex2-B(OC12H25)2 was polymerized via ferric chloride chemical oxidation with an estimated numb er average molecular weight of 14,600 g mol-1. A solubility of 15 mg mL-1 in chloroform was reached, which is attributed to the ProDOT hexyl substituents. Four analogues of the narrow band-gap pol y(3,4-propylenedioxythi ophene-dialkyl)-cyanop -phenylene vinylene (PProDOT-R2:CNPPV) polymer family have been synthesized via

PAGE 15

15 Knoevenagel condensation with number averag e molecular weights ranging between 9,000 and 24,000 g mol-1. Linear and branched alkoxy substituents were introduced along the polymer backbone yielding organo-sol uble materials (15 mg mL-1 in chloroform) with improved film quality and variable optical properties. Conjugated polyelectrolytes were successfully synthesized from the ferric chloride oxidative polymerization of amino-substitute d ProDOTs, followed by post-polymerization quaternization of the amino substituents. These ma terials, well solvated in DMSO, are presently the most fluorescent red-shifted polyelectrolytes ever reported. The optical, redox, and electronic proper ties of the polymers were studied by electrochemical and spectroscopic methods. Owing to their solubility pr operties, the polymers could be processed into homogeneous thin-films by spin-coating or spray-casting, and applied to light-emitting diodes and photovoltaic devices. Part icularly when used as electron donors in tandem with the electron acceptor [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) in bulk heterojunction photovoltaic devices, PBT-B(OR)2 polymers exhibited power conversion efficiencies up to ~0.6%. PBProDOT-Hex2-B(OC12H25)2 cathodically switched between orange and highly transmissive gray colors, and the PProDOT-R2:CNPPV polymers switched between neutral blue/purple states and tr ansmissive gray oxidized and re duced states, which makes them attractive for large area electrochromic displays.

PAGE 16

16 CHAPTER 1 INTRODUCTION 1.1 Conjugated Polymers 1.1.1 Brief History Although semiconducting conjugated polymers have been known for ab out 30 years (with the discovery in 1977 by MacDiarmid, Shirakawa, and Heeger, that chemical doping of these materials resulted in increases in electronic conductivity over several orders of magnitude1,2), it was only in the early 90s that many developments started to grow both on the fundamental and on the manufacturing levels. In particular, the discovery of light-emitting polymers in 1990, by Richard Friend3 and his group, in the Cavendish Laborat ory at Cambridge University, was a major turning point in the rise of organic elec tronics. Polymeric materi als have the advantage that they are much more easily processed than metals. For instance, they can cover large and flexible surfaces and can be processed from solutions into complex architectures, using techniques such as spin-coating or spray-casti ng. Most plastics can be deformed reversibly, which is not true for metals. Also the syntheti c flexibility of polymers allows easy tailoring of their physical, electronic, and optical properties. All these parameters are the reasons that have motivated the development of syntheses and processing methods of conjugated polymer materials with unique properties, with the goal of applying them in light-emitting diodes, fieldeffect transistors, photovoltaic cells, and electr ochromics. Serious problems such as oxidative stability and device lifetimes have to be ove rcome for further development in commercial applications, but we may predict that one day, we will all go camping, carrying our flexible LED display with us, surfing the net and watching th e TV solar-powered by polymeric materials.

PAGE 17

17 1.1.2 Conjugated Polymers Electronic Properties The simplest possible form of conjugated polymer is of course polyacetylene (CH)n whose structure constitutes the core of all conjugated polymers having a conjugated backbone of carbon atoms. The essential structural characteristic of all conjugated polymers is their quasi-infinite system, with the electrons that constitute the -bonds being delocalized over a large number of recurring monomer units. This feat ure results in materials with directional conduc tivity, strongest along the axis of the chain. In pol yacetylene (PA), delocalization re sults in two-fold degeneracy in the ground state as illustrated in Figure 1-1a. In aromatic polymers, such as poly( para phenylene) (PPP), the alternating single and double bonds lead to electronic structures of varying energy levels (non-degenerate ground state) (Figure 1-1b).4 In a polymer, just as in a crystal, the interaction of a polymer unit cell with all its ne ighbors leads to the formation of electronic bands, the highest occupied electronic levels consti tute the HOMO or valence band (VB), and the lowest unoccupied electronic le vels constitute th e LUMO, or conduction band (CB). It is important to note that the -system of conjugated polymers is not a strand of atoms with equivalent bond distances betw een any two neighbouring atoms, as predicted by the Hckel theory (this would give propertie s of a metal). This simple pict ure is incorrect because of the Peierls-instability of one-dimensional systems.4-6 Peierls showed that, due to the coupling between electronic and elastic properties, the poly mer develops a structural distortion such as to open a gap in the electronic excitation spectrum. So, conjugated polymers exhibit a band gap due to the Peierls distortion, and they are referred to as semiconductors7 if their band gap values are below 3 or 4 eV (at higher values, they are insulators). By definition, the band gap is the difference between the VB and the CB. It is equa l to the lowest excita tion energy, which can be obtained from the onset value at the low en ergy edge of the optic al absorption spectra.

PAGE 18

18 a EnergyEnergetically equivalent forms of PA EnergyEnergetically equivalent forms of PAb Non-equivalent benzenoidand quinoidforms of PPP Energy Non-equivalent benzenoidand quinoidforms of PPP Energy Figure 1-1. Energetic representati ons of polyacetylene and poly( para -phenylene). (a) degenerate PA and (b) non-degenerate PPP. [Modified from Moliton, A.; Hiorns, R. C. Polym. Int. 2004 53 1397-1412].4 Being semiconductors with fairly large band gaps, conjugated polymer s do not conduct to a significant extent unless charged carriers ar e created within the conjugated framework8 (PPP reaches a conductivity of 500 -1 cm-1 when doped with charged carriers, whereas undoped PPP has a conductivity on the order of 10-13 -1 cm-1).4 The charge carriers, either positive (p-type) or negative (n-type), are the products of oxidizi ng or reducing the polymer respectively. This phenomenon is always accompanied with structural changes localized over a couple of rings (4 to 5 rings for PPP)9 and this gives rise to new electronic st ates within the band gap. J. L. Brdas and G. B Street have published a chemist-accessible explanation of these concepts.10 For the aromatic conjugated polymers, the entity consisting of charge and spin (radical cation or anion) along with an associated geometry distortion is known as a polaron as illustrated in Figure 1-2a. The charge and radical form a bound species, sin ce any increase in the distance between them would necessitate the creation of additional higher energy quinoid units. Upon removal of a second electron, either a separate polaron may form or, if the second electron is removed from the same site as the first, a bipolaron (Fi gure 1-2b). As the doping level increases, polaron and bipolaron states overlap and form bands, which will, at some point, merge with valence and conduction bands, as illustrated fo r the p-doping of PPP in Figure 1-3.

PAGE 19

19 a b polaron bipolaron Figure 1-2. Positively charged defects on poly( para -phenylene). (a) polaron, (b) bipolaron. CB VB Neutral state 1 charged default (polaron) 2 charged defaults (bipolaron) Bipolaron bands Heavily dopedp-doping CB VB Neutral state 1 charged default (polaron) 2 charged defaults (bipolaron) Bipolaron bands Heavily dopedp-doping Figure 1-3. Poly( para -phenylene) and evolution of energy levels with p-doping. [Modified from Moliton, A.; Hiorns, R. C. Polym. Int. 2004 53 1397-1412].4 In PA, the charges which appear upon doping are called solitons. They are termed differently because the charges can propagate al ong the chain without an increase in distortion energy and can readily separate since the geometri c structures that appear on each side of the charges are degenerate in energy (Figure 1-4). Doping dramatically alters the optical spectra of conjugated polymers, with optical transitions occurring between the VB and polaron states, and between polaron states. These tran sitions have lower energies th an interband transitions and a number of colored low band gap conjugate d polymers become transparent upon doping. It is important to note that since the charged defect is simply a boundary between two moieties of equal energy, it can mi grate in either dir ection without affecti ng the energy of the backbone, provided that there is no significant ener gy barrier to the process. It is this charge carrier mobility that leads to the high conductivity of these polymers, the conductivity ( ) of a

PAGE 20

20 conducting polymer being related to the number of charge carriers (n) and their mobility ( ). A major challenge is to raise the carrier mobility and the conductivity, which are currently limited by the defects in the polymers. When cast from solution as thin-films, the polymers remain largely a tangle of spaghetti-like strands. Tran sport along the ideal linear chain can proceed no farther than the length of the fu lly extended chain; then the char ge must hop to another chain. With improved ordering of the polymer chains however, the conductivity could reach those of even the best metals. -2e Figure 1-4. Illustration of the formation of two charged solitons on a chain of trans polyacetylene. [Modified from Chance, R. R.; Brdas, J. L.; Silbey, R. Physical Review B 1984 29 4491-4495].9 1.2 Band Gap Engineering The role of conjugated polymers in emerging el ectronic and display te chnologies is rapidly expanding, and with it, the need of a variety of polymers with different emissive or absorptive colors, electron or hole affinities, conducti vities, and many other properties. Band gap engineering is extensively exploited nowadays fo r these reasons. It allows varying the optical and electronic properties of a polymer by simple manipulation of the ch emical building blocks and the manner in which they are connected. In particular, five parameters influencing the band gaps were established: bond-le ngth alternation, resonance en ergy, deviation from planarity, inductive effects of the substituents, and interchain coupling in the solid state.11 Working around

PAGE 21

21 these parameters, researchers have developed various families of conjugated polymers with different band gaps, which are typi cally classified as low band gap12 or narrow band gap materials when Eg is less than ca. 1.80 eV, and as wide band gap materials for Eg > 1.80 eV [recall E (eV) = 1240/ (nm)]. A description and examples of the way these parameters influence the band gaps are given below as they help in understanding the work presented in this dissertation. As we discussed before for PA, bond-length alternation is the result of the Peierls effect and is responsible for the non-metallic behavior of neutral PA due to the existence of a band gap. Minimizing the bond-length altern ation along a conjugated polymer backbone is consequently an important way to reduce the band gap. In aromatic polymers, the benzenoid structure will prevail over the energetically unfavorable quinoid structure, which results in the existence of what are essentially single bonds between the arom atic rings and henc e a large bond-length alternation.11,13 Making the quinoidal struct ure more favorable will help increasing the doublebond character of the linkages between aromatic rings and reduce the band gap.14 For instance, polyisonaphthalene repres ented in Figure 1-5 (Eg = 1 eV) loses the aroma ticity of the thiophene ring when going from the aroma tic to the quinoid form, but at the same time its phenylene ring gains aromaticity, which minimizes the overall ar omaticity loss and increases the contribution of the quinoid form to the polymer structure compared to polythiophene (Eg = 2 eV).15 The donor-acceptor approach has also been part icularly developed as a means of reducing bond-length alternation for the building of narrow band gap polymers.13,16 In that concept, the strong interaction between an electron donor a nd an electron acceptor increases the double bond character between aromatic ri ngs, and the high-lying HOMO of the donor fragment combined with the low-lying LUMO of the acceptor gives ri se to a D-A monomer with an unusually small

PAGE 22

22 HOMO-LUMO separation and to a narrow band-gap upon polymer ization (Figure 1-6). By carefully selecting the struct ures of the donors and acceptors and their respective electron donating and withdrawing strengths it is possible to manipulate the magnitude of that band gap.17 As an example, by simply varying the donor strength in the dioxythiophene-cyanovinylene polymer family, Thompson et al. gained access to a variety of band gaps as illustrated in Figure 1-7 [recall: EDOT > propylenedioxythiophene (ProDOT) > thiophene for electron donating power].18 S S n aromatic quinoid n Figure 1-5. Aromatic and quinoid states of po lyisonaphthalene. The six-membered ring of polyisothianaphthalene gains aromaticity when the molecule goes from the aromatic to the quinoid state, resulting in a higher contribution of the quinoidal state compared to polythiophene. EnergyHOMO LUMO LUMO HOMO DD-AA Reduced band gap EnergyHOMO LUMO LUMO HOMO DD-AA EnergyHOMO LUMO LUMO HOMO DD-AA Reduced band gap Figure 1-6. Illustration of the donor (D) acceptor (A) concept. [Modified from van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Havinga, E. E.; Meijer, E. W. Mater. Sci. Eng. 2001 32 1-40].13 Hybridization of the high-lying HOMO of the donor fragment and the low-lying LUMO of the acceptor fragme nt yields a D-A unit with an unusually small HOMO-LUMO separation. Deviation from planarity due to unfavorable intramolecular interactions and interchain interactions will reduce orbital overlap, decrease the stacking and affect the band gap as

PAGE 23

23 well.8,19,20 Let us take the example of the polyth iophene family: polyt hiophene is highly crystalline and completely insoluble, but as alkyl chains are introduced at the 3and 4positions of the thiophene ring for solubility purposes, th e steric interactions between adjacent rings generate twisting of the backbone, destroyi ng the conjugation and widening the band gap.21 6.2 eV 5.9 eV 5.8 eV 5.4 eV5.4 eV 3.5 eV 3.6 eV 3.4 eV 3.5 eV 3.8 eV 3.5 eV Vacuum (0 eV)S NC CN C12H25 O n O C12H25H25C12S NC C12H25 S CN nS NC CN O O n O C12H25H25C12O Hex Hex S NC CN O O O C12H25H25C12O Hex Hex S O O Hex Hex nS NC O O Hex Hex S O O Hex Hex n S O O S O O NC CN n Eg5.0 eV 2.1 eV 2.7 eV 2.3 eV 2.0 eV 1.8 eV 1.5 eV 6.2 eV 5.9 eV 5.8 eV 5.4 eV5.4 eV 3.5 eV 3.6 eV 3.4 eV 3.5 eV 3.8 eV 3.5 eV Vacuum (0 eV)S NC CN C12H25 O n O C12H25H25C12S NC C12H25 S CN nS NC CN O O n O C12H25H25C12O Hex Hex S NC CN O O O C12H25H25C12O Hex Hex S O O Hex Hex nS NC O O Hex Hex S O O Hex Hex n S O O S O O NC CN n Eg5.0 eV 2.1 eV 2.7 eV 2.3 eV 2.0 eV 1.8 eV 1.5 eV Figure 1-7. Polymer band structures and optical band gaps of the dioxythiophene-cyanovinylene polymer family. [Modified from Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.; Reynolds, J. R. J. Am. Chem. Soc. 2006 128 12714-12725].18 Finally, the substitution of the polymer ch ains with electron ri ch or electron poor substituents will have an influence on the HOM O and LUMO levels and consequently on the band gap too. A close example to this Ph.D. resear ch is the narrowing of the band gaps in hybrid thienylene-phenylene polymers by replacing alkyl side chains with alkoxy groups due to an increased electron density and reduced steric effect brough t by the electron donating oxygen atoms: the onset of the transition, in solution, of 3 eV for poly(2,5-dihexyl-1,4-bis(2thienyl)phenylene) is reduced to 2.4 eV fo r the analogous alkoxy derivatized polymer.22

PAGE 24

24 1.3 Polymerization of Thiophene Based Molecules There are great synthetic adva ntages working with thiophene based molecules and one of the most important is the variety of polymerizat ion methods available such as oxidative chemical and electrochemical polymerizations, along with me tal mediated and solid state polymerizations. General principles, drawbacks, and advantages of the methods covered in this dissertation are given below. 1.3.1 Oxidative Polymerizations Oxidative polymerizations can be carried out either chemically or electrochemically. The generally accepted mechanism for the oxidativ e polymerization of heterocycles involves oxidation of the monomer to form a radical ca tion intermediate. The coupling of two radical cations, or of one radical cati on and one neutral mono mer followed by rearomatization with the loss of two protons leads first to a dimer unit, and finally to a polymer after repeated coupling. A detailed mechanism can be found in J. A. Irvin ’s dissertation.23 Typically, electron-rich monomers are easier to oxidize and allow milder oxidative poly merization conditions, fewer side reactions such as overoxidati on and the formation of more stable oxidized polymers.24 For instance, the oxygen atoms of the ethylenedioxy bri dge of EDOT increase the electron density of the thiophene ring and lower its oxidation potential. Indeed, th e EDOT oxidation peak is found25 at +0.88 V vs ferrocene (Fc/Fc+) while thiophene oxidation was reported26 around +1.22 V vs Fc/Fc+ (assuming that the half-wave potential (E1/2) of Fc/Fc+ = 0.38 V vs the saturated calomel electrode (SCE) and E1/2 of Ag/Ag+ = 0.26 V vs SCE).27 A major drawback in the oxidative polymerization of thiophenes is that it does not li nk the thiophenes exclusively at the 2and 5positions of the thiophene ring. Mislinking of th e polymer through the 3and 4positions can happen leading to backbone irregul arities and crosslinking and cons equently to poor electronic properties and solubility problems.23 This problem can be overcome by substituting the 3and 4-

PAGE 25

25 positions of the thiophene units, as with EDOT.28 Regioirregularities can also be found in the oxidative polymerization of uns ymmetrical 3-substituted thi ophenes due to the lack of regiochemical control over head-to-tail couplings between adjacent thiophene rings.29 Head-tohead and tail-to-tail couplings can also occur, lead ing to irregular polymers with sterically driven twisted backbones and poorer packin g density. This results in a loss of conjugation, and a poorer orbital overlap and electronic connectivity in three dimensions. Non-oxidative coupling methods30 with a high degree of regioselectivity (e.g., Rieke method31 and McCullough methods32) have been developed for the synthesis of regioregular polymers. But the most attractive route to achieve a high degree of or der, which does not re ly on highly controlled polymerization conditions, is the use of symmetrical m onomers and will be one of the focuses of the present dissertation. The advantage of using chemical oxidative methods (in the bulk) over electrochemical methods is the possibility of getting high yields based on monomer. Chemical oxidations are also quite inexpensive re lative to metal coupling, usually accomplished with the FeCl3 oxidant. The chain length is usually limited by solubility problems: the oxidized polymers are less soluble than the neutral polymers due to their increased ri gidity and can precipitate out of the solution, stopping the progress of the polyme rization. This can be reduced by the introduction of flexible substituents on the polymer backbone. As an example, 2,5-dialkoxy-substituted 1,4-bis(2thienyl)phenylene polymers synthesized via FeCl3 oxidation precipitate out of the chloroform solution when they are substituted with hept oxy groups, but remain in solution with longer hexadecyloxy groups.22 Reduction to the neutral polymer is accomplished using a strong reducing agent such as hydrazine or ammonium hydroxide. The major drawback of oxidative

PAGE 26

26 chemical polymerization over electropolymerizati on is that ferric ions coming from the oxidants (FeCl3, Fe(ClO4)3) are often trapped in the polymer bac kbone, affecting the device properties.33 1.3.2 Metal Mediated Polymerizations Metal mediated couplings such as Grignard metathesis, Suzuki, and Ni(0) mediated Yamamoto polymerizations are typically used fo r the polymerization of heterocycles. Grignard Metathesis polymerization developed by the McCullough group32c has been used to produce a variety of polythiophenes with high molecular weights and high de gree of regioregularity. This method requires the synthesis of the 2,5-dibr omo-thiophene derivative, which is then polymerized with a Grignard reagent, such as the readily available and inexpensive methyl magnesium bromide (MeMgBr), an d catalytic amounts of Ni(dppp)Cl2 as illustrated for the synthesis of disubstituted PProDOTs34 in Figure 1-8. It proceeds via an unusual quasi-living chain-growth mechanism, which allows the synt hesis of polymers with predetermined molecular weights and narrow molecular weight distributions.35 GriM is fast, easy, can be carried out on large scales, and does not re quire cryogenic temperatures. The use of GriM for the polymerization of monomers made of other kinds of heterocycles than substituted thiophenes has rarely been reporte d and it is consequently difficult to determine how efficient that method would be on such molecules. The closest example to the present research is the synthesis of high molecular weight electron rich poly(3,4-ethylenedioxyth iophene)-2,5-didodecyloxybenzene (LPEB) via GriM.36 S O O R R Br Br S O O R R 1. MeMgBr, THF 2. Ni(dppp)Cl2, reflux n Figure 1-8. GriM polymerization of disubstituted PProDOTs.

PAGE 27

27 The Yamamoto Coupling, using zerovalent bis(1,5-cyclooctadien e)nickel reagent (Ni(COD)2) is a powerful synthetic method to couple electron poor aromatic rings, and more interesting in that research, to couple electron ri ch aromatic rings which are more reluctant to metal oxidative addition and cons equently to most metal mediated coupling reactions. For instance, it has been effective for the polymeri zation of electron rich carbazoles with molecular weigths around 100,000 g. mol-1 (mechanism of the polymerization shown below in Figure 19).37 The mechanism involves the insertion of Ni(0) into the C-X bond of a halogenated heterocycle, disproportionation between two of the resulting derivatives and reductive elimination of the Ni(II) compound.38 Addition of the Ni(0) reagent is done slowly in order to avoid the formation of the less stable dinickel-substituted complex (Figure 1-9), which would result in the termination of the propagation of the polymer chain due to hydrolysis or decomposition. Each coupling is followed by the irreversible conversio n of Ni(0) to Ni(II)X2 and for this reason, the polymerization requires st oichiometric amounts of the expensive bis(1,5cyclooctadiene)nickel(0) [Ni(COD)2] reagent. Another drawback is that even if the Yamamoto coupling has been used for the polymerization of thiophene-based molecule s, it always led to relatively small molecular weights making it quite challenging for the synthesis of our polymers.39 Finally, it is important to not e first that the use of Ni(COD)2 requires expensive equipment since it has to be st ored cold (otherwise it decompos es quickly) and in an oxygen free atmosphere, and second that it is often trapped40 in the polymers. 1.3.3 Solid State Polymerization Solid state polymerization of polythiophene s was reported for the first time by Meng et al. in 2003.41 They found by chance, that 2,5-dibrom o-3,4-ethylenedioxythiophene (DBEDOT) polymerizes spontaneously, without the addition of catalyst. This was discovered after a sample of DBEDOT transformed into a highly conductive black material (up to 80 S cm-1) after two

PAGE 28

28 years of storage at room temperature. The reacti on takes place in air, vacuum, or light, heating decreases the reaction time, and elemental bromine is released during the reaction as illustrated by the mechanism in Figure 1-10.41 The resulting polymer is doped with bromine and can be reduced to its neutral form after dedoping w ith hydrazine. It was suggested that short intermolecular Hal ••• Hal contacts are required in order for the reaction to take place. Indeed, DBEDOT which has short Hal ••• Hal intermolecular contacts of 3.45 and 3.50 is much more reactive than 2,5-diiodo-3,4-ethy lenedioxythiophene (DIEDOT), which has an intermolecular Hal ••• Hal contact of 3.73 . These Hal ••• Hal intermolecular contacts are smaller than the sum of van der Waals radii (3.7 for Br ••• Br and 4.0 for I ••• I). Br-Ar-Br Br-Ar-Ni(II)-Br Oxidative Addition Ni(0) Br-Ni(II)-Ar-Ni(II)-Br + Br-Ar-Ni(II)-Ar-Br Br-Ni(II)-Ar-H H-Ar-H Hydrolysis or decomposition Termination of polymerization Br-Ar-Ar-Br Chain propagation Disproportionation Ni(II)Br2Reductive elimination Figure 1-9. Mechanism of aryl (Ar) polymerizati on via Yamamoto coupling and of the polymer chain degradation/termination occurri ng during the polymerization. [Mechanism modified from Zhang, Z.-B.; Fujiki, M.; Tang, H.-Z.; Motonaga, M.; Torimitsu, K. Macromolecules 2002 35 1988-1990].37 S O O Br Br S O O Br Br Br2 S O O Br Br S O O Br S O O Br Br Br S O O Br S O O Br -Br2 S O O n reduction Figure 1-10. Mechanism of the solid stat e polymerization of DBEDOT.

PAGE 29

29 1.3.4 Knoevenagel Polymerization The Knoevenagel condensation involves the nucleophilic addition of a carbanion to a carbonyl group (aldehyde or ketone) in the presence of a base, followed by an elimination reaction in which a molecule of water is lost as illustrated in Figure 1-11.42 The Knoevenagel polycondensation has proven very efficient for the synthesis of donor-acceptor type polymers,43 and especially of narrow band gap polymers,18,43 with the combination of electron poor diacetonitrile monomers and elec tron rich dialdehyde monomers. Usually these condensations are accomplished in THF/alcohol mixtures (e.g., THF/ t -butanol or THF/2propanol) as reaction media and with t -butoxide ( t -BuOK) or tetrabutylammonium hydroxide (Bu4NOH) strong bases.17,43,44 Crosslinking of the polymer by Thorpe-Ziegl er and/or Michael side reactions of the cyano or vinylene groups can be avoided by th e use of one equivalent of base per cyano group.42,43 Previous work reported by our group on the synthesis of thiophene-cyanovinylene polymers has also shown that the use of t -BuOK is preferred over Bu4NOH.43 The polymerizations proceeded gradually with t -BuOK and led to processabl e materials, whereas the use of Bu4NOH led to the rapid formation of black in soluble precipitates. These observations have been used as support for the work on the ProDOT:cyanovinylene polymers presented in this dissertation. R1R2CH2R1R2CHR1R2CH-+ ArCHO R1R2CHCH(Ar)O-R1R2C=CHAr + OHtBuO-/ t -BuOH R1R2CHCH(Ar)OH t -BuOH/ t -BuO-t -BuOH/ t -BuOFigure 1-11. Illustration of the Knoevenagel condensation steps.

PAGE 30

30 1.4 3,4-Alkylenedioxythiophene Based Polymers from Thiophene to EDOT to ProDOT Improvement of the properties and capabilitie s of basic conjugated polymers such as polythiophenes became of great importance in the mid 80s for the organic electronics community. More specifically, the quest for speci fic electronic and optic al properties led to diverse structural modifications of the thi ophene polymer building un it, and to the very interesting EDOT molecule. As discussed in the section on oxidative polymerizations of thiophene based molecules, the ethylenedioxy bridge of EDOT prevents parasite reactions at the 3and 4positions of thiophene, conferring a high reactivity to the free 2and 5positions, which gives rise to highly regular conjugated backbones upon pol ymerization. The electron donating oxygen atoms of the ethy lenedioxy-bridge bring also an increased elec tron density, which increases the HOMO level and lowers the oxidation potential of the EDOT based molecules compared to their thiophene counterp arts. This effect occu rs without introducing unfavorable steric interactions between adjacent side chains, as found with regular long alkoxy substituents. Also, the ethylenedioxy-bridge is to o strained for a high level of conjugation with the thiophene ring favoring its reactivity towards oxidative polymerization.45,46 These properties have been wi dely exploited for improving th e properties of conjugated polymers, such as milder oxidative polymerizati on conditions and the formation of more stable polymers. The most obvious and popular exam ple is of course PEDOT which has a low oxidation potential, is electrochromic (deep blue neutral state and highly transmissive oxidized state), is highly conductive and highly stable, and which is being used as a charge injecting layer in light emitting devices, as a component in electrochromic displays, and even as electrodes in field effect transistor s and photovoltaic cells.47,48 But a variety of copolymers which use EDOT as a building block,49 like the thienylene-phenylene family, al so benefit from its properties. This is illustrated for example by poly[1,4-bis[2-( 3,4-ethylenedioxy-thienyl )]-2,5-dialkoxybenzenes]

PAGE 31

31 (PBEDOT-B(OR)2)46 which exhibit band gap values between 1.75 eV and 2.0 eV, and polymer half wave potentials as low as -0.4 V versus Fc/Fc+, whereas poly[1,4-bis(2-thienyl)]-2,5dialkoxybenzenes]50 exhibit band gaps around 2.1 eV and minimum polymer half wave potentials of 0.15 V vs Fc/Fc+. The properties of EDOT have al so been exploited for improving the electron donating power of the donor moiety in donor-acceptor systems based on thiophene blocks and for building narrower band gap materials. This is illustrated in Figure 1-12 for different combinations of thiophene and ED OT donor moieties with cyanovinylene acceptor moieties.17 In that example, it is clearly seen that as the EDOT content increases, the band gap diminishes. 1.6 eV Vacuum 0 eV Eg1.4 eV 1.1 eVS S CN n S CN S O O n S CN S O O n O O Increasing donor strength HOMO LUMO 1.6 eV Vacuum 0 eV Eg1.4 eV 1.1 eVS S CN n S CN S O O n S CN S O O n O O Increasing donor strength HOMO LUMO Figure 1-12. Effect of increasing donor stre ngth in a donor-accepto r-donor configuration. [Modified from Thomas, C. A.; Zong, K.; Abboud, K. A.; Steel, P. J.; Reynolds, J. R. J. Am. Chem. Soc. 2004 126 16440-16450].17 With the recent emergence of soft and flexible plastic devices for use in solar cells, electrochromic devices, or light-emitting diodes (LEDs), it became particularly important to synthesize neutral soluble conjugated polymers, wh ich can be processed directly from solution into thin-films, for instance by spray-casting or sp in-coating. For that purpose, intense work has

PAGE 32

32 been done in the substitution of thiophe ne with solubilizi ng substituents,45,51 and ProDOT has emerged as the best compromise between the synt hetic flexibility of thiophene and the electronic properties of EDOT. First, similar to E DOT based monomers, the oxygen atoms of the propylenedioxy bridge of ProDOT increase the electron density of the thiophene ring and lower its oxidation potential (ProDOT oxi dation peak reported around +0.98 V vs. Fc/Fc+).52 The effect of the electron donating oxygens on the oxidation pot ential is a bit less for ProDOT than for EDOT due to its twisting conformation, which di minishes the overlap be tween the oxygen lone pairs and the aromatic thiophene ring. Second, various kinds of subs tituents (linear or branched, alkyl or alkoxy chains, etc.) can be introduced easily on the ProDOT ring which allows derivatization, chemical polymer ization, and inducing solubility of the polymers in organic solvents.53,54 Mishra et al. reported the synthesis of a hydroxyl substituted ProDOT, in a single step, from commercially available starting material s, which led to the preparation of a variety of electroactive derivatives.55 Also ProDOT can be disubstitu ted on the central carbon of the propylene bridge without disturbing the C2 symmetry. This was used by Reeves et al. who made a recent impact in the field of soft electronics with the development of regiosymmetric spraycoatable electrochromic ProDOT polymers, prepared via Grignard metathesis.34 This is a great advantage compared to EDOT whic h has been mostly unsymmetrical ly substituted (except in the case of PheDOT56,57) due to the poor yields and tedi ous synthesis enc ountered during the functionalization process. Researchers are now ta king advantage of the el ectron rich properties, synthetic flexibility and easy derivatization of the ProDOT molecules and are working on the design of a variety of soluble hybrid conjugated polymers containi ng ProDOT to have access to a broader range of electronic and optical properties. For instance, Thompson et al. recently reported the building of a soluble narrow band ga p polymer using the donor-acceptor approach,

PAGE 33

33 with a substituted ProDOT derivative as the donor unit and a cyanophenyl ene derivative as the acceptor unit as illust rated in Figure 1-13.18,43,58 S O O H O O H C6H13 C6H13 + OC12H25 OC12H25 CN NC tBuOK t -BuOH/THF (1:1) S O O C6H13 C6H13 NC CN O O C12H25H25C12 n Figure 1-13. Synthesis of poly(3,4propylenedioxythiophene-dihexyl)-cyanop -phenylenevinylene. 1.5 Applications A variety of parameters need to be consider ed for application of conjugated polymers in semiconductor devices and only th ose which can be manipulated by synthetic chemists are described below for each application. The properti es which are of interest in these applications (Light-Emitting Diodes (LEDs), solar cells, and elec trochromic devices) are of course the ability to synthesize soluble polymers in high bulk yiel ds for obtaining soluti on-processable or filmforming polymers, and the ability to produce large quantities. This can be accomplished by introducing flexible side chains on the polymer backbone. For inst ance, the solubility of the branched PProDOT(CH2OEtHx)2 (Mn = 47,000 g mol-1) is about four times more important (57 mg mL-1) than the solubility of PProDOT(Hx)2 (13 mg mL-1, Mn = 38,000 g mol-1) in toluene.34 In polymer LEDs, light emission results from the formation of excitons in the polymeric layer, which will emit light upon relaxation to the ground state. These excitons form by the meeting of electrons and holes injected by vary ing work function electrodes. The color of the emitted light is dependent on the band gap of the material, and consequently a wide range of band gaps are needed for PLED applications: th is is where band gap engineering intervenes.59 Band gap engineering has to be done keeping in mind that the backbone structure and

PAGE 34

34 conformation play an important role on the lumi nescence efficiency. Indeed, once an exciton is formed, strong intermolecular interactions between polymer chains form weakly emissive interchain species (ground-state aggregates or ex cimers) which lead to a spectral red-shift and reduced quantum yields.20 One extensively used method to prevent this photoluminescence quenching phenomenon is to introduce bulky side groups to separate the backbones from each other.60 But for effective charge injection and transport in LEDs, high carrier density and mobilities are also required, and consequently a high degree of -interactions and packing.61 All these parameters have to be taken into cons ideration by the chemist and carefully balanced. In electrochromic devices, we obviously need an electrochromic material which possesses the ability to reversibly change color by altering its redox state.62 Intrinsically, all conjugated polymers have the potential to be electrochromic. Th is phenomenon is the result of the change of conjugation which occurs upon oxida tion or reduction of the polym er (interconversion between the quinoid and the aromatic states and apparition of lower energy transitions due to the formation of polarons and bipol arons as detailed earlier). The HOMO level of the polymer controls the oxidation potential, and the LUMO le vel controls the reduction potential. As an example, PEDOT is a great electrochromic ma terial which switches be tween an opaque blue color in the undoped state and a transmissive sky blue color in the oxidized state.63 A variety of colors are needed in order to be able to develop a variety of applications, and this can be realized by fine-tuning of the band ga p (as explained earlier).64-66 The materials should also be stable while switching between their ox idized and reduced states (or neutral states) with a certain lifetime. A large number of reviews are available on pol ymer photovoltaics and there is no need here to go over an extensive summary of the principles and of all the parameters which need to be

PAGE 35

35 improved in order to attain solar efficiencies approaching 10%.43,67-69 Provided below is a summary of the most important points which have to be considered by a synthetic chemist. In organic solar cells, upon photoexcitation, an excit on is created (electro n-hole pair) in the polymer layer, and a current is created from the splitting of this bound exc iton, and the collection of the holes at a high work func tion electrode, and of electrons at a low work func tion electrode. The exciton-splitting process occu rs only at interfaces (at the j unction between the electrode and the conducting polymer or at the interface between polymers of diffe ring electron affinities). The lifetime of an exciton is short and only excitons that are formed within about 4-20 nm of the junction have a chance to reach it.67 Conjugated polymer bulk hetero junctions (interpenetrating networks of electron-accepting and electr on-donating polymers) sandwiched between two varying work function electrodes are currently the best answer to that pr oblem, and particularly those using a solubilized form of C60 such as (6,6)-phenyl C61-butyric acid me thyl ester (PCBM) as the acceptor layer. The photoinduced charge tran sfer in these blends happens on an ultrafast timescale of up to 45 femtoseconds, which is much faster than the recomb ination process, which happens in a microsecond regime (100 ns-10 ms).70-72 One of the main tasks of the synthetic chem ist now is to find the “ideal” electron-donating polymer. The best materials available right no w are poly(3-hexylthiophene) (P3HT),73-75 poly(2-methoxy-5-(2’-ethylhexoloxy)1,4-phenylenevinylene) (MEH-PPV),76 and poly(2methoxy-5-(3’,7’-dimethyloctyloxy)p -phenylenevinylen e) (MDMO-PPV),77 all contain side chains that make them soluble in common organic solvents. But th ere is a mismatch between the absorption spectrum of these materials and th e solar spectrum. While the photon flux of the AM1.5 solar spectrum peaks around 700 nm (1.8 eV), P3HT, MEH-PPV and MDMO-PPV absorb strongly over the 350-650 nm wavelength ra nge (3.5-1.9 eV). As a result, a film of P3HT

PAGE 36

36 (240 nm thick) absorbs only a bout 21% of the sun’s photons.67 Taking this information into consideration, a synthetic chemist should speci fically look at the synthesis of a polymer43 1) exhibiting a band-gap capable of strongly absorbing sunlight (Eg < 1.8 eV),68,74 2) being resistant to oxidation and consequently having a fair ly low lying HOMO (about 5.2 eV or lower,78 assuming that the energy level of the Saturate d Calomel Electrode (SCE) is 4.7 eV below the vacuum level79), and 3) having a LUMO offset of a bout 0.3-0.4 eV relative to the PCBM for effective charge tran sfer (above 3.8 eV).80 It is important to note that the HOMO and LUMO energy levels are negative values because they are under the vac uum level which is considered as the zero level. Consequently a HOMO level located at 5.4 eV is c onsidered as lower than 5.2 eV. Great improvement of the solar efficiency has also been observed upon in creasing the degree of order of the polymers. P3HT annealed above it s glass transition temperature shows enhanced crystallization and a dramatic increase in the hole mobility, which when applied in solar cells facilitates charge transport to the elect rodes and increases the solar efficiency.71,73,75,81 So for application in photovoltaics, a synthetic chemist s hould also consider the ordering capabilities of its polymers. An interesting pa th was taken recently by Hou et al. : to benefit from the ordering properties of P3HT and to get band gaps approaching 1.8 eV, they have built two-dimensional conjugated polythiophenes with bi(t hienylenevinylene) side chains. They were able to lower the band gap by 0.2 eV compared to P3HT and they reached solar efficiencies of 3.18%, whereas they obtained efficiencies of 2.41% with P3HT using the same conditions.82 1.6 Study Overview This work focuses on the design and synthesis of new processable conjugated polymers for optoelectronic devices such as electrochromic devices, solar cells, and light-emitting diodes. Two terms define the main lines of this project: processability and desi gn. Processability was one of our priorities in order to be able to use th e polymers on large and flexible surfaces. Design of

PAGE 37

37 the polymer structure was a way to induce pro cessability and to manipulate the optical and electronic properties in order to target specific applications. Both narrow and wide band gap polymers were synthesized in order to cover a broad range of applications. Chapter 2 describes briefly the techniques employed for the work presented in this dissertation. In chapter 3, the synthesis of wi de band gap polymers of the thienylene-phenylene family has been investigated, including the already known thiophene-dialkoxybenzene and EDOT-dialkoxybenzene derivatives, as well as a novel ProDOT-dialkoxybenzene derivative. The newly developed ProDOT-phenylene materials were electropolymerized in order to quickly look at their redox and electron ic properties. For all the de rivatives, various chemical polymerizations were studied (Yamamoto coupling, ferric chloride oxidative coupling, GriM), as well as solid state polymerizations, in order to develop methods for synthesizing the polymers in high bulk yields. Flexible linear alkyl and alkoxy substituents were grafted onto the monomers to induce solubility of the derived polymers in organic solvents. In ch apter 4, narrow band gap polymers were prepared by Knoevenage l condensation of electron rich 3,4propylenedioxythiophenes and electron poor cyanovi nylenes. A variety of substituents were introduced on the backbones of th e polymers to induce solubility in organic solvents (linear and branched alkoxy-substituents), a nd their effects on the optical a nd electronic properties were studied. Chapter 5 describes the synthesis of wide band gap amino-substituted PProDOTs for developing a new type of c onjugated polyelectrolyte. Along with the synthetic details and mo lecular characteriza tions, a complete characterization of the polymer s by electrochemical, optical a nd photophysical methods is given in chapters 3-5 in order to evaluate their optical and electronic properties, and their potential in certain optoelectronic applicat ions. Structural studies such as X-ray analyses and DSC

PAGE 38

38 measurements are also detailed in chapters 3 and 4 for a quick look at some of the materials ordering properties. These studies have led to the incorporation of the mate rials into devices by other members of the Reynolds gro up and this thesis will briefly outline the results at the end of Chapters 3-5.

PAGE 39

39 CHAPTER 2 EXPERIMENTAL Molecular and structural analyses as well as electrochemical and spectroscopic methods were used in this work for developing a deeper understanding of the newl y synthesized materials potential. The techniques are extensively de scribed in the Reynolds group dissertations,23,43,83-85 and only an overview of the points of interest and of the general experimental conditions employed will be given. More specific details can be found at the end of Chapters 3-5. 2.1 General Synthetic Methods All chemicals were purchased from Acros or Aldrich Chemicals and used as received unless stated otherwise. The monomer st ructure and purity were determined by 1H-NMR and 13C-NMR spectroscopy, elemental analysis, high-re solution mass spectrometry (HRMS), as well as infra-red (IR) spectroscopy and single crystal X-ray analysis when applicable. Melting point measurements were also performed on solids for complete characterization. 1H-NMR and 13C-NMR were recorded on Va rian-VXR 300 MHz, Gemini 300 MHz, and Mercury 300 MHz spectrometers. Elemental analyses were perfor med by Robertson Microana lytical Laboratories, Inc. or the University of Florida, Depart ment of Chemistry spect roscopic services. Highresolution mass spectrometry was performed by the spectroscopic services at the Department of Chemistry of the University of Florida w ith a Finnigan MAT 96Q mass spectrometer. IR measurements were accomplished with a Spec trum One Perkin Elmer FT-IR spectrometer. Single crystals X-ray measurements were accomp lished at the Center for X-ray Crystallography in the University of Florida Chemistry Depa rtment by Dr. Khalil A. Abboud. Single crystals were obtained either by the slow cooling recrysta llization method (single solvent or two solvents method), or in a closed vial, by diffusion of a poor solvent into a smaller vial containing the compound dissolved in a small amount of good so lvent. Data were collected at 173 K on a

PAGE 40

40 Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of da ta (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were re-m easured at the end of data collection to monitor instrument and crystal stability (m aximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6 (2000, Bruker-AXS, Madison, Wisconsin) and refined using full-matrix least squares. All polymers were purified by precipitation foll owed by Soxhlet extraction as described in Chapters 3-5. Characterization was accomplished by 1H-NMR, elemental analysis, matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), and infra-red spectroscopy when applicable. 1H-NMR was recorded on Inova 500 MHz and Mercury 300 MHz. MALDI-TOF MS was performed by Dr. Tracy D. McCarley with a Bruker ProFLEX III instrument at Louisiana State University. Met hylene chloride or chloroform were used as solvents, and terthiophene, dithranol, or 2-(-4-hydroxyphenylazo)benzoic acid (HABA) as matrix. Polymer molecular weights were estim ated by gel permeation chromatography (GPC). GPC was performed on two 300 x 7.5 mm Polymer Laboratories PLGel 5 M mixed-C columns with Waters Associates liqui d chromatography 2996 photodiode a rray detector. All molecular weights are relative to polysty rene standards (Polymer Labor atories; Amherst, MA). The polymer solutions were prepared in tetr ahydrofuran (THF) or chloroform (CHCl3) and a constant flow rate of 1 mL min-1 was used. Polymer thermal stability was assessed by thermogravimetric analysis (TGA). TGA measurements were perfo rmed on a Perkin-Elmer TGA 7 instrument under nitrogen at heat ing rates of 20C min-1 from 50C to 900C. The ordering properties were

PAGE 41

41 also characterized by differential scanning ca lorimetry (DSC). DSC scans were run under nitrogen on a DuPont 951 instrument or on a TA Instruments DSC Q1000, using sample weights of ~ 4 mg. 2.2 Electrochemical Methods 2.2.1 Introduction Electrochemistry is an important tool in the field of conjug ated polymers for having an idea of a monomer’s ability to polymerize (the lo wer the oxidation potential, the easier it is to oxidatively polymerize the monomer) and for de termining the resultant polymer’s redox and electronic properties. From the onsets of oxidation and reduction potentials, the HOMO and LUMO levels of a polymer can be estimated. This is usually accomplished by cyclic voltammetry (CV) or differen tial pulse voltammetry (DPV). Since all electrochemical measurements reported in this dissertation will be referenced86 versus Fc/Fc+, the conversion to the HOMO and LUMO energies was accomplished by adding 5.1 eV to the onsets of oxidation and reduction of the polymer respectively (assuming that Fc/Fc+ is at 5.1 eV below the vacuum level).27 2.2.2 Electrochemical Set-Up Electrochemistry was performed using a three-elect rode cell with a platinum (Pt) wire or a Pt flag as the counter electrode, a silver wire pseudo-reference electrode calibrated using a 5 mM solution of Fc/Fc+ in 0.1 M electrolyte solution, and a platinum (or gold) button (0.02 cm2) or ITO coated glass slide (7 50 0.7 mm, 5-15 ) as the working electrode. The ITO electrodes were purchased from Delta T echnologies, Ltd. Characterization of the polymer films was performed in 0.1 M electrolyte solution. An EG&G Princeton Applied Research Model 273 potentiostat was used under the co ntrol Corrware II software fr om Scribner and Associates. The electrolyte solutions were prepared from tetrabutylammonium perchlorate (TBAP) or

PAGE 42

42 tetrabutylammonium hexafluorophosphate (TBAPF6) electrolytes dissolved in freshly distilled acetonitrile (ACN), met hylene chloride (CH2Cl2), or propylene carbonate (PC). The experiments were performed under an argon blanket. For electrochemical analysis, the polymers we re either electrodeposited onto the working electrodes, or synthesized chemically and deposite d by drop-casting or spray-casting from 3-10 mg mL-1 chloroform or toluene solutions. The electrodeposition was accomplished either by repeated scanning or by holding the potential of the working electrode near the monomer’s oxidation peak (previously determined by CV) in a 10 mM monomer solution. The electrodeposited polymer films were rinsed with th e solvent used in the electrolyte preparation and in which films are not soluble. Cyclic voltammograms or differen tial pulse voltammograms were recorded after breaking in the polymer film with about 10 CV cycles for getting reproducible results. 2.2.3 CV/DPV The principles of CV have been extensively de veloped in dissertations from J. A. Irvin and C. A. Thomas.23,83 In CV, we measure the current create d at the working electrode when the potential is linearly cycled from a starting potential to a final potential and b ack to the starting potential. In polymer electrochemistry,79 the polymer is adhered to the electrode and charge transfer occurs by hopping (Figure 2-1). If the poly mer is well adhered to the electrode, the peak current will increase linearly as function of the scan rate.85 In the case of reversible systems and if the rate of reaction of the adsorbed species is much greater than of species in solution (situation mostly encountered in our labs), th e peak current can be expressed as shown in Equation 2-1. RT A F n ii O p4 /, 2 2 Equation (2-1)

PAGE 43

43 with n the number of electrons A the electrode area (in cm2), O,i the surface conc entration of adsorbed O (in mol cm-2) before the experiment begins, the scan rate (in V/s), and F Faradays constant (96,485 C mol-1). For such systems, the anodic wa ve on scan reversal is the mirror image of the cathodic wave reflected across the potential axis and Ep E1/2, and the curve i = f(E) is totally symmetrical if hopping faster than ( same charge before and after peak). But in reality, inhomogeneity of film, char ge transport, structural and resistive changes in the film, fast scan rate compared to hopping, and differences in adsorption strength of O and R give rise to asymmetry. Figure 2-1. Charge transport by hopping in polymer adsorbed to the electrode. Electron injection into the film results in the reduction of O to R and the entry (or expulsion) of counterions (Aor C+). In DPV,79,83,87,88 the potential is pulsed and each pulse has a certain amplitude (between 10100 mV) as illustrated in Figure 22. After each pulse the potential returns to a value slightly higher than prior to the pulse (s tep size usually between 1-2 mV), which gives a staircase shape. The current is measured just prior to application of the pulse and at the end of the pulse and the difference between the two currents is plotted as a function of the base potential. The duration of the pulse (step time) usually varies between 5-20 ms. Longer step times allow more time for the

PAGE 44

44 current to decay, and consequent ly a smaller difference in the sampled currents and a higher sensitivity. For a reversible sy stem, the peak potential is a bout the same on the forward and reverse scans and corresponds to E1/2. With increasing irreversibility, Ep moves away from E1/2 at the same time that peak width increases and its he ight diminishes. It is important to note that when doing DPV measurements on a polymer, the cal ibration of the pseudo re ference silver wire has to be done by DPV. E i i1 i2 Differential Pulse Waveform Final Potential (E) i2 i1 Step Height Amplitude Initial Potential Difference current ( i) = i2-i1 Step time E i E i i1 i2 Differential Pulse Waveform Final Potential (E) i2 i1 Step Height Amplitude Initial Potential Difference current ( i) = i2-i1 Step time Figure 2-2. Differential pulse wa veform. In DPV, the potential is pulsed and the current is measured just prior to application of the pulse (i1) and at the end of the applied pulse (i2). The difference between the two currents ( i) is plotted as a function of the base potential. The advantage of using DPV over CV is that the major component of the current difference measured is the faradaic current, which flows due to an oxidation or reduction at the electrode surface. The capacitive or charging current component, due to electr ical charging of the electrode double layer, is largely eliminated. This renders the peaks more symmetrical and increases the

PAGE 45

45 signal to noise ratio compared to the CV me thod. Consequently, the ons ets of oxidation and reduction are more defined, as will be the HOMO and LUMO levels. 2.3 Optical and Spectroscopic Methods Analysis of a conjugated polymer ’s interaction with light is essential for evaluating the polymer’s potential in optoelectronic applica tions. This interaction can vary depending on the polymer’s conformation, and consequently it is usually evaluated in the solid state and in solution (in good and bad solvents), and at vari ous temperatures, by UV-Vis-nIR absorption or emission measurements, and studies of color switching upon doping. 2.3.1 Absorption Spectra and Molar Absorptivities Measurement of the UV-Vis absorption of a polymer solution is a basic spectroscopic method rich with information. A comparison be tween the absorption sp ectra of a polymer solution and its monomer soluti on will tell if the polymeriza tion took place. Indeed, in a polymer, the increased degree of conjugation will induce a red-shift of the absorption maximum. Also, by recording the absorption spectra of polym er chains of different lengths, using a GPC equipped with a photodiode-array detector, it is possible to determine th e minimum chain length necessary to obtain optimum optical properties. A polymer’s exti nction coefficient, extracted from the absorption maxima of three polymer solu tions of different con centrations, will bring information on how efficiently a polymer absorbs light, which is of particular importance for application in solar cells. Finally, the UV-Vis ab sorption of polymer solutions gives information on how well a polymer is solvated in specific solvents, and this will be discussed below in the solvatochromic section. Absorption spectra were obt ained using a Varian Cary 500 Scan UV-vis-nIR spectrophotometer and quartz crystal cells (1 cm x 1 cm x 5.5 cm, Starna Cells, Inc.).

PAGE 46

46 2.3.2 Solvatochromism/Thermochromism The term solvatochromism is used to describe the change in position and sometimes intensity of a UV-Vis absorption spectrum following a change in polarity of the solvent in which the polymer is dissolved. A change of the UV-Vis absorption spectrum upon a temperature change is called thermochromism,89,90 and upon the addition of ions89,91 is called ionochromism. In all three cases, chromism is induced by a c onformational change of the conjugated backbone driven by both intrachain steric hindrance and interchain interactions (attractive interactions, interactions, excitons, etc.) that accompany the formation (or disruption) of small aggregates.92 The conformational change leads to a modifica tion of the effective conjugation length, which induces optical shifts in the UV-Vis absorption spectra of conjugated polymers. A planarization of the polymer backbone always leads to a red-sh ift of the absorption, but the direction of the shift caused by aggregation depends on the deta ils of the molecular packing. Also, polymer backbone planarity usually causes “fine struct ure” or shoulders to appear on the main absorption peak. Disordered polymers have a gr eat number of different, but similar energetic states (due to their conformational freedom) a nd therefore usually have broad UV-Vis spectra. However a fixing of the molecular conformation th rough planarization leads to a decrease of the number of energetic states, allo wing the fine vibronic structures to be resolved as additional peaks or shoulders. Specifically, in solvatochromic studies, going from a “good” solvent to a more poorly solvating solvent will induce aggregation and more delocalized assemblies, and create a red-shift of the absorption spectrum.93 A “good” solvent is assumed to disrupt the conjugation upon sidechain disordering and twisting of the backbone, and to affect th e effective conjugation length. This phenomenon has been observed for a variety of polythiophene derivatives. For instance, the

PAGE 47

47 absorption of poly(1,4-(2,5-dialkoxyphenylene)-2,5thiophene) shifts from 468 nm to 495 nm upon decreasing the quality of the solvent.93 Solvatochromic studies are an important tool for selecting the solvents best suited for dissolving th e selected polymers, which might be helpful for optimum polymer characterization and device pr eparation. In thermochromism, it is heating which is either assumed to disrupt the conjugation and create disorder, or to break the aggregates and isolate the polymer chains.57 Polymers exhibiting solvatochromic or thermochromic properties have the potentia l of being applied in se nsors or smart materials.94 For the solvatochromic study, the same e xperimental set up as for the absorption experiments described in the above secti on was employed. It was accomplished by first dissolving the polymer in a good solvent and then progressively adding a poor solvent, while maintaining a constant polymer concentration. A constant concentrati on was maintained using the following procedure (Figure 2-3): a polyme r solution of known concentration was prepared in the “good solvent”. Then equal volumes of that solution were poured into a couple of graduated flasks, and the flasks were filled up to the same maximum with different volumes of “good” solvent and “poor” solvent. The spectral changes which occurred upon heatin g could not be recorded with the UV-VisnIR spectrophotometer because the temperature needed to observe thermochromism was too high (however pictures of the color changes were taken and reported). 2.3.3 Photoluminescence Spectra and Fluorescence Quantum Efficiencies The luminescence properties of conjugated polym ers are of considerable interest because of their potential applications as the emissive materials in LEDs. A useful figure is the photoluminescence (PL) quantum yield ( ), defined as the number of photons emitted in photoluminescence per absorbed photon. It is easil y measured by a synthetic chemist for polymer solutions, and allows making a first selection of polymers which might have a potential in LEDs.

PAGE 48

48 Measurements of on thin-film solids are more representative but not as straightforward;95,96 they were accomplished in this work by Dr. J. Mwaura. The PL quantum yield of a polymer solution is much higher than of polymer thin-films coated from the same solution. This is due to the formation of less emissive interchain sp ecies which quenches the fluorescence in the solid state. PL quantum yields are determined using the comparative method of Williams et al. which involves the use of well characte rized standard samples with known values.97 The standard must be chosen such that its excitation wavelength is found at a slightly lower value than the absorption maximum of the polymer solution. The ab sorption values of the polymer and standard solutions should not exceed 0.1 at the excitation wavelength (in 10 mm fluorescence cuvettes) in order to avoid self-absorption.98 The PL quantum yield of a polymer solution is calculated according to Equation 2-2, where the subscript R refe rs to the standard (or reference) and A is the absorbance of the solution, E is the inte grated emission area across the band and is the refractive index of the solution. 2 210 1 10 1R R A A RE ER Equation (2-2) Prepare polymer solution of Known concentration in “good solvent” Solution 1 Pour same volume of solution 1 into a few flasks Complete the flasks with different volumes of “good”and “poor” solvents up to the same maximum. Step 1 Step 2 Step 3 Prepare polymer solution of Known concentration in “good solvent” Solution 1 Pour same volume of solution 1 into a few flasks Complete the flasks with different volumes of “good”and “poor” solvents up to the same maximum. Step 1 Step 2 Step 3 Figure 2-3. Example of the procedure used to maintain a constant polymer concentration in flasks containing varying am ounts of good and poor solvents.

PAGE 49

49 The photoluminescence spectra of the polymer so lutions were register ed on a Jobin Yvon Fluorolog-3 spectrofluorimeter in right-angle mode. Solution quantum efficiency measurements were carried out using a Spex F-112 photon counting fluorimeter, rela tive to oxazine 1 in ethanol ( = 0.11),99 coumarin 6 in ethanol ( = 0.78),100 or cresyl violet perchlorate in ethanol ( = 0.54),101 with the optical density of the solution kept below A = 0.1. 2.3.4 Spectroelectrochemistry Spectroelectrochemical measurements were performed in order to define the optical band gaps of the polymers and obser ve their electrochromic beha vior. The optical band gap is determined from the low-energy absorption edge (onset of the transition) of the neutral absorption spectrum of the polymer thin-film. The electrochromic behavior is observed by recording the spectral changes upon oxidation and reduction of the polymer thin-film. The polymer films were prepared either by spray-casting polymer solutions (5-10 mg mL-1 in chloroform) onto ITO coated glass using an air brush (Testor Corps) at 12 psi, or by using electropolymerization as descri bed previously. Characterizati on of the polymer films was performed in 0.1 M electrolyte solution using the electrochemical set-up described previously, with a Pt wire as the counter electrode in order to avoid bl ocking the incident light. The absorption spectra were recorded using a Vari an Cary 500 Scan UV-vis-nIR spectrophotometer for bench top experiments or a Stellarnet diode-array Vis-nIR sp ectrophotometer w ith fiber-optic capabilities for dry-box studies. 2.3.5 Colorimetry Colorimetry measurements are useful to give a quantitative description of the color states that an electrochromic polymer thin-film can reach as it is oxidized or reduced. Three attributes are used to describe colors: the hue (dominant wa velength), the saturation (l evel of white and/or black), and the luminance (the brightness of the transmitted light). Two color systems were

PAGE 50

50 specifically used in this dissertation to give a qu antitative representation of these attributes: the 1931 Yxy and the 1976 L*a*b systems, both established by the Commission Internationale de l’Eclairage (CIE) (detailed information can be found in the referenced citations). 64,102 In the CIE 1931 Yxy color space, Y represents the luminance, and x and y represent the hue and saturation. The luminance is usually presente d as a percentage rela tive to the background luminance, and called “relative luminance”. The two-dimensional xy diagram is known as the chromaticity diagram (illustration in Figure 2-4). It has the shape of a horseshoe, with the wavelengths of visible light found on the su rrounding line, and the shortest and longest wavelengths being connected by a straight line. Every color is contained in the horseshoe and the location of a point on the xy diagram gives information on the hue and saturation of the color. The xy chromaticity diagram is particularly useful to track the color states of a polymer for different doping levels. The CIE L*a*b* space is more commonly used in industry, with L* representing the luminance and a* and b* being related to the hue and saturation. Polymer thin-films were deposited by spray-ca sting onto ITO coated glass as for the spectroelectrochemical studies. Colorimetric m easurements were obtained with a Minolta CS100 Chroma Meter using the electrochemical set-up described previously, w ith a Pt wire as the counter electrode. The sample was illuminated fr om behind with a D50 (5000K) light source in a light booth designed to ex clude external light.

PAGE 51

51 Figure 2-4. CIE 1931 xy chromaticity diagram. [Modified from Thompson, B. C.; Schottland, P.; Zong, K.; Reynolds, J. R. Chem. Mater 2000 12 1563-1571].64

PAGE 52

52 CHAPTER 3 WIDE BAND GAP BIS-HETEROC YCLE-PHENYLENE POLYMERS 3.1 Introduction Thiophene-phenylene based copolymers have been extensively studied for their interesting electrical and optical properties such as redox electroactivit y and electrochromism, reactivity to chemical sensing, charge tr ansport and light emission.22,24,36,46,50,103-110 In addition, the various coupling reactions available for heterocycles, an d the variety of methods for the polymerization of thiophene based monomers render them fa irly easy to synthesize Phenylene rings are particularly convenient to de rivatize with variable substituents, and the subsequent polymerization of thiophene-pheny lene monomers yields material s with controllable band gaps and solubilities.22,46,50 As described in the general Intr oduction, simply replacing the phenylene alkyl substituents with alkoxy groups can reduce c onsiderably the band gap due to the electron donating effect and reduced ster ic effect brought by the oxygens.22 The regiosymmetric poly(1,4-bis(2-thienyl )-2,5-dialkoxyphenylene)s are particularly interesting members of that family (Figure 3-1) Their synthesis was orig inally accomplished by J. Ruiz et al.22,111 from the catalytic oxidation of bis-th iophene-dialkoxybenzen e monomers with ferric chloride. Low molecular weight ma terials were obtained (~ 2,000-3,800 g mol-1), and it was revealed that these polymers showed an X-ray diffraction pattern that indicated a high crystalline content rela tive to analogous polymers being unsymmetrically substituted. These polymers have a band gap only slightly larger th an P3HT (2.1 eV vs. 1.9 eV) and based on their ability to give polymer films with a high degree of order, they are of interest for use in solar cells.50 A synthetically interesting as pect about these regiosymmetric polymers is their ability to achieve a high degree of order without having to prepare unsy mmetrical monomers (which are

PAGE 53

53 usually more challenging to synthesize), or havi ng to rely on highly controlled polymerization conditions. Regiosymmetric poly[1,4-bis(2-(3,4-ethyl enedioxy)thienyl)-2,5-dialkoxybenzene]s, illustrated in Figure 3-1, can also be found in the literature.46,105 The ethylenedioxy bridge between the 3and 4-positions of the thiophene gave access to smaller band gaps (~ 1.7-2.0 eV) than the ones obtained for their thiophene analogs due to the electron donating effect of the oxygens atoms of EDOT, as explained earlier. This ma kes these derivatives also of interest for photovoltaics, but their synthesis needs to be fu rther investigated for improving their solution properties and molecular weights, and a study of their ordering properties has to be accomplished too. Indeed, the derivatives which have been reported have been s ynthesized either by electrochemical methods, which do not allow easy characterization, processing, and synthesis of the polymers in high bulk yields, or by chemi cal polymerizations, which have led to low molecular weight materials (4,000 g mol-1 via ferric-chloride-medi ated polymerization, and 2,900 g mol-1 via Ullman coupling) w ith poor film properties.23,46 In addition, the derivatives prepared by oxidative polymerization with FeCl3 were poorly solubl e, and difficult to characterize and to process, but it could not be determin ed if this insolubili ty was the result of crosslinking through the phe nylenes or if it was intr insic to the molecules. The chemical synthesis of these regios ymmetric thiophene-phenylene (PBT-B(OR)2) and EDOT-phenylene polymers (PBEDOT-B(OR)2) has been revisited (s ection 3.3) in order to obtain polymers with higher molecular weights th an the ones previously reported, while being able to analyze and process the materials easily for application in soft, and flexible, photovoltaic and electrochomic devices. The monomer synthe ses and characterizations are described in section 3.2. The redox, spectroelectrochemical, and electrochromic properties of the polymers

PAGE 54

54 have been studied, and the resu lts are detailed in sections 3.4 and 3.5. Application of PBTB(OR)2 in photovoltaic devices has b een investigated by members of the group and is detailed in section 3.7. The work was finalized by the addition of a new member to the regiosymmetric thienylene-phenylene family. This member cont ains ProDOT as the thienylene moiety, which allows taking advantage of its electron donating ab ility and of its easy deri vatization. This type of molecule was targeted in order to improve the solubility and processability of the thienylenephenylene polymer family. In particul ar, we report here the synthesis of methyl substituted (R = Me) and hexyl (R = Hex) substituted poly[1,4-bis[2-(3,4-propyl enedioxythienyl)]-2,5didodecyloxybenzene] [PBProDOT-R2-B(OC12H25)2], with the methyl substituted molecule studied for comparison with the more soluble hexyl derivatized molecule (Figure 3-1). The monomer syntheses and characterizations are de scribed in section 3.2. Both polymers were prepared by electropolymerization, and the BProDOT-Hex2-B(OC12H25)2 monomer was also polymerized by chemical oxidation using ferric ch loride to yield a polymer highly soluble in organic solvents as describe d in section 3.3. PBProDOT-Hex2-B(OC12H25)2 exhibits interesting electrochromic and solvatochromic properties, which are reported in sections 3.4, 3.5, and 3.6. Preliminary investigations utilizing this polymer as an emitter in LEDs, and as a hole transport layer in solar cells, have been accomplished by Reynolds group members and a brief overview of the results is incl uded in section 3.7. 3.2 Monomer Syntheses and Characterizations It was decided to synthesize the regiosymmetric PBT-B(OR)2, PBEDOT-B(OR)2, and PBProDOT-R2-B(OC12H25)2 from the corresponding sy mmetrical bis-thienylenedialkoxybenzene monomers (from their dibrominated version in most cases). The benzenes were substituted with long and flexib le heptoxy and/or dodecyloxy ch ains to induce solubility.

PAGE 55

55 S S OR O R O O O O n S S OR O R n S S O O O O OC12H25 O R R R R n H25C12PBT-B(OR)2PBEDOT-B(OR)2PBProDOT-R2-B(OC12H25)2 Figure 3-1. Targeted thie nylene-phenylene polymers. 3.2.1 Bis-thiophene-dialkoxybenzenes 1,4-Dibromo-2,5-dialkoxybenzene was prepared according to the literature by Williamson etherification of 1,4-dibrom o-2,5-dihydroxybenzene with the corresponding alkyl halide.22 The synthesis of the dibrominated 1,4-bis (2-thienyl)-2,5-diheptoxybenzene (Br2-BT-B(OC7H15)2), and 1,4-bis(2-thienyl)-2,5-didodecyloxybenzene (Br2-BT-B(OC12H25)2) monomers started by the deprotonation of thiophene with n -butyllithium, and further r eaction with trimethylstannyl chloride to give 2-(trimet hylstannyl)thiophene (Th-Sn(CH3)3) as illustrated in Figure 3-2. 1,4Bis(2-thienyl)-2,5-dia lkoxybenzene (BT-B(OR)2) was obtained by the S tille coupling of 1,4dibromo-2,5-dialkoxybenzene with Th-Sn(CH3)3. There is significant literature precedent for the preparation of this type of molecule via Negishi coupling instead.22,50,103,104 However, Stille coupling was chosen because it allows isola ting, purifying, characterizing, and storing ThSn(CH3)3. Finally, the Br2-BT-B(OR)2 monomers were prepared by bromination of BT-B(OR)2 with N -bromosuccinimide (NBS). Yellow needle s were obtained after purification by recrystallization (72% a nd 86% yields for R = C7H15 and R = C12H25, respectively). The monomers were fully characterized by 1H-NMR, 13C-NMR, HRMS, elemental analysis, melting point determination, and UV-Vis spectroscopy. They both e xhibit an absorption maximum at 376 nm (Figure 3-14), a nd extinction coefficients of 37,600 M-1 cm-1 for Br2-BTB(OC7H15)2 and of 27,160 M-1 cm-1 for Br2-BT-B(OC12H25)2.

PAGE 56

56 S S Li S Sn(CH3)3 nBuLi / THF -78 S Sn(CH3)3 RO OR Br Br S S RO OR 2 + Pd(PPh3)4 / DMF 110 Stille Coupling -78 to room temperature ~ 80% 77% Sn(CH3)3Cl, S S OR RO S S OR RO Br Br 2.1 eq NBS, 0 to room temperature DMF 72% for R = C7H1586% for R = C12H25 BT-B(OR)2Br2-BT-B(OR)2 Figure 3-2. Bis-thiophene-dialkoxy benzene monomer synthesis. Crystals of Br2-BT-B(OC7H15)2 were grown by slow diffusi on of ethanol into a vial containing a xylene solution of the monomer. Figur e 3-3a shows the molecular structure of the monomer, while Figure 3-3b shows the packing mode of the material as well as the crystalline unit (obtained by single crystal X-ray diffraction studies). Br2-BT-B(OC7H15)2 crystallizes in the monoclinic space group C2/c with the alkoxy chains and phenyl rings being coplanar. As illustrated in Figure 3-3c, the molecules have a relatively small dihedral angle of 20.8 between the central phenylene and thiophene rings, which allows efficient stacking of adjacent molecules with a good cofacial arrangement and an interchain distance of 5.79 . The intermolecular distance is a very important parameter for applic ation of organic material s to devices requiring high carrier mobility. Small distances are necessary for strong intermolecular overlap of the atomic orbitals and ch arge transfer by hopping.112 Materials such as thiophene oligomers or P3HT are of high interest because they exhibit small interchain distances (in the order of 3.8 for P3HT).113 The 5.79 interchain value found for Br2-BT-B(OC7H15)2 would not be great if extended to the polymer. Br2-BT-B(OC12H25)2 crystals were not of sufficient size for singlecrystal structure analysis.

PAGE 57

57 a b c Figure 3-3. Single crystals X-ray analysis of Br2-BT-B(OC7H13)2. (a) Molecular structure, (b) packing mode, (c) Side view. 3.2.2 Bis-EDOT-dialkoxybenzenes The synthesis of 1,4-bis[2-(5-bromo-3,4ethylenedioxy)thienyl ]-2,5-diheptoxybenzene [Br2-BEDOT-B(OC7H15)2], and of 1,4-bis[2-(5-bromo-3,4ethylenedioxy)thienyl]-2,5-didodecyloxybenzene [Br2-BEDOT-B(OC12H25)2] monomers started by the deprotonation of EDOT with n -butyllithium, and further reaction with trim ethylstannyl chloride to give 2-trimethyltin-3,4ethylenedioxythiophene (EDOT-Sn(CH3)3) as illustrated in Figu re 3-4. 1,4-Bis[2-(3,4ethylenedioxy)thienyl]-2,5-di alkoxybenzene (BEDOT-B(OR)2) was obtained by Stille coupling

PAGE 58

58 of 1,4-dibromo-2,5-dialkoxybe nzene with EDOT-Sn(CH3)3. As for the thiophene derivatives, the Stille route was chosen over th e Negishi coupling previously reported for these molecules,46 because of the possibility to is olate, purify, and store EDOT-Sn(CH3)3. The monomer precursors BEDOT-B(OR)2 were obtained in 70-80% yields after purification by recr ystallization. Their bromination was accomplished by addition of NBS in DMF at -78C, followed by progressive warming of the solution to 0C. This step was particularly challenging as oxidation problems arose easily. The electron donating power of EDOT considerably d ecreases the oxidation potential of BEDOT-B(OR)2 molecules compared to their th iophene counterparts (~ 0.35 V vs Fc/Fc+ for 1,4-bis[2-(3,4-ethylened ioxy)thienyl]-2,5-diheptoxybenzene46 versus 0.55 V for 1,4bis(2-thienyl)-2,5-diheptoxybenzene50), making them more sensitive to oxidation.23 Attempts in THF from -78C to 0C, led to black insoluble tars, probably resulting from the formation of oxidized polymer. The use of DMF at low temper atures allowed milder oxidative conditions and successful bromination.114 The reaction was stopped by addition of a solution of ammonium hydroxide, which reduced the crude product, and quenched unreacted NBS and the hydrogen bromide released.115 For purification, a combin ation of flash column chromatography on silica gel and of repeated recrystalliz ations was needed, in order to isolate the dibrominated monomer from its monobrominated version. Also a fast solvent flow was re quired for the column chromatography otherwise the monomers polymeri zed on the silica gel. Indeed, when slow elution was used, no monomer could be extracted from the column. Instead, an orange-pink material, highly fluorescent under UV light, was re covered after dumping th e contents of the column in a beaker containing hydrazine and re moving the silica gel by filtration. A toluene solution of that material was analyzed by UVVis spectroscopy and an absorption maximum of 455 nm was determined in the case of Br2-BEDOT-B(OC7H15)2, which provides evidence that

PAGE 59

59 some coupling occurred (the absorption maxima of the monomer are at 376 nm and 398 nm). The monomers were obtained in 40% and 57% yields for Br2-BEDOT-B(OC7H15)2 and Br2BEDOT-B(OC12H25)2, respectively. S O O S O O Li S O O Sn(CH3)3 n -BuLi / THF -78C S O O Sn(CH3)3 RO OR Br Br S O O S O O RO OR 2 + Pd(PPh3)4 / DMF 110C Stille Coupling -78C 70-80% 74% Sn(CH3)3Cl S S O O O O OR RO S S O O O O OR RO Br Br 2.2 eq NBS, -78C to 0C slowly, 4h DMF 42% for R = C7H1557% for R = C12H25BEDOT-B(OR)2Br2-BEDOT-B(OR)2 Figure 3-4. Bis-EDOT-dialkoxybe nzene monomer synthesis. The monomers were fully characterized by 1H-NMR, 13C-NMR, HRMS, elemental analysis, melting point determination, and single crystal X-ray studies. For X-ray analysis, the crystals of Br2-BEDOT-B(OC12H25)2 were grown from a methanol/THF mixture (1/1) and the crystals of Br2-BEDOT-B(OC7H15)2 from an ethanol/THF mixture (3/1). Figure 3-5a shows the molecular structure of Br2-BEDOT-B(OC7H15)2, while Figure 3-5b shows its packing mode. Br2BEDOT-B(OC7H15)2 crystallizes in the monoclinic space group P2(1)/n with the alkoxy chains and phenyl rings being coplanar The dihedral angle between the central phenylene and EDOT rings is very small (6.1), which renders the molecules almost planar. This quasi-planarity helps the molecules pack close to one another with a small interchain distance of 3.7 . Molecular planarity is a desirable feature since less energy is required to stabilize the bipolaron state upon

PAGE 60

60 polymer oxidation. Figure 3-6a show s the molecular structure of Br2-BEDOT-B(OC12H25)2, and Figure 3-6b shows its packing mode. Br2-BEDOT-B(OC12H25)2 crystallizes in the monoclinic space group C2/c with the alkoxy chains and phenyl rings be ing also coplanar. The dihedral angle between the central phenylene and EDOT rings is even smaller than the one found for Br2BEDOT-B(OC7H15)2 (1.7) and this extremely small devi ation from planarity, illustrated in Figure 3-6c, gives rise to closer -stacking with an interchain di stance of 3.5 . We noticed that the cofacial arrangement is not as great as what was observed for Br2-BT-B(OC7H15)2. The tight packing observed for the Br2-BEDOT-B(OR)2 monomers particularly motivates the development of oligomeric or polymeric deri vatives of these molecules, wher e a possible extension of these properties would lead to materials with high charge mobility. 3.2.3 Bis-ProDOT-dialkoxybenzenes The monomers BProDOT-Me2-B(OC12H25)2 and BProDOT-Hex2-B(OC12H25)2 were synthesized from 1,4-dibromo-2,5-didodecyloxybenzene and the corresponding substituted ProDOT unit by Negishi coupling. The substitut ed ProDOT derivatives were synthesized by transetherification of 3,4-dime thoxythiophene and the dialkyl-s ubstituted propane-1,3-diols as previously reported (Figure 3-7).34 The synthesis of 3,4-dimet hoxythiophene was accomplished using the synthetic route shown in Figure 3-7. It started with the tetrab romination of thiophene followed by debromination of the 2 and 5 positions of the thiophene ring with zinc dust in glacial acetic acid.116 Ullman type coupling between sodium methoxide and 3,4-dibromothiophene in the presence of copper oxide (CuO ) afforded 3,4-dimethoxythiophene.117 The ProDOT derivatives were lithiated with one equivalent of n -butyllithium and reacted with anhydrous zinc chloride (ZnCl2) (Figure 3-8). Coupling with 1,4-di bromo-2,5-didodecyloxybenzene was first attempted using tetrakis(tripheny lphosphine) palladium (0) [Pd(PPh3)4] as the catalyst, as

PAGE 61

61 previously reported for EDOT and thiophene derivatives,22,46 but was limited possibly by unfavorable steric interactions between the he terocycles. However, the Negishi coupling was more successful using a different catalyst sy stem made of commercially available Pd(0)2(dba)3 and trit -butylphosphine ligands [P( t -Bu)3] which has been proven very efficient for coupling sterically demanding molecules.118 Both monomers were obtained in decent yields ( ca. 40 %) after purification by column chromatogra phy, and were characterized by UV-Vis, 1H-NMR, 13CNMR, melting point determination, elemental an alysis, and HRMS. As expected, the monomer containing long and flexible hexyl chains on the ProDOT unit melts at a lower temperature (45 46 C) than the methyl s ubstituted monomer (80 -82 C). BProDOT-Me2-B(OC12H25)2 and BProDOT-Hex2-B(OC12H25)2 exhibit similar absorption maxi ma in toluene at 354 nm and 356 nm respectively, with extin ction coefficients of 16,430 M-1 cm-1 for the former and of 15,640 M-1 cm-1 for the latter. Replacement of the methyl groups by the longer hexyl ch ains on ProDOT does not lead to any observable change in the monomer’s optical properties. Suitable crystals for an X-ray diffraction study of BProDOT-Me2-B(OC12H25)2 were obtained by slow cooling recrys tallization from a hexanes/ethyl acetate mixture (5/1 ratio). BProDOT-Me2-B(OC12H25)2 crystallizes in the triclinic P1 space group. The molecular structure is shown in Figure 3-9a and the packing mode in Figures 3-9b and 3-9c. The molecules, which are located on inversion centers, are nearly planar with a dihedral angle of 6.6 between the central phenyl and thiophene ring s. The molecules stack with a close to perfect cofacial arrangement with a small interchain dist ance of 3.679 as evident in Figure 3-9c If extended to the polymers (or oligomers), these two features would greatly favor in ter-chain transport. BProDOT-Hex2-B(OC12H25)2 crystals were not of sufficien t size for single-crystal structure analysis.

PAGE 62

62 a b Figure 3-5. Single crystals X-ray analysis of Br2-BEDOT-B(OC7H13)2. (a) Molecular structure, (b) packing mode. 3.3 Polymer Syntheses and Characterizations 3.3.1 Polymerization Attempts via GriM As described in the gene ral Introduction, GriM has been used by Wang et al. for the preparation of the electron rich poly[(3,4-ethylenedioxythi ophene)-2,5-didodecyloxybenzene] (LPEB), whose repeat unit structure is similar to the molecules studied in this report (Figure 310).36 This polymer was synthesized at high molecular weights (~ 30,000 g mol-1) with a low polydispersity of 1.30.

PAGE 63

63 a c b Figure 3-6. Single crystals X-ray analysis of Br2-BEDOT-B(OC12H25)2. (a) Molecular structure, (b) packing mode, (c) quasi-planar arrangement of adjacent Br2-BEDOTB(OC12H25)2 molecules.

PAGE 64

64 S S Br Br Br Br 5 Br2CHCl343% 2.2 eq Zn AcOH 63% S Br Br NaOMe KI, MeOH S MeO MeO pTSA, toluene HO OH R R R = hexyl 83% yield R = Me 79 % yield 4 sieves, reflux S O O R R 44% CuO Figure 3-7. Synthesis of methyland hexyl-substituted ProDOTs. S O O S O O S O O O C1 2H2 5 O R R R R R R 1) n -BuLi 2) ZnCl23) Pd2(dba)3/P( t -Bu)3 (1:2 ratio) OC12H25 O Br Br R = Hexyl, Me ~ 40% THF/NMP (1:1) H25C12H25C12NBS DMF S O O S O O O C1 2H2 5 C12H25O Br Br R R R R -78C to room T 5 hours R = Hexyl 81% R = Me 64% BProDOT-R2-B(OC12H25)2Br2-BProDOT-R2-B(OC12H25)2 Figure 3-8. Synthesis of BProDOT-R2-dialkoxyphenylene and Br2-BProDOT-R2dialkoxyphenylene monomers.

PAGE 65

65 a b c Figure 3-9. Single crystals X-ray an alysis of BProDOT-Me2-B(OC12H25)2. (a) Molecular structure, (b) packing mode, (c) -stacking of BProDOT-Me2-B(OC12H25)2 illustrated without the phenylene side chains (OC12H25). S O O OC12H25 C12H25O n LPEB Figure 3-10. Structure of LPEB. It was decided to attempt the same conditions as the ones used by Wang et al. to polymerize the dibromo-thienyl ene-phenylene monomers (Br2-BT-B(OR)2, Br2-BEDOTB(OR)2, and Br2-BProDOT-R2-B(OC12H25)2), as illustrated in Figure 3-11. The monomers were treated with methylmagnesium bromide (MeMgBr) at reflux, and then Ni(dppp)Cl2 was added

PAGE 66

66 for coupling the bromomagnesio intermediates. Unfortunately, no polymer was formed, and in all cases the monomers were rec overed in ~ 90% yields after work up. In or der to check if the metalation of the thienyl bromide occurred, th e bromomagnesio intermediates were quenched with deionized water. This method had been used by Wang et al. in their work on LPEB for proving that the metalation was occurring at the bromo-EDOT site. In our case, no thiophene protons were observed proving that the metalati on did not take place. The Grignard reagent MeMgBr was switched for the le ss stable and more reactive t -butyl magnesium chloride, but the reaction failed again. One explanation could be that the three ring symmetrical system does not provide enough reactivity to the aryl-Br sites. Another explanation could be that with the addition of an extra heterocycle the system has become too electron rich to allow metalation of the bromo-aryl site. It had been reported that extremely limited lithiation of BEDOT-B(OR)2 could be accomplished after addition of n -BuLi or sec -BuLi, due to the too strong electron donating power of the molecule s, and this example supports the second explanation.23 There is very little literature precedent on the polymerization via GriM of multiple ring systems, and consequently it is difficult to give a definitiv e explanation for the failure encountered here. S S OR O 1. MeMgBr, THF, reflux 1h 2. Ni(dppp)Cl2, reflux 20h Br Br R O O O O S S OR O MgBr Br R O O O O S S OR O R O O O O n Figure 3-11. GriM route for th e polymerization of the dibrom o-thienylene-phenylene monomers.

PAGE 67

67 3.3.2 Polymerization via Yamamoto Coupling 3.3.2.1 Poly(bis-thiophene-dialkoxybenzene)s The polymerization of the Br2-BT-B(OR)2 monomers has been ca rried out via Yamamoto coupling according to the synthetic route shown in Figure 3-12. The zerova lent nickel reagent, Ni(COD)2, was mixed with 1,5-cyclooctadiene (COD), a molar equivalent of 2,2 -bipyridyl (Bpy), and DMF at 60 C, and th is mixture was added dropwise to the DMF monomer solution. The solution color changed from yellow to dark red and the red polymers precipitated out of the solution. The polymers were purified by Soxhlet ex traction with methanol followed by hexanes, to remove unreacted monomer, inorganic impur ities, and low molecular weight polymer. Final extraction with toluene afforded re d solids in 55% yield for PBT-B(OC7H15)2 and 40 % yield for PBT-B(OC12H25)2 after solvent evaporation. These materials exhibit a solubility of about 7 mg mL-1 in toluene. S S OR RO Br Br S S OR RO Ni(COD)2, COD, Bpy DMF, 60C, 24 to 42h R = C7H15 55% R = C12H25 40% n Figure 3-12. Polymerization of Br2-BT-B(OR)2 monomers via Yamamoto coupling. The polymers were characterized by 1H-NMR, GPC, MALDI, and elemental analysis. The results of the molecular weight (MW) analysis performed by GPC (polystyrene standards, THF as mobile phase, 40C) are summarized in Table 3-1. Number average molecular weights of ~ 5,000 g mol-1 and of ~ 3,000 g mol-1 were estimated for PBT-B(OC7H15)2 and PBT-B(OC12H25)2, respectively, which correspond to polymers of about 17 to 29 rings. The low polydispersity (1.30) is explained by the Soxhlet extraction w ith hexanes which removed the low molecular weight material. The low molecular weights may be explained by the electron donating-ability of the system, which as the molecular weight increased, deactivated more and more the bromo-

PAGE 68

68 thiophene reactive sites and rende red the oxidative addition of th e Ni(0) complex more difficult. The decrease in solubility, observed as the polym er chains were getting bigger (the polymers were precipitating out of the solution), could have stop ped the coupling process too. For improving the solubility, the polym erization has also been attemp ted in mixtures of DMF and toluene (1/2), but high er molecular weights could not be reached. Table 3-1. GPC estimated molecular weights of the PBT-B(OR)2 polymers (polystyrene standards, THF as mobile phase, 40C). Polymers Mn (g mol-1) Mw (g mol-1) PDI Average number of rings PBT-B(OC7H15)2 4,9606,3401.329 PBT-B(OC12H25)2 2,9453,9501.317 As structure proof, the polymers were char acterized by MALDI-MS using a terthiophene matrix. The MALDI spectra are disp layed in Figure 3-13 and show that the spacing between the peaks corresponds to 468 amu for PBT-B(OC7H15)2, and to ~ 609 amu for PBT-B(OC12H25)2, which correlates well with the calculated molecular weights of the repeat units (n) of the polymers. The different series in the MALDI spectra s how that there is a variety of end-groups: H/H, H/Br, Br/Br. A predominance of H/H end groups over H/Br or Br/Br end-groups at low molecular weights could have explained why a large degree of polymerization could not be reached. However a comparison between the peak intensities shows that there seems to be no preference for one type of end-group over the ot her. This comforts us in our assumption that solubility and electron density are the most probable parameters limiting the growing of the polymer chains. Figure 3-14 shows the solution UV-Vis abso rbance of the polymers in toluene. The solutions are orange (photograph in Figure 3-14) and the absorption maxima are found at 469 nm for PBT-B(OC7H15)2, and at 463 nm for PBT-B(OC12H25)2. Figure 3-14 also shows the UV-

PAGE 69

69 Vis absorbance of the monomers, which is blue-s hifted compared to the UV-Vis absorption of the polymers due to the lower degree of conjugation. 180021002400270030003300 0 50 100 150 468 468 n = 6 n = 5 n = 4 n = 7 Abundancem/z 468a 200030004000 0 100 200 n = 6 Abundancem/zn = 7n = 4 n = 5 n = 3 609b Figure 3-13. MALDI-MS of BT-B(OR)2 polymers. (a) PBT-B(OC7H15)2, (b) PBT-B(OC12H25)2. Terthiophene was used as the matrix. 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 Br 2 -BT-B(OC 12 H 25 ) 2 Br 2 -BT-B(OC 7 H 15 ) 2 PBT-B(OC 7 H 15 ) 2Absorption (Normalized)Wavelength (nm) PBT-B(OC 12 H 25 ) 2 Figure 3-14. Solution UV-Vis absorbance of Br2-BT-B(OR)2 monomers, and PBT-B(OR)2 polymers in toluene. The ordering properties of the polymers were studied by DSC as illustrated by the second DSC scans displayed in Figur es 3-15a and 3-15b. The symmet rically derivatized polymers exhibited two endothermic transi tions and one exothermic tran sition. The first endothermic

PAGE 70

70 transition (Tm1), observed at -39C for PBT-B(OC7H15)2 and at -41C and PBT-B(OC12H25)2, has been attributed to the melting of the side chai ns. Previous ordering st udies done by the Reynolds group on this type of molecule (synthesized via FeCl3) have shown that the highest transition (Tm2) can be attributed to an isotropic melt of the polymer backbone, and the first exothermic transition (Tc1) to their crystallization.22 The melting temperature Tm2 was lower for PBTB(OC12H25)2 (134C) than for PBT-B(OC7H15)2 (190C), probably due to the molecular weight differences. These DSC results confirmed the semicrystalline nature of the polymers. The thermal stability of the polymers was st udied by TGA both in ai r and in a nitrogen atmosphere using a 20C min-1 temperature ramp from 50C to 900C. The thermograms displayed in Figure 3-16 show that the polymers exhibit a high thermal st ability, losing less than 5% weight in air at 335C for PBT-B(OC7H15)2, and at 322C for PBT-B(OC12H25)2. A similar behavior was observed under nitrogen, w ith a loss of less than 5% weight at 352C for PBTB(OC7H15)2, and at 323C for PBT-B(OC12H25)2. A drastic degradation process occurred from these temperatures up to ~ 650C for PBT-B(OC7H15)2, and up to ~ 750C PBT-B(OC12H25)2. Above 850C, less than 7% of PBT-B(OC12H25)2 and less than 15% of PBT-B(OC7H15)2 remained. 3.3.2.2 Poly(bis-alkylenedioxythi ophene-dialkoxybenzene)s The polymerizations of the Br2-BEDOT-B(OR)2 and Br2-BProDOT-R2-B(OC12H25)2 monomers have also been carried out via Yamamo to coupling using the same conditions as those employed for PBT-B(OR)2. Unfortunately, a maximum of 3 repeat units for PBEDOTB(OC12H25)2 (Mn = 1,792, Mw = 2,497, DPI = 1.40) and of 4 repeat units for PBProDOT-R2B(OC12H25)2 [PBProDOT-Me2-B(OC12H25)2 : Mn = 3,394, Mw = 6,119, PDI = 1.80; PBProDOTHex2-B(OC12H25)2: Mn = 1,859, Mw = 2,525, PDI = 1.36] were coupled. Even though the size of the PBEDOT-B(OC12H25)2 oligomers was small, the material was difficult to solubilize.

PAGE 71

71 According to the work previously reported on these types of molecules,46 and the work presented in this dissertation, it is clear that these PBEDOT-B(OC12H25)2 molecules are likely not the best candidates for the production of highly processable films for opt oelectronic devices. It was consequently decided to stop further syntheti c work on them. However, the solubility and processing expectations were quite good for PBProDOT-R2-B(OC12H25)2, and it was decided to continue investigating other s ynthetic pathways and to study more deeply their electronic properties. -50050100150200 15 20 25 30 35 40 45 50 154C Heat flow (mW) (endo up)TemperatureC Tm1 Tm2 Tc1 -39C 190Ca -50050100150200 30 40 50 60 117CTc1134CTm1 Tm2 Temperature (C)Heat flow (mW) (Endo up)-41Cb Figure 3-15. DSC thermograms (second scans) of PBT-B(OR)2 polymers. (a) PBT-B(OC7H15)2, and (b) PBT-B(OC12H25)2. The temperature was cycled between -80 C and 200 C at 10C min-1. 3.3.3 Solid State Polymerization Attempts It was hypothesized that a so lid state polymerization, follo wing the same process as the one discovered for the spontaneous polymerization of Br2-EDOT, could happen for the dibromothienylene-phenylene monomers (as de tailed in the gene ral introduction).41 Crystals of Br2BEDOT-B(OC7H15)2 were progressively heated for 2 days up to 150C, and then from 150C to 180C, in a sublimation apparatu s under vacuum, in order to pr epare a polymer film on a glass

PAGE 72

72 substrate in situ (Figure 3-17). No sublimation occurred and as the temperature was increased, the crystals became darker and finally melted into a black gum once the melting temperature was reached. Once cold, this black insoluble material looked like charcoal and was extremely friable. It was stirred overnight in a mixture of AC N and hydrazine monohydrate, then filtered and washed with neat ACN. No color change occu rred upon addition of hydrazine and the material could not be dissolved in organic solvents. It also did not show any conductivity after being doped with iodine, and it was finally deduced that this material was probably the result of degradation, not polymerization. 200400600800 0 20 40 60 80 100 PBT-B(OC 7 H 15 ) 2 N2PBT-B(OC 12 H 25 ) 2 air PBT-B(OC 12 H 25 ) 2 N2Weight %Temperature (C) PBT-B(OC 7 H 15 ) 2 air Figure 3-16. Thermogravimetric analysis of the PBT-B(OR)2 polymers. Measurements performed both in air and in a nitr ogen atmosphere, using a 20C min-1 temperature ramp from 50C to 900C. Before pursuing further experiments, it was d ecided to first examine the bromine distances in the Br2-BEDOT-B(OC7H15)2 crystal structure. The smalle st bromine distance found between adjacent molecules in the same row, represented by a dashed line in Figure 3-18, had a value of 5.38 (7.54 between bromines on facing rings), bigger than the sum of the van der Waals radii. These distances were even bigger for Br2-BEDOT-B(OC12H25)2 (10.64 in the same row, and 7.76 between facing rings) and Br2-BT-B(OC7H15)2 (10.16 in the same row and 5.79

PAGE 73

73 between facing rings), and it wa s deduced that further inve stigation on the solid state polymerization of these molecules would not likely give a successful polymerization. S S O O O O OC7H15 O Br Br S S O O O O OC7H15 O Vacuum Sublimation Heat n H15C7H15C7 Figure 3-17. Attempt in the solid state polymerization of Br2-BEDOT-B(OC7H15)2. Figure 3-18. Crystal packing of Br2-BEDOT-B(OC7H15)2 illustrating the intermolecular distances between bromine atoms. 3.3.4 Electropolymerization The electropolymerization of the BEDOT-B(OR)2 and BT-B(OR)2 families is already well documented and was consequently not investigated in this work.46,50,105 In order to develop an understanding of the redox properties of polymer films of the new BProDOT-R2-B(OC12H25)2

PAGE 74

74 family, the two BProDOT-R2-B(OC12H25)2 monomers have been electrochemically polymerized on a platinum button electrode. The elec trodeposition was accomplished using an ACN/dichloromethane (CH2Cl2) (5/3) solution, with 0.1 M TB AP and saturated in monomer (0.01 M). Dichloromethane was requ ired due to the poor solubility of the monomers in ACN. However, too much CH2Cl2 hindered polymer formation and deposition on the electrode and only the use of monomer saturate d solutions helped to circumve nt that problem. The repeated scanning electropolymerizations of BProDOT-Me2-B(OC12H25)2 and of BProDOT-Hex2B(OC12H25)2 are shown in Figures 3-19a and 3-19b re spectively. During the first anodic scan, a single peak is observed which corresponds to ir reversible monomer oxidation and formation of cation radicals. The peaks of monomer oxidation (Ep,m) are observed at +0.55 V for BProDOTMe2-B(OC12H25)2 and at +0.52 V for BProDOT-Hex2-B(OC12H25)2 vs Fc/Fc+. With repeated potential scanning, a polymer film grows onto th e electrode surface in both cases. Cathodic and anodic redox processes are obser ved during polymer reduction and oxidation, and both increase in intensity with repeated scanning indicative of a successful effective electroactive polymer film deposition. The oxidation potential of the polymer also increases with film thickness due to the increase in polymer resistance. For spectroel ectrochemical studies, a polymer thin-film of PBProDOT-Me2-B(OC12H25)2 was also potentiostatically depos ited onto an ITO-coated glass electrode at +0.5 V for 50 s, us ing the same electrolyte and c oncentration as used for the electropolymerization on Pt button. 3.3.5 Oxidative Polymerization via Ferric Chloride As described in the Introducti on (section 3.1), the oxidative ch emical polymerizations of the BEDOT-B(OR)2 and BT-B(OR)2 families via FeCl3 has been previously reported. Low molecular weight materials resulted, with partic ularly poor processing properties in the case of PBEDOT-B(OR)2. It was hypothesized that the low oxidation potential of BProDOT-Hex2-

PAGE 75

75 B(OC12H25)2, as well as its solubility inducing hexyland dodecyloxy-substituents, would confer the material favorable conditions for bein g polymerized via oxidative polymerization. Consequently, the chemical polymerization of BProDOT-Hex2-B(OC12H25)2 was carried out by addition of a ferric chloride slurry (FeCl3, 3 equiv.) in chloroform to a chloroform solution of the monomer over a 2 hour period. The polymerization was carried out overnight at room temperature and the oxidized polymer was then precipitated in cold methanol, collected, dissolved in chloroform, and s tirred for 6 hours with about 10 mL of hydrazine monohydrate to reduce the polymer into its neutral form. The neutral polymer was preci pitated one more time into cold methanol, filtered through a cellulose thimble, and purified by Soxhlet extraction with methanol as the refluxing solvent to remove unreacted monomer and inor ganic impurities. Final extraction with chloroform afforded a red solid in 92 % yield after solvent evaporation. The polymer was soluble in common organic solvents such as THF, dichloromethane, chloroform and toluene. -0.10.00.10.20.30.40.50.60.7 -3 -2 -1 0 1 2 3 4 5 Current (mA/cm 2)Potential (V) vs. Fc/Fc +E on,m = +0.44V E p,m = +0.55V a -0.4-0.20.00.20.40.6 -2 -1 0 1 2 3 4 5 Current (mA/cm 2)Potential (V) vs. Fc/Fc +E on,m = +0.4V E p,m = +0.52V b Figure 3-19. Repeated potential sca nning electropolymerization of BProDOT-R2-B(OC12H25)2 monomers. (a) BProDOT-Me2-B(OC12H25)2 and (b) BProDOT-Hex2-B(OC12H25)2, 0.01 M saturated solution of 0.1 M TBAP in ACN/CH2Cl2 (5/3) at a scan rate of 50 mV s-1.

PAGE 76

76 The 1H-NMR spectra of the material obtained after polymerization was compared to the 1H-NMR spectrum of the BProDOT-Hex2-B(OC12H25)2 monomer (Figure 3-20). As expected, the methylene protons at 0.88, 1.27, 1.39, and 1.82 ppm give splitting patte rns in the monomer spectrum. They are found at about the same fre quency for the polymer (the peak at 1.82 ppm is shifted slightly down-field) but do not resolve. The alkoxy me thylene protons at 3.90, 3.91, and 3.99 ppm give also splitting patterns in the mo nomer but overlap into a broad multiplet at 3.964.06 ppm in the polymer. The signal of the phenyl ene proton (a) is shif ted down-field in the polymer by 0.11 ppm. The signal of the ProDOT proton end groups (6.45 ppm, (b)) disappeared as expected for polymerizati on to a substantial degree. As structure proof, the polymer was charac terized by MALDI mass spectrometry using a terthiophene matrix. Proton end groups were observed and the spacing between the peaks corresponds to 1090 amu, which corresponds to the calculat ed molecular weight of the repeat unit of the polymer. Iron and chlorine were effi ciently removed as demonstrated by elemental analysis, which shows the presen ce of only one iron per 47 sulfurs, and of one chlorine per 40 sulfurs. Molecular weight (MW) analysis perf ormed by GPC (polystyrene standards, THF as mobile phase) gave a number aver age molecular weight of 14,600 g mol-1 and a weight average molecular weight of 23,000 g mol-1 with a polydispersity index of 1.6. As illustrated in Figure 321, polymer elution was monitored with an inline photodiode array detector to record the UVVis absorption of selected fractions of the pol ymer. Spectra were recorded at various times which allowed monitoring the elec tronic spectra as a function of molecular weight. For fractions with MW higher than polystyr ene equivalents of 25,000 g mol-1, the optimum optical conditions are attained and the absorption maximum is at 573 nm. The narrow MW seen in the gel permeation chromatogram indicates that the polymer does not contain low MW oligomers

PAGE 77

77 (Appendix B). Interestingly, the absorption spect rum of the polymer in THF is red shifted compared to the absorption spectrum in toluene ( vide post ). Therefore THF is not as good a solvent as toluene for this polymer and induces conformational changes to a more planar and rigid structure. More details on the solvent eff ect will be given in the solvatochromism section (section 3.6). ppm (t1) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 (a)CDCl3 H2 O a b ppm ( t1 ) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 (b) a CDCl3S S O O O O OC12H25 C12H25O Hex Hex Hex Hex a bS S O O O O OC12H25 C12H25O Hex Hex Hex Hex a n Figure 3-20. 1H-NMR spectra. (a) 1H-NMR(CDCl3) spectrum of BProDOT-Hex2-B(OC12H25)2, (b) 1H-NMR(CDCl3) spectrum of PBProDOT-Hex2-B(OC12H25)2. The thermal stability of PBProDOT-Hex2-B(OC12H25)2 was studied by TGA in a nitrogen atmosphere using a 20C min-1 temperature ramp from 50C to 900C. The thermogram displayed in Figure 3-22 shows that the polymer e xhibits a high thermal stability, having lost less than 5% weight at 357C. Between that temper ature and 450C, a drastic degradation process occurred, leading to a ~ 70% weight loss, which matches with the side chain degradation. Above

PAGE 78

78 450C, the degradation became more progressive, and probably corresponds to the polymer backbone degradation. At 900C, less than 7% of the polymer remained. 300400500600700800 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 (6) 573 nm (5) 573 nm (4) 573 nm Absorbance (a. u.)Wavelength (nm) (1) 563 nm (2) 573 nm (3) 573 nm Figure 3-21. Absorption spect ra for molecular weight fractions of PBProDOT-Hex2B(OC12H25)2. Molecular weights are reported in g mol-1 vs. peak values for polystyrene. (1) 18,900, (2) 25,000, (3) 30,350, (4) 38,400, (5) 46,700, (6) 61,500. 200400600800 0 20 40 60 80 100 Weight (%)Temperature (C) Figure 3-22. Thermogravimetric analysis of the PBProDOT-Hex2-B(OC12H25)2 in a nitrogen atmosphere. A 20C min-1 temperature ramp from 50C to 900C was used. 3.4 Polymer Electrochemistry and Spectroelectrochemistry 3.4.1 PBT-B(OR)2 The redox properties of the PBT-B(OR)2 polymers were studied by electrochemistry. The polymers were deposited on Pt button el ectrodes by drop-cast ing from 3 mg mL-1 toluene

PAGE 79

79 solutions, and cyclic voltammograms were recorded in 0.1 M TBAP/PC. An onset of oxidation (Eonset,ox) of +0.25 V vs Fc/Fc+ and a E1/2 of +0.29 V were determined for PBT-B(OC7H15)2 (Figure 3-23a). According to these results, the po lymer has a HOMO energy of about 5.3-5.4 eV (as detailed in Chapter 2). Figure 3-23b shows the cyclic voltammograms of PBT-B(OC12H25)2 at different scan rates. The voltammograms are broa d and not well defined, and consequently it was not possible to determine E1/2. The onset of polymer oxi dation was found around +0.35 V, slightly more positive than the value found for the heptoxy analog. This locates the HOMO level at about 5.4-5.5 eV. These two PBT-B(OR)2 derivatives fulfill the energy requirements for stability to oxidation since their HOMO levels are lower than 5.2 eV (general Introduction). -0.4-0.20.00.20.40.6 -2 -1 0 1 2 3 4 E p,red = +0.1 VCurrent density (mA/cm 2 )E(V) vs. Fc/Fc + E p,ox = +0.48 V a E onset,ox -0.6-0.30.00.30.60.91.2 -4 -2 0 2 4 6 125 mV s -1 100 mV s -1 75 mV s -1Current density (mA/cm 2 )E(V) vs. Fc/Fc+25 mV s -1 50 mV s -1b E onset, ox Figure 3-23. PBT-B(OR)2 cyclic voltammetry. (a) CV of PBT-B(OC7H15)2 at 100 mV s-1, (b) CV and scan rate dependence of PBT-B(OC12H25)2. The polymers were deposited by drop-casting from 3 mg mL-1 toluene solutions, and the measurements were accomplished in 0.1 M TBAP in PC. Spectroelectrochemical studies were accomplished in order to finalize the estimation of the position of the HOMO and LUMO energies, and to observe the polymer spectral changes upon oxidation. Polymer thin-films were spray-cast onto ITO coated glass plates from 3 mg mL-1 toluene solutions, and UV-Vis-nIR spectra were reco rded in the neutral state and then at higher

PAGE 80

80 oxidizing potentials. Figure 3-24 show s the spectral changes of PBT-B(OC7H15)2 and photographs of the polymer film in the neutral and oxidized stat es, and Figure 3-25 shows the spectral changes of PBT-B(OC12H25)2. Both polymers are orange in the neutral state with absorption maxima at 447 nm for PBT-B(OC7H15)2, and at 454 nm for PBT-B(OC12H25)2. Once the oxidation potentials reached ~ 0.21 V for PBT-B(OC7H15)2, and ~ 0.30-0.35 V for PBTB(OC12H25)2, spectral changes started to occur, such as the progressive disappearance of the transition of the neut ral state, and the formation of po laron transitions in the 600-800 nm region, and of bipolaron transitions in the near -IR region. For each polymer, the starting point of these changes correlates well with the onset of oxidation determined by electrochemistry. Once completely oxidized, PBT-B(OC7H15)2 exhibits a new absorption ma ximum in the visible region at 738 nm, and its film color ch anges to blue. Similar color changes were observed for PBTB(OC12H25)2, which exhibits an absorption maximum in the visible at 662 nm in the oxidized state. Both polymers exhibit an absorption onset in the neutral state at 590 nm, corresponding to an optical band gap of approxima tely 2.1 eV. The LUMO energies of the polymers were deduced by adding this band gap value to the HOMO ener gies estimated by electrochemistry: 3.2-3.3 eV for PBT-B(OC7H15)2 and 3.3-3.4 eV for PBT-B(OC12H25)2. Consequently the polymers fulfill the energy requirements for transferring charges to PCBM (LUMO offsets >0.4 eV relative to PCBM) as explained in the general Introduction. 3.4.2 PBProDOT-R2-B(OC12H25)2 The polymer films of PBProDOT-R2-B(OC12H25)2 electrodeposited on Pt button (section 3.3.4) were rinsed w ith a monomer free solution of ACN/CH2Cl2 (5/3) in which the films are not soluble, and cyclic voltammograms were further recorded with scan rate values ranging from 25 to 250 mV s-1 (Figures 3-26a and 3-26b). Linear relationships were observed between the current

PAGE 81

81 and the scan rate, indicating that the films ar e electrode supported and electroactive. The redox processes for the BProDOT-Me2-B(OC12H25)2 system are broad and overlap well as expected for a nicely electroactive polymer, with the peak oxidation (Ep,ox) and reduction (Ep,red) potentials around +0.25 V and -0.01 V re spectively, at 100 mV s-1. However, Ep,ox and Ep,red for PBProDOT-Hex2-B(OC12H25)2 (+0.16 V and -0.04 V respectively, at 100 mV s-1) are highly separated as the longer and bulki er chains on the hexyl substi tuted ProDOT inhibit the fast movement of counter ions. The electrochemical results are summarized in Table 3-2. Both molecules have similar electrochemical values with half wave poten tials around +0.05-0.1 V, which shows that functionalizing the ProDOT unit w ith long solubilizing hexyl chains has little influence on the electronic properties. These pote ntials are lower than th e values measured for the analogous 1,4-bis(2-thienyl)-2,5-d iheptoxybenzene polymer which exhibits50 an E1/2 value of +0.36 V vs Fc/Fc+, showing the effect of the electron donating oxygens of the ProDOT unit on the polymer oxidation potential. A lower E1/2 of -0.40 V vs Fc/Fc+ has been reported for the analogous 1,4-bis(3,4-ethylenedio xythienyl)-2,5-didodecyloxybenzene polymer due to the stronger electron donati ng effect of EDOT.46 Comparative cyclic voltammetry studies have been done on the chemically synthesized PBProDOT-Hex2-B(OC12H25)2. A film of that polymer was deposited by drop-casting on a Pt button electrode from a 10 mg mL-1 chloroform solution, and cyclic voltammograms were recorded for different scan rates in 0.1 M TBAP/P C electrolyte as illustrated in Figure 3-27 and compared to the electrochemically synthesized films. The polymer exhibits an E1/2 of +0.23 V at 100 mV s-1, which is a bit higher than the value obtained for the elec tropolymerized film, but not surprisingly different due to th e different morphologies one woul d expect to form for the two film preparation methods. A HOMO energy of a bout 5.3-5.4 eV was deduced from the onset of

PAGE 82

82 oxidation at ~ +0.25 V, which is similar to what was determined for the PBT-B(OR)2 derivatives. A linear relationship is found betw een the peak current and the sc an rate indicating that the polymer is electroactive a nd bound to the electrode. 400600800100012001400 0.0 0.5 1.0 wAbsorption (a. u.)Wavelength (nm) Neutral a w a +0.21 V A B Figure 3-24. Spectroelectroche mical analysis of PBT-B(OC7H15)2 spray-cast onto ITO coated glass. (A) U.V.-Vis.-n.I.R. spectra taken in th e neutral state and at potentials of (a) -0.49 V, (b) -0.39V, (c) -0.29 V, (d) -0.19 V, (e) -0.09 V, (f) +0.01 V, (g) +0.11 V, (h) +0.21 V, (i) +0.22 V, (j) + 0.23 V, (k) +0.24 V, (l) +0.25 V, (m) +0.26 V, (n) +0.27 V, (o) +0.28 V, (p) +0.29 V, (q) +0.30 V, (r) +0.31 V, (s) +0.41 V, (t) +0.51 V, (u) +0.61 V, (v) +0.71 V, (w) +0.81 V vs Fc/Fc+ in 0.1 M TBAP/PC; (B) Film colors in the neutral and oxidized states. Table 3-2. Electrochemical results for BProDOT-R2-B(OC12H25)2 monomers and polymers. Eon,m (V)aEp,m (V)Ep,ox (V) b Ep,red (V) b E1/2 (V) b Eg (eV) BProDOT-Me2-B(OC12H25)20.440.550.25-0.010.122.1 BProDOT-Hex2-B(OC12H25)20.40.520.16-0.040.062.1 Note: All potentials reported vs Fc/Fc+ aEon,m: onset of monomer oxidation ; bScan rate = 100 mV s-1. The chemically prepared PBProDOT-Hex2-B(OC12H25)2 was studied by spectroelectrochemistry after film deposition by sp ray-casting onto ITO coated glass from a 10 mg mL-1 chloroform solution. A highly homogene ous film was obtained and dried under

PAGE 83

83 vacuum. The spectra were recorded in 0.1 M TBAP in PC in the neutral state, and stepping the potential from -0.02 V to +0.78 V ev ery 0.05 V as shown in Figure 3-28. 400600800100012001400 0.0 0.2 0.4 0.6 rAbsorption (a. u.)Wavelength (nm) a b r b + 0.35 V Figure 3-25. Spectroelectroche mical analysis of PBT-B(OC12H25)2 spray-cast onto ITO coated glass. U.V.-Vis.-n.I.R. spectra taken (a) in th e neutral state and at potentials of (b) -0.55 V, (c) -0.45 V, (d) -0.35 V, (e) -0.25 V, (f) -0.15V, (g) -0.05 V, (h) +0.05 V, (i) +0.15 V, (j) +0.20 V, (k) +0.25 V, (l) +0.30 V, (m) +0.35 V, (n ) +0.40 V, (o) +0.45 V, (p) +0.50 V, (q) +0.55 V, (r) +0.65 V vs Fc/Fc+ in 0.1 M TBAP/PC. -0.6-0.4-0.20.00.20.4 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 Current (mA/cm 2)Potential (V) vs. Fc/Fc+Ep,ox E p,red a -0.3-0.2-0.10.00.10.20.30.4 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 Current (mA/cm 2)Potential (V) vs. Fc/Fc+E p,red E p,ox b Figure 3-26. PBProDOT-R2-B(OC12H25)2 cyclic voltammograms. (a) CV of PBProDOT-Me2B(OC12H25)2, and (b) CV of PBProDOT-Hex2-B(OC12H25)2. Polymers electrodeposited on Pt button and measur ements accomplished in 0.1 M TBAP in ACN/CH2Cl2 (5/3) at scan rates of 25, 50, 100, 150, 200, and 250 mV s-1.

PAGE 84

84 -0.10.00.10.20.30.4 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 54 56 58 60 62 64 66 68 70 72 74 Current (mA/cm2)E(V) vs. Fc/Fc+1 2 3 45 Relative Luminance (%) Figure 3-27. Cyclic volta mmograms of PBProDOT-Hex2-B(OC12H25)2 as function of scan rate. (1) 100, (2) 150, (3) 200, (4) 250 mV s-1. Polymer deposited by drop-casting on Pt button electrode, in 0.1 M TBAP/PC electroly te. The CV are superimposed with % relative luminance versus applied potential ( ) for PBProDOT-Hex2-B(OC12H25)2. The polymer exhibits an orange -red color in the neutral stat e with two absorption maxima at 544 nm and 507 nm (Figure 3-28a) which can be attributed to vi bronic coupling. Upon oxidation, the transition of the ne utral state disappears and, as s oon as the pote ntial reaches about +0.3 V a polaron tr ansition appears in the 600-800 nm re gion with a maximum absorption at 738 nm, changing the film color to light bl ue (Figure 3-28i). Upon further increase in potential, this transition progr essively disappears and bipolar on transitions are observed (1500 nm peaks) (Figure 3-28, i-r), and the polymer film becomes highly transmissive with a light gray color. This demonstrates the potential utility of this polymer in electrochromic applications. Polymer overoxidation and decomposition seemed o ccurring above +0.9 V. An optical band gap of 2.1 eV was determined from the onset of absorption of the neutral polymer. For comparison, a thin-film of PBProDOT-Me2-B(OC12H25)2 was potentiostatically deposited onto an ITO-coated glass electrode (electropolymerization s ection). After washing with a CH2Cl2/ACN (3/5) solution, the orange polymer film was placed in a 0.1 M TBAP/PC electrolyte solution and various absorption spectra were recorded in the neutral state, and at

PAGE 85

85 stepped potentials sequentially from -0.28 V to +0.42 V oxidizi ng the polymer progressively (Figure 3-29). Overoxidation seemed to occur at higher potentials and the polymer film started to fall off the ITO electrode. As with PBProDOT-Hex2-B(OC12H25)2, PBProDOT-Me2-B(OC12H25)2 exhibits an optical band gap of 2.1 eV and a similar color change during redox switching, supporting our previous statement that the hexyl chains introduce little or no change in the optical properties. Surpri singly, the two PBProDOT-R2-B(OC12H25)2 polymers exhibit the same band gaps as the recently studied poly( 1,4-bis(2-thienyl)-2,5diheptoxybenzene).50 This result brings out the subtleties of the effect of side chains on the optical properties of -conjugated polymers. In this instance, the thiophene link ed polymers may be packing in an even more regular manner in the solid stat e than the polymers studied here. A 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Absorbance (a. u.)Wavelength (nm) a r i r a r a i B Thin Thin Thick Thick Neutral Oxidized -e +e Thin Thin Thick Thick Neutral Oxidized -e +e -e +e Figure 3-28. Spectroelectrochemi cal analysis of PBProDOT-Hex2-B(OC12H25)2 spray-cast onto ITO coated glass. (A) U.V.-Vis.-n.I.R. spect ra taken (a) in the neutral state and at potentials of (b) -0.02 V, (c) +0.03 V, (d ) +0.08 V, (e) +0.13 V, (f) +0.18 V, (g) +0.23 V, (h) +0.28 V, (i) +0.33 V, (j) +0.38 V, (k) +0.43 V, (l) +0.48 V, (m) +0.53 V, (n) +0.58 V, (o) +0.63 V, (p) +0.68 V, (q) +0.73 V, (r) +0.78 V vs Fc/Fc+ in 0.1 M TBAP/PC; (B) the film colors are displayed for thin and thick films.

PAGE 86

86 400600800100012001400 0.0 0.1 0.2 0.3 0.4 h aAbsorption (a. u.)Wavelength (nm) b h a Figure 3-29. Spectroelectrochemi cal analysis of PBProDOT-Me2-B(OC12H25)2 electropolymerized on ITO coated glass. U.V. -Vis.-NIR. spectra taken (a) in the neutral state and at potentials of (b) -0.28 V, (c) -0.08 V, (d) +0.02 V, (e) +0.12 V, (f) +0.22 V, (g) +0.32 V, (h) +0.42 V, vs Fc/Fc+ in 0.1 M TBAP/PC. 3.5 Colorimetry 3.5.1 PBT-B(OR)2 Thin-films of PBT-B(OC7H15)2 and PBT-B(OC12H25)2 were deposited on ITO by spraycasting from 3 mg mL-1 toluene solutions, and were analyzed by in-situ colorimetric analysis. The relative luminance was measured as the neut ral polymers were progressively oxidized. In the small 0.45-0.5 V potential window, the relative luminance of PBT-B(OC7H15)2 changed from 30% to 2.5% upon oxidation. There was also a considerable re lative luminance change for PBTB(OC12H25)2 (from 70% to 30%) between 0.45 and 0.55 V. The L*a*b* values of films of about 0.2 m in thickness were also determined to allow color matching. For PBT-B(OC7H15)2: L = 61; a = 50; b = 87 for the orange color (neutral state) and L = 24; a = -5; b = -23 for the bl ue color (doped state). For PBT-B(OC12H25)2: L = 86; a = 22; b = 68 for the orange color (neutral state) and L = 73; a = -6; b = -7 fo r the blue color (doped state).

PAGE 87

87 The available color states of thes e polymers were tracked using the xy chromaticity diagrams shown in Figures 3-30a an d 3-30b (as detailed in Chapter 2).119 As the potential was increased and the polymers were doped, the x and y coordinates decreased. The abrupt color changes observed in the luminance experime nts, can also be clearly seen on the xy chromaticity diagram by large changes in the xy coordinates between similar potential ranges (0.45-0.6 V for PBT-B(OC7H15)2 and 0.49-0.54 V for PBT-B(OC12H25)2) 0.10.20.30.40.50.6 0.10 0.15 0.20 0.25 0.30 0.35 0.40 yx -0.22 V +1.18 V d o p i n g +0.5 Va 0.150.200.250.300.350.400.450.50 0.20 0.25 0.30 0.35 0.40 0.45 -0.56 V to +0.49 Vyxb d o p i n g +1.14 V +0.54 V Figure 3-30. CIE 1931 xy chromaticity diagrams of PBT-B(OR)2 polymers. Circles linked by a dashed line represent the color tr ack for thin-films of (a) PBT-B(OC7H15)2, and (b) PBT-B(OC12H25)2, which go from orange to blue. The potential was increased in 0.05 V steps. 3.5.2 PBProDOT-R2-B(OC12H25)2 A thin-film of the chemically synthesized PBProDOT-Hex2-B(OC12H25)2 was deposited onto ITO by spray-casting from a 10 mg mL-1 chloroform solution and was also analyzed by insitu colorimetric analysis. The relative lumi nance was measured as the neutral polymer was progressively oxidized and the results are s uperimposed in Figure 3-27 onto the cyclic voltammogram to compare the optical changes along with the material oxidation. Optical changes started occurring at +0.23 V vs Fc/Fc+, which corresponds to the polymer’s onset of

PAGE 88

88 oxidation. At this potential, th ere was a sharp increas e in the luminance which went from 55 % to 70 % in less than 0.1 V. Finally, upon furthe r oxidation the luminance reached saturation at +0.6 V. The L*a*b* values of the thin-f ilm colors in the neutral a nd oxidized states were also determined. In the red-orange neutral state, L = 79, a = 40, b = 14, and in the fully oxidized light gray state, L = 90, a = -1 and b = -3 for a spray-cast film of about 0.2 m in thickness. The available color states that PBProDOT-Hex2-B(OC12H25)2 has to offer were al so tracked using the xy chromaticity diagram shown in Figure 3-31. As the potential was increased and the polymer was doped the x coordinate decrea sed and the y coordinate decrea sed after an initial increase. The abrupt color change which occurred at +0.23 V and was observed on the luminance spectrum in Figure 3-27, can also be clearly seen on the xy chromaticity diagram by a large change in the xy coordinates at that potential. Note that for clarity, this chromaticity diagram is a 25 x magnification of the region of interest of the full xy chromaticity diagram displayed in Chapter 2. A few differences were observed for th icker films, such as a more pronounced blue color in the oxidized state ( photograph in Figure 3-28), a lo wer luminance value (around 30 %) characteristic of a more opaque film, and no difference in the luminance values between the neutral and the fully oxidized states. 3.6 Solvatochromism, Thermochromism, and Ionochromism While heating (about 60C) 0.1 M TBAP in CH2Cl2/ACN solutions of the BProDOT-R2B(OC12H25)2 monomers, a reversible color change wa s surprisingly observed (from yellow to red as seen in Figure 3-32). This phenomenon was inte restingly not seen without the presence of the electrolyte. It was deduced that upon the increase in temperature, the bac kbone of the three rings system twisted and gained a certain conformation (i n this case more planar due to the red-shift),

PAGE 89

89 which favored the coordination of the ions coming from the electrolyte and the locking of that position. These observations motivated the solv atochromic study of PBProDOT-Hex2B(OC12H25)2. 0.340.360.380.400.420.440.46 0.365 0.370 0.375 0.380 0.385 0.390 0.395 yx0.23V 0.28 V 0.83 V Figure 3-31. CIE 1931 xy chromaticity diagram of a thin-film of PBProDOT-Hex2-B(OC12H25)2. Triangles linked by a dashed line represen t the color track for the polymer film which goes from orange to light gray. Th e potential was increased in 0.05 V steps. Figure 3-32. Thermochromic change s observed for a 0.1 M TBAP in CH2Cl2/ACN solution of the BProDOT-Me2-B(OC12H25)2 monomers. At room temperature, a 1.36 x 10-5 mol L-1 toluene solution of the chemically synthesized PBProDOT-Hex2-B(OC12H25)2 was yellow and exhibited an ab sorption maximum at 478 nm as illustrated in Figure 3-33. The resolution of the fine structure was not as well defined as it was in the film absorption spectrum (Figure 3-28), and the solution absorption was blue-shifted compared to the film absorption where th e maximum was observed at 544 nm. This was expected since solvated polymer chains are more disordered in solution a nd consequently have a lower conjugation length.

PAGE 90

90 Upon addition of methanol, wh ile maintaining a constant polymer concentration (1.36 x 10-5 mol L-1), the solution became more red and showed an absorption maximum at 503 nm, with a vibronic side band at 541 nm. In pure toluene, the polymer wa s highly solvated and poorly ordered. Upon addition of metha nol, the polymer exhibi ted more extensive conjugation as could be deduced from the shift of the absorption maximum to longer wavelengths. According to the literature, the energy diffe rence of 0.18 eV (1460 cm-1) from the main peak to the vibronic peak is consistent with a C=C stretc hing mode which would be exp ected to couple strongly to the electronic structure.120 This is an additional evidence for th e presence of more ordered molecules in the presence of poorly solvating solvents. The combined ionic and thermochromic properties observed for the BProDOT-R2B(OC12H25)2 monomers were also checked on the polymers. PBProDOT-Hex2-B(OC12H25)2 was dissolved in a CH2Cl2/ACN solution containing TBAP. As methanol, acetonitrile behaves as a poor solvent for the polymer and turned the poly mer solution into a deep red color, making it impossible to check for ionochromic/thermochromi c effects. Another attempt was performed on a pure methylene chloride polymer solution co ntaining TBAP. Upon heating, no color change could be observed suggesting that the chro mic phenomenon probably resulted from the simultaneous action of temperature, ions, and poor solvent. This was verified by heating a methylene chloride monomer solution containing TBAP, and indeed, no color change could be observed this time. 3.7 Application to Devices 3.7.1 Photovoltaic Devices 3.7.1.1 PBT-B(OR)2 Bulk heterojunction solar cells using the PBT-B(OR)2 polymers as the electron donors and PCBM as the electron a cceptor (device structure ITO/PEDOT-PSS/PBT-B(OR)2:PCBM/LiF/Al)

PAGE 91

91 were prepared by Dr. Young-Gi Kim in order to evaluate for the first time the photovoltaic properties of such materials. Blends containi ng 1:4 (w/w) of each pol ymer with PCBM were spin-coated from 1,2-dichlorobenz ene solutions into ~ 45 nm th ick photoactive layers. Figure 334a shows the i-V characteristics of the PBT-B(OC12H25)2 based device under AM 1.5 illumination for a calibrated solar simula tor with an intensity of 100 mW cm-2, and Table 3-3 summarizes the photovoltaic results. The PBT-B(OC7H15)2/PCBM device exhibited the best performance with a power conversion efficiency ( ) of ~ 0.6%, a short circuit current (Isc) of 2.49 mA cm-2, an open circuit voltage (Voc) of 0.74 V, and a fill factor (FF) of 32% 300400500600700800 0.0 0.5 80:20 100:0 60:40 50:50 40:60AbsorbanceWavelength (nm) Toluene:Methanol 30:70 a ) b) Figure 3-33. UV-vis absorption spectra of PBProDOT-Hex2-B(OC12H25)2 in toluene/methanol mixtures. Pictures: solutions (a) in tolu ene, (b) in a mixture of toluene and methanol. Incident photon to current efficiency measur ements (IPCE) match the polymer absorption spectra near the absorption maxima of the polym ers, indicating that the polymers are effective photoexcited electron donors that contribute mainly to the photocur rent in the device (Figure 334b). Both polymers exhibit IPCEs of ~ 16% at 410 nm. Consequently, PBT-B(OC7H15)2 and PBT-B(OC12H25)2 showed their potential for use in organic photovoltaic devices, harvesting

PAGE 92

92 incident light of the mid-range energy. It would be interesting to combine these polymers with lower or higher band gap polymers in order to absorb over a broader spectral range and to improve the photovoltaic efficiencies…but for that physicists have to take over that project now! -0.20.00.20.40.60.81.0 -4 -3 -2 -1 0 1 illuminated AM1.5 dark Current density (mA/cm2)Voltage (V)a 400500600700 0 4 8 12 16 IPCE(%)Wavelength (nm)b Figure 3-34. Photovoltaic results of solar cells made of a 1/4 blend (w/w) of PBTB(OR)2/PCBM. (a) Current voltage characteristic for PBT-B(OC12H25)2 under AM1.5 conditions (100 mW cm-2). (b) IPCE results for PBT-B(OC12H25)2 ( ) and PBT-B(OC7H15)2 ( ). Table 3-3. Summarized photovoltaic char acteristics of PBT-B(OR)2/PCBM based solar cells. 3.7.1.2 PBProDOT-Hex2-B(OC12H25)2 Bulk heterojunction solar cells using PBProDOT-Hex2-B(OC12H25)2 as the electron donor and PCBM as the electron acceptor have also been prepared by the group of Prof. Yang Yang at the University of California (UCLA), using the same conditi ons as the ones used for PBTB(OR)2 (see section above). The device exhibited a power conversion efficiency of 0.22%, a short circuit current of 0.98 mA cm-2, an open circuit voltage of 0.55 V, and a fill factor of 41% (see i-V characteristic of the device in Figure 3-35). The polymer’s photovoltaic properties are not as great as the ones determined for PBT-B(OR)2. This might be due to poorer hole transport Photosensitizer (%) FFVoc (V) Isc (mA cm-2) PBT-B(OC7H15)2 0.590.320.74 2.49 PBT-B(OC12H25)2 0.480.390.76 1.59

PAGE 93

93 properties, probably resulting from a less regular p acking in the solid state (as it had been already suggested from the band gap re sults, see section 3.4.2). -0.20.00.20.40.60.81.0 -2 -1 0 1 2 PCBM = 80 wt. % Current Density (mA/cm2)Voltage (V) Figure 3-35. Current voltage ch aracteristic of a solar cell ma de of a 1/4 blend (w/w) of PBProDOT-Hex2-B(OC12H25)2 /PCBM under AM1.5 conditions (100 mW cm-2). 3.7.2 LEDs The chemically synthesized PBProDOT-Hex2-B(OC12H25)2 exhibits a yellow-orange fluorescence in toluene with an evaluated quan tum efficiency of 54 % (against Coumarin 6 standard; = 0.78).100 The emission spectrum illustrated in Figure 3-36 exhibits two welldefined vibronic bands at 539 nm and 582 nm, a nd one poorly resolved band at approximately 630 nm in toluene. For a spin-coated film, the emission spectrum has a similar shape although it is red shifted due to a more organized conforma tion (Figure 3-36). The vi bronic bands are seen at 571, 617 and 679 nm (Photoluminescence Quantum Efficiency (PLQE) = 3.5 2 %). Dr. J. Mwaura investigated th e potential of this polymer in LEDs. For that study, devices of the following architecture were prep ared: ITO/PEDOT-PSS (40 nm)/PBProDOT-Hex2B(OC12H25)2 (50 nm)/Ca (5 nm)/Al (200 nm). As s hown in Figure 3-36, the device exhibits a broad emission dominated by a peak at max = 570 nm. The electrolumin escence (EL) spectrum

PAGE 94

94 is similar to the photoluminescence (PL) spectrum of the solid film, indicating that the electroluminescence results from a singlet exciton with the same structure as that produced by photoexcitation. The absence of red-shifting on the EL spectrum relative to the PL spectrum suggests that the electroluminescence is dominat ed by the non-aggregated polymer chains, with the interchain aggregates contri buting to little or no emission. On the device characteristics illustrated in Fi gure 3-37, it can be seen that the PBProDOTHex2-B(OC12H25)2 device turns on at 6 V. The EL intensity increases with voltage, peaking at 13 V, and decreasing at higher vo ltages, possibly due to device breakdown. At 13 V, the device emits the highest luminance at ~ 240 cd m-2 and a current density of 1100 mA cm-2. Figure 3-37 shows the external electronto-photon quantum efficiency (EQE) of the PBProDOT-Hex2B(OC12H25)2 EL device as a function of applied voltage The efficiency increases after turn on, peaking at 8 V at ~ 0.03 %, afte r which it steadily decreases as the applied voltage and current density increase. These low EQE sh ow that the polymer is not likely effective for development in LED applications. 500550600650700750800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 PL intensity (Normalized)Wavelength (nm) EL intensity (Normalized) Figure 3-36. Photoluminescence em ission spectrum of PBProDOT-Hex2-B(OC12H25)2 in toluene solution and in thin-film (bold line) superimposed with electroluminescence spectrum of an EL device with the following configuration: ITO/PEDOTPSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al. The inset picture represents the light emission of the EL device.

PAGE 95

95 2468101214 0 50 100 150 200 250 468101214 0.00 0.01 0.02 0.03 0.04 External Q.E. (%)Voltage (V)Luminance cd/m2Voltage (V)0 200 400 600 800 1000 1200 Current Density ( mA/cm2) Figure 3-37. LED properties of an ITO/PEDOT-PSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al device. Luminance spectrum ( ) and current density ( ). Left top inset: External quantum efficiency. 3.8 Conclusions and Perspective The packing properties (small interchain distance s, or cofacial arrangements of the rings of adjacent layers) of the regiosymmetric Br2-BT-B(OR)2 and Br2-BEDOT-B(OR)2 monomers, revealed that these materials might be interes ting building blocks for pr oducing hole transporting materials (oligomers or polymers) for organic elect ronic devices requiring high charge transport, like photovoltaics. This idea was supported also by previously reported studies on the ordering properties of PBT-B(OR)2, which have shown the propensity of these materials to crystallize.22 For that reason, their chemical polymerization ha s been revisited with the goal of obtaining higher molecular weight materials than the one previously reported, wi th good processability. Yamamoto coupling via Ni(COD)2 proved to be the most effective method among the methods which have been attempted in this work (GriM, solid state polymerization) or in the literature, for getting the monomers to couple between each other. However the molecular weights stayed limited, especially in th e case of PBEDOT-B(OR)2. This is due in part to its too powerful electron donating properties which diminish the reactivity of the growing chains to the Ni

PAGE 96

96 oxidative addition. It is also du e to its poor solubility probably resulting from its propensity to aggregate as suggested by the tig ht packing observed in the X-ra y crystal structures of the monomers. Polymers of reasonable size, processa bility, and film homoge neity, were obtained in the case of PBT-B(OR)2, and it was decided to investigate the electroni c, electrochromic, and photovoltaic properties of this ma terial only. DSC studies confirme d the semi-crystalline nature of this regiosymmetric polymer, and comforted us in our idea to built photovoltaics with this material. The electrochemical and spectroelec trochemical studies attested the PBT-B(OR)2 polymers ability to harvest incident li ght in the mid-visible energy range (Eg of 2.1 eV), stability to oxidation, and capacity to transfer charges to PCBM. When applied as the hole transporting layer in bulk heterojunction photovoltaic device s with PCBM as the acceptor, they effectively produced photocurrent, and power conversion e fficiencies up to 0.6% were reached. These results are of valuable importance and should not be compared to the 5% e fficiencies that have been obtained for P3HT:PCBM devices, since such performances are the results of years of optimization from various research groups.73-75 There are only a few examples of polymers which have been successfully em ployed in solar cells and most of them have never reached 1% efficiencies.121 Apart from their photovoltaic propert ies, these materials exhibit nice electrochromic properties, switchi ng between deep orange and bl ue colors, in the neutral and oxidized states, respectively. In order to overcome the solubility limitations of PBEDOT-B(OR)2 and to make a similarly electron rich material, we decided to replace the EDOT moiety of this regiosymmetric member by alkyl (Me or hexyl) -substituted ProDOT heterocy cles, the methyl substituted derivative being studied for comparison. Due to their novelty, these materials were first electropolymerized before investig ating their chemical polymerizat ion, in order to get a quick

PAGE 97

97 look at their redox and electroni c properties. The PBProDOT-R2-B(OC12H25)2 polymers exhibit band gaps of 2.1 eV, quite close to their thiophene counterparts likely due to a less regular packing in the solid state. Th is in turn compensates the el ectron donating effect of the oxygen substituents appended to the thi ophene ring and gives ri se to films having a similar orange color in the neutral state.103 Conversely, as the polymer was progressi vely oxidized a di fferent behavior was observed for PBProDOT-Hex2-B(OC12H25)2 and a highly transmissive state was reached while the thiophene analogues re tain a deeper blue color.50,103 A chemical synthesis was developed for this polymer, giving rise to a highl y soluble material that can be processed by spray-casting or spin-coating techniques. Thes e interesting solubility and color switching properties open the door to electrochromic applicat ions using large or flex ible surfaces such as electrochromic displays or smart windows. Unfortunately maximum power conversion efficiencies of 0.22% were reached, and these poorer photovoltaic properties compared to PBTB(OR)2, might be the result of a less regular packing of PBProDOT-Hex2-B(OC12H25)2 in the solid state. However, the particularly tight crys talline packing and the close to perfect cofacial arrangement of adjacent molecules of the three ring BProDOT-Me2-B(OC12H25)2 system could motivate the development of oligomers of this t ype for electronic applic ations requiring high charge carrier mobility. 3.9 Experimental 1,4-Dibromo-2,5-diheptoxybenzene (1a).22 Freshly recrystall ized 1,4-dibromo-2,5dihydroxybenzene (13.19 g, 4.90 10-2 mol) was dissolved in EtOH (75 mL) under argon to give a slightly pink solution. A 75 mL solution of KOH (7.01 g, 1.25 10-1 mol) in EtOH was slowly added and the solution color turned br own. The solution mixture was stirred at room temperature for 2 h. Then 1-bromoheptane (22.45 g, 1.25 10-1 mol) was dissolved in EtOH (20 mL) and this solution was added dropwise to the reaction mixture forming a beige

PAGE 98

98 precipitate. This solution was heated at 65-70 C for 18 h. It was cooled to room temperature and deionized water was added yielding a pink precipitate. The precipitate was filtered on a Bchner funnel and a slightly pink solid was collected and dried under vacuum. This solid was purified by recrystallization from ethanol/ben zene (3/1) to give 17.58 g (77% ) of white crystals [mp = 5658 C (lit.22 mp = 59-60 C)]. 1H-NMR (CDCl3, ppm): = 7.08 (s, 1H), 3.94 (t 2H), 1.80 (p, 2H), 1.48 (m, 2H), 1.31 (m, 6H), 0.89 (t, 3H). 13C-NMR (CDCl3, ppm): = 150.45, 118.94, 111.50, 70.67, 31.94, 29.36, 29.15, 26.11, 22.76, 14.21. Anal. Calcd for C20H32Br2O2: C, 51.74, H, 6.95. Found: C, 52.01, H, 7.26. 1,4-Dibromo-2,5-didodecyloxybenzene (1b).22 1,4-Dibromo-2,5-didodecyloxybenzene was prepared according to the procedure described for 1,4-dibromo-2,5-diheptoxybenzene utilizing freshly recrystallized 1,4dibromo-2,5-dihydroxybenzene (11.27 g, 4.20 10-2 mol), KOH (1.01 10-1 mol), and 1-bromododecane (1.01 10-1 mol). Recrystallization from ethanol/benzene (3/1) gave 23.89 g (94 %) of white crystals [mp = 75-77 C (lit.22 mp = 7779 C)]. 1H-NMR (CDCl3, ppm): = 7.09 (s, 1H), 3.95 (t, 2H), 1.81 (p, 2H), 1.48 (m, 2H), 1.29 (m, 16H), 0.89 (t, 3H). 2-(Trimethylstannyl)thiophene [Th-Sn(CH3)3].122 Thiophene was dried over calcium hydride overnight and then purified by disti llation under reduced pressure (bp = 30-35 C at 130 torr). Thiophene (4.38 g, 5.20 10-2 mol) was dissolved in a nhydrous THF (35 mL) under argon. The solution was cooled to -78 C and butyllithium (21.90 mL 2.50 M in hexanes, 5.50 10-2 mol) was added dropwise via an addition funnel The clear solution was stirred for 1 h and became slightly pink. Trimethylstannyl chloride (54.70 mL, 1 M in THF, 5.50 10-2 mol) was then added dropwise and the solution turned sli ghtly yellow. The mixture was allowed to warm to room temperature with stirring overnight and the color turned brown. Deionized water was

PAGE 99

99 added (30 mL) and the mixture was extracted with diethyl ether. The or ganic phase was washed with brine, dried over magnesium sulfate (MgSO4) and filtered through a Bchner funnel. The solvent was evaporated and a brown oil was collected. This oil was purified by distillation (bp = 93-97 C at 25 mmHg) and 9.90 g (77%) of a white solid were obtained and dried under vacuum. 1H-NMR (CDCl3, ppm): = 7.65 (d, 1H), 7.24 (m, 2H), 0.37 (s, 9H). 2-(Trimethylsilyl)-3,4-ethyle nedioxythiophene [EDOT(SnCH3)3].36 A solution of 3,4ethylenedioxythiophene (EDOT) in THF was dried overnight ove r potassium. A solution of EDOT (7.50 g, 5.28 10-2 mol) in anhydrous THF (50 mL) wa s cooled at -78C under argon and n -butyllithium (2.5 M in hexanes, 5.81 10-2 mol) was added dropwise via addition funnel. The mixture was stirred at -78C for 1 h and then warmed up to 0C for 30 min, changing the clear solution to an orange color. The solution was cool ed back to -78C and trimethylstannyl chloride (1 M in THF, 5.28 10-2 mol) was added dropwise thanks to an addition funnel. The orange solution was warmed to room temperature and st irred overnight. Deionize d water was added to the solution and the mixture was extracted with et her. The organic phase was washed with Brine and dried over MgSO4. After filtration through a Bchner funnel, the solvent was evaporated and a brown oil was obtained and purified by dist illation under vacuum (bp = 110C at 0.4 mmHg). After cooling, 11.93 g of white-clear solid (74%) were collected. 1H-NMR (CDCl3, ppm): = 6.56 (s, 1H), 6.30 (s, 2H), 4.16 (m, 4H), 0.35 (s, 9H). 1,4-Bis(2-thienyl)-2,5-diheptoxybenzene [BT-B(OC7H15)2].22 Th-Sn(CH3)3 (9.28 g, 3.76 10-2 mol) and 1,4-dibromo-2,5-diheptoxybenzene (8.69 g, 1.87 10-2 mol) were dissolved in anhydrous DMF (200 mL) under argon at 80 C. Argon was bubbled into the reaction mixture for 20 min. Then, Pd(PPh3)4 catalyst (1.68 g, 1.50 10-3 mol) was added quickly and the orange solution was warmed to 120 C and stirred overnight giving rise to a green-black mixture. It was

PAGE 100

100 then cooled to room temperature and poured in to deionized water (500 mL). The mixture was extracted with diethyl ether; the organic phase was collected, washed with brine and dried over MgSO4. An orange organic solution was obtained after filtration on a Bchner funnel. The solvent was evaporated and a yellow solid was collected and placed under vacuum. After recrystallization from ethanol/benze ne (3/1), 7.17 g (81%) of yellow crystals were obtained [mp = 76-77C (lit.22 mp = 77-78C)]. 1HNMR (CDCl3, ppm): = 7.54 (d, 1H), 7.34 (d, 1H), 7.26 (s, 1H), 7.10 (dd, 1H), 4.08 (t, 2H), 1.90 (p, 2H ), 1.52 (m, 2H), 1.32 (m, 6H), 0.90 (t, 3H). 1,4-Bis(2-thienyl)-2,5-didodecyloxybenzene [BT-B(OC12H25)2].22 BT-B(OC12H25)2 was prepared according to the pro cedure described for BT-B(OC7H15)2 utilizing Th-Sn(CH3)3 (9.80 g, 3.97 10-2 mol) 1,4-dibromo-2,5-didodecyloxybenzene (11.86 g, 1.96 10-2 mol), anhydrous DMF (300 mL) and Pd(PPh3)4 (9.06 10-1 g, 7.80 10-4 mol). The yellow solid was dried under vacuum and recrystallized fr om ethanol/benzene (3/1) to gi ve 9.35 g (78%) of thin yellow crystals [mp = 77-78C (lit.22 mp = 77-78C)]. 1H-NMR (CDCl3, ppm): = 7.54 (d, 1H), 7.33 (d, 1H), 7.26 (s, 1H), 7.09 (dd, 1H), 4.08 (t, 2H), 1.90 (p, 2H), 1.52 (m, 2H), 1.27 (m, 16H), 0.88 (t, 3H). 1,4-Bis[2-(3,4-ethylenedioxy)thienyl]2,5-diheptoxybenzene [BEDOT-B(OC7H15)2]. EDOT(SnCH3)3 (6.00 g, 1.96 10-2 mol) and 1,4-dibromo-2,5-diheptoxybenzene (4.54 g, 9.70 10-3 mol) were dissolved in anhydrous DMF ( 300 mL). The solution was heated at 80C to dissolve everything. Argon was bubbled into the solution for 15 min and Pd(PPh3)4 (5.04 10-3 g, 4.36 10-4 mol) was quickly added. The reacti on was stirred at 120C overnight and the yellow-orange solution turned black. The solution was cooled to room temperature and poured into deionized water. The mixture was extr acted with diethyl ethe r and the organic phase was washed with brine, dried over MgSO4 and filtered on a Bchner funnel. The solvent was

PAGE 101

101 evaporated and a yellow solid was collected a nd dried under vacuum. After recrystallization from ethanol/benzene (3/1), 4.62 g of yellow crys tals (81%) were obtained [mp = 84-87C (lit.46 mp = 85-87C)]. 1H-NMR (CDCl3, ppm): = 7.68 (s, 1H), 6.37 (s, 1H), 4.28 (m, 4H), 4.04 (t, 2H), 1.88 (p, 2H), 1.52 (m, 2H), 1.32 (m, 6H), 0.89 (t, 3H). 1,4-Bis[2-(3,4-ethylenedioxy)thienyl]2,5-didodecyloxybenzene [BEDOT-B(OC12H25)2]. BEDOT-B(OC12H25)2 was prepared according to the procedure described for BEDOTB(OC7H15)2 utilizing EDOT(SnCH3)3 (10.83 g, 3.56 10-2 mol), 1,4-dibromo-2,5didodecyloxybenzene, (10.73 g, 1.78 10-2 mol), anhydrous DMF (300 mL) and Pd(PPh3)4 (0.82 g, 7.10 10-4 mol). After recrystallization from etha nol/benzene (3/1), 9.12 g (71%) of yelloworange crystals were collected [mp = 92-96C (lit.46 mp = 92-95C)]. 1H-NMR (CDCl3, ppm): = 7.68 (s, 1H), 6.37 (s, 1H), 4.28 (m, 4H), 4.04 (t, 2H), 1.88 (p, 2H), 1.52 (m, 2H), 1.27 (m, 16H), 0.89 (t, 3H). 1,4-Bis(2-(5-bromo)thienyl )-2,5-diheptoxybenzene [Br2-BT-B(OC7H15)2]. BT-B(OC7H15)2 (2.07 g, 4.40 10-3 mol) was dissolved in anhydrous DMF (125 mL) under argon and the yellow slurry was cooled to 0C. Freshly recrystallized N-bromosuccinimide (NBS) (1.66 g, 9.38 10-3 mol) was added in small portions. Th e reaction was left at 0C for 3 h. Then it was warmed at room temperature and stirred overnight. Deioni zed water (300 mL) was added to the yellow slurry and th e mixture was extracted with di ethyl ether. The organic phase was washed with brine, dried over MgSO4 and filtered through a Bchner funnel. The solvent was evaporated and a yellow solid was collected and dried under vacuum. Pure crystals, 1.99 g (72%) were obtained by recrystallizations from ethanol/benzene (3/1) and ethanol/THF (3/1) [mp = 104-105C]. 1H-NMR (CDCl3, ppm): = 7.25 (d, 1H), 7.16 (s, 1H), 7.04 (d, 1H), 4.07 (t, 2H), 1.91 (p, 2H), 1.52 (m, 2H ), 1.34 (m, 6H), 0.91 (t, 3H). 13C-NMR (CDCl3): =

PAGE 102

102 149.30, 140.70, 129.50, 124.80, 122.80, 113.40, 111.60, 70.06, 31.98, 29.53, 29.27, 26.39, 22.85, 14.35. Anal. Calcd for C28H36Br2O2S2: C, 53.51, H, 5.77. Found: C, 53.64, H, 5.77. HRMS C28H36Br2O2S2: calcd, 626.0523; obsd, 626.0524. 1,4-Bis(2-(5-bromo)thienyl)2,5-didodecyloxybenzene [Br2-BT-B(OC12H25)2]. Br2-BTB(OC12H25)2 was prepared according to the procedure described for Br2-BT-B(OC7H15)2 utilizing BT-B(OC12H25)2 (8.86 g, 1.45 10-2 mol), anhydrous DMF (350 mL) and freshly recrystallized NBS (5.39 g, 3.05 10-2 mol). After successive recrystallizat ions from ethanol/benzene (2/1), ethanol/THF (2/1), and methanol/THF (2/1), 9.54 g (86%) of pure yellow crystals were obtained [mp = 101-103C]. 1H-NMR (CDCl3, ppm): = 7.25 (d, 1H), 7.17 (s, 1H), 7.04 (d, 1H), 4.08 (t, 2H), 1.92 (p, 2H), 1.52 (m, 2H), 1.27 (m, 16H), 0.89 (t, 3H). 13C-NMR (CDCl3): = 149.20, 140.60, 129.49, 124.80, 122.80, 113.20, 111.61, 70.06, 32.17, 29.92, 29.89, 29.84, 29.80, 29.61, 26.44, 22.94, 14.40. Anal. Calcd for C38H56Br2O2S2: C, 59.37, H, 7.34. Found: C, 59.67, H, 7.54. HRMS C38H56Br2O2S2: calcd, 766.2088; obsd, 766.2098. 1,4-Bis[2-(5-bromo-3,4-eth ylenedioxy)thienyl]-2,5-diheptoxybenzene [Br2-BEDOTB(OC7H15)2]. BEDOT-B(OC7H15)2 (1.00 g, 1.70 10-3 mol) was dissolved in anhydrous DMF (75 mL) and the solution was cooled at -78 C under argon. Freshly recr ystallized and dry NBS (0.75 g, 4.24 10-3 mol) was added in small portions to the yellow slurry. The temperature was raised slowly to 0 C as the slurry turned from yello w to green to blue. After 4 h, NH4OH (10 mL) was quickly added changing the solution colo r to yellow and the mi xture was stirred an extra 10 min. Deionized water was then added to the solution and the mixture was extracted with diethyl ether. The organic phase was washed with brine, dried over MgSO4 and filtered through a Bchner funnel. The solvent was evaporated and a yellow solid was collected and dried under vacuum. The solid was purified by column chromatography on silica gel using CH2Cl2/hexane

PAGE 103

103 (1/1) at a fast flow rate. The compound polymerizes on the column if the elution is too slow. The solid was finally purified by recrystallization in methanol/THF (3/1) to give 0.56 g (42%) of yellow crystals [mp = 162-163 C]. 1H-NMR (CDCl3, ppm): = 7.70 (s, 1H), 4.33 (m, 4H), 4.05 (t, 2H), 1.90 (p, 2H), 1.52 (m, 2H), 1.34 (m, 6H), 0.91 (t, 3H). 13C-NMR (CDCl3): = 148.57, 139.30, 137.86, 120.41, 113.74, 112.68, 88.20, 69.91, 64.78, 64.72, 31.77, 29.26, 29.07, 26.21, 22.62, 14.11. Anal. Calcd for C32H40Br2O6S2: C, 51.62, H, 5.41. Found: C, 51.82, H, 5.59. HRMS C32H40Br2O6S2: calcd, 744.0633; obsd, 744.0629. 1,4-Bis[2-(5-bromo-3,4-eth ylenedioxy)thienyl]-2,5-didodecyloxybenzene [Br2-BEDOTB(OC12H25)2]. Br2-BEDOT-B(OC12H25)2 was prepared according to the procedure described for Br2-BEDOT-B(OC7H15)2 utilizing BEDOT-B(OC12H25)2 (2.58 g, 3.55 10-3 mol), anhydrous DMF (250 mL) and freshly recrystallized NBS (1.57 g, 8.88 10-3 mol). After purification by column chromatography on silica gel with me thylene chloride/hexanes (1/2), followed by recrystallization from methanol /THF (1/1), 1.80 g (57%) of yello w crystals were obtained [mp = 126-127C]. 1H-NMR (CDCl3, ppm): = 7.70 (s, 1H), 4.33 (m, 4H), 4.05 (t, 2H), 1.90 (p, 2H), 1.52 (m, 2H), 1.27 (m, 16H ), 0.88 (t, 3H). 13C-NMR (CDCl3): = 148.81, 139.56, 138.09, 120.66, 113.99, 112.95, 88.43, 70.16, 65.01, 64.95, 32.15, 29.91, 29.87, 29.66, 29.59, 29.50, 26.50, 22.92, 14.30. Anal. Calcd for C42H60Br2O6S2: C, 57.01, H, 6.83. Found: C, 56.62, H, 6.94. HRMS C42H60Br2O6S2: calcd, 882.2198; obsd, 882.2199. Poly(1,4-bis(2-thienyl)-2,5diheptoxybenzene) [PBT-B(OC7H15)2]. Ni(COD)2 (1.04 g, 3.78 10-3 mol) and Bpy (4.95 10-1 g, 3.17 10-3 mol) were combined in a Schlenk flask under argon and dissolved in anhydrous DMF (30 mL). A solution of 1,5-cyclooctadiene (0.39 mL, 3.12 10-3 mol) was quickly added via a syringe The purple solution was warmed to 60 C for 40 min and slowly added to a 50 mL solution of Br2-BT-B(OC7H15)2 (1.98 g, 3.15 10-3

PAGE 104

104 mol) in anhydrous DMF. The color turned im mediately red. The reacti on was maintained at 60 C for 48 h in the dark. The solution was cool ed to room temperat ure and poured into methanol (1 L) yielding a red precipitate wh ich was filtered through a Soxhlet thimble. The precipitate was purified by Soxhlet extraction for 24 h with metha nol and 30 h with hexanes. The polymer was fractionated with toluene. The tolu ene was evaporated under reduced pressure to afford 0.82 g (55%) of red solid. 1H-NMR (CDCl3, ppm): = 7.50 (Th-H), 7.21 (Ar-H), 7.05 (Th-H), 4.15 (OCH2), 1.95 (OCH2CH2), 1.32 (CH2), 0.90 (CH3). GPC analysis: Mn = 4,960, Mw = 6,340, PDI = 1.28. Poly(1,4-bis(2-thienyl)-2,5-di dodecyloxybenzene) [PBT-B(OC12H25)2]. PBT-B(OC12H25) was prepared according to the procedure described for PBT-B(OC7H15)2 utilizing Ni(COD)2 (8.61 10-2 g, 3.13 10-3 mol), Bpy (4.90 10-1 g, 3.14 10-3 mol), anhydrous DMF (50 mL), 1,5-cyclooctadiene (0.32 mL, 2.62 10-3 mol) and Br2-BT-B(OC12H25)2 (2.00 g, 2.60 10-3 mol). The polymerization solution was stirred at 60 C for 24 h. A red solid (6.36 10-1 g, 40%) was recovered after Soxhlet extraction in toluene. 1H-NMR (CDCl3, ppm): = 7.50 (Th-H), 7.21 (Ar-H), 7.05 (Th-H), 4.13 (OCH2), 1.96 (OCH2CH2), 1.27 (CH2), 0.87 (CH3). GPC analysis: Mn = 2,945, Mw = 3,950, PDI = 1.34. 2,3,4,5-Tetrabromothiophene (3). Thiophene (80.00 g, 9.52 10-2 mol) and chloroform (35 mL) were combined in a 2L 3-neck flask equipped with a reflux conde nser and an addition funnel and vented to an empty 3-neck round botto m flask connected to a scrubber charged with a saturated sodium hydroxide solution and sodium bisulfite. The reaction mi xture was cooled at 0C with an ice bath and bromine (125 mL, 4.76 mol) was added slowly over a five hours period. The flask was warmed at room temperature an d stirred for 12 hours. A solution of ammonium hydroxide was added slowly to the solid mixture and the solid pieces we re broken via spatula.

PAGE 105

105 Chloroform was added and the solution heated at 60C for about 30 min to dissolve the solid. Then, the solution was transferred to a separato ry funnel and extracted with chloroform. The chloroform layer was collected and dried over ma gnesium sulfate. After filtration through a Bchner funnel, the solution was placed in the fridge and 162.80 g (43%) of white crystals were collected, filtered through a B chner funnel, washed with co ld chloroform and dried under vacuum. 13C-NMR (CDCl3, ppm): 116.9, 110.3. 3,4-Dibromothiophene (4).116 2,3,4,5-Tetrabromothiophe ne (162.80 g, 4.07 10-1 mol) was dissolved in glacial acetic acid (163 mL) in a 500 mL 3-neck round bottom flask equipped with a condenser. Zinc powder (58.60 g, 8.96 10-1 mol) was added in small portions and the reaction mixture was refluxed overn ight under nitrogen. Then the solution was cooled to room temperature, poured into deionized water and extr acted with diethyl ether. The ether layer was collected and dried over magnesium sulfate. After filtration through a Bchner funnel, the solvent was evaporated and a yellow oil was co llected. The oil was purified by distillation under reduced pressure and 61.08 g (63%) of 3,4-dibrom othiophene were obtained [bp: 110C at 17 mmHg (lit.123 94-95C, 12 mmHg)]. 1H-NMR (CDCl3, ppm): 7.30 (s, 2H); 13C-NMR (CDCl3, ppm): 123.8, 113.9. 3,4-Dimethoxythiophene (5).124 A solution of sodium methoxide was prepared by refluxing for 2 h under nitrogen anhydrous meth anol (250 mL) with sodium (20.00 g, 8.69 10-1 mol) in a 500 mL 3-neck round bottom flask equipped with a condenser. Then 3,4dibromothiophene (51.30 g, 2.14 10-1 mol) was added as well as cupper oxide (17.00 g, 2.14 10-1 mol) and potassium iodide (0.35 g, 2.14 10-3 mol). Every two days of reflux, another amount of potassium iodide (0.35 g, 2.14 10-3 mol) was added to the purple slurry. The reaction was kept under reflux for six days tota l. Then, the mixture was cooled to room

PAGE 106

106 temperature, poured into deionized water and extr acted with diethyl ether. The ether layer was washed with brine, dried over MgSO4, and after filtratio n through a Bchner funnel the solvent was evaporated to give a pink oil. The oil was purified under reduced pressure and 27.28 g (89%) of clear oil were collect ed [bp: 98C at 11 mmHg (lit.125 110C at 17 mmHg)]. 1H-NMR (CDCl3, ppm): 6.21 (s, 1H), 3.87 (s, 3H); 13C-NMR (CDCl3, ppm): 148.01, 96.45, 57.80. 3,3-Dimethyl-3,4-dihydro-2H-thieno[ 3,4-b][1,4]dioxepine [ProDOT-Me2].126 To a 500 mL three-necked flask equipped with a Soxhlet ex tractor containing a cellulose thimble with 4 molecular sieves was added 3,4-di methoxythiophene (5.94 g, 4.12 10-2 mol), 2,2-dimethyl-1,3propanediol (8.58 g, 8.25 10-3 mol), p -toluenesulfonic acid m onohydrate (0.78 g, 4.12 10-3 mol) and freshly distilled toluene (300 mL) unde r nitrogen. The solution was refluxed overnight. Then it was cooled at room temperature and wa shed with deionized wate r. The toluene fraction was washed with Brine and dried over MgSO4. After filtration through a Bchner funnel, the toluene was evaporated to give a yellow-br own solid. The solid was purified by column chromatography on silica gel with 2:3 methylene chloride/hexanes as eluent to yield 6.01 g (79%) of white product [mp = 42-43C (lit.126 mp = 49-51C)]. 1H-NMR (CDCl3, ppm): 6.48 (s, 1H), 3.74 (s, 2H), 1.04 (s, 3H); 13C-NMR (CDCl3, ppm): 150.22, 105.70, 80.30, 39.09, 21.89. 3,3-Dihexyl-3,4-dihydro2H-thieno[3,4-b][1,4]d ioxepine [ProDOT-Hx2].54 ProDOTHex2 was prepared according to the pr ocedure described for ProDOT-Me2 utilizing 3,4dimethoxythiophene (5.00 g, 3.47 10-2 mol), 2,2-dihexyl-1,3-pr opanediol (16.94 g, 6.94 10-2 mol), p -toluenesulfonic acid m onohydrate (0.66 g, 3.47 10-3 mol) and freshly distilled toluene (300 mL) under nitrogen. The brown oil was purified by column chromatography (2:3, methylene chloride, hexanes) to give 9.33 g (83%) of product as a yellow oil. 1H-NMR (CDCl3): 6.43 (s, 2H), 3.85 (s, 4H), 0.98-1.40 (20H, m), 0.89 (m, 6H).

PAGE 107

107 1,4-Bis[3,3-dimethyl-3,4-dihydro-2H-thieno [3,4-b][1,4]dioxepin-6-yl]-2,5-didodecyloxybenzene [BProDOT-Me2-B(OC12H25)2]. ProDOT-Me2 (5.00 g, 2.7 x 10-2 mol) was dissolved in anhydrous THF (150 mL) in a 1L 3-neck round bottom flask equipped with a condenser under nitrogen. The so lution was cooled to -78C and n -BuLi (2.90 x 10-2 mol) was added dropwise via syringe and the solution stirre d for 1 hour at -78C. Zinc chloride in THF (3.10 x 10-2 mol) was added dropwise via syringe and the solution was warmed to room temperature followed by addition via cannula of anhydrous NMP (200 mL). Then, 1,4-dibromo2,5-didodecyloxybenzene (5.48 g, 9.00 10-3 mol), Pd2(dba)3 (0.33 g, 3.60 10-4 mol) and P(tBu)3 (0.146 g, 7.20 10-4 mol) were dissolved in a mixture of anhydrous THF (100 mL) and anhydrous NMP (50 mL) in a Schlenk flask. This purple solution was tran sferred via cannula to the solution containing the zinc ch loride derivative of ProDOT-Me2 and the mixture was heated at 100C for 12 h. The light brown solution was cooled to room temper ature and poured into deionized water (500 mL). The mixture was extr acted with ethyl ether, the ether layer was washed with brine and dried over magnesium su lfate. After filtration through a Bchner funnel, the solvent was evaporated and a light brown solid collected. Th is solid was purified by column chromatography (1:1, benzene, hexanes) follo wed by recrystallization (1:5, ethyl acetate, hexanes) to give 3.02 g (42%) of yellow crystals [mp: 80-82C]. 1H-NMR (CDCl3): 7.49 (s, 1H), 6.53 (s, 1H), 4.01 (t, 2H), 3.81 (s, 2H), 3.79 (s, 2H), 1.84 (p, 2H), 1.47 (m, 2H), 1.27 (m, 16H), 1.07 (s, 6H), 0.88 (t, 3H); 13C-NMR (CDCl3): 149.9, 149.5, 146.8, 121.8, 118.7, 114.9, 104.9, 80.3, 80.1, 70.0, 39.1, 32.1, 29.9, 29.8, 29.7, 29.6, 29.5, 26.4, 22.9, 22.0, 14.3. HRMS: calcd for C48H74O6S2: 810.4927. Found: 810.4928. Anal. Calcd for C48H74O6S2: C, 71.07; H, 9.19. Found: C, 71.16, H, 9.38.

PAGE 108

108 1,4-Bis[3,3-dihexyl-3,4-dihydro-2H-thieno[ 3,4-b][1,4]dioxepin-6-yl]-2,5-didodecyloxybenzene [BProDOT-Hex2-B(OC12H25)2]. ProDOT-Hex2 (6.34 g, 2.0 x 10-2 mol) was dissolved in anhydrous THF (100 mL) in a 500 mL 3-neck round bottom flask equipped with a condenser under nitrogen. The soluti on was cooled to -78 C and n -BuLi (2.10 x 10-2 mol) was added dropwise via syringe and the solution stirred for 1 hour at -78 C. Zinc chloride in THF (2.30 x 10-2 mol) was added dropwise via syringe and th e solution was warmed to room temperature followed by addition via cannula of a nhydrous NMP (100 mL). 1,4-Dibromo-2,5didodecyloxybenzene (4.83 g, 8.00 10-3 mol), Pd2(dba)3 (0.293 g, 3.20 10-4 mol) and P( t -Bu)3 (0.129 g, 6.40 10-4 mol) were dissolved in anhydrous THF (100 mL) and anhydrous NMP (100 mL) in a Schlenk flask. This purple soluti on was transferred via cannula to the solution containing the zinc chloride derivative of ProDOT-Hex2 and the mixture was heated at 100 C for 12 hours. The light brown solution was cooled to room temperature and poured into deionized water (300 mL). The mixture was extracted with ethyl ether, th e ether layer was washed with brine and dried over magnesium sulfate. After filtration through a Bchne r funnel, the solvent was evaporated and a yellow oil collected. This oil was purified by column chromatography (1:3, benzene, hexanes) and dried under vacuum to give 3.82 g (44%) of a yellow solid [mp: 4546C]. 1H-NMR (CDCl3): 7.50 (s, 1H), 6.45 (s, 1H), 3.99 (t, 2H), 3.90 (s, 2H), 3.91 (s, 2H), 1.82 (p, 2H), 1.39 (m, 4H), 1.27 (m, 34H), 0.88 (m, 9H); 13C-NMR (CDCl3): 149.6, 149.3, 146.5, 121.6, 117.8, 114.7, 104.1, 69.9, 43.9, 32.3, 32.1, 32.0, 30.4, 29.9, 29.9, 29.8, 29.7, 29.6, 26.4, 23.1, 22.9, 22.8, 14.3, 14.2. HRMS: calcd for C68H114O6S2: 1090.8057. Found: 1090.8070. Anal. Calcd for C68H114O6S2: C, 74.81; H, 10.52. Found: C, 74.62, H, 10.64. Poly[1,4-Bis[3,3-dihexyl-3,4-dihydro-2H -thieno[3,4-b][1,4]dioxepin-6-yl]-2,5didodecyloxybenzene] [PBProDOT-Hex2-B(OC12H25)2]. BProDOT-Hex2-B(OC12H25)2 (8.03

PAGE 109

109 10-1 g, 7.30 x 10-4 mol) was dissolved in chloroform ( 15 mL) under nitrogen. A slurry of iron chloride (3.58 10-1 g, 2.2 x 10-3 mol) in chloroform (15 mL) was added dropwise to the monomer solution over a 2 hour period. With add ition of oxidant, the yellow solution turned dark purple. The mixture was stirred overnight at room temperature and then precipitated into methanol (500 mL). The precipitate was filtere d through a Soxhlet thimble and redissolved in chloroform (250 mL) where it was stirred for 6 h with excess hydrazine monohydrate (10 mL). The solution was concentrated by evaporation a nd the polymer solution poured into methanol (400 mL) where a red precipitate formed. The preci pitate was filtered through a Soxhlet thimble, purified via Soxhlet extraction fo r 18h with methanol and extrac ted for 8h with chloroform. The solvent was evaporated from the chloroform fr action and a red solid co llected (0.74 g, 92%). 1HNMR (CDCl3, ppm): = 7.61 (b, 1H), 3.96-4.06 (b, 6H), 1.92 (b, 2H), 1.0-1.50 (bm, 38H), 0.88 (bm, 9H). GPC analysis: Mn = 14,600, Mw = 22,990, PDI = 1.57. Anal. Calcd for C68H112O6S2: C, 74.94; H, 10.35; S, 5.88. Found: C, 70.90; H, 10.59; S, 4.73; Cl, 0.13; Fe, 0.22. 8,8’-(2,5-bis(dodecyloxy)-1,4phenylene)bis(6-bromo-3,3-dimethyl-3,4-dihydro2H thieno[3,4b ][1,4]dioxepine) [Br2-BProDOT-Me2-B(OC12H25)2]. BProDOT-Me2-B(OC12H25)2 (2.32 g, 2.86 x 10-3 mol) was dissolved in anhydrous DM F (250 mL) in a 500 mL three necked flask under nitrogen, and the solution was cooled at -78C. NBS was quickly added to the yellow slurry and the mixture was progres sively warmed to room temper ature. After 5 h, the reaction was stopped by addition of a solution of ammoni um hydroxide to the green slurry. The mixture was extracted with diethyl ether and the organic layer was dried over MgSO4. After filtration through a Bchner funnel the solv ent was evaporated and a bright yellow solid was collected. The crude product was purified by column chromatography on silica gel with hexanes/ methylene chloride (1:1) followed by recrystalli zation from hexanes/ethy l acetate (5:1) yielding

PAGE 110

110 1.76 g (64%) of pure white cr ystals [mp: 110-111C]. 1H-NMR (CDCl3): 7.56 (s, 1H), 4.02 (t, 2H), 3.87 (s, 2H), 3.83 (s, 2H), 1.83 (p, 2H), 1.47 (m, 2H), 1.27 (m, 16H), 1.08 (s, 6H), 0.88 (t, 3H). 13C-NMR (CDCl3): 149.16, 147.75, 145.95, 121.14, 118.24, 114.05, 94.22, 80.39, 80.31, 70.01, 39.17, 32.14, 29.91, 29.87, 29.84, 29.65, 29.58, 29.43, 26.44, 22.91, 21.96, 14.34. HRMS: calcd for C48H72Br2O6S2: 966.3137. Found: 966.3181. Anal. Calcd for C48H72Br2O6S2: C, 59.49; H, 7.49. Found: C, 59.62, H, 7.77. 8,8’-(2,5-bis(dodecyloxy)1,4-phenylene)bis(6-bromo-3,3-dihexyl-3,4-dihydro2H thieno[3,4b ][1,4]dioxepine) [Br2-BProDOT-Hex2-B(OC12H25)2]. Br2-BProDOT-Hex2B(OC12H25)2 was prepared according to the procedure described for Br2-BProDOT-Me2B(OC12H25)2 utilizing BProDOT-Hex2-B(OC12H25)2 (0.58 g, 5.32 10-4 mol), NBS (0.24 g, 1.33 10-3 mol) and anhydrous DMF (50 mL). Th e crude product was purified by column chromatography on silica gel with hexanes/ CH2Cl2 (2:1) followed by hexanes/CH2Cl2 (7:1) yielding 0.54 g (81%) of slightly yellow crystals. Mp: 75-77C. 1H-NMR (CDCl3): 7.58 (s, 1H), 4.02 (t, 2H), 3.98 (s, 2H), 3.94 (s, 2H), 1.87 (p, 2H), 1.44 (m, 6H), 1.27 (m, 32H), 0.90 (m, 9H). 13C-NMR (CDCl3): 148.99, 147.46, 145.75, 121.02, 117.37, 113.88, 93.32, 69.92, 44.05, 32.21, 32.15, 31.99, 30.37, 29.94, 29.88, 29.86, 29.69, 29.60, 26.46, 26.46, 23.07, 22.92, 22.88, 14.34, 14.29. HRMS: calcd for C68H112Br2O6S2: 1246.6267. Found: 1246.632. Anal. Calcd for C68H112Br2O6S2: C, 65.36; H, 9.03. Found: C, 65.64, H, 9.36.

PAGE 111

111 CHAPTER 4 NARROW BAND-GAP CYAN OVINYLENE POLYMERS 4.1 Introduction As discussed in the general Introduction, organic soluble narrow band-gap polymers are particularly desirable for photovol taics due to their sp ectral absorption whic h matches the solar terrestrial radiation.127-130 They are also needed for deep red and near-IR emitting devices,127 for applications using nand p-type conductors,131 and for electrochromic de vices especially due to their potentially multicolored states.132,133 The donor-acceptor approach (D-A) described earlier is one of the most effective ways of building a narrow band-gap polymer, and in particular significant effort has been applied to the combination of electron rich heterocycles with highly electron demanding cyano-substituted aryl units.13,134,135 Recently our group described the synthe sis of narrow band-gap cyanovinylenedioxythiophene polymers and the concepts for build ing an ideal light absorbing material for effective charge transfer to PCBM (see general Introduction).18,43,58 In that study, it was demonstrated that PProDOT-Hex2:CNPPV is a promising candi date of the cyanovinylenedioxythiophene family for photovoltaic devices. It is a strongly absorbing photoexcitable donor for PCBM, and exhibits good solubility in orga nic solvents, an optical band gap of 1.7 eV, a HOMO level of 5.7 eV, and a LUMO level of 3.5 eV. However, initial obs ervations have shown that spin-coated films of the polymer blende d with poly(2-methoxy-5 -(2’-ethyl-hexyloxy)-1,4phenylene vinylene) (MEH-PPV) and with the acceptor PCBM, have a discontinuous surface which becomes rougher as th e contents of PProDOT-Hex2:CNPPV increase, probably due to an aggregated polymer morphology. P hotovoltaic efficiencies of 0.1-0.2 % have been measured, suggesting the need of further polymer structural optimization. In parall el with the photovoltaic study, it has also been observed that this polymer provides appealing electrochromic properties,

PAGE 112

112 switching between deep blue neutral state and colorless tran smissive reduced and oxidized states. Finally, it is important to note that this polym er is synthesized by Knoevenagel polymerization and does not involve the use of transition metal cat alysts. Catalysts impurities are often trapped in the polymer and are respons ible for photoluminescence quenc hing, electrical shorts or preferred conduction paths in thin-film devices leading to decreased performance.136 In pursuit of enhanced processing for photovoltaics and to further investigate the electrochromic capabilities of propylenedioxy thiophene:cyanovinylene (ProDOT:cyanovinylene) polymers, we decided to synt hesize analogues of PProDOT-Hex2:CNPPV and study a variety of side chains as shown in Figure 4-1. The effects of the side chains on the optical and electronic properties, solubility, and film forming ability were studied. Specifically, we report on the substitution of the ProDOT moieties with alkoxy ch ains to attain higher solubility and greater processability relative to the alkyl substituted PProDOT-Hex2:CNPPV polymer.58 The first polymer, PProDOT-OHex2:CNPV-DDO was fully substituted with linear alkoxy substituents: linear dodecyloxy chains on the phenylene ring and linear hexyloxy chains on the ProDOT ring as illustrated in Figure 4-1. Disorder inducing br anches were introduced on the ProDOT moiety of the second polymer, PProDOT-OEtHex2:CNPV-DDO, this material being also substituted with linear dodecyloxy substituents on the phenyl ene ring but with 2-ethyl hexyloxy chains on the ProDOT ring. The branching location was cha nged on the third and fourth polymers by using linear hexyloxy chains on the ProDOT ring and unsymmetrically substituting the phenylene ring with methyloxy groups and 2ethylhexyloxy (PProDOT-OHex2:CNPV-MEH)) or 3,7dimethyloctyloxy groups (PProDOTOHex2:CNPV-MDMO). Also, with PProDOTOHex2:CNPV-MEH and PProDOT-OHex2:CNPV-MDMO we considered substitution

PAGE 113

113 mimicking those in MEH-PPV and MDMO-PPV, the most efficient polymers to date for organic solar cells [along with P3HT].76,77 CN CN S O O OR OR OC12H25 n PProDOT-OEtHex2:CNPV-DDO PProDOT-OHex2:CNPV-MEH O H25C12 CN CN S O O O O OR1 n OR2 PProDOT-OHex2:CNPV-MDMO R2 = R = PProDOT-OHex2:CNPV-DDO Hex Hex R1 = Me Figure 4-1. Family of ProDOT:cyanovinylene polymers synthesized via the Knoevenagel methodology. Molecular and macromolecular characterizat ion was accomplished by a combination of NMR and IR spectroscopy, MALDI mass spectro metry and GPC. The details of these characterizations will be described in section 4.2 along with the synthesis of the monomers and polymers. Section 4.3 will give a brief analysis of the ordering properties. A study of the spectroelectrochemical, redox, and electrochromic properties will be given in sections 4.4 and 4.5. An exploration of the polymers light emitting capacities, and light harvesting properties in bulk heterojunction polymer/PCBM sola r cells is included in section 4.6.

PAGE 114

114 4.2 Monomer and Polymer Synthesis and Characterization Knoevenagel condensation is the polymeriza tion method of choice for the synthesis of the propylenedioxythiophene:cyanovi nylene polymer family. Previous work done on this type of polymer has shown that dialde hyde-functionalized th iophenes are far more accessible than diacetonitrile-functionalized thiophenes.43 Consequently the polymers were built from the coupling of an electron donating ProDOT-dialde hyde moiety with and electron withdrawing phenylene-diacetonitrile moiety. The synthesis of the acetonitrile monomers 1 has been already deeply investigated, and it was deduced that the best synthetic pathway c onsists of alkylation of commercial hydroquinone or p -methoxyphenol, bromomethylation, and cyanide s ubstitution (Figure 4-2). All these steps have been previously repo rted in the literature.137-139 The ProDOT moieties were derivatized with linear and branched alkoxy-chains using nucleoph ilic substitution of the corresponding alcohols on the key ProDOT(CH2Br)2 precursor previously synthesized by our group34 (Figure 4-3). The synthesis of the dialdehyde monomers 2 was accomplished by lithiation of the ProDOT derivative with n -butyllithium, followed by addition of ex cess DMF. According to previous work done by the Reynolds group, this is the most eff ective method available for the formylation of ProDOT rings.43 The monomer structures an d purity were verified by 1H-NMR, 13C-NMR, elemental analysis, HRMS, along with melting point analysis and IR spectroscopy when applicable. The polymerization was accomplished by Knoevenagel condensation of the acetonitrile and aldehyde monomers in a 1:1 mixture of t -BuOH/THF with one equivalent of t -BuOK per cyano group as shown in Figure 4-4. After a 2 h reflux, the polymers were precipitated into methanol and filtered into a cellulose extractio n thimble. The thimble was placed in a Soxhlet apparatus and methanol was refluxed over th e thimble for 24 h to remove any unreacted

PAGE 115

115 monomer and base. Final extraction with chlorofo rm afforded blue or purple solids in yields ranging between 40 and 80% after solv ent evaporation (Table 4-1). OH OH 1. KOH 2. RBr OR1 OR2 OR1 OR2 Br Br (CH2O)n 33% HBr/HOAc NaCN DMF, 110C OR1 OR2 CN NC R1 = Me, R2 = R1 = R2 = C12H25 OH OMe R1 = Me, R2 = EtHx, 64% (CH2O)n 37% HCl/Ac2O R1 = R2 = C12H25, 53% R1 = Me, R2 = EtHx, 17% R1 = Me, R2 = 3,7-dimethyloctyl, 50% R1 = R2 = C12H25, 64% 1a R1 = Me, R2 = EtHx, 44-46% 1b R1 = Me, R2 = 3,7-dimethyloctyl = 27% 1c OR1 OR2 Cl Cl or 3,7-dimethyloctyl, 60% 1 R1 = Me, R2 = EtHx, 60% Figure 4-2. Synthesis of the phenylenediacetonitrile acceptor monomers. S O O Br Br S O O O H 1. n -BuLi (2.5 eq) 2. excess DMF ROH, NaH DMF S O O RO RO O H OR OR R = C6H13, 49% R = 2-EtHex, 99% R = C6H13 53% 2a R = 2-EtHex, 74% 2b 2 ProDOT-(CH2Br)2 Figure 4-3. Synthesis of the ProDOT-dialdehyde monomers.

PAGE 116

116 S O O O H O H OR OR OR1 OR2 CN NC + CN CN S O O OR OR OR1 OR2 n tBuOH/THF t -BuOK Figure 4-4. Synthesis of the ProDOT:cyanovi nylene family of polym ers via Knoevenagel polymerization. Table 4-1. GPC estimated molecular wei ghts of the ProDOT:cyanovinylene polymers (polystyrene standards, TH F as mobile phase) and yi elds of the Knoevenagel polymerizations. Mn (g mol-1) Mw (g mol-1) PDI Average number of rings Yield (%) PProDOT-OEtHex2:CNPV-DDO 10,30014,8001.420 61 PProDOT-OHex2:CNPV-DDO 13,00017,5001.328 77 PProDOT-OHex2:CNPV-MEH 23,70031,1001.366 45 PProDOT-OHex2:CNPV-MDMO 8,70011,4001.322 41 The polymers are highly soluble in common organic solvents su ch as hexanes, chloroform, methylene chloride and tetrahydrofuran. 1H-NMR, IR, and MALDI-MS support the proposed structures of the polymers. End-groups were not visible by 1H-NMR. Residual nitrile IR stretching bands at ~ 2250 cm-1 corresponding to the monomers were not observed, while bands were observed at ~ 2204-2206 cm-1 indicating the presence of conj ugated cyanovinylene linkages (Figure 4-5). MALDI analyses, performed in re flectron mode with a HABA matrix, confirmed the polymer structure, with a spacing between the peaks corre sponding interestingly to the molecular weight of two repe at units, and residual masses of 18 Da. This phenomenon has already been observed for PProDOT-Hex2:CNPPV18,43 and, as illustrated by the results of Figure 4-6, only even-numbered chains are seen in the MA LDI spectra. This effect has been observed in polycondensation reactions and has been explained by the cyclizati on of the polymer chains due to strong electronic interactions (e. g. donor-acceptor and dipole-dipole interactions)

PAGE 117

117 enforcing a parallel and coplanar alignment of the growing chains inducing a hair-pin conformation.140,141 Based on the observed m/z values for the polymers and the mass accuracy of our instrument, we are able to identify the oligom ers as linear species and rule out the possibility that they are cyclic. In fact, the obser ved residual mass of 18 Da, presumably H2O, is consistent with end groups of a phenylene unit with a sing le free acetonitrile an d a ProDOT unit with a single free aldehyde. 4000350030002500200015001000500 84 88 92 % (Transmittance)Wavenumber (cm -1 ) 2205a 4000350030002500200015001000500 78 80 82 84 86 88 90 92 94 % TransmittanceWavenumber (cm -1)2204 b 4000350030002500200015001000500 72 74 76 78 80 82 84 86 88 % Transmittance Wavenumber (cm -1)2204 c 4000350030002500200015001000500 84 86 88 90 92 94 % TransmittanceWavenumber (cm -1 ) 2205 d Figure 4-5. IR spectra of ProDOT:cya novinylene polymers. (a) PProDOT-OEtHex2:CNPVDDO, (b) PProDOT-OHex2:CNPV-DDO, (c) PProDOT-OHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-MDMO.

PAGE 118

118 2000400060008000100001200014000 0 200 400 600 800 1000 800012000 x 3n = 14 n = 12 n = 10 n = 8Abundancem/zn = 12 n = 10 n = 8 n = 6Abundancem/z n = 2 n = 41982.8 3962.7 5930.7 7897.6 9864.9 11829.7 2000400060008000100001200014000 900012000 x 3n=14 n= 8 n=10Abundancem/z n=12n= 2 n= 4 n= 6 n= 8 n=10Abundancem/z n=121870.1 3737.5 5593.6 7448.5 9304.1 11158.7 20004000600080001000012000 60008000 x 3n = 12 n = 10 n = 8Abundance m/zn = 12 n = 10 n = 8 n = 6 n = 4Abundancem/z2887.2 4331.8 5768.2 7203.8 500010000 0 500 1000 1500 2000 800012000 0 30 60 90 n = 18 n = 16 n = 14 n = 12 n = 10Abundancem/zx 3n = 14 n = 12 n = 10 n = 8 n = 6 n = 4Abundancem/z 1071.23008.9 4501.7 7485.2 8991.1 5993.5 Figure 4-6. MALDI-MS of ProDOT:cyanoviny lene polymers. (a) PProDOT-OEtHex2:CNPVDDO, (b) PProDOT-OHex2:CNPV-DDO, (c) PProDOT-OHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-MDMO. It illust rates that the dominant spacing pattern corresponds to two repeat units. HABA was us ed as the matrix. The inset is a 3 x magnification of the high m/z region. Molecular weight analyses performed by GPC (polystyrene standards, THF as mobile phase) gave number average molecula r weights ranging from 9,000 to 24,000 g mol-1 which corresponds to an average number of rings ranging from 20 to 66 per chain (Table 4-1). The use of stoichiometric proportions of acetonitrile and aldehyde monomers is a necessity in this A-A + B-B polycondensation. This is made difficult by the aldehyde monomers 2 being sticky oils, which makes accurate weighing difficult. This ma y explain the variations in the molecular

PAGE 119

119 weights obtained and we suppose that near stoichiometric c onditions were reached for the synthesis of PProDOT-OHex2:CNPV-MEH, which exhibits the highest molecular weight of about 24,000 g mol-1. MALDI analysis confirmed the presence of chains up to 12-18 repeat units (Figure 4-6), though no conclusion can be given on th e average molecular weights using this method since it is more difficult for high mol ecular weight mass components to undergo the desorption/ionization process, “fly” in the mass spectrometer, and be detected.142-144 As illustrated in Figure 4-7, chromatographi c polymer elution during GPC analysis was monitored with an in-line photodiode array detector to record the UV-Vis absorption of selected fractions of the polymers. Spec tra were recorded at various elution times which allowed monitoring polymer absorption as a function of mo lecular weight relative to the polystyrene standards. The polymers exhibit a broad ab sorption in the 500-700 nm visible region. For PProDOT-OEtHex2:CNPV-DDO we begin reaching the polymer limit when the molecular weight reaches about 12,000 g mol-1 (Figure 4-7-1d). Below that molecular weight, the absorption spectra exhibit maxima centered in the 530-580 nm region and a broad shoulder around 620 nm; above 12,000 g mol-1 the shoulder becomes more de fined giving rise to a second absorption maximum undergoing small changes from 617 nm to 627 nm as the chain size further increases. For PProDOT-OHex2:CNPV-DDO, PProDOT-OHex2:CNPV-MEH and PProDOTOHex2:CNPV-MDMO the polymer limits were reached after about 15,000 g mol-1, 20,000 g mol-1 and 12,000 g mol-1 respectively, since little variatio ns in the absorption maxima were observed at higher molecular weights. The co mparison between these results and the number average molecular weights summarized in Table 4-1 supports that our pol ymers have desirable degrees of polymerization and dispersity.

PAGE 120

120 300400500600700800 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 h) i) Absorbance (a. u.)Wavelength (nm) e) d) c) b) a) j) g) f) 1 300400500600700800 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 2a) b) c) d) e) f) g) Absorbance (a. u.)Wavelength (nm)k) j) i) h) 400500600700 0.00 0.05 0.10 0.15 3a) b) c) d) e) f) g) h)Absorbance (a. u.)Wavelength (nm)i) 300400500600700800 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 4a) b) c) d) e) f) g)Absorbance (a. u.)Wavelength (nm)h) Figure 4-7. Absorption spectra fo r molecular weight fractions of the ProDOT:cyanovinylene polymers. 1) PProDOT-OEtHex2:CNPV-DDO, 2) PProDOT-OHex2:CNPV-DDO, 3) PProDOT-OHex2:CNPV-MEH, 4) PProDOT-Hex2:CNPV-MDMO. Absorption maxima ( max) and molecular weights in g mol-1 vs polystyrene are reported. 1) (a) 534.1 nm, 5,000, (b) 562.1 nm, 6,500, (c) 574.3 nm, 8,900, (d) 581 nm and 612 nm, 12,200, (e) 582.8 nm and 617.1 nm, 15,100, (f) 623.2 nm, 20,000, (g) 624.4 nm, 27,000, (h) 626.8 nm, 36,000, (i) 626.8 nm, 49,300, (j) 626.8 nm, 69,500. 2) (a) 513.4 nm, 6,000, (b) 553.6 nm, 8,000, (c) 563.3 nm, 10,600, (d) 569.4 nm, 14,800, (e) 573.1 nm, 18,800, (f) 573.1 nm, 23,900, (g) 573.1 nm, 28,900, (h) 573.1 nm, 34,500, (i) 573.1 nm, 42,400, (j) 573.1 nm, 53,800, (k) 573.1 nm, 67,200. 3) (a) 554 nm, 10,100, (b) 565 nm, 14,000, (c) 573 nm, 20,200, (d) 577 nm, 30,100, (e) 579 nm, 38,200, (f) 579 nm, 50,500, (g) 579 nm, 69,300, (h) 579 nm, 95,600, (i) 579 nm, 132,700. 4) (a) 485.4 nm, 4,000, (b) 539 nm, 6,200, (c) 554 nm, 8,600, (d) 564.5 nm, 12,200, (e) 567 nm 16,200, (f) 567 nm, 22,700, (g) 567 nm, 31,900, (h) 567 nm, 47,900.

PAGE 121

121 The thermal stability of the polymers was studi ed by thermogravimetric analysis (TGA) in a nitrogen atmosphere using a 20C min-1 temperature ramp fr om 50C to 900C. The thermograms show that the polymers exhibit a high thermal stability losing less than 2-3% weight at 300C followed by a drastic degrada tion process at about 370C. Above 800C less than 20% of material remains (Figure 4-8). 200400600800 0 20 40 60 80 100 PProDOT-OHex2:CNPV-MDMO PProDOT-OHex2:CNPV-MEH PProDOT-OHex2:CNPV-DDO PProDOT-OEtHex2:CNPV-DDOWeight %Temperature (C) Figure 4-8. Thermogravimetric analysis of th e ProDOT:cyanovinylene polymers. Measurements performed in a nitrogen atmosphere using a 20C min-1 temperature ramp from 50C to 900C. Figure 4-9 shows the solution UV-Vis absorbance and photoluminescence of the polymers in toluene. They absorb over a broad spectral range ( ca. 500-700 nm), with absorption coefficients67 around 25,000 M-1 cm-1. The polymer substituted with linear chains on the phenylene and ProDOT rings (PProDOT-OHex2:CNPV-DDO, Figure 4-9b) exhibits an absorption maximum at 619 nm and the polymer solu tion is deep blue. As we introduce branches on the ProDOT ring (PProDOT-OEtHex2:CNPV-DDO, Figure 4-9a) the absorption maximum slightly shifts to 617 nm while it drastically falls to 606 nm (PProDOT-OHex2:CNPV-MEH, Figure 4-9c) as branches are introduced on the phenylene moiety, and the solution color becomes

PAGE 122

122 more red as demonstrated in the photographs in Figure 4-9. A max of 567 nm is observed for PProDOT-OHex2:CNPV-MDMO as the vibronic coupling wh ich yields splitting in the spectrum is reduced. Unsymmetrical bran ching on the phenylene ring i nduces a large influence on the polymer disorder and conjugation, shifting the ab sorption to the blue region, transmitting more red light and giving the solution a purple appe arance, whereas branching on the ProDOT unit seems to have no significant influence. The poly mers emit in the red and near-infrared region with emission maxima decreasing from 658 nm fo r the more ordered poly mer (Figure 4-9b) to 643 nm for the least ordered polymer (Fi gure 4-9d), as illustrated for PProDOT-OHex2:CNPVMEH in the photograph in Figure 4-9c. The fluo rescence quantum efficiency of the polymers was estimated around 12% (Oxazine 1 standard; = 0.11). 4.3 Ordering Properties While heating 1,2-dichlorobenzene solutions of the polymers, it was noted that they undergo a reversible thermochromi c transition: when heated, the color of the pol ymer solution changed from blue (or purple) to red, returning to blue when it was cooled to room temperature as illustrated in the photographs in Figure 4-10. This ther mochromic behavior can either be related to a more twisted bac kbone conformation at hi gher temperature, or to the breaking of aggregates (or both).57 Looking at the spectral changes and vibronic features would have helped being more specific, but these parameters could not be studied since the spectroscopic equipment available at the time did not support the high temperatures necessary to observe the full thermochromic changes (UV-Vis spectrometer e quipped with a water heating system supporting 95C maximum). For PProDOT-OHex2:CNPV-DDO a purple tint started appearing around 85C, but the distinct change from a deep bl ue color to a red solution happened between 100C and 130C.

PAGE 123

123 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (Normalized)Wavelength (nm) Photoluminescence (Normalized)a max = 617 nm 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (Normalized)Wavelength (nm) Photoluminescence (Normalized) b max = 619 nm a) abs = 617 nm, em = 656 nm b) abs = 619 nm, em = 658 nm c) abs = 606 nm, em = 647 nm d) abs = 567 nm, em = 643 nm 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (Normalized)Wavelength (nm) Photoluminescence (Normalized) c max = 606 nm 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (Normalized)Wavelength (nm) Photoluminescence (Normalized) d max = 567 nm Figure 4-9. Solution UV-Vis absorbance and photoluminescence of ProDOT:cyanovinylene polymers in toluene. (a) PProDOT-OEtHex2:CNPV-DDO, (b) PProDOTOHex2:CNPV-DDO, (c) PProDOT-OHex2:CNPV-MEH, (d) PProDOTOHex2:CNPV-MDMO. The photograph in the cen ter illustrates the colors of toluene solutions of the different polymer s and the left photograph illustrates the photoluminescence of PProDOT-OHex2:CNPV-MEH irradiated by UV light. Heat Heat Figure 4-10. Thermochromic behavior of PProDOT-OHex2:CNPV-DDO in 1,2-dichlorobenzene.

PAGE 124

124 DSC was employed to study the ordering propertie s of the polymers and the DSC curves of the second scans are displayed in Figure 4-11. Fo r reproducibility purposes, the first DSC scans were discarded because they are dependent of the heating and cool ing procedures applied to the sample before analysis (thermal history effect). All polymers showed about the same behavior at low temperatures. First, they exhibited a glas s transition (Tg) around -125C, which can be clearly seen on the DSC scan of PProDOT-OEtHex2:CNPV-DDO (Figure 4-11a), but was very difficult to detect for the other polymers. Fi gures 4-11c.1 and 4-11d.1 are magnifications of the Tg observed on the first scans of PProDOT-OHex2:CNPV-MEH and PProDOT-OHex2:CNPVDDO, respectively. By comparing the DSC curves of the first (Figures 4-11c.1 and 4-11d.1) and second scans (Figure 4-11c and 4-1 1d ) of these polymers, it is clea rly seen that as further DSC scans were accomplished, the Tg (and Tc1) became more and more diffi cult to detect because of the higher degree of ordering gained during the first scans. After the Tg, as the temperature was increased, the side chains of the polymers gained in mobility and finally reached a temperature where they had enough energy to crystallize as was observed by the exothermic transition (Tc1) around -90C. Then two endothermic transitions co rresponding to the melting of the side chains (Tm1 and Tm2) were observed around -48C and -38C respectively. The temperature was increased up to 250C and no other transitions c ould be observed for the polymers except for PProDOT-OEtHex2:CNPV-DDO, which exhibited an endot hermic transition corresponding to the melting of the backbone at 180C. The polymers were cooled back to -150C, and a first exothermic transition was observed for PProDOT-OEtHex2:CNPV-DDO at 147C corresponding to the bac kbone crystallization (Tc2). A second exothermic transition was observed for all polymers at temperatures ra nging between -70C to -90C, depending on the polymer, and corresponding to the crys tallization of the side chains (Tc3 for PProDOT-

PAGE 125

125 OEtHex2:CNPV-DDO and Tc2 for the other polymers). From the backbone melting and crystallization peaks observed for PProDOT-OEtHex2:CNPV-DDO it can be concluded that this polymer has a more semicrystalline nature th an the other polymers, which are amorphous. a b c c.1 0.1 W/g 0.1 W/g d d.1 0.1 W/g 0.1 W/g Figure 4-11. DSC curves of ProDOT:cyanovinyle ne polymers. (a) PProDOT-OEtHex2:CNPVDDO, (b) PProDOT-OHex2:CNPV-MDMO, (c) PProDOT-OHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-DDO, and low temperatur e magnification of the first scans at of (c.1) PProDOT-OHex2:CNPV-MEH and (d.1) PProDOTOHex2:CNPV-DDO. Heating and coo ling rates were 10C min-1.

PAGE 126

126 4.4 Polymer Electrochemistry and Spectroelectrochemistry For photovoltaic, electrochromic, or LED app lications it is necessary to have a good understanding of the redox propertie s of the polymers and to be able to estimate the HOMO and LUMO levels. Towards that end, cyclic voltamme try and differential pulse voltammetry were employed. Polymer films were deposited by drop casting on a Pt button electrode from a 5 mg mL-1 chloroform solution, and the voltammog rams were recorded in 0.1 M TBAPF6/ACN electrolyte. The measurements were performed in an oxygen and water free environment in an argon-filled glovebox due to th e instability of the redu ced form of the polymers.78 The oxidation and reduction processes were addressed separa tely as cycling over the full potential range resulted in rapid polymer degradation. Multiple cycling was used to break in the polymers, and the measurements were taken once the electrochemical response became constant. Figures 4-12 and 4-13 show respectively the CV and DPV results obtained for the polymers. The polymers exhibit onsets of oxi dation ranging from 0.6 V to 0.8 V vs Fc/Fc+ and onsets of reduction ranging from -1.4 V to -1.6 V as detailed in Table 4-2. The differences between the oxidation and reduction potentials yield electroche mical band-gaps varying between 2.0 and 2.4 eV, with the band-gaps obtained by DPV being slightly smaller than those obtained by CV. This is not surprising since the onsets of oxidation measured by DPV are generally more defined than those obtained by CV Indeed, DPV measures a current difference and the major component of that difference is the faradaic current. The capacitive component due to the charging of the electrode double layer is la rgely eliminated in comparison with CV measurements. DPV also avoids pre-peaks that are observed for instance on the CV spectrum of PProDOT-OHex2:CNPV-MDMO (Figure 4-12d) and which ar e attributed to trapped charges in the polymer film.17 The polymer HOMO and LUMO energies were estimated from the onsets of oxidation and reduction respectively. The polymers are relatively stable to oxidation with low

PAGE 127

127 lying HOMO levels varying between 5.7 and 5.9 eV. These low HOMO values allow the polymers to be easily handled in air without enc ountering undesired oxida tion. This is a useful property as we consider use of these materials in optoelectronic devices. With LUMO levels around 3.5-3.7 eV the polymers are also good candidates for charge transfer to C60-based acceptors (0.5-0.7 eV LUMO offsets with LUMO of PCBM being at 4.2 eV). These results are in accordance with those previous ly reported on the PProDOT-Hex2:CNPPV analogue.18,43,58 -2.0-1.5-1.0-0.50.00.51.01.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Current (mA/cm 2)E(V) vs. Fc/Fc+Eg = 2.3 eVa -2.0-1.5-1.0-0.50.00.51.01.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Current (mA/cm2)E(V) vs. Fc/Fc+ Eg = 2.4 eVb -2.0-1.5-1.0-0.50.00.51.01.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Current (mA/cm2)E(V) vs. Fc/Fc+c Eg = 2.1 eV -2.0-1.5-1.0-0.50.00.51.01.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Current (mA/cm 2)E(V) vs. Fc/Fc+ Eg = 2.2 eVd Figure 4-12. Cyclic voltammetry of Pr oDOT-cyanovinylene polymers. (a) PProDOTOEtHex2:CNPV-DDO (b) PProDOT-OHex2:CNPV-DDO (c) PProDOTOHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-MDMO. Measurements were performed on a 0.02 cm2 Pt button working electrode in 0.1 M TBAPF6/ACN with a Pt foil counter electrode and a s ilver wire pseudo reference electrode calibrated vs Fc/Fc+.

PAGE 128

128 -2.0-1.5-1.0-0.50.00.51.01.5 -0.06 -0.03 0.00 0.03 0.06 0.09 0.12 Current (mA/cm2)E(V) vs. Fc/Fc+ Eg = 2.1 eVa -2.0-1.5-1.0-0.50.00.51.01.5 -0.05 0.00 0.05 0.10 0.15 Current (mA/cm2)E(V) vs. Fc/Fc+ Eg = 2.1 eVb -2.0-1.5-1.0-0.50.00.51.01.5 -0.12 -0.09 -0.06 -0.03 0.00 0.03 0.06 0.09 0.12 Current (mA/cm2)E(V) vs. Fc/Fc+E g = 2.02 eV c -2.0-1.5-1.0-0.50.00.51.01.5 -0.05 0.00 0.05 0.10 0.15 0.20 Current (mA/cm2)E(V) vs. Fc/Fc+ Eg = 2.1 eVd Figure 4-13. Differential pulse voltammetry of ProDOT-cyanovinylene polymers. (a) PProDOTOEtHex2:CNPV-DDO (b) PProDOT-OHex2:CNPV-DDO (c) PProDOTOHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-MDMO. Measurements were performed on a 0.02 cm2 Pt button working electrode in 0.1 M TBAPF6/ACN with a Pt foil counter electrode and a silver wire pseudo reference el ectrode calibrated vs Fc/Fc+. Table 4-2. Summary of thin-film polymer elect rochemistry, and HOMO and LUMO energies of the ProDOT:cyanovinylene polymers derive d from the electrochemical results. Polymer Eonset,ox CV (V) HOMO CV (eV) Eonset,red CV (V) LUMO CV (eV) Eonset, ox DPV (V) HOMO DPV (eV) Eonset,red DPV (V) LUMO DPV (eV) Eg, opt (eV) PProDOTOEtHex2:CNPV-DDO 0.8 5.9 -1.5 3.6 0. 6 5.7 -1.5 3.6 1.75 PProDOT-OHex2:CNPV -DDO 0.8 5.9 -1.6 3.5 0. 6 5.7 -1.5 3.6 1.70 PProDOT-OHex2:CNPV -MEH 0.6 5.7 -1.5 3.6 0. 6 5.7 -1.4 3.7 1.70 PProDOT-Hex2:CNPV -MDMO 0.7 5.8 -1.5 3.6 0. 6 5.7 -1.5 3.6 1.75

PAGE 129

129 Spectroelectrochemical measurements were performed in order to define the optical band gaps of the polymers and observe their spec tral response to doping. Homogeneous and high quality polymer films were produced by sp ray-casting polymer solutions (5 mg mL-1 in chloroform) onto ITO coated glass using an ai r brush at 12 psi. The spectral changes upon oxidation were recorded in 0.1 M TBAP/PC elec trolyte as illustrated in Figure 4-14. In the neutral state, the polymers absorb across the entir e visible region, exhibiti ng deep blue or purple (for PProDOT-OHex2:CNPV-MDMO) colors, and optical band-gaps of 1.7-1.75 eV were calculated from the onset of the transition, right at the sola r radiation maximum. These values are lower than the electrochemical values and such disagreements have been previously reported for cyanovinylene polymers.18,43 It is important to note that for correlation to solar light absorption, and because CV and DPV measuremen ts involve charge transfer by hopping and the diffusion of ions coming from the electrolyte in to the polymer film, determination of the band gap for photovoltaic applica tions is best done usi ng spectroscopic results. An error of about 0.3 eV was estimated for the band gaps determined by DPV, and an error of about 0.4-0.5 eV was estimated for the band gaps determined by CV due to the more poorly defined onsets of oxidation and reduction. The polymer films were progressively oxidized by applying increasing positive potentials in 50 mV steps. Near the ons et potential fo r oxidation, the transition of the neutral state started to decrease in intensity and lower energy charge carrier associated peaks started to grow in the near-IR region changing the film color to a tr ansmissive light gray. It is interesting to note that these electrochromic proper ties are comparable to PEDOT which is most generally studied from electrochemically formed films, or from films prepared by casting/spin coating of PEDOT-

PAGE 130

130 PSS. At the same time, these organic soluble a nd processed polymers are more stable in their neutral forms allowing easy handling. 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 +0.76V +1.21V +0.76VAbsorbance (a. u.) Wavelength (nm) +1.21V aNeutral +0.86V 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 +1.1 V +0 VAbsorbance (a. u.)Wavelength (nm) Neutral +0 V +1.1 V b+0.6V 400600800100012001400 0.0 0.2 0.4 0.6 0.8 1.0 +0.32 V +0.87 VAbsorbance (a. u.)Wavelength (nm) +0.52 V +0.32 V +0.87 V Neutral +e -ec 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 +e Absorbance (a. u.)Wavelength (nm) Neutral +0 V +1.1 V -ed+0 V +1.1 V +0.65V Figure 4-14. Oxidative spectr oelectrochemistry of ProDOT :cyanovinylene polymers. (a) PProDOT-OEtHex2:CNPV-DDO, (b) PProDOT-OHex2:CNPV-DDO, (c) PProDOT-OHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-MDMO. Polymer films were spray-cast from chloroform solution on ITO coated glass. All potentials are reported vs Fc/Fc+. The supporting electrol yte consisted of 0.1 M TBAP/PC. The potential was increased in 50 mV steps. The spectral changes were also recorded upon reduction in 0.1 M TBAPF6/ACN electrolyte as illustrated in Figure 4-15. As fo r the CV and DPV measurements, these studies have been performed in an oxygen and water free environment. The polymer films were progressively reduced by applying increasing ne gative potentials in 100 mV steps. As the

PAGE 131

131 potentials reach the onset of re duction observed by electrochemistry (for instance between -1.5 V and -1.6 V for PProDOT-OHex2:CNPV-MEH), the transition of the neutral state decreases in intensity and lower energy charge carrier a ssociated peaks evolve in the near-IR region changing the film color to transmissive light gray, as was also obs erved for the oxidation process. No data is recorded between 860 nm and 890 nm because the detectors used with the fiber optic spectrophotometer in this experi ment do not cover this wavelength range. 400600800100012001400 -0.21 V to -1.51 V -1.51 V -2.31 V Absorbance (a.u.) Wavelength (nm)0 0.5 -1.61 V -0.21 V to -1.51 V -1.51 V -2.31 Vareduced 400600800100012001400 0.0 0.5 -1.68 V -2.35 VAbsorbance (a. u.)Wavelength (nm)-1.68 V -0.28 V to -1.68 V -0.28 V to -1.68 V b 400600800100012001400 0.0 0.5 1.0 -0.31 to -1.51 V -1.61 V -2.21 VAbsorbance (a.u.)Wavelength (nm)-1.61 V -0.31 to -1.51 V c reduced 400600800100012001400 0.0 0.1 0.2 0.3 0.4 -0.21 V to -1.41 V -1.51 VAbsorbance (a.u)Wavelength (nm)-0.21 V to -1.41 V -1.51 V d -2.62 V Figure 4-15. Reductive spectroelectroc hemistry of ProDOT:cyanovinylene polymers. (a) PProDOT-OEtHex2:CNPV-DDO, (b) PProDOT-OHex2:CNPV-DDO, (c) PProDOT-OHex2:CNPV-MEH, (d) PProDOT-OHex2:CNPV-MDMO. Polymer films were spray-cast from chloroform solution on ITO coated glass. All potentials are reported vs Fc/Fc+. The supporting electrol yte consisted of 0.1 M TBAPF6/ACN. The potential was increased in 0.1 V steps. No data is shown between 860 nm and 890 nm as the detect ors do not cover this wavelength range.

PAGE 132

132 4.5 Colorimetry Polymer films were deposited on IT O by spray-casting from 5 mg mL-1 chloroform solutions and were analyzed by in-situ colorimetric analysis using 0.1 M TBAP/PC as the supporting electrolyte. The relative luminance was measured as the polymers were progressively oxidized. Optical changes again occur once the pot entials reach the electrochemical onsets of oxidation as illustrated in Figure 4-16. For instan ce, the onset of oxidation measured by CV for PProDOT-OEtHex2:CNPV-DDO is at 0.8 V (Table 4-2) and the relative luminance starts increasing around this value. In the neutral state, the polymer films are quite opaque and colored, with a relative luminance varying between 27 a nd 37 %. In the fully oxidized state, the films become highly transmissive, with luminance va lues ranging from 65 to 82%, and a relative luminance change up to 50 % wa s observed for PProDOT-OHex2:CNPV-MEH, which is useful for electrochromic applications. The L*a*b* values of the colors were also determined to allow color matching and the results are summarized in Table 4-3 along with the corresponding colors in the neutral and oxidized states. Table 4-3. Colorimetric results for the neut ral and oxidized ProDOT:cyanovinylene polymers. Polymer film Charge State E(V)Lab Observed color PProDOT-OEtHex2:CNPV-DDO N 0.65581-35 blue PProDOT-OEtHex2:CNPV-DDO O 1.158432 gray PProDOT-OHex2:CNPV-DDO N 0.4567-4-22 blue PProDOT-OHex2:CNPV-DDO O 1.158522 gray PProDOT-OHex2:CNPV-MEH N 0.45634-28 blue PProDOT-OHex2:CNPV-MEH O 1.159005 gray PProDOT-OHex2:CNPV-MDMO N 0.45648-18 purple PProDOT-OHex2:CNPV-MDMO O 1.158311 gray Note: N = neutral, O = oxidized.

PAGE 133

133 0.300.450.600.750.901.051.20 30 40 50 60 70 80 Relative Luminance (%)E(V) vs. Fc/Fc+ PProDOT-OEtHex 2 :CNPV-DDO PProDOT-OHex 2 :CNPV-DDO PProDOT-OHex 2 :CNPV-MDMO PProDOT-OHex 2 :CNPV-MEH Figure 4-16. Relative luminance (%) as a function of applied potential for every ProDOT:cyanovinylene polymer. Polymer films were spray-cast from chloroform solution on ITO coated glass (5 mg mL-1). The supporting electrolyte consisted of 0.1 M TBAP/PC. 4.6 Application in Devices 4.6.1 Polymer Light-Emitting Diodes As was shown in Figure 4-9c, the polymers exhibit a red fluorescence in toluene. The thinfilm photoluminescence (PL) spectrum shown in Figure 4-17 for PProDOT-OHex2:CNPV-MEH has a similar shape to the solution photolumines cence, although it is red-sh ifted due to a more organized conformation expected in the solid state. To evaluate the polymer’s potential utility in LEDs, devices were prepared with the follo wing architecture: ITO/PEDOT-PSS (40 nm)/ PProDOT-OHex2:CNPV-MEH (50 nm)/Ca (5 nm)/Al (200 nm). As illustrated by the dotted line spectrum in Figure 4-17, the device exhibits a broad emission in th e red and near-infra-red region dominated by a peak at max = 704 nm. The bright red color observed is illustrated by the photograph in Figure 4-17. The electroluminescence ( EL) spectrum is similar to the PL spectrum (Devices prepared by Dr. J. Mwaura)

PAGE 134

134 of the solid film (Figure 4-17), indicating that the EL results from a singlet exciton with the same structure as that produced by photoexcita tion. Figure 4-18 shows the device characteristics, especially a turn-on voltage of 4 V and an EL inte nsity which increases with voltage up to 10 V. We note that the radiance decreases at higher voltages possibly due to device breakdown. At 10 V, the device emits its highest luminance at ~ 77 W cm-2 sr (526 cd m-2) and current density of 1556 mA cm-2. Unfortunately, the external electr on-to-photon quantum efficiency was determined to be low and it ha s been concluded that the polymer is not likely effective for development in LED applications. 7008009001000 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 EL intensity (a. u.)Wavelength (nm) PL intensity (a. u.) Figure 4-17. Normalized photoluminescen ce emission spectrum of PProDOT-OHex2:CNPVMEH in thin-film (solid line) superimposed with normalized electroluminescence spectrum and accompanying photograph of an ITO/PEDOT-PSS/PProDOTOHex2:CNPV-MEH/Ca/Al device (dotted line). 4.6.2 Photovoltaic Devices It was previously repor ted that the PProDOT-Hex2:CNPPV analogue of our polymers can transfer electrons to PCBM upon photoexcitation.43,58 This conclusion was based on PL quenching experiments showing that 95% of the PL was quenched in thin films blends with (Devices prepared by Dr. Y.-G. Kim).

PAGE 135

135 PCBM, and on IPCE measurements of PProDOT-Hex2:CNPPV/PCBM solar cells which indicate that the polymer is the major contributo r to the photocurrent in the device. 0246810 0 200 400 600 800 1000 1200 1400 1600 Current Density RadianceVoltage (V)Current Density ( mA/cm 2 )0 10 20 30 40 50 60 70 80 Radiance (W/cm2/sr ) Figure 4-18. LED properties of an ITO/PEDOT-PSS/PProDOT-OHex2:CNPV-MEH/Ca/Al device. Effect of applied voltage on current density ( ) and radiance ( ). We prepared bulk heterojunction solar cells using the PProDOT-R2:CNPV polymers as the electron donors and PCBM as the electr on acceptor (device structure ITO/PEDOTPSS/PProDOT-R2:CNPV/PCBM/LiF/Al). Blends containing 1:4 (w/w) of each polymer with PCBM were spin-coated from dichlorobenzene solutions and the photoactive layer thickness was kept between 30 and 40 nm. Thicker photoactive laye rs led to drops in photocurrent density and fill factor, a phenomenon which is attributed to an increase in the series resistance. Figure 4-19 shows the i-V characteristics of the PProDOT-OHex2:CNPV-MEH based device under AM 1.5 illumination for a calibrated solar simulator with an intensity of 100 mW cm-2. The photovoltaic results obtained for the other polymers ar e summarized in Table 4-4. PProDOT-OHex2:CNPVMEH exhibited the best performance, with a power conversion efficiency ( ) of about 0.4%, an open circuit voltage (Voc) of 0.76 V, a short circuit current (Isc) of 1.5 mA.cm-2 and a fill factor (FF) of 36%. According to the results summarized in the Table, there is a ~ 0.1-0.27% efficiency range for the other polymers which have lower mo lecular weights (vide an te). This observation

PAGE 136

136 suggests that higher molecular we ight materials are likely to e nhance the photoinduced current densities in the PCBM solar cells. Independent device fabrication and measurements were conducted in both University of Florida (UF) an d University of California (UCLA) laboratories for PProDOT-OEtHex2:CNPV-DDO/PCBM. Very similar pow er conversion efficiencies of 0.27% vs 0.26% were achieved, supporti ng the reproducibility of the results. Incident photon to current efficiency measur ements (IPCE) match the polymer absorption spectra near the absorption maximum of the polym ers, indicating that the polymers are effective photoexcited electron donors that contribute mainly to the photocurrent in the device. However, the IPCE values are quite low for all the polymer s, between 6-8% in the 500 590 nm region and below 2% above 680 nm as illustrated in Figure 4-19b for the PProDOT-OHex2:CNPVMEH/PCBM device. -0.20.00.20.40.60.8 -1.5 -1.0 -0.5 0.0 : 0.41% FF: 0.36 V oc :0.76 V I sc : 1.5 mA cm -2 Photocurrent density (mA/cm 2 )Voltage (V)a 500550600650700750 0 2 4 6 8 IPCE (%)Voltage (V)b Figure 4-19. Photovoltaic results for a device made of a 1/4 ble nd (w/w) of PProDOTOHex2:CNPV-MEH/PCBM. (a) Current vo ltage characteristic under AM1.5 conditions (100 mW cm-2). (b) IPCE of the device. Several parameters are suspected to be responsib le for the low efficiencies, and disorder is one of them. Disorder in a polymer inhibits hol e mobility, which is believed to be the bottleneck for the short circuit current. In addition, when hole mobility is significantly lower than that of the

PAGE 137

137 electron mobility in copolymer/P CBM blends, severe space charge effects lead to a poor fill factor. While our light absorption and energy level alignment are nearly optimal, reduced transport properties dominate and limit the device performance. Improving carrier mobility in these polymers is of primary importance for devi ce enhancement. As seen before, initial studies on the ordering properties of the polyme rs have shown that only PProDOT-OEtHex2:CNPVDDO exhibits semicrystalline properties. It woul d be of great interest to study the effect of thermal annealing on the charge mobility and phot ovoltaic performance of this material. This was accomplished for example for thin-films of P3HT and has allowed making great improvements in charge mobility and photovoltaic efficiencies.73-75 Table 4-4. Summarized charac teristics of ProDOT:cyanovinyl ene polymer/PCBM based solar cells. Polymers (%) FF Voc (V) Isc (mA/cm2) PAL thickness (nm) PProDOT-OEtHex2:CNPV-DDO 0.270.390.651.05 30 PProDOT-OHex2:CNPV-DDO 0.10.340.580.5 37 PProDOT-OHex2:CNPV-MEH 0.360.370.731.32 38 PProDOT-OHex2:CNPV-MDMO 0.130.280.720.66 38 Note: Averaged values for 3 pixels for each polymer. 4.7 Summary and Perspective This chapter gives an outlook on how small structural changes on a polymer backbone can affect the solubility, optical, and devi ce properties of a ma terial. PProDOT-Hex2:CNPPV was initially targeted by the Reynolds group and u tilized as a derivative of interest for electrochromics and photovoltaics. Working around its backbone stru cture and length, we were able to make progress towards improving film quality and photovoltaic properties. The replacement of the alkyl subs tituents by alkoxy substituents improved solubility without affecting the electronic propertie s. The highest molecular weight material was more efficient in enhancing the photoinduced current densities. The replacement of the linear substituents by

PAGE 138

138 branches did not have a significant influence on the solubility. However, it significantly induced disorder and backbone twisting in soluti on especially in the polymers containing unsymmetrically substituted phe nylene rings, shifting the abso rption maxima of the polymer solutions to the blue region. DSC studi es have shown that only PProDOT-OEtHex2:CNPVDDO is semicrystalline, and consequently that th e disorder induced by th e branched substituents on the phenylene rings is found in the solid state as well, and will affect intermolecular charge transport. It would be of great interest to study the influence of thermal annealing on the extent of ordering and on the photovoltaic performance of PProDOT-OEtHex2:CNPV-DDO. As was observed for PProDOT-Hex2:CNPPV, the polymers exhibit appealing electrochromic properties, switching between blue/purple co lors in the neutral state and highly transmissive light gray colors in the reduced and oxidized states. Thes e electrochromic properties, along with the improved film forming ability, make these mate rials of great interest for electrochromic applications involving large and flexible surfaces. 4.8 Experimental Methoxy-4-(2-ethylhexyloxy)benzene.145 p -Methoxyphenol (9.98 g, 8.05 10-2 mol) was dissolved in ethanol (200 mL) in a 500 mL th ree necked round bottom flask equipped with a condenser, under nitrogen. A solution of potassium hydroxide (5.01 g, 8.95 10-2 mol) in ethanol (50 mL) was slowly added and the solution was stirred at room temperature for 1 h. Then a solution of 2-ethylhexyl bromide (18.67 g, 9.67 10-2 mol) was added slowly and the mixture was stirred at 50C overnight. Af ter allowing the reaction to cool to ambient temperature, the solution was poured into a solution of sodium h ydroxide (10%) and extracted with chloroform. The organic layer was dried over MgSO4 and after filtration through a Bchner funnel the solvent was evaporated. The crude produc t was purified by column chromatography on silica gel using CH2Cl2:hexanes (1:2) and 12.17 g ( 64%) of product as a clea r oil were collected. 1H-NMR

PAGE 139

139 (CDCl3): 6.84 (s, 4H), 3.80 (d, 2H), 3.70 (s, 3H), 1.71 (m, 1H), 1.27-1.53 (m, 8H), 0.93 (m, 6H). 13C-NMR (CDCl3): 153.87, 115.68, 114.85, 71.49, 55.99, 39.71, 30.77, 29.32, 24.10, 23.29, 14.30, 11.33. HRMS: calcd for C15H24O2: 236.1776. Found: 236.1775. Anal. Calcd for C15H24O2: C, 76.23; H, 10.24; Found: C, 79.97, H, 10.58. 1-(3,7-Dimethyloctyloxy)-4-methoxybenzene.139 1-(3,7-Dimethyloctyloxy)-4-methoxybenzene was synthesized following the sa me procedure as for compound methoxy-4-(2ethylhexyloxy)benzene using p -methoxyphenol (14.00 g, 1.13 10-1 mol), ethanol (250 mL), a solution of KOH (6.96 g, 1.24 10-1 mol) in ethanol (50 mL) a nd 3,7-dimethyloctylbromide (29.97 g, 1.36 10-1 mol). The crude product was purifie d by column chromatography on silica gel using CH2Cl2:hexanes (1:3) and 14.58 g (49%) of produ ct as a clear oil were collected. 1HNMR (CDCl3): 6.80 (s, 4H), 3.95 (t, 2H), 3.78 (s, 3H ), 1.80 (m, 1H), 1.40-1.72 (m, 5H), 1.32 (m, 2H), 1.18 (m, 2H), 0.94 (d, 3H), 0.88 (d, 6H). HRMS: calcd for C17H28O2: 264.2089. Found: 264.2096. 1,4-Bis(bromomethyl)-2,5bis(dodecyloxy)benzene.43 To a solution consisting of 33% HBr in acetic acid (30 mL) and glacial acetic acid (110 mL), 1,4-bis(dodecyloxy)benzene (13.80 g, 3.10 10-2 mol) and paraformaldehyde (2.80 g, 9.30 10-2 mol) were quickly added. The white slurry was heated to 70-75C, resulting in the dissolution of all solids. The mixture was stirred at that temperature for 2 h, during wh ich time a precipitate formed. The solution was cooled to 0C, poured into cold water and ex tracted with chloroform The organic layer was washed with Brine and dried over sodium sulfate. After filtration throu gh a Bchner filter, the solvent was evaporated and a white solid was collected. After recrystallization in hexanes:methylene chloride (1:1), 10.23 g (53 %) of pure product were obtained [mp = 93-95 C (lit.146 mp = 93-94 C)]. 1H-NMR (CDCl3): 6.86 (s, 1H), 4.53 (s, 2H), 3.99 (s, 2H), 1.82 (m,

PAGE 140

140 2H), 1.50 (m, 2H), 1.27 (m, 16H), 0.89 (t, 3H). 13C-NMR (CDCl3): 150.91, 127.79, 114.93, 69.28, 32.14, 29.87, 29.86, 29.82, 29.58, 28.94, 26.31, 22.91, 14.33. HRMS: calcd for C32H56Br2O2: 630.2647. Found: 630.2651. Anal. Calcd for C32H56 Br2O2: C, 60.76; H, 8.92; Found: C, 61.11, H, 9.13. 2,5-Bis(bromomethyl)-1-methoxy-4-[(2-ethylhexyl)oxy]benzene.13 2,5-Bis(bromomethyl)-1-methoxy-4-[(2ethylhexyl)oxy]benzene was synthesized using the same procedure as for 1,4-bis(bromomethyl)-2,5bis(dodecyloxy)benzene using 33% HBr in glacial acetic acid (60 mL), glacial acetic acid (180 mL), 1-me thoxy-4-ethylhexyloxyphenylene (12.00 g, 5.08 10-2 mol) and paraformaldehyde (4.59 g, 1.53 10-1mol). The crude product was collected as a brown solid and purified by column chroma tography on silica gel, using methylene chloride:hexanes (1:5) for the elution, followed by recrystallizati on in hexanes. 3.60 g (17%) of white solid were obtained [mp = 80-82 C (lit.138 mp = 81-82 C)]. 1H-NMR (CDCl3): 6.88 (s, 1H), 6.87 (s, 1H), 4.54 (s, 4H), 3.89 (d, 2H), 3.87 (s, 3H), 1.77 (m, 1H), 1.40-1.58 (m, 4H), 1.301.40 (m, 4H), 0.95 (m, 6H). 13C-NMR (CDCl3): 151.18, 127.53, 127.68, 114.50, 113.98, 71.14, 56.44, 39.81, 30.84, 29.33, 28.92, 28.86, 24.23, 23.27, 14.32, 11.47. HRMS: calcd for C17H26Br2O2: 420.0300. Found: 420.0306. Anal. Calcd for C17H26Br2O2: C, 48.36; H, 6.21; Found: C, 48.63, H, 6.32. 2,5-Bis(chloromethyl)-1-(3,7-di methyloxy)-4-methoxybenzene.139 1-(3,7-Dimethyloctyloxy)-4-methoxybenzene (14.58 g, 55.20 10-2 mol) and paraformaldehyde (4.56 g, 1.52 10-1 mol), were put into a 500 mL three necked round bottom flask equipped with a condenser and an addition funnel, under nitrogen. After a ddition of 37% HCl (25 mL, 12M, 3.00 10-1 mol), acetic anhydride (56.38 g, 5.52 10-1 mol) was added dropwise at such a rate that the internal temperature did not exceed 70C. After being stirred for 4.5 h at 70 C, the mixture was cooled to

PAGE 141

141 room temperature. Then it was admixed with a cold saturated sodium acetate solution (50 mL) followed by a dropwise addition of 25% NaOH (36 mL). The mixture was heated to 52C and subsequently cooled in an ice bath while st irring. The cream colored solid was filtered off, washed with water and dissolved in hexanes (100 mL). After extraction with deionized water, the organic phase was dried over MgSO4, filtered through a Bchner filter and the solvent was evaporated. The crude product wa s purified by column chroma tography on silica gel, using CH2Cl2:hexanes (1:4) for the elution, followed by recrystalllization in CH2Cl2:ethanol (1:3). 10 g (50%) of white solid were collected [mp = 57-58 C]. 1H-NMR (CDCl3): 6.94 (s, 1H), 6.93 (s, 1H), 4.65 (s, 2H), 4.64 (s, 2H), 4.02 (m, 2H), 3.8 7 (s, 3H), 1.84 (m, 1H), 1,7 (m, 1H), 1.48-1.78 (m, 4H), 1.1-1.40 (m, 4H), 0.96 (d, 3H), 0.88 (d, 6H). 13C-NMR (CDCl3): 151.24, 150.90, 127.33, 127.01, 114.59, 113.52, 67.65, 56.48, 41.53, 39.43, 37.46, 36.50, 30.04, 28.20, 24.90, 22.92, 22.82, 19.92. HRMS: calcd for C19H30Cl2O2: 360.1623. Found: 360.1621. Anal. Calcd for C19H30Cl2O2: C, 63.15; H, 8.37; Found: C, 63.45, H, 8.48. 1,4-Bis(chloromethyl )-5-(2-ethylhexyloxy )-2-methoxybenzene.137 1,4-bis(chloromethyl)5-(2-ethylhexyloxy)-2-methoxybenzene was synthesi zed using the same procedure as for 2,5bis(chloromethyl)-1-(3,7-dimethyloxy)-4-met hoxybenzene using 1-methoxy-4-ethylhexyloxyphenylene (33.00 g, 1.40 10-1 mol), paraformaldehyde (11.53 g, 3.84 10-1 mol), 37% HCl (63 mL, 12 M, 7.69 10-1 mol) and acetic anhydride (142.72 g, 1.40 mol). After recrystallization of the crude product with hexanes, 27.80 g (60%) of white solid were obtained. 1H-NMR (CDCl3): 6.94 (s, 1H), 6.92 (s, 1H), 4.64 (s, 4H), 3.88 (d, 2H), 3.87 (s, 3H), 1.75 (m, 1H), 1.40 -1.60 (m, 4H), 1.30-1.40 (m, 4H), 0.88-1.00 (m, 6H). 1,4-Bis(cyanomethyl)-2,5-bis( dodecyloxy)benzene (1a).43 Sodium cyanide (1.94 g, 3.95 10-2 mol, 2.5 equiv.) and 1,4-bis(bromomethy l)-2,5-bis(dodecyloxy)benzene (10.00 g, 1.58

PAGE 142

142 10-2 mol) were dissolved in anhydrous DMF ( 250 mL) under nitrogen and the solution was heated to 110C. The reaction was stirred for th ree days, during which time the reaction turned dark orange. The mixture was cooled to room temperature and poured into cold water (750 mL) containing 0.5 M of sodium hydroxide. The prec ipitate was filtered th rough a Bchner funnel, collected, and dissolved in chloroform. The ch loroform solution was then extracted with deionized water; the organic la yer collected and dried over MgSO4. After solvent evaporation, a brown oil was obtained and purified by column chromatography on silica (1:1 hexanes and methylene chloride) followed by r ecrystallization from ethanol a nd chloroform (2:3) to give 5.32 g (64%) of the product as a sligh tly yellow solid [mp: 100-101C (lit.43 mp = 98-100 C)]. 1HNMR (CDCl3): 6.92 (s, 1H), 3.98 (t, 2H), 3.71 (s, 2H ), 1.80 (p, 2H), 1.43 (m, 2H), 1.28 (m, 16H), 0.89 (t, 3H). 13C-NMR (CDCl3): 150.25, 119.31, 118.06, 112.85, 69.24, 32.14, 29.88, 29.85, 29.82, 29.79, 29.59, 29.57, 29.47, 26.28, 22.91, 18.87, 14.34. IR (KBr cm-1) 2916, 2849, 2245, 1513, 1464, 1426, 1393, 1340, 1262, 1222, 1143, 1070, 1043, 999, 963, 923, 872, 846, 801, 759, 721. HRMS: calcd for C34H56N2O2: 524.4342. Found: 524.4324. Anal. Calcd for C34H56N2O2: C, 77.81; H, 10.76; N, 5.34. Found: C, 77.62, H, 10.97; N, 5.06. 2,5-Bis(cyanomethyl)-1-methoxy-4-[(2-ethylhexyl)oxy]benzene (1b).137 Same procedure as for the synthesis of 1,4-bis(cyanomet hyl)-2,5-bis(dodecyloxy)be nzene using sodium cyanide (8.71 10-1 g, 1.78 10-2 mol, 2.5 equiv.), 2,5-bis( bromomethyl)-1-methoxy-4-[(2ethylhexyl)oxy]benzene (3.00 g, 7.11 10-3 mol) and anhydrous DMF (125 mL). The crude product was purified by column chromatography on silica (1:5 hexanes and methylene chloride) followed by recrystallization from hexanes to give 0.97 g (44%) of slightly yellow solid [mp: 8082C (lit.137 mp = 91 C)]. 1H-NMR (CDCl3): 6.94 (s, 1H), 6.93 (s, 1H), 3.88 (d, 2H), 3.86 (s, 3H), 3.71 (s, 4H), 1.75 (m, 1H), 1.30-1.60 (m, 8H), 0.94 (m, 6H). IR (KBr cm-1) 3054, 2959,

PAGE 143

143 2933, 2874, 2248, 1513, 1466, 1421, 1406, 1318, 1231, 1195, 1187, 1107, 1036, 983, 915, 882, 844, 759. HRMS: calcd for C19H26N2O2: 314.1994. Found: 314.1994. Anal. Calcd for C19H26N2O2: C, 72.58; H, 8.33; N, 8.91. Found: C, 72.70, H, 8.40; N, 8.81. Or same procedure as for the synthesi s of 1,4-bis(cyanomethyl)-2,5-bis(dodecyloxy)benzene using sodium cyanide (10.23 g, 2.10 10-1 mol), 2,5-bis(chloromethyl)-1-methoxy4-[(2-ethylhexyl)oxy] benzene (27.80 g, 8.35 10-2 mol) and anhydrous DMF (500 mL). Reaction stirred at 110C for two days. After the workup, the crude product was purified by column chromatography on silica gel using methyl ene chloride/hexanes (5/1) for the elution and 12.00 g (46%) of slightly ye llow solid were obtained. 1H-NMR (CDCl3): 6.94 (s, 1H), 6.93 (s, 1H), 3.88 (d, 2H), 3.86 (s, 3H), 3.71 (s, 4H), 1.75 (m, 1H), 1.30-1.60 (m, 8H), 0.94 (m, 6H). HRMS: calcd for C19H26N2O2: 314.1994. Found: 314.1967. Anal. Calcd for C19H26N2O2: C, 72.58; H, 8.33; N, 8.91. Found: C, 72.84, H, 8.75; N, 8.76. 1,4-Bis(cyanomethyl)-2-(3,7-dimeth yloxy)-5-methoxybenzene (1c).147 Same procedure as for the synthesis of 1,4-bi s(cyanomethyl)-2,5-bis(dodecyloxy) benzene using sodium cyanide (4.00 g, 8.16 10-2 mol, 4.5 equiv.), 1,4-bischlorom ethyl-2-(3,7-dimethyloxy)-5-methoxybenzene (6.54 g, 1.81 10-2 mol) and anhydrous DMF (250 mL). The crude product was purified by column chromatography on silica (hexanes and dichloromethane (1:4)) followed by recrystallization from hexanes to give 1.70 g (27 %) of slightly yellow solid [mp: 81-82 C]. 1HNMR (CDCl3): 6.93 (s, 2H), 4.02 (t, 2H), 3.86 (s, 3H ), 3.71 (s, 4H), 1.84 (m, 1H), 1.50-1.70 (m, 5H), 1.10-1.40 (m, 4H), 0.96 (d, 3H), 0.88 (d, 6H). 13C-NMR (CDCl3): 150.72, 150.40, 119.36, 119.22, 118.0, 112.89, 112.0, 67.57, 56.34, 39.44, 37.49, 36.42, 30.12, 28.20, 24.9, 22.92, 22.82, 19.90, 18.88, 18.34. IR (KBr cm-1) 3054, 2953, 2927, 2870, 2248, 1517, 1467, 1422, 1407, 1317, 1231, 1188, 1155, 1030, 975, 916, 882, 760, 734. HRMS: calcd for

PAGE 144

144 C21H30N2O2: 342.2313. Found: 342.2307. Anal. Calcd for C21H30N2O2: C, 73.65; H, 8.83; N, 8.18. Found: C, 73.87, H, 8.88; N, 8.04. 3,3-Bis(bromomethy l)-3,4-dihydro-2 H -thieno[3,4b ][1,4]-dioxepine [ProDOT(CH2Br)2].34 3,4-Dimethoxythiophene (11.40 g, 6.61 10-2 mol), 2,2bis(bromomethyl)-1,3-propanediol (42.52 g, 1.62 10-1 mol) and p -toluene-sulfonic acid (1.51 g, 7.92 10-3 mol) were dissolved in toluene (300 mL) in a 500 mL three-necked round bottom flask equipped with a Soxhlet condenser cont aining type 4 molecular sieves. The clear solution was refluxed for 24 h during which time the color turned green. Then it was cooled to room temperature, poured into deionized water and extracted with tolu ene. The organic layer was washed with brine and dried over MgSO4. After filtration throug h a Bchner filter and solvent evaporation, a green solid was collected. The solid was purified by column chromatography on silica gel using CH2Cl2:hexanes (1:4) for the el ution yielding 19.95 g (74%) of pure product. 1H-NMR (CDCl3): 6.51 (s, 1H), 4.11 (s, 2H), 3.62 (s, 2H). 13C-NMR (CDCl3): 148.86, 105.97, 74.36, 46.4, 34.62. Anal. Calcd for C9H10Br2O2S: C, 31.60; H, 2.95. Found: C, 31.59, H, 2.82. 3,3-Bis(hexyloxy)-3,4-dihydro-2 H -thieno-[3,4b ][1,4]dioxepine [ProDOT(CH2OC6H13)2]. 1-Hexanol was refluxed overnight over magnesium turnings and distilled under reduced pressu re (bp: 156C at 760 mmHg). A 1 L 3 neck round bottom flask equipped with a condenser, filled with a nhydrous DMF (400 mL), 1-hexanol (17.90 g, 1.76 101 mol) and sodium hydride (8.45 g, 3.52 10-1 mol) was heated overnight at 110C. ProDOT(CH2Br)2 (18.00 g, 52.63 10-2 mol) was added, and the reaction continued at 110C for another 24 h, during which time the color turn ed brown. After completion, the solution was cooled to room temperature, deionized water wa s added, and the mixture extracted with diethyl

PAGE 145

145 ether. The ether layer was washed with brine and dried over MgSO4. After filtration through a Bchner funnel, the solvent wa s evaporated, and a brown oil was collected. The crude product was purified by column chromatography on silica usi ng methylene chloride as elution solvent to give 14.00 g (69%) of the product as a slightly yellow oil. 1H-NMR (CDCl3): 6.45 (s, 1H), 4.02 (s, 2H), 3.49 (s, 2H), 3.41 (t, 2H), 1.54 (p, 2H), 1.29 (m, 6H), 0.90 (t, 3H). 13C-NMR (CDCl3): 149.93, 105.27, 73.97, 71.96, 69.79, 47.92, 31.88, 29.71, 26.02, 22.84, 14.27. HRMS: calcd for C21H36O4S: 384.2334. Found: 384.2322. 3,3-Bis(2-ethylhexyloxy methyl)-3,4-dihydro-2 H -thieno-[3,4b ][1,4]dioxepine [ProDOT(CH2OEtHex)2].34 2-Ethyl-1-hexanol dried over calc ium hydride for 2 h and distilled under reduced pressure (bp: 183 -185C at 760 mmHg). ProDOT(CH2OEtHex)2 was synthesized according to the same procedure used for the synthesis of ProDOT(CH2OC6H13)2 with 2-ethyl-1hexanol (2.85 g, 2.19 10-2 mol), sodium hydride (1.76 g, 60% in oil dispersion, 4.38 10-2 mol, 6 equiv.), anhydrous DM F (125 mL) and ProDOT(CH2Br)2 (2.50 g, 7.30 10-2 mol). The crude product was purified by column chromat ography on silica using methylene chloride as elution solvent to give 2.97 g (99%) of th e pure product as a slightly yellow oil. 1H-NMR (CDCl3): 6.44 (s, 1H), 4.01 (s, 2H), 3.47 (s, 2H), 3.30 (s, 2H), 3.28 (d, 2H), 1.49 (m, 1H), 1.201.40 (m, 8H), 0.80-0.93 (m, 6H). 13C-NMR (CDCl3): 149.93, 105.14, 74.55, 74.01, 70.08, 48.11, 39.84, 30.90, 29.36, 24.23, 23.31, 14.32, 11.37. HRMS: calcd for C25H44O4S: 440.2960. Found: 440.2968. Anal. Calcd for C25H44O4S: C, 68.14; H, 10.06. Found: C, 71.19, H, 11.01. 3,3-Bis(hexyloxy)-3,4-dihydro-2 H -thieno-[3,4b ][1,4]dioxepine-6,8-dicarbaldehyde [ProDOT-(CH2OC6H13)2-(CHO)2] (2a). ProDOT(CH2OC6H13)2 (1.37 g, 3.98 10-3 mol) was dissolved in dry THF (40 mL) under nitrogen purge, and the so lution was cooled to -78C. n Butyllithium (2.3 equiv., 9.15 10-3 mol) was added via syringe, and the solution warmed to 0C

PAGE 146

146 for 30 min and then cooled back to -78C. Anhydrous DMF (1.5 10-2 mol, 3.8 equiv.) was added rapidly via syringe, and the solution warmed to room temperature and stirred for 1 hour. The solution was then poured into 3 M HCl and extracted with methylene chloride. The organic layer was washed wi th saturated NaHCO3 and dried with MgSO4. After filtra tion through a Bchner funnel, the solvent wa s evaporated, and a brown oil collected. The crude product was purified by column chromatography on silica us ing ethyl acetate/hexan es (1/3) yielding 0.817 g (51%) of product as a yellow oil. 1H-NMR (CDCl3): 9.98 (s, 1H), 4.19 (s 2H), 3.46 (s, 2H), 3.37 (t, 2H), 1.56 (p, 2H), 1.23 (m, 6H), 0.82 (t, 3H). 13C-NMR (CDCl3): 182.22, 155.04, 128.21, 74.91, 72.07, 69.54, 47.78, 31.83, 29.65, 26.01, 22.84, 14.26. IR (KBr cm-1) 3317, 2931, 2859, 2734, 2660, 1667, 1559, 1489, 1466, 1436, 1376, 1306, 1249, 1194, 1103, 1065, 925, 833, 760, 727, 694, 552. HRMS: calcd for C23H36O6S: 440.2233. Found: 440.2236. Anal. Calcd for C23H36O6S: C, 62.70; H, 8.24. Found: C, 63.06, H, 8.51. 3,3-Bis(2-ethylhexyloxy methyl)-3,4-dihydro-2 H -thieno-[3,4b ][1,4]dioxepine-6,8dicarbaldehyde [ProDOT-(CH2OEtHex)2-(CHO)2] (2b). Same procedure as for ProDOT(CH2OC6H13)2-(CHO)2 using ProDOT(CH2OEtHex)2 (2.4 g, 5.44 10-3 mol), dry THF (40 mL), n -BuLi (2.3 equiv., 12.53 10-3 mol), dry DMF (3.7 equiv., 20.13 10-3 mol). Most of the impurities were removed from the crude product by column chromatography on silica (1:1, methylene chloride/hexanes); the product was th en pushed out of the column with methylene chloride, decolorized with decolorizing carbon, a nd the rest of the impur ities were removed by a second column chromatography on silica (1:2, ethyl acetate: hexanes) to yield 2.0 g (74%) of product as a yellow oil. 1H-NMR (CDCl3): 10.06 (s, 2H), 4.27 (s, 4H), 3.53 (s, 4H), 3.33 (d, 4H), 1.2-1.57 (m, 18H), 0.90 (m, 12H). 13C-NMR (CDCl3): 182.20, 155.04, 128.13, 74.99, 74.60, 47.92, 339.79, 30.84, 29.31, 24.2, 23.28, 14.31, 11.35. IR (KBr cm-1) 3318, 2958, 2928,

PAGE 147

147 2859, 2734, 2661, 1666, 1559, 1489, 1460, 1436, 1376, 1307, 1248, 1193, 1103, 1064, 917, 833, 760, 728, 694, 552. HRMS: calcd for C27H44O6S: 496.2859. Found: 496.2859. Anal. Calcd for C27H44O6S: C, 65.29; H, 8.93. Found: C, 65.47, H, 9.20. PProDOT-OEtHex2:CNPV-DDO. ProDOT-(CH2OEtHex)2-(CHO)2 (0.5 g, 1 10-3 mol) and 1,4-bis(cyanomethyl)-2,5-bis(dodecyloxy)benzene (0.525 g, 1 10-3 mol) were dissolved in a mixture of dry THF (42 mL) and freshly distilled t -butanol (42 mL). Then, potassium t butoxide (0.224 g, 2 10-3 mol) was added, and the solution heated to 70C for 2 h. The color darkened progressively from yellow to blue to black. The solution was then cooled to room temperature and poured into ice cold methanol ( 600 mL) acidified with 1 mL of acetic acid. The resulting precipitate was isolated by filtration into a S oxhlet thimble and Soxhlet extracted for 48 h with methanol, 24 h with chloroform. The solven t was evaporated from the chloroform fraction and a blue solid collected (0.60 g, 61%). 1H-NMR (CDCl3, ppm): = 8.73 (b, 1H), 6.92 (b, 1H), 3.80-4.60 (bm, 6H), 3.20-3.80 (bm, 8H), 1.95 (b, 4H), 1.00-1.70 (bm, 34H), 0.92 (bm, 15H). IR (KBr cm-1) 2958, 2924, 2854, 2205, 1640, 1574, 1512, 1475, 1448, 1378, 1282, 1181, 1142, 1069, 1026, 920, 861, 802. GPC analysis: Mn = 10,300, Mw = 14,800, PDI = 1.43. Anal. Calcd: C, 74.35; H, 10.06; N, 2.80; S, 3.20. Found: C, 64.87; H, 10.63; N, 2.11; S, 2.87. PProDOT-OHex2:CNPV-DDO. Same procedure as for the synthesis of PProDOTOEtHex2:CNPV-DDO using ProDOT-(CH2OC6H13)2-(CHO)2 (0.427 g, 9.7 10-4 mol), 1,4bis(cyanomethyl)-2,5-bis(dod ecyloxy)benzene (0.509 g, 9.7 10-4 mol), dry THF (39 mL), t butanol (39 mL) and potassium t -butoxide (220 mg, 1.96 10-3 mol). During the polymerization, the solution color changed from yellow to black with a purple tint. Afte r purification by Soxhlet extraction as above, 0.66 g (77%) of blue solid were collected. 1H-NMR (CDCl3, ppm): = 8.70 (b, 1H), 6.90 (b, 1H), 3.804.70 (bm, 6H), 3.20-3.70 (bm, 8H), 1.93 (b, 2H), 1.00-1.70 (bm,

PAGE 148

148 34H), 0.89 (bm, 9H). IR (KBr cm-1) 2961, 2923, 2853, 2204, 1653, 1573, 1512, 1476, 1448, 1382, 1260, 1092, 1074, 1020, 862, 800, 706. GPC analysis: Mn = 13,100, Mw = 17,500, PDI = 1.34. Anal. Calcd: C, 73.68; H, 9.81; N, 2.96; S, 3.39. Found: C, 51.56; H, 9.56; N, 1.40; S, 1.74. PProDOT-OHex2:CNPV-MEH. Same procedure as for the synthesis of PProDOTOEtHex2:CNPV-DDO using ProDOT-(CH2OC6H13)2-(CHO)2 (0.41 g, 9.3 10-4 mol), 2,5bis(cyanomethyl)-1-methoxy-4[(2-ethylhexyl)oxy]benzene (0.32 g, 9.3 10-4 mol), THF (35 mL), t -butanol (35 mL) and potassium t -butoxide (210 mg, 1.88 10-3 mol). During the polymerization, the solution color changed from yellow to black. After purification by Soxhlet extraction as above, 0.286 g (41%) of purple solid were collected. 1H-NMR (CDCl3, ppm): = 8.10-8.40 (b, 2H), 6.80-6.90 (b, 2H), 3.95-4.40 (b m, 9H), 3.45-3.95 (bm, 8H), 1.10-1.70 (bm, 25H), 0.89 (bm, 12H). IR (KBr cm-1) 2955, 2925, 2858, 2205, 1647, 1578, 1505, 1476, 1445, 1378, 1281, 1261, 1217, 1100, 1067, 918, 868, 801. GPC analysis: Mn = 8,700, Mw = 11,400, PDI = 1.31. Anal. Calcd: C, 70.26; H, 8.50; N, 3.81; S, 4.36. Found: C, 54.10; H, 7.60; N, 2.30; S, 3.04. PProDOT-OHex2:CNPV-MDMO. Same procedure as for the synthesis of PProDOTOEtHex2:CNPV-DDO using ProDOT-(CH2OC6H13)2-(CHO)2 (0.45 g, 1.02 10-3 mol), 1,4bis(cyanomethyl)-2-(3,7-dimethyloxy)-5-methoxybenzene (0.321 g, 1.02 10-3 mol), THF (35 mL), t -butanol (35 mL) and potassium t -butoxide (230 mg, 2.05 10-3 mol). During the polymerization, the solution color changed from yellow to black with a purple tint. After purification by Soxhlet extractio n as above, 0.33 g (45%) of purple solid were collected. 1HNMR (CDCl3, ppm): = 8.10-8.40 (b, 2H), 6.90 (b, 2H ), 3.90-4.45 (bm, 9H), 3.45-3.90 (bm, 8H), 1.20-1.88 (bm, 26H), 0.90 (bm, 12H). IR (KBr cm-1) 2959, 2920, 2851, 2204, 1720, 1646, 1573, 1506, 1476, 1446, 1415, 1261, 1095, 1068, 1025, 862, 801. GPC analysis: Mn = 23,700,

PAGE 149

149 Mw = 31,100, PDI = 1.31. Anal. Calcd: C, 70.83; H, 8.72; N, 3.67; S, 4.20. Found: C, 62.44; H, 8.14; N, 2.97; S, 3.33.

PAGE 150

150 CHAPTER 5 POLYPROPYLENEDIOXYTHIOP HENE POLYELECTROLYTES 5.1 Introduction Incorporation of anionic or cationic functionality into a conjugated polymer yields a material that possesses the benefi cial properties of a conjugated po lymer along with solubility in polar solvents and possibly water.148 It also allows the polymer to be complexed with other polymers of the opposite charge,149 and consequently allows the building of multilayer films by the layer-by-layer thin-f ilm processing technique.150,151 This technique is an environmentally friendly method producing highly uniform multilayer films, with reproducible and controlled thicknesses and morphologies. Conjugated polyelectroly tes (CPEs) are of par ticular interest in solution-processed multilayer PLED devices. In such systems it is important to separate different functions such as charge injection, charge transport, and light emission. The multilayer deposition of conjugated polymers processed from organic solutions, and capable of accomplishing these functions, is difficult to achi eve because of dissolution and mixing of the subsequently deposited layers. Polymers which have an incompatible solubility with the emissive material can circum vent that problem.152-154 The most famous example is PEDOT-Poly(styrene sulfonate) (PEDOT-PSS) which is processed fr om water and successfully used as a hole transport layer in multilayer PLEDs.155 The interest in CPEs for organic photovoltaic devices is more recent than for LEDs, and one of the most relevant examples would be the layer-by-layer fabrication of photovoltaic cells based on the poly(phenylene ethynylene) ani onic electron donors and water-soluble cationic fullerene derivatives acceptors.156 Fluorescent CPEs which exhibit very high sensitivity to oppositely charged molecular quenc hers find also application in sensors.157-160

PAGE 151

151 A broad range of CPEs has been reported in th e literature, with most of them belonging to the families of poly( paraphenylene)s (PPPs), poly(phe nylene vinylene)s (PPVs), or poly(phenylene ethynylene)s (PPEs).148 Researchers have worked around the backbone of these polymers and introduced a variety of ioni c side chains carrying sulfonates (SO3 -), carboxylates (CO2 -), phosphonates (PO3 -) and ammoniums (NR3 +). This allowed access to absorption maxima varying between about 215 nm161 and 484 nm162 and emission maxima varying between 408 nm163 and 593 nm in polar solvents.157 However higher wavelength regions have been more difficult to reach and to circumvent that prob lem more complicated structures and syntheses leading to narrower band gap CPEs are currentl y being investigated, w ith the ultimate goal of discovering a red-emitting water soluble conjugated polymer.164 In order to shift the spectroscopic properties to the re d region, we decided to investig ate CPEs based on PProDOTs, which usually have solution absorptions cen tered in the 500-600 nm region and emissions centered in the 600-700 nm region.34,165,166 The synthesis of PProDOTs soluble in polar so lvents has recently been investigated by the Reynolds group with the design of PProDOTs with polar functional groups such as oligoethers, ethers, alcohols, and esters.165 However no cationic or anionic substituted PProDOTs have been reported as yet. In our quest for more red-shif ted conjugated polyelectrolytes, we decided to synthesize homopolymers of amino-functionalize d ProDOTs which can be fully characterized and then quaternized to the ammonium salt after a post-polymerization treatment. The structures of the targeted polymers are displayed in Figur e 5-1. Alkoxy chains endcapped with tertiary amines were used for the substitution. These chai ns were chosen with reasonable lengths to induce solubility in or ganic solvents for polymer charac terization, while not hindering the solubility in polar or aqueous systems after the post-polymerization treatment.

PAGE 152

152 One of the designated polymers, poly[3,3’-(3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine-3,3diyl)bis(methylene)bis(oxy)bis( N,N,N -trimethylpropan-1-aminium)] (PProDOT-NMe3 +), carries amines substituted with methyl groups (Figur e 5-1a). The other designated polymer, poly[ N,N’ (2,2’-(3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine-3,3-diyl)bis(m ethylene)bis(oxy)bis(ethane2,1-diyl))bis( N -isopropylN -methylpropan-2-aminium)] (PProDOT-NMe(Isop)2 +), carries amines with disorder inducing isopropyl gro ups and exhibits a more branched and bulky appearance (Figure 5-1b): it was chosen to enhance the solubi lity in organic solvents. The synthesis of the amino-substituted ProDOT monomers is described in section 5.2. The synthesis and macromolecular char acterization of the neutral polym ers are detailed in section 5.3. Sections 5.4 and 5.5 cover the redox, spectroe lectrochemical, and electrochromic properties of these materials. Finally, the post-polymer ization ionization of the polymers and their properties are devel oped in section 5.6. Figure 5-1. Structures of investigat ed amino-functionalized PProDOTs. 5.2 Monomer Synthesis and Characterization The amino-substituted ProDOT monomers we re synthesized by nucleophilic substitution of commercially available amino-alc ohols (dimethylamino-1-propanol and 2(diisopropylamino)ethanol) on the key ProDOT(CH2Br)2 molecule in the presence of sodium hydride as illustrated in Figure 52. The monomers were particularly difficult to purify due to the a. PProDOT-NMe3 + S O O O N O N n b. PProDOT-NMe(Isop)2 + S O O O O N N n

PAGE 153

153 presence of the highly polar amine groups which tend to stick on neutral si lica gel and make the separation from the monosubstituted products difficu lt. For these st ubborn amines, elution had to be accomplished with 10 percent in volume of ammonium hydroxide (14.8 N ) in a mixture of methanol and CH2Cl2 (making sure to not use more than 10 percent of methanol in order to not dissolve the silica gel), and in the case of ProDOT-NMe2 basic alumina had to be used instead of silica gel. Due to these purification difficulties, the pure monomers were obtained in low yields ( ca. 20-30 %). The monomers were characterized by 1H-NMR, 13C-NMR, elemental analysis, HRMS, and UV-Vis spectroscopy. They absorb in the UV, with absorption maxima in chloroform at 239 nm and 238 nm for PProDOT-NMe2 and ProDOT-NIsop2 respectively. The varying side chains do not lead to any obse rvable differences in the monomer’s optical properties. 1. FeCl3/CHCl3S O O O O N N n S O O O O N N n 2. Hydrazine 60% yield 64 % yield S O O Br Br OH N S O O O O N N NaH, DMF 27% S O O O O N N OH N NaH, DMF 23% Figure 5-2. Synthesis of amino-substitu ted ProDOT monomers and polymers. 5.3 Polymer Synthesis and Characterization The purification issues and low yields pr ecluded extensive chemistry on the aminosubstituted ProDOT unit and particularly th e preparation of the dibromo-derivative for polymerization via GriM. Consequently, the polym erization of the amino-substituted ProDOT

PAGE 154

154 monomers was accomplished by oxidative coupling using FeCl3 as the oxidant as illustrated in Figure 5-2. The oxidized polymers were washed 45 times with methanol to remove the ferric impurities. The neutral polymers were obtaine d after dedoping with hydrazine monohydrate. Further purification was accomplished either by extraction with deionized water or Soxhlet extraction with methanol. Finally, the polymer s were dissolved by Soxhlet extraction with chloroform, and isolated by solvent evapora tion. Approximately one third of the polymer samples, probably high molecular weight materi al, was insoluble during chloroform extraction and was not further characterized. The isolated polymers are bright red solids, which once dried strongly aggregate and are difficu lt to re-dissolve. PProDOT-NMe2 exhibits limited solubility in THF (~ 70-80%) and chloroform (~ 60%), while PProDOT-NIsop2 is almost fully soluble in chloroform (~ 90%) and partially soluble in THF (~ 70-80%). Th e extent of solubility was estimated by dissolving a known amount of polymer in a certain solvent, then filtering the polymer solution with 45 m filters, and finally weighting the amount of polymer recovered after filtration and solvent evaporation. PProDOT-NIsop2 has a higher degree of solubility due to the presence of more disorder inducing branches which gives rise to le ss aggregation. Neither polymer is soluble in toluene and acidic solutions (pH = 1-2). The polymers 1H-NMR spectra showed broad signals and the signals of the ProDOT proton end-group peaks essentially disappeared as expected w ith the polymerizations which proceeded to a substantial degree (assuming the polymerization to be terminated by protons). This is illustrated in Figure 5-3 with the comparison between the 1H-NMR spectra of ProDOTNIsop2 and PProDOT-NIsop2. The signal of the monomer Pr oDOT protons, observed at 6.45 ppm in Figure 5-3a, disappeared in the polymer spectrum (Figur e 5-3b), and a small new peak was observed at 6.19 ppm for PProDOT-N(Isop)2, which is attributed to the polymer proton end-

PAGE 155

155 groups. Looking at the integration of these peak s and making an assumption that each chain is terminated on both ends by hydrogen atoms, this suggests an average degr ee of polymerization of about 27. However this value is an upper limit as there are likely other chain ends such as chlorines (vide post). For PProDOT-NMe2 no oligomeric or polymeric proton end-groups could be detected. ppm (t1) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.82 2.00 ppm (t1) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.03 2.00 a b S O O O O N N nS O O O O N N Figure 5-3. 1H-NMR spectra. (a) 1H-NMR spectrum of ProDOT-NIsop2; (b) 1H-NMR spectrum of PProDOT-NIsop2. It was not possible to estimate the polymer s molecular weights by GPC (unsuccessful attempts were done in THF and chloroform, at room temperature and at elevated temperature (40C)). Even PProDOT-NIsop2 which is soluble in chloroform did not give any signal by GPC. The polymer solubility in these solvent and te mperature conditions is probably too poor and the

PAGE 156

156 polymers get stuck onto the GPC column. This is surprising since the molecular weights of a variety of amino-functionalized conjugated polymers have been estimated by GPC.167-169 In the examples where the instrumental details were specified, it even appeared that the GPC columns were the same as the ones used here. The polymers elemental analyses showed rela tively large amounts of iron and chlorine trapped inside the polymers, especi ally in the case of PProDOT-NIsop2. The analysis of PProDOT-NMe2 showed the presence of one iron per 36 sulfurs, and of one chlorine per 10 sulfurs, and the analysis of PProDOT-NIsop2 showed the presence of one iron per 13 sulfurs, and of one chlorine per 2 sulfurs. This is probabl y due to the highly aggregated morphology of the polymers which prevented efficient washing of thes e impurities. It is interesting to note that PProDOT-NMe2 was washed both with deionized wa ter and methanol, whereas PProDOTNIsop2 was only washed with methanol. Consequent ly there is also a possibility that water allowed a more efficient washing of the ferric impurities. This will be verified in the near-future on a scale-up polymerization of PProDOT-NIsop2. It should be noted that the carbon analyses were somewhat lower than expected. This might be explained by the fact that highly aromatic polymers are difficult to fully combust and some carbonization may have occurred during the measurements. As structure proof, the polymers were char acterized by MALDI mass spectrometry using a dithranol matrix. The spacing betw een the peaks corresponds to 384 amu for PProDOT-NMe2, and 469 amu for PProDOT-NIsop2, which correlates well with the calculated molecular weight of the repeat unit of the polymer. Poorly soluble polymers pose particular challenges to analysis by MALDI because they do not readily form the mixed polymer/matrix crystals. In the case of PProDOT-NMe2, the MALDI measurements were probably affected by the limited solubility of

PAGE 157

157 the polymer because they showed poor peak reso lution and intensity as illustrated in Figure 5-4 (each “peak” is a cluster of peaks that have similar masses). For this reason it was not possible to identify the end-group peaks. In th e MALDI spectrum of PProDOT-NIsop2 displayed in Figure 5-5, it seems that the masses of the main series match better with oligomers having chlorine endgroups than oligomers having hydrogen end-groups. Fo r example, if we take the oligomer series with m/z at 3,821, we get m/z of about 3,819 after removal of two hydrogens and m/z of about 3,750 after removal of two chlorines. It corresponds to 8.1 repeat units in the first case (hydrogen end-groups) and to exactly 8 repeat units in the second case (chlor ine end-groups). This could be an explanation for the high level of chlorine at oms observed in the polymer’s elemental analysis. Since only one reference170 could be found reporting such a ph enomenon, a deeper investigation will be accomplished on a new sample of PProDOT-NIsop2 thoroughly washed with a methanol solution containing 1,10-phenanthroline. Phenanthro line has the ability to form chelates with iron and is often used to remove ferric impur ities from polymers. Meanwhile, the mechanism involving chlorine ions, resul ting from the reduction of Fe(III) to Fe(II) upon polymer oxidation, has been speculated and is displayed in Figure 5-6. The observation of “peak s” (or clusters) up to m/z 7,000 (18 repeat units) for PProDOT-NMe2, and up to m/z 4,760 (10 repeat units) for PProDOT-NIsop2 in the MALDI results proves that th e materials are at least oligomers. The thermal stability of the polymers (previ ously dried under vacuum for a few days) was studied by thermogravimetric analysis (TGA) in a nitrogen atmosphere using a 20C min-1 temperature ramp from 50C to 900C (Figure 5-7) The polymer degradation seemed to occur in two steps, the first one being the thermal degrad ation of the amino chains (from ~ 280C up to ~ 380C for PProDOT-NIsop2, and from ~ 210C up to ~ 265C for PProDOT-NMe2), and the

PAGE 158

158 second one being the backbone degradation (from ~ 380C to 900 C for PProDOT-NIsop2 and from ~ 265C to 650 C for PProDOT-NMe2). At 900C less than 12% of materials remained. 01000200030004000500060007000 9000 18000 30004000500060007000 420 n = 6 n = 18 n = 16 n = 14 n = 12 n = 10Abundance m/z n = 8 x 25Abundancem/z Figure 5-4. MALDI-M S of PProDOT-NMe2. Dithranol was used as th e matrix and the peaks up to m/z 2000 are dithranol matrix clusters. 250030003500400045005000 60 120 n = 10 n = 9 n = 8 n = 7 4762 4289 3821 m/zAbundance2884 3352 n = 6 Figure 5-5. MALDI MS of PProDOT-NIsop2. Dithranol was used as the matrix. The peaks up to m/z 2000 are not displayed since they were hidden by dithranol matrix clusters.

PAGE 159

159 S O O R R S O O R R S O O R R S O O R R S O O R R [ox] S O O R R S O O R R S O O R R S O O R R S O O R R H H e + Fe(III)Cl3 Fe(II)Cl2 + Cl-S O O R R S O O R R S O O R R S O O R R S O O R R H Cl S O O R R S O O R R S O O R R S O O R R S O O R R Cl -H+ Figure 5-6. Speculated mechanism of the chlorine terminati on of PProDOT-NIsop2 growing chains. 200400600800 0 20 40 60 80 100 Weight (%)Temperature C PProDOT-NMe 2 PProDOT-NIsop 2 Figure 5-7. Thermogravimetric analysis of th e amino-functionalized PProDOTs in a nitrogen atmosphere. Figures 5-8a and 5-8b show the UV-Vi s absorption and photoluminescence of the polymers in chloroform. They absorb over a broad spectral range ( ca. 450-620 nm) and their solutions are purple-pink. The absorption maximum ( abs) of PProDOT-NIsop2 is a little bit blueshifted (525 nm) compared to the absorption maximum of PProDOT-NMe2 (536 nm) due to the

PAGE 160

160 increased degree of branching which creates more disorder and decreases the conjugation length. The polymers emit in the red and near-IR region with an emission maximum ( em) at 616 nm for PProDOT-NMe2, and at 618 nm for PProDOT-NIsop2. The UV-Vis absorption and photoluminescence behavior of the polymers is comparable to what was observed for the previously reported ester-substituted PProDOT family, with for instance an average 20 repeat units sample of PProDOT(CH2OC(O)C6H13)2 (molecular weight estimat ed by GPC) exhibiting a abs of 535 nm and a em of 604 nm in toluene.165 The fluorescence qua ntum yields were evaluated at 19% for PProDOT-NMe2 and 21 % for PProDOT-NIsop2 (Cresyl violet perchlorate standard; = 0.54).171 The polymer solutions we re filtered through 0.45 m filters prior to the fluorescence measurements, in order to remove the small amounts of non-solubilized aggregates which could hinder the fluorescence. It is also worth noting that the presence of iron impurities might have affected the PL efficiencies. 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Absorption (normalized)Wavelength (nm)abs = 536 nmem = 616 nm Photoluminescence (normalized) a 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (normalized)Wavelength (nm)abs = 525 nmem = 618 nm Photoluminescence (normalized) b Figure 5-8. UV-vis absorption and photoluminescen ce spectra of neutral amino-functionalized PProDOTs. (a) PProDOT-NMe2 in chloroform, (b) PProDOT-NIsop2 in chloroform. In each spectrum, the left photograph represents the color of the solution under visible light and the right photograph re presents the photoluminescence of the solution irradiated by UV-light.

PAGE 161

161 5.4 Polymer Spectroelectrochemistry and Electrochemistry Thin-films (~ 150 nm thick) of the amino-s ubstituted ProDOT polymers were spray-cast from chloroform solutions (3-5 mg mL-1) onto ITO coated glass electrodes, and studied by spectroelectrochemistry as illu strated in Figures 59a and 5-9b. The polymer films are pinkpurple in the neutral state with PProDOT-NMe2 exhibiting an absorption maximum at 547 nm, whereas PProDOT-NIsop2 exhibits an absorp tion maximum at 538 nm. Band-gaps of ~ 1.9 for PProDOT-NIsop2 and ~ 2.0 eV for PProDOT-NMe2 were determined from the onset of the to transition in the neutral spectra. The spect ral changes upon oxidation were recorded in 0.1 M TBAP/PC, with the po tential being stepped from -0.3 V to +0.8 V every 0.05 V for PProDOTNMe2, and from -0.38 V to +0.92 V every 0.05 V for PProDOT-NIsop2. The onsets of oxidation occur at about -0.05 V for PProDOT-NMe2 and -0.03 V for PProDOT-NIsop2. As the oxidation goes, the transition of the neutral state disappears and polaron and bipolaron transitions appear in the 600-1500 nm region ch anging the films to a highly tr ansmissive clear appearance. Such behavior is typical of PProDOTs and is one of the reasons why PProDOTs are so interesting for electrochemical applications.34,165 Similar color changes (from red to clear) have also been reported for poly(3,4ethylenedioxypyrrole)s (PEDOPs).172 It is important to specify that the color switching was only reversible fo r about 2-3 cycles, the polymer falling of the electrode with furt her redox cycling. The polymers were deposited by drop-casting on Pt button electrod es and their redox properties were recorded by CV and DPV, in 0.1 M TBAP in PC. The dedoping of the oxidized polymer was difficult to observe because the oxi dized polymer dissolved in the electrolyte solution, and after only one cycl e the signal almost completely disappeared. This phenomenon had been observed on esterand alcohol-substituted PProDOTs;165 changing the solvent used for

PAGE 162

162 the electrolyte preparation did not solve the problem (unsuccessf ul attempts were done using ACN, benzonitrile, and water), neither did the replacement of the Pt button electrode by a gold electrode. DPV measurements done on thinner film s were more sensitive and allowed capturing the reduction potential of the oxidized polymers as shown in Figures 5-10a and 5-10b. It is important to note that the oxidation and reducti on potentials observed by DPV are not accurate since no redox cycling could be performed, previ ous to recording the da ta, for breaking in the polymer film. The onset of oxidation of PProDOT-NMe2 is found around -0.07 V, which matches quite well with the onset of oxidation observed by spectroelectrochemistry, and an E1/2 value of 0.13 V has been determined by DPV. An onset of oxidation of ~ 0.08 V and an E1/2 of 0.35 V have been determined by DPV for PProDOT-NIsop2. This E1/2 value is quite bigger than the value found for PProDOT-NMe2 and the difference might be e xplained by the bulkier chains on PProDOT-NIsop2 which inhibit the fast movement of counter ions. However no definitive conclusion will be given since we do not know to what extent these valu es can be trusted, as explained before. The solubility of the polym ers in the oxidized state does not make these materials good candidates for absorptive/transmissive electrochromism. 5.5 Colorimetry Thin-films of the amino-substituted PProDOT s were deposited on ITO by spray-casting from 5 mg mL-1 chloroform solutions and were analyzed by in-situ colorimetric analysis. The relative luminance was measured as the neutra l polymers were progressively oxidized and the luminance changes confirmed the positioning of the onsets of oxidation observed by spectroelectrochemistry. It should be noted that in correlation w ith the electrochemical results this would not be reversib le. As illustrated in Figure 5-11a for PProDOT-NMe2, oxidation started at -0.05 V, and there was a luminance change of ~ 35% in the small -0.05 V – 0.1 V potential

PAGE 163

163 window. A luminance change of ~ 25% was observed for PProDOT-NIsop2 between the onset of oxidation at ~ 0.02 V and 0.20 V (Figure 5-11b). 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 -0.05 V +0.8 V -0.3VAbsorption (a. u.)Wavelength (nm) -0.3V +0.8 V 0V -e +e a 400600800100012001400 0.0 0.2 0.4 0.6 + 0.32 V + 0.92 V -0.38 VAbsorbance (a. u.)Wavelength (nm) 0.03 V Neutral -0.38 V + 0.92 V -e +eb Figure 5-9. Spectroelectrochemisty of thin-films of the neutral amino-functionalized PProDOTs. (a) PProDOT-NMe2 and (b) PProDOT-NIsop2. The polymer films were prepared by spray-casting chloroform soluti ons of the polymers (3-5 mg mL-1) onto ITO coated glass. The spectral changes were recorded in 0.1 M TBAP/PC and all potentials are reported vs Fc/Fc+. The potential was increased in 50 mV steps. The photographs represent the film colors in the neutral state (left) and afte r oxidation (right). -0.3-0.2-0.10.00.10.20.3 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 E onset,ox = -0.07 V E p,red = 0.11 VCurrent (mA/cm 2 )E(V) vs. Fc/Fc + E p,ox = 0.15 V a -0.3-0.2-0.10.00.10.20.30.4 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.00.10.20.30.4 -0.005 -0.004 -0.003 -0.002 E p,red = +0.33 V Current (mA/cm 2 )E(V) vs. Fc/Fc + E p,ox = +0.37 V E onset,ox = +0.08 V b Figure 5-10. Differential pulse voltammetry of amino-substituted PProDOTs. (a) DPV of PProDOT-NMe2, (b) DPV of PProDOT-NIsop2. Measurements were performed on a 0.02 cm2 Pt button working electrode in 0.1 M TBAP/PC with a Pt foil counter electrode and a s ilver wire pseudo referen ce electrode calibrated vs Fc/Fc+.

PAGE 164

164 The L*a*b* values of the colors were also determined to allow color matching. For PProDOT-NMe2 in the neutral purp le-pink state L = 66, a = 34, b = -15, and in the fully oxidized transparent state L = 87, a = -4 and b = -4. For PProDOT-NIsop2 in the neutral violet state L = 72, a = 27, b = -7, and in the fully oxidized transparent state L = 88, a = 2, and b = 2. The available color states were also tracked using the xy chromaticity diagrams shown in Figures 5-12a and 5-12b. Note that for clarity, these chromaticity diagrams are a 10 x magnification of the region of interest of the full xy chromaticity diagram displayed in Chapter 2. As the potential was increased and the polymers were doped the y coordinate increased and the x coordinate decreased after being stable durin g the beginning of oxidation. The abrupt color changes which occurred between -0.05 V and 0.10 V for PProDOT-NMe2 and between 0.02 V and 0.20 V for PProDOT-NIsop2, and which were observed on the luminance spectra in Figures 5-11a and 5-11b, can also be clea rly seen on the xy ch romaticity diagram by a large change in the xy coordinates between these potentials. -0.4-0.20.00.20.40.60.8 30 35 40 45 50 55 60 65 70 75 Relative Luminance (%)E(V) vs. Fc/Fc +a -0.4-0.20.00.20.40.60.81.0 40 45 50 55 60 65 70 75 Relative luminance (%)E(V) vs. Fc/Fc +b Figure 5-11. Relative luminance (%) versus app lied potential for amino-substituted PProDOTs. (a) for PProDOT-NMe2 and (b) for PProDOT-NIsop2. The films were prepared by spray-casting chloroform soluti ons of the polymers (5 mg mL-1) onto ITO. The measurements were performed in 0.1 M TBAP/PC and are reported vs. Fc/Fc+. The potential was increased in 50 mV steps.

PAGE 165

165 0.340.350.360.370.380.390.40 0.32 0.34 0.36 0.38 0.40 0.15 V -0.05 Vyx -0.3 V +0.7 V a 0.350.360.370.380.39 0.34 0.35 0.36 0.37 0.38 0.39 0.40 yx -0.38 V +0.92 V +0.02 V +0.17 V b Figure 5-12. CIE 1931 xy chromaticity diagram of amino-substituted PProDOTs. Circles linked by a dotted line represent the color track for thin films of (a) PProDOT-NMe2 and (b) PProDOT-NIsop2 which go from pink-violet colors to clear. All potentials are reported vs Fc/Fc+. The potential was increased in 50 mV steps. 5.6 Quaternization of the Amino-substituted PProDOTs The ionisation of PProDOT-NMe2 and PProDOT-NIsop2 was accomplished by reaction of the tertiary amines with the iodomethane methyl ating agent as previously reported for polymers substituted with amines (Figure 5-13).167,173 The quaternization was run at room temperature for 2 days in THF or CHCl3. The ionic polymers are violet soli ds which are both well solvated in polar aprotic solvents such as di methylsulfoxide (DMSO) and also N,N -dimethylformamide (DMF). The polymers were exposed to a variety of other solvents at room temperature to evaluate their solubility properties and the results are summarized in Table 5-1. PProDOTNMe3 + is interestingly moderately soluble in water. The higher degree of branching of PProDOT-NIsop2 allowed better solubility, and easier manipulation and characterization of the neutral polymer, but as opposed to PProDOT-NMe3 +, the hydrocarbon chains are too large to allow solubility of the quaternized derivative in water.

PAGE 166

166 It was not possible to give a detailed 1H-NMR description (peak pos ition and integration) of the polymers since most of the peaks were overlapped by a br oad water peak which shows up at 3.33 ppm in DMSO. However, the effective re moval of the excess of methyl iodide was confirmed by the disappearance of the MeI 1H-NMR peak at 2.21 ppm. The presence of a singlet at 3.09 ppm in the 1H-NMR spectrum of PProDOT-NMe(Isop)2 + proved that a certain amount of MeI effectively reacted with the amines. Iodi ne elemental analysis provides one method of determining the quaternization efficiency of th e reaction between the ne utral polymers and MeI. The N/I ratio determined by elemental analysis i ndicates quaternization of approximately 91% of the available amine sites of PProDOT-NMe3 +, and of about 98% of the available amine sites of PProDOT-NMe(Isop)2 +. MeI THF, 48h S O O O O N N nS O O O O N N n S O O O O N N nS O O O O N N n MeI CHCl3, 48h Figure 5-13. Quaternization of amin o-substituted PProDOTs using MeI. Table 5-1. Solubility of ionic amino-substitu ted PProDOTs in various solvents at room temperature. Polymer DMSO watermethanolethanolacetoneacetonitrile CHCl3DMF PProDOT-NMe3 + xxxx xxxx000 0xxx PProDOT-NMe(Isop)2 + xxxx 0xxx0xx xxxx 0 = insoluble; x = very slightly soluble; xx = slightly soluble; xxx = moderately soluble; xxxx = very soluble.

PAGE 167

167 Figures 5-14a and 5-15a show the UV-Vi s absorption and photoluminescence of PProDOT-NMe3 + and PProDOT-NMe(Isop)2 + in DMSO respectively. The solutions are pinkpurple, as illustrated by the photographs, w ith absorption maxima at 540 nm for PProDOTNMe3 + and 542 nm for PProDOT-NMe(Isop)2 +. These values are red-shifted (4-17 nm) compared to their correspondi ng neutral precurso r polymers. This phenomenon has been observed in similar polyelectroly tes and is due to the polyelec trolyte which has a more rigid chain conformation than the corresponding neutral precursors.168 The polyelectrolyte tends to optimize hydrophobic interactions between adjacent polymer chains by increasing the stacking, and at the same time allows the polar amine groups to fully extend into the polar solvent. As stated previously, PProDOT-NMe3 + is moderatly soluble in water (Table 5-1). The UV-Vis absorption spectrum in water shown in Figure 5-14b overlaps quite well the spectrum recorded in DMSO with just a small blue-shift of abs (9 nm) probably due to a solvatochromic effect. The effect of water on the increased de gree of aggregation compared to DMSO will be discussed in the fluorescence sec tion below (vide post). The higher degree of solubility of PProDOT-NMe(Isop)2 + in DMSO compared to methanol is clearly seen by comparing the UVVis absorption spectra of the polymer in these tw o systems. There is a 23 nm red-shift of the absorption maximum in methanol compared to DM SO, as well as a more defined fine structure with a shoulder at 617 nm (Figure 5-15b), and the solution has a more violet appearance as seen in the photograph in Figure 5-15. These observa tions are suggestive of a more aggregated structure imposing more -stacking and an increased -conjugation.174 The polymers emit a bright orange-red color in DMSO, with emission maxima at 612 nm for PProDOT-NMe3 + and 615 nm for PProDOT-NMe(Isop)2 + (see photographs in Figures 5-14a and 5-15a). PProDOT-NMe3 + and PProDOT-NMe(Isop)2 + exhibit fluorescence quantum

PAGE 168

168 efficiencies of 16 and 11% respectively in DMSO (Cresyl violet perchlorate standard; = 0.54).171 As a consequence of the lower degree of sol ubility in water and of a more aggregated state, the fluorescence quantum efficiencies of PProDOT-NMe3 + dropped to 1.5% in water. These values are encouraging since the most re d-shifted CPEs reported prior to this work ( em = 592-603 nm in methanol and 630-634 nm in water) exhibit fluorescence quantum efficiencies which do not exceed 3% in methanol and 0.06% in water.164 400500600700 0.0 0.2 0.4 0.6 0.8 1.0 em = 612 nm Absorbance (Normalized)Wavelength (nm)abs = 540 nma 400500600700 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (Normalized)Wavelength (nm) Water DMSO babs = 531 nm Figure 5-14. Solution spectroscopy for PProDOT-NMe3 +. (a) UV-Vis absorption and photoluminescence of PProDOT-NMe3 + in DMSO; left photograph: color of the solution under visible ligh t; right photograph: photoluminescence of the solution irradiated by UV-light; (b) UV-Vis absorption of PProDOT-NMe3 + in DMSO and deionized water; photograph: color of the water soluti on under visible light. 5.7 Summary and Perspective For the first time, conjugated polyelectrolytes of the PProDOT family have been designed. These polymers feature cationic (R–N+–R) side groups and were prepared by postpolymerization quaternization of alkoxyamine s ites along the ProDOT polymer backbone. This methodology was expected to facilitate the molecular weight characterization of the polyelectrolytes, but unfo rtunately, due to solubility limitations of the neutral precursors of the

PAGE 169

169 polymers in organic solvents, we were not able to take advantage of it and to estimate the molecular weights by GPC. 400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 em = 615 nm Absorbance (Normalized)Wavelength (nm)abs = 542 nma 400500600700800900 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 DMSOabs = 565 nmAbsorbance (Normalized)Wavelength (nm)abs = 542 nm Methanol b617 nm Figure 5-15. Solution spectroscopy for PProDOT-NMe(Isop)2 +. (a) UV-Vis absorption and photoluminescence of PProDOT-NMe(Isop)2 + in DMSO; left photograph: color of the solution under visible light; right photograph: photoluminescence of the solution irradiated by UV-light. (b) UVVis absorption of PProDOT-NMe(Isop)2 + in DMSO and methanol; photograph: color of the methanol solution under visible light. The neutral precursors of the polymers we re prepared by ferric chloride oxidative polymerization. They exhibit good film propertie s by spray-casting, a nd cathodically switch between purple colors in the neutral state an d a highly transmissive clear oxidized state. However, as was observed for previously report ed polar PProDOTs, the oxidized forms of the films dissolved in water, acetonitrile, or propy lene carbonate, making the neutral polymers poor candidates for electrochromic applications, but interesting for applications necessitating the processing of the conducting form in an environmentally friendly solvent. The polymers in their ionic forms can be added to the extremely small list of reported redshifted polyelectrolytes and are presently the most fluorescent of them.164 They are well solvated in DMSO, PProDOT-NMe3 + also exhibits moderate solubi lity in water, and PProDOT-

PAGE 170

170 NMe(Isop)2 + is partially soluble in methanol. The CPEs exhibit relati vely good fluorescence efficiencies in DMSO, but the fluorescence quenching, which occurs in methanol or water upon aggregation, suggests that the fluorescence from the polymers in the films will be probably strongly quenched. A new door ha s been opened for multilayer optoelectronic devices, and studies of the applicatio n of these materials in devices are now needed. 5.8 Experimental 3,3’-(3,4-Dihydro-2 H -thieno[3,4b ][1,4]dioxepine-3,3-diyl)bis (methylene)bis(oxy)bis( N,N -dimethylpropan-1-amine) [ProDOT-NMe2]. 3-Dimethylamino-1propanol was refluxed overnight over magnesium turnings and then di stilled under reduced pressure. 3-Dimethylamino1-propanol (4.51 g, 4.38 10-2 mol) and sodium hydride (2.10 g, 8.76 10-2 mol, 60% dispersion in oil) were dissolved in anhydrous DMF (80 mL) and the mixture was heated at 110C for 24 h under nitrogen. ProDOT(CH2Br)2 (5.00 g, 1.46 10-2 mol) was added and the solution stirred at 110C for an extra 24 h. The br own solution was cooled to room temperature, poured into deionized water and the mixture was ex tracted with diethyl ether. The organic layer was washed with Brine and dried over MgSO4. After filtration through a Bchner filter, the solvent was evaporated and th e crude product was collected as a brown oil. The product was purified by column chromatography on basic alumina using one volume of methanol/NH4OH (10/1) dissolved in 10 volumes of CH2Cl2 for the elution, yielding 1.55 g (27%) of the pure product as a yellow oil. 1H-NMR (CDCl3): 6.45 (s, 1H), 4.01 (s, 2H), 3.49 (s, 2H), 3.46 (t, 2H), 2.32 (t, 2H), 2.22 (s, 6H), 1.73 (m, 2H). 13C-NMR (CDCl3): 149.89, 105.32, 73.88, 70.08, 69.87, 56.89, 47.93, 45.77, 28.14. HRMS: calcd for C19H34N2O4S: 386.2239. Found: 386.2258. Anal. Calcd for C19H34N2O4S: C, 59.04; H, 8.87; N, 7.25. Found: C, 58.66, H, 9.42, N, 7.23. N,N’-(2,2’-(3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine-3,3-diyl)bis(methylene)bis (oxy)bis(ethane 2,1-diyl))bis( N -isopropylpropan-2-amine) [ProDOT-NIsop2]. 2-(Diisopro-

PAGE 171

171 pylamino)ethanol was refluxed overnight over magnesium turnings and then distilled under reduced pressure. 2-(Diisopropyl amino)ethanol (11.89 g, 8.18 10-2 mol) and sodium hydride (3.93 g, 1.64 10-1 mol, 60% dispersion in oil) were dissolved in anhydrous DMF (200 mL) and the mixture was heated at 110C for 24 h under nitrogen. ProDOT(CH2Br)2 (7.00 g, 2.04 10-2 mol) was added and the soluti on stirred at 110C for an ex tra 72 h. The brown solution was cooled to room temperature, poured into deionized water and the mixture was extracted with diethyl ether. The organi c layer was washed with Brine and dried over MgSO4. After filtration through a Bchner filter, the solvent was evaporated and the crude product was collected as a brown oil. The product was purified by column chromatography on silica gel using one volume of methanol/NH4OH (10/1) dissolved in 30 volumes of CH2Cl2 for the elution, yielding 2.17 g (23%) of the pure product as a yellow oil. 1H-NMR (CDCl3): 6.45 (s, 1H), 4.02 (s, 2H), 3.50 (s, 2H), 3.38 (t, 2H), 3.01 (m, 2H), 2.58 (t, 2H), 1.01 (d, 12H). 13C-NMR (CDCl3): 149.86, 105.22, 73.86, 73.63, 70.20, 49.59, 47.99, 44.91, 20.97. HRMS: calcd for C25H46N2O4S: 470.3178. Found: 470.3149. Anal. Calcd for C25H46N2O4S: C, 63.79; H, 9.85; N, 5.95. Found: C, 63.13, H, 10.32, N, 5.96. PProDOT-NMe2. ProDOT-NMe2 (0.55 g, 1.42 10-3 mol) was dissolved in dry CHCl3 (20 mL) and a slurry of FeCl3 (1.15 g, 7.10 10-3 mol) in chloroform (20 mL) was added by small portions over a 2 h period. A black gum fo rmed rapidly in the ye llow-brown solution. After 5 h, the solution was poured into a beaker of methanol (500 mL). The black pr ecipitate formed was filtered through a Soxhlet thimble, wa shed a couple of times with methanol (200 mL total), and then stirred for 15 h with excess hydrazine monohydrate (10 mL) in chloroform (200 mL). The polymer dissolved and the solution colo r turned purple-pink. Th is chloroform solution was extracted with deionized water to remove th e maximum of iron impurities. Then, the organic

PAGE 172

172 layer was collected, the solvent wa s evaporated and the red solid obtained was put in a Soxhlet thimble and Soxhlet extracted for 24 h with chloro form. A lot of insoluble polymer was left in the Soxhlet thimble. The solvent was evaporated from the chloroform fraction and a red solid was collected and dried under a nitrogen flow (0.33 g, 60%). 1H-NMR (CDCl3, ppm): = 4.16 (b, 2H), 3.63 (b, 2H), 3.50 (b, 2H), 2.34 (b, 2H), 2.23 (b, 6H), 1.72 (b, 2H). Anal. Calcd for C19H34N2O4S: C, 59.04; H, 8.87; N, 7.25; O, 16.56; S, 8.30. Found: C, 49.32; H, 8.30; N, 5.05; S, 5.03; Cl, 0.55; Fe, 0.24. PProDOT-NIsop2. ProDOT-NIsop2 (1.02 g, 2.16 10-3 mol) was dissolved in dry CHCl3 (30 mL) and a slurry of FeCl3 (1.75 g, 1.08 10-2 mol) in chloroform (30 mL) was added by small portions over a 2 h period. A black gum fo rmed rapidly in the ye llow-brown solution. After 5 h, the solution was poured into a beaker of methanol (500 mL). The black precipitate was filtered through a Soxhlet thimble, washed with methanol a couple of time (200 mL total), and then stirred for 15 h with excess hydrazine mon ohydrate (10 mL) in chlo roform (400 mL). The polymer dissolved and the solution color turned purple-red. The solvent was evaporated and a red solid collected and transferre d into a beaker of methanol ( 400 mL). The precipitate formed was filtered through a Soxhlet thimble, purified vi a Soxhlet extraction fo r 15 h with methanol, and extracted for 24 h with chlo roform. A lot of insoluble polym er was left in the Soxhlet thimble. The solvent was evaporated from the ch loroform fraction and a red solid was collected and dried under a nitrogen flow (0.65 g, 64%). 1H-NMR (CDCl3, ppm): = 6.19 (b, 0.03H), 4.34.1 (b, 2H), 3.9-3.3 (bm, 4H), 3.3-3.0 (b, 2H), 2. 9-2.6 (b, 2H), 1.3-1.0 (b, 12H). Anal. Calcd for C25H46N2O4S: C, 63.79; H, 9.85; N, 5.95; S, 6.81. F ound: C, 55.86, H, 8.39, N, 5.27; S, 6.58; Cl, 4.54; Fe, 0.85.

PAGE 173

173 General Quaternization Procedure. The amino-substituted PProDOTs were dissolved in THF or CHCl3, and the solutions were stirred with methyl iodide for 2 days at room temperature under nitrogen. Starting from the moment wh ere MeI was added, the red polymer solutions turned more and more violet due to the form ation of a precipitate. Then the solvent was evaporated and the polymers were precipitated in acetone, collected on 0.45 m filter papers, washed thoroughly with acetone and drie d under vacuum, yielding violet solids. PProDOT-NMe3 +. Use of PProDOT-NMe2 (4.50 10-2 g), THF (30 mL) and MeI (1mL). 1H-NMR (DMSO, ppm): = 3.0-3.6 (bm, 17H), 1.9-2.1 (b, 2H). Anal. Calcd for C19H34N2O4S • 2.0 CH3I: C, 37.62; H, 6.01; N, 4.18; S, 4.78; I, 37.86. Found: C, 33.96; H, 5.98; N, 2.64; S, 3.40; I, 23.53; Cl, 0.64. PProDOT-NMe(Isop)2 +. Use of PProDOT-NIsop2 (4.00 10-2 g), CHCl3 (15 mL) and MeI (2 mL). 1H-NMR (DMSO, ppm): = 3.1-3.5 (bm, 10H), 3.09 (s, 3H), 1.3 (b, 12H). Anal. Calcd for C25H46N2O4S • 2.0 CH3I: C, 42.98; H, 6.95; N, 3.71; S, 4.25; I, 33.64. Found: C, 35.77, H, 7.10, N, 1.92; S, 2.19; Cl, 1.01; I, 15.29.

PAGE 174

174 CHAPTER 6 SUMMARY The work assembled in this dissertation gives a broad overview of the variety of properties that conjugated polymers can offer to the field of optoelectronic devices, such as light emission, light absorption, and thermally-, electricallyor solvent-i nduced chromism. The various characterizations accomplished on the thienylene pol ymer families studied here, show that each conjugated polymer family has the potential of being used in multiple applications, and that research on a selected family is consequently truly interdisciplinary. This work also makes it evident how the synthetic flexibility and easy de rivatization of conjugated polymers can be used as a tool for manipulating the ba nd gaps, the optical and electr onic properties, as well as the solubility, for building optoelectronic materials with various properties. Chapter 3 described the quest for a wide ba nd gap polymer of the thienylene-phenylene polymer family, being organo-soluble and processa ble, and which could be synthesized in high bulk yields. Looking at the literature on thiophene-dialkoxybenzene (PBT-B(OR)2) and EDOTdialkoxybenzene (PBEDOT-B(OR)2) derivatives raised the potential of these molecules for electrochromics, or as hole transporting material s for photovoltaics, but al so suggested the need for further synthetic improvements. The polymer ization of derivatives having solubilizing alkoxy-substituents was revisited, and the synthetic versatility of the molecules allowed diverse polymerization methods to be attempted (Y amamoto coupling, GriM, and solid state polymerization). However they failed to give high molecular weights or highly processable materials, due to the low solubility propertie s of the growing molecules. This problem was overcome by designing a new member, PBProDOT-Hex2-B(OC12H25)2, which contains a dihexyl-functionalized ProDOT as the thieny lene ring. The functionalized ProDOT ring introduced electron donati ng properties similar to EDOT, as well as an increased degree of

PAGE 175

175 solubility. It allowed formation of a low oxidation potential mate rial, which could be spray-cast onto large and flexible surfaces. This material cathodically switches between a neutral orange state and a transparent oxidized state, which is of great interest for electrochromic display and smart window applications. The major focus of Chapter 4 was the optimizat ion of the processabil ity of the recently reported narrow band gap PProDOT-Hex2:CNPPV. Preliminary work had shown that this polymer exhibits nearly optimal light absorption properties and en ergy level alignment for use in photovoltaics with the electron accepto r PCBM, and is also an excellent electrochromic material. Replacing the hexyl side chains of the ProDOT ring by linear or branched alkoxy substituents improved the solubility in organic solvents and film quality as a consequence. It also introduced an increased degree of disorder as observe d by the blue-shift of the absorption spectra. Unsymmetrical and branched substitution of the phenylene ring did not brin g further solubility improvement, but important optical changes were observed, probably created by a change in the polymer conformation or interaction with the adjacent chains. Photovoltaic power conversion efficiencies of 0.4% were attained with this t ype of molecule, as opposed to the 0.6% attained with the higher band gap and semicrystalline PBT-B(OR)2 family synthesized by Yamamoto coupling and studied in Chapter 3. It appeared that even if the electronic properties were more favorable for absorbing photons, and even if hom ogeneous films could be prepared due to the improved solubility, the device performance was limited by the hi gher degree of disorder of these molecules. More attention needs to be directed towards improving the transport properties in this type of materials. As of now it seems th at the best application of these molecules would be in electrochromics. Indeed, similarly to PE DOT, they switched from neutral blue or purple

PAGE 176

176 colors to transparent films in the oxidized state with the extra advantages of being stable in the neutral state and spray-coatable. In Chapter 5, attention was turned to maki ng a new type of conjugated polyelectrolyte from amino-substituted PProDOTs. The design of the two ProDOT monomers studied here had to be thought through ca refully in order for the neutral polymers to be soluble in organic solvents for easy characterization, and for their ionic forms to be soluble in polar and aqueous solvents. The selected amino-substituted PProDOTs derivatives were synthesized via ferric chloride oxidative polymerization, and their ionizatio n was carried out by post-polymerization quaternization of the amine groups. The neutral derivatives exhibited partial solubility in organic solvents, which hindered their complete character ization, suggesting the need for further side chain manipulation. The polymers in their ionic forms were well solvated in DMSO and are presently the most fluorescent red-shifted polyel ectrolytes ever report ed. However, further structural adjustments need to be accomplished in order to induce a high de gree of solubility in water. This project was conse quently partially successful and is very promising for future research on PProDOT polyelectrolytes.

PAGE 177

177 APPENDIX A CRYSTALLOGRAPHIC INFORMATION FOR COMPOUNDS Figure A-1. Numbering system for Br2-BT-B(OC7H15)2 crystal structure. Table A-1. Crystal data and structure refinement for Br2-BT-B(OC7H15)2. Identification code eg01 Empirical formula C28H36Br2O2S2 Formula weight 628.51 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group C2/c Unit cell dimensions a = 30.2887(18) = 90 b = 5.7902(3) = 114.9510(10) c = 17.7458(10) = 90 Volume 2821.7(3) 3 Z 4 Density (calculated) 1.479 Mg/m 3 Absorption coefficient 3.044 mm -1 F(000) 1288 Crystal size 0.32 x 0.15 x 0.08 mm 3 Theta range for data collection 2.33 to 27.50 Index ranges -34 h 39, -6 k 7, -22 l 20 Reflections collected 8743 Independent reflections 3172 [R(int) = 0.0394] Completeness to theta = 27.50 97.7 %

PAGE 178

178 Absorption correction Integration Max. and min. transmission 0.8025 and 0.5065 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3172 / 0 / 154 Goodness-of-fit on F 2 1.025 Final R indices [I>2sigma(I)] R1 = 0.0243, wR2 = 0.0640 [2643] R indices (all data) R1 = 0.0321, wR2 = 0.0668 Largest diff. peak and hole 0.409 and -0.295 e. -3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants. Figure A-2. Numbering system for Br2-BEDOT-B(OC7H15)2 crystal structure. Table A-2. Crystal data and structure refinement for Br2-BEDOT-B(OC7H15)2. Identification code eg02 Empirical formula C32H40Br2O6S2 Formula weight 744.58 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 12.8685(8) = 90 b = 7.5486(4) = 99.761(2)

PAGE 179

179 c = 17.0305(10) = 90 Volume 1630.38(16) 3 Z 2 Density (calculated) 1.517 Mg/m 3 Absorption coefficient 2.656 mm -1 F(000) 764 Crystal size 0.22 x 0.20 x 0.04 mm 3 Theta range for data collection 1.84 to 27.99 Index ranges -16 h 15, -6 k 9, -18 l 22 Reflections collected 10309 Independent reflections 3767 [R(int) = 0.0400] Completeness to theta = 27.99 95.9 % Absorption correction Integration Max. and min. transmission 0.8933 and 0.5734 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3767 / 0 / 190 Goodness-of-fit on F 2 1.036 Final R indices [I>2sigma(I)] R1 = 0.0311, wR2 = 0.0821 [2897] R indices (all data) R1 = 0.0440, wR2 = 0.0854 Largest diff. peak and hole 0.596 and -0.512 e. -3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants. Figure A-3. Numbering system for Br2-BEDOT-B(OC12H25)2 crystal structure.

PAGE 180

180 Table A-3. Crystal data and structure refinement for Br2-BEDOT-B(OC12H25)2. Identification code eg03 Empirical formula C42H60Br2O6S2 Formula weight 884.84 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group C2/c Unit cell dimensions a = 30.0350(18) = 90 b = 7.7635(5) = 102.441(2) c = 18.8621(11) = 90 Volume 4294.9(5) 3 Z 4 Density (calculated) 1.368 Mg/m 3 Absorption coefficient 2.028 mm -1 F(000) 1848 Crystal size 0.51 x 0.13 x 0.05 mm 3 Theta range for data collection 2.21 to 27.49 Index ranges -38 h 38, -10 k 9, -24 l 19 Reflections collected 13547 Independent reflections 4871 [R(int) = 0.0470] Completeness to theta = 27.49 98.7 % Absorption correction Integration Max. and min. transmission 0.8974 and 0.5235 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4871 / 0 / 235 Goodness-of-fit on F 2 1.017 Final R indices [I>2sigma(I)] R1 = 0.0339, wR2 = 0.0864 [3598] R indices (all data) R1 = 0.0495, wR2 = 0.0899 Largest diff. peak and hole 0.780 and -0.677 e. -3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

PAGE 181

181 Figure A-4. Numbering system for BProDOT-Me2-B(OC12H25)2 crystal structure. Table A-4. Crystal data and stru cture refinement for BProDOT-Me2-B(OC12H25)2. Identification code eg04 Empirical formula C48H74O6S2 Formula weight 811.19 Temperature 173(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 5.6233(11) = 72.237(4) b = 11.932(2) = 86.101(4) c = 18.465(4) = 77.433(4) Volume 1151.6(4) 3 Z 1 Density (calculated) 1.170 Mg/m 3 Absorption coefficient 0.161 mm -1 F(000) 442 Crystal size 0.23 x 0.11 x 0.07 mm 3 Theta range for data collection 1.85 to 27.49 Index ranges -7 h 6, -9 k 13, -15 l 23 Reflections collected 4305 Independent reflections 3679 [R(int) = 0.0433] Completeness to theta = 27.49 69.3 % Absorption correction Integration Max. and min. transmission 0.9914 and 0.9739

PAGE 182

182 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3679 / 0 / 253 Goodness-of-fit on F 2 1.032 Final R indices [I>2sigma(I)] R1 = 0.0469, wR2 = 0.1158 [2881] R indices (all data) R1 = 0.0647, wR2 = 0.1290 Largest diff. peak and hole 0.204 and -0.255 e. -3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

PAGE 183

183 APPENDIX B GEL PERMEATION CHROMATO GRAMS OF POLYMERS Figure B-1. Gel permeation chromatogram of PBProDOT-Hex2-B(OC12H25)2.

PAGE 184

184 Figure B-1. Continued.

PAGE 185

185 Figure B-1. Continued.

PAGE 186

186 LIST OF REFERENCES 1. Chiang, C. K.; Fincher, C. R.; Park, Y. W.; Heeger, A. J.; Shirakawa, H.; Louis, E. J.; Gau, S. C.; MacDiarmid, A. G. Phys. Rev. Lett. 1977 39 1098-1101. 2. Heeger, A. J. Reviews of Modern Physics 2001 73 681-700. 3. Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay K.; Friend, R. H.; Burns, P. L.; Holmes, A. B.; Nature 1990 347 539-541. 4. Moliton, A.; Hiorns, R. C. Polym. Int. 2004 53 1397-1412. 5. Peierls R. E. Quantum Theory of Solids; Oxford University Press: London, 1955. 6. Kertesz, M.; Choi, C. H.; Yang, S. Chem. Rev. 2005 105 3448-3481. 7. Salzner, U. Curr. Org. Chem. 2004 8 569-590. 8. Menon, R.; Yoon, C. O.; Moses, D.; Heeger A. J. Metal-Insulator Transition in Doped Conducting Polymers. In Handbook of Conducting Polymers ; 2nd Ed.; Stockheim, T. A.; Elsenbaumer, R. L.; Re ynolds, J. R., Eds. Marcel Dekker: New York, 1998; Chapter 2. 9. Chance, R. R.; Brdas, J. L.; Silbey, R. Phys. Rev. B 1984 29 4491-4495. 10. Brdas, J. L.; Street, G. B. Acc. Chem. Res. 1985 18 309-315. 11. Roncali, J. Chem. Rev 1997 97 173-205. 12. Winder, C.; Matt, G.; Hummelen, J. C.; Janssen, R. A. J.; Sariciftci, N. S. ; Brabec, C. J. Thin Film Solids 2002 403-404 373-379. 13. van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Havinga, E. E.; Meijer, E. W. Mater. Sci. Eng. 2001 32 1-40. 14. Brdas, J. L. J. Chem. Phys. 1985 82 3808-3811. 15. Brdas, J. L.; Heeger, A. J.; Wudl, F. J. Chem. Phys. 1986 85 4673-4678. 16. Havinga, E. E.; Hoeve, W.; Wynberg, H. Polym. Bull. 1992 29 119-126. 17. Thomas, C. A.; Zong, K.; Abboud, K. A.; Steel, P. J.; Reynolds, J. R. J. Am. Chem. Soc. 2004 126 16440-16450. 18. Thompson, B. C.; Kim, Y.-G.; Mc Carley, T. D.; Reynolds, J. R. J. Am. Chem. Soc. 2006 128 12714-12725. 19. Brdas, J. L.; Street, G. B.; Thmans, B.; Andr, J. M.; J. Chem. Phys. 1985 83 1323-1329.

PAGE 187

187 20. Kim, J. Pure Appl. Chem. 2002 74 2031-2044. 21. Gustafsson-Carlberg, J. C.; Ingans, O. ; Andersson, M. R.; Booth, C.; Azens, A.; Granqvist, C. G. Electrochim. Acta 1995 40 2233-2235. 22. Ruiz, J. P.; Dharia, J. R.; Reynolds, J. R.; Buckley, L. J. Macromolecules 1992 25, 849-860. 23. Irvin, J. A. A. Low oxidatio n potential electroactive polymers. Ph.D. Thesis, University of Flor ida, Gainesville, FL, 1998. 24. Sotzing, G. A.; Reynolds, J. R.; Steel, P. J. Chem. Mater. 1996 8 882-889. 25. Sankaran, B.; Reynolds, J. R. Macromolecules 1997 30 2582-2588. 26. Tourillon, G. Polythiophene and its Derivatives. In Handbook of Conducting Polymers Skotheim, T. A., Ed.; Marcel Dekker: New York and Basel, 1986, volume 1, Chapter 9. 27. Pavlishchuk, V. V.; Addison, A. W. Inorg. Chim. Acta 2000 298 97-102. 28. Groenendaal, L. B.; Zotti, G.; Aubert, P. -H.; Waybright, S. M.; Reynolds, J. R. Adv. Mater. 2003 15 855-877. 29. McCullough, R. D.; Ewbank, P. C. Regi oregular, Head-to-Tail Coupled Poly(3alkylthiophene) and Its Derivatives. In Handbook of Conducting Polymers ; 2nd Ed. Stockheim, T. A.; Elsenbaumer, R. L. ; Reynolds, J. R., Eds.; Marcel Dekker: New York, 1998, Chapter 9. 30. Sentein, C.; Mouanda, B.; Rosilio, A.; Rosilio, C. Synth. Met. 1996 83 27-37. 31. Chen, T. A.; Rieke, R. D. Synth. Met. 1993 60 175-177. 32. (a) McCullough, R. D.; Lowe, R. D. J. Chem. Soc., Chem. Commun. 1992 70-72. (b) McCullough, R. D.; Lowe, R. D.; Jayaraman, M.; Anderson, D. L. J. Org. Chem. 1993 58 904-912. (c) Loewe, R. S.; Khersonsky, S. M.; McCullough, R. D. Adv. Mater. 1999 11 250-253. 33. Wu, C.-G.; Lin, Y.-C.; Wu, C.-E.; Huang, P.-H Polymer 2005 46 3748-3757. 34. Reeves, B. D.; Grenier, C. R. G.; Ar gun, A. A.; Cirpan, A.; McCarley, T. D.; Reynolds J. R. Macromolecules 2004 37 7559-7569. 35. (a) Sheina, E. E.; Liu, J.; Iovu, M. C.; Laird, D. W.; McCullough, R. D. Macromolecules 2004 37 3526-3528. (b) Iovu, M. C.; Sheina, E. E.; Gil, R. R.; McCullough, R. D. Macromolecules 2005 38 8649-8656. 36. Wang, F.; Wilson, M. S.; Rauh, R. D.; Schottland, P.; Thompson, B. C.; Reynolds, J. R. Macromolecules 2000 33, 2083-2091.

PAGE 188

188 37. Zhang, Z.-B.; Fujiki, M.; Tang, H.-Z.; Motonaga, M.; Torimitsu, K. Macromolecules 2002 35 1988-1990. 38. Yamamoto, T.; Wakabayashi, S.; Osakada, K. J. Organomet. Chem. 1992 428 223-237. 39. (a) Shiraishi, K.; Kanbara, T.; Yamamoto, T.; Groenendaal, L. B. Polymer 2001 42 7229-7232. (b) Asawapirom, U.; Scherf, U. Macromol. Rapid. Commun. 2001 22 746-749. 40. Yamamoto, T.; Ito, T.; Kubota, K. Chem. Lett. 1988 153-154. 41. Meng, H.; Perepichka, D. F.; Bendikov, M.; Wudl, F.; Pan, G. Z.; Yu, W.; Dong, W.; Brown, S. J. Am. Chem. Soc. 2003 125 15151-15162. 42. Boucard, V.; Ads, D.; Siove, A.; Romero, D.; Schaer, M.; Zuppiroli, L. Macromolecules 1999 32 4729-4731. 43. Thompson, B. C. Variable band ga p poly(3,4-alkylene dioxythiophene)-based polymers for photovoltaic and electrochr omic applications. Ph.D. Thesis, University of Florida, Gainesville, FL, 2005. 44. Cervini, R.; Holmes, A. B.; Moratti, S. C. ; Khler, A. ; Friend, R. H. Synth. Met. 1996 76 169-171. 45. Roncali, J. Advances in the Mol ecular Design of Functional Conjugated Polymers. In Handbook of Conducting Polymers ; 2nd Ed. Stockheim, T. A.; Elsenbaumer, R. L.; Reynolds, J. R., Eds.; Marcel Dekker: New York, 1998, Chapter 12. 46. Irvin, J. A.; Reynolds, J. R. Polymer 1998 39 2339-2347. 47. Groenendaal, L. B.; Jonas, F.; Freita g, D.; Pielartzik, H.; Reynolds, J. R. Adv. Mater. 2000 12 481-494. 48. Kirchmeyer, S.; Reuter, K. J. Mater. Chem. 2005 15 2077-2088. 49. Roncali, J.; Blanchard, P.; Frre, P. J. Mater. Chem. 2005 15 1589-1610. 50. Child, A. D.; Sankaran, B.; Larmat, F.; Reynolds, J. R. Macromolecules 1995 28 6571-6578. 51. Bhattacharya, A.; De, A. J. Macromol. Sci. Rev. Macromol. Chem. Phys. 1999 C39 17-56. 52. Kumar, A.; Welsh, D. M.; Morvant, M. C.; Piroux, F.; Abboud, K. A.; Reynolds, J. R. Chem. Mater. 1998 10 896-902.

PAGE 189

189 53. Welsh, D. M.; Kloeppner, L. J.; Madr igal, L.; Pinto, M. R.; Thompson, B. C.; Schanze, K. S.; Abboud, K. A.; Powell, D.; Reynolds, J. R. Macromolecules 2002 35 6517-6525. 54. Mishra, S. P.; Krishnamoor thy, K.; Sahoo, R.; Kumar, A. J. Polym. Sci.: Part A: Polym. Chem. 2005 43 419-428. 55. Mishra, S. P.; Sahoo, R.; Ambade, A. V.; Contractor, A. Q.; Kumar, A. J. Mater. Chem 2004 14 1896-1900. 56. Perepichka, I. F.; Roquet, S.; Leriche, P. ; Raimundo, J.-M. ; Frre, P. ; Roncali, J. Chem. Eur. J. 2006 12 2960-2966. 57. Grenier, C. R. G.; Pisula, W.; Jonche ray, T. J.; Mllen, K.; Reynolds, J. R. Angew. Chem. Int. Ed. In press. 58. Thompson, B. C.; Kim, Y.-G.; Reynolds, J. R. Macromolecules 2005 38 53595362. 59. Taranekar, P.; Abdulbaki, M.; Krishna moorti, R.; Phanichphant, S.; Waenkaew, P.; Patton, D.; Fulghum, T.; Advincula, R. Macromolecules 2006 39 3848-3854. 60. Yang, J. S.; Swager, T. M. J. Am. Chem. Soc. 1998 120 5321-5322. 61. Nguyen, T.-Q.; Schwartz, B. J. J. Chem. Phys. 2002 116 8198-8208. 62. Sonmez, G.; Chem. Commun. 2005 5251-5259. 63. Pei, Q.; Zuccarello, G.; Ahlskog, M.; Ingans, O. Polymer 1994 35 1347. 64. Thompson, B. C.; Schottland, P.; Zong, K.; Reynolds, J. R. Chem. Mater. 2000 12 1563-1571. 65. Schwendeman, I.; Hickman, R.; Snmez, G.; Schottland, P.; Zong, K.; Welsh, D. M.; Reynolds, J. R. Chem. Mater. 2002 14 3118-3122. 66. Snmez, G.; Shen, C. K. F.; Rubin, Y.; Wudl, F. Angew. Chem. Int. Ed. 2004 43 1498-1502. 67. Coakley, K. M.; McGehee, M. D. Chem. Mater. 2004 16 4533-4542. 68. Winder, C.; Sariciftci, N. S. J. Mater. Chem. 2004 14 1077-1086. 69. Mozer, A. J.; Sariciftci, N. S. C. R. Chimie 2006 9 568-577. 70. Brabec, C. J.; Zerza, G.; Cerullo, G.; De Silvestri, S.; Luzzati, S. ; Hummelen, J. C. ; Sariciftci, S. Chem. Phys. Lett. 2001 340 232-236.

PAGE 190

190 71. Padinger, F.; Rittberger, R. S.; Sariciftci, N. S. Adv. Funct. Mater. 2003 13 8588. 72. Montanari, I.; Nogueira, A. F.; Nelson, J. ; Durrant, J. R. ; Winder, C. ; Loi, M. A. ; Sariciftci, N. S. ; Brabec, C. Appl. Phys. Lett. 2002 81 3001-3003. 73. Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. Adv. Funct. Mater. 2005 15 1617-1622. 74. Reyes-Reyes, M.; Kim, K.; Carroll, D. L. Appl. Phys. Lett. 2005 87 083506. 75. Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. Nat. Mater. 2005 4 864-868. 76. Alem, S.; de Bettignies, R.; Nunzi, J.-M. Appl. Phys. Lett. 2004 84 2178-2180. 77. Padinger, F.; Fromherz, T. Appl. Phys. Lett. 2001 78 841-843. 78. de Leeuw, D. M.; Simenon, M. J. J.; Brown, A. R. ; Einerhand, R. E. F. Synth. Met. 1997 87 53-59. 79. Bard, A. J.; Faulkner, L. R. Elect rochemical Methods: Fundamentals and Applications, 2nd Ed.; Wiley: New York, 2001. 80. Meskers, S. C. J.; Hbner, J.; Oestreich, M.; Bssler, H. J. Phys. Chem. B 2001 105 9139-9149. 81. Kim, Y.; Cook, S.; Tuladhar, S. M.; Choulis, S. A.; Nelson, J.; Durrant, J. R.; Bradley, D. D. C.; Giles, M.; Mc Culloch, I.; Ha, C.-S.; Ree, M. Nature Materials 2006 5 197-203. 82. Hou, J. ; Tan, Z. ; Yan, Y. ; He, Y. ; Yang, C.; Li, Y. J. Am. Chem. Soc. 2006 128 4911-4916. 83. Thomas, C. A. Donor-acceptor methods for band gap reduction in conjugated polymers: the role of electr on rich donor heterocycles. P h.D. Thesis, University of Florida, Gainesville, FL, 2002. 84. Welsh, D. M. High contrast and threecolor electrochromic polymers. Ph.D. Thesis, University of Flor ida, Gainesville, FL, 2001. 85. Gaupp, C. L. Structure-property re lationships of electrochromic 3,4alkylenedioxyheterocycle-based polyme rs and copolymers. Ph.D. Thesis, University of Florida, Gainesville, FL, 2002. 86. Gritzner, G.; Kuta, G. J. Pure Appl. Chem. 1984 56 461-466. 87. Brett, C. M. A.; Brett, A. M. O. El ectrochemistry, Principles, Methods, and Applications; Oxford University: Oxford, 1993.

PAGE 191

191 88. Rieger, P. H. Electrochemistry; Pren tice-Hall: Englewood Cliffs, New Jersey, 1987. 89. Lvesque, I. ; Leclerc, M. Chem. Mater. 1996 8 2843-2849. 90. Garreau, S. ; Leclerc, M. ; Errien, N. ; Louarn, G. Macromolecules 2003 36 692697. 91. Bouachrine, M. ; Lre-Porte, J.-P. ; Moreau, J. J. E. ; Serein-Spirau, F. ; Torreilles, C. J. Mater. Chem. 2000 2 263-268. 92. Politis, J. K. ; Somoza, F. B. ; Kampf, J. W.; Curtis, M. D.; Ronda, L. G. ; Martin, D. C. Chem. Mater. 1999 11 2274-2284. 93. Dufresne, G.; Bouchard, J.; Bellette, M.; Durocher, G.; Leclerc, M. Macromolecules 2000 33 8252-8257. 94. Bernier, S.; Garreau, S.; Bra-Ab rem, M.; Gravel, C.; Leclerc, M. J. Am. Chem. Soc. 2002 124 12463-12468. 95. Greenham, N. C.; Samuel, I. D. W.; Hayes, G. R.; Phillips, R. T.; Kessener, Y. A. R. R.; Moratti, S. C.; Holmes A. B.; Friend R. H. Chem. Phys. Lett. 1995 241 89-96. 96. Plsson, L.-O.; Monkman, A. P. Adv. Mater. 2002 14 757-758. 97. Williams, A. T. R.; Winfield, S. A.; Miller, J. N. Analyst 1983 108 1067-1071. 98. Eaton, D. F. Pure & Appl. Chem. 1988 60 1107-1114. 99. Du, H.; Fuh, R. A.; Li, J.; Corkan, A.; Lindsey, J. S. Photochem. Photobiol. 1998 68 141-142. 100. Reynolds, G. A.; Drexhage, K. H. Optics Commun. 1975 13 222-225. 101. Magde, D.; Brannon, J. H.; Cremers, T. L.; Olmsted, J. J. Phys. Chem. 1979 83, 696-699. 102. Thompson, B. C.; Schottland, P.; Snmez, G.; Reynolds, J. R. Synth. Met. 2001 119 333-334. 103. Tada, K.; Onoda, M.; Yoshino, K. J. Phys. D: Appl. Phys. 1997 30 2063-2068. 104. Pei, J.; Yu, W.-L.; Ni, J.; Lai, Y.-H.; Huang, W.; Heeger, A. J. Macromolecules 2001 34 7241-7248. 105. Irvin, J. A.; Piroux, F.; Morvant, M. C.; Robertshaw, V. L.; Angerhofer, A.; Reynolds, J. R. Synth. Met. 1999 102 965-966.

PAGE 192

192 106. Bao, Z.; Chan, W.; Yu, L. Chem. Mater. 1993 5 2-3. 107. Pelter A.; Jenkins I.; Jones D. E. Tetrahedron 1997 53 10357-10400. 108. Bouachrine, M.; Bouzakraoui, S.; Hamidi M.; Ayachi, S.; Alimi K.; Lre-Porte J.-P.; Moreau J. Syn. Met. 2004 145 237-243. 109. Mushrush, M.; Facchetti A.; Lefenfeld, M.; Katz H. E.; Marks T. J. J. Am. Chem. Soc. 2003 125 9414-9423. 110. Xu M.-H.; Zhang H.-C.; Pu L. Macromolecules 2003 36 2689-2694. 111. Reynolds, J. R.; Ruiz, J. P.; Child, A. D.; Marynick, D. S.; Nayak, K. Macromolecules 1991 24 678-687. 112. Brdas, J. L.; Calbert, J. P.; da Silva Filho, D. A.; Cornil, J. Proc. Natl. Acad. Sci. 2002 99 5804-5809. 113. Beljonne, D.; Cornil, J.; Sirringhaus, H.; Brown, P. J.; Shkunov, M.; Friend, R. H.; Brdas, J.-L. Adv. Funct. Mater. 2001 11 229-234. 114. Mitchell. R. H.; Lai, Y.-H.; Williams, R. V. J. Org. Chem. 1979 44 4733-4735. 115. Cao, J.; Kampf, J. W.; Curtis, M. D. Chem. Mater. 2003 15 404-411. 116. Ertas, E.; Ozturk, T. Tetrahedron Lett. 2004 45 3405-3407. 117. DuBois, C. J. Donor-acceptor methods for band gap control in conjugated polymers. Ph.D. Thesis, University of Florida, Gainesville, FL, 2003. 118. Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2001 123 2719-2724. 119. Thompson, B. C.; Schottland, P.; Sonmez, G.; Reynolds, J. R. Synth. Met. 2001 119, 333-334. 120. Leclerc, M.; Dufresne, G.; Blondin, P.; B ouchard, J ; Bellette, M.; Durocher, G. Synth. Met. 2001 119 45-48. 121. (a) Perzon, E.; Wang, X.; Admassie, S. ; Ingans, O.; Andersson, M. R. Polymer 2006 47 4261-4268. (b) Lee, S. K.; Cho, N. S.; Kwak, J. H.; Lim, K. S.; Shim, H.-K.; Hwang, D.-H.; Brabec, C. J. Thin Solid Films 2006 511 157-162. (c) Wienk, M. M.; Struijk, M. P.; Janssen, R. A. J. Chem. Phys. Lett. 2006 422 488491. (d) Xia, Y.; Luo, J.; Deng, X.; Li, X.; Li, D.; Zhu, X.; Yang, W.; Cao, Y. Macromol. Chem. Phys. 2006 207 511-520. (e) Yang, R.; Tian, R.; Yan, J.; Zhang, Y.; Yang, J.; Hou, Q.; Ya ng, W.; Zhang, C.; Cao, Y. Macromolecules 2005 38 244-253. 122. Pratt, J. R.; Pinkerton, F. H.; Thames, S. F. J. Organomet. Chem. 1972 38 29-36.

PAGE 193

193 123. Gronowitz, S. Acta Chem. Scand. 1959 13 1045-1046. 124. Goldoni, F.; Langeveld-Voss, B. M. W.; Meijer, E. W. Synth. Comm. 1998 28 2237-2244. 125. Overberger, C. G.; Lal, J. J. Am. Chem. Soc. 1951 73 2956-2957. 126. Welsh, D. M.; Kumar, A.; Meije r, E. W.; Reynolds, J. R. Adv. Mater. 1999 11 1379-1382. 127. Yang, R.; Tian, R.; Yan, J.; Zhang, Y.; Yang, J.; Hou, Q.; Yang, W.; Zhang, C.; Cao, Y. Macromolecules 2005 38, 244-253. 128. Zhang, F.; Perzon, E.; Wang, X.; Mammo, W.; Andersson, M. R.; Ingans, O. Adv. Funct. Mater. 2005 15 745-750. 129. Xia, Y.; Luo, J.; Deng, X.; Li, X. ; Li, D.; Zhu, X.; Yang, W.; Cao, Y. Macromol. Chem. Phys. 2006 207 511-520. 130. Wienk, M. M.; Turbiez, M. G. R.; Struij k, M. P.; Fonrodona, M.; Janssen, R. A. J. Appl. Phys. Lett. 2006 88 153511. 131. Arbizzani, C.; Catellani, M.; Mastragostino, M.; Mingazzini, C. Electrochim. Acta 1995 40 1871-1876. 132. Arbizzani, C.; Cerroni, M. G.; Mastragostino, M. Sol. Energy Mater. Sol. Cells 1999 56 205-211. 133. Du Bois, C. J. Jr.; Larmat, F. ; Irvin, D. J.; Re ynolds, J. R. Synth. Met. 2001 119 321-322. 134. Salzner, U. Synth. Met. 2001 119 215-216. 135. Huang, H.; He, Q.; Lin, H.; Bai, F.; Cao, Y. Thin Solid Films, 2005 477 7-13. 136. Cacialli, F.; Wilson, J. S.; Michels, J. J.; Daniel, C.; Silva, C.; Friend, R. H.; Severin, N.; Samori, P.; Rabe, J. P.; O’C onnell, M. J.; Taylor, P. N.; Anderson, H. L. Nature Materials 2002 1 160–164. 137. Li, X.-C.; Liu, Y.; Liu, M. S. ; Jen, A. K.-Y. Chem. Mater. 1999 11 1568-1575. 138. Neef, C. J.; Ferraris, J. P. Macromolecules 2000 33 2311-2314. 139. Roex, H.; Adriaensens, P.; Vanderzande, D.; Gelan, J. Macromolecules 2003 36 5613-5622. 140. Kricheldorf, H. R.; Schwartz, G. Macromol. Rapid Commun. 2003 24 359-381.

PAGE 194

194 141. Kricheldorf, H. R.; Fritsch, D.; Vakhtangishvili, L.; Schwartz, G. Macromol. Chem. Phys. 2005 206 2239-2247. 142. Montaudo, G.; Montaudo, M. S.; Puglisi, C.; Samperi, F. Rapid Commun. Mass Spectrom. 1995 9 453-460. 143. Axelsson, J.; Scrivener, E.; Haddleton, D. M.; Derrick, P. J. Macromolecules 1996 29 8875-8882. 144. Schriemer, D. C.; Li, L. Anal. Chem. 1997 69 4169-4175. 145. Cho, N. S.; Hwang, D. H.; Shim, H. K.; Kim, J. C., Int. Pat. WO 03/016430A1. 146. Saito, H.; Ukai, S.; Iwatsuki, S.; Itoh, T.; Kubo, M. Macromolecules 1995 28 8363-8367. 147. Wagner, P.; Aubert, P. H.; Lutsen, L.; Vanderzande, D. Electrochem. Commun. 2002 4 912-916. 148. Pinto, M. R.; Schanze, K. S. Synthesis 2002 9 1293-1309. 149. Baur, J. W.; Kim, S.; Balanda, P. B.; Reynolds, J. R.; Rubner, M. F. Adv. Mater. 1998 10 1452-1455. 150. Decher, G.; Hong, J. D.; Schmitt, J.; Thin Solid Films 1992 210/211 831-835. 151. Decher, G. Science 1997 277 1232-1237. 152. Kim, S.; Jackiw, J.; Robinson, E.; Schanze, K. S.; Reynolds, J. R.; Baur, J.; Rubner, M. F.; Boils, D. Macromolecules 1998 31 964-974. 153. Ma, W.; Iyer, P., K.; Gong, X.; Liu, B.; Moses, D.; Bazan, G. C.; Heeger, A. J. Adv. Mater. 2005 17 274-277. 154. Shi, W.; Fan, S.; Huang, F.; Yang, W.; Liu, R.; Cao, Y. J. Mater. Chem. 2006 16 2387-2394. 155. Brown, T. M.; Kim, J. S.; Friend, R. H. ; Cacialli, F.; Daik, R.; Feast, W. J. Appl. Phys. Lett. 1999 75 1679-1681. 156. Mwaura, J. K.; Pinto, M. R.; Witker, D.; Ananthakrishnan, N.; Schanze, K. S.; Reynolds, J. R. Langmuir 2005 21 10119-10126. 157. Wang, D.; Gong, X.; Heeger, P. S.; Rinins land, F.; Bazan, G. C.; Heeger, A. J. Proc. Natl. Acad. Sci. 2002 99 49-53. 158. Pinto, M. R.; Schanze, K. S. Proc. Nat. Acad. Sci. 2004 101 7505-7510.

PAGE 195

195 159. Achyuthan, K. E.; Bergstedt, T. S.; Ch en, L.; Jones, R. M.; Kumaraswamy, S.; Kushon, S. A.; Ley, K. D.; Lu, L.; McBranch, D.; Mukundan, H.; Rininsland, F.; Shi, X.; Xia, W.; Whitten, D. G. J. Mater. Chem. 2005 15 2648-2656. 160. Herland, A.; Nilsson, K. P. R.; Olsson, J. D. M.; Hammarstrm, P.; Konradsson, P.; Ingans, O. J. Am. Chem. Soc. 2005 127 2317-2323. 161. Taylor, P. N.; O’Connell, M. J.; McNeil l, L. A.; Hall, M. J.; Aplin, R. T.; Anderson, H. L. Angew. Chem. Int. Ed. 2000 39 3456-3460. 162. Peng, Z.; Xu, B.; Zhang, J.; Pan, Y. Chem. Commun. 1999 1855-1856. 163. Harrison, B. S.; Ramey, M. B.; Reynolds, J. R.; Schanze, K. S. J. Am. Chem. Soc. 2000 122 8561. 164. Zhao, X.; Pinto, M. R.; Hardison, L. M.; Mwaura, J.; Mller, J.; Jiang, H.; Witker, D.; Kleiman, V. D.; Reynolds, J. R.; Schanze, K. S. Macromolecules 2006 39 6355-6366. 165. Reeves, B. D. Processable disubstitut ed poly(propylenedioxythiophenes). Ph.D. Thesis, University of Flor ida, Gainesville, FL, 2005. 166. Welsh, D. M.; Kloeppner, L. J.; Madr igal, L.; Pinto, M. R.; Thompson, B. C.; Schanze, K. S.; Abboud, K. A.; Powell, D.; Reynolds, J. R. Macromolecules 2002 35 6517-6525. 167. Ramey, M. B.; Hiller, J.’A.; Rubner, M. F.; Tan, C.; Schanze, K. S.; Reynolds, J. R. Macromolecules 2005 38 234-243. 168. Huang, F.; Hou, L.; Shen, H.; Yang, R.; Hou, Q.; Cao, Y. J. Polym. Sci. Part A: Polym. Chem. 2006 44 2521-2532. 169. Liu, B.; Yu, W.-L.; Lai, Y.-H. ; Huang, W. Chem. Commun. 2000 551-552. 170. McCarley, T. D.; Noble, C. O. IV; Dubois, C. J. Jr.; McCarley, R. L. Macromolecules 2001 34 7999-8004. 171. Magde, D.; Brannon, J. H.; Cremers, T. L.; Olmsted, J. J. Phys. Chem. 1979 83 696-699. 172. Gaupp, C. L.; Zong, K.; Schottland, P. ; Thompson, B. C.; Thomas, C. A.; Reynolds, J. R. Macromolecules 2000 33 1132-1133. 173. Wanli, M.; Iyer, P. K.; Gong, X.; Liu, B.; Moses, D.; Bazan, G.; Heeger, A. J. Adv. Mater. 2005 17 274-277. 174. Tan, C.; Pinto, M. R.; Schanze, K. S. Chem. Commun. 2002 446-447.

PAGE 196

196 BIOGRAPHICAL SKETCH Emilie M. Galand was born in Lille, France, in 1980. After high school she pursued twoyear intensive undergraduate studies in chemistr y, physics, and maths at the Graduate School of Chemistry of Lille (ENSCL), France, giving access to Elite French Graduate Schools of Chemistry. At the end of that program, she joined in August of 2000 the Graduate School of Chemistry and Physics of Bordeaux (ENSCPB), Fr ance, to complete her undergraduate studies. She accomplished two years of that 3-year program in Bordeaux, and then for the last year she decided to study at the University of Florida, USA, in order to ga in international experience. At the end of that year (June 2003) she obtained her master’s di ploma from ENSCPB (Engineer degree in chemistry and physics). She stayed in Florida for anot her three and a half years to pursue a Ph.D. in the area of el ectroactive polymers under the supervisio n of Prof. John R. Reynolds.


Permanent Link: http://ufdc.ufl.edu/UFE0017284/00001

Material Information

Title: Processable Variable Band Gap Conjugated Polymers for Optoelectronic Devices
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0017284:00001

Permanent Link: http://ufdc.ufl.edu/UFE0017284/00001

Material Information

Title: Processable Variable Band Gap Conjugated Polymers for Optoelectronic Devices
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0017284:00001


This item has the following downloads:


Table of Contents
    Title Page
        Page 1
        Page 2
    Acknowledgement
        Page 3
        Page 4
    Table of Contents
        Page 5
        Page 6
        Page 7
    List of Tables
        Page 8
    List of Figures
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Abstract
        Page 14
        Page 15
    Introduction
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
    Experimental
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
    Wide band gap bis-heterocycle-phenylene polymers
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
    Narrow band-gap cyanovinylene polymers
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
        Page 148
        Page 149
    Polypropylenedioxythiophene polyelectrolytes
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
        Page 155
        Page 156
        Page 157
        Page 158
        Page 159
        Page 160
        Page 161
        Page 162
        Page 163
        Page 164
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
        Page 170
        Page 171
        Page 172
        Page 173
    Summary
        Page 174
        Page 175
        Page 176
    Appendix A: Crystallographic information for compounds
        Page 177
        Page 178
        Page 179
        Page 180
        Page 181
        Page 182
    Appendix B: Gel permeation chromatograms of polymers
        Page 183
        Page 184
        Page 185
    References
        Page 186
        Page 187
        Page 188
        Page 189
        Page 190
        Page 191
        Page 192
        Page 193
        Page 194
        Page 195
    Biographical sketch
        Page 196
Full Text





PROCESSABLE VARIABLE BAND GAP CONJUGATED POLYMERS FOR
OPTOELECTRONIC DEVICES


















By

EMILIE M. GALAND


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2006

































Copyright 2006

by

Emilie M. Galand









ACKNOWLEDGMENTS

Going away from home for such a long time to pursue my Ph.D. studies was the most

difficult decision I ever had to make, and I would never have been able to go through this

adventure without my parents' support. I was also lucky to share every step of this experience

with Thomas Joncheray, who carried out his Ph.D. in polymer chemistry at the same time.

Of course this learning experience would not have been so rich without the guidance of my

research advisor Prof. John R. Reynolds. He handled the research group as a businessman,

educating us very well for our future industrial careers. I am very grateful for the time he put in

reviewing my publications, oral presentations, career launch, and dissertation, and also for his

consideration for my well being.

I would like also to acknowledge all the people I collaborated with, and who helped enrich

the work presented in this dissertation: Dr. Khalil Abboud for solving X-ray crystal structures,

Dr. Tracy McCarley for performing MALDI analyses, Dr. Jeremiah Mwaura for his work on

light-emitting diodes, Dr. Young-Gi Kim for his work on solar cells, Dr. Avni Argun for his

studies on charge transport, and Prof. Yang Yang and Dr. Vishal Shrotriya from UCLA for

performing comparative photovoltaic studies. Thanks go also to the administrative staff, Sara

Klossner, Tasha Simmons, Lorraine Williams and Gena Borrero, and to the members of my

committee: Prof. Kenneth B. Wagener, Prof. Randolph S. Duran, Prof. Paul H. Holloway and

Prof. Ronald K. Castellano.

A special thank you goes to my labmates, Dr. Barry Thompson, Dr. John Sworen, Dr.

Florence Courchay, James Leonard, Dr. Christian Nielsen, Trish Hooper, Kate Opper, Nihan

Cetinbas, and Pingjie Shi for making our lab such a nice place to work. I specifically want to

express my gratitude to Barry and John who taught me a lot about laboratory techniques. John

made me crazy with his music but I forgive him because his dancing moves always cheered me









up! Thanks go also to my hood neighbors Flo and James for being my coffee break companions

and for making me feel less lonely in front of my columns.

A lot of people spent a couple of hours of their precious time to train me on certain

techniques. For that I would like to show my appreciation to Garett Oakley and Genay Jones for

helping me with the GPC measurements, Erik Berda and Piotr Matloka for training me on the

differential scanning calorimetry and thermo gravimetric analysis instruments, James Leonard

for familiarizing me with the unfriendly X-ray software, and Christophe Grenier for helping me

with the stubborn computers and printers. The Butler laboratory was the best environment for

living a truly "team experience." I want to thank all the members for their contribution to

scientific discussions, for being so helpful, and for making this experience so enjoyable.

Thanks go also to the French mafia, Roxane Fabre, Thomas Joncheray, Florence

Courchay, Sophie Bernard, Rachid Matmour, Christophe Grenier, Benoit Lauly, Sophie Klein,

for their friendship and the get-togethers, which always helped me feel close to home.

Thanks go finally to my Florida tennis team who helped me stay in shape and healthy

during that tough time!









TABLE OF CONTENTS



A C K N O W L E D G M E N T S ...............................................................................................................3

L IST O F T A B L E S ......................................................................................................... ........ .. 8

LIST OF FIGURES ................................. .................... .9

A B S T R A C T .......................................................................................................... ..................... 14

CHAPTER

1 INTRODUCTION .................................. .. ........... ..................................... 16

1.1 C onjugated Polym ers ............. .. .................. .................. .. ......................... ............... 16
1 .1 .1 B rief H isto ry ................................................................................. .. ........................ 16
1.1.2 Conjugated Polym ers Electronic Properties...................................... ............... 17
1.2 B and G ap E ngineering............................... ............................................................ 20
1.3 Polymerization of Thiophene Based Molecules ............... ...................................24
1.3.1 O xidative P olym erizations ....................................... ...................... ................ 24
1.3.2 M etal M ediated Polym erizations....................................................... ................ 26
1.3.3 Solid State P olym erization ....................................... ...................... ................ 27
1.3.4 K noevenagel P olym erization ............................................................................... 29
1.4 3,4-Alkylenedioxythiophene Based Polymers, from Thiophene to EDOT to ProDOT ...30
1.5 A p p location s .................................................................................................... ........ .. 3 3
1.6 S tu dy O v erv iew ................................................................................................................ 3 6

2 EXPERIMENTAL ............................... .. ........... ............................... 39

2.1 G general Synthetic M ethods.. ..................................................................... ................ 39
2.2 Electrochem ical M ethods ..................... ................................................................. 41
2 .2 .1 In tro d u ctio n ............................................................................................................ 4 1
2 .2 .2 E lectrochem ical Set-U p .......................................... ........................ ................ 4 1
2 .2 .3 C V /D P V ................................................................................................................ 4 2
2.3 O ptical and Spectroscopic M ethods ............................................................ ................ 45
2.3.1 Absorption Spectra and M olar Absorptivities................................... ................ 45
2.3.2 Solvatochromism/Thermochromism .................... .......... ................46
2.3.3 Photoluminescence Spectra and Fluorescence Quantum Efficiencies ................47
2 .3.4 Spectroelectrochem istry ......................................... ........................ ................ 49
2 .3 .5 C o lo rim etry ............................................................................................................. 4 9

3 WIDE BAND GAP BIS-HETEROCYCLE-PHENYLENE POLYMERS......................... 52

3 .1 In tro d u ctio n ................. .... ... ...................................................................................... 5 2
3.2 Monomer Syntheses and Characterizations....................................................54
3.2.1 B is-thiophene-dialkoxybenzenes....................................................... ................ 55









3.2.2 B is-ED O T-dialkoxybenzenes............................................................ ................ 57
3.2.3 B is-ProD O T-dialkoxybenzenes......................................................... ................ 60
3.3 Polymer Syntheses and Characterizations...................................................................62
3.3.1 Polymerization Attempts via GriM ...................................................62
3.3.2 Polymerization via Yamamoto Coupling ............... ....................................67
3.3.2.1 Poly(bis-thiophene-dialkoxybenzene)s ............. .....................................67
3.3.2.2 Poly(bis-alkylenedioxythiophene-dialkoxybenzene)s...............................70
3.3.3 Solid State Polymerization Attempts....................................................71
3.3.4 E lectropolym erization ................................................. ...................... ................ 73
3.3.5 Oxidative Polymerization via Ferric Chloride ..................................................74
3.4 Polymer Electrochemistry and Spectroelectrochemistry.............................................78
3 .4 .1 P B T -B (O R )2 ...........................................................................................................7 8
3.4.2 PB ProD O T-R 2-B (O C 12H 25)2 ............................................................. ............... 80
3.5 C olorim etry .......................................................................... ...... ..... ..................... 86
3 .5 .1 P B T -B (O R )2 ...........................................................................................................8 6
3.5.2 PB ProD O T -R 2-B (O C 12H 25)2 .............. ......................................... ..................... 87
3.6 Solvatochromism, Thermochromism, and Ionochromism .................... ..................... 88
3 .7 A p p location to D ev ices ..................................................................................................... 9 0
3.7.1 P hotovoltaic D evices ..................................................................... ................ 90
3 .7 .1.1 P B T -B (O R )2 ............................................................................. .. .. ...... ........... 90
3.7.1.2 PBProD O T-H ex2-B (O C 12H 25)2 ............................................... ................ 92
3 .7 .2 L E D s ....................................................................................................................... 9 3
3.8 C conclusions and Perspective ................................................................... ................ 95
3 .9 E x p e rim e n ta l .....................................................................................................................9 7

4 NARROW BAND-GAP CYANOVINYLENE POLYMERS ..... ............................... 111

4 .1 In tro d u ctio n ...................................................... ..............................................................1 1 1
4.2 Monomer and Polymer Synthesis and Characterization...................... ...................114
4.3 O ordering Properties ............................................................ .. .... .... .. ................ 122
4.4 Polymer Electrochemistry and Spectroelectrochemistry..................... ..................1...26
4.5 C olorim etry .......................................................................... ....................... ....... 132
4 .6 A application in D evices ............................................ .. ........................... ................ 133
4.6.1 Polymer Light-Emitting Diodes ....... ......... ........ ......................133
4.6.2 Photovoltaic D evices ................... ............................................................. 134
4.7 Sum m ary and Perspective.. .................................................................. ............... 137
4 .8 E x p e rim e n ta l...................................................................................................................1 3 8

5 POLYPROPYLENEDIOXYTHIOPHENE POLYELECTROLYTES..............................150

5 .1 In tro d u ctio n ..................................................................................................................... 1 5 0
5.2 Monomer Synthesis and Characterization...... ........................... 152
5.3 Polymer Synthesis and Characterization ................................................................153
5.4 Polymer Spectroelectrochemistry and Electrochemistry..................... .................. 161
5.6 Quaternization of the Amino-substituted PProDOTs...... .................... ..................1...65
5.7 Sum m ary and Perspective.. .................................................................. ............... 168
5 .8 E x p e rim e n ta l ...................................................................................................................1 7 0


6









6 S U M M A R Y .......................................................................................................................... 1 7 4

APPENDIX

A CRYSTALLOGRAPHIC INFORMATION FOR COMPOUNDS ............................... 177

B GEL PERMEATION CHROMATOGRAMS OF POLYMERS ............... ...................183

L IST O F R E F E R E N C E S ....................................................... ................................................ 186

B IO G R A PH IC A L SK E T C H .................................................... ............................................. 196












































7









LIST OF TABLES


Table page

3-1 GPC estimated molecular weights of the PBT-B(OR)2 polymers (polystyrene
standards, TH F as m obile phase, 400C)........................................................ ................ 68

3-2 Electrochemical results for BProDOT-R2-B(OC12H25)2 monomers and polymers. ..........82

3-3 Summarized photovoltaic characteristics of PBT-B(OR)2/PCBM based solar cells.........92

4-1 GPC estimated molecular weights of the ProDOT:cyanovinylene polymers
(polystyrene standards, THF as mobile phase) and yields of the Knoevenagel
p o ly m eriz atio n s............................................................................................................... 1 16

4-2 Summary of thin-film polymer electrochemistry, and HOMO and LUMO energies of
the ProDOT:cyanovinylene polymers derived from the electrochemical results ..........128

4-3 Colorimetric results for the neutral and oxidized ProDOT:cyanovinylene polymers. .... 132

4-4 Summarized characteristics of ProDOT:cyanovinylene polymer/PCBM based solar
c e ll s ...................................................................................................... ........ . ....... 1 3 7

5-1 Solubility of ionic amino-substituted PProDOTs in various solvents at room
te m p e ra tu re .................................................................................................................. ... 1 6 6

A-i Crystal data and structure refinement for Br2-BT-B(OC7H5)2. .................................177

A-2 Crystal data and structure refinement for Br2-BEDOT-B(OC7Hi5)2............................ 178

A-3 Crystal data and structure refinement for Br2-BEDOT-B(OC12H25)2........................... 180

A-4 Crystal data and structure refinement for BProDOT-Me2-B(OC12H25)2 ...................... 181









LIST OF FIGURES


Figure page

1-1 Energetic representations of polyacetylene and poly(para-phenylene).......................... 18

1-2 Positively charged defects on poly(para-phenylene).. ................................. ................ 19

1-3 Poly(para-phenylene) and evolution of energy levels with p-doping .............................. 19

1-4 Illustration of the formation of two charged solitons on a chain of trans-
p o ly a c e ty le n e ................................................................................................................. ... 2 0

1-5 Aromatic and quinoid states of polyisonaphthalene. .................................... ................ 22

1-6 Illustration of the donor (D) acceptor (A) concept .................................... ................ 22

1-7 Polymer band structures and optical band gaps of the dioxythiophene-cyanovinylene
p o ly m e r fa m ily ................................................................................................................. .. 2 3

1-8 GriM polym erization of disubstituted PProDOTs .......................................... ............... 26

1-9 Mechanism of aryl (Ar) polymerization via Yamamoto coupling and of the polymer
chain degradation/termination occurring during the polymerization...............................28

1-10 Mechanism of the solid state polymerization of DBEDOT..........................................28

1-11 Illustration of the Knoevenagel condensation steps...................................... ................ 29

1-12 Effect of increasing donor strength in a donor-acceptor-donor configuration. ...............31

1-13 Synthesis of poly(3,4-propylenedioxythiophene-dihexyl)-cyano-p-
phenylenevinylene .............................. ............ ........................... 33

2-1 Charge transport by hopping in polymer adsorbed to the electrode ..............................43

2-2 D ifferential pulse w aveform ................................................................... ................ 44

2-3 Example of the procedure used to maintain a constant polymer concentration in
flasks containing varying amounts of good and poor solvents................ ................48

2-4 CIE 1931 xy chrom aticity diagram ...................................... ...................... ................ 51

3-1 Targeted thienylene-phenylene polym ers .................................................... ................ 55

3-2 Bis-thiophene-dialkoxybenzene monomer synthesis.................................... ................ 56

3-3 Single crystals X-ray analysis of Br2-BT-B(OC7H13)2. ................................ ................ 57









3-4 Bis-EDOT-dialkoxybenzene monomer synthesis......................................... ................ 59

3-5 Single crystals X-ray analysis of Br2-BEDOT-B(OC7H13)2 ........................................62

3-6 Single crystals X-ray analysis of Br2-BEDOT-B(OC12H25)2.......................................63

3-7 Synthesis of methyl- and hexyl-substituted ProDOTs..................................................64

3-8 Synthesis of BProDOT-R2-dialkoxyphenylene and Br2-BProDOT-R2-
dialkoxyphenylene m onom ers ........................................................................ ................ 64

3-9 Single crystals X-ray analysis of BProDOT-Me2-B(OC12H25)2 ....................... 65

3 -10 S tru ctu re o f L P E B ................................................................... ....... ........................... 6 5

3-11 GriM route for the polymerization of the dibromo-thienylene-phenylene monomers ......66

3-12 Polymerization of Br2-BT-B(OR)2 monomers via Yamamoto coupling........................67

3-13 M ALD I-M S of B T-B(OR)2 polym ers .......................................................... ................ 69

3-14 Solution UV-Vis absorbance of Br2-BT-B(OR)2 monomers, and PBT-B(OR)2
p oly m ers in tolu en e..................................................... ............................................... 6 9

3-15 DSC thermograms (second scans) of PBT-B(OR)2 polymers...................................71

3-16 Thermogravimetric analysis of the PBT-B(OR)2 polymers..........................................72

3-17 Attempt in the solid state polymerization of Br2-BEDOT-B(OC7H15)2 .......................... 73

3-18 Crystal packing of Br2-BEDOT-B(OC7H15)2 illustrating the intermolecular distances
between bromine atoms ........................................ ......... ....................... 73

3-19 Repeated potential scanning electropolymerization of BProDOT-R2-B(OC12H25)2
m onom ers ............................................................................... ....... .... ..................... 75

3 -2 0 1H -N M R sp e ctra ................................................................................................................. 7 7

3-21 Absorption spectra for molecular weight fractions of PBProDOT-Hex2-B(OC12H25)2.....78

3-22 Thermogravimetric analysis of the PBProDOT-Hex2-B(OC12H25)2 in a nitrogen
atm o sph ere ...................................................................................................... ....... .. 7 8

3-23 PB T-B (O R )2 cyclic voltam m etry........................................ ....................... ................ 79

3-24 Spectroelectrochemical analysis of PBT-B(OC7H15)2 spray-cast onto ITO coated
g lass ........................................................................................................... 82









3-25 Spectroelectrochemical analysis of PBT-B(OC12H25)2 spray-cast onto ITO coated
glass .......................................................................................................... 83

3-26 PBProDOT-R2-B(OC12H25)2 cyclic voltammograms. ..................................................83

3-27 Cyclic voltammograms of PBProDOT-Hex2-B(OC12H25)2 as function of scan rate .........84

3-28 Spectroelectrochemical analysis of PBProDOT-Hex2-B(OC12H25)2 spray-cast onto
IT O co ated g la ss. .............................................................................................................. 8 5

3-29 Spectroelectrochemical analysis of PBProDOT-Me2-B(OC12H25)2 electropolymerized
on ITO coated glass ............................. ............ ........................... 86

3-30 CIE 1931 xy chromaticity diagrams of PBT-B(OR)2 polymers ............... ..................... 87

3-31 CIE 1931 xy chromaticity diagram of a thin-film of PBProDOT-Hex2-B(OC12H25)2.......89

3-32 Thermochromic changes observed for a 0.1 M TBAP in CH2Cl2/ACN solution of the
BProD O T-M e2-B (O C 12H 25)2 m onom ers ...................................................... ................ 89

3-33 UV-vis absorption spectra of PBProDOT-Hex2-B(OC12H25)2 in toluene/methanol
m ix tu res........................................................................................................... ....... .. 9 1

3-34 Photovoltaic results of solar cells made of a 1/4 blend (w/w) of PBT-B(OR)2/PCBM.....92

3-35 Current voltage characteristic of a solar cell made of a 1/4 blend (w/w) of
PBProDOT-Hex2-B(OC12H25)2/PCBM under AM1.5 conditions (100 mW cm-2). ..........93

3-36 Photoluminescence emission spectrum of PBProDOT-Hex2-B(OC12H25)2 in toluene
solution and in thin-film (bold line) superimposed with electroluminescence
spectrum of an EL device with the following configuration: ITO/PEDOT-
PSS/PBProD OT-H ex2-B(OC12H25)2/Ca/Al .................................................. ................ 94

3-37 LED properties of an ITO/PEDOT-PSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al
d ev ic e .............................................................................................................. ........ .. 9 5

4-1 Family of ProDOT:cyanovinylene polymers synthesized via the Knoevenagel
m eth o d o lo g y ................................................................................................................. .. 1 1 3

4-2 Synthesis of the phenylene-diacetonitrile acceptor monomers.................................. 115

4-3 Synthesis of the ProDOT-dialdehyde monomers. .......................................................115

4-4 Synthesis of the ProDOT:cyanovinylene family of polymers via Knoevenagel
p o ly m eriz atio n ............................................................................................................... 1 16

4-5 IR spectra of ProDOT:cyanovinylene polymers.......... ...................................... 117

4-6 MALDI-MS of ProDOT:cyanovinylene polymers................................................118









4-7 Absorption spectra for molecular weight fractions of the ProDOT:cyanovinylene
polym ers ................................................................................................. 120

4-8 Thermogravimetric analysis of the ProDOT:cyanovinylene polymers .........................121

4-9 Solution UV-Vis absorbance and photoluminescence of ProDOT:cyanovinylene
polym ers in toluene ............. .. ................... .................. ........................ ... ............... 123

4-10 Thermochromic behavior of PProDOT-OHex2:CNPV-DDO in 1,2-dichlorobenzene .... 123

4-11 DSC curves of ProDOT:cyanovinylene polymers...... .... ..................................... 125

4-12 Cyclic voltammetry of ProDOT-cyanovinylene polymers......................................127

4-13 Differential pulse voltammetry of ProDOT-cyanovinylene polymers ..........................128

4-14 Oxidative spectroelectrochemistry of ProDOT:cyanovinylene polymers .....................130

4-15 Reductive spectroelectrochemistry of ProDOT:cyanovinylene polymers.....................131

4-16 Relative luminance (%) as a function of applied potential for every
ProD O T:cyanovinylene polym er ......................................................... ................ 133

4-17 Normalized photoluminescence emission spectrum of PProDOT-OHex2:CNPV-
MEH in thin-film (solid line) superimposed with normalized electroluminescence
spectrum and accompanying photograph of an ITO/PEDOT-PSS/PProDOT-
OHex2:CNPV-M EH/Ca/Al device (dotted line) ................................... ..................... 134

4-18 LED properties of an ITO/PEDOT-PSS/PProDOT-OHex2:CNPV-MEH/Ca/Al
d ev ic e ..................................................................................................... ........ . ....... 1 3 5

4-19 Photovoltaic results for a device made of a 1/4 blend (w/w) of PProDOT-
OHex2:CNPV-M EH/PCBM ....................................................... 136

5-1 Structures of investigated amino-functionalized PProDOTs................ ..................1...52

5-2 Synthesis of amino-substituted ProDOT monomers and polymers...............................153

5-3 1H-NMR spectra........................ .......... ...............155

5-4 M ALDI-M S of PProDOT-NM e2 ........... ... ........................................................ 158

5-5 M ALDI M S of PProD OT-N Isop2 ......................................................... ................ 158

5-7 Thermogravimetric analysis of the amino-functionalized PProDOTs in a nitrogen
atm o sp h ere ...................................................................................................... .......... 159

5-8 UV-vis absorption and photoluminescence spectra of neutral amino-functionalized
P P roD O T s. ..................................................................................................... .......... 160









5-9 Spectroelectrochemisty of thin-films of the neutral amino-functionalized PProDOTs... 163

5-10 Differential pulse voltammetry of amino-substituted PProDOTs. .................................. 163

5-11 Relative luminance (%) versus applied potential for amino-substituted PProDOTs...... 164

5-12 CIE 1931 xy chromaticity diagram of amino-substituted PProDOTs............................165

5-13 Quaternization of amino-substituted PProDOTs using Mel................. .................. 166

5-14 Solution spectroscopy for PProDOT-NM e3 .................. ....................................... 168

5-15 Solution spectroscopy for PProDOT-NMe(Isop)2 ............................. ................169

A-i Numbering system for Br2-BT-B(OC7H15)2 crystal structure ..................................177

A-2 Numbering system for Br2-BEDOT-B(OC7H15)2 crystal structure............................... 178

A-3 Numbering system for Br2-BEDOT-B(OC12H25)2 crystal structure. ............................. 179

A-4 Numbering system for BProDOT-Me2-B(OC12H25)2 crystal structure ......................... 181

B-i Gel permeation chromatogram of PBProDOT-Hex2-B(OC12H25)2 .............................. 183









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

PROCESSABLE VARIABLE BAND GAP CONJUGATED POLYMERS FOR
OPTOELECTRONIC DEVICES

By

Emilie M. Galand

December 2006

Chair: John. R. Reynolds
Major Department: Chemistry

Solution processable variable band gap thienylene-based conjugated polymers were

designed for application in various optoelectronic devices. The synthesis of wide band gap

regiosymmetric thiophene-dialkoxybenzene and 3,4-ethylenedioxythienyl-dialkoxybenzene

polymers was investigated, and organo-soluble isoregic poly(1,4-bis(2-thienyl)-2,5-dialkoxy-

benzenes) (PBT-B(OR)2) were successfully synthesized via Yamamoto coupling, with estimated

number average molecular weights ranging from 3,000 to 5,000 g mol-1, and a solubility

of about 7 mg mL-1 in toluene. 1,4-Bis[2-(3,3-dialkyl-(3,4-propylenedioxy)thienyl]-2,5-

didodecyloxybenzene derivatives, [BProDOT-R2-B(OC12H25)2)], were prepared by Negishi

coupling of the ProDOT and didodecyloxybenzene units in ca. 40% yields. They were efficiently

electropolymerized to form electroactive films exhibiting redox switching at fairly low potentials

(~ +0.1 V vs. Fc/Fc+). BProDOT-Hex2-B(OC12H25)2 was polymerized via ferric chloride

chemical oxidation with an estimated number average molecular weight of 14,600 g mol-1. A

solubility of 15 mg mL-1 in chloroform was reached, which is attributed to the ProDOT hexyl

substituents.

Four analogues of the narrow band-gap poly(3,4-propylenedioxythiophene-dialkyl)-cyano-

p-phenylene vinylene (PProDOT-R2:CNPPV) polymer family have been synthesized via









Knoevenagel condensation with number average molecular weights ranging between 9,000 and

24,000 g mol-1. Linear and branched alkoxy substituents were introduced along the polymer

backbone yielding organo-soluble materials (15 mg mL-1 in chloroform) with improved film

quality and variable optical properties.

Conjugated polyelectrolytes were successfully synthesized from the ferric chloride

oxidative polymerization of amino-substituted ProDOTs, followed by post-polymerization

quaternization of the amino substituents. These materials, well solvated in DMSO, are presently

the most fluorescent red-shifted polyelectrolytes ever reported.

The optical, redox, and electronic properties of the polymers were studied by

electrochemical and spectroscopic methods. Owing to their solubility properties, the polymers

could be processed into homogeneous thin-films by spin-coating or spray-casting, and applied to

light-emitting diodes and photovoltaic devices. Particularly when used as electron donors in

tandem with the electron acceptor [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) in bulk

heterojunction photovoltaic devices, PBT-B(OR)2 polymers exhibited power conversion

efficiencies up to -0.6%. PBProDOT-Hex2-B(OC12H25)2 cathodically switched between orange

and highly transmissive gray colors, and the PProDOT-R2:CNPPV polymers switched between

neutral blue/purple states and transmissive gray oxidized and reduced states, which makes them

attractive for large area electrochromic displays.









CHAPTER 1
INTRODUCTION

1.1 Conjugated Polymers

1.1.1 Brief History

Although semiconducting conjugated polymers have been known for about 30 years (with

the discovery in 1977 by MacDiarmid, Shirakawa, and Heeger, that chemical doping of these

materials resulted in increases in electronic conductivity over several orders of magnitude1'2), it

was only in the early 90s that many developments started to grow both on the fundamental and

on the manufacturing levels. In particular, the discovery of light-emitting polymers in 1990, by

Richard Friend3 and his group, in the Cavendish Laboratory at Cambridge University, was a

major turning point in the rise of organic electronics. Polymeric materials have the advantage

that they are much more easily processed than metals. For instance, they can cover large and

flexible surfaces and can be processed from solutions into complex architectures, using

techniques such as spin-coating or spray-casting. Most plastics can be deformed reversibly,

which is not true for metals. Also the synthetic flexibility of polymers allows easy tailoring of

their physical, electronic, and optical properties. All these parameters are the reasons that have

motivated the development of syntheses and processing methods of conjugated polymer

materials with unique properties, with the goal of applying them in light-emitting diodes, field-

effect transistors, photovoltaic cells, and electrochromics. Serious problems such as oxidative

stability and device lifetimes have to be overcome for further development in commercial

applications, but we may predict that one day, we will all go camping, carrying our flexible LED

display with us, surfing the net and watching the TV solar-powered by polymeric materials.









1.1.2 Conjugated Polymers Electronic Properties

The simplest possible form of conjugated polymer is of course polyacetylene (CH)n whose

structure constitutes the core of all conjugated polymers having a conjugated backbone of carbon

atoms. The essential structural characteristic of all conjugated polymers is their quasi-infinite 7t-

system, with the electrons that constitute the 7t-bonds being delocalized over a large number of

recurring monomer units. This feature results in materials with directional conductivity, strongest

along the axis of the chain. In polyacetylene (PA), delocalization results in two-fold degeneracy

in the ground state as illustrated in Figure 1-la. In aromatic polymers, such as poly(para-

phenylene) (PPP), the alternating single and double bonds lead to electronic structures of varying

energy levels (non-degenerate ground state) (Figure 1-1b).4 In a polymer, just as in a crystal, the

interaction of a polymer unit cell with all its neighbors leads to the formation of electronic bands,

the highest occupied electronic levels constitute the HOMO or valence band (VB), and the

lowest unoccupied electronic levels constitute the LUMO, or conduction band (CB). It is

important to note that the 7t-system of conjugated polymers is not a strand of atoms with

equivalent bond distances between any two neighboring atoms, as predicted by the Hiuckel

theory (this would give properties of a metal). This simple picture is incorrect because of the

Peierls-instability of one-dimensional systems.4-6 Peierls showed that, due to the coupling

between electronic and elastic properties, the polymer develops a structural distortion such as to

open a gap in the electronic excitation spectrum. So, conjugated polymers exhibit a band gap due

to the Peierls distortion, and they are referred to as semiconductors7 if their band gap values are

below 3 or 4 eV (at higher values, they are insulators). By definition, the band gap is the

difference between the VB and the CB. It is equal to the lowest excitation energy, which can be

obtained from the onset value at the low energy edge of the optical absorption spectra.














w 1
Ll. Ll.J



Energetically equivalent forms of PA Non-equivalent benzenoid and quinoid forms of PPP

Figure 1-1. Energetic representations of polyacetylene and poly(para-phenylene). (a) degenerate
PA and (b) non-degenerate PPP. [Modified from Moliton, A.; Hiorns, R. C. Polym.
Int. 2004, 53, 1397-1412].4

Being semiconductors with fairly large band gaps, conjugated polymers do not conduct to

a significant extent unless charged carriers are created within the conjugated framework8 (PPP

reaches a conductivity of 500 Q-1 cm-1 when doped with charged carriers, whereas undoped PPP

has a conductivity on the order of 10-13 Q-1 cm-1).4 The charge carriers, either positive (p-type) or

negative (n-type), are the products of oxidizing or reducing the polymer respectively. This

phenomenon is always accompanied with structural changes localized over a couple of rings (4

to 5 rings for PPP)9 and this gives rise to new electronic states within the band gap. J. L. Bredas

and G. B Street have published a chemist-accessible explanation of these concepts.10 For the

aromatic conjugated polymers, the entity consisting of charge and spin (radical cation or anion)

along with an associated geometry distortion is known as a polaron as illustrated in Figure 1-2a.

The charge and radical form a bound species, since any increase in the distance between them

would necessitate the creation of additional higher energy quinoid units. Upon removal of a

second electron, either a separate polaron may form or, if the second electron is removed from

the same site as the first, a bipolaron (Figure 1-2b). As the doping level increases, polaron and

bipolaron states overlap and form bands, which will, at some point, merge with valence and

conduction bands, as illustrated for the p-doping of PPP in Figure 1-3.









a



polaron
b


bipolaron

Figure 1-2. Positively charged defects on poly(para-phenylene). (a) polaron, (b) bipolaron.

p-doping
CB

VB- --

Neutral state 1 charged default 2 charged defaults Bipolaron Heavily
(polaron) (bipolaron) bands doped


Figure 1-3. Poly(para-phenylene) and evolution of energy levels with p-doping. [Modified from
Moliton, A.; Hiorns, R. C. Polym. Int. 2004, 53, 1397-1412].4

In PA, the charges which appear upon doping are called solitons. They are termed

differently because the charges can propagate along the chain without an increase in distortion

energy and can readily separate since the geometric structures that appear on each side of the

charges are degenerate in energy (Figure 1-4). Doping dramatically alters the optical spectra of

conjugated polymers, with optical transitions occurring between the VB and polaron states, and

between polaron states. These transitions have lower energies than interband transitions and a

number of colored low band gap conjugated polymers become transparent upon doping.

It is important to note that since the charged defect is simply a boundary between two

moieties of equal energy, it can migrate in either direction without affecting the energy of the

backbone, provided that there is no significant energy barrier to the process. It is this charge

carrier mobility that leads to the high conductivity of these polymers, the conductivity (c) of a









conducting polymer being related to the number of charge carriers (n) and their mobility (4t). A

major challenge is to raise the carrier mobility and the conductivity, which are currently limited

by the defects in the polymers. When cast from solution as thin-films, the polymers remain

largely a tangle of spaghetti-like strands. Transport along the ideal linear chain can proceed no

farther than the length of the fully extended chain; then the charge must hop to another chain.

With improved ordering of the polymer chains, however, the conductivity could reach those of

even the best metals.




-2e
(-, +




+

Figure 1-4. Illustration of the formation of two charged solitons on a chain of trans-
polyacetylene. [Modified from Chance, R. R.; Bredas, J. L.; Silbey, R. Physical
Review B 1984, 29, 4491-4495].9

1.2 Band Gap Engineering

The role of conjugated polymers in emerging electronic and display technologies is rapidly

expanding, and with it, the need of a variety of polymers with different emissive or absorptive

colors, electron or hole affinities, conductivities, and many other properties. Band gap

engineering is extensively exploited nowadays for these reasons. It allows varying the optical

and electronic properties of a polymer by simple manipulation of the chemical building blocks

and the manner in which they are connected. In particular, five parameters influencing the band

gaps were established: bond-length alternation, resonance energy, deviation from planarity,

inductive effects of the substituents, and interchain coupling in the solid state.11 Working around









these parameters, researchers have developed various families of conjugated polymers with

different band gaps, which are typically classified as low band gap12 or narrow band gap

materials when Eg is less than ca. 1.80 eV, and as wide band gap materials for Eg > 1.80 eV

[recall E (eV) = 1240/k (nm)]. A description and examples of the way these parameters influence

the band gaps are given below as they help in understanding the work presented in this

dissertation.

As we discussed before for PA, bond-length alternation is the result of the Peierls effect

and is responsible for the non-metallic behavior of neutral PA due to the existence of a band gap.

Minimizing the bond-length alternation along a conjugated polymer backbone is consequently an

important way to reduce the band gap. In aromatic polymers, the benzenoid structure will prevail

over the energetically unfavorable quinoid structure, which results in the existence of what are

essentially single bonds between the aromatic rings and hence a large bond-length

alternation.11,13 Making the quinoidal structure more favorable will help increasing the double-

bond character of the linkages between aromatic rings and reduce the band gap.14 For instance,

polyisonaphthalene represented in Figure 1-5 (Eg = 1 eV) loses the aromaticity of the thiophene

ring when going from the aromatic to the quinoid form, but at the same time its phenylene ring

gains aromaticity, which minimizes the overall aromaticity loss and increases the contribution of

the quinoid form to the polymer structure compared to polythiophene (Eg = 2 eV).15

The donor-acceptor approach has also been particularly developed as a means of reducing

bond-length alternation for the building of narrow band gap polymers.13'16 In that concept, the

strong interaction between an electron donor and an electron acceptor increases the double bond

character between aromatic rings, and the high-lying HOMO of the donor fragment combined

with the low-lying LUMO of the acceptor gives rise to a D-A monomer with an unusually small









HOMO-LUMO separation and to a narrow band-gap upon polymerization (Figure 1-6). By

carefully selecting the structures of the donors and acceptors and their respective electron

donating and withdrawing strengths, it is possible to manipulate the magnitude of that band

gap.17 As an example, by simply varying the donor strength in the dioxythiophene-cyanovinylene

polymer family, Thompson et al. gained access to a variety of band gaps as illustrated in Figure

1-7 [recall: EDOT > propylenedioxythiophene (ProDOT) > thiophene for electron donating

power].18




S n S n
aromatic quinoid

Figure 1-5. Aromatic and quinoid states of polyisonaphthalene. The six-membered ring of
polyisothianaphthalene gains aromaticity when the molecule goes from the aromatic
to the quinoid state, resulting in a higher contribution of the quinoidal state
compared to polythiophene.


LUMO -


) LUMO
uo) HM Reduced band gap
SHOMOHOMO




D D-A A

Figure 1-6. Illustration of the donor (D) acceptor (A) concept. [Modified from van Mullekom,
H. A. M.; Vekemans, J. A. J. M.; Havinga, E. E.; Meijer, E. W. Mater. Sci. Eng.
2001, 32, 1-40].13 Hybridization of the high-lying HOMO of the donor fragment and
the low-lying LUMO of the acceptor fragment yields a D-A unit with an unusually
small HOMO-LUMO separation.

Deviation from planarity due to unfavorable intramolecular interactions and interchain

interactions will reduce orbital overlap, decrease the 7t-7t stacking and affect the band gap as










well.8'19'20 Let us take the example of the polythiophene family: polythiophene is highly

crystalline and completely insoluble, but as alkyl chains are introduced at the 3- and 4- positions

of the thiophene ring for solubility purposes, the steric interactions between adjacent rings

generate twisting of the backbone, destroying the conjugation and widening the band gap.21


Vacuum (0 eV)
Hex Hex
l 1 NC 2 C12H25
0Ae eH 0 OC
H25C20 N 0 Nc
H Hx He x H exs


H25120 C12

C 12H25 N CN

S\\'H I Hex Hex

3.5eV 3.5 eV 3.4 eV 3.6 eV 3.5 eV
X3.5eV 353.8 eV
V2.0 eV 1.5 eV
2.3 eV 1.8 eV
Eg 2.7 eV 2.1 eV 5.0 eV
5.4 eV 5.4 eV

5.9 eV 5.8 eV
6.2 eV

Figure 1-7. Polymer band structures and optical band gaps of the dioxythiophene-cyanovinylene
polymer family. [Modified from Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.;
Reynolds, J. R. J. Am. Chem. Soc. 2006, 128, 12714-12725].18

Finally, the substitution of the polymer chains with electron rich or electron poor

substituents will have an influence on the HOMO and LUMO levels and consequently on the

band gap too. A close example to this Ph.D. research is the narrowing of the band gaps in hybrid

thienylene-phenylene polymers by replacing alkyl side chains with alkoxy groups due to an

increased electron density and reduced steric effect brought by the electron donating oxygen

atoms: the onset of the 7t-7t* transition, in solution, of 3 eV for poly(2,5-dihexyl-1,4-bis(2-

thienyl)phenylene) is reduced to 2.4 eV for the analogous alkoxy derivatized polymer.22









1.3 Polymerization of Thiophene Based Molecules

There are great synthetic advantages working with thiophene based molecules and one of

the most important is the variety of polymerization methods available such as oxidative chemical

and electrochemical polymerizations, along with metal mediated and solid state polymerizations.

General principles, drawbacks, and advantages of the methods covered in this dissertation are

given below.

1.3.1 Oxidative Polymerizations

Oxidative polymerizations can be carried out either chemically or electrochemically. The

generally accepted mechanism for the oxidative polymerization of heterocycles involves

oxidation of the monomer to form a radical cation intermediate. The coupling of two radical

cations, or of one radical cation and one neutral monomer followed by rearomatization with the

loss of two protons leads first to a dimer unit, and finally to a polymer after repeated coupling. A

detailed mechanism can be found in J. A. Irvin's dissertation.23 Typically, electron-rich

monomers are easier to oxidize and allow milder oxidative polymerization conditions, fewer side

reactions such as overoxidation and the formation of more stable oxidized polymers.24 For

instance, the oxygen atoms of the ethylenedioxy bridge of EDOT increase the electron density of

the thiophene ring and lower its oxidation potential. Indeed, the EDOT oxidation peak is found25

at +0.88 V vs ferrocene (Fc/Fc ) while thiophene oxidation was reported26 around +1.22 V vs

Fc/Fc+ (assuming that the half-wave potential (Ei/2) of Fc/Fc+ = 0.38 V vs the saturated calomel

electrode (SCE) and E1/2 of Ag/Ag+ = 0.26 V vs SCE).27 A major drawback in the oxidative

polymerization of thiophenes is that it does not link the thiophenes exclusively at the 2- and 5-

positions of the thiophene ring. Mislinking of the polymer through the 3- and 4- positions can

happen leading to backbone irregularities and crosslinking and consequently to poor electronic

properties and solubility problems.23 This problem can be overcome by substituting the 3- and 4-









positions of the thiophene units, as with EDOT.28 Regioirregularities can also be found in the

oxidative polymerization of unsymmetrical 3-substituted thiophenes due to the lack of

regiochemical control over head-to-tail couplings between adjacent thiophene rings.29 Head-to-

head and tail-to-tail couplings can also occur, leading to irregular polymers with sterically driven

twisted backbones and poorer packing density. This results in a loss of conjugation, and a poorer

orbital overlap and electronic connectivity in three dimensions. Non-oxidative coupling

methods30 with a high degree of regioselectivity (e.g., Rieke method31 and McCullough

methods32) have been developed for the synthesis of regioregular polymers. But the most

attractive route to achieve a high degree of order, which does not rely on highly controlled

polymerization conditions, is the use of symmetrical monomers and will be one of the focuses of

the present dissertation.

The advantage of using chemical oxidative methods (in the bulk) over electrochemical

methods is the possibility of getting high yields based on monomer. Chemical oxidations are also

quite inexpensive relative to metal coupling, usually accomplished with the FeCl3 oxidant. The

chain length is usually limited by solubility problems: the oxidized polymers are less soluble

than the neutral polymers due to their increased rigidity and can precipitate out of the solution,

stopping the progress of the polymerization. This can be reduced by the introduction of flexible

substituents on the polymer backbone. As an example, 2,5-dialkoxy-substituted 1,4-bis(2-

thienyl)phenylene polymers synthesized via FeCl3 oxidation precipitate out of the chloroform

solution when they are substituted with heptoxy groups, but remain in solution with longer

hexadecyloxy groups.22 Reduction to the neutral polymer is accomplished using a strong

reducing agent such as hydrazine or ammonium hydroxide. The major drawback of oxidative









chemical polymerization over electropolymerization is that ferric ions coming from the oxidants

(FeCl3, Fe(C104)3) are often trapped in the polymer backbone, affecting the device properties.33

1.3.2 Metal Mediated Polymerizations

Metal mediated couplings such as Grignard metathesis, Suzuki, and Ni(0) mediated

Yamamoto polymerizations are typically used for the polymerization of heterocycles. Grignard

Metathesis polymerization developed by the McCullough group32c has been used to produce a

variety of polythiophenes with high molecular weights and high degree of regioregularity. This

method requires the synthesis of the 2,5-dibromo-thiophene derivative, which is then

polymerized with a Grignard reagent, such as the readily available and inexpensive methyl

magnesium bromide (MeMgBr), and catalytic amounts of Ni(dppp)C12 as illustrated for the

synthesis of disubstituted PProDOTs34 in Figure 1-8. It proceeds via an unusual quasi-living

chain-growth mechanism, which allows the synthesis of polymers with predetermined molecular

weights and narrow molecular weight distributions.35 GriM is fast, easy, can be carried out on

large scales, and does not require cryogenic temperatures. The use of GriM for the

polymerization of monomers made of other kinds of heterocycles than substituted thiophenes has

rarely been reported and it is consequently difficult to determine how efficient that method

would be on such molecules. The closest example to the present research is the synthesis of high

molecular weight electron rich poly(3,4-ethylenedioxythiophene)-2,5-didodecyloxybenzene

(LPEB) via GriM.36

R R R R
1. MeMgBr, THF
0 0 0 0
BrBr 2. Ni(dppp)Cl2, reflux /
Figure 1-8. GriM polymerization of disuBr s PProDOTs.

Figure 1-8. GriM polymerization of disubstituted PProDOTs.









The Yamamoto Coupling, using zerovalent bis(1,5-cyclooctadiene)nickel reagent

(Ni(COD)2) is a powerful synthetic method to couple electron poor aromatic rings, and more

interesting in that research, to couple electron rich aromatic rings which are more reluctant to

metal oxidative addition and consequently to most metal mediated coupling reactions. For

instance, it has been effective for the polymerization of electron rich carbazoles with molecular

weigths around 100,000 g. mol-1 (mechanism of the polymerization shown below in Figure 1-

9).37 The mechanism involves the insertion of Ni(0) into the C-X bond of a halogenated

heterocycle, disproportionation between two of the resulting derivatives and reductive

elimination of the Ni(II) compound.38 Addition of the Ni(0) reagent is done slowly in order to

avoid the formation of the less stable dinickel-substituted complex (Figure 1-9), which would

result in the termination of the propagation of the polymer chain due to hydrolysis or

decomposition. Each coupling is followed by the irreversible conversion of Ni(0) to Ni(II)X2 and

for this reason, the polymerization requires stoichiometric amounts of the expensive bis(1,5-

cyclooctadiene)nickel(0) [Ni(COD)2] reagent. Another drawback is that even if the Yamamoto

coupling has been used for the polymerization of thiophene-based molecules, it always led to

relatively small molecular weights making it quite challenging for the synthesis of our

polymers.39 Finally, it is important to note first that the use of Ni(COD)2 requires expensive

equipment since it has to be stored cold (otherwise it decomposes quickly) and in an oxygen free

atmosphere, and second that it is often trapped40 in the polymers.

1.3.3 Solid State Polymerization

Solid state polymerization of polythiophenes was reported for the first time by Meng et al.

in 2003.41 They found by chance, that 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT)

polymerizes spontaneously, without the addition of catalyst. This was discovered after a sample

of DBEDOT transformed into a highly conductive black material (up to 80 S cm-1) after two









years of storage at room temperature. The reaction takes place in air, vacuum, or light, heating

decreases the reaction time, and elemental bromine is released during the reaction as illustrated

by the mechanism in Figure 1-10.41 The resulting polymer is doped with bromine and can be

reduced to its neutral form after dedoping with hydrazine. It was suggested that short

intermolecular Hal***Hal contacts are required in order for the reaction to take place. Indeed,

DBEDOT which has short Hal**Hal intermolecular contacts of 3.45 and 3.50 A is much more

reactive than 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT), which has an intermolecular

Hal***Hal contact of 3.73 A. These Hal***Hal intermolecular contacts are smaller than the sum of

van der Waals radii (3.7 A for Br***Br and 4.0 A for I...I).

Oxidative Addition
Br-Ar-Br -- N Br-Ar-Ni(II)-Br + Br-Ni(II)-Ar-Ni(II)-Br
Ni(0)
Disproportionation Hydrolysis
or decomposition

Reductive elimination / ,
Br-Ar-Ar-Br ---- Br-Ar-Ni(II)-Ar-Br Br-Ni(II)-Ar-H H-Ar-H
Ni(II)Br2
Chain propagation N(II)Br

Termination of polymerization

Figure 1-9. Mechanism of aryl (Ar) polymerization via Yamamoto coupling and of the polymer
chain degradation/termination occurring during the polymerization. [Mechanism
modified from Zhang, Z.-B.; Fujiki, M.; Tang, H.-Z.; Motonaga, M.; Torimitsu, K.
Macromolecules 2002, 35, 1988-1990].37

Br-S Br
0 0 0 0
0 0 Br2 0 / Br reduction S Br
+ ,.-.Br S S Br Br B
Br Br Br Br Br rBrr2 0 S n
0 0


Figure 1-10. Mechanism of the solid state polymerization of DBEDOT.









1.3.4 Knoevenagel Polymerization

The Knoevenagel condensation involves the nucleophilic addition of a carbanion to a

carbonyl group aldehydee or ketone) in the presence of a base, followed by an elimination

reaction in which a molecule of water is lost as illustrated in Figure 1-11.42 The Knoevenagel

polycondensation has proven very efficient for the synthesis of donor-acceptor type polymers,43

and especially of narrow band gap polymers,18'43 with the combination of electron poor

diacetonitrile monomers and electron rich dialdehyde monomers. Usually these condensations

are accomplished in THF/alcohol mixtures (e.g., THF/t-butanol or THF/2-propanol) as reaction

media and with t-butoxide (t-BuOK) or tetrabutylammonium hydroxide (Bu4NOH) strong

bases.17'43'44 Crosslinking of the polymer by Thorpe-Ziegler and/or Michael side reactions of the

cyano or vinylene groups can be avoided by the use of one equivalent of base per cyano

group.42'43 Previous work reported by our group on the synthesis of thiophene-cyanovinylene

polymers has also shown that the use of t-BuOK is preferred over Bu4NOH.43 The

polymerizations proceeded gradually with t-BuOK and led to processable materials, whereas the

use of Bu4NOH led to the rapid formation of black insoluble precipitates. These observations

have been used as support for the work on the ProDOT:cyanovinylene polymers presented in this

dissertation.

t-BuO-/t-BuOH
R1R2CH2 R1R2CH-
t-BuOH/t-BuO-
R1R2CH- + ArCHO -- R1R2CHCH(Ar)O- -- RR2CHCH(Ar)OH

t-BuOH/t-BuO-
SR1R2C=CHAr + OH-

Figure 1-11. Illustration of the Knoevenagel condensation steps.









1.4 3,4-Alkylenedioxythiophene Based Polymers, from Thiophene to EDOT to ProDOT

Improvement of the properties and capabilities of basic conjugated polymers such as

polythiophenes became of great importance in the mid 80s for the organic electronics

community. More specifically, the quest for specific electronic and optical properties led to

diverse structural modifications of the thiophene polymer building unit, and to the very

interesting EDOT molecule. As discussed in the section on oxidative polymerizations of

thiophene based molecules, the ethylenedioxy bridge of EDOT prevents parasite reactions at the

3- and 4- positions of thiophene, conferring a high reactivity to the free 2- and 5- positions,

which gives rise to highly regular conjugated backbones upon polymerization. The electron

donating oxygen atoms of the ethylenedioxy-bridge bring also an increased electron density,

which increases the HOMO level and lowers the oxidation potential of the EDOT based

molecules compared to their thiophene counterparts. This effect occurs without introducing

unfavorable steric interactions between adjacent side chains, as found with regular long alkoxy

substituents. Also, the ethylenedioxy-bridge is too strained for a high level of conjugation with

the thiophene ring favoring its reactivity towards oxidative polymerization.45'46

These properties have been widely exploited for improving the properties of conjugated

polymers, such as milder oxidative polymerization conditions and the formation of more stable

polymers. The most obvious and popular example is of course PEDOT which has a low

oxidation potential, is electrochromic (deep blue neutral state and highly transmissive oxidized

state), is highly conductive and highly stable, and which is being used as a charge injecting layer

in light emitting devices, as a component in electrochromic displays, and even as electrodes in

field effect transistors and photovoltaic cells.47'48 But a variety of copolymers which use EDOT

as a building block,49 like the thienylene-phenylene family, also benefit from its properties. This

is illustrated for example by poly[1,4-bis[2-(3,4-ethylenedioxy-thienyl)]-2,5-dialkoxybenzenes]









(PBEDOT-B(OR)2)46 which exhibit band gap values between 1.75 eV and 2.0 eV, and polymer

half wave potentials as low as -0.4 V versus Fc/Fc whereas poly[1,4-bis(2-thienyl)]-2,5-

dialkoxybenzenes]50 exhibit band gaps around 2.1 eV and minimum polymer half wave

potentials of 0.15 V vs Fc/Fc The properties of EDOT have also been exploited for improving

the electron donating power of the donor moiety in donor-acceptor systems based on thiophene

blocks and for building narrower band gap materials. This is illustrated in Figure 1-12 for

different combinations of thiophene and EDOT donor moieties with cyanovinylene acceptor

moieties.17 In that example, it is clearly seen that as the EDOT content increases, the band gap

diminishes.

Vacuum 0 eV
Increasing donor strength

LUMO

1.1 eV
Eg 1.4 eV
1.6 eV
S HOMO










R. J. Am. Chem. Soc. 2004, 126, 16440-16450].17

With the recent emergence of soft and flexible plastic devices for use in solar cells,

electrochromic devices, or light-emitting diodes (LEDs), it became particularly important to

synthesize neutral soluble conjugated polymers, which can be processed directly from solution

into thin-films, for instance by spray-casting or spin-coating. For that purpose, intense work has









been done in the substitution of thiophene with solubilizing substituents,45'51 and ProDOT has

emerged as the best compromise between the synthetic flexibility of thiophene and the electronic

properties of EDOT. First, similar to EDOT based monomers, the oxygen atoms of the

propylenedioxy bridge of ProDOT increase the electron density of the thiophene ring and lower

its oxidation potential (ProDOT oxidation peak reported around +0.98 V vs. Fc/Fc+).52 The effect

of the electron donating oxygens on the oxidation potential is a bit less for ProDOT than for

EDOT due to its twisting conformation, which diminishes the overlap between the oxygen lone

pairs and the aromatic thiophene ring. Second, various kinds of substituents (linear or branched,

alkyl or alkoxy chains, etc.) can be introduced easily on the ProDOT ring which allows

derivatization, chemical polymerization, and inducing solubility of the polymers in organic

solvents.53'54 Mishra et al. reported the synthesis of a hydroxyl substituted ProDOT, in a single

step, from commercially available starting materials, which led to the preparation of a variety of

electroactive derivatives.55 Also ProDOT can be disubstituted on the central carbon of the

propylene bridge without disturbing the C2 symmetry. This was used by Reeves et al. who made

a recent impact in the field of soft electronics with the development of regiosymmetric spray-

coatable electrochromic ProDOT polymers, prepared via Grignard metathesis.34 This is a great

advantage compared to EDOT which has been mostly unsymmetrically substituted (except in the

case of PheDOT56'57) due to the poor yields and tedious synthesis encountered during the

functionalization process. Researchers are now taking advantage of the electron rich properties,

synthetic flexibility and easy derivatization of the ProDOT molecules and are working on the

design of a variety of soluble hybrid conjugated polymers containing ProDOT to have access to a

broader range of electronic and optical properties. For instance, Thompson et al. recently

reported the building of a soluble narrow band gap polymer using the donor-acceptor approach,









with a substituted ProDOT derivative as the donor unit and a cyanophenylene derivative as the

acceptor unit as illustrated in Figure 1-13. 18,43,58

C6H13 C6H13 C6H13 .H13
0 0 NC H012H25

H O\ H NC t-BuOH/THF (1:1) I \ n
0 0 O012H25
H250120

Figure 1-13. Synthesis of poly(3,4-propylenedioxythiophene-dihexyl)-cyano-p-phenylene-
vinylene.

1.5 Applications

A variety of parameters need to be considered for application of conjugated polymers in

semiconductor devices and only those which can be manipulated by synthetic chemists are

described below for each application. The properties which are of interest in these applications

(Light-Emitting Diodes (LEDs), solar cells, and electrochromic devices) are of course the ability

to synthesize soluble polymers in high bulk yields for obtaining solution-processable or film-

forming polymers, and the ability to produce large quantities. This can be accomplished by

introducing flexible side chains on the polymer backbone. For instance, the solubility of the

branched PProDOT(CH2OEtHx)2 (Mn = 47,000 g mol-1) is about four times more important

(57 mg mL-1) than the solubility of PProDOT(Hx)2 (13 mg mL-1, Mn = 38,000 g mol-1) in

toluene.34

In polymer LEDs, light emission results from the formation of excitons in the polymeric

layer, which will emit light upon relaxation to the ground state. These excitons form by the

meeting of electrons and holes injected by varying work function electrodes. The color of the

emitted light is dependent on the band gap of the material, and consequently a wide range of

band gaps are needed for PLED applications: this is where band gap engineering intervenes.59

Band gap engineering has to be done keeping in mind that the backbone structure and









conformation play an important role on the luminescence efficiency. Indeed, once an exciton is

formed, strong intermolecular interactions between polymer chains form weakly emissive

interchain species (ground-state aggregates or excimers) which lead to a spectral red-shift and

reduced quantum yields.20 One extensively used method to prevent this photoluminescence

quenching phenomenon is to introduce bulky side groups to separate the backbones from each

other.60 But for effective charge injection and transport in LEDs, high carrier density and

mobilities are also required, and consequently a high degree of 7t-interactions and packing.61 All

these parameters have to be taken into consideration by the chemist and carefully balanced.

In electrochromic devices, we obviously need an electrochromic material which possesses

the ability to reversibly change color by altering its redox state.62 Intrinsically, all conjugated

polymers have the potential to be electrochromic. This phenomenon is the result of the change of

conjugation which occurs upon oxidation or reduction of the polymer (interconversion between

the quinoid and the aromatic states and apparition of lower energy transitions due to the

formation of polarons and bipolarons as detailed earlier). The HOMO level of the polymer

controls the oxidation potential, and the LUMO level controls the reduction potential. As an

example, PEDOT is a great electrochromic material which switches between an opaque blue

color in the undoped state and a transmissive sky blue color in the oxidized state.63 A variety of

colors are needed in order to be able to develop a variety of applications, and this can be realized

by fine-tuning of the band gap (as explained earlier).64-66 The materials should also be stable

while switching between their oxidized and reduced states (or neutral states) with a certain

lifetime.

A large number of reviews are available on polymer photovoltaics and there is no need here

to go over an extensive summary of the principles, and of all the parameters which need to be









improved in order to attain solar efficiencies approaching 10%.43,67-69 Provided below is a

summary of the most important points which have to be considered by a synthetic chemist. In

organic solar cells, upon photoexcitation, an exciton is created (electron-hole pair) in the

polymer layer, and a current is created from the splitting of this bound exciton, and the collection

of the holes at a high work function electrode, and of electrons at a low work function electrode.

The exciton-splitting process occurs only at interfaces (at the junction between the electrode and

the conducting polymer or at the interface between polymers of differing electron affinities). The

lifetime of an exciton is short and only excitons that are formed within about 4-20 nm of the

junction have a chance to reach it.67 Conjugated polymer bulk heterojunctions (interpenetrating

networks of electron-accepting and electron-donating polymers) sandwiched between two

varying work function electrodes are currently the best answer to that problem, and particularly

those using a solubilized form of C60 such as (6,6)-phenyl C61-butyric acid methyl ester (PCBM)

as the acceptor layer. The photoinduced charge transfer in these blends happens on an ultrafast

timescale of up to 45 femtoseconds, which is much faster than the recombination process, which

happens in a microsecond regime (100 ns-10 ms).70-72

One of the main tasks of the synthetic chemist now is to find the "ideal" electron-donating

polymer. The best materials available right now are poly(3-hexylthiophene) (P3HT),73-75

poly(2-methoxy-5-(2'-ethylhexoloxy)-1,4-phenylenevinylene) (MEH-PPV),76 and poly(2-

methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylenevinylene) (MDMO-PPV),77 all contain side

chains that make them soluble in common organic solvents. But there is a mismatch between the

absorption spectrum of these materials and the solar spectrum. While the photon flux of the

AM1.5 solar spectrum peaks around 700 nm (1.8 eV), P3HT, MEH-PPV and MDMO-PPV

absorb strongly over the 350-650 nm wavelength range (3.5-1.9 eV). As a result, a film of P3HT









(240 nm thick) absorbs only about 21% of the sun's photons.67 Taking this information into

consideration, a synthetic chemist should specifically look at the synthesis of a polymer43 1)

exhibiting a band-gap capable of strongly absorbing sunlight (Eg < 1.8 eV),68'74 2) being resistant

to oxidation and consequently having a fairly low lying HOMO (about 5.2 eV or lower,78

assuming that the energy level of the Saturated Calomel Electrode (SCE) is 4.7 eV below the

vacuum level79), and 3) having a LUMO offset of about 0.3-0.4 eV relative to the PCBM for

effective charge transfer (above 3.8 eV).80 It is important to note that the HOMO and LUMO

energy levels are negative values because they are under the vacuum level which is considered as

the zero level. Consequently a HOMO level located at 5.4 eV is considered as lower than 5.2 eV.

Great improvement of the solar efficiency has also been observed upon increasing the degree of

order of the polymers. P3HT annealed above its glass transition temperature shows enhanced

crystallization and a dramatic increase in the hole mobility, which when applied in solar cells

facilitates charge transport to the electrodes and increases the solar efficiency.71'73'75'81 So for

application in photovoltaics, a synthetic chemist should also consider the ordering capabilities of

its polymers. An interesting path was taken recently by Hou et al.: to benefit from the ordering

properties of P3HT and to get band gaps approaching 1.8 eV, they have built two-dimensional

conjugated polythiophenes with bi(thienylenevinylene) side chains. They were able to lower the

band gap by 0.2 eV compared to P3HT and they reached solar efficiencies of 3.18%, whereas

they obtained efficiencies of 2.41% with P3HT using the same conditions.82

1.6 Study Overview

This work focuses on the design and synthesis of new processable conjugated polymers for

optoelectronic devices such as electrochromic devices, solar cells, and light-emitting diodes.

Two terms define the main lines of this project: processability and design. Processability was one

of our priorities in order to be able to use the polymers on large and flexible surfaces. Design of









the polymer structure was a way to induce processability and to manipulate the optical and

electronic properties in order to target specific applications. Both narrow and wide band gap

polymers were synthesized in order to cover a broad range of applications.

Chapter 2 describes briefly the techniques employed for the work presented in this

dissertation. In chapter 3, the synthesis of wide band gap polymers of the thienylene-phenylene

family has been investigated, including the already known thiophene-dialkoxybenzene and

EDOT-dialkoxybenzene derivatives, as well as a novel ProDOT-dialkoxybenzene derivative.

The newly developed ProDOT-phenylene materials were electropolymerized in order to quickly

look at their redox and electronic properties. For all the derivatives, various chemical

polymerizations were studied (Yamamoto coupling, ferric chloride oxidative coupling, GriM), as

well as solid state polymerizations, in order to develop methods for synthesizing the polymers in

high bulk yields. Flexible linear alkyl and alkoxy substituents were grafted onto the monomers to

induce solubility of the derived polymers in organic solvents. In chapter 4, narrow band gap

polymers were prepared by Knoevenagel condensation of electron rich 3,4-

propylenedioxythiophenes and electron poor cyanovinylenes. A variety of substituents were

introduced on the backbones of the polymers to induce solubility in organic solvents (linear and

branched alkoxy-substituents), and their effects on the optical and electronic properties were

studied. Chapter 5 describes the synthesis of wide band gap amino-substituted PProDOTs for

developing a new type of conjugated polyelectrolyte.

Along with the synthetic details and molecular characterizations, a complete

characterization of the polymers by electrochemical, optical and photophysical methods is given

in chapters 3-5 in order to evaluate their optical and electronic properties, and their potential in

certain optoelectronic applications. Structural studies such as X-ray analyses and DSC









measurements are also detailed in chapters 3 and 4 for a quick look at some of the materials

ordering properties. These studies have led to the incorporation of the materials into devices by

other members of the Reynolds group and this thesis will briefly outline the results at the end of

Chapters 3-5.









CHAPTER 2
EXPERIMENTAL

Molecular and structural analyses as well as electrochemical and spectroscopic methods

were used in this work for developing a deeper understanding of the newly synthesized materials

potential. The techniques are extensively described in the Reynolds group dissertations,23'43'83-85

and only an overview of the points of interest and of the general experimental conditions

employed will be given. More specific details can be found at the end of Chapters 3-5.

2.1 General Synthetic Methods

All chemicals were purchased from Acros or Aldrich Chemicals and used as received

unless stated otherwise. The monomer structure and purity were determined by 1H-NMR and

13C-NMR spectroscopy, elemental analysis, high-resolution mass spectrometry (HRMS), as well

as infra-red (IR) spectroscopy and single crystal X-ray analysis when applicable. Melting point

measurements were also performed on solids for complete characterization. 1H-NMR and

13C-NMR were recorded on Varian-VXR 300 MHz, Gemini 300 MHz, and Mercury 300 MHz

spectrometers. Elemental analyses were performed by Robertson Microanalytical Laboratories,

Inc. or the University of Florida, Department of Chemistry spectroscopic services. High-

resolution mass spectrometry was performed by the spectroscopic services at the Department of

Chemistry of the University of Florida with a Finnigan MAT 96Q mass spectrometer. IR

measurements were accomplished with a Spectrum One Perkin Elmer FT-IR spectrometer.

Single crystals X-ray measurements were accomplished at the Center for X-ray Crystallography

in the University of Florida Chemistry Department by Dr. Khalil A. Abboud. Single crystals

were obtained either by the slow cooling recrystallization method (single solvent or two solvents

method), or in a closed vial, by diffusion of a poor solvent into a smaller vial containing the

compound dissolved in a small amount of good solvent. Data were collected at 173 K on a









Siemens SMART PLATFORM equipped with a CCD area detector and a graphite

monochromator utilizing MoKa radiation (k = 0.71073 A). Cell parameters were refined using

up to 8192 reflections. A full sphere of data (1850 frames) was collected using the co-scan

method (0.30 frame width). The first 50 frames were re-measured at the end of data collection to

monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption

corrections by integration were applied based on measured indexed crystal faces. The structure

was solved by the Direct Methods in SHELXTL6 (2000, Bruker-AXS, Madison, Wisconsin) and

refined using full-matrix least squares.

All polymers were purified by precipitation followed by Soxhlet extraction as described in

Chapters 3-5. Characterization was accomplished by 1H-NMR, elemental analysis, matrix

assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), and

infra-red spectroscopy when applicable. 1H-NMR was recorded on Inova 500 MHz and Mercury

300 MHz. MALDI-TOF MS was performed by Dr. Tracy D. McCarley with a Bruker ProFLEX

III instrument at Louisiana State University. Methylene chloride or chloroform were used as

solvents, and terthiophene, dithranol, or 2-(-4-hydroxyphenylazo)benzoic acid (HABA) as

matrix. Polymer molecular weights were estimated by gel permeation chromatography (GPC).

GPC was performed on two 300 x 7.5 mm Polymer Laboratories PLGel 5 |tM mixed-C columns

with Waters Associates liquid chromatography 2996 photodiode array detector. All molecular

weights are relative to polystyrene standards (Polymer Laboratories; Amherst, MA). The

polymer solutions were prepared in tetrahydrofuran (THF) or chloroform (CHCl3) and a constant

flow rate of 1 mL min-1 was used. Polymer thermal stability was assessed by thermogravimetric

analysis (TGA). TGA measurements were performed on a Perkin-Elmer TGA 7 instrument

under nitrogen at heating rates of 200C min'1 from 500C to 9000C. The ordering properties were









also characterized by differential scanning calorimetry (DSC). DSC scans were run under

nitrogen on a DuPont 951 instrument or on a TA Instruments DSC Q1000, using sample weights

of- 4 mg.

2.2 Electrochemical Methods

2.2.1 Introduction

Electrochemistry is an important tool in the field of conjugated polymers for having an

idea of a monomer's ability to polymerize (the lower the oxidation potential, the easier it is to

oxidatively polymerize the monomer) and for determining the resultant polymer's redox and

electronic properties. From the onsets of oxidation and reduction potentials, the HOMO and

LUMO levels of a polymer can be estimated. This is usually accomplished by cyclic

voltammetry (CV) or differential pulse voltammetry (DPV). Since all electrochemical

measurements reported in this dissertation will be referenced86 versus Fc/Fc the conversion to

the HOMO and LUMO energies was accomplished by adding 5.1 eV to the onsets of oxidation

and reduction of the polymer respectively (assuming that Fc/Fc+ is at 5.1 eV below the vacuum

level).27

2.2.2 Electrochemical Set-Up

Electrochemistry was performed using a three-electrode cell with a platinum (Pt) wire or a

Pt flag as the counter electrode, a silver wire pseudo-reference electrode calibrated using a 5 mM

solution of Fc/Fc+ in 0.1 M electrolyte solution, and a platinum (or gold) button (0.02 cm2) or

ITO coated glass slide (7 x 50 x 0.7 mm, 5-15 Q) as the working electrode. The ITO electrodes

were purchased from Delta Technologies, Ltd. Characterization of the polymer films was

performed in 0.1 M electrolyte solution. An EG&G Princeton Applied Research Model 273

potentiostat was used under the control Corrware II software from Scribner and Associates. The

electrolyte solutions were prepared from tetrabutylammonium perchlorate (TBAP) or









tetrabutylammonium hexafluorophosphate (TBAPF6) electrolytes dissolved in freshly distilled

acetonitrile (ACN), methylene chloride (CH2C12), or propylene carbonate (PC). The experiments

were performed under an argon blanket.

For electrochemical analysis, the polymers were either electrodeposited onto the working

electrodes, or synthesized chemically and deposited by drop-casting or spray-casting from

3-10 mg mL-1 chloroform or toluene solutions. The electrodeposition was accomplished either

by repeated scanning or by holding the potential of the working electrode near the monomer's

oxidation peak (previously determined by CV) in a 10 mM monomer solution. The

electrodeposited polymer films were rinsed with the solvent used in the electrolyte preparation

and in which films are not soluble. Cyclic voltammograms or differential pulse voltammograms

were recorded after breaking in the polymer film with about 10 CV cycles for getting

reproducible results.

2.2.3 CV/DPV

The principles of CV have been extensively developed in dissertations from J. A. Irvin and

C. A. Thomas.23'83 In CV, we measure the current created at the working electrode when the

potential is linearly cycled from a starting potential to a final potential and back to the starting

potential. In polymer electrochemistry,79 the polymer is adhered to the electrode and charge

transfer occurs by hopping (Figure 2-1). If the polymer is well adhered to the electrode, the peak

current will increase linearly as function of the scan rate.85 In the case of reversible systems and

if the rate of reaction of the adsorbed species is much greater than of species in solution

(situation mostly encountered in our labs), the peak current can be expressed as shown in

Equation 2-1.

iP = -n 2F2vAF /(4RT) Equation (2-1)









with n the number of electrons, A the electrode area (in cm2), Fo,i the surface concentration of

adsorbed 0 (in mol cm-2) before the experiment begins, v the scan rate (in V/s), and F Faradays

constant (96,485 C mol-1). For such systems, the anodic wave on scan reversal is the mirror

image of the cathodic wave reflected across the potential axis and Ep & E1/2, and the curve i = f(E)

is totally symmetrical if hopping faster than v ( same charge before and after peak). But in

reality, inhomogeneity of film, charge transport, structural and resistive changes in the film, fast

scan rate compared to hopping, and differences in adsorption strength of 0 and R give rise to

asymmetry.

Electrode Adsorbed polymer Solution



diffusion
A-- A-


diffusion
C+ C+ C+ C+

Charge transfer by hoping

Figure 2-1. Charge transport by hopping in polymer adsorbed to the electrode. Electron injection
into the film results in the reduction of 0 to R and the entry (or expulsion) of
counterions (A- or C+).

In DPV,79'83'87'88 the potential is pulsed and each pulse has a certain amplitude (between 10-

100 mV) as illustrated in Figure 2-2. After each pulse the potential returns to a value slightly

higher than prior to the pulse (step size usually between 1-2 mV), which gives a staircase shape.

The current is measured just prior to application of the pulse and at the end of the pulse and the

difference between the two currents is plotted as a function of the base potential. The duration of

the pulse (step time) usually varies between 5-20 ms. Longer step times allow more time for the









current to decay, and consequently a smaller difference in the sampled currents and a higher

sensitivity. For a reversible system, the peak potential is about the same on the forward and

reverse scans and corresponds to E1/2. With increasing irreversibility, Ep moves away from E1/2 at

the same time that peak width increases and its height diminishes. It is important to note that

when doing DPV measurements on a polymer, the calibration of the pseudo reference silver wire

has to be done by DPV.

Differential Pulse Waveform
Final Potential (E) --------------------------------------------------------------------
Difference current (8i) = i2-il




Step Height
Amplitude
Initial Potential -------- I ------------------------- -- -------------------------


il i2 8i








E
Step time

Figure 2-2. Differential pulse waveform. In DPV, the potential is pulsed and the current is
measured just prior to application of the pulse (ii) and at the end of the applied pulse
(i2). The difference between the two currents (6i) is plotted as a function of the base
potential.

The advantage of using DPV over CV is that the major component of the current difference

measured is the faradaic current, which flows due to an oxidation or reduction at the electrode

surface. The capacitive or charging current component, due to electrical charging of the electrode

double layer, is largely eliminated. This renders the peaks more symmetrical and increases the









signal to noise ratio compared to the CV method. Consequently, the onsets of oxidation and

reduction are more defined, as will be the HOMO and LUMO levels.

2.3 Optical and Spectroscopic Methods

Analysis of a conjugated polymer's interaction with light is essential for evaluating the

polymer's potential in optoelectronic applications. This interaction can vary depending on the

polymer's conformation, and consequently it is usually evaluated in the solid state and in

solution (in good and bad solvents), and at various temperatures, by UV-Vis-nIR absorption or

emission measurements, and studies of color switching upon doping.

2.3.1 Absorption Spectra and Molar Absorptivities

Measurement of the UV-Vis absorption of a polymer solution is a basic spectroscopic

method rich with information. A comparison between the absorption spectra of a polymer

solution and its monomer solution will tell if the polymerization took place. Indeed, in a

polymer, the increased degree of conjugation will induce a red-shift of the absorption maximum.

Also, by recording the absorption spectra of polymer chains of different lengths, using a GPC

equipped with a photodiode-array detector, it is possible to determine the minimum chain length

necessary to obtain optimum optical properties. A polymer's extinction coefficient, extracted

from the absorption maxima of three polymer solutions of different concentrations, will bring

information on how efficiently a polymer absorbs light, which is of particular importance for

application in solar cells. Finally, the UV-Vis absorption of polymer solutions gives information

on how well a polymer is solvated in specific solvents, and this will be discussed below in the

solvatochromic section. Absorption spectra were obtained using a Varian Cary 500 Scan

UV-vis-nlR spectrophotometer and quartz crystal cells (1 cm x 1 cm x 5.5 cm, Starna Cells,

Inc.).









2.3.2 Solvatochromism/Thermochromism

The term solvatochromism is used to describe the change in position and sometimes

intensity of a UV-Vis absorption spectrum following a change in polarity of the solvent in which

the polymer is dissolved. A change of the UV-Vis absorption spectrum upon a temperature

change is called thermochromism,89'90 and upon the addition of ions89'91 is called ionochromism.

In all three cases, chromism is induced by a conformational change of the conjugated backbone

driven by both intrachain steric hindrance and interchain interactions (attractive interactions, X-K

interactions, excitons, etc.) that accompany the formation (or disruption) of small aggregates.92

The conformational change leads to a modification of the effective conjugation length, which

induces optical shifts in the UV-Vis absorption spectra of conjugated polymers. A planarization

of the polymer backbone always leads to a red-shift of the absorption, but the direction of the

shift caused by aggregation depends on the details of the molecular packing. Also, polymer

backbone planarity usually causes "fine structure" or shoulders to appear on the main 7t-7t*

absorption peak. Disordered polymers have a great number of different, but similar energetic

states (due to their conformational freedom) and therefore usually have broad UV-Vis spectra.

However a fixing of the molecular conformation through planarization leads to a decrease of the

number of energetic states, allowing the fine vibronic structures to be resolved as additional

peaks or shoulders.

Specifically, in solvatochromic studies, going from a "good" solvent to a more poorly

solvating solvent will induce aggregation and more delocalized assemblies, and create a red-shift

of the absorption spectrum.93 A "good" solvent is assumed to disrupt the conjugation upon side-

chain disordering and twisting of the backbone, and to affect the effective conjugation length.

This phenomenon has been observed for a variety of polythiophene derivatives. For instance, the









absorption of poly(1,4-(2,5-dialkoxyphenylene)-2,5-thiophene) shifts from 468 nm to 495 nm

upon decreasing the quality of the solvent.93 Solvatochromic studies are an important tool for

selecting the solvents best suited for dissolving the selected polymers, which might be helpful for

optimum polymer characterization and device preparation. In thermochromism, it is heating

which is either assumed to disrupt the conjugation and create disorder, or to break the aggregates

and isolate the polymer chains.57 Polymers exhibiting solvatochromic or thermochromic

properties have the potential of being applied in sensors or smart materials.94

For the solvatochromic study, the same experimental set up as for the absorption

experiments described in the above section was employed. It was accomplished by first

dissolving the polymer in a good solvent and then progressively adding a poor solvent, while

maintaining a constant polymer concentration. A constant concentration was maintained using

the following procedure (Figure 2-3): a polymer solution of known concentration was prepared

in the "good solvent". Then equal volumes of that solution were poured into a couple of

graduated flasks, and the flasks were filled up to the same maximum with different volumes of
"good" solvent and "poor" solvent.

The spectral changes which occurred upon heating could not be recorded with the UV-Vis-

nIR spectrophotometer because the temperature needed to observe thermochromism was too

high (however pictures of the color changes were taken and reported).

2.3.3 Photoluminescence Spectra and Fluorescence Quantum Efficiencies

The luminescence properties of conjugated polymers are of considerable interest because

of their potential applications as the emissive materials in LEDs. A useful figure is the

photoluminescence (PL) quantum yield (P), defined as the number of photons emitted in

photoluminescence per absorbed photon. It is easily measured by a synthetic chemist for polymer

solutions, and allows making a first selection of polymers which might have a potential in LEDs.










Measurements of P on thin-film solids are more representative but not as straightforward;95'96

they were accomplished in this work by Dr. J. Mwaura. The PL quantum yield of a polymer

solution is much higher than D of polymer thin-films coated from the same solution. This is due

to the formation of less emissive interchain species which quenches the fluorescence in the solid

state. PL quantum yields are determined using the comparative method of Williams et al. which

involves the use of well characterized standard samples with known D values.97 The standard

must be chosen such that its excitation wavelength is found at a slightly lower value than the

absorption maximum of the polymer solution. The absorption values of the polymer and standard

solutions should not exceed 0.1 at the excitation wavelength (in 10 mm fluorescence cuvettes) in

order to avoid self-absorption.98 The PL quantum yield of a polymer solution is calculated

according to Equation 2-2, where the subscript R refers to the standard (or reference) and A is

the absorbance of the solution, E is the integrated emission area across the band and rj is the

refractive index of the solution.

(-10 AR) E 72
0 0 = 0 _x-10- ) E x -E R x Equation (2-2)
R 1 -10) ER -2

Step 1 Step 2 Step 3


Complete the flasks
with different volumes
of "good" and "poor"
solvents up to the
same maximum.




Prepare
polymer solution of
Known concentration
in "good solvent" Pour same volume of solution 1 into a few flasks
Solution 1

Figure 2-3. Example of the procedure used to maintain a constant polymer concentration in
flasks containing varying amounts of good and poor solvents.









The photoluminescence spectra of the polymer solutions were registered on a Jobin Yvon

Fluorolog-3 spectrofluorimeter in right-angle mode. Solution quantum efficiency measurements

were carried out using a Spex F-i 12 photon counting fluorimeter, relative to oxazine 1 in ethanol

(PD = 0.11),99 coumarin 6 in ethanol (PD = 0.78),100 or cresyl violet perchlorate in ethanol ((D =

0.54),101 with the optical density of the solution kept below A = 0.1.

2.3.4 Spectroelectrochemistry

Spectroelectrochemical measurements were performed in order to define the optical band

gaps of the polymers and observe their electrochromic behavior. The optical band gap is

determined from the low-energy absorption edge (onset of the 7t-7t* transition) of the neutral

absorption spectrum of the polymer thin-film. The electrochromic behavior is observed by

recording the spectral changes upon oxidation and reduction of the polymer thin-film. The

polymer films were prepared either by spray-casting polymer solutions (5-10 mg mL-1 in

chloroform) onto ITO coated glass using an air brush (Testor Corps) at 12 psi, or by using

electropolymerization as described previously. Characterization of the polymer films was

performed in 0.1 M electrolyte solution using the electrochemical set-up described previously,

with a Pt wire as the counter electrode in order to avoid blocking the incident light. The

absorption spectra were recorded using a Varian Cary 500 Scan UV-vis-nlR spectrophotometer

for bench top experiments or a Stellarnet diode-array Vis-nIR spectrophotometer with fiber-optic

capabilities for dry-box studies.

2.3.5 Colorimetry

Colorimetry measurements are useful to give a quantitative description of the color states

that an electrochromic polymer thin-film can reach as it is oxidized or reduced. Three attributes

are used to describe colors: the hue (dominant wavelength), the saturation (level of white and/or

black), and the luminance (the brightness of the transmitted light). Two color systems were









specifically used in this dissertation to give a quantitative representation of these attributes: the

1931 Yxy and the 1976 L*a*b systems, both established by the Commission Internationale de

l'Eclairage (CIE) (detailed information can be found in the referenced citations). 64,102

In the CIE 1931 Yxy color space, Y represents the luminance, and x and y represent the hue

and saturation. The luminance is usually presented as a percentage relative to the background

luminance, and called "relative luminance". The two-dimensional xy diagram is known as the

chromaticity diagram (illustration in Figure 2-4). It has the shape of a horseshoe, with the

wavelengths of visible light found on the surrounding line, and the shortest and longest

wavelengths being connected by a straight line. Every color is contained in the horseshoe and the

location of a point on the xy diagram gives information on the hue and saturation of the color.

The xy chromaticity diagram is particularly useful to track the color states of a polymer for

different doping levels. The CIE L*a*b* space is more commonly used in industry, with L*

representing the luminance and a* and b* being related to the hue and saturation.

Polymer thin-films were deposited by spray-casting onto ITO coated glass as for the

spectroelectrochemical studies. Colorimetric measurements were obtained with a Minolta CS-

100 Chroma Meter using the electrochemical set-up described previously, with a Pt wire as the

counter electrode. The sample was illuminated from behind with a D50 (5000K) light source in a

light booth designed to exclude external light.





















0.6 ------





S70-770



0 W^ 700 780






0.0 4Z 0.2 0.4 0.6 0.8
x


Figure 2-4. CIE 1931 xy chromaticity diagram. [Modified from Thompson, B. C.; Schottland, P.;
Zong, K.; Reynolds, J. R. Chem. Mater. 2000, 12, 1563-1571].64









CHAPTER 3
WIDE BAND GAP BIS-HETEROCYCLE-PHENYLENE POLYMERS

3.1 Introduction

Thiophene-phenylene based copolymers have been extensively studied for their interesting

electrical and optical properties such as redox electroactivity and electrochromism, reactivity to

chemical sensing, charge transport and light emission.22,24,36,46,50,103-110 In addition, the various

coupling reactions available for heterocycles, and the variety of methods for the polymerization

of thiophene based monomers render them fairly easy to synthesize. Phenylene rings are

particularly convenient to derivatize with variable substituents, and the subsequent

polymerization of thiophene-phenylene monomers yields materials with controllable band gaps

and solubilities.22,46'50 As described in the general Introduction, simply replacing the phenylene

alkyl substituents with alkoxy groups can reduce considerably the band gap due to the electron

donating effect and reduced steric effect brought by the oxygens.22

The regiosymmetric poly(1,4-bis(2-thienyl)-2,5-dialkoxyphenylene)s are particularly

interesting members of that family (Figure 3-1). Their synthesis was originally accomplished by

J. Ruiz et al.22'111 from the catalytic oxidation of bis-thiophene-dialkoxybenzene monomers with

ferric chloride. Low molecular weight materials were obtained (~ 2,000-3,800 g mol-1), and it

was revealed that these polymers showed an X-ray diffraction pattern that indicated a high

crystalline content relative to analogous polymers being unsymmetrically substituted. These

polymers have a band gap only slightly larger than P3HT (2.1 eV vs. 1.9 eV) and based on their

ability to give polymer films with a high degree of order, they are of interest for use in solar

cells.50 A synthetically interesting aspect about these regiosymmetric polymers is their ability to

achieve a high degree of order without having to prepare unsymmetrical monomers (which are









usually more challenging to synthesize), or having to rely on highly controlled polymerization

conditions.

Regiosymmetric poly[1,4-bis(2-(3,4-ethylenedioxy)thienyl)-2,5-dialkoxybenzene]s, illus-

trated in Figure 3-1, can also be found in the literature.46'105 The ethylenedioxy bridge between

the 3- and 4-positions of the thiophene gave access to smaller band gaps (~ 1.7-2.0 eV) than the

ones obtained for their thiophene analogs due to the electron donating effect of the oxygens

atoms of EDOT, as explained earlier. This makes these derivatives also of interest for

photovoltaics, but their synthesis needs to be further investigated for improving their solution

properties and molecular weights, and a study of their ordering properties has to be accomplished

too. Indeed, the derivatives which have been reported have been synthesized either by

electrochemical methods, which do not allow easy characterization, processing, and synthesis of

the polymers in high bulk yields, or by chemical polymerizations, which have led to low

molecular weight materials (4,000 g mol-1 via ferric-chloride-mediated polymerization, and

2,900 g mol-1 via Ullman coupling) with poor film properties.23'46 In addition, the derivatives

prepared by oxidative polymerization with FeCl3 were poorly soluble, and difficult to

characterize and to process, but it could not be determined if this insolubility was the result of

crosslinking through the phenylenes or if it was intrinsic to the molecules.

The chemical synthesis of these regiosymmetric thiophene-phenylene (PBT-B(OR)2) and

EDOT-phenylene polymers (PBEDOT-B(OR)2) has been revisited (section 3.3) in order to

obtain polymers with higher molecular weights than the ones previously reported, while being

able to analyze and process the materials easily for application in soft, and flexible, photovoltaic

and electrochomic devices. The monomer syntheses and characterizations are described in

section 3.2. The redox, spectroelectrochemical, and electrochromic properties of the polymers









have been studied, and the results are detailed in sections 3.4 and 3.5. Application of PBT-

B(OR)2 in photovoltaic devices has been investigated by members of the group and is detailed in

section 3.7.

The work was finalized by the addition of a new member to the regiosymmetric

thienylene-phenylene family. This member contains ProDOT as the thienylene moiety, which

allows taking advantage of its electron donating ability and of its easy derivatization. This type

of molecule was targeted in order to improve the solubility and processability of the thienylene-

phenylene polymer family. In particular, we report here the synthesis of methyl substituted

(R = Me) and hexyl (R = Hex) substituted poly[1,4-bis[2-(3,4-propylenedioxythienyl)]-2,5-

didodecyloxybenzene] [PBProDOT-R2-B(OC12H25)2], with the methyl substituted molecule

studied for comparison with the more soluble hexyl derivatized molecule (Figure 3-1). The

monomer syntheses and characterizations are described in section 3.2. Both polymers were

prepared by electropolymerization, and the BProDOT-Hex2-B(OC12H25)2 monomer was also

polymerized by chemical oxidation using ferric chloride to yield a polymer highly soluble in

organic solvents as described in section 3.3. PBProDOT-Hex2-B(OC12H25)2 exhibits interesting

electrochromic and solvatochromic properties, which are reported in sections 3.4, 3.5, and 3.6.

Preliminary investigations utilizing this polymer as an emitter in LEDs, and as a hole transport

layer in solar cells, have been accomplished by Reynolds group members and a brief overview of

the results is included in section 3.7.

3.2 Monomer Syntheses and Characterizations

It was decided to synthesize the regiosymmetric PBT-B(OR)2, PBEDOT-B(OR)2, and

PBProDOT-R2-B(OC12H25)2 from the corresponding symmetrical bis-thienylene-

dialkoxybenzene monomers (from their dibrominated version in most cases). The benzenes were

substituted with long and flexible heptoxy and/or dodecyloxy chains to induce solubility.









R R
0 0
O 0 OC1 2H25


RO \ I n RO 0 n H25120 0

R R
PBT-B(OR)2 PBEDOT-B(OR)2 PBProDOT-R2-B(OC12H25)2

Figure 3-1. Targeted thienylene-phenylene polymers.

3.2.1 Bis-thiophene-dialkoxybenzenes

1,4-Dibromo-2,5-dialkoxybenzene was prepared according to the literature by Williamson

etherification of 1,4-dibromo-2,5-dihydroxybenzene with the corresponding alkyl halide.22 The

synthesis of the dibrominated 1,4-bis(2-thienyl)-2,5-diheptoxybenzene (Br2-BT-B(OC7Hi5)2),

and 1,4-bis(2-thienyl)-2,5-didodecyloxybenzene (Br2-BT-B(OC12H25)2) monomers started by

the deprotonation of thiophene with n-butyllithium, and further reaction with trimethylstannyl

chloride to give 2-(trimethylstannyl)thiophene (Th-Sn(CH3)3) as illustrated in Figure 3-2. 1,4-

Bis(2-thienyl)-2,5-dialkoxybenzene (BT-B(OR)2) was obtained by the Stille coupling of 1,4-

dibromo-2,5-dialkoxybenzene with Th-Sn(CH3)3. There is significant literature precedent for the

preparation of this type of molecule via Negishi coupling instead.22'50'103'104 However, Stille

coupling was chosen because it allows isolating, purifying, characterizing, and storing Th-

Sn(CH3)3. Finally, the Br2-BT-B(OR)2 monomers were prepared by bromination of BT-B(OR)2

with N-bromosuccinimide (NBS). Yellow needles were obtained after purification by

recrystallization (72% and 86% yields for R = C7H15 and R = C12H25, respectively).

The monomers were fully characterized by 'H-NMR, 13C-NMR, HRMS, elemental

analysis, melting point determination, and UV-Vis spectroscopy. They both exhibit an absorption

maximum at 376 nm (Figure 3-14), and extinction coefficients of 37,600 M-1 cm-1 for Br2-BT-

B(OC7H15)2 and of 27,160 M-1 cm1 for Br2-BT-B(OC12H25)2.









S nBuLi/THF S Li Sn(CH3)3C0, Sn(CH3)3

-78 -78 to room temperature
77%
RO
2 S Sn(CH3)3 RO Br Pd(PPh3)4 / DMF S
2 +- I,
Br OR 1100
Stille Coupling OR
~ 80%
OR
ft \ S 2.1 eq NBS, 0 to room temperature O \ .OR
I DMF Br S Br
RO 72% for R = C7H15 RO'' \
86% for R = C12H25
BT-B(OR)2 Br2-BT-B(OR)2

Figure 3-2. Bis-thiophene-dialkoxybenzene monomer synthesis.

Crystals of Br2-BT-B(OC7Hi5)2 were grown by slow diffusion of ethanol into a vial

containing a xylene solution of the monomer. Figure 3-3a shows the molecular structure of the

monomer, while Figure 3-3b shows the packing mode of the material as well as the crystalline

unit (obtained by single crystal X-ray diffraction studies). Br2-BT-B(OC7H15)2 crystallizes in the

monoclinic space group C2/c with the alkoxy chains and phenyl rings being coplanar. As

illustrated in Figure 3-3c, the molecules have a relatively small dihedral angle of 20.8 between

the central phenylene and thiophene rings, which allows efficient stacking of adjacent molecules

with a good cofacial arrangement and an interchain distance of 5.79 A. The intermolecular

distance is a very important parameter for application of organic materials to devices requiring

high carrier mobility. Small distances are necessary for strong intermolecular overlap of the K7-

atomic orbitals and charge transfer by hopping.112 Materials such as thiophene oligomers or

P3HT are of high interest because they exhibit small interchain distances (in the order of 3.8 A

for P3HT).113 The 5.79 A interchain value found for Br2-BT-B(OC7H15)2 would not be great if

extended to the polymer. Br2-BT-B(OC12H25)2 crystals were not of sufficient size for single-

crystal structure analysis.







































C

Figure 3-3. Single crystals X-ray analysis of Br2-BT-B(OC7H13)2. (a) Molecular structure,
(b) packing mode, (c) Side view.

3.2.2 Bis-EDOT-dialkoxybenzenes

The synthesis of 1,4-bis[2-(5-bromo-3,4-ethylenedioxy)thienyl]-2,5-diheptoxybenzene

[Br2-BEDOT-B(OC7H15)2], and of 1,4-bis[2-(5-bromo-3,4-ethylenedioxy)thienyl]-2,5-didodecyl-

oxybenzene [Br2-BEDOT-B(OC12H25)2] monomers started by the deprotonation of EDOT with

n-butyllithium, and further reaction with trimethylstannyl chloride to give 2-trimethyltin-3,4-

ethylenedioxythiophene (EDOT-Sn(CH3)3) as illustrated in Figure 3-4. 1,4-Bis[2-(3,4-

ethylenedioxy)thienyl]-2,5-dialkoxybenzene (BEDOT-B(OR)2) was obtained by Stille coupling









of 1,4-dibromo-2,5-dialkoxybenzene with EDOT-Sn(CH3)3. As for the thiophene derivatives, the

Stille route was chosen over the Negishi coupling previously reported for these molecules,46

because of the possibility to isolate, purify, and store EDOT-Sn(CH3)3. The monomer precursors

BEDOT-B(OR)2 were obtained in 70-80% yields after purification by recrystallization. Their

bromination was accomplished by addition of NBS in DMF at -780C, followed by progressive

warming of the solution to 0C. This step was particularly challenging as oxidation problems

arose easily. The electron donating power of EDOT considerably decreases the oxidation

potential of BEDOT-B(OR)2 molecules compared to their thiophene counterparts (~ 0.35 V vs

Fc/Fc+ for 1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-diheptoxybenzene46 versus 0.55 V for 1,4-

bis(2-thienyl)-2,5-diheptoxybenzene50), making them more sensitive to oxidation.23 Attempts in

THF from -780C to 0C, led to black insoluble tars, probably resulting from the formation of

oxidized polymer. The use of DMF at low temperatures allowed milder oxidative conditions and

successful bromination.114 The reaction was stopped by addition of a solution of ammonium

hydroxide, which reduced the crude product, and quenched unreacted NBS and the hydrogen

bromide released.115 For purification, a combination of flash column chromatography on silica

gel and of repeated recrystallizations was needed, in order to isolate the dibrominated monomer

from its monobrominated version. Also a fast solvent flow was required for the column

chromatography otherwise the monomers polymerized on the silica gel. Indeed, when slow

elution was used, no monomer could be extracted from the column. Instead, an orange-pink

material, highly fluorescent under UV light, was recovered after dumping the contents of the

column in a beaker containing hydrazine and removing the silica gel by filtration. A toluene

solution of that material was analyzed by UV-Vis spectroscopy and an absorption maximum of

455 nm was determined in the case of Br2-BEDOT-B(OC7Hi5)2, which provides evidence that










some coupling occurred (the absorption maxima of the monomer are at 376 nm and 398 nm).

The monomers were obtained in 40% and 57% yields for Br2-BEDOT-B(OC7Hi5)2 and Br2-

BEDOT-B(OC12H25)2, respectively.

S n-BuLi / THF S Li Sn(CH3)3CI SSn(CH3)3

O O -78C O 0 -78C O 0
/ 74%

0 0
S Sn(CH3)3 Br Pd(PPh3)4 / DMF RO S R/
2 o+ RO OR 11OR s S
Br' Stille Coupling OR
70-80% 0 0

O 0 0 0
O/r\ OR 2.2 eq NBS, -78oC to 0C slowly, 4h O OR
S DMF Br S S Br
RO "' 42% for R = C7H1 RO
0 0 57% for R = C12H25 O 0

BEDOT-B(OR)2 Br2-BEDOT-B(OR)2

Figure 3-4. Bis-EDOT-dialkoxybenzene monomer synthesis.

The monomers were fully characterized by H-NMR, 3C-NMR, HRMS, elemental

analysis, melting point determination, and single crystal X-ray studies. For X-ray analysis, the

crystals of Br2-BEDOT-B(OC12H25)2 were grown from a methanol/THF mixture (1/1) and the

crystals of Br2-BEDOT-B(OC7H15)2 from an ethanol/THF mixture (3/1). Figure 3-5a shows the

molecular structure of Br2-BEDOT-B(OC7H15)2, while Figure 3-5b shows its packing mode. Br2-

BEDOT-B(OC7H15)2 crystallizes in the monoclinic space group P2(1)/n with the alkoxy chains

and phenyl rings being coplanar. The dihedral angle between the central phenylene and EDOT

rings is very small (6.10), which renders the molecules almost planar. This quasi-planarity helps

the molecules pack close to one another with a small interchain distance of 3.7 A. Molecular

planarity is a desirable feature since less energy is required to stabilize the bipolaron state upon









polymer oxidation. Figure 3-6a shows the molecular structure of Br2-BEDOT-B(OC12H25)2, and

Figure 3-6b shows its packing mode. Br2-BEDOT-B(OC12H25)2 crystallizes in the monoclinic

space group C2/c with the alkoxy chains and phenyl rings being also coplanar. The dihedral angle

between the central phenylene and EDOT rings is even smaller than the one found for Br2-

BEDOT-B(OC7H15)2 (1.70) and this extremely small deviation from planarity, illustrated in

Figure 3-6c, gives rise to closer 7t-stacking with an interchain distance of 3.5 A. We noticed that

the cofacial arrangement is not as great as what was observed for Br2-BT-B(OC7Hi5)2. The tight

packing observed for the Br2-BEDOT-B(OR)2 monomers particularly motivates the development

of oligomeric or polymeric derivatives of these molecules, where a possible extension of these

properties would lead to materials with high charge mobility.

3.2.3 Bis-ProDOT-dialkoxybenzenes

The monomers BProDOT-Me2-B(OC12H25)2 and BProDOT-Hex2-B(OC12H25)2 were

synthesized from 1,4-dibromo-2,5-didodecyloxybenzene and the corresponding substituted

ProDOT unit by Negishi coupling. The substituted ProDOT derivatives were synthesized by

transetherification of 3,4-dimethoxythiophene and the dialkyl-substituted propane-1,3-diols as

previously reported (Figure 3-7).34 The synthesis of 3,4-dimethoxythiophene was accomplished

using the synthetic route shown in Figure 3-7. It started with the tetrabromination of thiophene

followed by debromination of the 2 and 5 positions of the thiophene ring with zinc dust in glacial

acetic acid.116 Ullman type coupling between sodium methoxide and 3,4-dibromothiophene in

the presence of copper oxide (CuO) afforded 3,4-dimethoxythiophene.117 The ProDOT

derivatives were lithiated with one equivalent of n-butyllithium and reacted with anhydrous zinc

chloride (ZnC12) (Figure 3-8). Coupling with 1,4-dibromo-2,5-didodecyloxybenzene was first

attempted using tetrakis(triphenylphosphine) palladium (0) [Pd(PPh3)4] as the catalyst, as









previously reported for EDOT and thiophene derivatives,22,46 but was limited possibly by

unfavorable steric interactions between the heterocycles. However, the Negishi coupling was

more successful using a different catalyst system made of commercially available Pd(0)2(dba)3

and tri-t-butylphosphine ligands [P(t-Bu)3] which has been proven very efficient for coupling

sterically demanding molecules.118 Both monomers were obtained in decent yields (ca. 40 %)

after purification by column chromatography, and were characterized by UV-Vis, 1H-NMR, 13C-

NMR, melting point determination, elemental analysis, and HRMS. As expected, the monomer

containing long and flexible hexyl chains on the ProDOT unit melts at a lower temperature (45-

46C) than the methyl substituted monomer (80-82C). BProDOT-Me2-B(OC12H25)2 and

BProDOT-Hex2-B(OC12H25)2 exhibit similar absorption maxima in toluene at 354 nm and 356

nm respectively, with extinction coefficients of 16,430 M-1 cm-1 for the former and of 15,640 M-

cm-1 for the latter. Replacement of the methyl groups by the longer hexyl chains on ProDOT does

not lead to any observable change in the monomer's optical properties.

Suitable crystals for an X-ray diffraction study of BProDOT-Me2-B(OC12H25)2 were

obtained by slow cooling recrystallization from a hexanes/ethyl acetate mixture (5/1 ratio).

BProDOT-Me2-B(OC12H25)2 crystallizes in the triclinic P-I space group. The molecular structure

is shown in Figure 3-9a and the packing mode in Figures 3-9b and 3-9c. The molecules, which

are located on inversion centers, are nearly planar with a dihedral angle of 6.6 between the

central phenyl and thiophene rings. The molecules stack with a close to perfect cofacial

arrangement with a small interchain distance of 3.679 A as evident in Figure 3-9c. If extended to

the polymers (or oligomers), these two features would greatly favor inter-chain transport.

BProDOT-Hex2-B(OC12H25)2 crystals were not of sufficient size for single-crystal structure

analysis.






















a
















b


Figure 3-5. Single crystals X-ray analysis of Br2-BEDOT-B(OC7H13)2. (a) Molecular structure,
(b) packing mode.

3.3 Polymer Syntheses and Characterizations

3.3.1 Polymerization Attempts via GriM

As described in the general Introduction, GriM has been used by Wang et al. for the

preparation of the electron rich poly[(3,4-ethylenedioxythiophene)-2,5-didodecyloxybenzene]

(LPEB), whose repeat unit structure is similar to the molecules studied in this report (Figure 3-

10).36 This polymer was synthesized at high molecular weights (- 30,000 g mo1-) with a low

polydispersity of 1.30.




























a V







C




















b


Figure 3-6. Single crystals X-ray analysis of Br2-BEDOT-B(OC12H25)2. (a) Molecular structure,
(b) packing mode, (c) quasi-planar arrangement of adjacent Br2-BEDOT-
B(OC12H25)2 molecules.










5 Br2
CHC13
43%


NaOMe
KI, MeOH
CuO
44%


Br Br

Br S Br


MeO MeO

S


2.2 eq Zn
AcOH
63%


pTSA, toluene

HO -X'\OH
4A sieves, reflux
4A sieves, reflux


R = hexyl 83% yield
R= Me 79%yield

Figure 3-7. Synthesis of methyl- and hexyl-substituted ProDOTs.


R R




R = Hexyl, Me

R = Hexyl, Me


1) n-BuLi

2) ZnCl2

3) Pd2(dba)3/P(t-Bu)3 (1:2 ratio)
Br -OC12H25
I THF/NMP (1:1)
H25012O Br


R R

0 0 0
0 \0


H25C120

~ 40%
BProDOT-R2-B(OC12H25)2


NBS

DMF

-78C to room T
5 hours


R 'O R

0 o0
0 0

Br Br
C012H250


Br2-BProDOT-R2-B(OC12H25)2
R = Hexyl 81%
R = Me 64%

Figure 3-8. Synthesis of BProDOT-R2-dialkoxyphenylene and Br2-BProDOT-R2-
dialkoxyphenylene monomers.


Br Br




RR

0 0
S






































b


Figure 3-9. Single crystals X-ray analysis of BProDOT-Me2-B(OC12H25)2. (a) Molecular
structure, (b) packing mode, (c) 7t-stacking of BProDOT-Me2-B(OC12H25)2
illustrated without the phenylene side chains (OC12H25).

o o
SC012H25

C12H250 n
LPEB

Figure 3-10. Structure of LPEB.

It was decided to attempt the same conditions as the ones used by Wang et al. to

polymerize the dibromo-thienylene-phenylene monomers (Br2-BT-B(OR)2, Br2-BEDOT-

B(OR)2, and Br2-BProDOT-R2-B(OC12H25)2), as illustrated in Figure 3-11. The monomers were

treated with methylmagnesium bromide (MeMgBr) at reflux, and then Ni(dppp)C12 was added









for coupling the bromomagnesio intermediates. Unfortunately, no polymer was formed, and in

all cases the monomers were recovered in ~ 90% yields after work up. In order to check if the

metalation of the thienyl bromide occurred, the bromomagnesio intermediates were quenched

with deionized water. This method had been used by Wang et al. in their work on LPEB for

proving that the metalation was occurring at the bromo-EDOT site. In our case, no thiophene

protons were observed proving that the metalation did not take place. The Grignard reagent

MeMgBr was switched for the less stable and more reactive t-butyl magnesium chloride, but the

reaction failed again. One explanation could be that the three ring symmetrical system does not

provide enough reactivity to the aryl-Br sites. Another explanation could be that with the

addition of an extra heterocycle the system has become too electron rich to allow metalation of

the bromo-aryl site. It had been reported that extremely limited lithiation of BEDOT-B(OR)2

could be accomplished after addition of n-BuLi or sec-BuLi, due to the too strong electron

donating power of the molecules, and this example supports the second explanation.23 There is

very little literature precedent on the polymerization via GriM of multiple ring systems, and

consequently it is difficult to give a definitive explanation for the failure encountered here.



/\ OR OR
Br S S Br 1. MeMgBr, THF, reflux 1h Br S MgBr
RO .RO /
0 0 0 0

O OR
2. Ni(dppp)Cl2, reflux 20h / \ OR
R \s

O 0


Figure 3-11. GriM route for the polymerization of the dibromo-thienylene-phenylene monomers.









3.3.2 Polymerization via Yamamoto Coupling

3.3.2.1 Poly(bis-thiophene-dialkoxybenzene)s

The polymerization of the Br2-BT-B(OR)2 monomers has been carried out via Yamamoto

coupling according to the synthetic route shown in Figure 3-12. The zerovalent nickel reagent,

Ni(COD)2, was mixed with 1,5-cyclooctadiene (COD), a molar equivalent of 2,2'-bipyridyl

(Bpy), and DMF at 60 C, and this mixture was added dropwise to the DMF monomer solution.

The solution color changed from yellow to dark red and the red polymers precipitated out of the

solution. The polymers were purified by Soxhlet extraction with methanol followed by hexanes,

to remove unreacted monomer, inorganic impurities, and low molecular weight polymer. Final

extraction with toluene afforded red solids in 55% yield for PBT-B(OC7H15)2 and 40 % yield for

PBT-B(OC12H25)2 after solvent evaporation. These materials exhibit a solubility of about 7 mg

mL-1 in toluene.

/Br OR Ni(COD)2, COD, Bpy O
Br _S_" s Br IN -'- S S
RO "--' DMF, 60C, 24 to 42h RO
R = C7H15 55%
R = C12H25 40%

Figure 3-12. Polymerization of Br2-BT-B(OR)2 monomers via Yamamoto coupling.

The polymers were characterized by 1H-NMR, GPC, MALDI, and elemental analysis. The

results of the molecular weight (MW) analysis performed by GPC (polystyrene standards, THF

as mobile phase, 400C) are summarized in Table 3-1. Number average molecular weights of-

5,000 g mol-1 and of- 3,000 g mol-1 were estimated for PBT-B(OC7H15)2 and PBT-B(OC12H25)2,

respectively, which correspond to polymers of about 17 to 29 rings. The low polydispersity

(1.30) is explained by the Soxhlet extraction with hexanes which removed the low molecular

weight material. The low molecular weights may be explained by the electron donating-ability of

the system, which as the molecular weight increased, deactivated more and more the bromo-









thiophene reactive sites and rendered the oxidative addition of the Ni(0) complex more difficult.

The decrease in solubility, observed as the polymer chains were getting bigger (the polymers

were precipitating out of the solution), could have stopped the coupling process too. For

improving the solubility, the polymerization has also been attempted in mixtures of DMF and

toluene (1/2), but higher molecular weights could not be reached.

Table 3-1. GPC estimated molecular weights of the PBT-B(OR)2 polymers (polystyrene
standards, THF as mobile phase, 400C).
Mn Mw Average number
Polymers (g mol ) (g mol ) PD of rings
PBT-B(OC7H15)2 4,960 6,340 1.3 29

PBT-B(OC12H25)2 2,945 3,950 1.3 17


As structure proof, the polymers were characterized by MALDI-MS using a terthiophene

matrix. The MALDI spectra are displayed in Figure 3-13 and show that the spacing between the

peaks corresponds to ~ 468 amu for PBT-B(OC7H15)2, and to ~ 609 amu for PBT-B(OC12H25)2,

which correlates well with the calculated molecular weights of the repeat units (n) of the

polymers. The different series in the MALDI spectra show that there is a variety of end-groups:

H/H, H/Br, Br/Br. A predominance of H/H end groups over H/Br or Br/Br end-groups at low

molecular weights could have explained why a large degree of polymerization could not be

reached. However a comparison between the peak intensities shows that there seems to be no

preference for one type of end-group over the other. This comforts us in our assumption that

solubility and electron density are the most probable parameters limiting the growing of the

polymer chains.

Figure 3-14 shows the solution UV-Vis absorbance of the polymers in toluene. The

solutions are orange (photograph in Figure 3-14), and the absorption maxima are found at 469

nm for PBT-B(OC7H15)2, and at 463 nm for PBT-B(OC12H25)2. Figure 3-14 also shows the UV-











Vis absorbance of the monomers, which is blue-shifted compared to the UV-Vis absorption of

the polymers due to the lower degree of conjugation.


n=4
150- n= 5

468
100-
-n
n=6 n=7
< 50 468
4 468


1800 2100 2400 2700 3000 3300


m/z


Figure 3-13. MALDI-MS of BT-B(OR)2 polymers. (a) PBT-B(OC7H15)2, (b) PBT-B(OC12H25)2.
Terthiophene was used as the matrix.


400 500 600
Wavelength (nm)


700 800


Figure 3-14. Solution UV-Vis absorbance of Br2-BT-B(OR)2 monomers, and PBT-B(OR)2
polymers in toluene.

The ordering properties of the polymers were studied by DSC as illustrated by the second

DSC scans displayed in Figures 3-15a and 3-15b. The symmetrically derivatized polymers

exhibited two endothermic transitions and one exothermic transition. The first endothermic









transition (Tmi), observed at -390C for PBT-B(OC7H15)2 and at -410C and PBT-B(OC12H25)2, has

been attributed to the melting of the side chains. Previous ordering studies done by the Reynolds

group on this type of molecule (synthesized via FeCl3) have shown that the highest transition

(Tm2) can be attributed to an isotropic melt of the polymer backbone, and the first exothermic

transition (Toi) to their crystallization.22 The melting temperature Tm2 was lower for PBT-

B(OC12H25)2 (1340C) than for PBT-B(OC7H15)2 (1900C), probably due to the molecular weight

differences. These DSC results confirmed the semicrystalline nature of the polymers.

The thermal stability of the polymers was studied by TGA both in air and in a nitrogen

atmosphere using a 200C min- temperature ramp from 500C to 9000C. The thermograms

displayed in Figure 3-16 show that the polymers exhibit a high thermal stability, losing less than

5% weight in air at 3350C for PBT-B(OC7Hl5)2, and at 3220C for PBT-B(OC12H25)2. A similar

behavior was observed under nitrogen, with a loss of less than 5% weight at 3520C for PBT-

B(OC7H15)2, and at 3230C for PBT-B(OC12H25)2. A drastic degradation process occurred from

these temperatures up to ~ 6500C for PBT-B(OC7H15)2, and up to ~ 7500C PBT-B(OC12H25)2.

Above 8500C, less than 7% of PBT-B(OC12H25)2 and less than 15% of PBT-B(OC7H15)2

remained.

3.3.2.2 Poly(bis-alkylenedioxythiophene-dialkoxybenzene)s

The polymerizations of the Br2-BEDOT-B(OR)2 and Br2-BProDOT-R2-B(OC12H25)2

monomers have also been carried out via Yamamoto coupling using the same conditions as those

employed for PBT-B(OR)2. Unfortunately, a maximum of 3 repeat units for PBEDOT-

B(OC12H25)2 (Mn = 1,792, Mw = 2,497, DPI = 1.40) and of 4 repeat units for PBProDOT-R2-

B(OC12H25)2 [PBProDOT-Me2-B(OC12H25)2 : Mn = 3,394, Mw = 6,119, PDI = 1.80; PBProDOT-

Hex2-B(OC12H25)2: Mn = 1,859, Mw = 2,525, PDI = 1.36] were coupled. Even though the size of

the PBEDOT-B(OC12H25)2 oligomers was small, the material was difficult to solubilize.










According to the work previously reported on these types of molecules,46 and the work presented

in this dissertation, it is clear that these PBEDOT-B(OC12H25)2 molecules are likely not the best

candidates for the production of highly processable films for optoelectronic devices. It was

consequently decided to stop further synthetic work on them. However, the solubility and

processing expectations were quite good for PBProDOT-R2-B(OC12H25)2, and it was decided to

continue investigating other synthetic pathways and to study more deeply their electronic

properties.


a b
50- .Tm2 60"- Tm2
45- 190o ^ C

0 Tm1 50- 134*C
35- .39oC
E 30- Tm"
25- 154C 40-
441 1174

I 20- Tc1
15- 30-
-50 6 50' 100 150 200 -50 6 50o 100 150 200
TemperatureoC Temperature (C)





Figure 3-15. DSC thermograms (second scans) of PBT-B(OR)2 polymers. (a) PBT-B(OC7Hi5)2,
and (b) PBT-B(OC12H25)2. The temperature was cycled between -80C and 200C
at 10C min-1.

3.3.3 Solid State Polymerization Attempts

It was hypothesized that a solid state polymerization, following the same process as the

one discovered for the spontaneous polymerization of Br2-EDOT, could happen for the dibromo-

thienylene-phenylene monomers (as detailed in the general introduction).41 Crystals of Br2-

BEDOT-B(OC7Hi5)2 were progressively heated for 2 days up to 150C, and then from 150C to

180C, in a sublimation apparatus under vacuum, in order to prepare a polymer film on a glass









substrate in situ (Figure 3-17). No sublimation occurred and as the temperature was increased,

the crystals became darker and finally melted into a black gum once the melting temperature was

reached. Once cold, this black insoluble material looked like charcoal and was extremely friable.

It was stirred overnight in a mixture of ACN and hydrazine monohydrate, then filtered and

washed with neat ACN. No color change occurred upon addition of hydrazine and the material

could not be dissolved in organic solvents. It also did not show any conductivity after being

doped with iodine, and it was finally deduced that this material was probably the result of

degradation, not polymerization.



100-

80-

S60 PBT-B(OC7H15)2 N2
PBT-B(OC12H25)2 -air
40- ^ PBT-B(OC12H25)2 N2
20- PBT-B(OC7H15)2 air


0-
200 400 600 800
Temperature (C)


Figure 3-16. Thermogravimetric analysis of the PBT-B(OR)2 polymers. Measurements
performed both in air and in a nitrogen atmosphere, using a 200C min-1
temperature ramp from 500C to 9000C.

Before pursuing further experiments, it was decided to first examine the bromine distances

in the Br2-BEDOT-B(OC7H15)2 crystal structure. The smallest bromine distance found between

adjacent molecules in the same row, represented by a dashed line in Figure 3-18, had a value of

5.38 A (7.54A between bromines on facing rings), bigger than the sum of the van der Waals

radii. These distances were even bigger for Br2-BEDOT-B(OC12H25)2 (10.64 A in the same row,

and 7.76 A between facing rings) and Br2-BT-B(OC7H15)2 (10.16 A in the same row and 5.79 A









between facing rings), and it was deduced that further investigation on the solid state

polymerization of these molecules would not likely give a successful polymerization.


OC7H15 O Vacuum

Br S Br, Sublimation S / \ S
/Br yHeat n
HisCFr70 3 H15C70 O -O H
0 0 0 0


Figure 3-17. Attempt in the solid state polymerization of Br2-BEDOT-B(OC7Hl5)2.


Figure 3-18. Crystal packing of Br2-BEDOT-B(OC7H15)2 illustrating the intermolecular distances
between bromine atoms.

3.3.4 Electropolymerization

The electropolymerization of the BEDOT-B(OR)2 and BT-B(OR)2 families is already well

documented and was consequently not investigated in this work.46'50'105 In order to develop an

understanding of the redox properties of polymer films of the new BProDOT-R2-B(OC12H25)2









family, the two BProDOT-R2-B(OC12H25)2 monomers have been electrochemically polymerized

on a platinum button electrode. The electrodeposition was accomplished using an

ACN/dichloromethane (CH2C12) (5/3) solution, with 0.1 M TBAP and saturated in monomer

(0.01 M). Dichloromethane was required due to the poor solubility of the monomers in ACN.

However, too much CH2Cl2 hindered polymer formation and deposition on the electrode and

only the use of monomer saturated solutions helped to circumvent that problem. The repeated

scanning electropolymerizations of BProDOT-Me2-B(OC12H25)2 and of BProDOT-Hex2-

B(OC12H25)2 are shown in Figures 3-19a and 3-19b respectively. During the first anodic scan, a

single peak is observed which corresponds to irreversible monomer oxidation and formation of

cation radicals. The peaks of monomer oxidation (Ep,m) are observed at +0.55 V for BProDOT-

Me2-B(OC12H25)2 and at +0.52 V for BProDOT-Hex2-B(OC12H25)2 vs Fc/Fc With repeated

potential scanning, a polymer film grows onto the electrode surface in both cases. Cathodic and

anodic redox processes are observed during polymer reduction and oxidation, and both increase

in intensity with repeated scanning indicative of a successful effective electroactive polymer film

deposition. The oxidation potential of the polymer also increases with film thickness due to the

increase in polymer resistance. For spectroelectrochemical studies, a polymer thin-film of

PBProDOT-Me2-B(OC12H25)2 was also potentiostatically deposited onto an ITO-coated glass

electrode at +0.5 V for 50 s, using the same electrolyte and concentration as used for the

electropolymerization on Pt button.

3.3.5 Oxidative Polymerization via Ferric Chloride

As described in the Introduction (section 3.1), the oxidative chemical polymerizations of

the BEDOT-B(OR)2 and BT-B(OR)2 families via FeCl3 has been previously reported. Low

molecular weight materials resulted, with particularly poor processing properties in the case of

PBEDOT-B(OR)2. It was hypothesized that the low oxidation potential of BProDOT-Hex2-










B(OC12H25)2, as well as its solubility inducing hexyl- and dodecyloxy-substituents, would confer

the material favorable conditions for being polymerized via oxidative polymerization.

Consequently, the chemical polymerization of BProDOT-Hex2-B(OC12H25)2 was carried out by

addition of a ferric chloride slurry (FeCl3, 3 equiv.) in chloroform to a chloroform solution of the

monomer over a 2 hour period. The polymerization was carried out overnight at room

temperature and the oxidized polymer was then precipitated in cold methanol, collected,

dissolved in chloroform, and stirred for 6 hours with about 10 mL of hydrazine monohydrate to

reduce the polymer into its neutral form. The neutral polymer was precipitated one more time

into cold methanol, filtered through a cellulose thimble, and purified by Soxhlet extraction with

methanol as the refluxing solvent to remove unreacted monomer and inorganic impurities. Final

extraction with chloroform afforded a red solid in 92 % yield after solvent evaporation. The

polymer was soluble in common organic solvents such as THF, dichloromethane, chloroform

and toluene.


5- a E =+0.52V
4-
4-
302



-1
0--
1 E E +0.5 +0.44V 0-1 \ =

Eon,m = +04V
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 -0.4 -0.2 0.0 0.2 0.4 0.6
Potential (V) vs. Fc/Fc+ Potential (V) vs. Fc/Fc+





Figure 3-19. Repeated potential scanning electropolymerization of BProDOT-R2-B(OC12H25)2
monomers. (a) BProDOT-Me2-B(OC12H25)2 and (b) BProDOT-Hex2-B(OC12H25)2,
0.01 M saturated solution of 0.1 M TBAP in ACN/CH2C12 (5/3) at a scan rate of 50
mV s1.









The 1H-NMR spectra of the material obtained after polymerization was compared to the

1H-NMR spectrum of the BProDOT-Hex2-B(OC12H25)2 monomer (Figure 3-20). As expected,

the methylene protons at 0.88, 1.27, 1.39, and 1.82 ppm give splitting patterns in the monomer

spectrum. They are found at about the same frequency for the polymer (the peak at 1.82 ppm is

shifted slightly down-field) but do not resolve. The alkoxy methylene protons at 3.90, 3.91, and

3.99 ppm give also splitting patterns in the monomer but overlap into a broad multiple at 3.96-

4.06 ppm in the polymer. The signal of the phenylene proton (a) is shifted down-field in the

polymer by 0.11 ppm. The signal of the ProDOT proton end groups (6.45 ppm, (b)) disappeared

as expected for polymerization to a substantial degree.

As structure proof, the polymer was characterized by MALDI mass spectrometry using a

terthiophene matrix. Proton end groups were observed and the spacing between the peaks

corresponds to -1090 amu, which corresponds to the calculated molecular weight of the repeat

unit of the polymer. Iron and chlorine were efficiently removed as demonstrated by elemental

analysis, which shows the presence of only one iron per 47 sulfurs, and of one chlorine per 40

sulfurs. Molecular weight (MW) analysis performed by GPC (polystyrene standards, THF as

mobile phase) gave a number average molecular weight of 14,600 g mol-1 and a weight average

molecular weight of 23,000 g mol-1 with a polydispersity index of 1.6. As illustrated in Figure 3-

21, polymer elution was monitored with an in-line photodiode array detector to record the UV-

Vis absorption of selected fractions of the polymer. Spectra were recorded at various times

which allowed monitoring the electronic spectra as a function of molecular weight. For fractions

with MW higher than polystyrene equivalents of 25,000 g mol-1, the optimum optical conditions

are attained and the absorption maximum is at 573 nm. The narrow MW seen in the gel

permeation chromatogram indicates that the polymer does not contain low MW oligomers









(Appendix B). Interestingly, the absorption spectrum of the polymer in THF is red shifted

compared to the absorption spectrum in toluene videe post). Therefore THF is not as good a

solvent as toluene for this polymer and induces conformational changes to a more planar and

rigid structure. More details on the solvent effect will be given in the solvatochromism section

(section 3.6).


70 60 50 40 30 20 10 00
ppm (tl)

Figure 3-20. 1H-NMR spectra. (a) 1H-NMR(CDCl3) spectrum of BProDOT-Hex2-B(OC12H25)2,
(b) 1H-NMR(CDCl3) spectrum of PBProDOT-Hex2-B(OC12H25)2.

The thermal stability of PBProDOT-Hex2-B(OC12H25)2 was studied by TGA in a nitrogen

atmosphere using a 200C min- temperature ramp from 500C to 9000C. The thermogram

displayed in Figure 3-22 shows that the polymer exhibits a high thermal stability, having lost less

than 5% weight at 357C. Between that temperature and 4500C, a drastic degradation process

occurred, leading to a ~ 70% weight loss, which matches with the side chain degradation. Above









4500C, the degradation became more progressive, and probably corresponds to the polymer


backbone degradation. At 9000C, less than 7% of the polymer remained.


300 400 500


600 700 800


Wavelength (nm)


Figure 3-21.


Absorption spectra for molecular weight fractions of PBProDOT-Hex2-
B(OC12H25)2. Molecular weights are reported in g mol-1 vs. peak values for
polystyrene. (1) 18,900, (2) 25,000, (3) 30,350, (4) 38,400, (5) 46,700,
(6) 61,500.


Temperature (oC)


Figure 3-22. Thermogravimetric analysis of the PBProDOT-Hex2-B(OC12H25)2 in a nitrogen
atmosphere. A 200C min- temperature ramp from 500C to 9000C was used.

3.4 Polymer Electrochemistry and Spectroelectrochemistry

3.4.1 PBT-B(OR)2

The redox properties of the PBT-B(OR)2 polymers were studied by electrochemistry. The

polymers were deposited on Pt button electrodes by drop-casting from 3 mg mL1 toluene










solutions, and cyclic voltammograms were recorded in 0.1 M TBAP/PC. An onset of oxidation

(Eonset,ox) of +0.25 V vs Fc/Fc+ and a E1/2 of +0.29 V were determined for PBT-B(OC7Hi5)2

(Figure 3-23a). According to these results, the polymer has a HOMO energy of about 5.3-5.4 eV

(as detailed in Chapter 2). Figure 3-23b shows the cyclic voltammograms of PBT-B(OC12H25)2 at

different scan rates. The voltammograms are broad and not well defined, and consequently it was

not possible to determine E1/2. The onset of polymer oxidation was found around +0.35 V,

slightly more positive than the value found for the heptoxy analog. This locates the HOMO level

at about 5.4-5.5 eV. These two PBT-B(OR)2 derivatives fulfill the energy requirements for

stability to oxidation since their HOMO levels are lower than 5.2 eV (general Introduction).



4- a Ep,ox=+0.48V 6- b 125mVs-1
c I 100 mV s"1
E 3- ( E" 4- 75mVs-1
2. 50 mVs-1
SEonset,ox Eonset, ox 25 mV s-1

1o0-
0-
S-1- -2-
-2- Ep,red = +0.1 V
-0.4 -0.2 0.0 0.2 0.4 0.6 -0.6 -0.3 0.0 0.3 0.6 0.9 1.2
E(V) vs. Fc/Fc+ E(V) vs. Fc/Fc+




Figure 3-23. PBT-B(OR)2 cyclic voltammetry. (a) CV of PBT-B(OC7Hi5)2 at 100 mV s-1, (b) CV
and scan rate dependence of PBT-B(OC12H25)2. The polymers were deposited by
drop-casting from 3 mg mL1 toluene solutions, and the measurements were
accomplished in 0.1 M TBAP in PC.

Spectroelectrochemical studies were accomplished in order to finalize the estimation of the

position of the HOMO and LUMO energies, and to observe the polymer spectral changes upon

oxidation. Polymer thin-films were spray-cast onto ITO coated glass plates from 3 mg mL1

toluene solutions, and UV-Vis-nIR spectra were recorded in the neutral state and then at higher









oxidizing potentials. Figure 3-24 shows the spectral changes of PBT-B(OC7H15)2 and

photographs of the polymer film in the neutral and oxidized states, and Figure 3-25 shows the

spectral changes of PBT-B(OC12H25)2. Both polymers are orange in the neutral state with

absorption maxima at 447 nm for PBT-B(OC7H15)2, and at 454 nm for PBT-B(OC12H25)2. Once

the oxidation potentials reached ~ 0.21 V for PBT-B(OC7H15)2, and ~ 0.30-0.35 V for PBT-

B(OC12H25)2, spectral changes started to occur, such as the progressive disappearance of the 7t-

x7* transition of the neutral state, and the formation of polaron transitions in the 600-800 nm

region, and of bipolaron transitions in the near-IR region. For each polymer, the starting point of

these changes correlates well with the onset of oxidation determined by electrochemistry. Once

completely oxidized, PBT-B(OC7H15)2 exhibits a new absorption maximum in the visible region

at 738 nm, and its film color changes to blue. Similar color changes were observed for PBT-

B(OC12H25)2, which exhibits an absorption maximum in the visible at 662 nm in the oxidized

state. Both polymers exhibit an absorption onset in the neutral state at 590 nm, corresponding to

an optical band gap of approximately 2.1 eV. The LUMO energies of the polymers were deduced

by adding this band gap value to the HOMO energies estimated by electrochemistry: 3.2-3.3 eV

for PBT-B(OC7Hi5)2 and 3.3-3.4 eV for PBT-B(OC12H25)2. Consequently the polymers fulfill the

energy requirements for transferring charges to PCBM (LUMO offsets >0.4 eV relative to

PCBM) as explained in the general Introduction.

3.4.2 PBProDOT-R2-B(OC12H25)2

The polymer films of PBProDOT-R2-B(OC12H25)2 electrodeposited on Pt button (section

3.3.4) were rinsed with a monomer free solution of ACN/CH2Cl2 (5/3) in which the films are not

soluble, and cyclic voltammograms were further recorded with scan rate values ranging from 25

to 250 mV s-1 (Figures 3-26a and 3-26b). Linear relationships were observed between the current









and the scan rate, indicating that the films are electrode supported and electroactive. The redox

processes for the BProDOT-Me2-B(OC12H25)2 system are broad and overlap well as expected for

a nicely electroactive polymer, with the peak oxidation (Ep,ox) and reduction (Ep,red) potentials

around +0.25 V and -0.01 V respectively, at 100 mV s-1. However, Ep,ox and Ep,red for

PBProDOT-Hex2-B(OC12H25)2 (+0.16 V and -0.04 V respectively, at 100 mV s-1) are highly

separated as the longer and bulkier chains on the hexyl substituted ProDOT inhibit the fast

movement of counter ions. The electrochemical results are summarized in Table 3-2. Both

molecules have similar electrochemical values, with half wave potentials around +0.05-0.1 V,

which shows that functionalizing the ProDOT unit with long solubilizing hexyl chains has little

influence on the electronic properties. These potentials are lower than the values measured for

the analogous 1,4-bis(2-thienyl)-2,5-diheptoxybenzene polymer which exhibits50 an E1/2 value of

+0.36 V vs Fc/Fc showing the effect of the electron donating oxygens of the ProDOT unit on

the polymer oxidation potential. A lower E1/2 of -0.40 V vs Fc/Fc+ has been reported for the

analogous 1,4-bis(3,4-ethylenedioxythienyl)-2,5-didodecyloxybenzene polymer due to the

stronger electron donating effect of EDOT.46

Comparative cyclic voltammetry studies have been done on the chemically synthesized

PBProDOT-Hex2-B(OC12H25)2. A film of that polymer was deposited by drop-casting on a Pt

button electrode from a 10 mg mL-1 chloroform solution, and cyclic voltammograms were

recorded for different scan rates in 0.1 M TBAP/PC electrolyte as illustrated in Figure 3-27 and

compared to the electrochemically synthesized films. The polymer exhibits an E1/2 of +0.23 V at

100 mV s-1, which is a bit higher than the value obtained for the electropolymerized film, but not

surprisingly different due to the different morphologies one would expect to form for the two

film preparation methods. A HOMO energy of about 5.3-5.4 eV was deduced from the onset of









oxidation at ~ +0.25 V, which is similar to what was determined for the PBT-B(OR)2 derivatives.

A linear relationship is found between the peak current and the scan rate indicating that the

polymer is electroactive and bound to the electrode.











Neutral

400 600 800 1000 1200 1400
Wavelength (nm)

B
A


Figure 3-24. Spectroelectrochemical analysis of PBT-B(OC7H15)2 spray-cast onto ITO coated
glass. (A) U.V.-Vis.-n.I.R. spectra taken in the neutral state and at potentials of
(a) -0.49 V, (b) -0.39V, (c) -0.29 V, (d) -0.19 V, (e) -0.09 V, (f) +0.01 V,
(g) +0.11 V, (h) +0.21 V, (i) +0.22 V, (j) +0.23 V, (k) +0.24 V, (1) +0.25 V,
(m) +0.26 V, (n) +0.27 V, (o) +0.28 V, (p) +0.29 V, (q) +0.30 V, (r) +0.31 V,
(s) +0.41 V, (t) +0.51 V, (u) +0.61 V, (v) +0.71 V, (w) +0.81 V vs Fc/Fc+ in 0.1 M
TBAP/PC; (B) Film colors in the neutral and oxidized states.

Table 3-2. Electrochemical results for BProDOT-R2-B(OC12H25)2 monomers and polymers.
Eon,m (V)a Ep,m (V) Ep,ox (V)b Ep,red (V) E1/2 (V) Eg (eV)
BProDOT-Me2-B(OC12H25)2 0.44 0.55 0.25 -0.01 0.12 2.1
BProDOT-Hex2-B(OC12H25)2 0.4 0.52 0.16 -0.04 0.06 2.1
Note: All potentials reported vs Fc/Fc+
aEon,m: onset of monomer oxidation; bScan rate = 100 mV s-1.

The chemically prepared PBProDOT-Hex2-B(OC12H25)2 was studied by

spectroelectrochemistry after film deposition by spray-casting onto ITO coated glass from a 10

mg mL1 chloroform solution. A highly homogeneous film was obtained and dried under











vacuum. The spectra were recorded in 0.1 M TBAP in PC in the neutral state, and stepping the


potential from -0.02 V to +0.78 V every 0.05 V as shown in Figure 3-28.


0.6-,


Wavelength (nm)


Figure 3-25.








8.0-
6.0-
E 4.0-
< 2.0-
E
E 0.0--
-2.0
C-


Spectroelectrochemical analysis of PBT-B(OC12H25)2 spray-cast onto ITO coated
glass. U.V.-Vis.-n.I.R. spectra taken (a) in the neutral state and at potentials of
(b) -0.55 V, (c) -0.45 V, (d) -0.35 V, (e) -0.25 V, (f) -0.15V, (g) -0.05 V, (h) +0.05
V, (i) +0.15 V, (j) +0.20 V, (k) +0.25 V, (1) +0.30 V, (m) +0.35 V, (n ) +0.40 V,
(o) +0.45 V, (p) +0.50 V, (q) +0.55 V, (r) +0.65 Vvs Fc/Fc+ in 0.1 M TBAP/PC.


-0.6 -0.4 -0.2 0.0
Potential (V) vs. Fc/Fc+


0.2 0.4


"'Ep,red
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4
Potential (V) vs. Fc/Fc+


Figure 3-26. PBProDOT-R2-B(OC12H25)2 cyclic voltammograms. (a) CV of PBProDOT-Me2-
B(OC12H25)2, and (b) CV of PBProDOT-Hex2-B(OC12H25)2. Polymers
electrodeposited on Pt button and measurements accomplished in 0.1 M TBAP in
ACN/CH2C12 (5/3) at scan rates of 25, 50, 100, 150, 200, and 250 mV s-1.











1.4- 5 74
1.2- 4 *' 72
1.0- 3 70 (
0.8- 2 68 8
S0.6- 1 66
E 0.4- 64
S0.2- 62 >
; 0.0 -0 60
-0.2- 58
-0.4
-0.6- ** 56
54
-0.1 0.0 0.1 0.2 0.3 0.4
E(V) vs. Fc/Fc


Figure 3-27. Cyclic voltammograms of PBProDOT-Hex2-B(OC12H25)2 as function of scan rate.
(1) 100, (2) 150, (3) 200, (4) 250 mV s-1. Polymer deposited by drop-casting on Pt
button electrode, in 0.1 M TBAP/PC electrolyte. The CV are superimposed with %
relative luminance versus applied potential (*) for PBProDOT-Hex2-B(OC12H25)2.

The polymer exhibits an orange-red color in the neutral state with two absorption maxima

at 544 nm and 507 nm (Figure 3-28a) which can be attributed to vibronic coupling. Upon

oxidation, the 7t-7t* transition of the neutral state disappears and, as soon as the potential reaches

about +0.3 V a polaron transition appears in the 600-800 nm region with a maximum absorption

at 738 nm, changing the film color to light blue (Figure 3-28i). Upon further increase in

potential, this transition progressively disappears and bipolaron transitions are observed (1500

nm peaks) (Figure 3-28, i-r), and the polymer film becomes highly transmissive with a light gray

color. This demonstrates the potential utility of this polymer in electrochromic applications.

Polymer overoxidation and decomposition seemed occurring above +0.9 V. An optical band gap

of 2.1 eV was determined from the onset of absorption of the neutral polymer.

For comparison, a thin-film of PBProDOT-Me2-B(OC12H25)2 was potentiostatically

deposited onto an ITO-coated glass electrode (electropolymerization section). After washing

with a CH2C2/ACN (3/5) solution, the orange polymer film was placed in a 0.1 M TBAP/PC

electrolyte solution and various absorption spectra were recorded in the neutral state, and at









stepped potentials sequentially from -0.28 V to +0.42 V oxidizing the polymer progressively

(Figure 3-29). Overoxidation seemed to occur at higher potentials and the polymer film started to

fall off the ITO electrode. As with PBProDOT-Hex2-B(OC12H25)2, PBProDOT-Me2-B(OC12H25)2

exhibits an optical band gap of 2.1 eV and a similar color change during redox switching,

supporting our previous statement that the hexyl chains introduce little or no change in the

optical properties. Surprisingly, the two PBProDOT-R2-B(OC12H25)2 polymers exhibit the same

band gaps as the recently studied poly(1,4-bis(2-thienyl)-2,5-diheptoxybenzene).50 This result

brings out the subtleties of the effect of side chains on the optical properties of 7t-conjugated

polymers. In this instance, the thiophene linked polymers may be packing in an even more

regular manner in the solid state than the polymers studied here.


-e


Thin Thick
Neutral


Thin Thick
Oxidized


Wavelength (nm)


Figure 3-28.


Spectroelectrochemical analysis of PBProDOT-Hex2-B(OC12H25)2 spray-cast onto
ITO coated glass. (A) U.V.-Vis.-n.I.R. spectra taken (a) in the neutral state and at
potentials of (b) -0.02 V, (c) +0.03 V, (d) +0.08 V, (e) +0.13 V, (f) +0.18 V, (g)
+0.23 V, (h) +0.28 V, (i) +0.33 V, (j) +0.38 V, (k) +0.43 V, (1) +0.48 V, (m) +0.53
V, (n) +0.58 V, (o) +0.63 V, (p) +0.68 V, (q) +0.73 V, (r) +0.78 V vs Fc/Fc in
0.1 M TBAP/PC; (B) the film colors are displayed for thin and thick films.














0.3

E- 0.2- h
h

0.1

0.0 .
400 600 800 1000 1200 1400
Wavelength (nm)


Figure 3-29. Spectroelectrochemical analysis of PBProDOT-Me2-B(OC12H25)2 electro-
polymerized on ITO coated glass. U.V.-Vis.-NIR. spectra taken (a) in the
neutral state and at potentials of (b) -0.28 V, (c) -0.08 V, (d) +0.02 V,
(e) +0.12 V, (f) +0.22 V, (g) +0.32 V, (h) +0.42 V, vs Fc/Fc in 0.1 M
TBAP/PC.

3.5 Colorimetry

3.5.1 PBT-B(OR)2

Thin-films of PBT-B(OC7H15)2 and PBT-B(OC12H25)2 were deposited on ITO by spray-

casting from 3 mg mL-1 toluene solutions, and were analyzed by in-situ colorimetric analysis.

The relative luminance was measured as the neutral polymers were progressively oxidized. In the

small 0.45-0.5 V potential window, the relative luminance of PBT-B(OC7Hi5)2 changed from

30% to 2.5% upon oxidation. There was also a considerable relative luminance change for PBT-

B(OC12H25)2 (from 70% to 30%) between 0.45 and 0.55 V.

The L*a*b* values of films of about 0.2 |tm in thickness were also determined to allow

color matching. For PBT-B(OC7H15)2: L = 61; a = 50; b = 87 for the orange color (neutral state)

and L = 24; a = -5; b = -23 for the blue color (doped state). For PBT-B(OC12H25)2: L = 86; a =

22; b = 68 for the orange color (neutral state) and L = 73; a = -6; b = -7 for the blue color (doped

state).










The available color states of these polymers were tracked using the xy chromaticity

diagrams shown in Figures 3-30a and 3-30b (as detailed in Chapter 2).119 As the potential was

increased and the polymers were doped, the x and y coordinates decreased. The abrupt color

changes observed in the luminance experiments, can also be clearly seen on the xy chromaticity

diagram by large changes in the xy coordinates between similar potential ranges (0.45-0.6 V for

PBT-B(OC7H15)2 and 0.49-0.54 V for PBT-B(OC12H25)2).


a -0.22 V 0.45 b -0.56 Vto +0.49 V
0.40-
0.40-
0.35-
0.30- 0.+0.5 V 035-

0.25- 0.30-
1- +1.14 VV
0.20- +1.18 V 0.25-

0.15 0.20- --- +0.54V
0.10 1
0.1 0.2 0.3 0.4 0.5 0.6 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
x x





Figure 3-30. CIE 1931 xy chromaticity diagrams of PBT-B(OR)2 polymers. Circles linked by a
dashed line represent the color track for thin-films of (a) PBT-B(OC7H15)2, and (b)
PBT-B(OC12H25)2, which go from orange to blue. The potential was increased in
0.05 V steps.

3.5.2 PBProDOT-R2-B(OC12H25)2

A thin-film of the chemically synthesized PBProDOT-Hex2-B(OC12H25)2 was deposited

onto ITO by spray-casting from a 10 mg mL-1 chloroform solution and was also analyzed by in-

situ colorimetric analysis. The relative luminance was measured as the neutral polymer was

progressively oxidized and the results are superimposed in Figure 3-27 onto the cyclic

voltammogram to compare the optical changes along with the material oxidation. Optical

changes started occurring at +0.23 V vs Fc/Fc which corresponds to the polymer's onset of









oxidation. At this potential, there was a sharp increase in the luminance which went from 55 %

to 70 % in less than 0.1 V. Finally, upon further oxidation the luminance reached saturation at

+0.6 V.

The L*a*b* values of the thin-film colors in the neutral and oxidized states were also

determined. In the red-orange neutral state, L = 79, a = 40, b = 14, and in the fully oxidized light

gray state, L = 90, a = -1 and b = -3 for a spray-cast film of about 0.2 |tm in thickness. The

available color states that PBProDOT-Hex2-B(OC12H25)2 has to offer were also tracked using the

xy chromaticity diagram shown in Figure 3-31. As the potential was increased and the polymer

was doped the x coordinate decreased and the y coordinate decreased after an initial increase.

The abrupt color change which occurred at +0.23 V and was observed on the luminance

spectrum in Figure 3-27, can also be clearly seen on the xy chromaticity diagram by a large

change in the xy coordinates at that potential. Note that for clarity, this chromaticity diagram is a

25 x magnification of the region of interest of the full xy chromaticity diagram displayed in

Chapter 2. A few differences were observed for thicker films, such as a more pronounced blue

color in the oxidized state (photograph in Figure 3-28), a lower luminance value (around 30 %)

characteristic of a more opaque film, and no difference in the luminance values between the

neutral and the fully oxidized states.

3.6 Solvatochromism, Thermochromism, and lonochromism

While heating (about 600C) 0.1 M TBAP in CH2C2/ACN solutions of the BProDOT-R2-

B(OC12H25)2 monomers, a reversible color change was surprisingly observed (from yellow to red

as seen in Figure 3-32). This phenomenon was interestingly not seen without the presence of the

electrolyte. It was deduced that upon the increase in temperature, the backbone of the three rings

system twisted and gained a certain conformation (in this case more planar due to the red-shift),










which favored the coordination of the ions coming from the electrolyte and the locking of that

position. These observations motivated the solvatochromic study of PBProDOT-Hex2-

B(OC12H25)2.


0395- 0.28 V
..- /
0390-
0 385-
>" 0380- 0.83 V
0375-
\ 0.23V
0370- /
0 365-
034 036 038 040 042 044 046



Figure 3-3 1. CIE 1931 xy chromaticity diagram of a thin-film of PBProDOT-Hex2-B(OC12H25)2.
Triangles linked by a dashed line represent the color track for the polymer film
which goes from orange to light gray. The potential was increased in 0.05 V steps.



A






Figure 3-32. Thermochromic changes observed for a 0.1 M TBAP in CH2C2/ACN solution of
the BProDOT-Me2-B(OC12H25)2 monomers.

At room temperature, a 1.36 x 10-5 mol L-1 toluene solution of the chemically synthesized

PBProDOT-Hex2-B(OC12H25)2 was yellow and exhibited an absorption maximum at 478 nm as

illustrated in Figure 3-33. The resolution of the fine structure was not as well defined as it was in

the film absorption spectrum (Figure 3-28), and the solution absorption was blue-shifted

compared to the film absorption where the maximum was observed at 544 nm. This was

expected since solvated polymer chains are more disordered in solution and consequently have a

lower conjugation length.









Upon addition of methanol, while maintaining a constant polymer concentration (1.36 x

10-5 mol L-1), the solution became more red and showed an absorption maximum at 503 nm, with

a vibronic side band at 541 nm. In pure toluene, the polymer was highly solvated and poorly

ordered. Upon addition of methanol, the polymer exhibited more extensive conjugation as could

be deduced from the shift of the absorption maximum to longer wavelengths. According to the

literature, the energy difference of 0.18 eV (1460 cm1) from the main peak to the vibronic peak

is consistent with a C=C stretching mode which would be expected to couple strongly to the

electronic structure.120 This is an additional evidence for the presence of more ordered molecules

in the presence of poorly solvating solvents.

The combined ionic and thermochromic properties observed for the BProDOT-R2-

B(OC12H25)2 monomers were also checked on the polymers. PBProDOT-Hex2-B(OC12H25)2 was

dissolved in a CH2C12/ACN solution containing TBAP. As methanol, acetonitrile behaves as a

poor solvent for the polymer and turned the polymer solution into a deep red color, making it

impossible to check for ionochromic/thermochromic effects. Another attempt was performed on

a pure methylene chloride polymer solution containing TBAP. Upon heating, no color change

could be observed suggesting that the chromic phenomenon probably resulted from the

simultaneous action of temperature, ions, and poor solvent. This was verified by heating a

methylene chloride monomer solution containing TBAP, and indeed, no color change could be

observed this time.

3.7 Application to Devices

3.7.1 Photovoltaic Devices

3.7.1.1 PBT-B(OR)2

Bulk heterojunction solar cells using the PBT-B(OR)2 polymers as the electron donors and

PCBM as the electron acceptor (device structure ITO/PEDOT-PSS/PBT-B(OR)2:PCBM/LiF/Al)










were prepared by Dr. Young-Gi Kim in order to evaluate for the first time the photovoltaic

properties of such materials. Blends containing 1:4 (w/w) of each polymer with PCBM were

spin-coated from 1,2-dichlorobenzene solutions into ~ 45 nm thick photoactive layers. Figure 3-

34a shows the i-V characteristics of the PBT-B(OC12H25)2 based device under AM 1.5

illumination for a calibrated solar simulator with an intensity of 100 mW cm-2, and Table 3-3

summarizes the photovoltaic results. The PBT-B(OC7H15)2/PCBM device exhibited the best

performance with a power conversion efficiency (rq) of ~ 0.6%, a short circuit current (Is) of

2.49 mA cm-2, an open circuit voltage (Voc) of 0.74 V, and a fill factor (FF) of 32%.


Toluene: Methanol
30:70
40:60

8 0.5- 50:50
60:40
o 80:20
100:0




0.0
300 400 500 600 700 800
Wavelength (nm)


Figure 3-33. UV-vis absorption spectra of PBProDOT-Hex2-B(OC12H25)2 in toluene/methanol
mixtures. Pictures: solutions (a) in toluene, (b) in a mixture of toluene and
methanol.

Incident photon to current efficiency measurements (IPCE) match the polymer absorption

spectra near the absorption maxima of the polymers, indicating that the polymers are effective

photoexcited electron donors that contribute mainly to the photocurrent in the device (Figure 3-

34b). Both polymers exhibit IPCEs of 16% at 410 nm. Consequently, PBT-B(OC7H15)2 and

PBT-B(OC12H25)2 showed their potential for use in organic photovoltaic devices, harvesting










incident light of the mid-range energy. It would be interesting to combine these polymers with

lower or higher band gap polymers in order to absorb over a broader spectral range and to

improve the photovoltaic efficiencies.. .but for that physicists have to take over that project now!


1 16- b g.

a o
---------------- ---- ----^--- / 0 0 o .
E -1- o o
-- 8- 0,eo
*t ^ y8-
5 -2-
4- o
S-3- e
illuminated o
AM1.5 *ooooo
-4 0 e-
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 400 500 600 700
Voltage (V) Wavelength (nm)




Figure 3-34. Photovoltaic results of solar cells made of a 1/4 blend (w/w) of PBT-
B(OR)2/PCBM. (a) Current voltage characteristic for PBT-B(OC12H25)2 under
AM1.5 conditions (100 mW cm-2). (b) IPCE results for PBT-B(OC12H25)2 (e) and
PBT-B(OC7Hi5)2 (0).

Table 3-3. Summarized photovoltaic characteristics of PBT-B(OR)2/PCBM based solar cells.

Photosensitizer r (%) FF Voc (V) Isc (mA cm-2)

PBT-B(OC7H15)2 0.59 0.32 0.74 2.49

PBT-B(OC12H25)2 0.48 0.39 0.76 1.59


3.7.1.2 PBProDOT-Hex2-B(OC12H25)2

Bulk heterojunction solar cells using PBProDOT-Hex2-B(OC12H25)2 as the electron donor

and PCBM as the electron acceptor have also been prepared by the group of Prof. Yang Yang at

the University of California (UCLA), using the same conditions as the ones used for PBT-

B(OR)2 (see section above). The device exhibited a power conversion efficiency of 0.22%, a

-2
short circuit current of 0.98 mA cm-2, an open circuit voltage of 0.55 V, and a fill factor of 41%

(see i-V characteristic of the device in Figure 3-35). The polymer's photovoltaic properties are

not as great as the ones determined for PBT-B(OR)2. This might be due to poorer hole transport









properties, probably resulting from a less regular packing in the solid state (as it had been already

suggested from the band gap results, see section 3.4.2).




PCBM = 80 wt. %

2 -
E
0-





-0.2 0.0 0.2 0.4 0.6 0.8 1.0
Voltage (V)


Figure 3-35. Current voltage characteristic of a solar cell made of a 1/4 blend (w/w) of
PBProDOT-Hex2-B(OC12H25)2/PCBM under AM1.5 conditions (100 mW cm-2).

3.7.2 LEDs

The chemically synthesized PBProDOT-Hex2-B(OC12H25)2 exhibits a yellow-orange

fluorescence in toluene with an evaluated quantum efficiency of 54 % (against Coumarin 6

standard; PD = 0.78).100 The emission spectrum illustrated in Figure 3-36 exhibits two well-

defined vibronic bands at 539 nm and 582 nm, and one poorly resolved band at approximately

630 nm in toluene. For a spin-coated film, the emission spectrum has a similar shape although it

is red shifted due to a more organized conformation (Figure 3-36). The vibronic bands are seen

at 571, 617 and 679 nm (Photoluminescence Quantum Efficiency (PLQE)= 3.5 + 2 %).

Dr. J. Mwaura investigated the potential of this polymer in LEDs. For that study, devices

of the following architecture were prepared: ITO/PEDOT-PSS (40 nm)/PBProDOT-Hex2-

B(OC12H25)2 (50 nm)/Ca (5 nm)/Al (200 nm). As shown in Figure 3-36, the device exhibits a

broad emission dominated by a peak at Xmax = 570 nm. The electroluminescence (EL) spectrum










is similar to the photoluminescence (PL) spectrum of the solid film, indicating that the

electroluminescence results from a singlet 7r,7r* exciton with the same structure as that produced

by photoexcitation. The absence of red-shifting on the EL spectrum relative to the PL spectrum

suggests that the electroluminescence is dominated by the non-aggregated polymer chains, with

the interchain aggregates contributing to little or no emission.

On the device characteristics illustrated in Figure 3-37, it can be seen that the PBProDOT-

Hex2-B(OC12H25)2 device turns on at 6 V. The EL intensity increases with voltage, peaking at

13 V, and decreasing at higher voltages, possibly due to device breakdown. At 13 V, the device

emits the highest luminance at ~ 240 cd m-2 and a current density of 1100 mA cm-2. Figure 3-37

shows the external electron-to-photon quantum efficiency (EQE) of the PBProDOT-Hex2-

B(OC12H25)2 EL device as a function of applied voltage. The efficiency increases after turn on,

peaking at 8 V at ~ 0.03 %, after which it steadily decreases as the applied voltage and current

density increase. These low EQE show that the polymer is not likely effective for development in

LED applications.


1.0- 1.0

0.8- 0.8
0.6-


S0.4- 0.4

0.2- 0.2

0.0- 0.0
500 550 600 650 700 750 800
Wavelength (nm)


Figure 3-36. Photoluminescence emission spectrum of PBProDOT-Hex2-B(OC12H25)2 in toluene
solution and in thin-film (bold line) superimposed with electroluminescence
spectrum of an EL device with the following configuration: ITO/PEDOT-
PSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al. The inset picture represents the light
emission of the EL device.












004 r .1200
200- 0 03 -1000
g002
150- 001oo -800
o // 0
4 6 8 10 12 14 -600 B
100 Voltage (V)
S/ / -400
E 50- //
S/ -200 0
0- ,, .2 -> -0
2 4 6 8 10 12 14
Voltage (V)


Figure 3-37. LED properties of an ITO/PEDOT-PSS/PBProDOT-Hex2-B(OC12H25)2/Ca/Al
device. Luminance spectrum (o) and current density (A). Left top inset: External
quantum efficiency.

3.8 Conclusions and Perspective

The packing properties (small interchain distances, or cofacial arrangements of the rings of

adjacent layers) of the regiosymmetric Br2-BT-B(OR)2 and Br2-BEDOT-B(OR)2 monomers,

revealed that these materials might be interesting building blocks for producing hole transporting

materials (oligomers or polymers) for organic electronic devices requiring high charge transport,

like photovoltaics. This idea was supported also by previously reported studies on the ordering

properties of PBT-B(OR)2, which have shown the propensity of these materials to crystallize.22

For that reason, their chemical polymerization has been revisited with the goal of obtaining

higher molecular weight materials than the one previously reported, with good processability.

Yamamoto coupling via Ni(COD)2 proved to be the most effective method among the methods

which have been attempted in this work (GriM, solid state polymerization) or in the literature,

for getting the monomers to couple between each other. However the molecular weights stayed

limited, especially in the case of PBEDOT-B(OR)2. This is due in part to its too powerful

electron donating properties which diminish the reactivity of the growing chains to the Ni









oxidative addition. It is also due to its poor solubility probably resulting from its propensity to

aggregate as suggested by the tight packing observed in the X-ray crystal structures of the

monomers. Polymers of reasonable size, processability, and film homogeneity, were obtained in

the case of PBT-B(OR)2, and it was decided to investigate the electronic, electrochromic, and

photovoltaic properties of this material only. DSC studies confirmed the semi-crystalline nature

of this regiosymmetric polymer, and comforted us in our idea to built photovoltaics with this

material. The electrochemical and spectroelectrochemical studies attested the PBT-B(OR)2

polymers ability to harvest incident light in the mid-visible energy range (Eg of 2.1 eV), stability

to oxidation, and capacity to transfer charges to PCBM. When applied as the hole transporting

layer in bulk heterojunction photovoltaic devices with PCBM as the acceptor, they effectively

produced photocurrent, and power conversion efficiencies up to 0.6% were reached. These

results are of valuable importance and should not be compared to the 5% efficiencies that have

been obtained for P3HT:PCBM devices, since such performances are the results of years of

optimization from various research groups.73-75 There are only a few examples of polymers

which have been successfully employed in solar cells and most of them have never reached 1%

efficiencies.121 Apart from their photovoltaic properties, these materials exhibit nice

electrochromic properties, switching between deep orange and blue colors, in the neutral and

oxidized states, respectively.

In order to overcome the solubility limitations of PBEDOT-B(OR)2 and to make a

similarly electron rich material, we decided to replace the EDOT moiety of this regiosymmetric

member by alkyl (Me or hexyl) -substituted ProDOT heterocycles, the methyl substituted

derivative being studied for comparison. Due to their novelty, these materials were first

electropolymerized before investigating their chemical polymerization, in order to get a quick









look at their redox and electronic properties. The PBProDOT-R2-B(OC12H25)2 polymers exhibit

band gaps of 2.1 eV, quite close to their thiophene counterparts likely due to a less regular

packing in the solid state. This in turn compensates the electron donating effect of the oxygen

substituents appended to the thiophene ring and gives rise to films having a similar orange color

in the neutral state.103 Conversely, as the polymer was progressively oxidized a different behavior

was observed for PBProDOT-Hex2-B(OC12H25)2 and a highly transmissive state was reached

while the thiophene analogues retain a deeper blue color.50'103 A chemical synthesis was

developed for this polymer, giving rise to a highly soluble material that can be processed by

spray-casting or spin-coating techniques. These interesting solubility and color switching

properties open the door to electrochromic applications using large or flexible surfaces such as

electrochromic displays or smart windows. Unfortunately maximum power conversion

efficiencies of 0.22% were reached, and these poorer photovoltaic properties compared to PBT-

B(OR)2, might be the result of a less regular packing of PBProDOT-Hex2-B(OC12H25)2 in the

solid state. However, the particularly tight crystalline packing and the close to perfect cofacial

arrangement of adjacent molecules of the three ring BProDOT-Me2-B(OC12H25)2 system could

motivate the development of oligomers of this type for electronic applications requiring high

charge carrier mobility.

3.9 Experimental

1,4-Dibromo-2,5-diheptoxybenzene (la).22 Freshly recrystallized 1,4-dibromo-2,5-

dihydroxybenzene (13.19 g, 4.90 x 10-2 mol) was dissolved in EtOH (75 mL) under argon to

give a slightly pink solution. A 75 mL solution of KOH (7.01 g, 1.25 x 10-1 mol) in EtOH was

slowly added and the solution color turned brown. The solution mixture was stirred at room

temperature for 2 h. Then 1-bromoheptane (22.45 g, 1.25 x 10-1 mol) was dissolved in EtOH

(20 mL) and this solution was added dropwise to the reaction mixture forming a beige









precipitate. This solution was heated at 65-700C for 18 h. It was cooled to room temperature and

deionized water was added yielding a pink precipitate. The precipitate was filtered on a Btichner

funnel and a slightly pink solid was collected and dried under vacuum. This solid was purified by

recrystallization from ethanol/benzene (3/1) to give 17.58 g (77%) of white crystals [mp = 56-

580C (lit.22 mp = 59-600C)]. 1H-NMR (CDCl3, ppm): 6 = 7.08 (s, 1H), 3.94 (t, 2H), 1.80 (p, 2H),

1.48 (m, 2H), 1.31 (m, 6H), 0.89 (t, 3H). 13C-NMR (CDCl3,ppm): 6 = 150.45, 118.94, 111.50,

70.67, 31.94, 29.36, 29.15, 26.11, 22.76, 14.21. Anal. Calcd for C20H32Br202: C, 51.74, H, 6.95.

Found: C, 52.01, H, 7.26.

1,4-Dibromo-2,5-didodecyloxybenzene (1b).22 1,4-Dibromo-2,5-didodecyloxybenzene

was prepared according to the procedure described for 1,4-dibromo-2,5-diheptoxybenzene

utilizing freshly recrystallized 1,4-dibromo-2,5-dihydroxybenzene (11.27 g, 4.20 x 10-2 mol),

KOH (1.01 x 10-1 mol), and 1-bromododecane (1.01 x 10-1 mol). Recrystallization from

ethanol/benzene (3/1) gave 23.89 g (94%) of white crystals [mp = 75-770C (lit.22 mp = 77-

790C)]. 1H-NMR (CDCl3, ppm): 6 = 7.09 (s, 1H), 3.95 (t, 2H), 1.81 (p, 2H), 1.48 (m, 2H),

1.29 (m, 16H), 0.89 (t, 3H).

2-(Trimethylstannyl)thiophene [Th-Sn(CH3)3].122 Thiophene was dried over calcium

hydride overnight and then purified by distillation under reduced pressure (bp = 30-350C at 130

torr). Thiophene (4.38 g, 5.20 x 10-2 mol) was dissolved in anhydrous THF (35 mL) under argon.

The solution was cooled to -780C and butyllithium (21.90 mL, 2.50 M in hexanes, 5.50 x 10-2

mol) was added dropwise via an addition funnel. The clear solution was stirred for 1 h and

became slightly pink. Trimethylstannyl chloride (54.70 mL, 1 M in THF, 5.50 x 10-2 mol) was

then added dropwise and the solution turned slightly yellow. The mixture was allowed to warm

to room temperature with stirring overnight and the color turned brown. Deionized water was









added (30 mL) and the mixture was extracted with diethyl ether. The organic phase was washed

with brine, dried over magnesium sulfate (MgSO4) and filtered through a Buchner funnel. The

solvent was evaporated and a brown oil was collected. This oil was purified by distillation

(bp = 93-970C at 25 mmHg) and 9.90 g (77%) of a white solid were obtained and dried under

vacuum. 1H-NMR (CDCl3, ppm): 6 = 7.65 (d, 1H), 7.24 (m, 2H), 0.37 (s, 9H).

2-(Trimethylsilyl)-3,4-ethylenedioxythiophene [EDOT(SnCH3)3].36 A solution of 3,4-

ethylenedioxythiophene (EDOT) in THF was dried overnight over potassium. A solution of

EDOT (7.50 g, 5.28 x 10-2 mol) in anhydrous THF (50 mL) was cooled at -780C under argon and

n-butyllithium (2.5 M in hexanes, 5.81 x 10-2 mol) was added dropwise via addition funnel. The

mixture was stirred at -780C for 1 h and then warmed up to 0C for 30 min, changing the clear

solution to an orange color. The solution was cooled back to -780C and trimethylstannyl chloride

(1 M in THF, 5.28 x 10-2 mol) was added dropwise thanks to an addition funnel. The orange

solution was warmed to room temperature and stirred overnight. Deionized water was added to

the solution and the mixture was extracted with ether. The organic phase was washed with Brine

and dried over MgSO4. After filtration through a Btichner funnel, the solvent was evaporated and

a brown oil was obtained and purified by distillation under vacuum (bp = 1100C at 0.4 mmHg).

After cooling, 11.93 g of white-clear solid (74%) were collected. 1H-NMR (CDCl3, ppm):

6 = 6.56 (s, 1H), 6.30 (s, 2H), 4.16 (m, 4H), 0.35 (s, 9H).

1,4-Bis(2-thienyl)-2,5-diheptoxybenzene [BT-B(OC7Hi5)2].22 Th-Sn(CH3)3 (9.28 g,

3.76 x 10-2 mol) and 1,4-dibromo-2,5-diheptoxybenzene (8.69 g, 1.87 x 10-2 mol) were dissolved

in anhydrous DMF (200 mL) under argon at 800C. Argon was bubbled into the reaction mixture

for 20 min. Then, Pd(PPh3)4 catalyst (1.68 g, 1.50 x 10-3 mol) was added quickly and the orange

solution was warmed to 1200C and stirred overnight giving rise to a green-black mixture. It was









then cooled to room temperature and poured into deionized water (500 mL). The mixture was

extracted with diethyl ether; the organic phase was collected, washed with brine and dried over

MgSO4. An orange organic solution was obtained after filtration on a Buchner funnel. The

solvent was evaporated and a yellow solid was collected and placed under vacuum. After

recrystallization from ethanol/benzene (3/1), 7.17 g (81%) of yellow crystals were obtained

[mp = 76-77C (lit.22 mp = 77-780C)]. 1HNMR (CDCl3, ppm): 6 = 7.54 (d, 1H), 7.34 (d, 1H),

7.26 (s, 1H), 7.10 (dd, 1H), 4.08 (t, 2H), 1.90 (p, 2H), 1.52 (m, 2H), 1.32 (m, 6H), 0.90 (t, 3H).

1,4-Bis(2-thienyl)-2,5-didodecyloxybenzene [BT-B(OC12H25)2].22 BT-B(OC12H25)2 was

prepared according to the procedure described for BT-B(OC7H15)2 utilizing Th-Sn(CH3)3 (9.80 g,

3.97 x 10-2 mol) 1,4-dibromo-2,5-didodecyloxybenzene (11.86 g, 1.96 x 10-2 mol), anhydrous

DMF (300 mL) and Pd(PPh3)4 (9.06 x 10-1 g, 7.80 x 10-4 mol). The yellow solid was dried under

vacuum and recrystallized from ethanol/benzene (3/1) to give 9.35 g (78%) of thin yellow

crystals [mp = 77-780C (lit.22 mp = 77-780C)]. 1H-NMR (CDCl3, ppm): 6 = 7.54 (d, 1H),

7.33 (d, 1H), 7.26 (s, 1H), 7.09 (dd, 1H), 4.08 (t, 2H), 1.90 (p, 2H), 1.52 (m, 2H), 1.27 (m, 16H),

0.88 (t, 3H).

1,4-Bis[2-(3,4-ethylenedioxy)thienyl]-2,5-diheptoxybenzene [BEDOT-B(OC7H15)21]

EDOT(SnCH3)3 (6.00 g, 1.96 x 10-2 mol) and 1,4-dibromo-2,5-diheptoxybenzene (4.54 g,

9.70 x 10-3 mol) were dissolved in anhydrous DMF (300 mL). The solution was heated at 80C

to dissolve everything. Argon was bubbled into the solution for 15 min and Pd(PPh3)4

(5.04 x 10-3 g, 4.36 x 10-4 mol) was quickly added. The reaction was stirred at 1200C overnight

and the yellow-orange solution turned black. The solution was cooled to room temperature and

poured into deionized water. The mixture was extracted with diethyl ether and the organic phase

was washed with brine, dried over MgSO4 and filtered on a Btichner funnel. The solvent was