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Synthetic Control of Order in Soluble Dioxythiophene Polymers

HIDE
 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Experimental methods
 Synthetic control of order in branched...
 Synthetic control of order in branched...
 Chiral substituted poly (3,...
 Soluble poly (3, 4-phenylenedi...
 References
 Biographical sketch
 

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SYNTHETIC CONTROL OF ORDER IN SOLUBLE DIOXYTHIOPHENE POLYMERS By CHRISTOPHE R. G. GRENIER 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

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Copyright 2006 by Christophe R. G. Grenier

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To my family,

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iv ACKNOWLEDGMENTS I would like to first thank my advisor for his continuous guidance throughout the five years, and a little extra of my Ph.D. studies in Florid a. I believe this is a highly challenging time for a young inexperienced re searcher growing into a responsible scientific leader, and that appr opriate advice is the catalyst of this intellectual growth. In this regard, Prof. John R. Reynolds has always provided the right balance of encouragement, objective criticism, and pati ence. His insight and advice greatly helped me perform the work discussed in this disse rtation. I learned a lot from him. I extend these thanks to my supervisory committee for their support and invaluable discussions: Prof. William R. Dolbier, Prof. Anthony B. Brennan, Prof. Lisa McElwee-White and Prof. Randy S. Duran. I also owe thanks to Subi George and Pr of. “Bert” Meijer whom I was lucky to meet and collaborate with and who have offere d me twice their generous hospitality at the Technical University of Eindhoven, The Ne therlands. In addition, I am thankful to Dr. Wojciech Pisula, Nok Tsao and Prof. Klau s Mllen from the Max-Planck Institute for Polymer Science in Mainz, Germany, with whom I also had a very productive collaboration and exciting scientific discussions. I wish to thank my best friends in Ga inesville for their unwavering friendship thoughout these five years. Without their s upport, I would have never made it through these five years: Daniel Serra, Magdalena Swiderska, Emine Boz, Dalia Lopez Colon, Dalianis, Guillermo Mathias, Avni Argun and Pierre-Henry Aubert. I am indebted to

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v them forever, and I hope to repay them some day, provided I learn how to cook or make better coffee. I have to thank those friends that have jo ined me numerous times for coffee break, exercise, lunches and dinner: Ali Cirpan, E ce Unur, Thomas Joncheray, Rachid Matmour, Emilie Galand, Geoffroy and Delphine So mmen, Aleksa Jovanovic, Prof. Pierre Audebert, Dr. Mohammed Bouguettaya and Benoit Lauly. I would like to also thank pe ople that have greatly helped me scientifically, helped improve my English writing proficiency a nd with whom I always had interesting conversations: Genay Jones (I will always re member a 3am drive to Waffle House), Aubrey Dyer, Benjamin Reeves (a great me ntor to me and a very wise man), Barry Thompson (who has set an unreachable standard for hard-work and scientific excellence), and Nisha Ananthakrishnan, Jeremiah Mwaura Robert Brookins a nd Tim Steckler. In addition, special thanks go to Lorraine W illiams, Sara Klossner, Tasha Simmons and Gena Borrero for doing all the “little things” without which I could not have had anything done. I also thank my family, especially my parents, for supporting me during this long time so far away from their home. I know it wa s a difficult and painful sacrifice for them. Finally, I want to offer special thoughts to two of my greatest friends departed during the course of my P h.D. studies: Jean-Baptiste A ndrault and Landry Bourely. I miss them both dearly.

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vi TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................ix LIST OF FIGURES.............................................................................................................x ABSTRACT....................................................................................................................... xv CHAPTER 1 INTRODUCTION........................................................................................................1 1.1. Introduction to C onjugated Polymers....................................................................1 1.2. Electronic Properties of Conjugated Polymers......................................................2 1.3. Doping-induced Properties of Conjugated Polymers............................................5 1.3.1. Chemical Doping.........................................................................................6 1.3.2. Electrochemical Doping..............................................................................6 1.3.3. Fluorescence and Photoche mical Charge Transfer.....................................8 1.3.4. Interfacial Doping........................................................................................8 1.4. Improving Active Material Performance.............................................................10 1.4.1. OFETs........................................................................................................10 1.4.2. Photovoltaic Application...........................................................................11 1.4.3. Polymer Electroluminescent Diodes (PLEDs)..........................................13 1.4.4. Electrochromic Devices.............................................................................15 1.5. Synthetic Control in Conjugated Polymers.........................................................16 1.5.1. Substituent Effects.....................................................................................17 1.5.2. Intrachain Interactions...............................................................................17 1.5.3. Interchain Interactions...............................................................................20 1.6. Towards Soluble Conjugated Polymers...............................................................24 2 EXPERIMENTAL METHODS.................................................................................29 2.1. General Synthetic Methods..................................................................................29 2.2. Molecular Characterization.................................................................................29 2.3. Electrochemical Characterization........................................................................30 2.4. Polymer Characterization....................................................................................31 2.4.1. Structural Characterization........................................................................31 2.4.2. Thermal Characterization..........................................................................31

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vii 2.4.3. Morphology Characterization....................................................................32 2.4.4. Solution Optical Characterization.............................................................32 2.4.5. Solution Processing Techniques................................................................33 2.4.5.1. Drop-casting....................................................................................34 2.4.5.2. Spin-coating....................................................................................34 2.4.5.3. Spray-coating..................................................................................35 2.4.6. Film Fluorescence Characterization..........................................................36 2.4.7. Spectroelectrochemical Characterization..................................................36 2.4.8. Circular Dichroism....................................................................................40 2.4.9. Conductivity Measurements......................................................................40 3 SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKYL POLY(3,4PROPYLENEDIOXYTHIOPHENES) (PProDOT-R2).............................................43 3.1. Introduction..........................................................................................................43 3.2. Electropolymerized PProDOT-R2.......................................................................47 3.2.1. Electropolymerizable Monomer Synthesis................................................47 3.2.2. Electrodeposition and Electrochemistry....................................................48 3.3. Chemically Polymerized Soluble PProDOT-R2..................................................51 3.3.1. Synthesis and Polymer Characterization...................................................51 3.3.2. Solution Properties....................................................................................53 3.3.3. Optoelectronic Properties of Solution Processed Films............................56 3.3.4. Conductivity Measurements......................................................................61 3.4. High Performance Electrochromic Devices........................................................62 3.5. Conclusion...........................................................................................................63 3.6. Chapter Synthetic Details....................................................................................64 4 SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKOXYMETHYL POLY(3,4-PROPYLENEDIOXYTH IOPHENES) (PPRODOT-(CH2OR)2).............71 4.1. Introduction..........................................................................................................71 4.2. Electropolymerized PProDOT-(CH2OR)2...........................................................72 4.2.1. Electropolymerizable Monomer Synthesis................................................72 4.2.2. Electrodeposition and Electrochemistry....................................................73 4.3. Chemically Polymerized Soluble PProDOT-(CH2OR)2......................................75 4.3.1. Synthesis and Polymer Characterization...................................................75 4.3.2. Solution properties.....................................................................................76 4.3.3. Optoelectronic Properties of Solution Processed Films............................78 4.3.4. Conductivity Measurement.......................................................................82 4.4. High Performance Electrochromic Devices........................................................83 4.5 Conclusion............................................................................................................85 4.6. Chapter Synthetic Details....................................................................................85 5 CHIRAL SUBSTITUTED POLY(3,4PROPYLENEDIOXYTHIOPHENES)........90 5.1. Introduction..........................................................................................................90 5.1.1. CD Spectroscopy.......................................................................................90

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viii 5.1.2. Applications of Chiral Polymers and CD Spectroscopy...........................93 5.1.3. Thermochromism/Solvatochromism in Chiral Substituted Polymers.......93 5.1.3. Chiral Substituted PProDOTs....................................................................95 5.2. Synthesis of PProDOT-Based Chiral Polymers..................................................96 5.2.1 New Chiral Reagents Synthesis..................................................................96 5.2.2 Electrochemically Polymerizable Monomer and Electrodeposition..........97 5.3. Chiral Ordering in Chiral PProDOTs................................................................100 5.3.1. Optical Properties in “Good” Solvent Solutions.....................................100 5.3.2. Solvatochromism Effects in PProDOTs Solutions..................................102 5.3.3. Thermochromism in PProDOTs Aggregated Solutions..........................105 5.3.4. Chiral Order in Spray-cast Films.............................................................110 5.4. Conclusion.........................................................................................................114 5.5. General Synthetic Details..................................................................................115 6 SOLUBLE POLY(3,4-PHENY LENEDIOXYTHIOPHENES)...............................129 6.1. Introduction........................................................................................................129 6.2 Synthesis of Soluble Substituted PheDOT.........................................................131 6.3. Electropolymerization of Substituted PheDOTs...............................................132 6.3.1. Electrodeposition and Electronic Properties...........................................132 6.3.2. Spectroelectrochemical Characteriz ation of Electrodeposited Films......135 6.4 Synthesis of Soluble Substituted PPheDOT.......................................................137 6.5 Solutions Properties............................................................................................139 6.6. PPheDOT(C12)2: A Soluble, Ordered Polymer..................................................141 6.7. PPheDOTC12EtHx: a Disordered Polymer........................................................148 6.8. Conclusion.........................................................................................................151 6.9. Closing Statements............................................................................................152 6.10. Synthetic Details..............................................................................................155 LIST OF REFERENCES.................................................................................................170 BIOGRAPHICAL SKETCH...........................................................................................179

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ix LIST OF TABLES Table page 3-1. ProDOT-R2 monomer oxidation onset and peak potentials.......................................48 3-2. Molecular weight analysis of GriM polymerized PProDOT-R2................................52 3-3. Optical properties of alkyl subst ituted PProDOTs in toluene solution......................55 3-4. Solution, cast films and electroche mically oxidized and reneutralized films absorption properties................................................................................................58 3-5. Coloration Efficiency study on PProDOT-R2 spray-coated films..............................60 3-6. Conductivity measurements on spray-coat ed films gas phase doped with iodine.....61 4-1. Comparison of alkyl and alkoxymethyl substituted PProDOTs polymer oxidation..75 4-2. Molecular weight analysis of GriM polymerized PProDOT-(CH2OR)2....................76 4-3. Optical properties of alkoxymethyl subs tituted PProDOTs in toluene solution........77 4-4. Optical properties of PProDOT(CH2O-2-alkyloxymethyl)2 polymers in solution, spray-coated films before and af ter electrochemical switching...............................79 4-5. Coloration Efficiency of PProDOT-(CH2OR)2 films sprayed on ITO-coated glass slides......................................................................................................................... 81 4-6. Conductivity measurement for PProDOT(CH2OR)2 spray-coated films...................82 5-1. GPC data for chiral substituted PProDOTs................................................................99 5-2. Comparison of chiral a nd racemic PProDOTs polymers.........................................100 6-1. Electrochemical properties of substituted PheDOTs electropolymerizable monomers and electrodeposited disubstituted PPheDOTs films...........................133 6-2. Optical properties of electrodeposite d films onto ITO-coated glass slides..............136 6-3. GPC data for PPheDOTC12EtHx and PPheDOT(C12)2............................................138

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x LIST OF FIGURES Figure page 1-1. Evolution of published work on conducting polymers.................................................1 1-2. Representative structur es of conducting polymers.......................................................2 1-3. Doping in poly(acetylene)............................................................................................4 1-4. The two non-degenerate forms of poly(pphenylene): aromatic, left and quinoidal, right.......................................................................................................................... ..4 1-5. Spectroelectrochemistry of PProDOT-Me2 as a function of applied potential.............5 1-6. Chemical p-doping by iodine (revers ible) and nitrosoniu m hexafluorophosphate (irreversible) in the case of polythiophene.................................................................6 1-7. Schematic representation of a LEC device...................................................................7 1-8. Schematic diagram of a thin film transistor..................................................................9 1-9. Representative luminescence colo rs of some conjugated polymers...........................13 1-10. Effect of structural regularity on poly(3-octylthi ophene) chain conformation........19 1-11. Color tuning of film lumine scence though intrachain twisting................................20 1-12. Fluorescence quantum yield depe ndence on substituents bulk................................22 1-13. Davydov splitting in interchain aggregates..............................................................23 1-14. Polymerization method leading to re gioregular Poly(3-a lkylthiophene)s................26 1-15. Proposed chain growth mechanism for Grignard Metathesis polymerization.........27 2-1. Three electrodes (Pt button, large Pt foil counter, Ag wire reference) electrochemical setup...............................................................................................30 2-2. Spray-coated films of PProDOT-(CH2O(2-ethylhexyl))2 and PProDOT(CH2OC18H37)2.........................................................................................................36

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xi 2-3. Time evolution of transmittance and in jected charge for an electropolymerized film of PProDOT-Me2..............................................................................................39 2-4. Four-point probe conductivity method.......................................................................40 2-5. Four-point conductivity measurement........................................................................42 3-1. Conformational and substituents effects on 3,4-ethylenedioxythiophenes................44 3-2. Two most stable co nformations of ProDOT...............................................................46 3-3. Family of branched dialkyl PProDOTs......................................................................47 3-4. Synthesis of electropolymerizable alkyl substituted ProDOTs..................................48 3-5. Electrodeposition of PProDOT-(2-ethylhexyl)2 on platinum button electrode..........49 3-6. Polymer oxidation in the PProDOT-R2 series............................................................50 3-7. Grignard Metathesis polym erization of soluble PProDOT-R2...................................51 3-8. Evolution of UV-Vis absorption spectru m with molecular weight for PProDOT(2ethylhexyl)2..............................................................................................................52 3-9. Absorption and photoluminescen ce spectrum of PProDOT-Hexyl2 and PProDOT(2-ethylhexyl)2..........................................................................................53 3-10. Evolution of absorption spectrum with increasing distorti on between the ground state and the excited state ........................................................................................54 3-11. Doping/Casting induced re arrangement in linear vs. br anched alkyl substituted PProDOTs................................................................................................................57 3-12. X-ray crystal structure of BisProDOT-Et2 showing that a mixture of chair and twisted conformations are present............................................................................58 3-13. Spectroelectrochemistry experiment for PProDOT-Hx2 (left) and PProDOT-(2ethylhexyl)2 (right)...................................................................................................59 3-14. Luminance change with applied potential................................................................60 3-15. Schematic representation of a refl ective/absorptive EC device using spraycoated PProDOT(CH2O-2-ethylhexyl)2 as the active and storage layer..................62 3-16. Reflectance plot for a reflective/ab sorptive EC device using spray-coated PProDOT(CH2O-2-ethylhexyl)2 as the active a nd storage layer.............................63 4-1. Family of branched dial koxymethyl substituted PProDOTs......................................72

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xii 4-2. Synthesis of electropolymerizab le alkoxymethyl substituted ProDOTs....................73 4-3. Electrodeposition of PProDOT(CH2O-2-ethylhexyl)2 on Pt Button..........................73 4-4. Polymer oxidation in the PProDOT-(CH2OR)2 series................................................74 4-5. Polymerization of PProDOT-(CH2OR)2 by Grignard Metathesis..............................75 4-6. Absorption and photolumines cence spectrum of PProDOT(CH2O-2-methylbutyl)2 and PProDOT(CH2O-2-ethylhexyl)2........................................................................76 4-7. Doping/Casting induced rearrangement in linear vs. branched alkyl substituted PProDOTs................................................................................................................78 4-8. Spectroelectrochemistry experiment for PProDOT-(CH2O-2-ethylhexyl)2 (left) and PProDOT-(CH2OC18H37)2 (right)......................................................................80 4-9. Luminance change vs. appl ied potential in PProDOT(CH2OR)2 polymers...............81 4-10. Electrochemical device us ing spray-coated PProDOT(CH2O2-ethylhexyl)2 as the anodically coloring polymer and Poly(BisEDOT-N-methylcarbazole) electropolymerized film as th e cathodically colo ring polymer................................83 4-11. Luminance plot of a dual-wind ow EC device using spray-coated PProDOT((CH2O-2-ethylhexyl)2) as the anodically coloring polymer and electrolpolymerized Poly(BisEDOT-N -methylcarbazole) as the anodically coloring polymer......................................................................................................84 5-1. CD spectroscopy principle..........................................................................................91 5-2. CD signal of exciton-coupled chro mophores with varying chromophores arrangement..............................................................................................................92 5-3. Cholesteric packing in aggreg ated chiral poly(thiophenes).......................................95 5-4. New soluble Chiral PProDOTs polymers obtained by Grignard Metathesis.............96 5-5. Synthesis of 2S-ethylhexyl substituents using a pseudoephedrine chiral auxiliary...97 5-6. Cyclic voltammetry of elect rodeposited PProDOT((2S)-methylbutyl)2 and PProDOT((2S)methylbutyl)2....................................................................................98 5-7. Comparison of PProDOT-((2S)methylbutyl)2 and PProDOT-((2S)methylbutyl)2 spectroelectrochemistry............................................................................................99 5-8. Temperature dependence of PProDOT(CH2O-2S-methylbutyl)2 in xylenes solution...................................................................................................................101 5-9. Thermochromism of PProDOT((2S)-methylbutyl)2 in xylenes solution.................102

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xiii 5-10. Optical properties of PProDOT((2S)-methylbutyl)2 solutions in Xylenes/DMF mixtures (C= 8.610-6M)......................................................................................104 5-11. Thermochromism of PProDOT((2S)ethylhexyl)2 in xylenes/DMF mixtures.......106 5-12. Fluorescence thermochromi sm of 50/50 xylenes/DMF PProDOT((2S)methylbutyl)2 and PProDOT((2S)ethylhexyl)2..............................107 5-13. UV-Vis absorption of a 50/50 xylenes /DMF aggregated solution at 95C............108 5-14. Evolution of absorption spectrum of 40/60 and 50/50 xylenes/DMF PProDOT((2S)ethylhexyl)2 solution following heating/slow cooling cycle..........................109 5-15. Polymer optical properties evolution during heating/slow cooling cycle. PProDOT(2S)-ethylhexyl)2 50/50 xylenes/DMF...................................................110 5-16. Absorption and CD signal for PProDOT-((2S)-ethylhexyl)2) spray-coated films.112 5-17. CD signal of chiral PProDOT(CH2O-2-methyl)2 spray-cast films.........................114 6-1. X-ray crystal structure of PheDOTBr2.....................................................................130 6-2. Family of Soluble Substituted PPheDOTs under study............................................131 6-3. Synthesis of monoa nd disubstituted PheDOTs......................................................132 6-4. Electrodeposition and electrochemi stry of substituted PPheDOTs films.................134 6-5. PheDOT(C12)2 oxidation at various scan rates.........................................................134 6-6. Synthesis of PPheDOT(C12)2 by Grignard Metathesis.............................................137 6-7. Solution optical properties of monosubstituted PPheDOTs.....................................137 6-8. Solution thermochromism of Poly[PheDOT-(C12)2] in xylenes.............................140 6-9. Absorption and Emission spectrum of PPheDOTC12EtHx. Sample excited at 550nm.....................................................................................................................140 6-10. Cyclic voltammetry of disubstituted PPheDOT(C12)2 in 0.1M TBAP in ACN at a scan rate of 50mV/s................................................................................................141 6-11. Spectroelectrochemistry of soluble disubstituted PPheDOT(C12)2 film on ITOcoated glass slides..................................................................................................142 6-12. Self-assembly of PPheDOT(C12)2 polymer chains in films spin-coated on mica from a hot ODCB solution (C= 0.2 mg mL 1)......................................................143

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xiv 6-13. AFM picture (5 5m2) of PPheDOT-(C12)2 spin-coated on mica from ODCB solution at room temperature (C= 0.2 mg mL 1)..................................................144 6-14. DSC (2nd scan) of PPheDOT-(C12)2......................................................................145 6-15. Ordering in mechanically aligned PPheDOT(C12)2 fibers......................................146 6-16. 2D-WAXS pattern of PPheDOT-(C12)2 at 150 C.................................................147 6-17. 2D-WAXS analysis of higher molecular weight PPheDOT(C12)2 fraction............148 6-18. Absorption spectrum of PPheDOTC12EtHx: in xylenes solution, film spray-cast from toluene, film spray-cast after el ectrochemical doping and reneutralization..149 6-19. Electrochemistry and spectroelectrochemistry of PPheDOTC12EtHx cast films...150 6-20. DSC (2nd scan) of PPheDOTC12EtHx...................................................................151

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xv 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 SYNTHETIC CONTROL OF ORDER IN DIOXYTHIOPHENE POLYMERS By Christophe R. G. Grenier December 2006 Chair: John R. Reynolds Major Department: Chemistry The synthesis of electron-rich, highl y soluble and processable conjugated poly(3,4-propylenedioxythiophe nes) (PProDOTs) is de veloped. The polymers are substituted with side chains carefully chosen to obtain high solubility while controlling the polymers’ physical, optical and electroni c properties necessary for the targeted applications. The polymers have been a pplied to device platforms that probe electrochromism, light-emission a nd charge-carrier mobilities. A synthetic methodology to prepare disubstituted poly(3,4-propylenedioxythiophenes) ha ving branched alkyl and alkoxymethyl substituents for electrochromic applications is described The branched polymers display significantly higher solubility than their lin ear analogs and are easily processed by spincoating or spray-casting. The polymers have high electrochromic contrasts, subsecond switching times, and high coloration efficien cies, allowing them to be successfully applied to the construction of highly efficient and fast switching electrochromic devices.

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xvi Using enantiomerically pure reagents, chiral alkyl and alkoxymethyl PProDOTs were synthesized. Since few enantiomerically pu re reagents are commercially available, an easy, efficient and versatile synthesis was developed to yield new, original chiral polymers. Introduction of side chain chiralit y allows control of the ordering of the polymer chains, with formation of cholesteric aggregates in poor solvents and the solid state. Solvatochromism and thermochromi sm experiments coupled with circular dichroism (CD), along with fluorescence a nd absorption spectroscopy, yield important information on the morphology and self-assembly of the polymer chains from solution to the solid state. The first synthesis of soluble poly(3,4phenylenedioxythiophenes) (PPheDOTs) is described. Solubility was induced by introduci ng substituents at the 4 and 5 positions of the veratrole moiety. Monosubstituted PPheDOT s were found to be poorly soluble, but could be obtained by electrodeposition. On the other hand, disubstituted PPheDOT polymers are soluble. Symmetrically dodecyl substituted PPheDOT(C12)2, soluble above 80C in aromatic and chlorinated solvents, shows a high degree of order in the solid state and is a promising candidate for high mobility and high conductivity applications. Asymmetric, disordered PPheDOT(C12)EtHx is soluble at room temperature in most organic solvents. The polyme r shows solid state fluorescence and is a promising candidate for light-emitting applications.

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1 CHAPTER 1 INTRODUCTION 1.1. Introduction to Conjugated Polymers Following the exciting discovery in 1977 of high conductivity in chemically doped polyacetylene, the conjugated polymers (CP) research field has developed exponentially (Figure 1.1). As a result, ma ny other CPs with diverse chemical structures have been investigated. Their exceptional physical, elect ronic and optical properties have been well characterized and a deep understa nding of their incredible prope rties is now available. In 2000, the importance of the discovery and de velopment of conducting polymers was recognized when the Chemistry Nobel Pri ze was awarded to Alan Heeger, Hideki Shirakawa and Alan MacDiarmid. 196019701980199020002010 0 500 1000 1500 2000 2500 3000 Number of Publications / YearYear First report on high conductivity in doped Polyacetylene Figure 1-1. Evolution of publishe d work on conducting polymers

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2 As Heeger described, conjugated polyme rs (often called c onducting polymers) “offer a unique combination of properties not available from any other materials.”1 Of special interest is the ability to finely t une their properties through synthetic changes, both at the monomer and polymer level. This enables the use of conducting polymers in many applications such as photovoltaic devi ces (PVs), electrochromic devices (ECDs), organic field-effect transistors (OFETs), and light-emitting diodes (LEDs). Their performance has improved dramatically lead ing to their increasing use in commercial applications. 1.2. Electronic Properties of Conjugated Polymers On a basic level, conjugated polymer s are a continuous array of overlapping orbitals supported by -bond backbone. As long as this ar ray is present, many different backbones can be used. Examples of commonly used -conjugated polymer structures are given in Figure 1-2. OO S S n n O O n PEDOT P3HT MEH-PPV N H n PPy n trans-PA Figure 1-2. Representative structures of conducting polymers. The polymers represented are some of the most used a nd best performing materials. To understand the properties of conducting po lymers, I will describe polyacetylene. Going from ethylene to 1,3-butad iene, the overall energy of th e molecule is stabilized by overlap between the two double bonds. The HOM O is raised, and the LUMO is lowered leading to a smaller HOMO-LUMO gap. By increasing the number of overlapping double bonds, the number of energy levels (o ccupied and unoccupied) increases, and the

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3 HOMO-LUMO gap is compressed further. As the degree of conjugati on grows large, the multiple electronic states are better describe d by continuous bands. This simple approach can be applied to most conjugated polymers. Complete theoretical calculations giving more precise results have been pe rformed for many conjugated polymers.2 Theoretically, if the number of overlappi ng orbitals becomes infinite, then the band gap is expected to disappe ar. However, this is not observed due to Peierls distortion. Peierls distortion arises from the interaction between electron ic and vibrational states, not taken into account in Hckel theory. This interaction induces the formation of alternating long and short bonds with single and double bond character, and th e creation of a band gap.3 Many other interactions participate in determining the bandgap in conjugated polymers, and will be discussed later. By analogy to inorganic materials, conjugated polymers with typical bandgaps between 1 a nd 3 eV are semiconducting materials with a conduction band and a valence band. Poly(acetylene) is a we ll understood polymer with a degenerate ground state.4 Two resonance forms of equal energy exist differi ng only by the order of the single and double bonds (Figure 1-3A).5 One can switch between phase A and phase B by introducing a radical defect within the chains (Figure 13B).This radical defect called a soliton, is localized over severa l carbons and has an energy leve l at mid-gap, occupied by one electron. The electron in the intragap state can be removed to create a positively charged soliton (p-doping), or another el ectron can be added to create a negatively charged soliton (n-doping) (Figure 1-3C).

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4 PhaseA PhaseB PhaseAPhaseB Soliton E E EVB VB VB CB CB CBNeutral Soliton Positive Soliton Negative Soliton p-dopingn-doping A) C) B) Figure 1-3. Doping in poly(acetyl ene). (A) The two degenerate forms of poly(acetylene); (B) Self-localized neutra l soliton defect in poly( acetylene); (C) p-doping and n-doping in poly(acetylene). For polymers with a non-degenerate ground stat e, the picture is slightly different. Two resonance forms exist as in polyacetylen e, but with different energies: the most stable is the benzenoid form and the less stab le is the quinoid form (Figure 1-4). Upon doping, either a radical-cation pa ir, or a radical-anion pair is created. Thes e defects are called polarons and are responsible for conduc tivity observed at low doping levels. Upon further doping, a second electron can be rem oved, and a dicationic species is formed, called a bipolaron. At high doping levels, bipola rons are the charge carriers responsible for conductivity. At a hypothetical doping leve l of 100% (one dopant ion per repeat unit), Bredas et al. have calculated that the intrag ap states merge with the valence or conduction band giving metallic behavior.6 n n Figure 1-4. The two non-degenerate forms of poly(p-phenylene): aromatic, left and quinoidal, right.

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5 Polarons and bipolarons have specific op tical signature. Polaron charge carriers have two characteristic absorptions in th e near-IR region, as shown in Figure 1-5 for poly(3,4-(2,2-dimethylpropylene) dioxythiophene) (PProDOT-Me2), a p-dopable polymer.7 The first transition corresponds to the transition from the top of the valence band to the single occupied lo wer intragap state. The sec ond transition is the near-IR transition from the lower intragap state to th e higher intragap state. When the chains are oxidized to the bipolaron state, the lower energy intragap state is depleted of its electron, and only the first transition is seen. For dege nerate ground state poly( acetylene), only one transition with an onset near half the ener gy of the bandgap is seen due to solitons, not polarons charge carriers. 40060080010001200140016001800 0.0 0.5 1.0 1.5 2.0 1 V -1 V -1 V 1 V S O O nAbsorbanceEnergy (eV) -1 V 1 V 0V S S S n S S S n S S S n Neutral Polaron Bipolaron ConductionBand ValenceBandO O OO OO OO OO OO OO O O O O ValenceBand ValenceBand ConductionBandConductionBand Figure 1-5. Spectroelectroc hemistry of PProDOT-Me2 as a function of applied potential between –1 V and 1V vs. Ag wire in 0.1 M TBAP/ACN. Energy levels, electronic transitions for the neutral and organic structures of polaron, and bipolaron forms of PProDOT-Me2 with the organic structures are also depicted. 1.3. Doping-induced Properties of Conjugated Polymers The conjugated polymers can be used in many applications. These applications depend on the mechanism by which the doping is achieved. In this section, I will describe

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6 the different doping mechanisms and introduce a pplications derived from them. I will not describe the applications in deta il but only their working principle. 1.3.1. Chemical Doping Conjugated polymers can be doped by electr on transfer to or from chemical species. Some examples are I2, and NOPF6 (p-doping), along with Na-naphthalide, and Li (n-doping). Figure 1-6 shows th e reversible oxidation of polyt hiophene by iodine, as well as the irreversible oxidation by NOPF6. In this case, doping charges are compensated by species derived from the oxidizing/reducing agent. (T)n 3/2nyI22(T)n 2nyNOPF6 [(T)+y(I3 -)y]n[(T)+y(PF6 -)y]nnyN2O2 Figure 1-6. Chemical p-doping by iodine (reversible) and nitrosonium hexafluorophosphate (irreversible) in the case of polythiophene; n refers to the number of repeat units. Upon careful choice of the dopant ion, high conductivity can be achieved leading to applications of conjugated polymers as anti -static coatings, hole-injecting layers, holetransport layers and conductive fibers. Becau se charges with corresponding counterions are introduced during doping, solubility and processability in pol ar solvent can be obtained. For example, poly(3,4-ethylene dioxythiophene) (PEDOT) doped with bulky poly(styrenesulfonate) (PEDOT:PSS) forms a queous dispersions in water which can be processed into highly conductive films.8 1.3.2. Electrochemical Doping If a conducting polymer is deposited onto an electrode, and a potential is applied to the electrode, electrons can be added or removed depending on the magnitude of the

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7 potential applied. The polymer is then positivel y or negatively charged. These charges are compensated by counterions (dopant ions) diffu sing into the polymer from the electrolyte solution. If the doped and ne utral states are stable, then the electrochemical doping/dedoping is reversib le and the polymers are electroactive For many conjugated polymers, the electrochemical oxidation/reducti on processes cause a change of optical absorption and, if the changes occur in the visible range, a change of color. This phenomenon is called electrochromism This property can be used in applications such as electrochromic devices (ECDs), “smart” windows, and absorptive/reflective devices.9,10 In the case of light-emitting electrochemical cells (LEC), a blend of an emitting conjugated polymer with an ion-transport polym er and an electrolyte salt (for example, MEH-PPV, PEO and lithium trifluorometha nesulfonate) is sandw iched between two metal electrodes (Figure 1-7).11 Figure 1-7. Schematic representation of a LEC device. A) LEC device with no voltage applied; B) LEC device shortly after a pplication of a volta ge bias showing electrochemical doping at the interfaces ; C) LEC device after diffusion of the charge carrier in the material bulk and recombination, leading to lightemission.

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8 When a sufficient voltage is applied to th e polymer, holes and electrons are injected at the cathode and anode crea ting p-type and n-type ch arge carriers, which are compensated by counterions from the solid elec trolyte. A front of charge carriers moves from each electrode to the center under the in fluence of the electric field applied between the electrodes. Eventually, the hole and elec tron recombine, forming an excimer which relaxes to the ground state by emi ssion of light (Figure 1-7C). 1.3.3. Fluorescence and Photoche mical Charge Transfer When light is absorbed by a conjugated polymer, an electron is promoted from the valence band to the conduction band. Normally, these excited states would recombine and return to the ground state yieldi ng their excess energy by fluorescence, phosphorescence or non-radiative decay. Anothe r process is energy transfer to an acceptor. If an electric fiel d is applied, or if an elect ron-accepting or electron-donating species (with appropriate HOMO and LUMO levels) is nearby, then charge separation of the two charge carriers may also occur. Th is is the general idea behind photovoltaic devices, where the sunlight en ergy is collected and convert ed into electrical power. A complete literature review on photovoltaic s was recently written in the Reynolds group.27c 1.3.4. Interfacial Doping Interfacial doping is similar to electrochemical char ge injection, but lacks charges compensation by electrolyte. This is seen in or ganic field-effect tran sistors. As shown in Figure 1-7, a typical OFET is made of two elect rodes (source and drain) separated from a third electrode (the gate) by a semiconducting la yer coated on dielectric material. When a voltage is applied at the gate the dielectric material behaves like a capacitor and charges build at the gate electrode. Opposite charges build at the conjugated polymer/dielectric

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9 material interface. Figure 1-8 shows the ex ample of a p-dopable material. As p-doped sites appear, current flows from the source to the drain. As the gate voltage is increased, the current rises as the number of charge carriers increase. Figure 1-8. Schematic diagram of a thin film transistor. The semi-conducting material is a p-dopable material. Since current is directly proportional to the charge mobility of the material, the thin film transistor configuration can be us ed to measure hole or electron mobilities. An important point is that other methods can be used to measure mobilities, yielding different values due to thei r different configurations.12 These methods include hole-only devices or time-of-flight measurements. In hole-only devices, the p-dopable semiconducting material is sandwiched between two electrodes. At the cathode, a low work function metal creates a large ba rrier for electron inje ction. The result is that the mobile charges circulating in the device are only holes, not electrons. Another essential difference is that the two electrode configur ations probe the bulk material, whereas the gate-source-drain configuration probes only th e mobility of a thin la yer at the dielectricsemiconductor interface. Therefore, one must consider carefully how the mobilities were obtained when comparing mobility values. In organic light-emitting diodes (OLEDs), electrons and holes are injected at electrodes interfaces into a conjugated polymer by applying a given voltage between two electrodes. Contrary to the LEC configuration, no electr olyte is present, and the

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10 electrodes must match the HOMO and LUMO le vels to allow easy charge injection. The remaining concepts are essentially identical. 1.4. Improving Active Material Performance In this part, I will examine selected a pplications to see what properties are necessary to obtain high performance, focusing on the active materials. Still, device engineering plays a significant role in impr oving the efficiency of conjugated polymer devices. I will later discuss how synthetic changes in CP s can achieve these desired properties. Each application requires speci fic structural change s to obtain maximum performance. This is the advantage of CP s and their unique synthetic versatility. 1.4.1. OFETs As described previously, the efficiency of organic field-effect transistors depends mainly on the charge mobility of the semi conducting material. In conjugated polymers, the charge mobility is limited by the ability of charge carriers to hop between neighboring localized states on polymer chains. With this, a high degree of interchain order is required in the polymer. As a result, conjugated pol ymers with a typically high amorphous content yield lower mobilities than small molecules. To obtain high mobility, polymers with a high degree of crystallinity and long range order must be synthesized. P3HT, a semicrystalline polymer, has led to p-type mobilities up to 0.1-0.2 cm2 V-1 s-1.13 The crystalline regions consist of lamellar orga nized interchain stacks, possessing a high degree of interchain interacti on. For most ordered films, it is believed that there is twodimensional interchain charge transport. Mo re recent work on liqui d crystalline polymer yield the highest mobility reported to date with a value of 0.7 cm2 V-1 s-1.14 To some extent, the mobility can be increas ed by careful depositi on of the films. In P3HT, the polymer can be processed easily from solution. The conditions of processing

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11 (solvent, temperature, concentration, etc.) can be tuned to obtain the highest amount of order within the polymer films.15 But this method requires a soluble polymer. Most conjugated polymers, due to -stacking interactions are insoluble. The mobility is also dependent on the molecular weight. Studies show that increased molecular weights lead to dramatically higher mobilities.16,17 This can be explained by higher planarity of the polymer chains leading to increased interchain order and the ability of charge car riers to travel further along the chains before hopping to neighboring chains. 16 Other authors have argued that the improvement observed with increasing molecular weight is due to a difference in morphology. The higher molecular weight polymers form large interconnected domains while the lower molecular weight polymers forms small crystalline doma ins separated by the amorphous matrix.17 It was also shown that impurities or defect s must be avoided. For example, partial doping, although it leads to higher mob ilities, is detrimental to fi eld-effect transistors as it yields poor “On-Off” ratios, m eaning that even when no voltage is present at the gate the transistor still conducts current. 1.4.2. Photovoltaic Application To be a commercially interesting alternativ e to inorganic materials, it is estimated that a power-conversion efficiency of at le ast 10% is required for photovoltaic devices.18 Much work has already been performed in the last few years towards this objective. Power-conversion efficiencies up to 3-5% have now been obtained.19 However, it is clear that new concepts and new materials are need ed to improve this value even further. Several factors can be tuned syntheti cally to increase photovoltaic powerconversion efficiency. 1) The absorption of photons can be improved. The polymers used so far have too high bandgap and most of th e solar energy is not ab sorbed. Therefore, a

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12 low band-gap polymer able to absorb the intense NIR emission (700 nm, 1.4 eV) of the sun must be synthesized. Blends of conjugated polymers can also be used to broaden the absorption profile of the devices.20 2) Increase the interfacial surface area. This has already been accomplished by replacing th e bilayer device configuration with a bicontinuous bulk heterogenous junction conf iguration in donor-acceptor photovoltaic devices. In bulk heterojunction devices, both donor and acceptor are intimately mixed, resulting in a significant im provement of the efficiency.21 Further improvement can be obtained by decreasing the domain size in the blend layers. However, the domain size must be large enough so that recombination is prevented and the charges are carried efficiently to the electrodes. It is estimated that an exciton ca n travel an average of 10 nm before returning to the ground state implying an optimum distance of 20 nm for the size of the layers, so that the accep tor is within reach of all ex citons generated in the donor materials. This morphology control can possi bly be obtained in block copolymers. By maintaining a low polydispersity, controlling the nature and size of the blocks, precise control of the morphology is achieved. 3) C ontrol of the active materials’ HOMO and LUMO levels is essential. As fullerene and its derivatives have proven to be the best acceptors, I will look only at the donor HOMO and LUMO levels. Control of the LUMO level plays a decisive role in the charge sepa ration process. It is estimated that the value of the donor HOMO must be at least 0.3 eV above the LUMO of the fullerene LUMO level to enable efficient charge separa tion by overcoming the exciton binding energy.22 The HOMO of the donor is important too, as it is believed to control the open-circuit voltage and the power-conversion efficiency.18 4) In addition, the materials used in photovoltaic devices must have high mobility values. High electron and hole mobilities

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13 will afford fast transport of charges to the electrodes and avoid recombination. Low mobility of either holes or electrons will resu lt in an increase of the series resistance, decreasing the current generated by the device.19 Therefore, a material having significant interchain interactions and some crystallinity should improve the ch arge transport in the photovoltaic cells. 1.4.3. Polymer Electroluminescent Diodes (PLEDs) Essential to PLEDs is to control the ba ndgap. By modifying the bandgap, albeit is possible to change the color emitted by the polymer. Obtaining blue, red and green emitting polymers opens the way for full-colo r display applications. In Figure 1-9, several conjugated polymer along with thei r emitted colors ar e introduced. These materials afford access to every color required for display applications. S n Red/near-IR n PFO Blue n PFO-BT N S N O O n MEH-PPV Green Red-orange POPT Figure 1-9. Representative luminescence co lors of some conj ugated polymers. Netherveless, if any colors can be obta ined, the efficiency of the light-emission process and the brightness are no t satisfying. Part of the limited efficiency comes from a theoretical limit inherent to the electrolumin escence process in conjugated polymers. In PLEDs, electrons and holes are injected at bot h electrodes. When an electron-hole pair is

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14 formed, simple spin-statistics predicts that 25 % of the excited states are singlet states, and 75% are triplet states. It is believed that 25% percent is the theoretical maximum efficiency achievable in polymer light-emitti ng diodes. However, more recent theoretical studies have since suggested that th is might not apply to all polymers.22 To estimate the efficiency of the emission once a singlet excited state is formed, it is necessary to look at the photoluminescence quantum efficiency. Film photoluminescence quantum yield, the ratio of the amount of emitted photons to the absorbed photons, gives us a good gauge of whether a polymer is a good candidate for OLED applications. The quantum yield is highl y dependent on the extent of interchain interactions. After recomb ination the presence of -stacking interactions in conjugated polymers leads to efficient interchain energy transfer to non-emissive, low energy traps. The excitation energy is thus lost thr ough non-radiative decay. In highly ordered materials, although the solution quantum yields are often very high, the film quantum yields are very low. To obtai n higher quantum yield values, in terchain interactions must be prevented. Poly(2methoxy-5-(2-ethylhe xyl)oxy-paraphenylen evinylene) (MEHPPV), shown in Figure 1-9 is one of the most efficient polymers re ported to date in PLEDs. It displays high quantum yield in th e solid-state due to several factors: 1) presence of bulky and flexible 2-ethylhexyloxy si de chains, 2) main chain disorder due to the presence of both syn and trans substitu ted double bonds, 3) interchain disorder induced by the asymmetry of the monome r with methyloxy and ethylhexyloxy side chains, and 4) presence of te trahedral defects due to inco mplete conversion from the saturated precursor to the unsaturated polymer.

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15 Low mobilities are an advantage as charge s spend more time within the active layer and chances of recombination increase. But the mobilities of elect rons and holes also need to be balanced so that recombination oc curs within the active materials, not at the electrode interface. This is difficult as ther e are few polymers having similar electron and hole mobilities. Introducing additional layers at the electrodes to transport or block charges solves the problem. Solubility of the polymers is of course required for inexpensive, easy proces sing of the polymers. 1.4.4. Electrochromic Devices As mentioned before, the redox process in el ectrochemical devices is very different as counterions balance the doped states. This implies that for efficient switching of an electrochromic device, the dopa nt ion must be able to penetrate the polymer film efficiently and the electrons mu st be able to move from the electrode inside the polymer films.23 Highly ordered polymers dope slowly since they possess cr ystalline regions, where the dopant ions cannot penetrate easily. Amorphous materials are therefore excellent candidates for these applications. However, some interchain interactions are necessary for electron transport between the electrode and the polymer bulk. PEDOT, used in electrochromic windows, switches from a dark blue absorptive color to a highly transmissive sky blue color with a switching spee d of ~2s. This is much shorter than most inorganic electrochromic materials. In creasing amorphous domains and decreasing interchain interactions is expected to impr ove switching speeds. This should increase the doping level resulting in better contrast between neutral and doped state.24 Moreover, the control of both the neutra l and oxidized state colors must be obtained. By tuning the bandgap, a vari ety of colors are now available.25 Large bandgap polymers, with absorptions in the UV region of the electromagnetic spectrum, are clear in

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16 the neutral state but colored in the doped state, as polaron and bipolaron intragap optical transitions are shifted to lower energies in the visible spectrum range. Polymers with absorptions in the visible region will display a bathochromic shift in the doped state and can be colorless. This is the case for PProDOT-Me2 and PEDOT, which absorb in the red and have a dark blue color in the neutral state. When doped, the polymers absorb in the infra-red and are mostly transparent. Polymer solubility is also essential for inexpensive processing, as electrochemical polymerization is problematic when c onsidering large area applications. 1.5. Synthetic Control in Conjugated Polymers This section will highlight how synthetic changes can affect the properties of conjugated polymers. Discussing bandgap modification through s ynthetic changes, Roncali has shown that the bandgap is determined by the sum of several contributions: Peirls distortion (or bond-length alternation (BLA)), substituents eff ects, intrachain interactions, interchain interactions and resonance effects.26 A donor-acceptor contribution can be added to provide a more complete description, as this effect does not obviously fit in the above. It must be noted that all contributions ar e connected and that tuning the individual contributions will result in changing the others. All the parameters described above are not only defining the bandgap value, but also the properties of the conjugated polymers. In this section, only the substituents effects, and interand intrachain interactions will be detailed as they are most relevant to the work presented in this dissertation. Mo re information on donor-acceptor systems can be found elsewhere.27

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17 1.5.1. Substituent Effects By introducing substituents on the co njugated polymer backbone, HOMO and LUMO levels can be controll ed precisely. By attaching el ectron-donating or electronwithdrawing chains in dir ect conjugation with the conj ugated backbone, the HOMO and LUMO will be increased and decreased, respectively. Poly(3,4-alkylenedioxythiophenes) (PXDOTs) are examples of a donor substituen t effect. By introducing the oxygen at the 3and 4positions of the thiophene, -donation of the lone pair s into the thiophene ring occurs. As a result, the HOMO level is ra ised (-4.1 eV for neutral PEDOT, -5.3eV for P3HT) and the bandgap is decreased (1.6 eV for PEDOT, 2.35eV for P3HT). PXDOTs are therefore much easier to oxidize than pol ythiophenes and a bathochromic shift is observed in their absorption spectrum (polymer s are more blue). If electron-withdrawing species are introduced in conjugation with the conjugated backbone, the result is a lower LUMO level and a smaller bandgap. The oxyge ns have also an inductive electronwithdrawing effect but it is overwhelmed by the resonance donating effect. But if a methylene spacer is introduced between the backbone and the oxygen, then the resonance effect no longer occurs. The inductive effect is dominant and the oxidation potential is raised. Compared to poly(thioph enes), it was shown that poly(3alkyloxymethylthiophenes) have 100mV highe r oxidation potential, corresponding to 0.1 eV lower HOMO levels.28 1.5.2. Intrachain Interactions When the backbone of a conducting polymer is twisted out of planarity, the orbital overlap decreases, resulting in a decrease of the effective conjugation length.29 The bandgap will be much higher in twisted poly mers than in planar polymers. This leads to blue-shifted absorption and emission spectra.

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18 Internal twisting has a dramatic effect on conductivity and charge transport in the solid state. With increased twisting, intrachain charge tran sport along polymer chains will decrease strongly. This results also in cha nges in interchain ordering which is highly dependent on the individual chains confor mations. Normally, polymers chains with a strongly twisted backbone cannot order easily in the solid state. One exception is possible where the twisting is regular leading to a formation of a helical structure.30 Polyfluorenes and polycarbazoles are good ex amples of highly twisted materials. They are transparent in the neutral state, and emit blue light. Ster ic repulsions from neighboring hydrogens on adjacent aryl rings prevent a planar conformation. Since interchain ordering is strongl y hindered, these two polymers are excellent candidates for light-emitting applications having high fluorescence quantum yield efficiencies.31 In addition, these polymers are cathodically colori ng polymers. When oxidized, they absorb in the visible range and are colored. When neut ral, the polymers are highly transmissive, as they mostly absorb UV radiations. Draw backs of these polymer s include high turn-on voltages in PLEDs, high oxidati on potential in electrolytes, and problems of degradation over time leading to color changes. Another striking example of the importance of intrachain order is found in poly(3alkylthiophenes). The monomer is not symmet ric and can lead to Head-to-Tail (HT), Head-to-Head (HH) and Tail-to-Tail (TT) ar rangements during polymerization (Figure 110A). When the polymer is obtained from el ectropolymerization (see chapter 2) or FeCl3 mediated chemical polymerization, the polymer is regiorandom and contains significant amounts of HH and TT couplings. This creates steric interactions between every other thiophene unit, as shown in Figure 1-10B, fo rcing twisting of the conjugated backbone.

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19 Figure 1-10. Effect of structural regulari ty on poly(3-octylthiophe ne) chain conformation. (A) Regioregular P3OT; (B) Regioirregul ar P3OT; twisting arises from steric interaction at the H-H site. Adapted from ref. 32. This torsion results in low intercha in interactions, low mobilities and low conductivities. On the other hand, if the polym er is obtained by Rieke polymerization or Grignard metathesis polymerization, then a high degree of regioregularity (HT >95%) is obtained.32 These polymers can adopt a planar conformation with higher conjugation lengths. The planarity enables a high degree of in terchain interactions in the solid state, leading to an increase of conductivity and mobility of several orders of magnitude.33 In solution, the regioregular samples absorption displays a bathochromic shift (20-30 nm), indicating a more planar (rod-like) co nformation and longer conjugation length.34 This is much less than the shift observed in the soli d state (140 nm), which implies that alkyl poly(thiophene) chains have a significant degree of confor mational freedom in solution,

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20 and therefore display smaller regioregular ity dependence. Because of the increased planarity, P3ATs are strongly colored in th e neutral states, with a bandgap around 2.3 eV. When oxidized, the absorption is shifted to l onger wavelengths and the polymer is blue colored. Intrachain twisting also leads to change s in emission colors. Figure 1-11 shows a series of different substituted polyt hiophenes with their emission colors.39 Disubstitution of thiophene leads to a high degree of twisting arising from steric re pulsions between side chains on adjacent thiophenes, and also steric interactions between side chains and the large sulfur atom. The polymers then have shorter conjugation lengt hs, and their emission shifts to higher energy (blue-shift) as the twisting increases. S n Green S n S n BlueBlue S n G r een S n R ed / nea r -I R Figure 1-11. Color tuning of film lumine scence though intrachain twisting. The driving force is steric repulsion between bulky groups. 1.5.3. Interchain Interactions As seen above, intrachain planarity fa vors interchain inte ractions. Another important parameter is the regul arity of the chains. In poly( m -phenylene) polymers, strong intermolecular order is observed despit e that the chains having a helical, nonplanar backbone.30 The same regularity in the side chains is needed to allow interchain order.

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21 The density and the nature of si de chains also play a role in the solid state ordering of the chains, as shown by Wegner et al. on substituted poly( p -phenyleneterephthalate) rigidrod polymers.35 When a high density of identical side chain is used, the polymer yields two-dimensional lamellar packing. When a spacer without side chains is used between terephthalic units bear ing linear alkyl side ch ains, the side chains on neighboring lamellar stacks are interdigitated. With higher side chain density, interd igitation is not possible. The packing described above is general to rigid-rod polymers and applies to most regioregular conjugated polymers. Winokur et al. demonstrated that poly(3hexylthiophenes) form n on-interdigitated stacks.36 The side chains are essential to the solid state packing as in plan ar alkyl polythiophenes side chains extend into the plane of the backbone, and do not present any hindrance to the chains stacki ng. Since the tendency of the side chains to crystallize increase s with the number of carbons, more order is observed in poly(thiophenes) with longer side chains. Th is leads to significant improvements in conductivity.33 Introduction of bulky groups instead of linear considerably decrea se the interchain interactions, as steric hind rance is introduced in the st acking direction. Poly(3-(2Smethylbutyl)thiophene) displays much lower mobility (10-3 cm2V-1s-1), even though the branched group is small.37 By introducing larger branching, interchain interactions can be decreased further. This has proved a very efficient method for the synthesis of highly luminescent polythiophenes.39,71 The presence of the heavy sulfur atom helps intersystem crossing to the triplet state, resu lting in limited solution fluorescence quantum yields (0.2-0.4).38 A much bigger issue is that poly( thiophenes) have a high degree of interchain order in the solid state resulting in low film quantum yields. By introducing

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22 steric bulk in the side chains, interchain interactions are strongly decreased and the photoluminescence quantum yield can be greatly improved (Figure 1-12).39 Poly(3-(2,5dioctylphenyl)thiophene), which has the phenyl ring perpendicular to the poly(thiophene) backbone, has a high film quantum yield of 0.24 (0.37 in CHCl3). S n S n S n QY(CHCl3)=0.37 QY(film)=0.24 QY(CHCl3)=0.27 QY(film)=0.04 QY(CHCl3)=0.26 QY(film)=0.09 S n QY(CHCl3)=0.18 QY(film)=0.09 HT=70% HT=70% HT=94% HT=90% Figure 1-12. Fluorescence quantum yield depe ndence on substituents bulk. Both solution and film fluorescence quantum yield ar e provided. The regioregularity is provided as some polymers have limited HT content, which might result in higher film quantum yield. All polymers are red-emitters. Adapted from ref. 39. Interchain interactions also have a strong effect on the bandgap and the absorption/emission properties of conjugated polymers. Strong -stacking interactions lead to significant shifts of the bandgap. The shift depends he avily on the relative orientation of neighboring chai ns, as shown in Figure 1-13.40,41 For H-aggregates, formed when two chromophores are in cofacial arra ngement, the transition from the ground state to the lower level of the excited state is fo rbidden but the transition from the ground state to the upper level is allowed, leading to a blue-shifted absorption. For the same reason, the emission for such aggregates is expected to be strongly quenched. 42 For J-aggregates, formed when two chromophores are in a stagge red (“brick-work”) arrangement, there is a

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23 bathochromic shift, as the transition from the ground state to the uppe r level of the dimer excited state is forbidden and the transition from the ground state to the lower level is allowed. In this type of aggr egate, strong emission is seen.43 A third type of aggregate, where each chromophores is tilted relative to its neighbors, leads to lit tle or no shift of the absorption since both transitions to the ex cited state are allowed. Only if the Davydov splitting is large enough, it is possible to observe splitting in the absorbance spectrum. S S S S S S S S S S J-aggregate a S S S S S S S S S S b ObliqueArrangementS S S S S S S S S S H-aggregate Figure 1-13. Davydov splitting in interchain aggregates. The resulting energy levels and absorption spectrum are also shown. Solid Lines: allowed transition; dashed lines: forbidden transitions. Adapted from reference 77. Oblique chromophores arrangement has been reported by Swager et al.44 Using a poly(phenylene ethynylene) (PPE ) copolymer with alternated pentiptycene and chiral

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24 dimethyloctyl side chains, they showed that the film fluorescence quantum yield is 0.65, one of the highest reported to date. 1.6. Towards Soluble Conjugated Polymers Unsubstituted polythiophene, polypyrrole, polyphenylene and other CPs are insoluble, intractable and infusible. This makes them practica lly useless for most applications. On the other hand, soluble organic conjugated polymers can be spraycoated, spin-coated, or even printed. Obtain ing solubility in conjugated polymers is, however, a difficult task due to thei r propensity to form interchain -stacks. The individual interactions are weak, but they ad d up to a strong interaction. To induce solubility, it is necessary to decrease interc hain interactions, and to make the solventpolymer interactions more favorable. Substitu ents increase the entropy of the polymer chains, and increase the solvent-polymer in teractions. By selecting polar or ionic substituents (oligoethers chains, phosphate, carboxylate, sulfonate, ammonium, etc.), solubility in polar solvents (i ncluding water) can be achieved.45 With nonpolar substituents (alkyl chains for example) solu bility in organic solv ents can be obtained. Bulky substituents create a la rger increase in en tropy, and prevent a close chain packing. But as discussed earlier, this will decrease m obility and conductivity of the materials. For applications where high mobility or conductiv ity is required, substitution with linear substituents is then a better approach. Another possibility is to intr oduce regioirregularity in the backbone or induce intrachain twisting bu t this often leads to decreased interchain interactions. It is therefore important to consider the application when choosing which method will be the most appropriate to obtain solubility. Soluble polymers can be obtained thr ough a wide variety of polymerization methods.46 The most used is FeCl3 polymerization. It directly uses the

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25 electropolymerizable monomer and does not require further functionalization. The polymerization mechanism proceeds through fo rmation of the radical cation of the monomer that propagates through coupling w ith other monomer units. The polymer is obtained in the oxidized state, and reduction of the polymer ba ck to the neutral state as well as removal of the iron catalyst is difficu lt. Also, the high reactivity of the cation radical leads to numerous side reactions (in the case of al kyl poly(thiophene)s crosslinking through the 3 position of th iophene can occur), leading to high polydispersity. In addition, this method yields highly regioirregular polymers. By using metal-mediated polymerization, side reactions can be eliminated. The process requires functionalization of the monomer with halogen or organometallic groups (organomagnesium, organotin or organoborates). Introduction of the metal catalyst yields the neutral polymer, removing the chemical reduction step. Regioregularity can be obtained if the functionality of the monomer, catalyst and reaction conditions are well chosen. Figure 1-14 presents polymerization co nditions leading to re gioregular polymers. One drawback of this polymerization conditions is that they require cryogenic conditions. A new method developed by the McCullough group, Grignard Metathesis (GriM) polymerization removes that constraint, pr oviding a simple and convenient way to prepare regioregular, neut ral conjugated polymers.32,33,46,47,48,49,85 It requires preparation and purification of a dibrominated analog of the electropolymerizable monomer. For the polymerization step, the hal ogenated monomer is reacted with one equivalent of methylmagnesium bromide, converting one bromine to an organomagnesium functionality. After the convers ion is complete, a coupling ca talyst such as Ni(II)dpppCl2 is introduced, leading to a fast polymerization.

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26 Figure 1-14. Polymerization method leading to regioregular Poly(3-alkylthiophene)s. Adapted from reference 47j. The mechanism of the reaction is still unde r investigation. It may proceed through a chain growth process (Figure 1-14).48 During initiation and reduction of the Ni(II) catalyst to Ni(0), the Ni(0) forms an associat ed pair with the coupling product. Following a cycle of oxidative addition, transmetalation and reductive elimination, a monomer unit is added to the chain, and the associated pair is reformed. This implies that the polymerization is controlled not by stoich iometry of bromide to organomagnesium functionalities as would be expected in a condensati on polymerization, but by the monomer to catalyst concentr ation ratio. The McCullough group also demonstrated that Grignard Metathesis is a “ quasi-living” polymerization, wi th the chain end remaining active at the end of the polymerization process,49 allowing for the func tionalization of the chain ends and the synthe sis of block copolymers.

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27 Figure 1-15. Proposed chain growth mechanis m for Grignard Metathesis Polymerization. Adapted from ref 48. Grignard metathesis is therefore a very promising method for obtaining tailored block copolymers with controlled morphology, cr ucial in photovoltaic devices and lightemitting applications. However, it must be pointed out that chain termination still occurs at high conversion, and the polymerization is therefore not ye t “controlled”. The polydispersity, although quite low, is still much higher than anionic or cationic living polymerizations. It is also not obvious that the study for poly(3-hexylthiophene) can be transferred to other monomers such as more electron-poor or electr on-rich monomers, or that the molecular weights can be obtained re producibly. Much work must still be carried out to achieve true living polymerization but initial re ports so far are truly exciting.

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28 In this dissertation, after giving a general experimental overview in Chapter 2 and a detailed introduction to dioxythiophene-based polymers in Chapter 3, I will discuss how electrochromic properties of disubst ituted poly(3,4-propylenedioxythiophenes) (PProDOT) are greatly improved by introduci ng branched substituents that decrease interchain interactions an d yield more amorphous polymers. The branched alkyl substituted PProDOTs, presented in Chapter 3, yield polymers that self-assemble during processing and give ordered aggregates of stacked chains. Alkoxy substituted PProDOTs, described in Chapter 4, yield more disordered aggregates. This leads to Chapter 5 which describes the synthesis and properties of chir al branched PProDOTs along with the use of circular dichroism (CD) to investigate the aggregation and ordering behavior in PProDOTs. Finally, Chapter 6 shows the synt hesis and properties of the first soluble poly(3,4-phenylenedioxythiophene)s (PPh eDOTs). Regiosymmetric didodecyl PPheDOTs with linear substituents have a high degree of order and provide an excellent platform for the development of high mobility and high conductivity materials, while asymmetric disubstituted PPheDOTs containing dodecyl and ethylhexyl substituents are highly disordered and provide an excellent pl atform for the development of light-emitting materials.

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29 CHAPTER 2 EXPERIMENTAL METHODS In Chapter 1, the theory and concepts wh ich control the chemistry and properties behind conjugated polymers were presented. So me areas where CPs find applications and what can be done synthetically to improve th e performance of the materials were also described. In this chapter, all of the expe rimental methods used to characterize the structure as well as the electronic and optical properties of the molecules and polymers presented in this dissertation will be introduced. 2.1. General Synthetic Methods All chemical and solvents were purchased from Aldrich or Acros and used without further purification unless othe rwise noted. Dry THF and dry di ethyl ether were obtained by distillation from Na/benzophenone ketyl. Dry dichloromethane and dry acetonitrile were obtained by distillation from CaH2. All reactions were performed under argon atmosphere using standard Schlenk technique s. Detailed synthesis of each compound presented in this dissertation can be found at the end of each chapter. 2.2. Molecular Characterization All the new molecules presented in this di ssertation were structurally characterized by 1H NMR and 13C NMR, High Resolution Mass Spectrometry. 1H, 13C NMR were obtained from a Gemini 300 FT-NMR, Me rcury 300 FT-NMR, or VXR 300 FT-NMR. HRMS was obtained on a Finnigan MAT 95Q mass spectrometer. The purity was evaluated using elemental analysis carried out by the elemental service at the University of Florida (C, H, N) or Robert son Microlit Laboratories, Mich igan (C, H, N, S, Br). IR

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30 spectroscopy was also used for functional group identification and was recorded on a Perkin-Elmer Spectrum One FT-IR spectrophotometer. 2.3. Electrochemical Characterization Monomer electrochemistry, polymer electrodeposition and polymer electrochemistry were performed using a st andard three electrode s configuration: a platinum button working electrode (area= 0.02 cm2), a platinum foil counter-electrode (S~1 cm2>>0.02 cm2) and a silver wire pseudo-referen ce (Figure 2-1). Th e potential is applied from an EG&G Potentiostat/Galva nostat 273A. The Pt counter-electrode was cleaned by Bunsen-burner flaming. The silver quasi-reference was polished using sand paper. The Pt button working electrode was cleaned by rubbing gently with a kimwipe wetted with toluene. The silver wire was sy stematically calibrated with a ferrocene solution following experiments. To determin e with precision the monomer and polymer oxidation potential, an immediate calibration with ferrocene is performed following each experiment. A solution of 0.1M tetrabutylammo nium perchlorate (TBAP, prepared from tetrabutylammonium bromide and perchloric ac id solution, recr ystallized in methanol) in dry acetonitrile (from CaH2) wa s used as electrolyte. Figure 2-1. Three electrodes (Pt button, larg e Pt foil counter, Ag wire reference) electrochemical setup.

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31 2.4. Polymer Characterization 2.4.1. Structural Characterization The polymers were characterized by 1H NMR, 13C NMR (if polymer soluble), and elemental analysis. Due to the fast relaxati on from the polymers, up to 20,000 scans were often needed. Either CDCl3 or C6D6 was used depending on the polymers solubility. GPC was performed on two 300 x 7.5 mm Polymer Laboratories PL Gel 5 M mixed-C columns with a 2996 photodiode array detector at the max of the polymer solution. A constant flow rate of 1 mL/min was used. Molecular weights were obtained relative to polystyrene standards. Polymer solutions (0.5 mg/mL) were prepared in THF and filtered through a 450 nm GPC filter before injection. In the case of PPheDOT(C12)2 described in Chapter 7, which is only soluble in chlorinate d or aromatic solvent above 80C, the NMR was carried out in 1,1,2, 2-tetrachloroethane-d2 at 120C. GPC analysis on PPheDOT(C12)2 (Chapter 6) was carried out by Dr Steve Eyles at the University of Massachusetts, Amherst. It was performe d on a PL220 high temperature GPC (Polymer Laboratories, Inc., Amherst MA). The sample was injected at 5 mg/mL concentration using 1,2,4-trichlorobenzene at 135 C, 1 mL /min as mobile phase. Separation was achieved using a set of four Polymer Labs Mixed A columns (7.5 x 300 mm). The polymer was detected by differential refrac tive index. Molecular weights were obtained relative to polystyrene standards. 2.4.2. Thermal Characterization All polymers were characterized by ther mogravimetric (TGA) and differential scanning calorimetry (DSC) analysis. TGA wa s carried out on a Perkin-Elmer TGA7 thermogravimetric analyzer. DSC was car ried out on a TA Instrument DSC Q1000 calorimeter.

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32 2.4.3. Morphology Characterization This work was carried out in collaboration with Dr Wojciech Pisula, Nok Tsao and Pr Klaus Mullen of the Max Planck Institut e for Polymer Science, Mainz, Germany. The 2D-WAXS experiments were performed by m eans of a rotating anode (Rigaku 18 kW) X-ray beam with a pinhole co llimation and a 2D Siemens detector. A double graphite monochromator for the Cu-K radiation ( =0.154 nm) was used. For this experiment, fibers were extruded using a home-built mini-extruder.50 A photograph of a poly(paraphenyleneethynylene) extruded fiber can be found in the literature.51 AFM work was done in collaboration with Thomas Joncheray. AFM imaging was carried out in tapping mode with a Nanoscope III AFM (Digital Instruments, Inc., Santa Barbara, CA) using silicon probes (Nanosensor dimensions: T = 3.8-4.5 m, W = 26-27 m, L = 128 m). The images were processed with a second-order flattening routine. 2.4.4. Solution Optical Characterization Polymer solutions were prepared using spectrophotometric grade solvents. New bottles were used, especially with chlorina ted solvents, as old bottles develop acidity leading to oxidation of the polymers. All ab sorption spectra were obtained using a Varian Cary 500 scan UV-vis-NIR spectrophotometer. Thermochromism studies were performed using a SPV 1*1 Varian Cary dua l-cell Peltier accessory. Solution fluorescence spectra of the pol ymers and fluorescence solvatochromism were recorded on a Fluorolog 3. Solution fl uorescence quantum yields were measured relative to a standard. The standard was chosen by analyzing the absorbance and fluorescence spectra of many possible candi dates listed on the Oregon Medical Laser Center website under the Alphabetica l Index of Photochem CAD Spectra.52 Either

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33 Rhodamine 6G (ethanol, ex=480 nm, f= 0.95) or sulforhodamine (ethanol, ex=550 nm, f= 0.9) were found appropriate as standard, depending on the absorption spectrum of the specific polymer considered. The integration ti me and the slits (excitation and emission) were respectively set at 0.5s and 2mm. Wh en doing a quantum yield measurement, it is necessary to record the standard and the fluor escence with the same slits and integration value. The slit size should be increased if the fluorescence signal is low and noisy. However, the signal intensity at max should always be kept well under 107 counts s-1, as the response of the detector is not proportional to the em ission intensity at such high value, resulting in large errors in quantum yields. Integration time can be increased to improve the signal-to-noise ratio (it does not change the signal intensity though). Only spectrophotometric grade solvents were used. Unless specified, absorption of the samples was kept under 0.1 (at max) to prevent intermolecular quenching due to aggregation excessive concentration. The following equa tion was used to calculate the solution fluorescence quantum yield: Equation 2-1: ) (I ) (I ) ( ) ( ) 10 1 ( ) 10 1 (standard sample 2 standard 2 sample sample standard standard sample n n A A A is the absorbance at the excitation wa velength, n is the refr active index of the solvent used to take the fluorescence spectrum, and I is the number of emitted photons (obtained by integrating the fluorescence spectrum). 2.4.5. Solution Processing Techniques The processing of conjugated polymers from solution is an extremely important step in their characterization and application. Different methods are available that lead to various film qualities, control of thickness, and different ea se of processing. In this

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34 section, a description of the processing techniqu es used in this dissert ation is given: dropcasting, spin-coating and spray-coating. 2.4.5.1. Drop-casting Drop-casting is the easiest technique to ma ke a film. But it is also the technique leading to the poorest film quality. The polym er solutions are generally deposited on polar materials (mica, glass, ITO, and most metals). The wettability of the polymer solutions on polar substrates is very low, as all polymers presented in this dissertation are hydrophobic. As a result, the solution tends to concentrate at specific spots and poor film quality is obtained. To improve film quality, it is possible to use a razor blade to spread the solution on the surface as the solvent drie s up but the resulting films still have poor quality. The concentration used is usually 5mg/mL in toluene. 2.4.5.2. Spin-coating Spin-coating leads to the best film quality of all the film deposition techniques. In this method, a substrate is placed in the middl e of the spin-coater and vacuum is applied underneath. The polymer solution is deposited with a pipette all ove r the surface of the substrate. The substrate is then rotated at th e desired rate and after solvent evaporation, a uniform film is formed on the surface. Many factors contribute to the quality of the spin-coated films, as well as the thickness of the deposited layer. The main factors are rotati on speed, solvent, evaporation rate, concentration of the polymer solution and polymer molecular weight. Below is the AFM of a spin-coated film on glass. For AFM imaging, a concentration of 0.2 mg/mL was used. The best solvent, leading to the most ordering was found to be ortho-dichlorobenzene for all polymers. The spin-coating rate used was 2000 rpm. This typi cally led to the formation of homogenous

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35 monolayer thick films. For film fluorescen ce, thicker films are needed, so a higher concentration of 5-10 mg/mL was used, with a spin-coati ng rate between 1000-2000 rpm. Toluene was used as the solvent since it is a good solvent for all of the polymers analyzed for film fluorescence in this dissertation. To increase film thickness, higher solution concentrations or lower spin rates can be us ed, but using excessive concentration or too low a spin-rate can lead to polymer aggr egation, which leads to poor film quality. Spin-coating is the preferred method for making LEDs, LECs or OFETs where high film quality is a requirement. Draw backs of the methods include the loss of materials since most of the deposited solution is ejected off the subtra te (it is possible to recover part of this lost mate rial but it is very tedious), th e fact that only thin films (<300 nm) can be deposited and that a symmetrical su bstrate must be used (disc, square). Also, the method is hard to apply to large surface areas. 2.4.5.3. Spray-coating The spray-coating method is a very practic al method to form uniform films on any kind of surface and applicable to large surface areas. In this method, the polymer solution is placed in a reservoir cup of a spray-brush (Aztek A470), and sprayed through a nozzle using compressed air. The resulting films are very homogenous to the eyes as seen in Figure 2-2. However, a closer look by profilometry reveals that the roughness is much higher than observed in spin-coated films, although it is clear that the films are fully covered. Thick films (1-2m) can be obtaine d through this method. If the conditions are well controlled, the solvent evaporates rapidl y and does not have enough time to dissolve the lower deposited layers. These conditions are pressure (it was found 12 psi to be appropriate for our films), polymer c oncentration (often 5mg/mL, but higher concentration must be used for low molecular weights polymers), solvent (highest quality

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36 films with toluene for all polymers studied) a nd distance from the s ubstrate (at least 1020 cm distance from the substrate is needed, to allow the dispersion of thin droplets from the spray-brush nozzle). For colored films, th e film thickness can be simply controlled by eye during spray-coating, as 50nm differen ces in film thickness are easily seen. Figure 2-2. Spray-coated films of PProDOT-(CH2O(2-ethylhexyl))2 and PProDOT(CH2OC18H37)2. Films are sprayed from a 5mg/ mL solution in toluene at an air pressure of 12 psi. This is a method of choice for electrochr omism characterization and electrochromic devices. 2.4.6. Film Fluorescence Characterization Film quantum yield were obtained using a PTI MOD A1010 white light illumination and an Instruments SA, Inc. monochromator. The light from the source or fluorescence was collected using an ORIEL 70451 integrating sphere and a SpectrumOne CCD detector. The fluorescence quantum yield is then calculated following a published method.53 2.4.7. Spectroelectrochemical Characterization The properties of conjugated polymers, as discussed earlier depend heavily on the redox state. The spectroelectroc hemistry experiment (see Chap ter 1) is used to monitor the variation of optical spectrum with applie d potential. This experiment follows the fundamental optical changes of a polymer as a function of the doping levels, as described in Chapter one. The films’ absorption spect ra were obtained using a Varian Cary 500

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37 scan UV-vis-NIR spectrophotometer. The optical bandgap is obtained from the onset of the neutral polymer transition. A three electrode setup connected to an EG&G Potentiostat/Galvanostat 273 was used to ch ange the potential app lied to the films. Another measurement, allowing one to follow the color with doping, is in-situ colorimetry analysis.54 According to the Yxy color sy stem developed by the Commission Internationale de l’Eclairag e (CIE) in 1931, the color is de fined by its chromaticity (x,y) and by its luminance (Y). These paramete rs were defined based on the “standard observer”, meaning that they were designe d based on how colors are perceived by an average of multiple people. The luminan ce parameter Y can be thought to be the brightness of a color as perceived by the human eye. For example, white is perceived as a very bright color where grey is perceived as less bright, although they have the same chromaticity. The chromaticity is define d by the two parameters x and y, which characterized the color itself, independently of its brightness. They represent two variables defining the color pe rceived and are a mathematical combination of what is detected by the three receptors present in our eyes (often refered to as blue, green, red receptors), each detecting a range of the visible light wavelength. In this dissertation, x,y and Y values were recorded by a Minolta Chromameter CS100. Y is given in Cd/m2 (x,y have no units). Sample was illuminated from behind using a D50 (500K) light source. A background meas urement was recorded using a blank ITO slide in the appropriate electrolyte solution in a quartz cuvette. The colorimetry was recorded using the following settings: calibra tion set at “PRESET”, measuring mode set at “Abs”. And response set at “SLOW”. These settings must be used as other settings will lead to erroneous data All films (except PPheDOT(C12)2) used in

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38 spectroelectrochemistry, luminance and CE e xperiments were prepar ed by spray-coating onto Indium Tin Oxide (ITO) coated gla ss slides (Delta Technologies, 8-12 / ). PPheDOT(C12)2 films were prepared by drop-casting on ITO-coated glass slides from a hot (100C) solution in xylenes, as it is in soluble at room temp erature and cannot be spray-coated. Another useful tool in electrochromic ma terials characterization is the composite coloration efficiency.24 In this measurement, the transmittance of the film at max and the charge injected into the film are recorded as a function of time dur ing a potential step from a potential where the polymer is fully ne utral to a potential where the polymer is fully oxidized. As shown in Figure 2-3 for PProDOTMe2, as the potential is stepped from -0.5V to 1.2V, the transmittance at 585 nm incr eases strongly as the polymer is oxidized and the visible optical transition is bleached, r eaching a plateau when it is fully oxidized. The time required to obtain 95% of the optimum contrast is taken as the switching time of the polymer and is a critical parameter to characterize a material designed for an electrochromic application. Th e coloration efficiency is calculated from the following equations: Equation 2.2: OD= log[T(ox at 95%)/Tred] Equation 2.3: CE= OD/Qd Qd is the charge required to obtain 95% of the total opti cal contrast. T(ox at 95%) is the film transmittance at 95% of the total contrast. Tred is the film transmittance in the neutral state.

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39 Figure 2-3. Time evolution of transmittance and injected charge for an electropolymerized film of PProDOT-Me2. Adapted from ref. 24. The CE value provides a practical way of comparing color change charge efficiency between different materials. Fo r example, our research group showed that PEDOT, PProDOT and PProDOT-Me2 have increasing CE values: 183 cm2/C, 255cm2/C, 375cm2/C.64 This trend correlates well with PProDOTs having a higher contrast than PEDOT (51% %T at max of 585 nm for PEDOT, 63% %T at max of 578 nm for PProDOT, 72% %T at max of 585 nm for PProDOTMe2). PProDOTs also requires less charge to obtain full doping of the polymer. This is explained by PEDOT having more ordered, packed morphology than PProDOT, as the more flexible sevenmembered ring provides steric hindrance to chain packing and allows for easier penetration of the dopant ion. Substitution of the seven-membered ring with methyl groups hinders interchain interaction. This could result in more capacitive contributions

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40 to the current (not contributing to poly mer doping) for PEDOT, than PProDOT and PProDOT-Me2. 2.4.8. Circular Dichroism The method will be discussed in details in Chapter 5 concerning chiral PProDOTs. CD spectra were measured on a JASCO J-815 CD spectrometer, with a Peltier Temperature Programmer model JASCO PTC-348WI. 2.4.9. Conductivity Measurements In this work, most conductivity values we re measured using the four-point probe method. The experimental setup is shown in Figure 2-4. Figure 2-4. Four-point probe conductivity method. This method has several advantages. If th e voltmeter has a high impedance, then problem of contact resistance met in two poi nts measurements is avoided. This method also allows the conductivity to be measured at several locations in the films. An average measurement is then obtained, which is useful since the presence of cracks or morphology defects will alter the measured c onductivity. This cannot be done in methods

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41 involving thermal evaporation of meta l electrodes onto the film, used for PPheDOT(C12)2. The films used for this measurement were all spray-coated onto glass slides (1 square inch), except for PPheDOT(C12)2 which cannot be spay-c oated (a procedure is described later for this polymer). The spray-co ated films were exposed to iodine vapor in an iodine chamber overnight and then qui ckly brought to the Signatone S-301-4 fourpoint probe apparatus for conductivity measur ement. As seen in Figure 2-5, a constant current I (between 1A and 100 A) is a pplied between electrode 1 and 4 using a Keithley 224 current generator (voltage thres hold was set at 30 V, intensity threshold was set at 510-3 A), and the voltage drop between electrodes 2 and 3 ( V) was monitored using a Keithley 197 voltammeter. After obtai ning the film thickness t from a Sloan Dektak 3030 profilometer, the conductivity is then calculated by the following equation: Equation 2.4: = ( V/I) (t /ln2) F where F(t/d) is a correction factor approaching zero when t<
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42 conductivity for the polymer film. Usually, the current applied to electrodes 1 and 4 is set at 100 A. However, it was discovered that fo r the lower conductivity films, the voltage needed to obtain this current quickly rose above the threshol d of 30V after the four-point probe is applied on the film. In this case, th e current was decreased to down to 10 A or 1-2 A. In the case of PPheDOT(C12)2, films could not be spraycoated. Spin-coating from hot toluene solutions (100 C) afforded hom ogenous thin films. Four gold electrodes were thermally evaporated onto the spincast films (Figure 2-5) Copper wires were soldered to the 4 electrodes and connected to the current generator and voltmeter described above for the 4 point conductivity measurement. The films were placed in a specially designed chamber, and sealed unde r vacuum. Bromine was introduced through a septum via syringe and the voltage drop wa s measured. After measurement of the film thickness, conductivity was cal culated using Equation 2.4. Figure 2-5. Four-point conductivity measur ement. Gold electrodes are thermally evaporated on spin-coated polymer film.

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43 CHAPTER 3 SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKYL POLY(3,4PROPYLENEDIOXYTHIOPHENES) (PPRODOT-R2) 3.1. Introduction Chapter 1 described the properties of soluble alkyl poly(thiophene)s. These polymers have good solubilities, but high oxi dation potentials. By introducing two electron-donating oxygens onto the 3and 4-pos itions of the thiophene ring, the oxidation potential is considerably lowe red, and the polymers become stab le in their oxidized state. It also prevents crosslinking at the 3-and 4positions of the thiophene ring, as observed in alkyl poly(thiophene)s. Poly(3,4-ethylenedioxy thiophene) (PEDOT) is an electron-rich, highly conductive polymer that has been used in many applications including anti-static coatings, capacitors, and “smart windows”.56 PEDOT has conductivities up to 200500 S cm-1 in the oxidized form.8 The polymer is highly inso luble because of the high degree of interchain interactions due to a more planar intrachain conformation. This was shown by studies on EDOT oligomer s and theoretical calculations.57 Multiple factors contribute to the planariza tion of the backbone: mesome ric effect induced by the electron-donating oxygens, low ster ic interactions between the sulfur atom and the small oxygen atoms (much smaller than methylene), and attractive sulfuroxygen interactions.58 Also, the two alkoxy substituents are tied toge ther in the six-membered ring. The ring structure is critical since poly(3,4-dialkoxythiophenes) have b een shown to exhibit much lower conductivities,59 attributed to the flexibility of the alkoxy substituents generating intrachain steric repulsion be tween substituents on adjacent thiophenes. As discussed

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44 earlier, this steric repulsion results in in trachain twisting and decreased interchain interactions. Substitution of the six-membered rings of PEDOT with linear tetradecyl alkyl chain induces solubility in organic solvent.60 Shorter linear alkyl chains (C1-C10) do not create sufficient steric hindrance to overcome the -stacking, leading to in soluble polymers. The introduction of such long linear alkyl chains does not disturb the packing of the chains. This is a bit surprising given as inter and intrachain would be expected (the polymer is regioirregular) side chain re pulsion. Theoretical calculations in our group by Alejandro Perdomo (in collaboration with the Bredas research group) show the six-membered ring adopts a twisted chair conformation, in which the substituent lies in an equatorial position within the polythiophene b ackbone plane (Figure 3-1). Figure 3-1. Conformational and substituents effects on 3,4-ethylenedioxythiophenes. (a) side view and (b) back view of EDOT in the “twisted” conformation, calculated to be the most stable conformer using ANNEALING method as implemented in AMPAC and optimized at the B3LYP/6-31G* level of theory. (c) Structures and conductivitie s for a series of alkylated PEDOTs. The conductivities were all obta ined by in-situ conductivity on electropolymerized films.62

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45 As a result, crystallization of the long lin ear alkyl chains yields an improvement of the stacking of the polymer chains and allows for hi gher conductivities.61 With shorter chains that do not order eas ily, the regioirregularity of th e side chains dominates and lower conductivities are observed compared to PEDOT.62 This trend is also illustrated in Figure 3-1. One drawback of neutral PEDOT based polymers is their instability to ambient conditions (air, light and water). Th e polymers easily oxidize in air and degrade over time. This is different with the neutral form of the poly(3,4propylenedioxythiophenes) (PProDOT) based polymers. Although the only difference lies in the presence of the larger 7-membered ring in place of the six-membered ring, PProDOTs are much more stable to ambient conditions and can be stored in air for extended periods of time without oxidizing. Theoretical calculati ons (by Alejandro Perdomo) show that this increased stability may originate from the greater flexibility of the seven-membered ring with two stable conformations: the “twisted” conformation, similar to PEDOT (both in conformation and in energy), and a lower energy chair type conformation (Figure 3-2). The predominant fo rm depends heavily on the substitution of the seven-membered ring. X-ray crystal struct ure on crystalline Pro DOT derivatives have confirmed the existence of these two conformers.63 To induce solubilit y, alkyl chains can be introduced at the 2-position of the pr opylene bridge. This substitution leads to a regiosymmetric monomer; theref ore regioregularity of the side chains in the polymer is induced. Also, interactions between substituen ts of adjacent thiophenes are minimized at this position. Early attempts using methyl (PProDOT-Me2) and ethyl (PProDOT-Et2) substituents yielded insoluble polymers. 24,64 Electropolymerized films of PProDOT-Me2,

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46 PProDOT-Et2 displayed enhanced properties, wi th higher coloration efficiency, and shorter switching times than PProDOT and PEDOT Figure 3-2. Two most stable conf ormations of ProDOT. A) The “ chair ” conformation; B) The “ twisted ” conformation. Calculations were performed using ANNEALING method as implemented in AMPAC. Each conformer found was subsequently optimized at the B3 LYP/6-31G* level of theory. Hydrogens are white; carbons are grey; oxygens are red; sulfurs are yellow. To induce solubility, longer alkyl chains were required. The synthesis of PProDOTBu2 indeed provided the first soluble PProDOT,63a but the solubility was limited to the lower molecular weight fractions (Mn= 3000 g mol-1). To further increase the solubility, the first approach employed was to increase th e length of the linear al kyl side chains. The second was to introduce steric bulk and branched substitu ents. In this chapter are introduced PProDOTs symmetrically substitute d with various branched alkyl groups and the effect of substitution on the properties of the conjugated polymers is discussed thoroughly. The family of polymers synthesized a nd described in this Chapter is shown in Figure 3-3.

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47 S O O S O O nn S O O n S O O nPProDOT(2-methylbutyl)2PProDOT(2-ethylbutyl)2(onlyelectrodeposited) PProDOT-hexyl2PProDOT-(2-ethylhexyl)2 Figure 3-3. Family of branched dialkyl PProDOTs. PProDOT-Hexyl2 was synthesized for comparison and discussion of branching effects. 3.2. Electropolymerized PProDOT-R 2 3.2.1. Electropolymerizable Monomer Synthesis The electropolymerizable monomers were synthesized by transe therification of 3,4dimethoxythiophene and 2,2-dialkyl -propane-1,3-diol, as show n in Figure 3-4. All diols used in this dissertation were synthesized by malonic ester synthesis followed by lithium aluminum hydride reduction as indicated in Figure 3-4.65 The synthesis is easily scalable and the starting materials are inexpensive. In the case of 2,2-dihe xylpropane-1,3-diol, the synthesis was scaled up to a several hundred grams scale in a collaborative work with Benjamin Reeves and Barry Thompson. The key intermediate, 3,4-dimethoxythiophene, was prepared from a copper-mediated Ullm ann ether reaction of 3,4-dibromothiophene. The preparation of 3,4-dibromothiophene from th iophene is also included since much of the 3,4-dibromothiophene used for this diss ertation work was obtained by this method. This product is now commercially available at a competitive price, avoiding large scale, tedious and potentially dange rous steps. These steps include tetrabromination of thiophene (with a large amount of HBr released), followed treatment of

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48 tetrabromothiophene with either two equivale nts of n-butyllithium or Zn metal in acetic acid. S MeO OMe OHOH R R pTSA Toluene S O O R R S MeO OMe S Br2CHCl3S Br Br Br Br 2eq.n-BuLi,-780C orZndust, AceticAcid S Br Br NaOMe,CuO,KI MeOH OHOH R R OO OEt EtO 1)NaH 2)R-Br OO OEt EtO R R LAH Et2O 90% 80% 70-85% 25-50%fromdiethylmalonate 60-80% R=-(2-methylbutyl) -(2-ethylbutyl) -hexyl -(2-ethylhexyl) Figure 3-4. Synthesis of elec tropolymerizable alkyl subst ituted ProDOTs. Branched 2methylbutyl and 2-ethylhexyl derivatives are prepared from racemic reagents. 3.2.2. Electrodeposition and Electrochemistry After thorough purification of the electr opolymerizable monomers, polymer films were electrodeposited onto platinum butt on electrodes. As seen in Table 3-1, the monomer oxidation depends lit tle on the substitution. Table 3-1. ProDOT-R2 monomer oxidation onset and peak potentials. Scan-rate is 50 mV/s. R Eonset (V) Epeak (V) -butyl 0.99 V 1.10 V -hexyl 0.97 V 1.11 V -2-methylbutyl 0.88 V 1.08 V -2-ethylbutyl 0.98 V 1.11 V -2-ethylhexyl 1.03 V 1.11 V All onsets of oxidation or peak potentials are within a range of less than 100mV from each other, consistent with the fact that the substituents are remote from the dioxythiophene ring and do not affect significantly the el ectronic propert ies of the thiophenes. All PProDOT-R2 polymers are easily elec trodeposited in a polar,

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49 electrochemically stable solven t such as acetonitrile. The mo nomers used in this study are soluble in this solvent, but the polymers are not, allowing a smooth deposition of films with various thicknesses. Figure 3-5 illustrates the deposition of a PProDOT-(2ethylhexyl)2 film on a platinum button. -1.0-0.50.00.51.0 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 OO S H H I (mA/cm2)E(V) vs. Fc/Fc+ Figure 3-5. Electrodeposition of PProDOT-(2-ethylhexyl)2 on platinum button electrode. The film was deposited from a 0.01M monomer solution in 0.1M TBAP/ACN, at a scan rate of 50 mV/s. After deposition of the polymers from each of the monomers, the films were rinsed and studied in monomer-free 0.1M TBAP/ACN solution. In contrast to the monomer oxidation, significant differences are observed in polymer oxidati on as the side chains are modified. Figure 3-6 presents the overla yed cyclic voltammetry of all PProDOT-R2 polymers studied. In the butyl substituted se ries, as methyl and ethyl branching are introduced on the 2-position of the butyl side chains, the oxidation peaks are shifted to higher oxidation potentials. In addition, the redox waves become narrower as steric bulk is introduced. In the hexyl series, the sa me trend is observed going from PProDOTHexyl2 to PProDOT-(2-ethylhexyl)2. As the chains with the stronger interchain

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50 interactions are expected to have lower oxidation potential, th is trend is consistent with decreased interchain interactions as the steric bulk of substituents increases. The narrowing of the redox waves may possibly be explained by the increasing open morphology of the polymer films as steric bulk is increased. Figure 3-6. Polymer oxidation in the PProDOT-R2 series. All the polymers were deposited by cyclic voltammetry at 50 mV/s scan rate from 0.01M monomer solution in 0.1M TBAP/ACN. The polyme r oxidation curves we re recorded in monomer-free electrolyte at 50mV/s. Comparing the oxidation curv es of PProDOT-(2-ethylhexyl)2 and PProDOT-(2ethylbutyl)2, it seems that although the st eric bulk of ethylhexyl is greater than ethylbutyl, PProDOT-(2-ethylbutyl)2 has the higher oxidation potential. Examining the onset of polymer oxidation, PProDOT-(2-ethylhexyl)2 has a higher onset poten tial, consistent with a decrease of interchain interactions. The higher oxidation peak for PProDOT-(2ethylbutyl)2 is explained by considering the penetr ation of dopant ions into the polymer film. We speculate that cyclic voltammetry is not only probing thermodynamic behavior of the polymer but also the kinetic diffusion of the dopant ion inside the polymer film. In

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51 the lower potential region of the oxidati on wave, the oxidation of the polymer is thermodynamically controlled and the chains with the lowest oxidation potentials will oxidize first. At higher potent ial the current is limited by the penetration of the dopant ions into the film, which is diffusion li mited. In the case of PProDOT-(2-ethylhexyl)2, the bulkier side chains provide more distance between chain stacks (different from the interchain -stacking distance) and the diffusion of th e dopant ion is easi er, resulting in a lower peak potential. 3.3. Chemically Polymerized Soluble PProDOT-R 2 3.3.1. Synthesis and Polymer Characterization After bromination of the electropolymerizab le monomer, the polymer is prepared by Grignard Metathesis polymerization (Figure 3-7).47 In this method, the chemically polymerizable monomer is reac ted in THF at reflux temperat ure with one equivalent of methylmagnesium bromide (titrated by a published method66). After the halogen-metal exchange is complete, Ni(dppp)Cl2 is added in one portion, in itiating the polymerization. Within a few seconds, the yellow color of the catalyst turns red or purple as polymer is formed. The polymerization is complete a few hours following introduction of the catalyst. S O O R R NBS DMF S O O R R S O O R R 1.MeMgBr,THF 2.Ni(dppp)Cl2 Br Br n Figure 3-7. Grignard Metathesis po lymerization of soluble PProDOT-R2. After purification by Soxhlet extraction in MeOH (to remove magnesium salts, polar impurities) and Soxhlet extraction with hexanes (to remove low molecular weight

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52 polymer), the polymer is extracted with dich loromethane, chloroform or toluene. All polymers show high solubility in many organic solvents (e.g. toluene, chloroform, THF). Proton and carbon NMR confirmed the structur e (see Experimental Section). Molecular weights were estimated by GPC analysis in THF and are shown in Table 3-2. PProDOTHx2 could be obtained in 5-10 g quantity, demons trating that the synthesis is scalable. Table 3-2. Molecular weight analys is of GriM polymerized PProDOT-R2. Molecular weights are estimated vs. polystyrene standards. Mn (g mol-1) Xn Mw (g mol-1) PDI Butyl 6,000 22 n/a n/a Hexyl 27,000 83 47,600 1.73 2-methylbutyl 17,000 57 40,000 1.76 2-ethylhexyl 43,000 113 62,600 1.6 It is important to point out that the numb er-average molecular weight is well above the effective conjugation length, and the opti cal and electronic prope rties are saturated. Figure 3-8 shows the evolution of UV-Vis absorp tion spectrum as it is eluted out of the GPC columns. Up to a number-avera ge molecular weight of 5,700 g mol-1, there is a significant shift of the max. Above this molecular weight the maxima of absorption remain constant, suggesting an effective c onjugation length of ca. 15 repeat units. 200300400500600700800 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Absorbance (nm) Mn Xn 14,300 (46) 10,700 (28) 8,600 (23) 7,500 (19) 5,700 (15) 4,000 (10) 2,800 (7) 576 573 539 538 539 572 570 537 536 567 532 526200300400500600700800 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Absorbance (nm) Mn Xn 14,300 (37) 17,600 (46) 21,100 (55) 27,000 (71) 28,800 (75) 29,500 (77) 32,200 (84) 576 539 539 577 578 539 540 579 577 540 540 576 539 576 Figure 3-8. Evolution of UV-Vis absorption spectrum with molecular weight for PProDOT(2-ethylhexyl)2. Number-average molecular weights are estimated vs. polystyrene standards.

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53 The thermal properties of the bulk po lymers were studi ed by TGA and DSC analysis. TGA indicates that the polymers have good thermal stability, reaching 5% weight loss at ca. 350C. For each polymer, th e weight loss corresponds to the loss of the 2,2-dialkylpropyl unit. DSC anal ysis revealed no transition in the -150 to 250C range suggesting the polymers are amorphous, as e xpected from introducing bulky branched substituents. 3.3.2. Solution Properties The solution properties we re studied by UV-Vis abso rbance and fluorescence spectroscopy. Figure 3-9 shows the spectra for PProDOT-Hexyl2 and PProDOT(2ethylhexyl)2. 400500600700800 0.00 0.02 0.04 0.06 0.08 0.10 0.12 (nm)AbsorbanceStokes shift= 860cm-1548 nm 585 nm0.0 0.2 0.4 0.6 0.8 1.0 1.2 Fluorescence616 nm 672 nm 740 nm PProDOT-Hexyl2 400500600700800 0.00 0.02 0.04 0.06 0.08 0.10 0.12 (nm)AbsorbancePProDOT-EtHx2595 nm 553 nm Stokes shift= 652 cm-10.0 0.2 0.4 0.6 0.8 1.0 1.2 Fluorescence677 nm 619 nm 747 nm Figure 3-9. Absorption and photolumin escence spectrum of PProDOT-Hexyl2 and PProDOT(2-ethylhexyl)2. The polymers were excited at 550 nm. The striking features of the solution optic al properties are the presence of wellresolved vibronic features, and the small stokes shifts (<700 cm-1). Some controversy still exists on the origin of vibronic coupling and whether it is an interchain or intrachain phenomenon as reviewed in our research group.67 Overall, there is overwhelming support that vibronic features in CP s absorption and emission spectra arise from the coupling of electronic absorption with vibrational mode s of the polymer backbone and have an

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54 intramolecular origin.69 In the spectra shown above, the polymer solutions are diluted but still have well-resolved vi bronic features, also sugges ting an intramolecular, not intermolecular origin of vibronic coupli ng. This was confirmed by dilution studies showing no dependence of the peak wavele ngths on the absorpti on on concentration. As described by Bredas et al.,69 vibronic coupling depends on the respective geometries of the ground and excited state (Figure 3-10). In a molecule where ground state and excited state have identical geometri es, such coupling is forbidden. The result is that a single identical peak should be observed for absorpti on and emission. But when the ground state and the excited state geometries ar e different, then vibr onic coupling can be seen.68 Figure 3-10. Evolution of absorption spectru m with increasing di stortion between the ground state and the excited state. Adapted from ref. 69.

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55 According to Kasha’s rule,70 the fluorescence will occur from the lowest vibrational state of the excited state resulting in a bathoc hromic shift of the emission compared to the absorption. This is the origin of the Stokes sh ift, defined as the energy difference between the energy at the maximum of absorption a nd the energy at the maximum of emission. The larger the Stokes shift, the more distor tion exists between the ground and the excited states. As a quinoidal planar form is predicted in the excited state, it follows that a small Stokes shift indicates a planar arrangem ent of the chain in the ground state. In the case of PProDOT-R2 polymers, the presence of two clear vibronic peaks in absorption and three in emission, assigned to the 0-0, 0-1 and 0-2 (only in emission) vibronic transitions, along with a small St okes shift indicate a small displacement of geometry between the ground and the first exci ted state along with a planar conformation of the chains. In poly(3-alkylthiophene )s, which have much higher intrachain conformational flexibility in solution, the absorption is broad and featureless and the Stokes shift is much higher at 5500 cm-1 71 Table 3-3 shows the solu tion properties for all alkyl substituted PProDOTs studied here. Table 3-3. Optical properties of alkyl substituted PProDOT s in toluene solution. Also indicated is the relative intens ity of the vibronic bands. R max absorption (nm) max emission (nm) Stokes Shift (cm-1) sol.a Hexyl 585 ( 1 ), 548 ( 0.96 ) 616 ( 1 ), 672 ( 0.46 ), 740 ( 0.13 ) 860 0.35 2-methylbutyl 602 ( 1 ), 556 ( 0.74 ) 621 ( 1 ), 677 ( 0.40 ), 746 ( 0.10 ) 482 0.36 2-ethylhexyl 595 ( 1 ), 553 ( 0.82 ) 619 ( 1 ), 677 ( 0.44 ), 747 ( 0.11 ) 652 0.37 (a) Quantum yield was calculated using sulf orhodamine excited at 550 nm as standard. From the solution optical data above, it is clear that branched substituted PProDOTs have a more planar backbone and less conformational freedom than linear substituted PProDOTs, as indicated by a smalle r Stokes shift and more resolved vibronic

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56 features. As expected, such differences are no t seen in the fluorescence spectrum as there is vibrational relaxation to the more st able, planar quinoidal conformation before emission. The quantum yield remains mostly unaffected by the increasing steric bulk, suggesting interchain interacti ons are not involved in toluene solution and that the chains are molecularly dissolved. 3.3.3. Optoelectronic Properties of Solution Processed Films To characterize the optical properties of the PProDOT-R2 polymers in the solid state, films were spray-cast from toluene so lution. The solutions were all red-colored. For branched alkyl polymers, as the solvent drie d out on the substrate, the red color changed to a blue-purple color in the solid state. The corresponding absorption spectrum, shown in Figure 3-11 for PProDOT(2-methylbutyl)2, shows a 20 nm bathochromic shift in absorption between the toluene solution and the film as cast, indicating that the polymer chains order during solvent evaporation a nd that there is significant interchain interactions between polymer chains in the solid state. The vibronic coupling of the spray-coated films becomes more resolved, c onsistent with planariz ation of the chains induced by the aggregation process. When the films are oxidized and reneutralized electrochemically, no further changes of optical absorption are observed. PProDOT-Hx2 behaves differently. The red color of the solution is maintained in the film state. As seen in Figure 3-11, the absorption spectra of solution and spray-coated films have identical max. This indicates that the polymer chains retain a solution conformation upon casting. The br oader absorption of the f ilm state suggests that aggregation does occur, but that the aggreg ates are ill-defined. Upon redox switching of PProDOT-Hx2 spray-coated films, the color change s to blue-purple and the absorption spectrum undergoes a 20 nm bathochromic shift. This behavior was also observed in

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57 PProDOT-Bu2.63a The absorption shift is attributed to a doping-induced rearrangement of the polymer chains. In the oxidized state, the chains adopt the more planar quinoidal structure, forcing intrachain but also interchain rearra ngements. These changes are preserved upon reduction to the neutral po lymer and no further shift is observed upon further redox cycles. 400500600700 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Film as cast After Switching Toluene Solution 533 571 623 625 Doping induced shift PProDOT-(2-methylbutyl)2 racemicAbsorbance (nm) 602 556 400500600700 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Oxidized and reneutralized Film as cast Oxidized and reneutralized Toluene SolutionDoping-induced rearrangement of PProDOT-Hx2 cast from toluene585 598 587 557 552 548 Normalized Absorbance (nm) As cast Figure 3-11. Doping/Casting induced rearrangement in linear vs. branched alkyl substituted PProDOTs. (left) PProDOT(2-methylbutyl)2; (right) PProDOTHx2. A possible explanation for the differe nt behavior is that PProDOT-Hx2, is that the linear substituted seven-membered ring can adopt both chair and tw isted conformations discussed above. This is supported by X-ra y structures carried out on BisProDOT-(Et)2, presented in Figure 3-12, and also theore tical calculations predicting a very small difference of energy between the two confor mers, in favor of the chair conformation.63a In the case of branched substituents, theore tical calculations predict the twisted (more planar) conformer to be significantly lower in energy than the chair conformer. As a result, the branched polymer chains would ha ve a much higher pl anarity and regularity. This would favor strong interchain intera ctions and spontaneous organization during

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58 casting. In the case of PProDOT-Hx2, the irregular distribution of the two conformers within a polymer chain is expected to prev ent efficient packing in the solid state. Figure 3-12. X-ray crystal structure of BisProDOT-Et2 showing that a mixture of chair and twisted conformations are present.7 Theoretical calcul ation (A. Perdomo) shows the difference of energy between the two conformers to be less than 2.5kJ/mole (kBT at room temperature). As demonstrated from the solution propert ies, the linear substituted PProDOTs are more twisted than branched PProDOTs. This intrachain twisted conformation is expected to easily hinder solid state packing and can also explain why linear PProDOTs form disordered aggregates. Oxidation during elec trochemical switching will force a more planar conformation. Also, some authors suggest that in the oxidized state, -dimers might form to stabilize th e polaron and bipolaron state.72 These two effects would allow the reordering observed during switching. Ta ble 3-4 displays the absorption maximum for all polymers freshly cast from tolu ene, and following electrochemical doping. Table 3-4. Solution, cast films and electroc hemically oxidized and reneutralized films absorption properties (a) (sh)= shoulder R= max (nm) Eg (eV) max (cast) (nm) Eg (eV) (cast) max (nm) (switched) Eg (eV) (redox) Hexyl 552, 585 2.01 548, 585 1.97 576 1.85 2-methylbutyl 602, 556, 517 (sh)a 1.98 623, 571, 533 1.88 625, 572, 533 1.88 2-ethylhexyl 552, 595 1.99 612, 559, 525 1.94 618, 564, 523 1.93

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59 Films spray-cast onto ITO were studied by spectroelectrochemistry. The behavior is highly dependent on the type of substituents. As the steric bulk is increased, the optical changes with increasing potential become more abrupt. PProDOT-Hx2 switches within 600mV potential increase, but PProDOT(2-methylbutyl)2 and PProDOT(2-ethylhexyl)2 switch within 350mV and 250mV, respectively (Figure 3-13). It was also observed that the absorption of PProDOT-Hx2 does not exhibit a well define d vibronic structure, in contrast to the branched derivatives i ndicating that the hexyl polymer retains conformational disorder in th e solid state, even followi ng doping-induced rearrangement. Consistent with electrochemical results sugges ting decreasing intercha in interactions with steric bulk, the bandgap is increased from 1.85 eV for the hexyl polymer to 1.92eV for the ethylhexyl polymer. Figure 3-13. Spectroelectrochemist ry experiment for PProDOT-Hx2 (left) and PProDOT(2-ethylhexyl)2 (right) in 0.1M TBAP/ACN. This trend is also reflected in the pote ntial dependence of the luminance seen in Figure 3-14. The luminance of PProDOT-Hx2 changes gradually (600mV) but the luminance of the branched polymers varies abruptly (<300mV). To compare the polymers electrochromic efficiency, coloration efficiency experiments were carried out on the polymers. The results are summed up in Table 3-5. All spray-ca st alkyl substituted 2004006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 S OO n Absorbance (nm) 1V 0.9V 0.8V 0.6V 0.5V 0.4V 0.3V 0.2V 0.1V -0.1V -0.3V 1V -0.3 V -0.3 V 1V 0.3V -0.3V 1V 2004006008001000120014001600 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 S O O n Absorbance (nm) 0.9 V 0.8 V 0.7 V 0.6 V 0.5V 0.4V 0V -0.5 V1V -0.3 V -0.3 V 1V 0.3V -0.3V 1V

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60 PProDOTs films display high color contrast, but the charge required to achieve 95% of this contrast is higher in the linear polymer s than the branched polymers, yielding higher coloration efficiencies for the branched polymers. This can be explained by the amorphous character of the branched polymers, with the bulky substituents providing more open volume for the dopant ions to pene trate the films, eff ectively decreasing the amount of capacitive currents contributions to the overall current during the polymers oxidation. -0.6-0.4-0.20.00.20.40.6 20 30 40 50 60 70 80 90 % Relative LuminanceE (V) vs. Fc/Fc+ PProDOT-(Hx)2 PProDOT-(2-methybutyl)2 PProDOT-(2-ethylhexyl)2 Figure 3-14. Luminance change with applied po tential. All films were spray-coated from toluene solution switched between 0.5V and 1V to eliminate any dopinginduced rearrangement effect. All films were ~150-200 nm thick as determined by profilometry. Table 3-5. Coloration Efficiency study on PProDOT-R2 spray-coated films. Substituent Switching Time (s) Y (%) T (%) OD Qd (mC/cm2) CE (cm2/C) Hexyl 0.37 58 65 0.52 0.61 850 2-methylbutyl 0.40 64 70 0.6 0.38 1020 2-ethylhexyl 0.73 70 79 N/A 0.87 1050

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61 3.3.4. Conductivity Measurements The conductivity of spray-coated PProDOT-R2 polymer films was determined by the four-point probe method and the experime ntal parameters are reported in Table 3-6.. The measurements are taken as an average of multiple locations of the films, and reproducibility was checked by measuring c onductivity on several films, leading to statistically consistent results. Table 3-6. Conductivity measurements on spra y-coated films gas phase doped with iodine. Measurements are average values of at least two films, taken at multiple locations of the films. R= I (A) V (mV) Average Thickness (nm) (S cm-1) Hexyl N/A N/A N/A 5-10 2-methylbutyl 100 203, 185 286, 251 3.8, 4.2 2-ethylhexyl 10 300, 194 222, 234 0.3, 0.5 The conductivity decreases by an order of magnitude with increasing steric bulk, going from hexyl to the ethylhexy l side chains. The methyl but yl derivative surprisingly gives a similar conductivity to the linear hexyl substituted polymer. This can be explained by considering both inter and intrachai n interactions. PProDOT-(2-methylbutyl)2 has less interchain interactions but has a more planar chain conformation. It is therefore expected to have lower interchain charge transpor t through the polymer stacks than PProDOT-Hx2, but higher intrachain charge tr ansport along the polymer chains. Also, as discussed for the polymer electrochemistry, the inter-stack distance is expected to be shorter in the butyl polymers corresponding to a higher ch arge transport and conductivity between stacks. Overall, introducing larger substituents prevents efficient charge transport in the bulk material. This is the drawback of using branched substituents instead of longer alkyl chains to induce solubility.

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62 3.4. High Performance Electrochromic Devices Because of the properties described above the dialkyl substituted PProDOTs, and in particular the branched compounds, seem ideal materials for high contrast electrochromic materials. This section descri bes the application of these polymers in an absorptive/reflective electrochromic de vice. The devices made with PProDOT-R2 were prepared by Aubrey Dyer and Harun Tu rkcu. Figure 3-15 gives a schematic representation of the device construction. Figure 3-15. Schematic representation of a reflective/absorptive EC device using spraycoated PProDOT(2-ethylhexyl)2 as the active and storage layer. A porous gold membrane is coated with an electrochromic polymer (spray-coated PProDOT(2-ethylhexyl)2), which constitutes the active layer of the device. The polymer is oxidized electrochemically prior to build ing the device. The de vice is assembled by placing the coated membrane on another layer of electrochromic polymer coated with gel electrolyte serving as a charge storage layer. Upon applying a negative bias to the device, the active polymer layer is reduced to the ne utral form, and the de vice is absorptive to

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63 visible light but highly reflective to NIR light, as shown in Figure 3-16 2004006008001000120014001600180020002200 10 20 30 40 50 60 70 80 90 100 110 S O O n Reflectance(normalized)Wavelength(nm) -800mV 800mV Figure 3-16. Reflectance plot for a reflectiv e/absorptive EC device using spray-coated PProDOT(2-ethylhexyl)2 as the active and storage layer. 3.5. Conclusion A series of soluble, regios ymmetrically substituted branched alkyl PProDOTs were synthesized by Grignard Metathesis. Introduc tion of branching results in significant improvement in solubility and electrochrom ic properties, leading to faster switching rates, higher contrasts and si gnificantly higher coloration e fficiencies. The improvement is attributed mainly to a decrease of interc hain interactions promot ed by the bulkiness of the branched substituents, resulting in the highest coloration effici encies, but also the lowest conductivities for PProDOT-(2-ethylhexyl)2 polymer. In addition, the branched polymers display unusual spectroelectrochemical properties, with most optical changes obtained in a narrow optical window (<350m V), in contrast to linear substituted polymers, requiring much larger potential incr ease (>600mV). This behavior is attributed

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64 to a more open morphology of the polymer films substituted with the bulky side chains, allowing easier penetration of dopant ions. The introduction of branched alkyl substituents also affects the intrachain conformation of the chains. Optical absorpti on studies on solutions indicate small Stokes shift, well-resolved vibronic features with a dominant 0-0 tr ansition, pointing to a mostly planar conformation of the polymer chains. Th e chains planarity allows easy interchain ordering of the polymer chains in the solid state, evidenced from the large bathochromic shift in absorption and a signi ficant change of color observe d during spray-casting of the polymers. In Chapter 5, the synthesis of chiral equivalents of these polymers will be described. These polymers can be studied using chiroptical techniques which are powerful tools to examine interchain and intrachain interacti ons, affording better understanding on how the branched substituen ts affect the electro chromic properties. 3.6. Chapter Synthetic Details 3,4-dimethoxythiophene: In a 250 mL 3-neck round bottom flask equipped with a reflux condenser 6.2 g (0.27 mol) of sodium wa s slowly dissolved in 90 mL of methanol under argon. Then 4.2 g (0.053 mol) of CuO, 0.9 g (0.0053 mol) of KI, and 13 g (0.053 mol) of 3,4-dibromothiophene were added. The black mixtur e was refluxed for 3 days. 0.9 g (0.0053 mol) of KI was added and the mi xture was refluxed for an additional 24 hours. The dark mixture was cooled, filtere d through Bchner, diluted with 150 mL of water, and extracted 3 times with ether. The combined ether layers were washed with water and dried with magnesium sulfate. The ether was removed under vacuum, and the crude product was purified by vacuum distillation (80-82 C / 1.0 mm Hg), (lit. 59-65 C

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65 / 0.5 mm Hg) to yield 5.0 g (65 %) of product. 1H NMR (300 MHz, CDCl3) 6.2 (s, 2H), 3.8 (s, 6H). General Procedure for the synthesi s of alkylated diethyl malonate: In a 5 L flame dried 3 neck round bottom flask equipped w ith an argon inlet, a condenser, and an addition funnel were combined 2L of dry THF, 3.5 mol of alkyl bromide (3eq), and 3.5 mol of NaH. The flas k was cooled to 0 C and 1.15 mol of freshly distilled diethyl malonate was added dropwise through the addition funnel. When the addition of the malonate was completed, the mixture was refl uxed overnight. The flask was then cooled at 0 C and the remaining sodium hydride was quenched by adding water dropwise. The mixture was then poured into brine (2 L), ex tracted two times with ether, and washed with brine. The solvent and the alkyl bromide were removed under vacuum. The crude oil obtained was then used in the next step without further purification. General Procedure for the synthesis of diols: In a 5 L flame dried 3 neck round bottom flask equipped with an argon inlet, a condenser, and an addition funnel, were combined 2 L of dry ethyl ether and 1.7 mol of LiAlH4 powder. The crude dialkyl malonate (1.13 mol) was added dropwise at 0 C. When the addition was completed, the mixture was allowed to warm to room temp erature. The reaction mixture was stirred under argon for 20 hr. The excess LiAlH4 was SLOWLY quenched w ith one liter of 1M HCl at 0C. The aqueous phase was extrac ted with 2500 mL ether and the combined organic phases were washed with water (4 500 mL). The organic phase was dried with magnesium sulfate and the solvent was evaporated under vacuum. The resulting product is purified by column chromatography (90% DCM/10% acetonitrile product revealed

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66 with vanillin dip as black spots). After purification, yield obtained is 25-50% for branched derivatives, 65-80% for the linear derivatives. 2,2-Dihexylpropane-1,3-diol: White crystalline solid. 1H NMR (300 MHz, CDCl3) 3.59 (d, 4H, J = 5.3 Hz), 2.39 (t, 2H, J = 5.3 Hz), 1.40-1.10 (m, 20H), 0.90 (t, 6H, J = 7.3 Hz); 13C NMR (75 MHz, CDCl3) 69.7, 41.2, 32.0, 31.1, 30,5, 29.9, 23.1, 22.9, 14.3; HRMS calculated for C15H32O2: 245.2481 Found: 245.2475 Elemental Anal. Calcd for C15H32O2: C 73.71; H 14.20. Found: C 74.12; H 14.18. 2,2-Bis-(2-methylbutyl )-propane-1,3-diol: white amorphous solid. 1H NMR (300 MHz, CDCl3) 0.73-0.97 (m, 12H), 1.05-1.26 (m, 4H), 1.26-1.51 (m, 6H), 2.21-2.32 (br, 2H), 3.51-3.66 (br, 4H); 13C NMR (75 MHz, CDCl3) 11.73, 21.92, 29.56, 32.21, 39.18, 42.82, 70.21. 2,2-Bis-(2-ethylhexyl)-propane-1,3-diol: clear oil. 1H NMR (300 MHz, CDCl3) 3.65 (s, 4H), 2.41 (s, 2H), 1.40-1.10 (m, 22H), 0.95-0.80 (m, 12H); 13C NMR (75 MHz, CDCl3) 70.1, 42.8, 37.1, 34.9, 33.7, 29.0, 27.9, 23.4, 14.4, 10.8 HRMS Calcd for C19H41O2 (M+H)+ 301.3106 Found 301.3103; Elemental Anal. Calcd for C19H40O2 C 75.94; H 13.42. Found C 75.95 H 12.35. General procedure for the transetherifica tion of 3,4-dimethoxyt hiophene with diols: 21 mmol of 3,4-dimethoxythiophene, 22 mmol of diol, 2.1 mmol of p -toluenesulfonic acid, and 200 mL toluene were combined in a 500 mL flask equipped with a soxhlet extractor with type 4A molecular sieves or CaCl2 in a cellulose thimble. The solution was refluxed overnight. The reaction mixture was cooled and washed once with water. The toluene was removed under vacuum, and the crude product was purified by column chromatography on silica gel with 3: 2 hexanes / methylene chloride.

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67 3,3-Dihexyl-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(Hx) 2 ): clear oil (95 % yield); 1H NMR (300 MHz, CDCl3) 6.42 (s, 2H), 3.88 (s, 4H), 1.45-1.20 (m, 20 H), 0.95-0.82 (m, 6H). 13C NMR (75 MHz, CDCl3) 149.9, 104.9, 77.8, 43.9, 32.0, 32.0, 30.4, 23.0, 22.9, 14.3. HRMS calculated for C19H32O2S: 324.2123 Found: 324.2120. Elemental Anal. Calcd for C19H32O2S: C 70.32; H 9.94; S 9.88 Found: C 70.48; H 10.48; S 9.78. 3,3-bis(2-methylbutyl)-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(2-methylbutyl) 2 ): clear oil (70% yield); 1H NMR (300 MHz, CDCl3) 0.771.01 (m, 12H), 1.07-1.63 (m, 10H), 3.794.05 (m, 4H), 6.42 (s, 2H); 13C NMR (75 MHz, CDCl3) 11.69, 22.06, 22.08, 29.66, 29.68, 32.17, 32.21, 40.85, 40.88, 45.57, 78.24, 78.35, 78.39, 104.65, 149.92. 3,3-Bis-(2-ethylbutyl)-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(2ethylbutyl) 2 ): The crude oil obtained was purified by column chromatography (3:2) hexanes/dichloromethane followed by another column using 3:1 hexanes/dichloromethane to afford a clear oil (66% yield). 1H NMR (300MHz, CDCl3) 0.78-0.95 (t, 12H), 1.21-1.47 (m, 14H) 3.93 (s, 4H), 6.42 (s, 2H); 13C NMR (75MHz, CDCl3) 10.94, 27.57, 35.17, 38.23, 45.44, 77.98, 104.66, 149.97. 3,3-Bis-(2-ethylhexyl)-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(2ethylhexyl) 2 ): The crude oil obtained was purified by column chromatography (3:2) hexanes/dichloromethane followed by another column using 3:1 hexanes/dichloromethane to afford 6.0 g of clear oil (57%). 1H NMR (300MHz, CDCl3) 6.43 (s, 2H), 3.93 (s, 4H), 1.2-1.5 (m, 22H), 0.75-1.0 (m, 12H); 13C NMR (75MHz, CDCl3) 150.0, 104.61, 78.0 (t), 45.5, 38.7, 35.0, 33.8, 29.0, 28.0, 23.3, 14.4, 10.8.;

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68 HRMS Calcd for C23H40O2S 380.2749. Found 380.2753; HRMS calculated for C23H40O2S: 380.2749 Found: 380.2753. Elemental Anal. Calcd for C23H40O2S: C 72.58; H 10.59; O 8.41; S 8.42. Found: C 72.78; H 10.30; O 8.68; S 8.24. General procedure for the bromination of ProDOT-R 2 : In a 2-neck 250 mL round bottom flask filled with 80 mL chloroform 1.5g (2.1 mmol) of ProDOT was added and the solution was bubbled under argon fo r 60 minutes. Then 1.12 g (6.24 mmols) N bromosuccinimde was added and the solution was stirred for 20 hr. After completion, the solvent was removed by rotary evaporation under reduced pressure and the resulting residue was purified by column chromatography on SiO2 with (4:1) hexanes/dichloromethane 6,8-Dibromo-3,3-Dihe xyl-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(Hx) 2 Br 2 ): clear oil obtained (91% yield).1H NMR (300MHz, CDCl3) 3.93 (s, 4H), 1.45-1.15 (m, 20H), 0.90 (t, 6H, J = 7.0 Hz); 13C NMR (75MHz, CDCl3) 147.4, 104.8, 90.8, 78.3, 44.2, 31.9, 30.3, 22.9, 14.3; HRMS calculated for C19H30O2SBr2: 480.0333 Found: 480.0334. Elemental Anal. Calcd for C19H30O2SBr2: C 47.31; H 6.27; S 6.65; Br 33.13. Found: C 47.83; H 6.79; S 6.88; Br 32.79. 6,8-Dibromo-3,3-bis(2-meth ylbutyl)-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(2-methylbutyl) 2 Br 2 ): product obtained as a clear oil (86%).1H NMR (300MHz, CDCl3) 0.8-1.0 (m, 12H), 1.08-1.27 (m, 2H), 1.27-1.59 (m, 8H), 3.86-4.10 (m, 4H); 13C NMR (75MHz, CDCl3) 11.67, 21.93, 21.96, 29.67, 29.70, 32.08, 32.13, 40.81, 40.83, 40.85, 45.87, 78.98, 79.07, 79.11, 90.64, 147.31. 6,8-Dibromo-3,3-Bis-(2-eth ylbutyl)-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(2-ethylbutyl) 2 Br 2 ): The crude oil obtained was purified by column

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69 chromatography (4:1) hexanes/dichloromethan e to afford 1.2 g of clear oil ( 81%). 1H NMR (300MHz, CDCl3) 0.77-0.92 (t, 12H), 1.2-1.45 (m, 14H), 4.0 (s, 4H); 13C NMR (75MHz, CDCl3) 10.92, 27.48, 35.19, 38.27, 45.72, 78.59, 90.65, 147.30; HRMS Calcd for C23H38O2SBr2 483.0386. Found 483.0380; Elemental Anal. Calcd for C19H30O2SBr2: C 47.31; H 6.27 Found: C 47.43; H 6.40. 6,8-Dibromo-3,3-Bis-(2-eth ylhexyl)-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine (ProDOT(EtHx) 2 Br 2 ): The crude oil obtained was purif ied by column chromatography (4:1) hexanes/dichloromethane to afford a clear oil (80 %). 1H NMR (300MHz, CDCl3) 4.00 (s, 4H), 1.15-1.5 (m, 22H), 0.8-1.0 (m, 12H); 13C NMR (75MHz, CDCl3) 147.3, 90.5, 78.6, 45.8, 38.8, 35.0, 29.0, 28.0, 23.3, 14.4, 10.8; HRMS Calcd for C23H38O2SBr2 538.0940. Found 538.0944; Elemental Anal. Calcd for C23H38O2SBr2: C 51.31; H 7.11; S 5.96 Found: C 51.28; H 7.00; S 6.04. General Procedure for Grignard meta thesis polymerization of ProDOTR 2 Br 2 : In a flame dried 250 mL round bottom flask, dry THF (150 mL) and 3.0 g (0.34 mmol) of ProDOT(R)2Br2 was added under argon. Then methyl magnesium bromide (3.75 mL, 3.45 mmol, 0.918 M) was slowly added by syringe. The mixture was then refluxed for 2 hrs. After, the flask was cooled and Ni(dppp)Cl2 (18.4 mg, 0.0341 mmol) was added and the reaction was heated at reflux overnight under argon. The solution was then cooled and the polymer was precipi tated by pouring the solution in 400 mL methanol. The dark purple solid was purified by soxhlet extraction with methanol for 24 hr, hexanes for 48 hr, and finally chloroform for 24 hr. The chloroform was evaporated under reduced pressure to afford purple solid.

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70 Poly(3,3-Dihexyl-3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine) (PProDOT(Hexyl) 2 ): shiny brown solid obtained (66 %). 1H NMR (300 MHz, CDCl3) 3.95 (bs, 4H), 1.62-1.2 (m, 20H), 0.97-0.80 (m, 6H); 13C (75 MHz, benzened6) 146.4, 115.3, 78.0, 44.3, 32.6, 31.0, 23.5, 14.8; Elemental Anal. Calcd for (C19H30O2S)164HBr: C 70.65; H 9.38; S 9.91, Br 0.15 Found: C 69.87; H 9.99; S 9.52; Br 0.15; Ni <0.01. GPC analysis: Mn= 38,100, Mw=65,900 PDI=1.73. Poly(3,3-bis(2-methylbutyl) 2 -3,4-dihydro-2 H -thieno[3,4b ][1,4]dioxepine) (PProDOT(2-methylbutyl) 2 ): shiny brown solid obtained (60%). 1H NMR (300 MHz, CDCl3) 0.82-1.16 (br, 12H), 1.16-1.3 (br, 4H), 1.31.5 (br, 4H), 1.5-1.65 (br, 2H), 3.94.15 (br, 4H); 13C (75 MHz, benzened6) 12.15, 22.61, 30.10, 32.67, 32.77, 41.22, 45.93, 78.72, 114.98, 145.87; GPC analysis: Mn=17,000, Mw=30,000 PDI= 1.76.

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71 CHAPTER 4 SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKOXYMETHYL POLY(3,4-PROPYLENEDIOXYTH IOPHENES) (PPRODOT-(CH2OR)2) 4.1. Introduction The previous chapter demonstrated that in creasing the steric bulk in branched alkyl PProDOT polymers, these having all carbon based substituents, results in a decrease of stacking interactions and possibly an increase of the distance between -stacks as well. This leads to polymers with high er solubility in or ganic solvents, higher contrast and fast switching electrochromic devices due to the fast diffusion of dopant ions into the polymer films being facilitated. To enhance the pol ymer solubility and further optimize the electrochromic properties, alkoxymethyl spacers were placed between the 2position of the ProDOT propylene bridge and the branched alkyl side chains to provide ether linked substituents. The presence of this spacer in the side chains will provide more steric hindrance and prevent ordering due to the c onformational flexibility of the alkoxy chains. Combined with the steric bulk of the bran ched side chains s hould lead to a strong decrease in interchain interac tions, and more disorder in so lution and solid state. On the other hand, as the branching groups are furthe r away from the seven-membered ring and have more flexibility than the rigid alkyl group, less effect of the branching group on the ring conformation could be expected, leadi ng to important intrach ain and interchain changes. Figure 4-1 displays the structures described and studied in this Chapter. PProDOT-(CH2OC18H37)2, synthesized by Ben Reeves, is used to demonstrate the differences between branched and linear polymers.

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72 S O O O O S O O O O n n S O O O O n S O O O O n PProDOT-(CH2O-2-ethylbutyl)2PProDOT-(CH2O-2-methylbutyl)2PProDOT-(CH2O-2-ethylhexyl)2PProDOT-(CH2OC18H37)2 Figure 4-1. Family of branched dialk oxymethyl substituted PProDOTs. PProDOT(CH2OC18H37)2 was synthesized by Ben Reeves and will be used for comparison and discussion of branching effects. 4.2. Electropolymerized PProDOT-(CH 2 OR) 2 4.2.1. Electropolymerizable Monomer Synthesis An advantage of the synthesis of dialkoxy methyl substituted ProDOTs, compared to the alkyl substituted polymers, is their ea se of synthesis. As shown in Figure 4-2, the substituents are placed in the last step of the synthesis using a simple Williamson etherification between the corr esponding alcohol and PProDOT-(CH2Br)2. PProDOT(CH2Br)2 is prepared by transetherificati on between 3,4-dimethoxythiophene and 2,2bis(bromomethyl)-propane-1,3-di ol, both commercially availa ble. The alkyl substituted

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73 ProDOTs, described in Chapter 3 are more di fficult to synthesize, as the disubstituted 2,2-propane-1,3-diol must be prepared. On the contrary, many linear and branched alcohols are commercially availabl e. Also, in the case of bran ched derivatives, the diol synthesis has a low overall yield, which is a problem when the starting materials are expensive or difficult to obtain. S MeO OMe OHOH pTSA Toluene S O O 60-80% R=-2-methylbutyl -2-ethylbutyl -2-ethylhexyl -C18H37Br Br S O O OR OR B r B r ROH,NaH DMF Figure 4-2. Synthesis of el ectropolymerizable alkoxymet hyl substituted ProDOTs. Branched 2-methylbutyl and 2-ethylhe xyl derivatives are prepared from racemic reagents. 4.2.2. Electrodeposition and Electrochemistry The alkoxymethyl substituted ProDOT electropolymerizable monomers were electrodeposited on a platinum button fr om a 0.01M monomer solution in 0.1M TBAP/ACN. Figure 4-3 shows the electrodeposition of PProDOT-(CH2O-2-ethylhexyl)2. -1.0-0.50.00.51.01.5 -2 -1 0 1 2 3 4 5 S O O O O nI / mA cm-2E(V) vs. Fc/Fc+ Figure 4-3. Electrodepo sition of PProDOT(CH2O-2-ethylhexyl)2 on Pt Button. The film was deposited from a 0.01M monomer solution in 0.1M TBAP/ACN, at a scan rate of 50 mV/s.

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74 After electrodeposition on platinum butt on electrodes, the poly mers oxidations in monomer-free electrolyte were compared (F igure 4-4). A similar trend to the alkyl derivatives was observed, where in creasing the steric bulk of the side chains results in an increase of the onset and peak oxidation poten tials. This shift is consistent with less interchain interactions when the substituents are bulkier. Again, as seen with the alkyl substituted PProDOT, the ethylhexyloxymethyl derivative has a lower peak oxidation potential than PProDOT-(CH2O-2-ethylbutyl)2, although the ethylhe xyloxy chains are bulkier. This behavior might be explained by easier diffusion of the dopant ions between polymer stacks. -0.8-0.6-0.4-0.20.00.20.4 -1.0 -0.5 0.0 0.5 1.0 Normalized IntensityE(V) vs. Fc/Fc+ ethylhexyloxy ethylbutyloxy methylbutyloxy Figure 4-4. Polymer oxidation in the PProDOT-(CH2OR)2 series. All the polymers were deposited by cyclic voltammetry at 50 mV/s scan rate from 0.01M monomer solution in 0.1M TBAP/ACN. The polyme r oxidation curves we re recorded in monomer-free electrolyte at 50mV/s. Table 4-1 compares the polymer oxidation values of the PProDOT-R2 and PProDOT-(CH2OR)2 series. Overall, introduction of the oxygens does not seem to have a strong effect on the polymer oxidation, excep t in the case of the methyl branched polymers. PProDOT-(2-methylbutyloxymethyl)2 has a significantly poo rer reversibility in

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75 oxidation than PProDOT-(2-methylbutyl)2. In the case of the bigger branching ethyl group, the oxidation peaks are all quasi-reversible. This trend indicates that the branching groups are mainly responsible for the increas e in polymer oxidation due to steric bulk. The introduction of the oxymethyl spacer seems to have a minor effect, especially with small branching groups, where a broad twopeak reduction suggests different chain conformations or aggregates exist in the oxidized state. Table 4-1. Comparison of alkyl and al koxymethyl substituted PProDOTs polymer oxidation. Potentials are vs. Fc/Fc+. PProDOT Substituents Eonset monomer E1/2 (mV) Polymer Ep (mV) Polymer I[ox], p / I[red], p Polymer Butyl 0.99 V -65 (-180a) 129 (281) 2.15 Hexyl 0.97 V -66(-165 a) 54 (252) 1.12 2-methylbutyl 0.88 V -3 135 1.14 2-methylbutyloxymethyl 1.02V 0 (-269) 50 (295) 3.51 2-ethylbutyl 0.98 V 155 107 1 2-ethylbutyloxymethyl 0.97V 52 124 1 2-ethylhexyl 1.03 V 28 34 1.3 2-ethylhexyloxymethyl 1.01V 75 139 1 4.3. Chemically Polymerized Soluble PProDOT-(CH 2 OR) 2 4.3.1. Synthesis and Polymer Characterization After bromination of the electrochemi cally polymerizable monomer with Nbromosuccinimide, the soluble polymers were obtained by Grignard Metathesis (Figure 4-5). S O O NBS DMF S O O S O O 1.MeMgBr,THF 2.Ni(dppp)Cl2 Br Br n OR OR OR OR OR OR Figure 4-5. Polymerization of PProDOT-(CH2OR)2 by Grignard Metathesis. After purification by Soxhlet extraction with MeOH and hexanes, the polymers were extracted with chloroform, and obtai ned as shiny brown solids after solvent

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76 evaporation. The polymers are highly solubl e in chloroform, toluene, and THF. For PProDOT-(CH2O-2-methylbutyl)2, heat was required to obtai n dissolution of the polymer chains. The polymer chains remained in soluti on but a change of color from red to purple suggests aggregation might occur as the soluti ons are cooled to room temperature. The polymer structures were confirmed by 1H and 13C NMR. GPC analysis of the polymers show molecular weights between 10,000 and 20,000 g mol-1 (Table 4-2), corresponding to a molecular structure of more than 30 repeating units. Table 4-2. Molecular weight analysis of GriM polymerized PProDOT-(CH2OR)2. The molecular weights are determined vs. polystyrene standards. R Mn (g mol-1) Xn Mw (g mol-1) PDI CH2O-2-methylbutyl N/A N/A N/A N/A CH2O-2-ethylbutyl 12,400 33 17,500 1.4 CH2O-2-ethylhexyl 13,000 30 22,200 1.7 4.3.2. Solution properties The solution properties we re studied by UV-Vis abso rbance and fluorescence spectroscopy. Figure 4-6 shows the spectrum for PProDOT-(CH2O-2-methylbutyl)2 and PProDOT-(CH2O-2-ethylhexyl)2 in xylenes solutions. 400500600700800 0.02 0.04 0.06 0.08 (nm)Absorbance548 581 PProDOT-(CH2O-2-methylbutyl)25.0x1051.0x1061.5x1062.0x1062.5x106 Fluorescence Intensity845cm-1 611 663 400500600700800 0.00 0.02 0.04 0.06 0.08 0.10 (nm)Absorbance545 578 PProDOT(CH2O-2-ethylhexyl)20 1x1062x1063x1064x1065x1066x106 Emission Intensity604 659 721 744cm-1 Figure 4-6. Absorption and photolum inescence spectrum of PProDOT(CH2O-2methylbutyl)2 and PProDOT(CH2O-2-ethylhexyl)2. For fluorescence, ex=550nm.

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77 UV-Vis absorption and fluores cence results for PProDOT(CH2O-2-methylbutyl)2, PProDOT(CH2O-2-ethylbutyl)2 and PProDOT(CH2O-2-ethylhexyl)2 are summarized in Table 4-3. The alkoxymethyl substituted polymers have clear vibronic f eatures, attributed to the 0-0 and 0-1 vibrational transitions. The 0-1 vibronic trans ition is the dominant vibronic feature, in contrast with branched alkyl substituted PPr oDOTs, where the 0-0 transition is domina nt. In PProDOT-Hx2, the two vibronic transitions have similar intensities. As described in Figure 3-12, str onger higher energy vibr onic transitions for alkoxymethyl substituted polymers (and PProDOT-Hx2) suggest these polymers have more intrachain conf ormational disorder. Table 4-3. Optical properties of alkoxymethyl substituted PProDOTs in toluene solution. Also indicated in parenthese is the re lative intensity of the vibronic bands R max absorption (nm) max emission (nm) Stokes Shift (cm-1) sol.a 2-methylbutyl 548 ( 1 ), 581 ( 0.92 ) 611 ( 1 ), 663 ( 0.71 ) 845 0.18 2-ethylbutyl 545 ( 1 ), 584 ( 0.99 ) 605 ( 1 ), 658 ( 0.55 ), 721 ( 0.17 ) 595 0.37 2-ethylhexyl 545 ( 1 ), 578 ( 0.98 ) 604 ( 1 ), 659 ( 0.62 ), 721 (0.25) 744 0.34 (a) Quantum yield was calculated using sulf orhodamine excited at 550 nm as standard. PProDOT(CH2O-2-ethylbutyl)2 and PProDOT(CH2O-2-ethylhexyl)2 in solution have quantum yields of 0.34 and 0.37, sim ilar to values obtained for PProDOT-R2. The minimal dependence of the quantum yields on the polymer structure suggests that interchain interactions are not involved a nd the chains are molecularly dissolved. If interchain interactions were involved in solution, signifi cant differences of quantum yields would be expected as interchain distance varies with steric bulk. PProDOT(CH2O-2-methylbutyl)2, on the other hand, has a lower quantum yield of 0.18. The decreased quantum yield is consistent with interchain quenching in solution as the polymer has low solubility at room temperat ure and required heating to dissolve. Another possible explanation is that the more twiste d polymer conformation allows for intrachain

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78 folding. Intrachain quenching between chromop hores within a single chain will lead to energy transfer to traps, leading to a decrease in quantum yield. 4.3.3. Optoelectronic Properties of Solution Processed Films Films were spray-cast from either toluen e or chloroform solution (5mg/ mL, 12 psi) onto ITO-coated glass slides. Absorbance was recorded after casting and following redox switching of the films. Results for the al koxymethyl substituted PProDOTs are presented in Table 4-4, and in Figure 4-7 for PProDOT(CH2O-2-methylbutyl)2 and PProDOT(CH2O-2-ethylhexyl)2. 400500600700 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Film as cast Oxidized and reneutralized CHCl3 solutionNormalized Absorbance (nm) PProDOT(CH2O-2-methylbutyl)2 400500600700 0.0 0.2 0.4 0.6 0.8 1.0 1.2 604 555 582 544 PProDOT-(CH2OEtHx)2 cast film (from toluene) before and after switchingNormalized Absorption film as cast oxidized and reneutralized toluene solution electrochemically polymerized film (nm) Figure 4-7. Doping/Casting i nduced rearrangement in li near vs. branched alkyl substituted PProDOTs. (left) PProDOT(CH2O-2-methylbutyl)2; (right) PProDOT-(CH2O-2-ethylhexyl)2. The behavior of PProDOT-(CH2O-2-ethylhexyl)2 and PProDOT-(CH2O-2ethylbutyl)2 is similar to the one observed in PProDOT-Hx2. Upon casting, the polymer films retain a solution conformation, as they have similar absorption spectrum. PProDOT(CH2O-2-methylbutyl)2 spray-cast film, although its absorbance maxima are identical for both cast film and solution, has a broader absorption spectrum dominated by the 0-1 vibronic transition, different from ch loroform solution wher e the 0-0 vibronic

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79 features dominate. This suggests that the polymer forms disordered aggregates with limited interchain interactions and that th e individual chains are highly twisted. Upon switching the polymer f ilm electrochemically, the absorption spectra of the spray-cast films undergo a bathochromic shif t, the optical bandgap is lowered, and the vibronic features become better resolved. Th e well-resolved vibroni c structure supports a planar intrachain conformation of the pol ymer chains, which can also explain the absorption bathochromic shift and lower bandgap. An increase of interchain interactions after redox switching is also lik ely, as the planarity favor interchain ordering of the polymer chains. Table 4-4. Optical properties of PProDOT(CH2O-2-alkyloxymethyl)2 polymers in solution, films as cast and f ilms following electrochemical oxidation/reneutralization cycle. R= max (toluene) Eg (Toluene) max (cast) Eg (cast) max (switched) Eg (switched) 2-methylbutyl 588, 549 2.0 586, 5441.96 612, 561, 528 (sh) 1.91 2-ethylbutyl 579, 545 2.01 581, 5441.98 607, 556, 520 1.95 2-ethylhexyl 575, 544 2.01 582, 5442.0 604, 555, 520 1.97 The spray-cast films were then analyzed by spectroelectrochemistry. For the branched ethylhexyloxymethyl polymer, shown in Figure 4-8, a similar effect to the branched alkyl analogs is observed, with sh arp optical changes as the potential is increased. For PProDOT-(CH2O-2-ethylhexyl)2, most optical changes are obtained with less than 150 mV potential increase. This is sharper than the ethylhexyl alkyl substituted polymer, possibly indicating a sy nergistic effect between th e steric bulk from the ethyl branching group and the flexibility provided by introduction of the oxygens. In contrast the linear octadecyloxymethyl substituted polymer, also shown in Figure 4-8, switches

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80 gradually and requires 600mV potential increase to obtain similar optical changes. These differences can be rationalized in terms of morphology of th e polymer films. In the case of the octadecyloxy methyl substituted polym er, crystallization of the side chains, evidenced by melting and crystallizations transitions in the DSC thermal analysis, hinders the penetration of the dopant i ons inside the polymer film.73 In the case of the bulky substituents, the interchain and interstack di stance increase, leaving more space for the dopant ions to penetrate. 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 S OO O OnAbsorbance (nm) +1.20 V +1.00 V +0.80 V +0.60 V +0.50 V +0.40 V +0.10 V -0.50 V 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 AbsWavelength (nm) 0.75 V 0.55 V 0.35 V 0.25 V 0.15 V 0.10 V 0.05 V -0.05 V -0.15 V -0.25 V -0.45 V -0.65 V -0.95 VPProDOT-(CH2OC18H37)2 Figure 4-8. Spectroelectrochemist ry experiment for PProDOT-(CH2O-2-ethylhexyl)2 (left) and PProDOT-(CH2OC18H37)2 (right). Luminance studies on spra y-cast films confirm the trend observed in the spectroelectrochemistry experiment. Figure 49 shows the overlayed luminance plot as a function of potential of alkoxymethyl PPr oDOT polymers. The alkyl substituted PProDOT-(2-ethylhexyl)2 is added for comparison. As expected, as the steric bulk is increased by introducing larger branching, the optical changes with potential are sharper. This demonstrates that the branching group is responsible for these unusual optical changes. The introduction of alkoxy in place of alkyl substituents seems to reinforce this

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81 effect as the ethylhexyloxyme thyl polymer display sharpe r optical changes than the ethylhexyl polymer. -0.6-0.4-0.20.00.20.40.6 20 30 40 50 60 70 80 90 PProDOT-(2-ethylhexyl)2 PProDOT-(CH2OC18H35)2 PProDOT-(CH2O-2-ethylhexyl)2 PProDOT-(CH2O-2-ethylbutyl)2% Relative LuminanceE (V) vs. Fc/Fc+ Figure 4-9. Luminance change vs. applied potential in PProDOT(CH2OR)2 polymers. All films were spray-coated from toluen e solution switched between -0.5V and 1V to eliminate any doping-induced r earrangement effect. All films were ~150-200 nm thick as determined by profilometry. To evaluate the efficiency of the electr ochromic transition, coloration efficiency experiments on the spray-cast films were carried out (Table 4-5). Table 4-5. Coloration Efficiency of PProDOT-(CH2OR)2 films sprayed on ITO-coated glass slides. Substituent Switching Time (s)a T (%) OD Qd (mC/cm2) CE (cm2/C) 2-methylbutyl 0.7 72 1.1 1.2 923 2-ethylbutyl 0.4 70 0.8 0.65 1240 2-ethylhexyl 0.6 80 1.12 0.9 1235 a time to achieve 95% of total color contrast; b color contrast between fully oxidized and neutral states; c log(Tox(95%)/Tred) The results indicate that as the branching size increases, the coloration efficiency increases as well. PProDOT-(CH2O-2-methylbutyl)2, compared to PProDOT-(CH2O-2ethylhexyl)2, requires more charges to obtain a si milar change of optical density. The switching time is also sma ller for ethylhexyl polymer. The increasing coloration

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82 efficiency trend can therefore be explained by the increased interchain and interstacks distance, allowing more efficien t penetration of the dopant ions into the polymer films. 4.3.4. Conductivity Measurement The conductivity of spray-coated PProDOT-CH2OR2 polymer films was determined by the four-point probe method. The measurements are taken as an average of multiple locations of the films, and reproducibility was checked by measuring conductivity on several films, l eading to consistent results. The value obtained for the alkoxymethyl substituted PProDOTs are given in Table 4-6, along with the voltage drop obtained for a constant intensity applied to the doped spray-coated films. The conductivity decreases sharply wi th increasing size of the br anching group. Interestingly, increasing the size of the main chain from butyl to hexyl does not appear to affect significantly the film conductivity.63a This correlates well with our assumption that the branching size, not the main chain size, is controlling the interchain distance. Table 4-6. Conductivity measurement for PProDOT(CH2OR)2 spray-coated films. Films were gas phased doped for 12 hours in an iodine chamber prior to measuring conductivity. R= I (V) a V (mV) b Thicknessc(nm) (S cm-1) 2-ethylbutyloxymethyl 2 83 658 0.08 2-ethylhexyloxymethyl 1 246 367 0.07 2-ethylhexyl 10 300, 194 222, 234 0.3, 0.5 2-methylbutyloxymethyl 10 148, 165 233, 246 0.54, 0.64 2-methylbutyl 100 203, 185 286, 251 3.8, 4.2 Hexyl N/A N/A N/A 5-10 (a) Intensity setting; (b) Average voltage drop; (c) Average thickness obtained by profilometry. Comparing the properties of alkyl and alkoxy polymers, the conductivity of the alkoxymethyl substituted polymers is one orde r of magnitude lowe r than their alkyl analogs. Given the electronic and optical resu lts presented above, a possible explanation is that the alkoxymethyl substituted polyme rs have a higher degree of intrachain and

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83 interchain disorder. Further studies on the ch iral equivalents of these polymers, presented in Chapter 5, will provide additional data supporting it. The lower conductivities of branched polymers are further evidence that th e coloration efficiency of these polymers is limited by the diffusion of dopant ion into the films, not the electr onic conductivity. 4.4. High Performance Electrochromic Devices Figure 4-10 shows a schematic representati on of the construction of a dual-window electrochromic device. Figure 4-10. Electrochemical device using spray-coated PProDOT(CH2O2-ethylhexyl)2 as the anodically coloring polymer a nd Poly(BisEDOT-N-methylcarbazole) electropolymerized film as the cathodical ly coloring polymer. (a) Schematic diagram of the dual-window electrochromic device; (b) Polymer colors for an applied bias of -1V (colored st ate) and +1V (bleached state). The electrochromic device is built from two ITO-coated glass slides, one coated with an anodically coloring polymer (in our case spray-cast PProDOT-(CH2OEtHx)2) and a second coated with an electrochemically oxidized, cathodically coloring polymer (in

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84 this work, the polymer used is (Poly(BisE DOT-N-methylcarbazole)). The two ITO slides are then combined, facing each other, with a layer of gel electrolyte. When a negative bias (-1V) is applied to the device both pol ymers are colored, giving a dark absorptive color to the film (Figure 4-10). When a pos itive potential of +1V is applied then PProDOT-(CH2OEtHx)2) is fully oxidized in its highly transmissive, sky blue color state while Poly(BisEDOT-N-methylcarbazole)2 is reduced to its neutra l, highly transmissive yellow color state. As presented in Figure 4-11, PProDOT(CH2O-2-ethylhexyl)2 yields an electrochromic device with high luminance c ontrast and high coloration efficiency (4800 cm2/C). The device can be fully switched up to rates of 2Hz. Figure 4-11. Luminance plot of a dualwindow EC device using spray-coated PProDOT((CH2O-2-ethylhexyl)2) as the anodically coloring polymer and electrolpolymerized Poly(BisEDOT-N -methylcarbazole) as the anodically coloring polymer. Similar devices, using a spray-coated PProDOT(CH2O-C18H37)2, led to CE values of only 1300 cm2 C-1. This work was carried out by Ali Cirpan and Avni Argun. It demonstrates nicely the difference of pr operties obtained between branched and long linear alkyl chains, both displaying high solubility.

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85 4.5 Conclusion Soluble PProDOTs, symmetrically substitute d with flexible, ether-linked branched alkyl groups, were synthesized by Grignard Meta thesis. Similarly to the alkyl substituted polymers studied in Chapter 4, increasing the branching size leads to shorter switching times, higher coloration efficiencies, higher ox idation potentials but lower conductivities. In spectroelectrochemistry and luminance e xperiments, abrupt optical changes with increasing potentials are also observed but the changes occur in a much narrower potential window (<150mV). In addition, upon spra y-casting, the polymer chains retain a “solution” conformation, suggesting little interc hain order is present in the films. This behavior can be explained by increased in trachain torsion of the polymer chains, preventing self-assembly in the solid state and leading to a more open morphology of the polymer chains. By oxidizing and reneutra lizing the polymer films, a significant bathochromic shift is observed, correspondi ng to intrachain and possibly interchain rearrangement of the polymer chains. As mentioned in Chapter 3, further studies using chiral equivalents of the alkoxy substituted PProDOTs will be described in Chapter 5 and provide substantial information on the interchain and intrachain interactions of the polymer chains in solution and in the solid state. 4.6. Chapter Synthetic Details 3,3-Bis(bromomethyl)-3,4-dihydro2H -thieno[3,4b ][1,4]dioxepine (ProDOT-(CH 2 Br) 2 ): The intermediate was obtained by transetherification, as described in the experimental section of Chapter 3. The product is a white crystalline solid obtained (73 %). mp 66-68 C. 1H NMR (300 MHz, CDCl3) 6.49 (s, 2H), 4.10 (s, 4H), 3.61 (s, 4H); 13C NMR (75 MHz, CDCl3) 148.5, 105.7, 74.1, 46.1, 34.4. HRMS calculated for

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86 C9H10O2Br2S: 339.8768 Found: 339.8820. Elemental Anal. Calcd for C9H10O2Br2S: C 31.60; H 2.95; S 9.37 Found: C 31.83; H 2.99; S 9.20. General procedure for the Williamson etherification of ProDOT(CH 2 Br) 2 : A 250 mL flame dried round bottom flask filled wi th 50 mL of DMF, 8.7 mmols of alcohol (3eq), and 17.5 mmols of NaH (6eq) was heated at 110 C overnight. Then 2.92 mmols of ProDOT(CH2Br)2 was added and the reaction continued at 110 C for another 24 hr. After completion, the flask was cooled and a dded to 200 mL brine and extracted 3 times with ethyl ether. The organic layer was th en washed 3 times with water, dried over magnesium sulfate, and the solvent was re moved by rotary evapor ation under reduced pressure. The resulting orange oil was purifie d by column chromatography (3:2 hexanes, methylene chloride). 3,3-Bis-(2-methylbutyloxymet hyl)-3,4-dihydro-2H-thien o[3,4-b][1,4]dioxepine (ProDOT(CH 2 O-2-methylbutyl) 2 ): The crude oil obtained was purified by column chromatography affording a clear oil (91%). 1H NMR (300 MHz, CDCl3) 0.81-0.93 (m, 12H), 1.02-1.20 (m, 2H), 1.32-1.48 (m, 2H), 1.51-1.69 (m, 2H), 3.11-3.28 (m, 4H), 3.423.5 (m, 4H), 3.99 (s, 4H); 13C NMR (75 MHz, CDCl3) 11.57, 16.80, 26.42, 35.08, 48.08, 69.91, 73.94, 76.96, 105.21, 149.90. HRMS calculated for C25H44O4S: 356.2021 Found 356.2048. Elemental Anal. Calcd for C25H44O4S: C 64.01; H 9.50 Found: C 64.03; H 9.05. 3,3-Bis-(2-ethylbutyloxymethyl)-3,4-dih ydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT(CH 2 O-2-ethylbutyl) 2 ): Purification by column chromatography (CH2Cl2) to afford a clear oil (88%). 1H NMR (300 MHz, CDCl3) 0.79-0.94 (t, 12H), 1.20-1.50 (m, 10H), 3.29 (d, 4H, J=5.96Hz), 3.47 (s, 4H), 4.01 (s, 4H); 13C NMR (75 MHz, CDCl3)

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87 11.40, 23.68, 41.34, 48.06, 69.99, 73.97, 74.05, 105.16, 149.88. HRMS calculated for C25H44O4S: 384.2334 Found: 384.2328. Elemental Anal. Calcd for C25H44O4S: C 65.59; H 9.44 Found: C 65.66; H 9.66. 3,3-Bis-(2-ethyl-hexyloxym ethyl)-3,4-dihydro-2H-thie no[3,4-b][1,4]dioxepine (ProDOT(CH 2 OEtHex) 2 ): The crude oil obtained was purified by column chromatography to afford a clear oil (70 %). 1H NMR (300 MHz, CDCl3) 6.42 (s,4H), 3.98 (s, 4H), 3.44 (s, 4H), 3.25 (d, 4H), 1.2-1.6 (m, 18H), 0.8-1.0 (m, 12H); 13C NMR (75 MHz, CDCl3) 149.7, 104.9, 74.3, 73.8, 69.8, 47.9, 39.6, 30.7, 29.1, 24.0, 23.1, 14.1, 11.1. HRMS calculated for C25H44O4S: 440.2960 Found: 440.2964. Elemental Anal. Calcd for C25H44O4S: C 68.14; H 10.06; S 7.28. Found: C 68.17; H 10.39; S 7.26. General procedure for the bromination of ProDOTs: In a 2-neck 250 mL round bottom flask filled with 80 mL DMF, 1.5g ( 2.1 mmol) of ProDOT was added and the solution was bubbled under argon for 60 minutes. Then 1.12 g (6.24 mmols) of N bromosuccinimide was added and the solution was stirred for 20 hr. After completion, the solvent was removed by rotary evaporation under reduced pressure and the resulting residue was purified by column chromatography on SiO2 with (4:1) hexanes/dichloromethane as eluent. 6,8-Dibromo-3,3-bis-(2-methylbutyloxymet hyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDOT(CH 2 O-2-methylbutyl) 2 Br 2 ): The crude oil obtained was purified by column chromatography (4:1) hexa nes/dichloromethane to afford 1.3 g of product (90%).1H NMR (300 MHz, CDCl3) 0.83-0.93 (m, 12H), 0.99-1.20 (m, 2H), 1.29-1.47 (m, 2H), 1.53-1.66 (m, 2H), 3.11-3.27 (m, 4H), 3.43-3.52 (m, 4H), 4.09 (m,

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88 4H); 13C NMR (300MHz, CDCl3) 11.59, 16.81, 26.42, 35.11, 69.80, 74.52, 76.81, 91.12, 149.45; HRMS Calcd for C25H42O4SBr2 514.0232. Found 514.0227. 6,8-Dibromo-3,3-bis-(2-ethylbutyloxym ethyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDOT(CH 2 O-2-ethylbutyl) 2 Br 2 ): The crude oil obtained was purified by column chromatography (4:1) he xanes/dichloromethane to afford 0.990g of product (92%). 1H NMR (300MHz, CDCl3) 0.79-0.92 (t, 12), 1.15-1.5 (m, 6H), 3.29 (d, 4H, 5.4Hz), 3.49 (s, 4H), 4.08 (s, 4H); 13C NMR (300MHz, CDCl3) 11.41, 23.68, 41.35, 48.18, 69.91, 74.07, 74.55, 91.00, 147.19. Elemental Anal. Calcd for C25H42O4SBr2: C 46.85; H 6.32 Foun d: C 46.85; H 6.42. 6,8-Dibromo-3,3-bis-(2-eth yl-hexyloxymethyl)-3,4dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDOT(CH 2 OEtHx) 2 Br 2 ): The crude oil obtained was purified by column chromatography (4:1) hexanes/dichlo romethane to afford a clear oil (98 %). 1H NMR (300MHz, CDCl3) 4.09 (s, 4H), 3.49 (s, 4H), 3.28 (d, 4H), 1.2-1.6 (m, 18H), 0.81.0 (m, 12H); 13C NMR (300MHz, CDCl3) 147.2, 91.0, 74.6, 70.0, 48.2, 39.9, 30.9, 29.4, 24.2, 23.3, 14.4, 11.4; HRMS Calcd for C25H42O4SBr2 596.1171. Found 596.1161; Elemental Anal. Calcd for C25H42O4SBr2: C 50.17; H 7.07; S 5.36. Found: C 50.43; H 7.09; S 5.16. General Procedure for Grignard metathesis polymerization of ProDOT(CH 2 OR) 2 Br 2 : In a flame dried 250 mL round bottom flask, dry THF (150 mL) and 3.0 g (0.34 mmol) of ProDOT(R)2Br2 was added under argon. Then methyl magnesium bromide (3.75 mL, 3.45 mmol, 0.91 8 M) was slowly added by syringe. The mixture was then refluxed for 2 hr. The flask was cooled and Ni(dppp)Cl2 (18.4 mg, 0.0341 mmol) was added and the reaction was heated at reflux overnight under argon.

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89 The solution was then cooled and the polym er was precipitated by pouring the solution in 400 mL methanol. The dark purple solid was purified by soxhlet extraction with methanol for 24 hr, hexanes for 48 hr, and fi nally chloroform for 24 hr. The chloroform was evaporated under reduced pressure to afford a dark shiny solid. Poly(3,3-bis-(2-methylbutyloxymet hyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine) (PProDOT(CH 2 O-2-methylbutyl) 2 : 0.47g of purple solid obtained (68%). 1H NMR (300 MHz, benzened6) 0.68-0.97 (br, 12H), 1-1.24 (br, 2H), 1.24-1.47 (m, 2H), 1.47-1.69 (m, 2H), 2.87-3.27 (br doublet, 4H), 3.37-3.74 (br, 4H), 3.96-4.7 (br, 4H); 13C (75 MHz, benzened6) 11.24, 16.77, 26.55, 35.22, 70.61, 77.11. Poly(3,3-bis-(2-ethyl-hexyloxymet hyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine) (PProDOT(CH 2 O-2-ethylbutyl) 2 ): 0.310g of purple solid obtained ( %). 1H NMR (300 MHz, benzened6) 0.85-1.07 (br, 12H), 1.28-1.56 (bs, 10H), 3.243.32 (br, 4H), 3.43-3.67 (br, 4H), 4.1-4.4 (br, 4H); 13C (75 MHz, benzened6) 11.91, 24.43, 30.6, 41.9, 48.62, 70.90, 74.24, 75.15, 115.47, 146.20 ; GPC analysis: Mn= 12,400, Mw= 17,500, PDI=1.4. Poly(3,3-bis-(2-ethyl-hexyloxymet hyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine) (PProDOT(CH 2 OEtHx) 2 ): 0.350 g of purple solid obtained (93 %). 1H NMR (300 MHz, benzened6) 4.25 (br, 4H), 3.58 (br, 4H), 3.25 (br, 4H), 1.621.30 (br, 22H), 1.09-0.99 (m, 12H); 13C (75 MHz, benzened6) 146.2, 115.3, 75.1, 74.8, 71.0, 48.7, 40.4, 31.6, 30.0, 25.0, 24.0, 14.9, 11.9 ; GPC analysis: Mn= 21,400, Mw= 36,100 PDI=1.72.

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90 CHAPTER 5 CHIRAL SUBSTITUTED POLY(3,4PROPYLENEDIOXYTHIOPHENES) 5.1. Introduction 5.1.1. CD Spectroscopy It is essential to co ntrol the ordering of -conjugated molecules from their assembly at the mesoscopic level to their applicatio ns at the macroscopic level. Many tools, recently reviewed by the Meijer group, are ava ilable to control the assembly process of conjuguated systems.74 One of these tools is the introduc tion of chiral substituents, which strongly influence the self-assemb ly of molecules, often leadi ng to intra or intermolecular chiral assemblies. Such chiral assemblies can be analyzed by chiroptical techniques. One of them, circular dichroism (CD), is commonly used to analyze the secondary and tertiary structures of proteins and biomolecules such as the -helix, -helix or -sheet, each having a specific CD signature.75 CD is also a highly se nsitive technique as small changes of conformation in the chiral asse mblies will induce changes in the CD signal. As a result, there is a stro ng dependence of CD on temperat ure while in solution, solvent and concentration also affect the CD signal. In a CD spectrophotometer, plane polarized light, which is the sum of left and right circularly polarized light of equal am plitudes with a phase difference of 180,76 passes through a sample in solution or a cast film on a transp arent substrate. If the sample is CD active, then either the left or the right polari zed light will be preferentially absorbed. This is circular dichroism. As a re sult of the preferential absorpti on of one circularly polarized light radiation, recombination no longer gives planar polarized light but elliptically

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91 polarized light, as seen in Figure 5-1. The variation of the elliptical angle as a fuction of wavelength yields the CD spectrum. This spectr um is equivalent to the regular absorption spectrum, where the absorption of unpolari zed light is followed with wavelength. Figure 5-1. CD spectroscopy principle. is the value measured by the spectrophotometer. Like absorbance, the CD signal is directly proportional to the concentration of the sample. Concentration-independent and anisotropy factor g ( / ) are sometimes reported and are calculated by: ) ( 32980 deg) (1 1 cm M C m 32980 deg) ( A m g where is elliptical angle, and A are the extinction coefficient and the absorbance at a given wavelength. To observe a CD signal, absorbing chromophor es must either be chiral or possess a helical arrangement. Both thei r electrical and magnetic tran sitions dipoles must also be different from zero. This is different than unpolarized absorption, where only the electrical transition dipole must be different than zero and heli cal order is not required. In

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92 the case of exciton-coupled chromophores in a chiral oblique arrangement, described in Chapter 1 and Figure 5-2, both optical tran sitions are electrica lly and magnetically allowed, and a CD signal is observed. Ex citon-coupling theory predicts that the transitions corresponding to the two Da vydov energy levels have opposite rotations, leading to a bisignate CD signal.77 Exciton-coupled J-aggregates or H-aggregates, on the other hand, have optical tran sitions which are magnetically forbidden, and no CD signal can be observed. Figure 5-2. CD signal of exciton-couple d chromophores with varying chromophores arrangement. Adapted from ref. 77. In exciton-coupled chromophores, the CD signal amplitude is at a maximum when interacting chromophores are at projection angle of 70. The si gnal is also proportional to

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93 the square of the extinction coefficient and proportional to the square of the chromophores distance.77 5.1.2. Applications of Chiral Polymers and CD Spectroscopy Many applications utilizing the unique propertie s of chiral polymers have been studied. As the chiral polymers often emit circ ularly polarized light, circularly polarized light-emitting devices have been studied.78 These polymers are also interesting candidates for non-linear optics as the chiral aggregates are noncentrosymmetric.79 In addition, the chiral polymers have been utilized in chiral membranes and sensors.80 However, most authors utilize chiral conjugated molecules and polymers as a unique tool to understand and control the se lf-assembly. This is important as film processing conditions, chain conformations, a nd film morphology have been shown to strongly influence the performance of -conjugated materials in devices.81, 13 By synthesizing chiral equivalents of the polym ers and studying them via circular dichroism, information on conformation and organization of the polymer chains from solution to the solid state can be extracted. This was eleg antly demonstrated by Swager in chiral substituted poly(p-phenyleneethynylene) (PPE).82 Analysis of these polymers by CD, absorption and fluorescence spectroscopy demons trated that, when dissolved in varying good solvent/ poor solvent mixtures, different type aggregates are formed, some having unusually high fluorescence. Other works have shown that the polymer chains conformation and their organization in solutio n and solid state are greatly modified by tuning solvent, temperature or film processing conditions.83 5.1.3. Thermochromism/Solvatochromism in Chiral Substituted Polymers Thermochromism has long been used to study conformational changes of polymer chains with temperature. In substituted poly( thiophenes), important changes of color are

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94 observed with temperature both in solution and in the solid state. When cooled, solutions of substituted polythiophenes undergo a progressive bathochromic shift and vibronic features appear. There is often presence of an isosbestic point, show ing that two distinct forms are in equilibrium. At longer times a ggregation and precipitation often occur. The mechanism of this thermochromic transition, even today, is the cen ter of great debate. Some authors have argued that the phenomenon is interchain related, while others argued it is intrachain in origin. The intrachain m echanism was first proposed by Heeger on the basis that dilution do not result in significant optical changes.84 The aggregation is then seen as a result of the intrachain planarity, fa voring strong interchain interactions. In this mechanism, the thermochromic transition is attr ibuted to a rod-coil transition within the polymer chains with the presence of ordere d regions (rod-like) a nd disordered regions (coiled-like). The interchain mechanism proposes that the thermochromic transition arises from equilibrium between aggregated chains in suspension and molecularly dissolved chains.85 A recent study using a dendrimer capped oligothiophene support that mechanism.86 It suggests that intrachain changes only play a pre-organization role in the change of optical absorption with temperatur e. Leclerc and his group later demonstrated that thermochromism in s ubstituted polythiophenes is highly dependent on the substitution and regioregularity.84b With a regioirregular back bone, or when substituents prevent the polymer chains from adopting a plan ar conformation, neither isosbestic point, nor appearance of vibronic coupling are observed. By using chiral polythiophenes and CD sp ectroscopy, Meijer et al. showed that interchain interactions such as those illustra ted in Figure 5-3 play a crucial role in the thermochromism process, as demonstrated by the appearance of a strong bisignate CD

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95 signal corresponding to the optical transition when the solutions were cooled to low temperatures. 87 The CD signal was attributed to Davydov exciton coupling between chains involved in chol esteric aggregates. Chiral aggregation could also be induced by solvatochromism. In chloroform, a good solvent for the chiral pol ythiophenes, no CD signal is observed as the polymer chains are molecularly dissolved. As methanol a poor solvent of the polymer, is added, a bisignate CD signal is observed, indicating presence of interchain helical aggregates. The chiral aggregates were also formed in the solid state, as evidenced by the presence of a CD signal in films cast from chloroform. The films emitted circularly polarized light, suggesting that the chiral aggregates are main tained in the excited state. Figure 5-3. Cholesteric pack ing in aggregated chiral poly(thiophenes). Only the polythiophene backbone is displayed. 5.1.3. Chiral Substituted PProDOTs In Chapter 3 and 4, the focus was on the unique properties of branched dialkyl and dialkoxymethyl substituted PProDOTs. Thei r applications as highly efficient electrochromic materials we re also described, with high contrasts and subsecond switching times. Most of these branched substi tuents are chiral chains, but were obtained from racemic reagents, resulting in polymers with a random distributi on of R and S chiral centers. In this chapter, the synthesis and pr operties of fully chiral polymers, shown in Figure 5-4, obtained from enan tiomerically pure reagents are described. The polymers

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96 were studied by fluorescence, absorption and circular dichroism. In addition, a unique, versatile synthesis yielding enantiomerically pure chiral substituents is presented. These substituents were utilized in the synthesis of unique chiral polymers. S S O O O O n nPProDOT-((2S)-methylbutyl)2PProDOT-(CH2O-(2S)-methylbutyl)2 O O S O O n PProDOT-((2S)-ethylhexyl)2 Figure 5-4. New soluble Chir al PProDOTs polymers obtaine d by Grignard Metathesis 5.2. Synthesis of PProDOT-Based Chiral Polymers 5.2.1 New Chiral Reagents Synthesis As shown in the previous two chapters, subs titution with branched alkyl chains is a highly effective method for inducing solubi lity in otherwise insoluble conjugated polymers (CPs) and improving electrochrom ic properties. PProDOT-(2-ethylhexyl)2 and PProDOT-(CH2O-2-ethylhexyl)2 yielded the highest contra st and highest coloration efficiency of the PProDOTs series. PProDOTs substituted with linear substituents yield materials with much lower performance. It was also observed th at the two polymers undergo a very sharp optical transition in luminance and absorption spectrum as a function of increasing potentials. Another 2-ethylhexyl substi tuted polymer, poly(2methoxy, 5-(2-ethylhexyloxy),1,4-phenylenevin ylene) (MEH-PPV), is one of the most studied and efficient polymers in ligh t-emitting and photovoltaic applications.88 In that work, it is therefore of high inte rest to synthesize chiral et hylhexyl substituted polymers. But to date, only one conjugate d polymer with chiral 2-ethyl hexyl side chains, poly(9.9(bis((R)-2-ethylhexyl)fluorene2,7-diyl) has been reported.89 The chiral substituents were

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97 obtained by enzymatic catalysis but the method gives low yields (10%) and the substrates that can be used, as well as the products th at can be obtained with this method, are limited. Often, only one enantiomer is accessible. In this work, 2S-ethylhexanol was synthesized by enantioselective al kylation of an acylated pseudoephedrine, as detailed in Figure 5-5, modifying a proce dure outlined by Myers et al..90 The enantiomeric excess of the alcohol was determined to be 96% by GC of the Mosher ester de rivative. This route uses inexpensive materials, gives high yi eld and can be easily scaled up. Both enantiomeric products can be obtained by using either of the two inexpensive enantiomeric dand l-pseudoephedrines. In addition, it utilizes a flexible method allowing the efficient synthesi s of many different chiral pr imary alcohols with variable substituents on the position along with othe r derivatives including chiral acids, acyl chlorides, and aldehydes. N OH O N OH O O OH S O S OH S H O Cl S (f) 96%ee (a) (b) N OH H (d) (e) (c) Figure 5-5. Synthesis of 2S -ethylhexyl substituents using a pseudoephedrine chiral auxiliary. (a) butyric anh ydride, RT, THF, 23C; (b) LDA, 6 eq. LiCl, -78C, 1 hr 0C, 15min 23C, 5 min then butyliodide, 30 min, 0C; (c) 18N H2SO4, dioxane, reflux; (d) LiAlH4, Et2O, reflux;(e) LiAlH(OEt)3, THF; (f) SOCl2, DCM, reflux. 5.2.2 Electrochemically Polymerizab le Monomer and Electrodeposition The electropolymerizable monomers we re obtained through the same synthetic methods described in Chapter 3 and 4 for the racemic polymers except for a slight change in the synthesis of the chiral alkyl PProDOT s. The alkyl bromides used in the malonic

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98 ester synthesis were replaced by tosylated al cohols, as 2S-methylbutyl alcohol is less expensive than 2S-methylbutylbromide and the 2S-ethylhexyltosylate is easily obtained from the alcohol obtained through the synthe tic method presented above. Purification of the tosylate is also easier, as ethylhexylbromide is highly volatile. Electrodeposited films of the chiral poly mers were studied by electrochemistry. As seen in Figures 5-6, PProDOT-(2-methylbutyl)2 and PProDOT-(2S-methylbutyl)2 have similar half-wave and onset potentials, sugge sting that the introduc tion of chiral side chains does not change th e macroscopic properties. -0.8-0.6-0.4-0.20.00.20.4 -4 -2 0 2 4 S O O nI (mA/cm2) E(V) vs. Fc/Fc+E1/2=-31mV 23mV -85mVa-1.0-0.8-0.6-0.4-0.20.00.20.4 -4 -3 -2 -1 0 1 2 3 4 S O O nI (mA/cm2)E(V) vs Fc/Fc+55mV -77mV E1/2= -11mVb Figure 5-6. Cyclic voltammetry of el ectrodeposited PProDOT((2S)-methylbutyl)2 and PProDOT((2S)methylbutyl)2. Scan rate is 50mV/s. Potential are reported against Fc/Fc+. Following Grignard metathesis, PProDOT((2S)-methylbutyl)2, PProDOT(CH2O(2S)-methylbutyl)2 and PProDOT((2S-ethylhexyl)2) were obtained as shiny brown solids. After Soxhlet purification with methanol and hexanes, PProDOT((2S)-methylbutyl)2 was extracted with dichloromethane. A fraction of this polymer remained in the Soxhlet thimble, but was successfully extracted w ith chloroform. As expected, GPC results, detailed in Figure 5-1, indicate that the fr action soluble in dichloromethane has a lower molecular weight than the chloroform fraction. PProDOT(CH2O-2S-methylbutyl)2 was

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99 insoluble in dichloromethane, but was su ccessfully extracted with chloroform. For PProDOT-(2S-ethylhexyl)2, the polymer was soluble in both dichloromethane and chloroform. GPC analysis revealed a simila r molecular weight distribution than the highest molecular weight fract ion of PProDOT((2S)-methylbutyl)2, showing that the larger branched substituents yiel d significantly higher solubility. Table 5-1. GPC data for chiral substitute d PProDOTs. Molecular weights are versus polystyrene standards. Substituents Mn Mw DPI XnSolubility 2S-methylbutyl 5,400 8,400 1.5 18DCM, CHCl3 8,400 13,8001.6 28CHCl3 2S-ethylhexyl 8,700 14,2001.6 22DCM, CHCl3 2S-methylbutyloxymethyl 18,90032,0001.7 53CHCl3 After spray-casting of the polymers onto ITOcoated glass slides, the optoelectronic properties of the films were analyzed. Spectroelectrochemistry experiments, carried out on PProDOT-(2-methylbutyl)2 and PProDOT-(2S-methylbutyl)2 spray-cast films, indicate that the maxima of absorption and the vibronic features vary little between the racemic and chiral polymers as displayed in Figure 5-7. Also, for both PProDOT-(2Smethylbutyl)2 and its racemic analog, most optical changes are obtained within only a 350 mV potential increase. 4006008001000120014001600 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 S O O nAbsorbance (nm) 1V 0.8V 0.7V 0.6V 0.5V 0.4V 0.3V 0.2V 0V 627 573 5314006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 S O O nAbsorbance (nm) 1V 0.8V 0.7V 0.6V 0.5V 0.4V 0.3V 0.2V 0.1V 625 571 533 Figure 5-7. Comparison of PProDOT-((2S)methylbutyl)2 and PProDOT-((2S)methylbutyl)2 spectroelectrochemistry. Both films were spraycast from toluene.

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100 For PProDOT-((2S)-ethylhexyl)2 and PProDOT-(CH2O-(2S)-methylbutyl)2, the polymer properties are also comparable to the racemic polymers (Table 5-2). Table 5-2. Comparison of chiral and racemic PProDOTs polymers. PProDOT-(2-ethylhexyl)2 PProDOT-(CH2O-2methylbutyl)2 Racemic Chiral Racemic Chiral Ep,a (mV)a 45 89 26 N/A Ep,c (mV)a 11 43 -29 (-269) N/A max cast filmb (nm) 618, 564, 523 617, 564, 524 612, 561, 528 615, 564, 529 Ega 1.93 1.92 1.91 1.91 Conductivityc (S cm-1) 0.4 N/A 0.6 0.8 (a) Electrodeposited films Potential vs. Fc/Fc+; (b) Neutral films spray-coated on ITO after electrochemical switching; (c) Films gas phase doped with iodine. Although the macroscopic properties indica te clearly no significant dependence on the chirality, circular dichroism spectroscopy indicates significant differences in their ordering behavior. 5.3. Chiral Ordering in Chiral PProDOTs 5.3.1. Optical Properties in “Good” Solvent Solutions The thermochromism of the chiral polymers was studied in xylenes, a good solvent of the polymer. The absorption thermochromism for PProDOT-(CH2O-2S-methylbutyl)2 in xylenes is shown in Figure 5-8a. As the te mperature is raised, a gradual blue-shift of the absorption is observed and the vibroni c features progressively disappear. The decrease is bigger for the 0-0 transition than the 0-1 transition, lead ing to a dominant 0-1 vibration above 45C. No clear isosbestic poi nt can be seen in the temperature range studied. When the absorbance at 591nm is followe d with temperature, a linear variation is observed, as shown in the in set of Figure 5-8a. As it was shown that interchain and intrachain mechanisms display different temp erature dependence, th e linear variation of

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101 the optical maximum suggests e ither an intrachain or inte rchain-only mechanism for the thermochromism of PProDOT-(CH2O-2S-methylbutyl)2.86 The other PProDOTs (chiral or racemic) display a similar behavior wh en dissolved in a g ood solvent. When the polymers are dissolved in more polar solvents such as chloroform ( = 4.8) or orthodichlorobenzene ( = 9.9), a bathochromic shift is observed, as seen in Figure 5-8b. The vibronic features are identical and the shift therefore cannot be due to changes in the intrachain conformation of the polymer chains. The shift is rather due to an increased stabilization of the polar ized excited state by th e more polar solvents. 300400500600700 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 280300320340360380 0.3 0.4 0.5 0.6 0.7 0.8 Absorbance at 591nmT(K) 5CS O O n O O Absorbance (nm) 95C(a) 500550600650 0.0 0.2 0.4 0.6 0.8 1.0 S O O nAbsorbance(nm) ODCB CHCl3Xylenes(b) Figure 5-8. Temperature dependence of PProDOT(CH2O-2S-methylbutyl)2 in xylenes solution. To eliminate the possibility that intercha in interactions are involved in the thermochromic transition of PProDOTs in good solvent solutions, the solutions were examined by fluorescence and circular dichro ism spectroscopy. As shown in Figure 5-9 for PProDOT-(2S-ethylhexyl)2, the fluorescence decreases a nd is blue-shifted with increasing temperature. A possi ble explanation for the decreased fluorescence is that the number of photons absorbed decrea se at the excitation wavelength ( exc=550 nm). Closely inspecting at the absorption, a decrease in absorption is indeed seen, but is much smaller than the decrease in fluorescence intensity. It follows that the decreased

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102 absorption at the excitation wavelength cannot account for the weaker emission. Such decrease of emission also demonstrates that interchain quenching cannot be involved in the pure solvent solutions, as interchain interaction would break up as the temperature is increased, leading to an increase in fluorescen ce intensity. Moreover, CD analysis carried out on xylenes solutions reveals no CD signal, and dilution experime nts indicate no shift in absorption spectrum, confirming the absence of interchain interactions. As a result, thermochromism and vibronic features in PPr oDOTs, dissolved in good solvent solutions, are attributed to intrachain interactions only. 400450500550600650 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 Absorption (nm) 95C 5C ex= 550 550600650700750800 0.0 2.0x1054.0x1056.0x1058.0x1051.0x1061.2x106 (b)S O O n ex= 550 95CEmission Intensity (nm) 5C(a) Figure 5-9. Thermochromism of PProDOT((2S)-methylbutyl)2 in xylenes solution. (a) Fluorescence spectrum with excitati on at 550nm; (b) Absorbance spectrum. 5.3.2. Solvatochromism Effects in PProDOTs Solutions When the chiral polymers are dissolv ed in good solvent (xylenes, orthodichlorobenzene, chloroform THF) / poor solvent (methanol, DMF) mixtures, their

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103 optical properties are drastically affected. Figure 5-10 illustrates the effect of adding DMF to a xylenes solution of PProDOT(2S-methylbutyl)2 on the absorption, emission and circular dichroism spect ra. At low DMF content ( 30%), the absorbance remains constant, no CD signal is observed and the fluorescence intensity decreases slightly. These observations indicate that no aggregati on has occurred. The decreased fluorescence intensity could possibly be explained by the energy gap law, predic ting that rate of nonradiative decay increases as the differen ce of energy between the ground and excited state. As the DMF content is increased, the polarity of the solvent mixture increases, resulting in a stabilization of the excited state, as show n earlier in Figure 5-8. The stabilization is expected to result in an increase of non-ra diative decay, as predicted by the energy gap law. This behavi or is observed up to a 70/30 xy lenes/DMF ratio. At a ratio of 60/40, abrupt optical ch anges are observed. The absorption spectrum undergoes a 20nm bathochromic shift, the emission is strongly quenched and a well-defined CD signal appears. These changes correspond to an aggregation of the polymer chains, with highly efficient interchain quenching of the photoluminescence. As shown in Figure 510c and Figure 5-10d, the CD signal is bisignate and matches with the first derivative of the absorption, fully consiste nt with Davydov exciton splitting.87,91 The CD signal is reminiscent of the signal observed in aggregated poly(3,4-bis((S)-2methylbutoxy)thiophene), suggesti ng that PProDOT((2S)-methylbutyl)2 forms cholesteric interchain aggregates in poor solvent mixtures. The maximum anisotropy factor is gmax=1.610-2 at 642 nm and is close to the va lues reported for poly(3,4-bis((S)-2methylbutoxy)thiophene).87 PProDOT((2S)-ethylhexyl)2 displays a similar behavior to PProDOT((2S)-methylbutyl)2 in xylenes/DMF mixtures. At a 60/40 ratio, aggregation

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104 again occurs, leading to a sharp decrease in fluorescence, a bathochromic shift in absorption and the appearance of a bisignate CD signal. The maximum anisotropy factor of the CD signal is gmax= 2.410-2, comparable to the chiral methylbutyl analog. 550600650700750800 0.0 2.0x1054.0x1056.0x1058.0x1051.0x1061.2x1061.4x1061.6x106 % xylenes % xylenes 100% 90% 80% 70% 60% 50% 40%Emission Intensity / nm% xylenes400500600700 -20 0 20 40 60 70% 60% 50% (d) (c) (b) CD signal /mdeg/nm (a)300400500600700800 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 First Derivative of Absorption Spectrum Normalized CD signal (nm)400500600700 0.00 0.05 0.10 0.15 0.20 100% 70% 60% 50% 40% 10%Absorbance / nm Figure 5-10. Optical properties of PProDOT((2S)-methylbutyl)2 solutions in Xylenes/DMF mixtures (C= 8.610-6M). (a) absorption spectra; (b) photoluminescence spectra, exc=550nm; (c) CD spectra; (d) comparison between CD spectrum and first derivative of the absorbance of a 30/70 xylenes/DMF solution. The alkoxymethyl substituted PProDOT(CH2-O-2S-methylbutyl)2, however, behaves differently. When poor solvent is added to a xylenes solution of PProDOT(CH2O-2S-methylbutyl)2, although a clear red sh ift is observed at a 60/40 xylenes/DMF ratio indicating aggregation of the polymer ch ains, no CD signal is observed. Possible explanations for the abse nce of CD signal are:

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105 1. Alkoxymethyl substituted polymers chains have a more distorted backbone. (see Chapter 4). 2. ProDOT seven-membered ring conformational flexibility between “chair” and “twisted” conformations (see Chapter 3) hinder polymer chains self-assembly. 3. The chiral centers are too remote from the conjugated backbone to induce preferential helical order. 4. The flexibility of the alkoxymethyl preven ts ordering of the ch iral side chains. The two last explanations are unlikely as previous studies in chiral poly(3alkylthiophenes) show that introducing alkyl or alkoxy spacers do not prevent the formation of chiral aggregates.92 5.3.3. Thermochromism in PProDOTs Aggregated Solutions Thermochromism was carried out on PProDOT(2S-ethylhexyl)2 polymer solutions dissolved in various xylene s/DMF solvent mixtures. The evolution of the optical properties with temperature was probed with CD, fluorescence and absorption spectroscopy. For each solvent com position, the absorbance at the max of the 5C spectrum is followed with temperature, as observed in Figure 5-11. In pure xylenes, a linear trend is observed within the temperat ure range probed (Figur e 5-11a), as already seen with PProDOT((CH2O-(2S)-methylbutyl)2. The linear trend is also observed for the 10/90 xylenes/DMF solutions (Figure 5-11d) These results sugge st that a single mechanism operates in the thermochromic changes.86 For the 50/50 and 40/60 xylenes/DMF solutions (Figures 5-11b and 5-11c), the maximum of absorption also varies linearly, but there is a clear change of slope between 40 and 60C for the 50/50 solution and between 60 and 70C for the 40/60 solution. The CD intensity, followed at 616 nm, decreases for both solutions with increasing temperature indicating that aggregates progressively break up and chains become molecularly dissolved (Figure 514a and 5-14b). At temperatures close to th e change of slope in absorption, the CD becomes zero, indicating the polymer chains become molecularly dissolved and that

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106 further changes in absorption are due only to intrachain interactions. The interchain breakup temperature highly depends on the xylenes/DMF ratio, as increasing the DMF content leads to higher interchain breakup temperatures. At higher DMF content than 60%, the aggregates cannot be fully reversed within the temperature experimentally accessible (0-100C). 300320340360380 100% Xylenes Absorbance 595nm Thermochromism of PProDOT-(2S)ethylhexyl)2in Xylenes/DMF solution300320340360380 50% XylenesAbsorbance 605nm 300320340360380 40% XylenesAbsorbance 609nm 300320340360380 (d)10% Xylenes(c) (b)Absorbance 614nm (a) Figure 5-11. Thermochromism of PProDOT((2S)ethylhexyl)2 in xylenes/DMF mixtures. The max at of the absorption spectrum at 5C is followed with temperature in: (a) 100% xylenes; (b) 50/50 xylenes/D MF; (c) 40/60 xylenes/DMF (d) 90/10 xylenes/DMF. Looking at the fluorescence spectra for 50/50 xylenes/DMF solutions of PProDOT(2S-ethylhexyl)2 and PProDOT(2S-methylbutyl)2, a strong increase in fluorescence is observed as the temperature is increased (Figure 5-12). For PProDOT(2Sethylhexyl)2, the fluorescence increases until 70C, as aggregates progressively breakup,

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107 shown by the decrease in CD intensity. Above this temperature, th e fluorescence levels off, likely to what is observed in the pure xyl enes solutions, indicating that, as expected, no interchain interaction remains and the optical changes above 70C are only due to intrachain interactions. For PProDOT(2S-methylbutyl)2, there is a continual increase in fluorescence even up to 90C (upper te mperature limited by water chiller). 550600650700750800 0.0 5.0x1041.0x1051.5x1052.0x1052.5x1053.0x1053.5x1054.0x1054.5x1055.0x105 S O O n Emission Intensity (nm) 80C 70C 60C 50C 40C 30C550600650700750800 0.0 2.0x1044.0x1046.0x1048.0x1041.0x1051.2x1051.4x1051.6x1051.8x1052.0x1052.2x1052.4x1052.6x1052.8x1053.0x1053.2x105 S O O nEmission Intensity / nm 90C 80C 70C 60C 50C 40C 30C Figure 5-12. Fluorescence thermoch romism of 50/50 xylenes/DMF PProDOT((2S)methylbutyl)2 and PProDOT((2S)ethylhexyl)2. The results above show two different mechanisms are responsible for the thermochromic changes. In good solvent solu tions or thermoreversible aggregates solutions above the interchain breakup temperat ure, intrachain distor tions are responsible for the optical changes with temperature. On the other hand, in thermo-irreversible aggregates or thermoreversible aggregat es studied below the interchain breakup temperature, interchain interactions are play ing a large role in the optical changes, as shown by the progressive decrease of the CD intensity at 616nm. As seen in Figure 5-13, the absorption spectrum at 95C of the thermoreversible PProDOT(2S-ethylhexyl)2 50/50 xylenes/DMF aggregated so lution is almost identical to the absorption in pure xylenes at 95C, showing that intrachain interactions also play a role in the thermochromic changes.

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108 3004005006007008000.0 0.2 0.4 0.6 0.8 1.0 Absorbance / nm Xylenes/DMF 50/50, 95C xylenes 25C xylenes 95C Figure 5-13. UV-Vis absorption of a 50/50 xyl enes/DMF aggregated solution at 95C. Comparison with pure xylenes solution at 95C and 25C. By cooling slowly (12C/hr) the 50/50 xyl enes/DMF solution from the molecularly dissolved state, the aggregates reform with a significant hysteresis as shown in Figure 514a, as the CD intensity at 616nm only reapp ears at a temperature of ca. 40C. At room temperature, after slow cooli ng treatment, the CD intensity at 616nm is fully recovered, but the CD signal shape is different, as disp layed in Figure 5-15a. The CD signal of the slowly cooled solution indicates that new, thermodynamically stable chiral aggregates form. Such dependence on the cooling rate was observed in oligothiophenes as well.93 The hysteresis depends strongly on the xyl enes/DMF ratio. At a 40/60 xylenes/DMF ratio, only part of the CD intensity at 616 nm as presented in Figure 5-14b, is recovered and the corresponding CD signal is also sign ificantly modified. A possible explanation for the lower CD intensity, illustrated in Fi gures 5-14c and 5-14d, is that in the case of the 40/60 xylenes/DMF ratio, the chiral aggreg ates reform at a much higher temperature than the 50/50 solution. At such higher temperature, the intrachain conformation is expected to be more twisted, hindering the chains self-assembly. The absorbance spectra

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109 after slow cooling are fully consistent with this assumption, as the maximum of absorption is blue shifted for the 40/60 xyl enes/DMF solution compared to the 50/50 xylenes/DMF solution. In addition, the 0-1 vibronic transition becomes dominant for the 40/60 xylenes/DMF solution, characteristic of a more twisted intrachain conformation. 20304050607080900 5 10 15 20 25 30 CD signal (mdeg)T(C)50% xylenes12/hr2/min (a)20406080100 0 10 20 30 40 50 60 (b) 40% xylenes 12/hrCD Signal (mdeg)T(C)2/min 4005006007008000.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 max595 605 610 As prepared At 90 oC After coolingAbsorbance/ nm50% xylenes(c) 300400500600700800 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 After slow cooling As preparedAbsorbance / nm40/60 xylenes551 595 613 559 523(d) Figure 5-14. Evolution of absorption sp ectrum of 40/60 and 50/50 xylenes/DMF PProDOT-((2S)ethylhexyl)2 solution following heating/ slow cooling cycle. (a) CD signal, 50% xylenes; (b) CD signal 40% xylenes; (c) UV-Vis absorption, CD signal, 50% xylenes; (d) UV-Vis ab sorption, CD signal, 40% xylenes. Thermoreversibility was not obser ved in PProDOT((2S-methylbutyl)2 solutions. Figure 5-15 compares the CD signa ls for PProDOT-((2S)-methylbutyl)2 and PProDOT((2S)ethylhexyl)2 dissolved in 50/50 xylenes/DMF as a function of temperature. As the temperature is increased up to 100C for PProDOT((2S-methylbutyl)2, the CD signal is

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110 decreased but still present. This observation is consistent with increased -stacking interactions. (Figure 5-15d). U pon slow cooling of the hot so lutions, a hysteresis in CD spectrum is also seen (F igures 5-15c and 5-15d). 204060801000 10 20 30 Heating 2C/min Slow cooling 12C/hrS O O n (b)CD intensity at 616nm/ nm 300400500600700 -10 0 10 20 30 S O O n Afterslowcooling As preparedCD signal / mdeg / nm(a)300400500600700 -20 -10 0 10 20 30 40 50 (c) As prepared After slow cooling 90CCD signal / mdeg / nm 0204060801000 10 20 30 40 50 CD intensity at 616nm(d) Heating 2C/min Slow cooling 12C/hr T / C Figure 5-15. Polymer optical properties evol ution during heating/slow cooling cycle. PProDOT(2S)-ethylhexyl)2 50/50 xylenes/DMF (a) CD spectrum “as prepared” and after slow cooling, (b ) evolution of the CD signal at 616nm with temperature; PProDOT(2S)-methylbutyl)2 50/50 xylenes/DMF; (c) CD spectrum “as prepared”, at 90C and afte r slow cooling, (d ) evolution of the CD signal at 616nm with temperature. 5.3.4. Chiral Order in Spray-cast Films Films were spray-cast from toluene solution onto ITO-coated glass slides and analyzed by CD and absorption spectroscopy. The chiral branched alkyl PProDOTs both yield CD signals. The shape of the CD si gnal for spray-cast PProDOT-(2S-methylbutyl)2 is similar to the solution aggregates, but the maximum anisotropy factor value is slightly lower with gmax = 0.710-2 at 637nm, possibly indicating th at the aggregates are more disordered than in aggregated solution.

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111 PProDOT-(2S-ethylhexyl)2 yields a much higher CD signal, leading to an anisotropy factor comparable to its aggregated solutions with gmax = 2.910-2 at 627 nm. Remarkably, the shape of the CD signal is identical to the CD signal observed for the slowly cooled polymer solution, and is attr ibuted to the formation of thermodynamically stable aggregates. Figure 5-16 shows the ev olution of the absorption and CD spectra during a gas phase iodine dopi ng/ hydrazine vapor reneutra lization cycle. Upon exposure to iodine, the film CD signal is dramatically changed. The UV-Vis spectrum indicates the polymer film is fully oxidized to the bi polaron state (Figure 5-16b). The corresponding CD signal (Figure 5-16a), seen in the visible range of the absorption spectrum, is much less intense and blue shifted compared to the neutra l film. This suggests that undoped chromophores with short conjugation lengths re main in the film and, more importantly, that the polymer chains retain a chiral orientation in the doped state. Similar observation were made in chiral poly(d ithieno[3,2-b:2’,3 ’-d]pyrroles).94 A negative CD signal is also observed between 700 nm and 900 nm (Inset of Figure 5-16a), sugge sting the bipolaron band is CD active. Such results are quite unique as the presence of CD activity in the bipolaron state has not been reported mostly due to limitations of CD spectrophotometers in the near-IR region, where the bipolaron band absorbs. Upon exposure of the films to hydrazine vapor, the neutral polymer CD signal is fully recovered, demonstrating the stability of the chiral a ggregates upon oxidation and the absence of doping-induced re arrangements. Studies on chir al poly(3-alkyl thiophenes), on the other hand, showed that doping/dedoping cycles often resu lt in significant CD signal changes.95 After two days, the UV-vis and CD spect ra of the cast films were examined again. The results indicate the polymer was de doped to the polaron state, as noted by the

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112 presence of the characteristic absorption peak centered at 950 nm No CD signal is observed for this band showing the pola ron absorption is not CD active. Conversely to the aggregated solution study, significan t differences between the first derivative of the absorp tion spectrum and the CD spectrum are observed. As seen in Figure 5-16, the wavelengths corresponding to the CD signal maxima now coincide with the wavelengths of the absorption spectrum ma xima. Such behavior was not observed in chiral alkyl poly(thiophenes), as the CD signals for both a ggregated solutions and films match the first derivative of the absorption spectra.87 300400500600700800900 0.0 0.4 0.8 1.2 400500600700 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (nm)AGGREGATED SOLUTION SPRAY-CAST FILM Cast film I2 doping 1st cycle Hydrazine reduced I2 doping 2nd cycleAbsorbance / nm(b)I2absorption 300400500600700800900 -500 0 500 1000 1500 600700800900 -100 -50 0 50 100 CD SIGNAL CD / mdeg / nm (a) Figure 5-16. Absorption and CD signal for PProDOT-((2S)-ethylhexyl)2) spray-coated films. (a) CD signal with doping/dedopi ng cycle. Inset shows a magnification of the 600-900nm region. (b) Absorption with doping/dedoping cycle. Inset shows a comparison of the absorption of a 30/70 xylenes/DMF aggregated solution to the spray-cast film absorption. Given that the CD signals of the films a nd aggregated solutions are very close to one another, the differen ce between the CD signal of PProDOT((2S)-ethylhexyl)2 in the

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113 film state and the first derivative of the abso rption spectrum could be explained from the difference of absorption spectra which are shif ted 20 nm from one another (Inset, Figure 5-16b). This would suggest that achiral aggregates, absorbi ng on the low energy side of the optical transition (550-750nm), are also fo rmed during film casting. However, a more likely explanation is that a ne w type of chiral aggregates is formed during casting. This possibility is supported by the high CD signals observed for this polymer, and also the stability of the CD signal to oxidation/rene utralization cycles. R ecent results by Swager also indicate that multiple aggregates can form in the solid state depending on the processing conditions.83a PProDOT(CH2O-2S-methylbutyl)2, spray-coated from a CHCl3 solution on ITO, yields no CD signal, as seen in Figure 517. Upon electrochemical doping, a CD signal appears. The CD signal is quite weak and its shape is not well-defin ed, showing that the aggregates, although more ordered than the fresh cast film, remain disordered. The formation of chiral aggregates after an oxida tion/reneutralization cycle demonstrates that, in addition to the doping-induced intrachain rearrangements created by the formation of the more planar quinoidal form in the oxidized state, interchain rearrangements occur. It also suggests that the disorder of th e aggregates in alkoxy substituted PProDOTs originates from intrachain torsion of the chains in solution. This assumption is consistent with studies from Verbiest et al. on chiral poly(3,7-dimethyloctyloxythiophene) with varying degrees of regioregularity showing that regioregular samples, having much higher intrachain planarity (see Chapter 1), give much higher CD signal in the film state.96 Regioirregular samples, having a more twisted backbone, were found to give no CD signal.

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114 300400500600700 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Not Switched SwitchedPProDOT-(CH2O(2S)methylbutyl)2 on ITO glass slide from CHCl3Absorbance(nm) 300400500600700800 -20 -10 0 10 20 PProDOT-(CH2O(2S)methylbutyl)2 on ITO glass slide from CHCl3 Not Switched Switched CD (mdeg)Wavelength, nm Figure 5-17. CD signal of chiral PProDOT(CH2O-2-methyl)2 spray-cast films. (left) UV absorption spectra; (right) CD signal. 5.4. Conclusion Three regiosymmetric, soluble chiral polymers, PProDOT(CH2O-2S-methylbutyl)2, PProDOT(2S-methylbutyl)2 and PProDOT(2S-ethylhexyl)2 were synthesized by Grignard Metathesis. The synthesis of the latter polym er was made possible by a new synthesis of chiral 2S-ethylhexanol. The s ynthesis is simple, scalable, extremely versatile and should prove useful to many research ers in the field of soluble -conjugated polymers. Using UV-Vis absorption, fluorescence and circular dichroism spectroscopy, a clear distinction between the role of inter and intrachai n interactions in thermochromism and solvatochromism of ProDOT-based polymers was obtained. The alkyl substituted chiral polymers were found to form cholesteric a ggregates similar to chiral substituted polythiophenes. Remarkably, the chiral ag gregates in solution were found to be thermoreversible for PProDOT((2S)ethylhexyl)2 but not for PProDOT(CH2O-2Smethylbutyl)2. This behavior is cons istent with decreased -stacking interchain interactions arising from introduction of the larger ethylhexyl substituents. In the solid

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115 state, the polymers seem to form new chiral aggregates, stable to oxidation/reneutralization cycles, giving rise to intense CD signals. On the other hand, the ether linked PProDOT(CH2O-2S-methylbutyl)2 does not form chiral aggregates in solution or in freshly cast films. Some limite d chiral aggregation occurs upon oxidation and reneutralization cycle, i ndicated by the apparition of a weak, ill-defined CD signal. This behavior is attributed to intrachain torsion of the ether li nked polymer preventing self-assembly of the molecules into helically ordered structures. 5.5. General Synthetic Details Lithium chloride was dried under 0.1 mmHg vacuum at 150C overnight. Dry THF, ether, toluene were obtained by di stillation from Na/benzophenone ketyl. Dry diisopropylamine, hexane and ethyl acetat e were obtained by di stillation from CaH2. Dry dimethylformamide was obtaine d by distillation from MgSO4. n-BuLi was titrated with N-pivaloyl-o-benzylaniline. (1R,2R)-pseudoephedrinepropionamide In a flame-dried 500 mL round bottom flask (1R,2R)-(-)-pseudoephedrine (10g, 60.6 mmo l, 1 eq.) was dissolved in 200 mL of dry THF. The flask was equipped with a pr essure-equalizing addi tion funnel equipped with an argon inlet containing butyric anhydride (10.25g, 64.85 mmol, 1.07eq.). The reaction flask was placed in a water bath (25C), and the anhydride was added dropwise over 15 minutes. The solution was stirred fo r one hour, after whic h the excess anhydride was quenched by slow addition of saturated sodium bicarbonate (300 mL). The product was extracted with ethyl acetate (3200 mL) a nd washed with water (2100 mL water). After drying the organic phase with magnesi um sulfate, the solvent was removed under vacuum to yield a white solid. Recrystalliz ation was accomplished in toluene to yield 12.3 g of white needle like crystals (86%). 1H NMR (C6D6, 300 MHz) 0.61 (d), 0.82 (t),

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116 0.98 (t), 1.55-1.67 (m), 1.74-1.88 (m), 2.1 (s), 2.45 (m), 2.84 (s), 3.74-3.86 (m), 4.06 (d), 4.25-4.42 (m), 4.52-4.62 (t), 4.98-5.18 (br), 7.00-7.42 (m); 13C NMR (CDCl3, 75 MHz) 14.135, 14.711, 15.539, 18.628, 18.979, 33.234, 35.867, 36. 498, 58.924, 75.686, 126.539, 127.087, 127.774, 128.511, 128.869, 142.676, 175.645 (NMR are complex because of the amide geometrical isomerism); HRMS [M+H]+ calcd. 236.1650, found 236.1662. (1R,2R)-pseudoephedrine-2S-ethylhexanamide A flame-dried, 1L 3-neck flask equipped with an argon inlet was charged with dry lithium chloride (13.98 g, 330mmol), dry diisopropylamine (17.47 mL) (distilled from CaH2) and 60 mL dry THF. After cooling at -78C, nBuLi (51.5 mL, 2.23M, 115 mmol) was added via syringe over 15 min time. The reaction was warmed at 0C for 5 min and cooled back to -78C. (1R,2R)-(-)pseudoephedrine, cooled at 0C, was tran sferred by cannula into the reaction over 15 min. The reaction is stirred at -78C for one hour, 0C for 15 min 5 min at 25C and then cooled down to 0C where butyliodide (15. 35 g, 83.31 mmol) was added dropwise. After 15 min, 5 mL of saturated a mmonium chloride was added a nd the reaction was poured in 500 mL saturated ammonium chloride. The aqueous phase was extracted with ethyl acetate (3250 mL). After washing with wa ter (250 mL) the organic phase was dried over magnesium sulfate and the solvent was removed under vacuum, to yield a slight yellow viscous oil. The product was purified by column chromatography on silica gel (eluent: hexanes/ethylacetate (1/1)) and obtaine d as a colorless viscous oil (10g, 71%). 1H NMR (C6D6, 300MHz) 0.72-0.76 (d), 0.8-1.25 (m), 2.61-2.83 (m), 2.1-2.23 (m), 2.3-2.36 (s), 2.65-2.72 (br), 2.92-2.94 (s), 4.1-4.25 (b r), 4.45-4.62 (t), 5.2-5. 4 (br), 7.04-7.38 (m); 13C NMR (C6D6, 75 MHz) 12.43, 14.56, 14.91, 23.60, 26.83, 30.27, 33.06, 33.34, 44.34,

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117 58.54, 60.92, 75.81, 76.72, 127.04, 127.64, 144.35, 178.20 (NMR are complex because of the amide geometrical isomerism); HRMS [M+H]+ calcd. 292.2277, Found 292.2280. 2S-ethylhexylhexanoic acid A 250 mL round-bottom flask was charged with (1R,2R)-pseudoephedrine-2S-ethylhexanamide (7g, 24mmol), sulfuric acid (45 mL, 18N) and dioxane (45 mL). The mixt ure was refluxed for one hour. After cooling to 25C, the pH was brought to >10 by slow addition of 50% aqueous sodium hydroxide. The mixture was extracted with dichloromethane (2100 mL ). The aqueous phase was acidified to pH 1 and extracted again with dichloromethane (3100 mL) to collect the product. After drying of the organic phase, the solvent is evaporated unde r vacuum (15C, 20 mmHg) to obtain the product as a slight ly yellow oil (2.4g, 70%). 1H NMR (CDCl3, 300MHz) 0.8-1.0 (m, 6H), 1.25-1.4 (m, 4H), 1.42-1.75 (m, 4H), 2.2-2.35 (m, 1H), 11-12 (br, 1H); 13C NMR (CDCl3, 75MHz) 11.98, 14.13, 22.86, 25.41, 29.75, 31.69, 47.31, 67.28, 182.93; HRMS calcd. [M+H]+ 145.1231; exp. 145.1245; IR (C=O); [ ]D (C=1.3g/100 mL, acetone)= +10.0. 2S-ethylhexanal. In a flame-dried 100 mL schl enk flask under argon atmosphere, lithium aluminum hydride (0.68g, 17.9 mmol) was suspended in 40 mL dry hexane. The flask was cooled to 0C where dry ethyl aceta te (2.3g, 26.1 mmol) was added very slowly over 90 minutes. After cooling the resulting suspension -78C, a solution of (1R,2R)pseudoephedrine-2S-ethylhexanamide (2.2g, 7.9 mmol) in 30 mL THF was transferred via cannula over 10 min. The reaction is then warmed to 0C and stirred at this temperature for one hour. The solution is then transferred via cannul a into a three neck round-bottom flask containing tr ifluoroacetic acid (7 mL, 90 mmol) in 100 mL of 1N HCl solution. After 5 min, th e solution is transferred in 300 mL 1N HCl and extracted

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118 with ethyl acetate (3100 mL). The organi c phase was washed with saturated sodium bicarbonate solution (2100 mL). After drying with magnesium sulfat e, the solvent is removed under vacuum (15C, 20 mmHg) to give a yellow-brown oil. The product was purified by column chromatography on silica gel (eluent: hexanes/ethyl acetate 9/1, product revealed using 2,4-dini trophenylhydrazine dip as bright yellow spots) to yield 2S-ethylhexanal as a slightly yellow oil (290mg, 30% yield). 1H NMR (CDCl3, 300MHz) 0.75-0.9 (m, 6H), 1.14-1.65 (m, 8H), 2. 04-2.18 (m, 1H), 9.5 (d, 1H, J=3Hz). 13C NMR (CDCl3, 75 MHz) 11.68, 14.10, 22.08, 22.99, 28.38, 29.44, 53.64, 205.92; HRMS [M+H]+ calcd. 129.1282 found 129.1290. 2S-ethylhexanoyl chloride In a flame-dried 250 mL round-bottom flask under argon atmosphere 2S-ethylhexanoic acid ( 500mgs, 3.4mmol) was dissolved in dry dichloromethane. Thionyl chloride (3.2g, 27mmol, 8eq.) was added in one portion. The reaction was equipped with a condenser and reflux under argon overnight. The solvent and the excess thionyl chloride were remove d under rotary evaporation, yielding the product as a slightly yellow-ora nge oil (510 mgs, 92% yield). 1H NMR (CDCl3, 300MHz) 0.78-0.95 (m, 6H), 1.18-1.26 (m, 4H), 1.43-1.8 (m, 4H), 2.58-2.7 (m,1H); 13C NMR (CDCl3, 75MHz) 11.53, 14.02, 22.70, 25.33, 29.27, 31.49, 58.95; [ ]D (C=1.2g/100 mL, acetone)= +7.4. Synthesis of 2S-ethylhexanol. In a flame-dried 3-neck flask equipped with a condenser and an argon inlet, Lithium aluminum hydride (1 .74g, 46 mmol, 3 eq.) was dispersed in 100 mL of dry di ethyl ether. A solution of 2S-ethylhexanoic acid (2.2g, 15.2mmol) in 50 mL of diethyl ether is added via cannula to the LiAlH4 suspension. The reaction was then refluxed for one hour. Afte r cooling the solution at 0C, the excess

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119 hydride was quenched (dropwise) by addition of water. When the hydride was quenched, 100 mL of water is added and the two phase s were separated. The aqueous phase was further extracted with diethyl ether (2100 mL). The combined organic fractions were washed with 1M HCl (100 mL), and water (2100 mL). After drying with magnesium sulfate, the solvent was evaporated (20mmH g, 15C) and the produc t was recovered as a transparent oil. 1H NMR (CDCl3, 300MHz) 0.8-1.05 (m, 6H), 1.05-1.45 (m, 9H), 3.453.65 (br, 2H); 13C NMR (CDCl3, 75MHz) 11.31, 14.30, 23.30, 23.56, 29.33, 30.34, 42.19, 65.55. [ ]D (C=1.2g/100 mL, acetone)= +3.1. To de termine the enantiomeric excess, the chiral alcohol was derivatizated with Mosher ’s reagent. Chiral 2S-ethylhexanol (20mgs, 0.15 mmol) was dissolved in 1 mL CCl4 and R-(+)-methoxytrifluoromethylphenylacetic acid chloride (50mgs, 0.2 mmol) was added. The reaction was stirred for 48hrs and water (10 mL) was a dded. After extraction with diethylether (2*10 mL), the organic phase was dried with magnesium sulfate and evaporated under reduced pressure. The resulting product was analyzed by GC to determine the enantiomeric excess of the alcohol (Chira sil-Dex CB column, 0.25mm25cm). ee= 96%; Retention time: 23.9 min (corresponding to the minor R enantiomer of the alcohol, derivatized with Mosher’s reagent) and 24.13 min (cor responding to the major S enantiomer of the alcohol deriva tized with Mosher’s reagent). 2S-ethylhexyltosylate: In a 100 mL round bottom flask was dissolved 2Sethylhexanol (2.2g, 17 mmol) in 25 mL pyridin e. Tosyl chloride (6.84g, 36mmol, 2eq.) was added in one portion. The reaction was stir red overnight at room temperature. Water (100 mL) and diethyl ether were added to the reaction. After se paration of the two phases, the aqueous phase was further extr acted with diethyl ether (250 mL). The

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120 combined organic fractions were washed with water. The organic phase was dried with magnesium sulfate and the solvent was remove d under vacuum to yield a yellow oil. The product was purified by column chromatogra phy (Hexanes/dichloromethane) to yield a slightly yellow, visc ous oil (4.1g, 85%); 1H NMR (CDCl3, 300MHz) 0.76-0.88 (m, 6H), 1.05-1.18 (m, 8H), 1.5-1.6 (m, 1H), 2.43 (s, 3H), 3.85-3.98 (m, 2H), 7.36 (d, 2H), 7.8 (d,2H); 13C NMR (CDCl3, 75MHz) 10.97, 14.18, 21.85, 23.05, 23.46, 28.87, 30.02, 39.28, 72.73, 128.12, 129.97. 2,2-((2S)-ethylhexyl)-propane-1,3-diol. In a 100 mL flam e-dried 3-neck round bottom flask equipped with an argon inlet, a condenser, and an addition funnel were combined 30 mL of dry DMF, 2S-ethylhexylto sylate (4g, 14mmol, 2.5 eq.). After cooling at 0 C, NaH (60% dispersion, 0.67g, 16.8m mol, 3eq) was added The flask was maintained at 0 C and freshly distilled di ethyl malonate (0.9g, 5.6 mmol, 1eq.) in 20 mL dry DMF was added dropwise through the addition funnel. When the addition of the malonate was completed the mixture was heated to 100 C for three days. The flask was then cooled at 0 C and the remaining sodium hydride was quenched by adding water dropwise. The mixture was then poured into water (200 mL), extracted with ether (2100 mL), and washed with brine (100 mL). The solvent was removed under vacuum yielding a viscous oil. In a flame-dried 3 neck-flask, equipped with an argon inlet, a condenser and an addition funnel, lithium aluminum hydrid e (0.64g, 17mmol, 3eq.) was dispersed in 100 mL of dry diethyl ether. A solution of th e dialkylated malonate in 50 mL of diethyl ether was added dropwise to the hydride dispersion. The addition funnel was removed and the reaction was refluxed for one hour. Af ter cooling the solution at 0C, the excess hydride was quenched (dropwise) by addition of water. When the hydride was quenched,

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121 100 mL of water is added and the two phase s were separated. The aqueous phase was further extracted with diethyl ether (2100 mL). The combined organic fractions were washed with 1M HCl (100 mL), and water (2100 mL). After drying with magnesium sulfate, the solvent was evaporated and th e product was recovered as brown oil. The product was purified by column chromatogra phy to yield a white solid (550 mgs, 33% yield). 1H NMR (CDCl3, 300MHz) 0.78-0.94 (m, 12H), 1.15-1.42 (m, 22H), 2.58 (s, 2H), 3.63 (s, 4H); 13C NMR (CDCl3, 75MHz) 10.79, 14.38, 23.35, 27.86, 29.04, 33.73, 34.94, 37.17, 42.81, 70.00. [ ]D (C=2.7g/100 mL, acetone)= -10.0. 3,3-bis((S)-2-ethylhexyl)-3,4-dihyd ro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT((2S)-ethylhexyl) 2 ). 3,4-dimethoxythiophene (0.24mgs, 1.69mmol), 2,2-((2S)ethylhexyl)-propane-1,3-d iol (500mgs, 1.67mmol), p -toluenesulfonic acid (32mgs, 0.17mmol) with 50 mL of dry toluene were co mbined in a 100 mL flask equipped with a soxhlet extractor with CaCl2 molecular sieves in a cellulo se thimble. The solution was refluxed overnight. The reaction mixture was c ooled and 5 mL triethyl amine is added. Ether (100 mL) is added and the organic solu tion is washed once with water (100 mL). The solvent was removed under vacuum, and the crude product was purified by column chromatography on silica gel with 4:1 hexa nes/methylene chloride to yield the pure product as a clear viscous oil (440mgs, 70%). 1H NMR (CDCl3, 300MHz) 0.75-0.92 (m, 12H), 1.15-1.5 (m, 22H), 3.92 (s, 4H), 6.42 (s, 2H); 13C NMR (CDCl3, 75MHz) 10.82, 14.38, 23.34, 28.02, 29.02, 33.87, 35.09, 38.79, 45.56, 78.07, 104.60, 149.99. 6,8-dibromo-3,3-bis((S)-2-ethylhexy l)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDOT((2S)-ethylhexyl) 2 -Br 2 ). ProDOT((2S-ethylhexyl)2 (420 mgs, 1.1mmol, 1eq.) was dissolved in 100 mL dry DMF in a 250 mL round-bottom flask. The

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122 solvent was degassed by bubbling arg on in the solution for one hour. Nbromosuccinimide (500mgs, 2.8mmol, 2.5eq.) was added in one portion, and the reaction was stirred under argon overnight, at room temperature. Water (200 mL) was added to the reaction and the aqueous phase was extr acted with diethylether (3100 mL). The organic phase was washed with water (3100 mL), dried with magne sium sulfate. After solvent evaporation, the resu lting oil was purified by colu mn chromatography on silica gel (hexanes/dichloromethane 4/1) to afford ProDOT((2S)-ethylhexyl)2-Br2 as a clear, colorless viscous oil (512mgs, 86% yield). 1H NMR (CDCl3, 300MHz) 0.78-0.96 (m, 12H), 1.17-1.46 (m, 22H), 3.99 (s, 4H); 13C NMR (CDCl3, 75MHz) 10.81, 14.38, 23.32, 27.97, 29.01, 33.93, 35.01, 38.88, 45.81, 78.61, 90.54, 147.30; HRMS [M]+ Calcd. 536.1028 Found 536.0990 Poly(3,3-bis((S)-2-ethylhe xyl)-3,4-dihydro-2H-thieno [3,4-b][1,4]dioxepine) (PProDOT((2S)-ethylhexyl) 2 ). To a two-neck round botto m flask equipped with a condenser and an argon inle t, ProDOT((2S)-ethylhexyl)2Br2 (440mgs, 0.82mmol, 1eq.) was dissolved in 25 mL of dry THF. Me thylmagnesium bromide (0.85mL, C=0.96M, 0.82 mmol, 1eq.) was added via syringe. The reaction was refluxed for one hour, after which Ni(dppp)Cl2 (9mgs, 0.016mmol, 0.02 eq.) was added. After a few seconds, the solution turned bright red. The reaction was refluxed overnight, and then allowed to cool to room temperature. The polymer was pr ecipitated in 200 mL of MeOH and filtered through a soxhlet thimble. The polymer wa s purified by Sohlet Extraction with MeOH (24hrs) then Hexanes (24hrs). It was then extracted with CHCl3, to yield after rotary evaporation 180 mgs of shiny-brown colored solid. GPC (THF, 25C) Mn= 8,700 g mol-1, Mn= 14,200 g mol-1, PDI=1.6; 1H NMR (300MHz, CDCl3) 0.75-0.92 (br, 12H), 1.12-1.63

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123 (br, 22H), 3.8-4.3 (br, 4H); 13C NMR (75MHz, CDCl3) 10.91, 14.44, 23.44, 27.80, 28.98, 33.88, 35.22, 38.65, 45.66, 78.16, 115.75, 144.93. 2S-methylbutyltosylate: In a 100 mL round bottom flask was dissolved 2Smethylbutanol (5g, 57 mmol) in 100 mL pyridin e. Tosyl chloride (21.6g, 113mmol, 2eq.) was added in one portion. The reaction was stir red overnight at room temperature. Water (300 mL) and diethyl ether were added to the reaction. After se paration of the two phases, the aqueous phase was further extract ed with diethyl ether (2150 mL). The combined organic fractions were washed with water. The organic phase was dried with magnesium sulfate and the solvent was remove d under vacuum to yield a yellow oil. The product was purified by column chromatogra phy (Hexanes/dichloromethane) to yield a clear viscous oil (11.9g, 92%); 1H NMR (CDCl3, 300MHz) 0.78-0.92 (m, 6H), 1.04-1.23 (m, 1H), 1.3-1.46 (m, 1H), 1.62-1.78 (m, 1H), 2.44 (s, 3H), 3.77 (m, 2H), 7.35 (d,2H), 7.77 (d, 2H); 13C NMR (CDCl3, 75MHz) 10.97, 14.18, 21.85, 23.05, 23.46, 28.87, 30.02, 39.28, 72.73, 128.12, 129.97. 2,2-((2S)-methylbutyl)-propane-1,3-diol. In a 100 mL flame-dried 3-neck round bottom flask equipped with an argon inlet, a condenser, and an addition funnel were combined 100 mL of dry DMF, 2S-ethylhe xyltosylate (11g, 49mmol, 2.5 eq.). After cooling at 0 C, NaH (60% dispersion, 2.34g, 58.4mmol, 3eq) was added. The flask was maintained at 0 C and freshly distilled di ethyl malonate (3.14g, 19.6 mmol, 1eq.) in 50 mL dry DMF was added dropwise through the addition funnel. When the addition of the malonate was completed the mixture was heated to 100 C for three days. The flask was then cooled at 0 C and the remaining sodium hydride was quenched by adding water dropwise. The mixture was then poured into water (500 mL), extracted with ether (3200

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124 mL), and washed with brine (200 mL). The solvent was removed under vacuum yielding a viscous oil, used without further purifica tion. In a flame-dried 3 neck-flask, equipped with an argon inlet, a co ndenser and an addition funnel, lithium aluminum hydride (2.24g, 17mmol, 3eq.) was dispersed in 300 mL of dry diethyl ether. A solution of the dialkylated malonate in 150 mL of diet hyl ether was added dr opwise to the hydride dispersion. The addition funne l was removed and the reaction was refluxed for one hour. After cooling the solution at 0C, the excess hydride was quenched (dropwise) by addition of water. When the hydride was que nched, 300 mL of water is added and the two phases were separated. The aqueous phase was further extracte d with diethyl ether (3200 mL). The combined organic fractions were washed with 1M HCl (200 mL), and water (2200 mL). After drying with magnesium sulfate, the solvent was evaporated and the product was recovered as yellow o il. The product was purified by column chromatography to yield a white solid (1.3 g, 31% yield). 1H NMR (CDCl3, 300MHz) 0.82-0.95 (m, 12H), 1.08-1.53 (m, 10H), 2.54 (t, 2H), 3.62 (d, 4H); 13C NMR (CDCl3, 75MHz) 11.70, 21.91, 29.55, 32.20, 39.19, 42.81, 70.13; HRMS [M+H]+ Calcd. 217.2168 Found 217.2178. 3,3-bis((2S-methylbutyl)-3,4-dihydro -2H-thieno[3,4-b][1,4]dioxepine (ProDOT((2S)-methylbutyl) 2 ). 3,4-dimethoxythiophene (0.66mgs, 4.62mmol), 2,2((2S)-methylbutyl)-propane-1 ,3-diol (1g, 4.62mmol), p -toluenesulfonic acid (32mgs, 0.46mmol) with 250mL of dry toluene were co mbined in a 500 mL flask equipped with a soxhlet extractor with CaCl2 molecular sieves in a cellulo se thimble. The solution was refluxed overnight. The reaction mixture was c ooled and 5 mL triethyl amine is added. Ether (300 mL) is added and the organic solu tion is washed once with water (200 mL).

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125 The solvent was removed under vacuum, and the crude product was purified by column chromatography on silica gel with 4:1 hexa nes/methylene chloride to yield the pure product as a clear viscous oil (1.08mgs, 79%). 1H NMR (CDCl3, 300MHz) 0.88 (t, 6H), 0.95 (d, 6H), 1.22-1.57 (m, 10H), 3.92 (m, 4H), 6.41 (s, 2H); 13C NMR (CDCl3, 75MHz) 11.67, 22.09, 29.71, 32.24, 40.98, 45.61, 78.36, 104.63, 149.96. HRMS [M]+ Calcd. 296.1810 Found 296.1798. 6,8-dibromo-3,3-bis(2S-methylbutyl )-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDO T((2S)-methylbutyl) 2 -Br 2 ) ProDOT((2S-methylbutyl)2 (0.8g, 2.7 mmol, 1eq.) was dissolved in 250 mL dr y DMF in a 500 mL round-bottom flask. The solvent was degassed by bubbling arg on in the solution for one hour. Nbromosuccinimide (1.2g, 6.8mmol, 2.5eq.) was added in one portion, and the reaction was stirred under argon overnight, at room temperature. Water (500 mL) was added to the reaction and the aqueous phase was extr acted with diethylether (3200 mL). The organic phase was washed with water (3200 mL), and dried with magnesium sulfate. After solvent evaporation, th e resulting oil was purified by column chromatography on silica gel (hexanes/dichloromethane 4/ 1) to afford ProDOT((2S)-methylbutyl)2-Br2 as a clear, colorless viscous oil (1.1gs, 90% yield). 1H NMR (CDCl3, 300MHz) 0.89 (t, 6H), 0.95 (d, 6H), 1.12-1.54 (m, 10H), 3.99 (s, 4H); 13C NMR (CDCl3, 75MHz) 11.63, 21.96, 29.67, 32.12, 40.83, 45.84, 79.00, 90.64, 147.30; HRMS [M]+ Calcd. 452.0021 Found 452.0015. Poly(3,3-bis((2S-methylbutyl)-3,4-dihyd ro-2H-thieno[3,4-b][1,4]dioxepine) (PProDOT((2S)-methylbutyl) 2 ). To a two-neck round bottom flask equipped with a condenser and an argon inle t, ProDOT((2S)-methylbutyl)2Br2 (0.95g, 2.1mmol, 1eq.) was

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126 dissolved in 25 mL of dry THF. Methyl magnesium bromide (1.95 mL, C=1.07M, 2.1 mmol, 1eq.) was added via syringe. The reac tion was refluxed for tw o hours, after which Ni(dppp)Cl2 (23mgs, 0.042mmol, 0.02 eq.) was a dded. After a few seconds, the solution turned bright red. The reaction was refluxed ove rnight, and then allowe d to cool to room temperature. The polymer was precipitated in 200 mL of MeOH and filtered through a soxhlet thimble. The polymer was purifie d by Soxhlet extraction with MeOH (24hrs) then Hexanes (24hrs). It wa s then extracted with CHCl3, to yield after ro tary evaporation 460 mgs of shiny-brown colore d solid. GPC (THF, 25C) Mn= 8,400 g mol-1, Mn= 13,800 g mol-1, PDI=1.6; 1H NMR (300MHz, C6D6) 0.7-0.95 (br, 6H), 0.95-1.07 (br, 6H), 1.071.27 (br, 2H), 1.27-1.65 (br, 8H), 3.65-4.3 (br, 4H); 13C NMR (75MHz, C6D6) 12.15, 22.63, 30.09, 32.77, 41.24, 45.95, 78.65, 114.97, 145.89. 3,3-Bis-(2S-methylbutyloxymethy l)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDOT(CH 2 O-2S-methylbutyl) 2 ). A 250 mL flame dried round bottom flask filled with 60 mL of DMF, 23.4 mmols of alcohol (4eq), and 23.4 mmols of NaH (4eq) was heated at 110 C overnight. Then 5.85 mmols of ProDOT(CH2Br)2 was added and the reaction continued at 110 C for another 24 hr. After completion, the flask was cooled and added to 200 mL brine and extracted 3 times with ethyl ether. The organic layer was then washed 3 times with water, dried over magnesium sulfate, and the solvent was removed by rotary evaporation under reduced pressure. The resulting orange oil was purified by column chromatography (3:2 hexanes, methylene chloride).The crude oil obtained was purified by column chromatography (CH2Cl2) to afford 2.1g of clear oil (95%). 1H NMR (300 MHz, CDCl3) 0.81-0.91 (m, 12H), 1.01-1.21 (m, 2H), 1.33-1.48 (m, 2H), 1.55-1.68 (m, 2H), 3.14-3.29 (m, 4H), 3.45-3.53 (m, 4H), 4.09 (s, 4H); 13C

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127 NMR (75 MHz, CDCl3) 11.80, 17.05, 26.68, 35.36, 48.36, 70.21, 74.20, 77.88, 105.42, 150.15. HRMS calculated for C25H44O4S: 356.2021 Found 356.2026. Elemental Anal. Calcd for C25H44O4S: C 64.01; H 9.05; S 8.99 F ound: C 64.04; H 9.41; S 8.78. 6,8-Dibromo-3,3-bis-(2-methylbutyloxymet hyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine (ProDOT(CH 2 O-2-methylbutyl) 2 Br 2 ) ProDOT(CH2O-(2Smethylbutyl)2 (2.8g, 7.9 mmol, 1eq.) was dissolved in 250 mL dry DMF in a 500 mL round-bottom flask. The solvent was degassed by bubbling argon in the solution for one hour. N-bromosuccinimide (3.5g, 20mmol, 2. 5eq.) was added in one portion, and the reaction was stirred under argon overnight, at room temperature. Water (500 mL) was added to the reaction and the aqueous phase was extracted with diethylether (3200 mL). The organic phase was washed with water (3200 mL), and dried with magnesium sulfate. After solvent evaporation, the resulting oil was purified by column chromatography on silica gel (hexanes/dichl oromethane 4/1) to afford ProDOT(CH2O(2S)-methylbutyl)2-Br2 as a clear, colorless viscous oil (3.5gs, 86% yield).1H NMR (300 MHz, CDCl3) 0.84-0.91 (m, 12H), 1.04-1.21 (m, 2H), 1.33-1.48 (m, 2H), 1.55-1.69 (m, 2H), 3.13-3.29 (m, 4H), 3.44-3.53 (m, 4H), 4.09 (m, 4H); 13C NMR (300MHz, CDCl3) 11.57, 16.83, 26.45, 35.14, 69.86, 74.52, 77.01, 91.11, 147.27; HRMS Calcd for C25H42O4SBr2 514.0232. Found 514.0226; Elemental Anal. Calcd for C25H42O4SBr2: C 44.37; H 5.88; S 6.23; Br 31.07 Found: C 44.46; H 6.16; S 6.08; Br 30.84. Poly(3,3-bis-(2S-methylbutyloxymet hyl)-3,4-dihydro-2H-thieno[3,4b][1,4]dioxepine) (PProDOT(CH 2 O-2S-methylbutyl) 2 To a two-neck round bottom flask equipped with a condenser and an argon inlet, ProDOT(CH2O-(2S)methylbutyl)2Br2 (0.82g, 1.6 mmol, 1eq.) was diss olved in 25 mL of dry THF.

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128 Methylmagnesium bromide (1.45 mL, C=1.1M, 2.1 mmol, 1eq.) was added via syringe. The reaction was refluxed for tw o hours, after which Ni(dppp)Cl2 (15mgs, 0.032mmol, 0.02 eq.) was added. After a few seconds, the solution turned bright red. The reaction was refluxed overnight, and then allowed to cool to room temperature. The polymer was precipitated in 200 mL of MeOH and filtered through a soxhlet thimble. The polymer was purified by Soxhlet extracti on with MeOH (24hrs) then Hexanes (24hrs). It was then extracted with CHCl3, to yield after rotary evapora tion 450 mgs of shiny-brown colored solid.g of purple solid obtained ( 80%). 1H NMR (300 MHz, benzened6) 0.82-1.07 (br, 12H),1.1-1.27 (br, 2H), 1.34-1.53 (br, 2H), 1.55-1.72 (br, 2H), 3.04-3.26 (br doublet, 4H), 3.46-3.64(br singlet, 4H), 4.1-4.35 (br singlet, 4H); 13C (75 MHz, benzened6) 11.93, 17.37, 27.07, 35.69, 70.8, 75.21, 77.7.

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129 CHAPTER 6 SOLUBLE POLY(3,4-PHENY LENEDIOXYTHIOPHENES) 6.1. Introduction As discussed earlier, regioreg ular poly(3-alkylthiophene)s provide some of the best performing semiconducting polymeric material s and are increasingly finding use in device applications which include organic field-effect transistors,13,17c,88,97 and photovoltaics98,19, where their high degree of order yields high charge carrier mobilities. The more easily oxidized poly(3,4-ethylenedio xythiophene) (PEDOT) has been used as the active material in electrochromic devices, anti-static coatings and capacitors, and as a hole injecting layer in OLEDs.56Poly(3,4-ethylenedioxythiophe ne):poly(styre nesulfonate) (PEDOT:PSS) provides an interesting altern ative to indium tin oxide (ITO), showing better mechanical properties, low surface r oughness and more facile processing from aqueous dispersions. While it was used successf ully in the fabrica tion of flexible, allplastic electrochromic devices,99 PEDOT:PSS has a relatively low conductivity compared to ITO (100-500 S cm-1 vs. 4000 S cm-1).8 It is desirable to s ynthesize easily oxidized, low band gap conjugated polymers with a high de gree of order, useful processability and flexible mechanical properties. In recent publications, both Ritter100 and Roncali101 introduced 3,4phenylenedioxythiophene (PheDOT) as an at tractive synthon fo r obtaining highly ordered polythiophenes. X-ray crystal structures of 2,5-di bromo-PheDOT show that the thiophene and phenylene rings are fully copl anar (Figure 6-1). This should provide a strong driving force for a high degree of orde ring in the solid state. PheDOT, and more

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130 recently its dimer and trimer, were electr opolymerized to yield electroactive films.101,102 As is common with electropolymerized materi als, the resulting polymers are insoluble arising from strong stacking interactions, and theref ore cannot be solution-processed. Figure 6-1. X-ray crystal structure of PheDOT-Br2. Yellow spheres are sulfurs; blue spheres are carbons, black spheres ar e hydrogens, small red spheres are oxygens and large red spheres are bromides. In this Chapter, the synthesis of the fi rst soluble and processable PolyPheDOTs is introduced. Solubility is obtained by substitu tion at the 4and 5positions of the veratrole moiety with either dodecyl or ethy lhexyl substituents (Figure 6-2). The side chains extend within the plan e of the polythiophene backbone and are expected to have a strong effect on the polymers properties. Dodecyl side chains should provide a supplementary driving force for ordering, while the bulk of the ethylhexyl substituent should provide high solubility and strongl y decrease interchain interactions.

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131 S O O nS O O n S O O n S O O n PPheDOTEtHxPPheDOTC12PPheDOT(C12)2PPheDOTC12EtHx Figure 6-2. Family of Soluble Substituted PPheDOTs under study. 6.2 Synthesis of Soluble Substituted PheDOT PheDOT-(C12)2 was synthesized using a modified procedure outlined by Roncali et al. who synthesized PheDOT(C6)2 (Figure 6-3).101 The synthesis starts with a FriedelCrafts acylation of veratrole, followe d by reduction of the ketone using AlCl3/LiAlH4. Dialkyl substituted veratroles are synthesized by repeating this two-steps procedure. The 4,5-bis(2-ethylhexyl)-veratrole derivative could not be obtaine d as the steric hindrance of the branched substituent in 4-(2-ethylhexyl)-v eratrole prevented a second Friedel-Crafts reaction with 2-ethylhexanoyl chloride. On the other ha nd, 4,5-bis(2-ethylhexyl)veratrole could react in a Frie del-Crafts reaction with lauroyl chloride to yield 4-dodecyl5-(2-ethylhexyl)-veratrole after reduction. In terestingly, the Friedel-Crafts reaction between 4-dodecyl-veratrole and 2-ethylhexa noyl chloride was unsuccessful although it yields the same produc t after reduction. The substituted veratroles are converted to the substituted catechols using boron tribromide. Transetherification between the substituted catechols and 3,4-

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132 dimethoxythiophene yields the electropolymeri zable monomers in 20-30% yield. The low yield arise from the lower nucleophilicity of the catechols compared to 1,3-propanediols that are used in the synthesis of substituted PProDOTs, as presented in Chapter 3,4 and 5. OMe OMe OMe OMe O AlCl3 OMe OMe R Cl O AlCl3 MeO MeO S OMe MeO Toluene pTSA R OO S DCM R1 DCM R' Cl O R1 R2 HO HO R1 R2 BBr3DCM R2 R1 Et2O AlCl3 MeO MeO R1 R' O LiAlH4/AlCl3Et2O LiAlH4R1=-C12H25,R2=-C12H25: PheDOT(C12)2R1=-C15H25,R2=-2-ethylhexyl: PheDOTC12EtHx R1=-H,R2=-2-ethylhexyl: PheDOTEtHx R1=-C12H25,R2=-H: PheDOTC1280-90% 70-90% R'=C11H2390% R'=3-heptyl45% 80-90% 80-90% 10-30% Figure 6-3. Synthesis of monoand disubs tituted PheDOTs. Substituents are either dodecyl or 2-ethylhexyl. 6.3. Electropolymerization of Substituted PheDOTs 6.3.1. Electrodeposition and Electronic Properties After purification of the electropolymerizable monome rs, polymer films were electrodeposited on a platinum button electr ode. The electrodepos ition by cyclic voltammetry was more difficult than for PProD OTs derivatives as evidenced by the slow growth (Figure 6-4a). This behavior can be explained by the increased stability of the PheDOT radical-cation, whic h is the reactive in termediate in electropolymerization.27a Roncali et al. carried out calculations dem onstrating that the SOMO of the PheDOT radical cation has only little electron density on the 2and 5positions of the thiophene conversely to the EDOT radical-cation, ha ving strong electronic density at these two positions.101 As a result, EDOT polymerizes fast while PheDOT polymerizes slowly. Another issue is that the dioxybenzene unit ox idizes irreversibly at potentials close to the monomer oxidation, as demonstrated for veratrole, which forms cyclic trimers

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133 when oxidized electrochemically.103 The electropolymerizati on must therefore be performed at a potential suffi ciently high to have electr odeposition but low enough to limit side reactions. Another approach is to synthesize the dimer or trimer of PheDOT, which can be electropolymerized at potential well below the oxidati on potential of the dioxybenzene unit.102 Table 6-1 summarizes the el ectronic properties of the electropolymerizable monomers and polym ers deposited by cyclic voltammetry. Substitution of PheDOT results in a decrease of the monomer oxidation due to a slight electron donation by the alkyl s ubstituents into the benzene ring. In some cases, toluene was added to the acetonitrile monomer solution to achieve complete solubilization of the monomer. The amount of toluene must be as li ttle as possible, as an excess toluene will cause delamination of the electrodeposited films. Table 6-1. Electrochemical properties of substituted PheDOTs electropolymerizable monomers and electrodeposited disubstituted PPheDOTs films. Potentials are given vs. Fc/Fc+ standard. Eonset Monomer (mV)a Eonset Polymer (mV)b E1/2 Polymer (mV) Ep (mV) Ia/Ic PheDOT 980 N/A N/A N/A N/A PheDOTC12 970c 139 520 80 1.23 PheDOTEtHx 920 8 465 76 1.07 PheDOTC12EtHx 910c 395 607 260 1.22 PheDOT(C12)2 870c 330 629 320 1.65 (a) electrodeposition in 0.1M TBAP ACN; (b ) determined by cyclic voltammetry; (c) Toluene added dropwise until full monomer dissolution Overall, the polymer films oxidation is shif ted to higher potentia ls with increasing steric bulk, with disubstituted PPheDOTs ha ving the highest oxidation potentials. Figure 6-4a shows the slow electrodepositio n by cyclic voltammetry of PheDOTC12 on a platinum button electrode. In Figure 6-4b, cyclic voltammet ry between -1V and 1.3V of an electrodeposited film of PPheDOTEtHx shows the presence of an irreversible

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134 oxidation reaction, resulting in a strong decrease of elect roactivity of the conjugated polymer. The degradation also occurs with other substitu ted or unsubstituted PPheDOT and is attributed to the degr adation of the phenylene unit. -1.0-0.50.00.51.01.5 -1 0 1 2 3 4 S O O n Intensity (mA/cm2)E(V) vs. Fc/Fc+(a) -1.0-0.50.00.51.01.5 -1 0 1 2 3 4 5 6 S O O n I (mA/cm2)E vs. Fc/Fc+ Dioxybenzene moiety irreversible oxidation Polymer oxidation (b) Figure 6-4. Electrodeposition and electrochemistry of substituted PPheDOTs films. (a) Electrodeposition of PPheDOT-C12 by cyclic voltammetry. Scan rate is 50mV s-1. Every 5th cycle shown (out of 50 cycles ); (b) PPheDOT-EtHx degradation of PPheDOTs at high potentials. The disubstituted electropolymerizable monomers display unusual oxidation behavior. Figure 6-5 shows the monomer oxidation for PheDOT(C12)2 at various scan rates. -1.0-0.50.00.51.01.5 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 S O O n Normalized IntensityE(V) vs. Fc/Fc+ 500mV/s 5mV/s 50mV/s Figure 6-5. PheDOT(C12)2 oxidation at various scan ra tes. Monomer concentration is 0.01M in 0.1M TBAP/(3:1 ACN/toluene).

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135 At a scan rate of 50mV s-1, the scan rate is partially re versible as a reduction peak for the oxidized monomer is observed. By increasing the scan rate to 500 mV s-1, the oxidation wave becomes more reversible wh ile decreasing the scan rate to 5 mV s-1 yields an irreversible wave. The reversibility arises from the increased stability of the disubstituted PheDOTs radical through el ectron donation by the al kyl groups, supported by theoretical calculations.101 By decreasing the scan rate, the radical cations have more time to propagate and polymerize, and th e oxidation peak become irreversible. 6.3.2. Spectroelectrochemical Charact erization of Electrodeposited Films Following electrodeposition of the polymers onto ITO-coated glass slides, the polymer films properties were probed by spectro electrochemistry (Table 6-2). The results indicate that upon introducing linear dod ecyl substituents, there are no significant changes of the optical bandgap. In th e symmetrically substituted PPheDOT(C12)2, the bandgap is even slightly decreased, possibly indicating an ordering effect of the dodecyl chains. It also shows that, as expected, the dodecyl offer little steric hindrance to interchain interactions. Intr oduction of 2-ethylhexyl substitu ents in PPheDOTEtHx leads to an increase of the optical bandgap by 50 meV compared to electrodeposited PPheDOT. In PPheDOTC12EtHx, the bandgap is 100meV higher showing a clear decrease of interchain interactions, due to introduction of the dodecyl chain in place of the smaller hydrogen present in PPheDOTEtHx. Beside PPheDOT(C12)2, all substituted monomers are unsymmetrical leading to regioirregular polymers, which could lead to intrachain torsion th rough steric repulsion between every other PheDOT repeat units. Ho wever, evidence that the chains remain planar despite the regioirregular distribution of the side chains will be presented later in this chapter.

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136 Table 6-2. Optical properties of electrodepos ited films onto ITO-coated glass slides. Polymers were deposited from 0.01M monomer solution in 0.1M TBAP in ACN. In the case where the monomer is not fully soluble, a minimal amount of toluene was added to obtain full solubility. max (nm) Eg (eV)(a) Yxy Luminance Neutral film (c) Yxy Luminance oxidized film PPheDOT 560 1.82 N/A N/A PPheDOT (b) 623, 568 1.81 14% 45% PPheDOTEtHx 609, 559 1.85 N/A N/A PPheDOTC12 626, 572 1.80 30%, 0.314, 0.329 63%, 0.362, 0.398 PPheDOT(C12)2 620, 567 1.78 31%, 0.333, 0.337 58%, 0.372, 0.392 PPheDOTC12EtHx 608, 557, 518 1.92 18%, 0.329, 0.298 56%, 0.371, 0.407 (a) optical bandgap; (b) electropolymerized from PheDOT dimer; (c) Yxy CIE 1931 color coordinates, with Y bei ng the relative luminance in %. In Table 6-2, the optical properties of PPheDOT deposited from PheDOT or PheDOT dimer (BiPheDOT) are compared. BiPheDOT is electrodeposited at much lower potential, and the polymer films obtained ha ve higher quality than the films obtained from PheDOT, with two well-resolved vibron ic structures. Films electrodeposited from PheDOT have a broader absorption with no well-resolved vibronic features, indicating that the films morphology is changed, proba bly because of the side reactions involved with PheDOT, which are not occuring at the potential where BiPheDOT is electrodeposited. Luminance studies carried on electrodeposited films of substituted PPheDOT show that the films switch from a purple absorptive color in the neutral state to a pale green color in the oxidized state. Th is color change corresponds to a luminance change of ca. 30%-40%, much lower than the luminance contrast observed in PProDOT polymers (50% to 80%). Given their poor stability in the fully oxidized state, it follows that these materials are not suited for electrochromic applications.

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137 6.4 Synthesis of Soluble Substituted PPheDOT Following bromination with N-bromosuccinimi de at the 2and 5positions of the thiophene, the monomers were chemically polymerized using Grignard Metathesis (GriM) polymerization (Figure 6-6).47,104 OO S R1 R2 H H OO S R1 R2 Br Br OO S R1 R2 n NBS DMF 1.MeMgBr,THF,reflux 2.Ni(dppp)Cl2 R1=-C11H23,R2=-C11H23: PPheDOT(C12)2R1=-C11H23,R2=-2-ethylhexyl: PPheDOTC12EtHx R1=-H,R2=-2-ethylhexyl: PPheDOTEtHx R1=-C11H23,R2=-H: PPheDOTC12 Figure 6-6. Synthesis of PPheDOT(C12)2 by Grignard Metathesis. Monosubstituted PPheDOTC12 and PPheDOTEtHx have poor solubility and form colloidal suspension in THF, toluene and chloroform. Heating the solution does not improve the solubility and does not yield si gnificant optical cha nges (Figure 6-7). The lack of solubility is attributed to strong -stacking interchain interactions, favored by the lower side chains density, possibly allowing significant interdigitation between polymer stacks. 400500600700800 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 S O O n Filtration 0.45 mmax= 638 nmAbsorbance (nm)(a)400500600700800 0.0 0.2 0.4 0.6 0.8 1.0 S O O n Absorbance (nm) 25C 80C 95C(b) Figure 6-7. Solution optical properties of monosubstituted PPheDOTs. (a) PPheDOTC12 solution absorption spectrum in THF be fore and after 450nm filtration; (b) Absorption spectrum of PPheDOTEtHx xyl enes solution at 25C, 80C, 95C.

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138 To obtain higher solubility, disubstituted PPheDOT(C12)2 and PPheDOT(C12)EtHx were synthesized. The GPC results are give n in Table 6-3. At room temperature, PPheDOT(C12)2 also forms purple colloidal suspensi ons in toluene, tetrachloroethane, xylenes and THF, consistent with the presence of strong interchain interactions forcing aggregation. However, upon heating to ~80C, PPheDOT(C12)2 becomes readily soluble in a variety of aromatic or halogenated solven ts. Solubility of the polymer is important, as it enables easy processing along with allowi ng full characterization of the polymer’s structure, in particular mol ecular weight determination. Hi gh temperature GPC, carried at 140C in trichlorobenzene, yields a number-average molecular weight Mn =14,800 g.mol1 and a polydispersity of 1.95, corresponding to a number-average molecular structure of ~30 number-average repeat units. A second polymerization yielded a higher molecular weight Mn= 29,400 g.mol-1 and PDI=2.42. Table 6-3. GPC data for PPheDOTC12EtHx and PPheDOT(C12)2. Mn (g mol-1) Mw (g mol-1) PDI Xn PPheDOTC12EtHxa 56, 200 82,700 1.5 110 PPheDOT(C12)2 b #1 14,800 28,900 1.95 30 PPheDOT(C12)2 b #2 29,400 71,300 2.42 60 a GPC determined at room temperature in THF; b molecular weight determined in 1,2,4trichlorobenzene at 135C; mol ecular weights are given for tw o different polymerization. By substituting a dodecyl chain on the monomer by a more bulky 2-ethylhexyl side chains in PPheDOTC12EtHx, solubility is dramatically improved. PPheDOTC12EtHx is readily soluble at room temperature in most organic solvent such as hexanes, THF, chlorinated solvents and aromatic solvents. GP C, carried out in THF at room temperature yields a number-average molecular weight of Mn=56,200 g mol-1 and a polydispersity of 1.5, corresponding to a number-average mol ecular structure of 110 repeat units. The

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139 increased solubility could be due either to a strong decrease in interchain -stacking or a strong intrachain twisting of the PPheDOT backbone. 6.5 Solutions Properties In solution, PPheDOT(C12)2 displays a strong thermoch romic effect changing from a dark purple color at low temperature to a red-orange color above 80C. Figure 6-8 shows the UV-Vis spectrum of a polymer solution in xylenes as it is heated from 25 to 95 C. The absorption maximum shifts by almost 70 nm from 614 nm to 546 nm as the temperature increases. The presence of vibr onic features at high temperature indicates that the chains retain a planar (or highly conjugate d) conformation. In poly(3alkylthiophene)s, the absorption spectrum above the phase transition is broad and featureless, arising from intrachain twisting of the polythiophene backbone.105 This difference is consistent with studies on short oligothiophenes with alkyl or alkoxy substituents showing that the presence of the oxygens induces planar conformations of the oligomers. This effect is attributed to the smaller steric demand of the oxygens, mesomeric effects, as well as sulfur-oxygen interactions.57a,106 PPheDOTC12EtHx displays a different behavior. At room temperature in xylenes solution, there is a strong hypsochromic shift, and the absorpti on spectrum resembles the spectrum of PPheDOT(C12)2 above the phase transition. Thermochromism experiment on PPheDOTC12EtHx dissolved in xylenes leads to a progressive bathochromic shift of the absorption. Comparing the solution ab sorption spectra of both polymers ( max and vibronic features) indicate that a bove the phase transition of PPheDOT(C12)2, the absorption spectra of both polymers at equal temperatures are almost identical. This result confirms the observation made in Chapter 5 that intrachain twisting is also involved in the thermochromic changes below the phase transition. However, in

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140 aggregated solutions, intrachain twisting i nduce only minor optical changes, and the breakup of the interchain interactions is responsible for the most optical changes observed. 400500600700 0.0 0.1 0.2 0.3 0.4 0.5 0.6 25C 35C 45C 55C 65C 75C 85C 95CAbsorbance (nm) 25 C 95C 546 nm 614 nm 300350400450500550600650700 0.0 0.2 0.4 0.6 0.8 1.0 1.2 OO S C12H25 n Absorbance (nm) 5C 15C 25C 35C 45C 55C 65C 75C 85C 95C554 513 540 509 Figure 6-8. Solution thermochromism of Poly[PheDOT-(C12)2] in xylenes. Concentration is 6x10 5 M (relative to the repeat unit). Pictures show the solution at 25C (right) and 95C. Due to aggregation, PPheDOT(C12)2 is not fluorescent at room temperature. However, if heated above 80C, temperature where the polymer chains become molecularly dissolved, the polymer become s strongly fluorescent, emitting a bright orange color. PPheDOTC12EtHx is fluorescent at room temperature, emitting the same bright orange color, shown in (Figure 6-9). 400500600700800 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 nmAbsorbanceStokes shift= 600 cm10.0 0.2 0.4 0.6 0.8 1.0 Fluorescence Figure 6-9. Absorption and Em ission spectrum of PPheDOTC12EtHx. Sample is excited at 550nm.

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141 The fluorescence of PPheDOTC12EtHx at room temperature or PPheDOT(C12)2 above 80C is further evidence that intercha in interactions are broken and the chains molecularly dissolved. The small Stokes shift and the well-resolved vibronic coupling for PPheDOTC12EtHx in xylenes solution indicate that the polymer chains are mostly planar. 6.6. PPheDOT(C 12 ) 2 : A Soluble, Ordered Polymer Spray-coated films of Poly(PheDOT-(C12)2) are electroactive, switching from a dark purple color to a transmissive green in the oxidized state. Cyclic voltammetry (Figure 6-10) shows a low onset of oxidation at -0.2V vs. Fc/Fc+ for Poly(PheDOT(C12)2), corresponding to a HOMO level at 4.6 eV, which is substantially lower in energy (higher oxidation potential) than neutral PEDOT (4.1 eV).107108 -1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 OO S n I (mA/cm2)E(V) vs. Fc/Fc+ Figure 6-10. Cyclic voltammetr y of disubstituted PPheDOT(C12)2 in 0.1M TBAP in ACN at a scan rate of 50mV/s. Film was drop cast onto platinum button electrode from a 5mg/ mL toluene solution. The higher oxidation potential is consistent with the trend reported recently, where theroretical and experimental studies on the PheDOT dime r and trimer showed that resonance of the oxygens with the phenylene ring induces a decrease in el ectron release of the oxygens into the thiophene.102 Higher oxidation potential gives the neutral polymer

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142 greater air stability and allows for long te rm storage without the need to keep the materials under inert atmosphere. Spectroelectrochemistry was carried out on films cast onto an ITO-coated glass slides. As PPheDOT(C12)2 is not soluble at room temperature, spray-casting was not possible and drop-casti ng was used instead. As shown in Figure 611, as the potential applied to the PPheDOT(C12)2 film is increased to 0.2V, the transition is progressively bleached, while tw o near-infrared optical transitions appear, characteristic of the polaronic and bipolaron ic states. The optical bandgap, determined from the onset of absorption is estimated at 1.88 eV, 0.25 eV hi gher than PEDOT (1.6 eV). The presence of vibronic features in the films absorption spectrum suggests planarity of the polymer chains. 2004006008001000120014001600 0.00 0.05 0.10 0.15 0.20 OO S n 1.1V 1V 0.9V 0.8V 0.7V 0.6V 0.5V 0.4V 0.3V 0.2V 0.1V -1VAbsorbance (nm)623 nm 571 nm 526 nm UV Visible NIR Eg=1.88eV Figure 6-11. Spectroelectrochemistry of soluble disubstituted PPheDOT(C12)2 film on ITO-coated glass slides. The film wa s drop-cast from 5mg/mL hot toluene solution (100C). The film was el ectrochemically oxidized in 0.1M TBAP/propylene carbonate solution. A silver wire was used as a quasireference and was calibrated against Fc/Fc+. The conformation of the polymer chains in the processing solution (aggregated versus isolated chains) plays an important ro le in the solid state ordering. AFM imaging was carried out for films spin-coated onto mica from either hot (130C) or cold (25C)

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143 ortho-dichlorobenzene (ODCB) solutions. As seen in Figure 6-12, the films spin-coated from the hot ODCB solution yield nano-fibrilla r structures. The average height of the fibrils is 3 nm, a value slightly lower, but close to the polym er chain width for a conformation where the thiophenes are in a trans conformation and the dodecyl chains are extended. This lower value is not surpri sing given that at hi gh temperature in ODCB the dodecyl chains are expected to be disord ered. During spin-coating of the hot solution, the fast evaporation of the solvent does not allow the side chains to order properly. The fibrils are estimated to be about 10 nm in width (after correction for the lateral tip broadening effect109), which is consistent with the estimated length of the polymer chains in their fully extended conformation. From th ese data, the followi ng model is proposed: the material forms nanoribbons of -stacked polymer chains, with the polymer chains arranged perpendicular to the plane of the substrate (Figure 6-12). Figure 6-12. Self-assembly of PPheDOT(C12)2 polymer chains in films spin-coated on mica from a hot ODCB solution (C= 0.2 mg.mL 1). (A) AFM picture (5 5m2) of PPheDOT(C12)2; (B) cross section analysis and magnification (1 1m2). The fibril marked by the red arrow in the surface profile has a height of 3.2 nm; (C) Proposed 3D-model of the nanoribbons arrangement on the mica surface.

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144 Similar self-assembled nanostructures have been proposed for alkyl substituted poly(phenyleneethynylene) (PPE), po lyfluorene copolymers and poly(3alkylthiophenes).110 For the films obtained by spin-coating from a cold ODCB solution, there is formation of heteroge nous aggregates both in struct ure and size (Figure 6-13). This can be explained by comparison with th e solution thermochromism results described earlier. Similar to the xylenes solution, the pol ymer chains in ODCB form stable colloidal suspensions of aggregates at room temperatur e. During the spin-coating of this solution, the solvent evaporates and the concentration of the aggregates increases, leading to their collapse into larger, ill-define d structures. This difference of morphology is an important result as order within crystalline domains, and order of the crystalline domains with respect to one another, have dramatic consequences on charge mobilities, as previously shown in regioregular poly(3-hexylthiophene).17c Figure 6-13. AFM picture (5 5m2) of PPheDOT-(C12)2 spin-coated on mica from ODCB solution at room te mperature (C= 0.2 mg mL 1) The thermal behavior of PPheDOT(C12)2 in the solid state was investigated. TGA analysis shows that the po lymer is thermally stable up to 300C, under both oxygen and nitrogen atmosphere. After conditioning with a ramp at 10C per minute up to 220C and

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145 cooling to 0C, the second DSC scan show s an endothermic transition at 132 C on heating and an exothermic tr ansition at 110C on cooling (F igure 6-14). The small phase transition enthalpy suggests that there is little structural rearrangement during the transition. This thermal transition is assigne d to the melting and recrystallization of the side chains. No further transitions corres ponding to a melting of the crystalline regions are observed. This confirms the presence of strong intermolecular stacking interactions, as expected from the planarit y of the monomer. As mentioned earlier, the presence of sulfur-oxygen interactions and mesomeric effects contributes to a rigidification of the planar conformation of the phenylene dioxythiophene backbone. As a result, only the transition corresponding to th e melting of the side chains is observed. Figure 6-14. DSC (2nd scan) of PPheDOT-(C12)2. Sample was heated and cooled at a rate of 10C/min. The organization of PPheDOT(C12)2 in the solid-state has been investigated by using two-dimensional wide-angle X-ray sc attering (2D-WAXS) measurements, carried out by Dr Wojciech Pisula at the Max Planck Institute for Polymer Science, Mainz, Germany. The samples were prepared by shear-alignment at 150 C using a home-built mini-extruder.50 At ambient temperatures, the 2D pa ttern displayed sh arp and distinct

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146 reflections indicating a wellordered structure of the c onjugated polymer with a pronounced alignment of the chains in the extrusion direction. (Figure 6-15a). The equatorial small-angle reflection was related to the lateral distance of 3.88 nm of the polymer chains. This relatively large dist ance is in good accordance with the polymer configuration, as illustrated in Figure 6-15b, in which the monomer units are arranged in one plane, forming a lamella structure of rigid stacked conjugated chains. Figure 6-15. Ordering in mech anically aligned PPheDOT(C12)2 fibers.(a) 2D-WAXS pattern at 30 C (the inset displays the small-angle reflections at a lower contrast) and (b) p acking of PPheDOT(C12)2 as indicated by the X-ray results; (c) Equatorial reflection intensity distri bution recorded at 30 C as a function of the scattering angle. Reflections are indexed by the Miller’s indexes. Additional higher-order equatorial reflections, positioned at multiple angle values, confirmed the well-defined organization of th e filament (Figure 615c). The wide-angle reflection, positioned also in the equatorial plane of the X-ray pattern, is assigned to the

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147 -stacking distance of 0.46 nm of the pol ymer chains, whereby the low-intensity anisotropic halo was assigned to the poorly ordered alkyl side chains, which filled the periphery between the rigid conjugated units. The meridiona l reflection corresponded to the period of 0.76 nm and therefore to every second monomer unit along the polymer backbone being in an identical arrangement as illustrated in Figure 6-15b. The organization of the polymer changed s lightly above the phase transition of 132 C (Figure 6-16). The equatorial reflections showed an unchanged shape and intensity, but were shifted to lower angl es indicating smaller lateral distances of 3.15 nm at the higher temperature phase. Such distance d ecrease between rigid well-packed polymer chains might be explained by the melting of the alkyl substituents. Indeed, the diffuse anisotropic halo was characteristic for the me lting of the alkyl side chains. The change of the side chain dynamics did not affect the co rrelations between the repeat units along the polymer chain, but led to an increase of their steric demand and thus to a hindrance of the polymer stacking. This was reflected by the lowered reflection intensity corresponding to the stacking distance, whereas the full inte nsity was recovered by cooling the sample back to 30 C. Figure 6-16. 2D-WAXS pattern of PPheDOT-(C12)2 at 150C. The higher molecular weight fraction disp lays significantly di fferent behavior. DSC analysis reveals that the melting and crystallization transitions of the side chains are

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148 shifted to lower temperatures (Tm= 100C, Tc= 70C). The enthalpies of these transitions are also higher than for the lower molecular weight sample (10-20 J g-1 vs. 4-6 J g-1). The 2D-WAXS profiles, shown in Figure 6-17, indicate similar packing as the lower molecular weight fraction. Figure 6-17. 2D-WAXS an alysis of higher molecular weight PPheDOT(C12)2 fraction. The diffraction profile is shown below a nd above DSC transition attributed to the melting of the side chains. The reflections for the higher molecular weights are more intense and broader, indicating higher macroscopic order but lower crystallinity. The lower crystallinity also explains the lower melting and crystallizati on temperatures. Such increase of the longer order with increased molecular weight was al so observed in alkyl polythiophenes and is believed to be the origin of the enhancement of the charge-carrier mobilities with increasing molecular weight. 6.7. PPheDOTC 12 EtHx: a Disordered Polymer As mentioned earlier, PPheDOTC12EtHx polymer chains ar e molecularly dissolved in solution although having a planar confor mation, as indicated by the presence of vibronic coupling and the small Stokes shift value. The absence of interchain interactions

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149 in solution, at room temperature, indicates that asymmetric substitution of PheDOT with ethylhexyl and dodecyl substituents effectively hinders ordering, contrarily to PPheDOT(C12)2, PPheDOTC12 and PPheDOTEtHx, all strongly aggregating at room temperature. PPheDOTC12EtHx was spray-cast from toluene onto ITO-coated glass slides and the cast films absorption spect ra were examined. As observed in Figure 6-18, the cast films have almost identical maxima of absorption than the polymer in xylenes solution, showing that the polymer chains retain a “solution” conformation. The broader absorption may arise from some intrachain twis ting of the chains in the solid state, or presence of a small amount of interchain interactions. When i rradiated under 365nm UV lamp, the film show solid-state fluorescence, confirming that the polymer does not display strong interchain interactions. Af ter several electrochemical doping/de-doping cycles between +0.9V and -0.5V, the absorpti on of the cast film is mostly unchanged. 400600800 0.0 0.4 0.8 Normalized absorbance(nm) After Redox As Cast xylenes 25C 551 554 556 Figure 6-18. Absorption spectrum of PPheDOTC12EtHx: in xylenes solution, film spraycast from toluene and film spray-cast after electrochemical doping/reneutralization.

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150 Electrochemistry was carried out on films drop-cast on a platinum button electrode (Figure 6-19). The onset of oxi dation is similar to the electro polymerized film at 0.3V vs. Fc/Fc+ (5.1eV HOMO107). The onset potential is much higher than PPheDOT(C12)2, arising from the decreased interchain interactions. Spectroelectrochemistry experiment carried out on a spray-cast film of PPheDOTC12EtHx yields significantly higher bandgap (2.1eV) than the electropolymerized film. Also the neutral state optical spectrum of the electrodeposited films displays an additional vibronic feature at 608nm, not seen in the spray-cast film. As observed in PPheDOT(C12)2 solution thermochromism, the transition at 608nm is characteristic of interchain a ggregates, showing that electrodeposited films have higher interchain order, possibly aris ing from the side ch ain reactions at the oxidation potential used for th e electrodeposition. Similarl y to substituted PProDOTs, introduction of the bulky 2-ethylhexyl subst ituents also leads to large optical changes within a narrow potential wi ndow (300mV), explained by a more open morphology of the polymer film and decreased interchain interactions. -0.9-0.6-0.30.00.30.60.91.2 -0.2 -0.1 0.0 0.1 0.2 0.3 OO S C12H25 n I (mA/cm2)E(V) vs. Fc/Fc+EOnset= 281mV 4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.96V 0.86V 0.76V 0.66V 0.56V 0.46V 0.36V 0.26V OO S C12H25 n Absorbance (nm) Eg=2.08eV 515 556 Figure 6-19. Electrochemistry and sp ectroelectrochemistry of PPheDOTC12EtHx cast films. (left) Cyclic voltammetry in 0.1M TBAP/ACN electrolyte solution of a PPheDOTC12EtHx drop-cast on a platinum button electrode; (right) Spectroelectrochemistry of a PPheDOTC12EtHx spray-cast on an ITO-coated glass slide in 0.1M TBAP/propylene carbona te electrolyte. Po tentials are vs. ferrocene.

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151 The bulk polymer was analyzed by differe ntial scan calorimetry (Figure 6-20). Small melting and crystallization peaks corr esponding to the dodecyl substituents chains are observed, indicating some interchain or dering through the side chains. The enthalpy associated with these transitions is much lower than PPheDOT(C12)2. -200-1000100200300 -3 -2 -1 1 2 3 0.18 J/gHeat Flow (W/g)T / C W/g 2nd Cycle PPheDOTC12EtHx 0.17 J/g Figure 6-20. DSC (2nd scan) of PPheDOTC12EtHx. Heat and cooling rate= 10C/min. Also, the melting and crystallization occu r well below room temperature (ca. 50C) contrarily to PPheDOT(C12)2, displaying high temper ature transitions ( ca. 100C). As a result, the polymer is highly amorphous at room temperature, which is confirmed by the observation of solid state fluorescence. 6.8. Conclusion In conclusion, new electron rich, electroactive mono and di-substituted soluble polymers based on the (3,4-phenylenedioxythio phene) unit were synthesized by chemical polymerization. The monosubstituted polymers, as well as Poly(PheDOT(C12)2), possess a high degree of intraand inter-chain order, both in solution and solid state. At high temperature in ODCB or xylen es solutions, Poly(PheDOT(C12)2) possesses a planar conformation, leading to aggr egation at low temperature. Spin-coating of this polymer

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152 from a hot ODCB solution leads to the forma tion of nanoribbons. Stru ctural investigation by 2D-WAXS of mechanica lly aligned Poly(PheDOT(C12)2) filaments revealed a pronounced 2D organization of the conjugate d polymer. Strong correlations along the polymer backbone and between the polymer chains have been observed. PPheDOTC12EtHx, on the other hand, although having a mostly planar chain conformation do not order strongly in the solid stat e, as steric hindrance of the side chains prevent interchain interactions. Since the order of conjugated polymers, as organic semiconductors, is an essential requirement for charge carrier transport, and thus for their implementation in electronics, this work has shown that PPheDOT(C12)2 is a promising candidate for device applications. PPheDOTC12EtHx, having little interchain order in the solid state, is not suitable for such app lications, but is promising in light-emitting applications, where interchain interactions are undesirable. 6.9. Closing Statements To be successfully applied commercially, solubility of the conducting polymers is required, allowing inexpensive and easy pro cessing. Thanks to their unique synthetic versatility, conducting polymers can be tailored and modified to achieve that goal. One of the strategies is to introd uce substituents on the conjuga ted backbone. However, it should be clear from Chapter 1 that the ultimate a pplication must be take n into account when considering what substituents to use a nd where to place these substituents on the conjugated backbone. In Chapter 3 and 4, bulky branched substituents were successfully used to increase the solubility of poly(3,4propylenedioxythiophenes) (PPro DOTs), which are promising materials for electrochromic applications. The bulkiness of the substituents induces a decrease of interchain inte ractions and leads to a more open morphology of the polymer

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153 films. As a result, the branched polymers are better electrochromic materials, with higher contrasts, shorter switching times and higher co loration efficiencies. The alkyl substituted PProDOT-R2 were found to spontaneously self-assem ble during film casting, in contrast with the ether-linked PProDOT-(CH2OR)2 polymers that retain a solution conformation. This behavior was attributed to intrachain twisting of the PProDOT-(CH2OR)2 polymer chains preventing their self-asse mbly in the solid state, s upported by the studies detailed in Chapter 5 on the chiral analogs of these po lymers. Theoretical work should be carried out on branched PProDOTs oligomers substituted with either alkyl or alkoxymethyl side chains to gain more insight on the reason behind the more twisted conformation observed for the ether linked substituted PProDOTs. Such work would be helpful to design highly ordered polymers needed in high conductivity and high mobilities applications, or highly disordered polymers needed in light-emitting applications. In Chapter 5, the synthesis of chiral e quivalents of the PProDOTs investigated in Chapter 3 and 4 is described. The self-assembly of the chiral polymer chains were studied through thermochromism and solvatochrom ism experiments, probed by absorption, fluorescence and circular dichroism spectrosc opy, leading to an unprecedented level of understanding on the structure-property rela tionships. Especially promising is the introduction of the chiral substituents synthe sis, opening the door to new chiral polymers with unseen chiral ordering. Of particular interest for future work would be the synthesis of stackable chiral substituents, which should l ead to stronger chiral ordering. The effect of side chain crystallization on the ordering of the PProDOT backbone is unknown. It is expected to be quite differe nt from poly(3-alkylthiophenes) as the side chains do not

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154 extend within the plan e of the polythiophene backbone but rather above and below this plane. The focus of Chapter 6 was to synthesi ze the first soluble conjugated poly(3,4phenylenedioxythiophenes) (PPheDOTs). This objective was accomplished by attaching either dodecyl or ethylhexyl substituent at both the 4and 5positions of the benzene ring, as monosubstituted compounds were found to have poor solubility. Didodecyl substituted PPheDOT(C12)2 has high solubility at temper atures above 80C. The polymer has a high degree of order in the solid st ate and is a promising candidate for high conductivity and high mobili ty applications. Asymmetrically substituted PPheDOTC12EtHx, on the other hand, is highly so luble at room temperature. The polymer is highly disordered in the solid st ate and is a promising material for lightemitting applications. The considerable differences between the two polymers’ properties, although they differ little structur ally, illustrates perfectly the importance the side chains in the ordering of polymer chains. Future work in PPheDOTs polymers should investigate the structur e-properties relationships in PPheDOTs. An essential study would be to investigate the effect of th e chain length on the properties of linear disubstituted PPheDOTs polymers. As descri bed in Chapter one, the conductivity and mobility of substituted polythiophenes often go through an optimum with increasing side chains length. Also, the efficiency of the synthesis of disubstituted PPheDOT suffers greatly from a low yield in the transetherification step, a late step in the synthesis. This step of the synthesis will re quire significant improvement for these materials to become commercially interesting.

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155 6.10. Synthetic Details 1-(3,4-dimethoxyphenyl)dodecan-1-one: In a 2L 3-neck flask equipped with an argon inlet and a pressure-equa lizing addition funnel was dissolved aluminum trichloride (26g, 200 mmol, 1.1 eq.) in dry dichloromethane (700mL, distilled from CaH2). The reaction was cooled at 0C, and a solution of veratrole (25g, 180 mmol, 1 eq.) in dry dichloromethane (150 mL) was added dropw ise followed by addition of a lauroyl chloride solution (40g, 180 mmol, 1eq.) in dr y dichloromethane (150 mL). The mixture is refluxed for 24 hours, then cool ed at 0C. The excess aluminum chloride was quenched by slow addition of 6M HCl (100 mL). The aqueous phase is further extracted with dichloromethane (2200 mL). The combined organic layers are washed with water (3400 mL), and dried with magnesium sulfat e. The solvent is removed under vacuum to yield a white solid, purified by recrystalliza tion from toluene. The product is obtained as a white solid (52g, 90% yield); 1H NMR (300MHz, CDCl3) 0.83-0.93 (t, 3H), 1.18-1.43 (m, 16H), 1.64-1.8 (m, 2H), 2.88-2.95 (m, 2H), 3.94 (s, 3H), 3.95 (s, 3H), 6.88 (d, 1H, J1=8.3Hz), 7.54 (d, 1H, J2=1.9Hz), 7.59 (dd, 1H, J1= 8.3Hz and J2=1.9Hz) ; 13C NMR (75 MHz, CDCl3) 14.32, 22.90, 25.03, 29.55, 29.72, 29.84, 32.12, 38.38, 56.18, 110.16, 110.42, 122.84, 130.57, 149.2, 153.28, 199.44. 4-dodecyl-1,2-dimethoxybenzene: In a 3L 3-neck flask equipped with an argon inlet was dissolved LAH (12.6g, 331.4 mmol 4.5eq) in dry diethyl ether (500 mL, distilled from Na/benzophe none). A solution of AlCl3 (14.8g, 110.5 mmol, 1.5eq.) in dry diethylether (500 mL) was adde d via cannula to the LAH soluti on, cooled at 0C. After 15 min, a solution of 1-(3,4-dimethoxyphenyl )dodecan-1-one (23.6g, 73.64 mmol, 1eq.) in diethylether (500 mL) was added dropwise to the reaction (maint ained at 0C). Upon completion of the addition, the mixture was allowed to warm up to room temperature.

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156 After four hours, the reaction was cooled back to 0C and quenched slowly by addition of 200 mL of 6M HCl. The organic layer was washed with water (3400 mL) and dried with magnesium sulfate. The organic solv ent was removed under vacuum, to yield a white solid purified by column chro matography on silica gel using 50/50 dichloromethane/hexanes as eluent. This yi elds the product as a white solid (14g, 62% yield). 1H NMR (300MHz, CDCl3) 0.83-0.92 (t, 3H), 1.2-1.38 (m, 18H), 1.52-1.65 (m, 2H), 2.5-2.58 (m, 2H), 3.86 (s, 3H), 3.88 (s, 3H), 6.68-6.82 (m, 3H); 13C NMR (75 MHz, CDCl3) 14.34, 22.92, 29.58, 29.77, 29.90, 31.95, 32.16, 35.82, 56.02, 56.16, 111.41, 112.01, 120.32, 135.87, 147.21. 4-dodecylbenzene-1,2-diol: In a 2L three-neck flask equipped with an argon inlet was added 1-dodecyl-4,5-dimethoxybenzene (4g, 13 mmol, 1eq.) in dry dichloromethane (500 mL, distilled from CaH2). Boron tribromide (13 mL 137mmol, 4eq.) was added dropwise using a pressure-equalizing addition funnel. After 12 hours, the mixture was poured in a 2L Erlenmeyer filled with 1L of ice. The aqueous phase was further extracted with dichloromethane (2200 mL) and the comb ined organic layers were washed with water (3300 mL). The organic phase is dr ied with magnesium sulfate and the solvent was evaporated under vacuum to yield the product as an off-white solid (2.8g, 77% yield). 1H NMR (300MHz, CDCl3) 0.84-0.92 (t, 3H), 1.2-1.36 (m, 20H), 1.47-1.62 (m, 2H), 2.42-2.52 (t, 2H), 4.91 (br s, 1H), 5.05 (br s, 1H), 6.58-6.62 (dd, 1H), 6.68-6.70 (d, 1H); 6.76 (d,1H); 13C NMR (75 MHz, CDCl3) 14.35, 22.93, 29.48, 29.59, 29.76, 29.91, 31.82, 32.16, 35.49, 115.45, 115.73, 121.03, 136.57, 141.35, 143.50;HRMS [M+] calcd for C18H30O2 278.2246 amu Found 278.2242 amu.

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157 PheDOT-C 12 : In a 100 mL round bottom flask, 4-dodecylbenzene-1,2-diol (2g, 7.04 mmol,1eq) was dissolved in 60 mL of dry toluene (distilled from Na/benzophenone). To this solution was a dded 3,4-dimethoxythiophe ne (1g, 7.04 mmol, 1eq.) and p-toluenesulfonic acid (136 mg, 0. 7mmol, 0.1eq). The fl ask was equipped with a soxhlet apparatus containi ng a thimble filled with CaCl2. The mixture was refluxed for three days. Triethylamine (1 mL) and water (200 mL) were added and the product was extracted with diethylether (3100 mL). After drying with sodium sulfate and removal of the solvent under redu ced pressure, the resulting brow n solid was purified by column chromatography on silica gel using pentane as eluent. The produc t was obtained as a white solid (0.4g, 15% yield). 1H NMR (300MHz, CDCl3) 0.82-0.94 (t, 3H), 1.2-1.37 (m, 18H), 1.46-1.52 (m, 2H), 2.44-2.57 (m, 2H), 6.38-6.42 (m, 2H), 6.67-6.74 (m, 2H), 6.796.83 (m, 1H); 13C NMR (75 MHz, CDCl3) 14.36, 22.92, 29.38, 29.88, 31.53, 32.16, 35.32, 100.96, 116.54, 116.67, 123.63, 138.96; HRMS [M+] calcd for C22H30O2S 358.1967 amu Found 358.1973 amu. PheDOT-C 12 -Br 2 : PheDOT-C12 (0.25g, 0.7 mmol) was dissolved in 100 mL of DMF. After the solution wa s bubbled with argon for one hour, N-bromosuccinimide (0.27g, 1.54 mmol, 2.2 eq.) was added in one portion. The solution was stirred overnight after which 200 mL of water was added. The product was extracted with ether, washed with water and the organic layer dried with magnesium sulfate. The solvent was evaporated under vacuum and the resulting yellowish white solid was purified by column chromatography on silica using pentane as eluent. The product was obtained as a white solid (0.245g, 70% yield). 1H-NMR (300MHz, CDCl3) 0.88 (t, J= 6.7Hz, 3H), 1.171.37 (bs, 36H), 1.5-1.65 (bs, 4H), 2.52 (t, J=7.6Hz, 4H), 6.83 (dd, J1= 8.3Hz, J2= 2.2Hz,

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158 1H), 6.86 (d, J2= 2Hz, 1H), 6.925 (d, J1= 8.3Hz, 1H); 13C-NMR (75MHz, CDCl3) 14.34, 22.91, 29.32, 29.57, 29.58, 29.67, 29.77, 29.84, 29.86, 29.89, 31.40, 32.14, 35.29, 86.88, 86.99, 116.75, 116.85,124.39 137.95, 139.64, 139.65, 139.83; HRMS [M+] calcd for C22H28O2SBr2 514.0177 amu Found 514.0223 amu; Elem ental analysis Calcd. For C22H28O2SBr2 %C 51.18 %H 5.47, %S 6.21 Found %C 51.03, %H 5.41; %S 6.15. PPheDOTC 12 : To a solution of PheDOT-C12-Br2 (220 mg, 0.43 mmol) in 30 mL of freshly distilled THF (fro m Na/benzophenone), was added CH3MgBr via syringe (solution freshly titrated, C= 0.94M) (0.45 mL, 0.43 mmol). The solution was refluxed for 2 hours. Then Ni(dppp)Cl2 (5mgs, 0.009 mmol) was added in one portion. The solution was refluxed for 24hrs. The polymer was then precipitated in 100 mL MeOH and filtered through a soxhlet thimble. The polymer was purified via soxhlet extraction with MeOH, hexanes and then extracted with toluene. Th e product was obtained as a dark purple solid (120mg, 79% yield). 1-(2-dodecyl-4,5-dimethoxyphenyl)dodecan-1-one: In a 1L 3-neck flask equipped with an argon inlet and a pressure -equalizing addition funnel was dissolved aluminum chloride (7.2g, 55 mmol, 1.1 eq.) in dry dichloromethane (300 mL, distilled from CaH2). To the reaction cooled at 0 C, a solution of 4-dodecyl-1,2dimethoxybenzene (15.2g, 50 mmol, 1 eq.) in dry dichloromethane (100 mL) was added dropwise followed by the addition of a soluti on of lauroyl chloride (10.82g, 50 mmol, 1eq.). The mixture is refluxed for 24 hours, then cooled at 0C. The excess aluminum chloride was quenched by slow addition of 6M HCl (150 mL). The aqueous phase is further extracted with dichloromethane (2 200 mL). The combined organic layers are washed with water (3200 mL), and dried with magnesium sulfate. The solvent is

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159 removed under vacuum to yield a ye llow-white solid, purified by column chromatography on silica gel (50/50 hexanes/di chloromethane as eluent). The product is obtained as a white solid (16.2g, 67% yield); 1H NMR (300MHz, CDCl3) 0.82-0.96 (t, 6H), 1.18-1.42 (m, 34H), 1.45-1.60 (m, 2H), 1. 62-77 (m, 2H), 2.74-2.9 (m, 4H), 3.88 (s, 3H), 3.92 (s, 3H), 6.72 (s, 1H), 7.12 (s, 1H); 13C NMR (75 MHz, CDCl3) 14.33, 22.92, 24.98, 29.59, 29.76, 29.88, 30.03, 32.15, 32.4, 34.23, 41.99, 56.11, 56.41, 112.36, 113.88, 137.70, 146.45, 151.28, 203.53; HRMS [M+] calcd for C32H56O3 488.4229 amu Found 488.4219 amu. 1,2-didodecyl-4,5-dimethoxybenzene: In a 2L 2-neck flask equipped with an argon inlet was dissolved LAH (8.76g, 230 mmo l, 6eq) in dry diethyl ether (250 mL, distilled from Na/benzophe none). A solution of AlCl3 (7.56g, 60 mmol, 2eq.) in dry diethylether (250 mL) was adde d via cannula to the LAH soluti on, cooled at 0C. After 15 min, a solution of 1-(2-dodecyl-4,5-di methoxyphenyl)dodecan-1-one (16.2g, 33mmol, 1eq.) in diethylether (200 mL) was added dr opwise to the reaction (maintained at 0C). Upon completion of the addition, the mixt ure was allowed to warm up to room temperature. After four hours, the reaction was cooled to 0C and quenched slowly by addition of 100 mL of 6M HCl. The reacti on mixture was poured in 500 mL water. The aqueous phase was further extracted with diethylether (2200 mL) and the combined organic layers were washed with water (3300 mL). After drying with magnesium sulfate, the organic so lvent was removed under vacuum, to yield a white solid purified by column chromatography on silica gel using 50/50 dichloromethane/hexanes as eluent. This yields the product as a white solid (13g, 80% yield). 1H NMR (300MHz, CDCl3) 0.84-0.93 (t, 6H), 1.18-1.42 (m, 36H), 1.44-1.6 (m, 4H), 2.47-2.57 (m, 4H), 3.84 (s, 6H),

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160 6.65 (s, 2H); 13C NMR (75 MHz, CDCl3) 14.36, 22.94, 29.91, 31.95, 32.17, 32.71, 56.17, 112.87, 132.86, 146.99. 4,5-didodecylbenzene-1,2-diol: In a 2L three-neck flask equipped with an argon inlet was added 1,2-didodecyl-4,5-dimet hoxybenzene (13g, 27.4mmol, 1eq.) in dry dichloromethane (600 mL, distilled from CaH2). Boron tribromide (10.5 mL, 110mmol, 4eq.) was added dropwise using a pressure-e qualizing addition funnel. After 12 hours, the mixture was poured in a 2L Erlenmeyer filled with 1L of ice. The aqueous phase was further extracted with dichloromethane (2 200 mL) and the combined organic layers were washed with water (3300 mL). The orga nic phase is dried with magnesium sulfate and the solvent was evaporated under vacuum to yield the product as an off-white solid (11g, 90% yield). 1H NMR (300MHz, CDCl3) 0.84-0.93 (t, 6H), 1.27-1.4 (m, 36H), 1.421.58 (m, 4H), 2.42-2.5 (m, 4H), 6.65 (s, 2H); 13C NMR (75 MHz, CDCl3) 14.35, 22.93, 29.60, 29.93, 31.68, 32.17, 32.29, 116.36, 133.66, 141.27; HRMS [M+] calcd for C30H54O2S 446.4124 amu Found 446.4118 amu. PheDOT-(C 12 ) 2 : In a 100 mL round bottom flask, 4,5-didodecylbenzene-1,2-diol (5g, 11.2 mmol,1eq) was dissolved in 60 mL of dry toluene (distilled from Na/benzophenone). To this solution was added 3,4-dimethoxythiophene (1.6g, 11.2 mmol, 1eq.) and p-toluenesulfonic acid (213 mg, 1.12mmol, 0.1eq). The flask was equipped with a soxhlet apparatus containing a thimble filled with CaCl2. The mixture was refluxed for three days. Triethylamine (1 mL) and water (200 mL) were added and the product was extracted with diethylether (3100 mL). After drying with sodium sulfate and removal of the so lvent under reduced pressure, the resulting brown solid was purified by column chromatography on silica gel using pentane as eluent. The product

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161 was obtained as a white solid (1.15g, 20% yield). 1H NMR (300MHz, CDCl3) 0.84-0.95 (t, 6H), 1.2-1.42 (m, 36H), 1.45-1.6 (m, 4H), 2.44-2.56 (m, 4H), 6.4 (s, 2H), 6.7 (s, 2H); 13C NMR (75 MHz, CDCl3) 14.35, 22.92, 29.59, 29.76, 29.79, 29.82, 29.88, 29.90, 29.92, 31.28, 32.16, 32.17, 100.74, 117.01, 136.36, 138.53, 139.66; HRMS [M+] calcd for C34H54O2S 526.3845 amu Found 526.3863 amu. PheDOT-(C 12 ) 2 -Br 2 : PheDOT-(C12)2 (0.5g, 0.95 mmol) was dissolved in 100 mL of DMF. After the solution was bubbled with argon for one hour, N-bromosuccinimide (0.42g, 2.37 mmol, 2.5 eq.) was added in one portion. The solution was stirred overnight after which 200 mL of water was added. The product was extracted with ether, washed with water and the organic layer dried with magnesium sulfate. The solvent was evaporated under vacuum and the resulting yellowish white solid was purified by column chromatography on silica using pentane as eluent. The product was obtained as a white solid (0.48g, 74% yield). 1H-NMR (300MHz, CDCl3) 0.87 (t, 6H), 0.97-1.4 (m, 36H), 1.4-1.6 (bs, 4H), 2.5 (t, 4H), 6.81 (s, 2H); 13C-NMR (75MHz, CDCl3) 14.35, 22.92, 29.59, 29.76, 29.79, 29.81, 29.90, 31.14, 32.16, 32.18, 86.73, 117.13, 137.21, 137.53, 137.94; HRMS [M+] calcd for C34H52O2SBr2 682.2055 amu Found 682.2038 amu; Elemental analysis Calcd. For C34H52O2SBr2 %C 59.65, %H 7.66 Found %C 59.53, %H 7.43. MP 77-79C. PPheDOT(C 12 ) 2 : To a solution of PheDOT-(C12)2-Br2 (415 mg, 0.606 mmol) in 30 mL of freshly distilled THF (f rom Na/benzophenone), was added CH3MgBr via syringe (solution freshly tit rated, C=0.94M) (0.67 mL, 0. 606 mmol). The solution was refluxed for 2 hours. Then Ni(dppp)Cl2 (6.6mg, 0.012 mmol) was added in one portion. The solution was refluxed for 24hrs. The polymer was then precipitated in 100 mL

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162 MeOH and filtered through a soxhlet thimbl e. The polymer was purified via soxhlet extraction with MeOH, hexanes and then ex tracted with toluene. The product was obtained as a dark purple solid (220mg, 69% yield). The pr oduct after toluene soxhlet extraction was a dark black-purple solid. 1H NMR (300MHz, C2D2Cl4, 120C) 0.9-1.1 (bs, 6H), 1.25-1.6 (bs, 36H), 1.6-1.8 (bs, 4H ), 2.6-2.8 (bs, 4H), 6.9-7.1 (bs, 2H); GPC (135C, trichlorobenzene) Mn= 14,800 g mol-1, Mw= 28,900 g mol-1, PDI= 1.95. Elemental analysis Calcd. For C34H52O2S (repeat unit) %C 77.51 %H 10.33 Found %C 74.82; %H 10.6. 1-(3,4-dimethoxyphenyl )-2-ethylhexan-1-one: In a 2L 3-neck flask equipped with an argon inlet and a pressure-equaliz ing addition funnel was dissolved aluminum trichloride (28.7g, 217 mmol, 1.3 eq.) in dr y dichloromethane (700 mL, distilled from CaH2). The reaction was cooled at 0C, and a so lution of veratrole ( 25g, 180 mmol, 1 eq.) in dry dichloromethane (150 mL) was adde d dropwise followed by addition of a 2ethylhexanoyl chloride soluti on (32.3g, 200 mmol, 1.2 eq.) in dry dichloromethane (150 mL). The mixture is refluxed for 24 hours, then cooled at 0C. The excess aluminum chloride was quenched by slow addition of 6M HCl (100 mL). The aqueous phase is further extracted with dichloromethane (2 200 mL). The combined organic layers are washed with water (3400 mL), and dried with magnesium sulfate. The solvent is removed under vacuum to yield a yellow-oran ge oil, purified by column chromatography (SiO2, 75/25 DCM/Hexanes The product is obta ined as a clear oil (41g, 86% yield); 1H NMR (300MHz, CDCl3) 0.8-0.94 (m, 6H), 1.17-1.38 (m, 4H), 1.42-1.62 (m, 2H), 1.651.83 (m, 2H), 2.27-2.38 (m, 1H), 3.96 (s, 6H ), 6.84-6.94 (d, 1H), 7.56-7.64 (m, 2H); 13C NMR (75 MHz, CDCl3) 12.27, 14.17, 23.16, 26.01, 30.07, 32.35, 47.31, 56.16, 56.26,

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163 110.14, 110.59, 122.82, 131.29, 149.29, 153.32, 203.45; HRMS [M+] calcd for C16H24O3 264.1725 amu Found 264.1734 amu. 4-(2-ethylhexyl)-1,2-dimethoxybenzene: In a 3L 3-neck flask equipped with an argon inlet was dissolved LAH (3.77g, 100 mmo l, 1 eq) in dry diethyl ether (500 mL, distilled from Na/benzophe none). A solution of AlCl3 (13.13g, 100 mmol, 1eq.) in dry diethylether (500 mL) was adde d via cannula to the LAH soluti on, cooled at 0C. After 15 min, a solution of 1-(3,4-dimethoxyphenyl)-2 -ethylhexan-1-one (26g, 100 mmol, 1eq.) in diethylether (500 mL) was added dropwise to the reaction (maint ained at 0C). Upon completion of the addition, the mixture was allowed to warm up to room temperature. After four hours, the reaction was cooled back to 0C and quenched slowly by addition of 200 mL of 6M HCl. The organic layer was washed with water (3400 mL) and dried with magnesium sulfate. The organic solv ent was removed under vacuum, to yield a white solid purified by column chro matography on silica gel using 50/50 dichloromethane/hexanes as eluent. This yi elds the product as a clear oil (21g, 85% yield). 1H NMR (300MHz, CDCl3) 0.77-0.96 (m, 6H), 1.17-1.38 (m, 8H), 1.45-1.60 (m, 1H), 2.47 (d, J= 7Hz, 2H), 3.86 (s, 3H), 3.87 (s, 3H), 6.66-6.71 (m, 2H), 6.75-6.81 (m, 1H); 13C NMR (75 MHz, CDCl3) 11.02, 14.37, 23.31, 25.66, 29.07, 29.72, 32.52, 39.98, 41.36, 56.05, 56.12, 111.23, 112.70, 121.27, 134.68, 147.18, 148.82; HRMS [M+] calcd for C16H26O2 250.1933 amu Found 250.1935 amu; Elemental analysis Calcd. For C16H26O2 %C 76.75 %H 10.47 Found %C 77.05, %H 10.76. 4-(2-ethylhexyl)benzene-1,2-diol: In a 2L three-neck flask equipped with an argon inlet was added 1-(2-ethylhexyl)-4,5 -dimethoxybenzene (16g, 64 mmol, 1eq.) in dry dichloromethane (500 mL, distilled from CaH2). Boron tribromide (24 mL, 256

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164 mmol, 4eq.) was added dropwise using a pr essure-equalizing add ition funnel. After 12 hours, the mixture was poured in a 2L Erlenmey er filled with 1L of ice. The aqueous phase was further extracted with dichlorome thane (2200 mL) and the combined organic layers were washed with water (3300 mL). The organic phase is dried with magnesium sulfate and the solvent was evaporated under vacuum to yield the product as a slightly yellow oil (12.2g, 86% yield). 1H NMR (300MHz, CDCl3) 0.88-0.94 (m, 6H), 1.14-1.35 (m, 8H), 1.47-1.55 (m, 1H), 2.35-2.42 (d, 2H), 5.18 (br s, 2H), 6.55-6.62 (d, 1H), 6.626.72 (s, 1H); 6.72-6.8 (d,1H); 13C NMR (75 MHz, CDCl3) 11.00, 14.37, 23.28, 25.56, 29.09, 32.52, 39.64, 41.34, 115.29, 116.42, 121.84, 135.37, 141.36, 143.41. PheDOT-EtHx: In a 100 mL round bottom flask, 4-(2-ethylhexyl)-benzene-1,2diol (5g, 22.5 mmol,1eq) was dissolved in 60 mL of dry toluene (distilled from Na/benzophenone). To this solution was added 3,4-dimethoxythiophene (3.2g, 22.5 mmol, 1eq.) and p-toluenesulfonic acid (427 mg, 2.25mmol, 0.1eq). The flask was equipped with a soxhlet apparatus containing a thimble filled with CaCl2. The mixture was refluxed for three days. Triethylamine (1 mL) and water (200 mL) were added and the product was extracted with diethylether (3100 mL). After drying with sodium sulfate and removal of the so lvent under reduced pressure, the resulting brown solid was purified by column chromatography on silica gel using pentane as eluent. The product was obtained as a clear oil (0.76g, 11% yield). 1H NMR (300MHz, CDCl3) 0.82-0.93 (m, 6H), 1.14-1.37 (m, 8H), 1.42-1.55 (m, 1H), 2.38-2.45 (m, 2H), 6.42 (s, 2H), 6.67-6.74 (m, 2H), 6.78-6.84 (d, 1H); 13C NMR (75 MHz, CDCl3) 11.01, 14.36, 23.24, 25.60, 29.07, 32.51, 39.51, 41.25, 100.88, 100.97, 116.41, 117.37, 124.43, 137.94.

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165 PheDOT-EtHx-Br 2 : PheDOT-EtHx (0.5g, 1.99 mmol) was dissolved in 100 mL of DMF. After the solution was bubbled with argon for one hour, N-bromosuccinimide (0.78g, 4.4 mmol, 2.2 eq.) was added in one portion. The solution was stirred overnight after which 200 mL of water was added. The product was extracted with ether, washed with water and the organic layer dried with magnesium sulfate. The solvent was evaporated under vacuum and the resulting yellowish white solid was purified by column chromatography on silica using pentane as el uent. The product was obt ained as a clear oil (0.78g, 85% yield). 1H-NMR (300MHz, CDCl3) 0.82-0.93 (m, 6H), 1.15-1.36 (m, 8H), 1.43-1.6 (m, 2H), 2.45 (d, J=7.1Hz, 2H), 6.76 (dd, J1= 8.3Hz, J2= 1.9Hz, 1H), 6.83 (d, J2= 2.1Hz, 1H), 6.92 (d, J1= 8.3Hz, 1H); 13C-NMR (75MHz, CDCl3) 10.98, 14.34, 23.21, 25.57, 29.06, 32.49, 39.54, 41.25, 86.88, 86.99, 116.62, 117.52, 126.16, 137.94, 138.84, 139.56 ;HRMS [M+] calcd for C34H52O2SBr2 514.0177 amu Found 514.0223 amu; Elemental analysis Calcd. For C18H20O2SBr2 %C 46.98 %H 4.38, %S 6.97 Found %C 47.07, %H 4.11; %S 7.33. PPheDOTEtHx: To a solution of PheDOT-EtHx-Br2 (719 mg, 1.56 mmol) in 30 mL of freshly distilled THF (fro m Na/benzophenone), was added CH3MgBr via syringe (solution freshly titrated, C= 0.92M) (1.7 mL, 1.56 mmol). The solution was refluxed for 2 hours. Then Ni(dppp)Cl2 (5mgs, 0.031 mmol) was added in one portion. The solution was refluxed for 24hrs. The polymer was then precipitated in 100 mL MeOH and filtered through a soxhlet thimble. The polymer was purified via soxhlet extraction with MeOH, hexanes and then extracted with toluene. The product was obtaine d as a shiny brown solid solid (350mgs,70% yield).

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166 1-(2-(2-ethylhexyl)-4,5-dimethoxyphenyl)dodecan-1-one: In a 1L 3-neck flask equipped with an argon inlet and a pressure -equalizing addition funnel was dissolved aluminum chloride (14.45g, 110 mmol, 1.3 eq.) in dry dichloromethane (600 mL, distilled from CaH2). To the reaction cooled at 0C, a solution of 4-(2-ethylhexyl)-1,2dimethoxybenzene (21g, 84 mmol, 1 eq.) in dry dichloromethane (200 mL) was added dropwise followed by the addition of a solution of lauroyl chloride in 200 mL (26.4g, 101 mmol, 1.2 eq.). The mixture is refluxed fo r 24 hours, then cooled at 0C. The excess aluminum chloride was quenched by slow addition of 6M HCl (150 mL). The aqueous phase is further extracted with dichloromethane (2200 mL). The combined organic layers are washed with water (3200 mL), a nd dried with magnesium sulfate. The solvent is removed under vacuum to yield a ye llow-white solid, purified by column chromatography on silica gel (50/50 hexanes/di chloromethane as eluent). The product is obtained as a clear oi l (16g, 45% yield); 1H NMR (300MHz, CDCl3) 0.78-0.96 (m, 9H), 1.1-1.42 (m, 24H), 1.42-1.47 (m, 1H), 1.62-1.78 (m, 2H), 2.75-2.9 (m, 4H), 3.92 (s, 6H), 6.68 (s, 1H), 7.09(s, 1H); 13C NMR (75 MHz, CDCl3) 10.95, 14.34, 22.90, 23.34, 24.95, 25.69, 28.85, 29.56, 29.62, 29.72, 29.74, 29.85, 32.13, 32.53, 37.97, 41.19, 42.23, 56.09, 56.33, 112.15, 114.65, 131.43, 136.23, 146.43, 150.79, 204.03. 1-dodecyl-2-(2-ethylhexy l)-4,5-dimethoxybenzene: In a 2L 2-neck flask equipped with an argon inlet was dissolved L AH (4.11g, 108.3 mmol, 6eq) in dry diethyl ether (250 mL, distilled from Na /benzophenone). A solution of AlCl3 (4.77g, 36.1 mmol, 2eq.) in dry diethylether (250 mL) was added via cannula to the LAH solution, cooled at 0C. After 15 min, a solution of 1-(2-(2 -ethylhexyl)-4,5-dimethoxyphenyl)dodecan-1-one (15.6g, 36.1 mmol, 1eq.) in diethylether ( 200 mL) was added dropwise to the reaction

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167 (maintained at 0C). Upon completion of the addition, the mixture was allowed to warm up to room temperature. After four hours, the reaction was cooled to 0C and quenched slowly by addition of 100 mL of 6M HCl. The reaction mixture was poured in 500 mL water. The aqueous phase was further extract ed with diethylether (2200 mL) and the combined organic layers were washed with water (3300 mL). After drying with magnesium sulfate, the orga nic solvent was removed under vacuum, to yield a white solid purified by column chromatography on silica gel using 50/50 dichloromethane/hexanes as eluent. This yi elds the product as a clear oil (14g, 93% yield). 1H NMR (300MHz, CDCl3) 0.8-0.95 (m, 12H), 1.18-1.42 (m, 26H), 1.42-1.6 (m, 3H), 2.43-2.57 (m, 4H), 3.83 (s, 3H), 3.84 (s, 3H), 6.6 (s, 1H), 6.65 (s, 1H). 4-dodecyl-5-(2-ethylhexyl)-benzene-1,2-diol: In a 2L three-neck flask equipped with an argon inlet was added 1-dodecyl-2-(2-ethylhe xyl)-4,5-dimethoxybenzene (14g, 33.4mmol, 1eq.) in dry dichloromethane (500 mL, distilled from CaH2). Boron tribromide (12.64 mL, 134mmol, 4eq.) was added dropwise using a pressure-equalizing addition funnel. After 12 hours, the mixture wa s poured in a 2L Erlenmeyer filled with 1L of ice. The aqueous phase was further extracted with dichloromethane (2200 mL) and the combined organic layers were washed with water (3300 mL ). The organic phase is dried with magnesium sulf ate and the solvent was evaporated under vacuum to yield the product as a viscous, br own oil (11.7g, 90% yield). 1H NMR (300MHz, CDCl3) 0.80.92 (m, 6H), 1.14-1.39 (m, 26H), 1.40-1.58 (m, 3H), 2.36-2.51 (m, 4H), 4.83-4.93 (bs, 2H), 6.61 (s, 1H), 6.65 (s,1H); 13C NMR (75 MHz, CDCl3) 11.12, 14.34, 14.37, 22.91, 23.33, 25.77, 29.17, 29.58, 29.80, 29.85, 29.87, 29.91, 31.71, 32.15, 32.27, 32.76, 36.71,

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168 40.88, 116.33, 117.41, 132.54134.28, 140.99, 141.31; HRMS [M+] calcd for C26H46O2 446.4124 amu Found 446.4118 amu. PheDOTC 12 EtHx: In a 100 mL round bottom flask, 4,5-didodecylbenzene-1,2diol (5g, 12.8 mmol,1eq) was dissolved in 60 mL of dry toluene (distilled from Na/benzophenone). To this solution was added 3,4-dimethoxythiophene (1.82g, 12.8 mmol, 1eq.) and p-toluenesulfonic acid (250 mg, 1.3mmol, 0.1eq). The flask was equipped with a soxhlet apparatus containing a thimble filled with CaCl2. The mixture was refluxed for three days. Triethylamine (1 mL) and water (200 mL) were added and the product was extracted with diethylether (3100 mL). After drying with sodium sulfate and removal of the so lvent under reduced pressure, the resulting brown solid was purified by column chromatography on silica gel using pentane as eluent. The product was obtained as a clear oil (1.4g, 23% yield). 1H NMR (300MHz, CDCl3) 0.77-0.97 (m, 9H), 1.15-1.41 (m, 26H), 1.41-1.59 (m, 3H), 2.27-2.58 (m, 4H), 6.39 (s, 2H), 6.66 (s, 1H), 6.70 (s,1H); 13C NMR (75 MHz, CDCl3) 11.11, 14.36, 22.92, 23.29, 25.79, 29.15, 29.58, 29.75, 29.82, 29.88, 29.91, 31.34, 32.15, 32.19, 32.74, 36.66, 40.71, 100.75, 117.00, 118.02, 135.28, 136.91, 138.28, 138.59, 139.67; HRMS [M+] calcd. for C30H42O2S 470.3219 amu Found 470.3214 amu; Elemental analysis Calcd. For C30H42O2S %C 76.54, %H 9.85, %S 6.80 Found %C 76.57, %H 10.05, %S 6.65. PheDOT-(C 12 ) 2 -Br 2 : PheDOT-(C12)2 (1.15g, 2.44 mmol) was dissolved in 100 mL of DMF. After the solution was bubbled with argon for one hour, Nbromosuccinimide (1.09g, 6.2 mmol, 2.5 eq.) was added in one portion. The solution was stirred overnight after which 200 mL of water was added. Th e product was extracted with ether, washed with water and the organic laye r dried with magnesium sulfate. The solvent

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169 was evaporated under vacuum and the resul ting yellowish white solid was purified by column chromatography on silica using pentan e as eluent. The product was obtained as a clear oil (1.4g, 91% yield). 1H-NMR (300MHz, CDCl3) 0.82-0.93 (m, 9H), 1.16-1.41 (m, 26H), 1.42-1.61(m, 3H), 2.38-2.54 (m 4H), 6.77 (s, 1H), 6.82 (s, 1H); 13C-NMR (75MHz, CDCl3) 11.12, 14.35, 22.92, 23.28, 25.79, 29.18, 29.58, 29.75, 29.80, 29.88, 31.23, 32.15, 32.21, 32.76, 36.71, 40.73, 86.73, 117.14, 118.13, 136.18, 137.29, 137.59, 137.77, 137.95; HRMS [M+] calcd for C30H40O2SBr2 626.1429 amu Found 626.1476 amu; Elemental analysis Calcd. For C30H40O2SBr2 %C 57.33, %H 7.06, %S 5.10 Found %C 57.41, %H 6.86, %S 5.09. PPheDOTC 12 EtHx: To a solution of PheDOT-C12EtHx-Br2 (1.37g, 2.18 mmol) in 75 mL of freshly distilled THF (from Na/benzophenone), was added CH3MgBr via syringe (solution freshly tit rated, C=0.99M) (2.21 mL, 2.18 mmol). The solution was refluxed for 2 hours. Then Ni(dppp)Cl2 (23.6mg, 0.435 mmol) was added in one portion. The solution was refluxed for 24hrs. The polymer was then precipitated in 100 mL MeOH and filtered through a soxhlet thimbl e. The polymer was purified via soxhlet extraction with MeOH, hexanes and then ex tracted with toluene. The product was obtained as a dark purple solid (220mg, 69% yield). The pr oduct after toluene soxhlet extraction was a shiny brown solid. 1H NMR (300MHz, CDCl3) 0.34-0.98 (bs, 12H), 0.98-1.50 (bs, 26H), 1.50-1.87 (bs, 3H), 1.88-2.96 (bs, 4H), 6.45-7.11 (bs, 2H); 13C NMR (75MHz, CDCl3) 11.31, 14.31, 22.92, 23.40, 25.93, 29.64, 29.98, 32.18, 40.84, 107.43, 110.56, 117.34, 134.75, 136.73, 138.30; GPC (THF, RT) Mn= 58,900 g mol-1, Mw= 87,700 g mol-1, PDI= 1.5.

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170 LIST OF REFERENCES 1. Heeger, A. J. Ang. Chem.Int. Ed. 2001, 40 2591-2611. 2. Salzner, U., Lagowski, J. B., Pi ckup, P. G., Poirier, R. A. Synth. Met. 1998, 96 177-189. 3. Bredas, J. L. J. Chem. Phys. 1985, 82 3808-3811. 4. Heeger, A. J., Kivelson, S., Schrieffer, J. R., Su, W. P. Reviews of Modern Physics 1988, 60 781-850. 5. Bredas, J. L., Street, G. B. Acc. Chem. Res. 1985, 18 309-315. 6. Bredas, J. L., Themans, B., Fripiat, J. G., Andre, J. M., Chance, R. R. Phys. Rev. B. 1984, 29 6761-6773. 7. Welsh, D. M., Kumar, A., Meijer, E. W., Reynolds, J. R. Adv. Mater. 1999, 11 1379-1382. 8. Ouyang, J., Chu, C.-W., Chen, F.-C., Xu, Q., Yang, Y. Adv. Funct. Mater. 2005, 15 203-208. 9. Carpi, F., De Rossi, D. Optics and Laser Technology 2006, 38 292-305. 10. Schwendeman, I., Hickman, R., Soenmez, G., Schottland, P., Zong, K., Welsh, D. M., Reynolds, J. R. Chem. Mater. 2002, 14 3118-3122. 11. Pei, Q. B., Yu, G., Zhang, C., Yang, Y., Heeger, A. J. Science 1995, 269 10861088 12. Karl, N. Synth. Met. 2003, 133 649-657. 13. (a) Sirringhaus, H., Brown, P. J., Friend, R. H., Nielsen, M. M., Bechgaard, K., Langeveld-Voss, B. M. W., Spiering, A. J. H., Janssen, R. A. J., Meijer, E. W. Synth. Met. 2000, 111 129-132.; (b) Sirringhaus, H., Br own, P. J., Friend, R. H., Nielsen, M. M., Bechgaard, K., Langeveld -Voss, B. M. W., Spiering, A. J. H., Janssen, R. A. J., Meijer, E. W., Herwig, P., de Leeuw, D. M. Nature 1999, 401 685-688; (c) Wang, G. M., Swensen, J., Moses, D., Heeger, A. J. J. Appl. Phys. 2003, 93 6137-6141.

PAGE 187

171 14. Mcculloch, I., Heeney, M., Bailey, C., Genevicius, K., Macdonald, I., Shkunov, M., Sparrowe, D., Tierney, S., Wagner, R., Zha ng, W. M., Chabinyc, M. L., Kline, R. J., Mcgehee, M. D., Toney, M. F. Nat. Mater. 2006, 5 328-333.. 15. (a) Chang, J. F., Sun, B. Q., Breiby, D. W., Nielsen, M. M., Solling, T. I., Giles, M., McCulloch, I., Sirringhaus, H. Chem. Mater. 2004, 16 4772-4776. 16. Zen, A., Pflaum, J., Hirschmann, S., Zhua ng, W., Jaiser, F., Asawapirom, U., Rabe, J. P., Scherf, U., Neher, D. Adv. Funct. Mater. 2004, 14 757-764. 17. (a) Kline, R. J., McGehee, M. D., Kadnikova E. N., Liu, J. S., Frechet, J. M. J., Toney, M. F. Macromolecules 2005, 38 3312-3319; (b) Kline, R. J., McGehee, M. D., Kadnikova, E. N., Liu, J. S., Frechet, J. M. J. Adv. Mater. 2003, 15 1519; (c) Yang, H. C., Shin, T. J., Yang, L., Cho, K., Ryu, C. Y., Bao, Z. N. Adv. Funct. Mater. 2005, 15 671-676; (d) Verilhac, J.-M., Po krop, R., LeBlevennec, G., Kulszewicz-Bajer, I., Buga, K., Zagorska, M., Sadki, S., Pron, A. J. Phys. Chem. B 2006, 110 13305-13309; (e) Zen, A., Saphiannik ova, M., Neher, D., Grenzer, J., Grigorian, S., Pietsch, U., Asawapirom, U., Janietz, S., Scherf, U., Lieberwirth, I., Wegner, G. Macromolecules 2006, 39 2162-2171. 18. Scharber, M. C., Wuhlbacher, D., Koppe, M ., Denk, P., Waldauf, C., Heeger, A. J., Brabec, C. L. Adv. Mater. 2006, 18 789-794. 19. Li, G., Shrotriya, V., Huang, J. S., Yao, Y., Moriarty, T., Emery, K., Yang, Y. Nat. Mater. 2005, 4 864-868. 20. Thompson, B. C., Kim, Y.-G, Reynolds, J. R. Macromolecules 2005, 38 53595362. 21. (a) Yu, G., Gao, J., Hummelen, J. C., Wudl, F., Heeger, A. J. Science 1995, 270 1789-1791.; (b) Halls, J. J. M., Walsh, C. A., Greenham, N. C., Marseglia, E. A., Friend, R. H., Moratti, S. C., Holmes, A. B. Nature 1995, 376 498-500. 22. Bredas, J. L., Beljonne, D., Coropceanu, V., Cornil, J. Chem. Rev. 2004, 104 49715003. 23. Rowley, N. M., Mortimer, R. J., Science Progress 2002, 85 243-262. 24. Gaupp, C. L., Welsh, D. M., Rauh, R. D., Reynolds, J. R. Chem. Mater. 2002, 14 3964-3970. 25. Argun, A. A., Aubert, P. H., Thompson, B. C., Schwendeman, I., Gaupp, C. L., Hwang, J., Pinto, N. J., Tanner, D. B., MacDiarmid, A. G., Reynolds, J. R. Chem. Mater. 2004, 16 4401-4412.. 26. Roncali, J. Chemical Reviews 1997, 97 173-205.

PAGE 188

172 27. (a) Thomas, C.A. Donor-Acceptor Methods For Band Gap Reduction in Conjugated Polymers: The Role of Electron Rich Donor Heterocyles University of Florida, Ph. D. Dissertation, 2001; (b) Dubois, C. J., Donor-Acceptor Methods for Band Gap Control in Conjugated Polymers University of Florida, Ph. D. Dissertation, 2003.; (c) Thompson, B. C. Variable Band-Gap Poly(3,4Alkylenedioxythiophene)-Based Polymers for Photovoltaic and Electrochromic Applications University of Florida, Ph. D. Dissertation, 2005. 28. Lemaire, M., Garreau, R., Roncali, J., Delabouglise, D., Youssoufi, H. K., Garnier, F. New J. Chem. 1989, 13 863-871. 29. Bredas, J. L., Street, G. B., Themans, B., Andre, J. M. J. Chem. Phys. 1985, 83 1323-1329. 30. Kobayashi, N., Sasaki, S., Abe, M., Wa tanabe, S., Fukumoto, H., Yamamoto, T. Macromolecules 2004, 37 7986-7991. 31. (a) Morin, J. F., Leclerc, M., Ades, D., Siove, A. Macromol. Rapid Commun. 2005, 26 761-778; (b) Scherf, U., List, E. J. W. Adv. Mater. 2002, 14 477-487. 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) Chen, T. A., Wu, X. M., Rieke, R. D. J. Am. Chem. Soc. 1995, 117 233-244. 33. Mccullough, R. D., Tristramnagle, S., Willia ms, S. P., Lowe, R. D., Jayaraman, M. J. Am. Chem. Soc. 1993, 115 4910-4911. 34. Rughooputh, S. D. D. V., Hotta, S., Heeger, A. J., Wudl, F. J. Polym. Sci., Part B: Polym. Phys. 1987, 25 1071-1078. 35. Rodriguez-Parada, J. M. Duran, R. S., Wegner, G. Macromolecules 1989, 22 2507-2516. 36. (a) Prosa, T. J., Winokur, M. J., Mou lton, J, Smith, P., Heeger, A. J. Macromolecules 1992, 25 4364-4372; (b) Prosa, T. J., Winokur, M. J., Moulton, J., Smith, P., Heeger, A. J. Synth. Met. 1993, 55 370-377; (c) Prosa, T. J., Winokur, M. J., McCullough, R. D. Macromolecules 1996, 29 3654-3656. 37. Bao, Z. N., Lovinger, A. J. Chem. Mater. 1999, 11 2607-2612. 38. (a) Kraabel, B., Moses, D., Heeger, A. J. J. Chem. Phys. 1995, 103 5102-5108; (b) Beljonne, D., Shuai, Z., Pourtois, G., Bredas, J. L. J. Phys. Chem. A 2001, 105 3899-3907. 39. Andersson, M. R., Thomas, O., Mammo, W ., Svensson, M., Theander, M., Inganas, O. J. Mater. Chem. 1999, 9 1933-1940.

PAGE 189

173 40. Siddiqui, S., Spano, F. C. Chem. Phys. Lett. 1999, 308 99-105; Cornil, J., Beljonne, D., Calbert, J. P., Bredas, J. L. Adv. Mater. 2001, 13 1053-1067. 41. Kasha, M., Rawls, H. R., El-Bayoumi, M. A. Pure Appl. Chem. 1965, 11 371-92. 42. (a) Cornil, J., dos Santos, D. A., Crispin, X., Silbey, R., Bredas, J. L. J. Am. Chem. Soc. 1998, 120 1289-1299; (b) Bredas, J. L., Cornil, J., Beljonne, D., dos Santos, D., Shuai, Z. G. Acc. Chem. Res 1999, 32 267-276; (c) Cornil, J., dos Santos, D. A., Silbey, R., Bredas, J. L. Synthetic Metals 1999, 101 492-495. 43. Wurthner, F., Thalacker, C., Diele, S., Tschierske, C. Chem.-Eur. J. 2001, 7 22452253. 44. Zahn, S., Swager, T. M. Ang. Chem.Int. Ed. 2002, 41 4225-4230. 45. Pinto, M. R., Schanze, K. S. Synthesis-Stuttgart 2002, 1293-1309. 46. McCullough, R. D. Adv. Mater. 1998, 10 93-116. 47. (a) Hou, J. H., Huo, L. J., He C., Yang, C. H., Li, Y. F. Macromolecules 2006, 39 594-603; (b) Hiorns, R. C., Khoukh, A., Gourdet, B., Dagron-Lartigau, C. Polym. Int. 2006, 55 608-620; (c) Iovu, M. C., Jeffries-El, M., Sheina, E. E., Cooper, J. R., McCullough, R. D. Polymer 2005, 46 8582-8586; (d) Jeffries-El, M., Sauve, G., McCullough, R. D. Macromolecules 2005, 38 10346-10352; (e) Jeffries-El, M., Sauve, G., McCullough, R. D. Adv. Mater. 2004, 16 1017; (f) Mao, Y. X., Wang, Y., Lucht, B. L. J. Polym. Sci., Part A: Polym. Chem. 2004, 42 5538-5547; (g) Zhai, L., Pilston, R. L., Zaiger, K. L., Stokes, K. K., McCullough, R. D. Macromolecules 2003, 36 61-64; (h) Endo, T., Takeoka, Y., Rikukawa, M., Sanui, K. Synth. Met. 2003, 135 333-334; (i) Liu, J. S., McCullough, R. D. Macromolecules 2002, 35 9882-9889; (j) Loewe, R. S., Ewbank, P. C., Liu, J. S., Zhai, L., McCullough, R. D. Macromolecules 2001, 34 4324-4333; (k) Loewe, R. S., Khersonsky, S. M., McCullough, R. D. Adv. Mater. 1999, 11 250; (l) Liu, J. S., Loewe, R. S., McCullough, R. D. Macromolecules 1999, 32 5777-5785. 48. Sheina, E. E., Liu, J. S., Iovu, M. C., Laird, D. W., McCullough, R. D. Macromolecules 2004, 37 3526-3528. 49. Liu, J. S., Sheina, E., Kowalewski, T., McCullough, R. D. Ang. Chem.Int. Ed. 2002, 41 329-332. 50. Pisula, W., Tomovic, Z., Simpson, C., Kastler, M., Pakula, T., Mullen, K. Chem. Mater. 2005, 17 4296-4303. 51. Carbonnier, B., Egbe, D. A. M., Birckne r, E., Grummt, U. W., Pakula, T. Macromolecules 2005, 38 7546-7554.

PAGE 190

174 52. http://omlc.ogi.edu/spectra/P hotochemCAD/html/alpha.html Last accessed on 11/08/2006. 53. Palsson, L. O., Monkman, A. P. Adv. Mater. 2002, 14 757-758. 54. (a) Thompson, B. C., Schottland, P., Zong, K. W., Reynolds, J. R. Chem. Mater. 2000, 12 1563-1571.; (b) Billmeyer, F. Appl. Opt. 1969, 8, 737. 55. Uhlir, A. Bell System Technical Journal 1955, 34 105-128. 56. (a) Kirchmeyer, S., Reuter, K. J. Mater. Chem. 2005, 15 2077-2088; (b) Groenendaal, B. L., Jonas, F., Freitag, D., Pielartzik, H., Reynolds, J. R. Adv. Mater. 2000, 12 481-494. 57. (a) Turbiez, M., Frere, P., Allain, M., Vi delot, C., Ackermann, J., Roncali, J. Chem.-Eur. J. 2005, 11 3742-3752.; (b) Apperloo, J. J., Groenendaal, L., Verheyen, H., Jayakannan, M., Janssen, R. A. J., Dkhissi, A., Beljonne, D., Lazzaroni, R., Bredas, J. L. Chem.-Eur. J. 2002, 8 2384-2396. 58. Spencer, H. J., Skabara, P. J., Giles, M., McCulloch, L., Coles, S. J., Hursthouse, M. B. J. Mater. Chem. 2005, 15 4783-4792. 59. Daoust, G., Leclerc, M. Macromolecules 1991, 24 455-459. 60. Kumar, A., Reynolds, J. R. Macromolecules 1996, 29 7629-7630. 61. Aubert, P. H., Groenendaal, L., Louwet, F., Lutsen, L., Vanderzande, D., Zotti, G. Synth. Met. 2002, 126 193-198.. 62. Groenendaal, L., Zotti, G., Jonas, F. Synth. Met. 2001, 118 105-109. 63. (a) Welsh, D. M., Kloeppner, L. J., Madrig al, L., Pinto, M. R., Thompson, B. C., Schanze, K. S., Abboud, K. A., Powell, D., Reynolds, J. R. Macromolecules 2002, 35 6517-6525; (b) Reeves, B. D., Thompson, B. C., Abboud, K. A., Smart, B. E., Reynolds, J. R. Adv. Mater. 2002, 14 717; (c) Kumar, A., Welsh, D. M., Morvant, M. C., Piroux, F., Abboud, K. A., Reynolds, J. R. Chem. Mater. 1998, 10 896-902. 64. Gaupp, C. L., Welsh, D. M., Reynolds, J. R. Macromol. Rapid Commun. 2002, 23 885-889. 65. Joshi V. M., Bhide B. V., Sir Parashurambhau Coll. P. J. Indian Chem. Soc. 1960, 37 461-464 66. B. E. Love, E. G. Jones J. Org. Chem. 1999, 64 3755-3756.

PAGE 191

175 67. I. Schwendeman Optical and Transport Properties of Conjugated Polymers and their Application to Electrochromic Devices University of Florida, Ph. D. Dissertation, 2002. 68. Hofkens, J., Vosch, T., Maus, M., Kohn, F., Cotlet, M., Weil, T., Herrmann, A., Mullen, K., De Schryver, F. C. Chem. Phys. Lett. 2001, 333 255-263. 69. J. L. Bredas, J. Cornil, F. Meyers, D. Beljonne Handbook of Conducting Polymers (2nd Edition) 2000, p. 1-22. 70. Kasha, M. Discussions of the Faraday Society 1950, 14-19. 71. Perepichka, I. F., Perepichka, D. F., Meng, H., Wudl, F. Adv. Mater. 2005, 17 2281-2305. 72. Hill, M. G., Mann, K. R., Miller, L. L., Penneau, J. F. J. Am. Chem. Soc. 1992, 114 2728-2730. 73. Reeves, B. D. Processable Disubstituted Po ly(propylenedioxythiophenes) University of Florida, Ph. D. Dissertation, 2005. 74. Hoeben, F. J. M., Jonkheijm, P., Meijer, E. W., Schenning, A. P. H. J. Chem. Rev. 2005, 105 1491-1546. 75. Fasman, G. D. Circular dichroism and the conformational analysis of biomolecules; Plenum Press: New York, 1996. 76. http://www.enzim.hu/~szia/cddemo/edemo1.htm Last accessed on 11/13/06 77. Lighthner, D. A., Gurst J. E.. Organic Conformational Analysis and Stereochemistry from Circular Dichroism Spectroscopy ; Wiley-VCH; New York, 2000. 78. Oda, M., Nothofer, H. G., Lieser, G., Sche rf, U., Meskers, S. C. J., Neher, D. Adv. Mater. 2000, 12 362. 79. (a) Verbiest, T., Sioncke, S., Koeckelber ghs, G., Samyn, C., Persoons, A., Botek, E., Andre, J. M., Champagne, B. Chem. Phys. Lett. 2005, 404 112-115.; (b) Samyn, C., Verbiest, T., Persoons, A. Macromol. Rapid Commun. 2000, 21 1-15; (c) Ochiai, K., Rikukawa, M., Sanui, K., Ogata, N., Ueno, Y., Ema, K. Synth. Met. 1999, 101 84-85. 80. (a) Huang, J. X., Egan, V. M., Guo, H. L., Yoon, J. Y., Briseno, A. L., Rauda, I. E., Garrell, R. L., Knobler, C. M., Zhou, F. M., Kaner, R. B. Adv. Mater. 2003, 15 1158-1161; (b) Tigelaar, D. M., Lee, W., Bate s, K. A., Saprigin, A., Prigodin, V. N., Cao, X. L., Nafie, L. A ., Platz, M. S., Epstein, A. J. Chem. Mater. 2002, 14 1430-1438.

PAGE 192

176 81. Schwartz, B. J. Annu. Rev. Phys. Chem. 2003, 54 141-172. 82. Zahn, S., Swager, T. M. Ang. Chem.Int. Ed. 2002, 41 4225-4230. 83. (a) Satrijo, A., Meskers, S. C. J., Swager, T. M. J. Am. Chem. Soc. 2006, 128 9030-9031; (b) Satrijo, A., Swager, T. M. Macromolecules 2005, 38 4054-4057. 84. (a) Rughooputh, S. D. D. V., Hotta S., Heeger, A. J., Wudl, F. J. Polym. Sci., Part B: Polym. Phys. 1987, 25 1071-1078; (b) Faid, K., Frechette, M., Ranger, M., Mazerolle, L., Levesque, I., Leclerc, M., Chen, T. A., Rieke, R. D. Chem. Mater. 1995, 7 1390-1396. 85. Yue, S., Berry, G. C., McCullough, R. D. Macromolecules 1996, 29 933-939. 86. Apperloo, J. J., Janssen, R. A. J., Male nfant, P. R. L., Frechet, J. M. J. Macromolecules 2000, 33 7038-7043. 87. (a) Bouman, M. M., Havinga, E. E., Janssen, R. A. J., Meijer, E. W. Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 1994, 256 439-448; (b) Langeveld-Voss, B. M. W., Janssen, R. A. J., Meijer, E. W. J. Mol. Struct. 2000, 521 285-301. 88. (a) Hoppe, H., Glatzel, T., Niggemann, M., Schwinger, W., Schaeffler, F., Hinsch, A., Lux-Steiner, M. C., Sariciftci, N. S. Thin Solid Films 2006, 511-512 587-592; (b) Friend, R. H., Gymer, R. W., Holmes, A. B., Burroughes, J. H., Marks, R. N., Taliani, C., Bradley, D. D. C., Dos Santos, D. A., Bredas, J. L., Logdlund, M., Salaneck, W. R. Nature 1999, 397 121-128; (c) Sirringhau s, H., Tessler, N., Friend, R. H. Science 1998, 280 1741-1744; Kraft, A., Grimsdale, A. C., Holmes, A. B. Ang. Chem.Int. Ed. 1998, 37 402-428. 89. Oda, M., Nothofer, H. G., Scherf, U., S unjic, V., Richter, D., Regenstein, W., Neher, D. Macromolecules 2002, 35 6792-6798. 90. (a) Myers, A. G., Yang, B. H ., Chen, H., Gleason, J. L. J. Am. Chem. Soc. 1994, 116 9361-9362; (b) Myers, A. G., Yang, B. H ., Chen, H., McKinstry, L., Kopecky, D. J., Gleason, J. L. J. Am. Chem. Soc. 1997, 119 6496-6511; (c) Myers, A. G., Yang, B. H., Chen, H. Org. Synth. 2000, 77 29-44; Myers, A. G., Yang, B. H. Org. Synth. 2000, 77 22-28. 91. Knox, R. S. J. Phys. Chem. 1994, 98 7270-7273. 92. Langeveld-Voss, B. M. W., Christiaans, M. P. T., Janssen, R. A. J., Meijer, E. W. Macromolecules 1998, 31 6702-6704. 93. Schenning, A. P. H. J., Kilbinger, A. F. M ., Biscarini, F., Cavallini, M., Cooper, H. J., Derrick, P. J., Feast, W. J., Lazzaroni, R., Leclere, P., McDonell, L. A., Meijer, E. W., Meskers, S. C. J. J. Am. Chem. Soc. 2002, 124 1269-1275.

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177 94. Koeckelberghs, G., De Cremer, L., Vanorme lingen, W., Verbiest, T., Persoons, A., Samyn, C. Macromolecules 2005, 38 4545-4547. 95. Zhang, Z. B., Fujiki, M., Motonaga, M., McKenna, C. E. J. Am. Chem. Soc. 2003, 125 7878-7881. 96. Koeckelberghs, G., Vangheluwe, M., Sam yn, C., Persoons, A., Verbiest, T. Macromolecules 2005, 38 5554-5559. 97. (a) Tanase, C., Meijer, E. J., Blom P. W. M., de Leeuw, D. M. Phys. Rev. Lett. 2003, 91 216601/1-216601/4; (b) Kaneto, K. Thin Solid Films 2001, 393 249-258. 98. (a) Padinger, F., Rittberger, R. S., Sariciftci, N. S. Adv. Funct. Mater. 2003, 13 8588; (b) Yang, X. N., Loos, J., Veenstra, S. C., Verhees, W. J. H., Wienk, M. M., Kroon, J. M., Michels, M. A. J., Janssen, R. A. J. Nano Lett. 2005, 5 579-583 (c) Reyes-Reyes, M., Kim, K., Carroll, D. L. Appl. Phys. Lett. 2005, 87 083506/1083506/3; (d) Ma, W. L., Yang, C. Y., Gong, X., Lee, K., Heeger, A. J. Adv. Funct. Mater. 2005, 15 1617-1622. 99. (a) Argun, A. A., Cirpan, A., Reynolds, J.R. Adv. Mat. 2003, 15 1338-1341; (b) P. Andersson, P., Nilsson, D., Svensson, P. O., Chen, M. X., Malmstrom, A., Remonen, T., Kugler, T., Berggren, M. Adv. Mater. 2002, 14 1460. 100. Storsberg, J., Schollmeyer, D., Ritter, H. Chem. Lett. 2003, 32 140-141. 101. Roquet, S., Leriche, P., Perepichka, I., J ousselme, B., Levillain, E., Frere, P., Roncali, J. J. Mater. Chem. 2004, 14 1396-1400. 102. Perepichka, I. F., Roquet, S., Leriche, P ., Raimundo, J. M., Frere, P., Roncali, J. Chem.-Eur. J. 2006, 12 2960-2966. 103. Lagrost, C., Carrie, D., Vaultier, M., Hapiot, P. J. Phys. Chem. A 2003, 107 745752. 104. Reeves, B. D., Grenier, C. R. G., Argun, A. A., Cirpan, A., McCarley, T. D., Reynolds, J. R. Macromolecules 2004, 37 7559-7569. 105. Leclerc, M., Frechette, M., Bergeron, J. Y., Ranger, M., Levesque, I., Faid, K. Macromol. Chem. Phys. 1996, 197 2077-2087. 106. (a) DiCesare, N., Belletete, M., Durocher, G., Leclerc, M. Chem. Phys. Lett. 1997, 275 533-539; (b) Roux, C., Bergeron, J.-Y., Leclerc, M. Makromol. Chem. 1993, 194 869-877. 107. HOMO level was estimated using EHOMO= Eonset (vs. Fc/Fc+) + 4.8eV 108. Sotzing, G. A., Reynolds, J. R., Steel, P. J. Adv. Mater. 1997, 9 795-796.

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178 109. Samori, P., Francke, V., Mangel, T., Mullen, K., Rabe, J. P. Optical Materials 1998, 9 390-393. 110. (a) Samori, P., Francke, V., Mullen, K., Rabe, J. P. Thin Solid Films 1998, 336 1315; (b) Kim, D. H., Park, Y. D., Jang, Y., Kim, S., Cho, K. Macromol. Rapid Commun. 2005, 26 834-839; (c) Surin, M., Marsit zky, D., Grimsdale, A. C., Mullen, K., Lazzaroni, R., Leclere, P. Adv. Funct. Mater. 2004, 14 708-715; (d) Leclere, P., Surin, M., Jonkheijm, P., Henze, O., Schenning, A. P. H. J., Biscarini, F., Grimsdale, A. C., Feast, W. J., Me ijer, E. W., Mullen, K., Bredas, J. L., Lazzaroni, R. Eur. Polym. J. 2004, 40 885-892.

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179 BIOGRAPHICAL SKETCH Christophe Grenier was born in Lille, France, on November 10th, 1979. He spent his childhood in Nieppe until 1990 where he went to high school in Armentieres. In 1997, he graduated from high school and went on to attend his undergraduate studies in Lycee Faidherbe in Lille until 1999. He developed there a strong interest in organic chemistry and later joined l’Ecole Nationale Suprieu re de Chimie de Montpellier (ENSCM) until 2001. There, he progressively specialized in polymer chemistry until he was convinced by the international st udies center staff, along with Prof essor Bruno Amduri to spend his last undergraduate year in the Chemistry Depa rtment of the University of Florida. After receiving his undergraduate degree, he decide d to pursue his Ph.D. in organic chemistry at the University of Florida under the superv ision of Professor John Reynolds in the area of conjugated polymer synthesis. Upon graduation, he will head Eindhoven, The Netherlands, for a postdoctoral position under th e supervision of Prof essor “Bert” Meijer and Professor Albert Schenning.


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Title: Synthetic Control of Order in Soluble Dioxythiophene Polymers
Physical Description: Mixed Material
Copyright Date: 2008

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Table of Contents
    Title Page
        Page i
        Page ii
    Dedication
        Page iii
    Acknowledgement
        Page iv
        Page v
    Table of Contents
        Page vi
        Page vii
        Page viii
    List of Tables
        Page ix
    List of Figures
        Page x
        Page xi
        Page xii
        Page xiii
        Page xiv
    Abstract
        Page xv
        Page xvi
    Introduction
        Page 1
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    Experimental methods
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    Synthetic control of order in branched alkyl poly (3, 4-propylenedioxythiophenes) pproDOT-R2)
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    Synthetic control of order in branched alkoxymethyl poly (3, 4-propylenedixoythiophenes) (pproDOT-(CH2OR)2)
        Page 71
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    Chiral substituted poly (3, 4-propylenedioxythiophenes)
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    Soluble poly (3, 4-phenylenedioxythiophenes)
        Page 129
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    References
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    Biographical sketch
        Page 179
Full Text












SYNTHETIC CONTROL OF ORDER IN SOLUBLE DIOXYTHIOPHENE
POLYMERS














By

CHRISTOPHE R. G. GRENIER


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

Christophe R. G. Grenier

































To my family,















ACKNOWLEDGMENTS

I would like to first thank my advisor for his continuous guidance throughout the

five years, and a little extra of my Ph.D. studies in Florida. I believe this is a highly

challenging time for a young inexperienced researcher growing into a responsible

scientific leader, and that appropriate advice is the catalyst of this intellectual growth. In

this regard, Prof. John R. Reynolds has always provided the right balance of

encouragement, objective criticism, and patience. His insight and advice greatly helped

me perform the work discussed in this dissertation. I learned a lot from him. I extend

these thanks to my supervisory committee for their support and invaluable discussions:

Prof. William R. Dolbier, Prof. Anthony B. Brennan, Prof. Lisa McElwee-White and

Prof. Randy S. Duran.

I also owe thanks to Subi George and Prof. "Bert" Meijer whom I was lucky to

meet and collaborate with and who have offered me twice their generous hospitality at

the Technical University of Eindhoven, The Netherlands. In addition, I am thankful to

Dr. Wojciech Pisula, Nok Tsao and Prof. Klaus Mtillen from the Max-Planck Institute for

Polymer Science in Mainz, Germany, with whom I also had a very productive

collaboration and exciting scientific discussions.

I wish to thank my best friends in Gainesville for their unwavering friendship

throughout these five years. Without their support, I would have never made it through

these five years: Daniel Serra, Magdalena Swiderska, Emine Boz, Dalia Lopez Colon,

Dalianis, Guillermo Mathias, Avni Argun and Pierre-Henry Aubert. I am indebted to









them forever, and I hope to repay them some day, provided I learn how to cook or make

better coffee.

I have to thank those friends that have joined me numerous times for coffee break,

exercise, lunches and dinner: Ali Cirpan, Ece Unur, Thomas Joncheray, Rachid Matmour,

Emilie Galand, Geoffroy and Delphine Sommen, Aleksa Jovanovic, Prof. Pierre

Audebert, Dr. Mohammed Bouguettaya and Benoit Lauly.

I would like to also thank people that have greatly helped me scientifically, helped

improve my English writing proficiency and with whom I always had interesting

conversations: Genay Jones (I will always remember a 3am drive to Waffle House),

Aubrey Dyer, Benjamin Reeves (a great mentor to me and a very wise man), Barry

Thompson (who has set an unreachable standard for hard-work and scientific excellence),

and Nisha Ananthakrishnan, Jeremiah Mwaura, Robert Brookins and Tim Steckler. In

addition, special thanks go to Lorraine Williams, Sara Klossner, Tasha Simmons and

Gena Borrero for doing all the "little things" without which I could not have had anything

done.

I also thank my family, especially my parents, for supporting me during this long

time so far away from their home. I know it was a difficult and painful sacrifice for them.

Finally, I want to offer special thoughts to two of my greatest friends departed

during the course of my Ph.D. studies: Jean-Baptiste Andrault and Landry Bourely. I

miss them both dearly.
















TABLE OF CONTENTS



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

LIST OF TABLES ..................................................... ix

L IST O F FIG U RE S .............. ......................... ........................... ....................... .. .. .... .x

ABSTRACT ................................................................................ xv

CHAPTER

1 IN TR O D U C T IO N ........ .. ......................................... ..........................................1.

1.1. Introduction to Conjugated Polym ers............................................... ...............1...
1.2. Electronic Properties of Conjugated Polymers ................................................2...
1.3. Doping-induced Properties of Conjugated Polymers ......................................5...
1.3.1. C hem ical D oping ....................................... .. ..................... .. ........... ... 6
1.3.2. Electrochem ical D oping ................ .......... ..... ...............6...
1.3.3. Fluorescence and Photochemical Charge Transfer .................................... 8
1.3.4. Interfacial D oping................................................................................. 8
1.4. Improving Active Material Performance ................ .................................... 10
1 .4 .1 O F E T s........................................................................................................ 10
1.4.2. Photovoltaic A application ............................................. ..... ............... 11
1.4.3. Polymer Electroluminescent Diodes (PLEDs) ....................................13
1.4.4. Electrochrom ic D evices.................. .................................................. 15
1.5. Synthetic Control in Conjugated Polym ers .................................... ................ 16
1.5.1. Substituent Effects ..................................... .. ........ ............ .. ........ .... 17
1.5.2. Intrachain Interactions ....................... ............................................... 17
1.5.3. Interchain Interactions ....................... ............................................... 20
1.6. Tow ards Soluble Conjugated Polym ers.......................................... ................ 24

2 EXPERIMENTAL METHODS .........................................................29

2.1. G general Synthetic M ethods............................................................. ................ 29
2.2. M molecular Characterization ......................................................... 29
2.3. Electrochem ical Characterization.................................................... 30
2.4. P olym er C haracterization ...................................... ...................... .................. 3 1
2.4.1. Structural Characterization....................................................... 31
2.4.2. Therm al Characterization ....................... ............................................. 31









2.4.3. Morphology Characterization.....................................................32
2.4.4. Solution O ptical Characterization ........................................ ................ 32
2.4.5. Solution Processing Techniques........................................... ................ 33
2.4.5. 1. D rop-casting ..................................... .. ........ .... ........ .. ............ 34
2.4.5.2. Spin-coating ..................................... .. .......... .......... .. ........ .... 34
2.4.5.3. Spray-coating ................................................. ........ .............. ... 35
2.4.6. Film Fluorescence Characterization.....................................................36
2.4.7. Spectroelectrochemical Characterization.............................................36
2 .4 .8. C ircular D ichroism ...................................... ...................... ................ 40
2.4.9. Conductivity M easurem ents................................................. ................ 40

3 SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKYL POLY(3,4-
PROPYLENEDIOXYTHIOPHENES) (PProDOT-R2).......................................43

3 .1 In tro d u ctio n .......................................................................................................... 4 3
3.2. Electropolymerized PProDOT-R2 ................................................................. 47
3.2.1. Electropolymerizable Monomer Synthesis...........................................47
3.2.2. Electrodeposition and Electrochemistry ...............................................48
3.3. Chemically Polymerized Soluble PProDOT-R2 .............................................51
3.3.1. Synthesis and Polymer Characterization..............................................51
3 .3 .2 S olu tion P rop erties .................................................................. ............... 53
3.3.3. Optoelectronic Properties of Solution Processed Films .........................56
3.3.4. Conductivity Measurements.....................................................61
3.4. High Performance Electrochromic Devices ..................................................62
3 .5 C o n clu sio n ........................................................................................................... 6 3
3.6. C chapter Synthetic D details ...................................... ...................... ................ 64

4 SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKOXYMETHYL
POLY(3,4-PROPYLENEDIOXYTHIOPHENES) (PPRODOT-(CH20R)2) .......... 71

4 .1 In tro d u ctio n .......................................................................................................... 7 1
4.2. Electropolymerized PProDOT-(CH2OR)2 ..................................................... 72
4.2.1. Electropolymerizable Monomer Synthesis...........................................72
4.2.2. Electrodeposition and Electrochemistry ......................... ..................... 73
4.3. Chemically Polymerized Soluble PProDOT-(CH2OR)2................................75
4.3.1. Synthesis and Polymer Characterization ........................ ..................... 75
4 .3 .2 S olu tion p rop erties................................................................... ............... 7 6
4.3.3. Optoelectronic Properties of Solution Processed Films .........................78
4.3.4. C onductivity M easurem ent .................................................. ................ 82
4.4. High Performance Electrochromic Devices ..................................................83
4 .5 C o n clu sio n ............................................................................................................ 8 5
4.6. C chapter Synthetic D details ...................................... ...................... ................ 85

5 CHIRAL SUBSTITUTED POLY(3,4-PROPYLENEDIOXYTHIOPHENES) ........ 90

5 .1 In tro d u ctio n .......................................................................................................... 9 0
5.1.1. C D Spectroscopy .... .. ... .............. .............................................. 90









5.1.2. Applications of Chiral Polymers and CD Spectroscopy ........................93
5.1.3. Thermochromism/Solvatochromism in Chiral Substituted Polymers....... 93
5.1.3. Chiral Substituted PProD O Ts..................................................... 95
5.2. Synthesis of PProDOT-Based Chiral Polymers .............................................96
5.2.1 N ew Chiral R agents Synthesis.......................................... ................... 96
5.2.2 Electrochemically Polymerizable Monomer and Electrodeposition ..........97
5.3. Chiral Ordering in Chiral PProDOTs ........................................................... 100
5.3.1. Optical Properties in "Good" Solvent Solutions ............................... 100
5.3.2. Solvatochromism Effects in PProDOTs Solutions............................... 102
5.3.3. Thermochromism in PProDOTs Aggregated Solutions........................105
5.3.4. Chiral Order in Spray-cast Film s ....................................... ............... 110
5.4 C onclu sion ......................................................................................................... 114
5.5. G general Synthetic D details ......................................................... 115

6 SOLUBLE POLY(3,4-PHENYLENEDIOXYTHIOPHENES)............................ 129

6 .1 In tro d u ctio n ........................................................................................................ 12 9
6.2 Synthesis of Soluble Substituted PheDOT .......... ....................................131
6.3. Electropolymerization of Substituted PheDOTs .................... ...................132
6.3.1. Electrodeposition and Electronic Properties ......................................132
6.3.2. Spectroelectrochemical Characterization of Electrodeposited Films......135
6.4 Synthesis of Soluble Substituted PPheDOT............................................. 137
6.5 Solutions P properties ................................................. ........ ........... .............. 139
6.6. PPheDOT(C12)2: A Soluble, Ordered Polymer...... ................. ...................141
6.7. PPheDOTC12EtHx: a Disordered Polymer...... .......................................148
6 .8 C o n clu sio n ......................................................................................................... 15 1
6.9. C losing Statem ents .............. .... .............. .............................................. 152
6.10. Synthetic D details ................................................................................. 155

LIST O F R EFEREN CE S .. .................................................................... ............... 170

BIOGRAPH ICAL SKETCH .................. .............................................................. 179















LIST OF TABLES


Table page

3-1. ProDOT-R2 monomer oxidation onset and peak potentials ..................................48

3-2. Molecular weight analysis of GriM polymerized PProDOT-R2 ..............................52

3-3. Optical properties of alkyl substituted PProDOTs in toluene solution ...................55

3-4. Solution, cast films and electrochemically oxidized and reneutralized films
absorption properties .............. .... .............. ................................................ 58

3-5. Coloration Efficiency study on PProDOT-R2 spray-coated films...........................60

3-6. Conductivity measurements on spray-coated films gas phase doped with iodine .....61

4-1. Comparison of alkyl and alkoxymethyl substituted PProDOTs polymer oxidation. .75

4-2. Molecular weight analysis of GriM polymerized PProDOT-(CH20R)2............... 76

4-3. Optical properties of alkoxymethyl substituted PProDOTs in toluene solution ........77

4-4. Optical properties of PProDOT(CH20-2-alkyloxymethyl)2 polymers in solution,
spray-coated films before and after electrochemical switching..............................79

4-5. Coloration Efficiency of PProDOT-(CH20R)2 films sprayed on ITO-coated glass
slid e s ...................................................................................................... ......... 8 1

4-6. Conductivity measurement for PProDOT(CH2OR)2 spray-coated films ................82

5-1. GPC data for chiral substituted PProD OTs........................................... ................ 99

5-2. Comparison of chiral and racemic PProDOTs polymers. .............. ...................100

6-1. Electrochemical properties of substituted PheDOTs electropolymerizable
monomers and electrodeposited disubstituted PPheDOTs films .........................133

6-2. Optical properties of electrodeposited films onto ITO-coated glass slides............136

6-3. GPC data for PPheDOTC12EtHx and PPheDOT(C12)2. ................ ...... .............138















LIST OF FIGURES


Figure page

1-1. Evolution of published work on conducting polymers...........................................1...

1-2. Representative structures of conducting polymers.................................................2...

1-3. D oping in poly(acetylene) ................................................................... ...............4...

1-4. The two non-degenerate forms of poly(p-phenylene): aromatic, left and quinoidal,
rig h t. ........................................................................................................ ......... .. 4

1-5. Spectroelectrochemistry of PProDOT-Me2 as a function of applied potential.............5

1-6. Chemical p-doping by iodine (reversible) and nitrosonium hexafluorophosphate
(irreversible) in the case of polythiophene............................................ ...............6...

1-7. Schem atic representation of a LEC device.............................................. ...............7...

1-8. Schem atic diagram of a thin film transistor............................................. ...............9...

1-9. Representative luminescence colors of some conjugated polymers........................ 13

1-10. Effect of structural regularity on poly(3-octylthiophene) chain conformation ........19

1-11. Color tuning of film luminescence though intrachain twisting ..............................20

1-12. Fluorescence quantum yield dependence on substituents bulk..............................22

1-13. D avydov splitting in interchain aggregates ......................................... ................ 23

1-14. Polymerization method leading to regioregular Poly(3-alkylthiophene)s .............26

1-15. Proposed chain growth mechanism for Grignard Metathesis polymerization ......... 27

2-1. Three electrodes (Pt button, large Pt foil counter, Ag wire reference)
electrochem ical setup ....................... .. ....................... .................................. 30

2-2. Spray-coated films of PProDOT-(CH20(2-ethylhexyl))2 and PProDOT-
(C H 20 C 18H 37)2. ........................................................................................................ 3 6









2-3. Time evolution of transmittance and injected charge for an electropolymerized
fi lm of PP roD O T -M e2 ........................................................................... .................. 39

2-4. Four-point probe conductivity m ethod ................................................. ................ 40

2-5. Four-point conductivity m easurem ent................................................... ................ 42

3-1. Conformational and substituents effects on 3,4-ethylenedioxythiophenes .............44

3-2. Two m ost stable conform nations of ProD OT.......................................... ................ 46

3-3. Fam ily of branched dialkyl PProD O Ts ................................................. ................ 47

3-4. Synthesis of electropolymerizable alkyl substituted ProDOTs..............................48

3-5. Electrodeposition of PProDOT-(2-ethylhexyl)2 on platinum button electrode..........49

3-6. Polymer oxidation in the PProDOT-R2 series ....................................... ................ 50

3-7. Grignard Metathesis polymerization of soluble PProDOT-R2..............................51

3-8. Evolution of UV-Vis absorption spectrum with molecular weight for PProDOT(2-
eth y lh ex y l)2 .............................................................................................................. 5 2

3-9. Absorption and photoluminescence spectrum of PProDOT-Hexyl2 and
P P roD O T (2-ethylhexyl)2.......................................... ........................ ................ 53

3-10. Evolution of absorption spectrum with increasing distortion between the ground
state and the excited state ........................................ ........................ ................ 54

3-11. Doping/Casting induced rearrangement in linear vs. branched alkyl substituted
P P ro D O T s ................................................................................................................ 5 7

3-12. X-ray crystal structure of BisProDOT-Et2 showing that a mixture of chair and
tw isted conform nations are present....................................................... ................ 58

3-13. Spectroelectrochemistry experiment for PProDOT-Hx2 (left) and PProDOT-(2-
ethylhexyl)2 (right). .......................... ....................... .................................... 59

3-14. Lum finance change with applied potential........................................... ................ 60

3-15. Schematic representation of a reflective/absorptive EC device using spray-
coated PProDOT(CH20-2-ethylhexyl)2 as the active and storage layer...............62

3-16. Reflectance plot for a reflective/absorptive EC device using spray-coated
PProDOT(CH20-2-ethylhexyl)2 as the active and storage layer. ..........................63

4-1. Family of branched dialkoxymethyl substituted PProDOTs.................................72









4-2. Synthesis of electropolymerizable alkoxymethyl substituted ProDOTs.................73

4-3. Electrodeposition of PProDOT(CH20-2-ethylhexyl)2 on Pt Button.......................73

4-4. Polymer oxidation in the PProDOT-(CH20R)2 series...........................................74

4-5. Polymerization of PProDOT-(CH20R)2 by Grignard Metathesis...........................75

4-6. Absorption and photoluminescence spectrum of PProDOT(CH20-2-methylbutyl)2
and PProD O T(CH 20 -2-ethylhexyl)2................................................... ................ 76

4-7. Doping/Casting induced rearrangement in linear vs. branched alkyl substituted
P P ro D O T s ................................................................................................................ 7 8

4-8. Spectroelectrochemistry experiment for PProDOT-(CH20-2-ethylhexyl)2 (left)
and PProD O T-(CH 2O C 18H 37)2 (right)................................................. ................ 80

4-9. Luminance change vs. applied potential in PProDOT(CH20R)2 polymers ............81

4-10. Electrochemical device using spray-coated PProDOT(CH202-ethylhexyl)2 as the
anodically coloring polymer and Poly(BisEDOT-N-methylcarbazole)
electropolymerized film as the cathodically coloring polymer...............................83

4-11. Luminance plot of a dual-window EC device using spray-coated
PProDOT((CH20-2-ethylhexyl)2) as the anodically coloring polymer and
electrolpolymerized Poly(BisEDOT-N-methylcarbazole) as the anodically
coloring g p oly m er ...................................................................................................... 84

5-1. C D spectroscopy principle.......................................... ........................ ................ 9 1

5-2. CD signal of exciton-coupled chromophores with varying chromophores
arran g em en t .............................................................................................................. 9 2

5-3. Cholesteric packing in aggregated chiral poly(thiophenes) .................................95

5-4. New soluble Chiral PProDOTs polymers obtained by Grignard Metathesis .............96

5-5. Synthesis of 2S-ethylhexyl substituents using a pseudoephedrine chiral auxiliary ...97

5-6. Cyclic voltammetry of electrodeposited PProDOT((2S)-methylbutyl)2 and
PProD O T((2S)m ethylbutyl)2 ............................................................... ................ 98

5-7. Comparison of PProDOT-((2S)methylbutyl)2 and PProDOT-((2S)methylbutyl)2
spectroelectrochem istry ........................................... ......................... ................ 99

5-8. Temperature dependence of PProDOT(CH20-2S-methylbutyl)2 in xylenes
so lu tio n ............................................................................................................. .. 1 0 1

5-9. Thermochromism of PProDOT((2S)-methylbutyl)2 in xylenes solution ...............102









5-10. Optical properties of PProDOT((2S)-methylbutyl)2 solutions in Xylenes/DMF
m fixtures (C= 8.6x 10-6M ) ......................................................... 104

5-11. Thermochromism of PProDOT((2S)ethylhexyl)2 in xylenes/DMF mixtures .......106

5-12. Fluorescence thermochromism of 50/50 xylenes/DMF
PProDOT((2S)methylbutyl)2 and PProDOT((2S)ethylhexyl)2 ........................... 107

5-13. UV-Vis absorption of a 50/50 xylenes/DMF aggregated solution at 95C ............108

5-14. Evolution of absorption spectrum of 40/60 and 50/50 xylenes/DMF PProDOT-
((2S)ethylhexyl)2 solution following heating/slow cooling cycle....................... 109

5-15. Polymer optical properties evolution during heating/slow cooling cycle.
PProDOT(2S)-ethylhexyl)2 50/50 xylenes/DMF ........................ ...................110

5-16. Absorption and CD signal for PProDOT-((2S)-ethylhexyl)2) spray-coated films .112

5-17. CD signal of chiral PProDOT(CH20-2-methyl)2 spray-cast films.......................114

6-1. X-ray crystal structure of PheDOTBr2 .........................................130

6-2. Family of Soluble Substituted PPheDOTs under study................. ...................131

6-3. Synthesis of mono- and disubstituted PheDOTs....... .................. ..................1... 32

6-4. Electrodeposition and electrochemistry of substituted PPheDOTs films...............134

6-5. PheDOT(C12)2 oxidation at various scan rates .............................. ..................... 134

6-6. Synthesis of PPheDOT(C12)2 by Grignard Metathesis.................................... 137

6-7. Solution optical properties of monosubstituted PPheDOTs...............................137

6-8. Solution thermochromism of Poly[PheDOT-(C12)2] in xylenes.......................... 140

6-9. Absorption and Emission spectrum of PPheDOTC12EtHx. Sample excited at
5 5 0 n m ................................................................................................................. .... 1 4 0

6-10. Cyclic voltammetry of disubstituted PPheDOT(C12)2 in 0.1M TBAP in ACN at a
scan rate of 50m V /s ....... ............................................................... .. ......... 14 1

6-11. Spectroelectrochemistry of soluble disubstituted PPheDOT(C12)2 film on ITO-
coated glass slides .............. ................... ............................................... 142

6-12. Self-assembly of PPheDOT(C12)2 polymer chains in films spin-coated on mica
from a hot ODCB solution (C= 0.2 mg mL-1)....... ................... ................... 143









6-13. AFM picture (5x 5[am2) of PPheDOT-(C12)2 spin-coated on mica from ODCB
solution at room temperature (C= 0.2 mg mL-1)....................... ................... 144

6-14. DSC (2nd scan) of PPheDOT-(C12)2 ....... ... .......................... 145

6-15. Ordering in mechanically aligned PPheDOT(C12)2 fibers................................. 146

6-16. 2D-WAXS pattern of PPheDOT-(C12)2 at 150 C .... ....................147

6-17. 2D-WAXS analysis of higher molecular weight PPheDOT(C12)2 fraction..........148

6-18. Absorption spectrum ofPPheDOTC12EtHx: in xylenes solution, film spray-cast
from toluene, film spray-cast after electrochemical doping and reneutralization.. 149

6-19. Electrochemistry and spectroelectrochemistry of PPheDOTC12EtHx cast films... 150

6-20. D SC (2nd scan) of PPheD O TC 12EtH x. .................................................................151















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

SYNTHETIC CONTROL OF ORDER IN DIOXYTHIOPHENE POLYMERS

By

Christophe R. G. Grenier

December 2006

Chair: John R. Reynolds
Major Department: Chemistry

The synthesis of electron-rich, highly soluble and processable conjugated

poly(3,4-propylenedioxythiophenes) (PProDOTs) is developed. The polymers are

substituted with side chains carefully chosen to obtain high solubility while controlling

the polymers' physical, optical and electronic properties necessary for the targeted

applications. The polymers have been applied to device platforms that probe

electrochromism, light-emission and charge-carrier mobilities.

A synthetic methodology to prepare disubstituted

poly(3,4-propylenedioxythiophenes) having branched alkyl and alkoxymethyl

substituents for electrochromic applications is described The branched polymers display

significantly higher solubility than their linear analogs and are easily processed by spin-

coating or spray-casting. The polymers have high electrochromic contrasts, subsecond

switching times, and high coloration efficiencies, allowing them to be successfully

applied to the construction of highly efficient and fast switching electrochromic devices.









Using enantiomerically pure reagents, chiral alkyl and alkoxymethyl PProDOTs

were synthesized. Since few enantiomerically pure reagents are commercially available,

an easy, efficient and versatile synthesis was developed to yield new, original chiral

polymers. Introduction of side chain chirality allows control of the ordering of the

polymer chains, with formation of cholesteric aggregates in poor solvents and the solid

state. Solvatochromism and thermochromism experiments coupled with circular

dichroism (CD), along with fluorescence and absorption spectroscopy, yield important

information on the morphology and self-assembly of the polymer chains from solution to

the solid state.

The first synthesis of soluble poly(3,4-phenylenedioxythiophenes) (PPheDOTs) is

described. Solubility was induced by introducing substituents at the 4 and 5 positions of

the veratrole moiety. Monosubstituted PPheDOTs were found to be poorly soluble, but

could be obtained by electrodeposition. On the other hand, disubstituted PPheDOT

polymers are soluble. Symmetrically dodecyl substituted PPheDOT(C12)2, soluble above

800C in aromatic and chlorinated solvents, shows a high degree of order in the solid state

and is a promising candidate for high mobility and high conductivity applications.

Asymmetric, disordered PPheDOT(C12)EtHx is soluble at room temperature in most

organic solvents. The polymer shows solid state fluorescence and is a promising

candidate for light-emitting applications.

















CHAPTER 1
INTRODUCTION

1.1. Introduction to Conjugated Polymers

Following the exciting discovery in 1977 of high conductivity in chemically doped

polyacetylene, the conjugated polymers (CP) research field has developed exponentially

(Figure 1.1). As a result, many other CPs with diverse chemical structures have been

investigated. Their exceptional physical, electronic and optical properties have been well

characterized and a deep understanding of their incredible properties is now available. In

2000, the importance of the discovery and development of conducting polymers was

recognized when the Chemistry Nobel Prize was awarded to Alan Heeger, Hideki

Shirakawa and Alan MacDiarmid.


3000-

2500 -

> 2000- /

150 0
0 First report on high conductivity n
in doped Polyacetylene /
1000- a

E 500 -

0-

1960 1970 1980 1990 2000 2010
Year



Figure 1-1. Evolution of published work on conducting polymers









As Heeger described, conjugated polymers (often called conducting polymers)

"offer a unique combination of properties not available from any other materials."1 Of

special interest is the ability to finely tune their properties through synthetic changes,

both at the monomer and polymer level. This enables the use of conducting polymers in

many applications such as photovoltaic devices (PVs), electrochromic devices (ECDs),

organic field-effect transistors (OFETs), and light-emitting diodes (LEDs). Their

performance has improved dramatically leading to their increasing use in commercial

applications.

1.2. Electronic Properties of Conjugated Polymers

On a basic level, conjugated polymers are a continuous array of overlapping 7t-

orbitals supported by c-bond backbone. As long as this array is present, many different

backbones can be used. Examples of commonly used 7t-conjugated polymer structures are

given in Figure 1-2.





00 0

n S
n n n H n
0 trans-PA PEDOT P3HT PPy
MEH-PPV

Figure 1-2. Representative structures of conducting polymers. The polymers represented
are some of the most used and best performing materials.

To understand the properties of conducting polymers, I will describe polyacetylene.

Going from ethylene to 1,3-butadiene, the overall energy of the molecule is stabilized by

overlap between the two double bonds. The HOMO is raised, and the LUMO is lowered

leading to a smaller HOMO-LUMO gap. By increasing the number of overlapping

double bonds, the number of energy levels (occupied and unoccupied) increases, and the









HOMO-LUMO gap is compressed further. As the degree of conjugation grows large, the

multiple electronic states are better described by continuous bands. This simple approach

can be applied to most conjugated polymers. Complete theoretical calculations giving

more precise results have been performed for many conjugated polymers.2

Theoretically, if the number of overlapping orbitals becomes infinite, then the

band gap is expected to disappear. However, this is not observed due to Peierls distortion.

Peierls distortion arises from the interaction between electronic and vibrational states, not

taken into account in Huickel theory. This interaction induces the formation of alternating

long and short bonds with single and double bond character, and the creation of a band

gap.3 Many other interactions participate in determining the bandgap in conjugated

polymers, and will be discussed later. By analogy to inorganic materials, conjugated

polymers with typical bandgaps between 1 and 3 eV are semiconducting materials with a

conduction band and a valence band.

Poly(acetylene) is a well understood polymer with a degenerate ground state.4 Two

resonance forms of equal energy exist differing only by the order of the single and double

bonds (Figure 1-3A).5 One can switch between phase A and phase B by introducing a

radical defect within the chains (Figure 1-3B).This radical defect, called a soliton, is

localized over several carbons and has an energy level at mid-gap, occupied by one

electron. The electron in the intragap state can be removed to create a positively charged

soliton (p-doping), or another electron can be added to create a negatively charged soliton

(n-doping) (Figure 1-3C).









A) C) E E
A) "^ Phase A )E I E
p-doping n-doping
t 1H + -w-

/s M Phase B

Positive Neutral Negative
Soliton Soliton Soliton
B)

Phase A Soliton Phase B


Figure 1-3. Doping in poly(acetylene). (A) The two degenerate forms of poly(acetylene);
(B) Self-localized neutral soliton defect in poly(acetylene); (C) p-doping and
n-doping in poly(acetylene).

For polymers with a non-degenerate ground state, the picture is slightly different.

Two resonance forms exist as in polyacetylene, but with different energies: the most

stable is the benzenoid form and the less stable is the quinoid form, (Figure 1-4). Upon

doping, either a radical-cation pair, or a radical-anion pair is created. These defects are

called polarons and are responsible for conductivity observed at low doping levels. Upon

further doping, a second electron can be removed, and a dicationic species is formed,

called a bipolaron. At high doping levels, bipolarons are the charge carriers responsible

for conductivity. At a hypothetical doping level of 100% (one dopant ion per repeat unit),

Bredas et al. have calculated that the intragap states merge with the valence or conduction

band giving metallic behavior.6



n n

Figure 1-4. The two non-degenerate forms of poly(p-phenylene): aromatic, left and
quinoidal, right.










Polarons and bipolarons have specific optical signature. Polaron charge carriers

have two characteristic absorptions in the near-IR region, as shown in Figure 1-5 for

poly(3,4-(2,2-dimethylpropylene)dioxythiophene) (PProDOT-Me2), a p-dopable

polymer. The first transition corresponds to the transition from the top of the valence

band to the single occupied lower intragap state. The second transition is the near-IR

transition from the lower intragap state to the higher intragap state. When the chains are

oxidized to the bipolaron state, the lower energy intragap state is depleted of its electron,

and only the first transition is seen. For degenerate ground state poly(acetylene), only one

transition with an onset near half the energy of the bandgap is seen due to solitons, not

polarons charge carriers.


20-- Conduction Band Conducton Band Conduction Band
20- I----

Ov V3
10- Valence Band Valence Band Valence Band

05- 1

00 1 V a n
400 600 800 1000 1200 1400 1600 1800
Energy (eV)
Neutral Polaron Bipolaron

Figure 1-5. Spectroelectrochemistry of PProDOT-Me2 as a function of applied potential
between -1 V and IV vs. Ag wire in 0.1 M TBAP/ACN. Energy levels,
electronic transitions for the neutral and organic structures of polaron, and
bipolaron forms of PProDOT-Me2 with the organic structures are also
depicted.

1.3. Doping-induced Properties of Conjugated Polymers

The conjugated polymers can be used in many applications. These applications

depend on the mechanism by which the doping is achieved. In this section, I will describe









the different doping mechanisms and introduce applications derived from them. I will not

describe the applications in detail but only their working principle.

1.3.1. Chemical Doping

Conjugated polymers can be doped by electron transfer to or from chemical

species. Some examples are 12, and NOPF6 (p-doping), along with Na-naphthalide, and Li

(n-doping). Figure 1-6 shows the reversible oxidation of polythiophene by iodine, as well

as the irreversible oxidation by NOPF6. In this case, doping charges are compensated by

species derived from the oxidizing/reducing agent.


(T)n + 3/2 ny 12 1 [(T)+(13 )y n


2(T)n + 2 ny NOPF6 A [(T)+Y(PF6-)yn + nyN202

Figure 1-6. Chemical p-doping by iodine (reversible) and nitrosonium
hexafluorophosphate (irreversible) in the case of polythiophene; n refers to the
number of repeat units.

Upon careful choice of the dopant ion, high conductivity can be achieved leading to

applications of conjugated polymers as anti-static coatings, hole-injecting layers, hole-

transport layers and conductive fibers. Because charges with corresponding counterions

are introduced during doping, solubility and processability in polar solvent can be

obtained. For example, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with bulky

poly(styrenesulfonate) (PEDOT:PSS) forms aqueous dispersions in water which can be

processed into highly conductive films.8

1.3.2. Electrochemical Doping

If a conducting polymer is deposited onto an electrode, and a potential is applied to

the electrode, electrons can be added or removed depending on the magnitude of the










potential applied. The polymer is then positively or negatively charged. These charges are

compensated by counterions dopantt ions) diffusing into the polymer from the electrolyte

solution. If the doped and neutral states are stable, then the electrochemical

doping/dedoping is reversible and the polymers are electroactive. For many conjugated

polymers, the electrochemical oxidation/reduction processes cause a change of optical

absorption and, if the changes occur in the visible range, a change of color. This

phenomenon is called electrochromism. This property can be used in applications such as

electrochromic devices (ECDs), "smart" windows, and absorptive/reflective devices.9'10

In the case of light-emitting electrochemical cells (LEC), a blend of an emitting

conjugated polymer with an ion-transport polymer and an electrolyte salt (for example,

MEH-PPV, PEO and lithium trifluoromethanesulfonate) is sandwiched between two

metal electrodes (Figure 1-7).11

A) B) AV C) V
Metal













PEO
+ligit-emitting polymer
+ electrolyte salt
Figure 1-7. Schematic representation of a LEC device. A) LEC device with no voltage
applied; B) LEC device shortly after application of a voltage bias showing
electrochemical doping at the interfaces; C) LEC device after diffusion of the
charge carrier in the material bulk and recombination, leading to light-
emission.









When a sufficient voltage is applied to the polymer, holes and electrons are injected

at the cathode and anode creating p-type and n-type charge carriers, which are

compensated by counterions from the solid electrolyte. A front of charge carriers moves

from each electrode to the center under the influence of the electric field applied between

the electrodes. Eventually, the hole and electron recombine, forming an excimer which

relaxes to the ground state by emission of light (Figure 1-7C).

1.3.3. Fluorescence and Photochemical Charge Transfer

When light is absorbed by a conjugated polymer, an electron is promoted from the

valence band to the conduction band. Normally, these excited states would recombine

and return to the ground state yielding their excess energy by fluorescence,

phosphorescence or non-radiative decay. Another process is energy transfer to an

acceptor. If an electric field is applied, or if an electron-accepting or electron-donating

species (with appropriate HOMO and LUMO levels) is nearby, then charge separation of

the two charge carriers may also occur. This is the general idea behind photovoltaic

devices, where the sunlight energy is collected and converted into electrical power. A

complete literature review on photovoltaics was recently written in the Reynolds
27c
group.

1.3.4. Interfacial Doping

Interfacial doping is similar to electrochemical charge injection, but lacks charges

compensation by electrolyte. This is seen in organic field-effect transistors. As shown in

Figure 1-7, a typical OFET is made of two electrodes (source and drain) separated from a

third electrode (the gate) by a semiconducting layer coated on dielectric material. When a

voltage is applied at the gate, the dielectric material behaves like a capacitor and charges

build at the gate electrode. Opposite charges build at the conjugated polymer/dielectric









material interface. Figure 1-8 shows the example of a p-dopable material. As p-doped

sites appear, current flows from the source to the drain. As the gate voltage is increased,

the current rises as the number of charge carriers increase.

e-
CP


VGate= OV VGate> OV

Figure 1-8. Schematic diagram of a thin film transistor. The semi-conducting material is a
p-dopable material.

Since current is directly proportional to the charge mobility of the material, the

thin film transistor configuration can be used to measure hole or electron mobilities. An

important point is that other methods can be used to measure mobilities, yielding

different values due to their different configurations. 12 These methods include hole-only

devices or time-of-flight measurements. In hole-only devices, the p-dopable semi-

conducting material is sandwiched between two electrodes. At the cathode, a low work

function metal creates a large barrier for electron injection. The result is that the mobile

charges circulating in the device are only holes, not electrons. Another essential

difference is that the two electrode configurations probe the bulk material, whereas the

gate-source-drain configuration probes only the mobility of a thin layer at the dielectric-

semiconductor interface. Therefore, one must consider carefully how the mobilities were

obtained when comparing mobility values.

In organic light-emitting diodes (OLEDs), electrons and holes are injected at

electrodes interfaces into a conjugated polymer by applying a given voltage between two

electrodes. Contrary to the LEC configuration, no electrolyte is present, and the









electrodes must match the HOMO and LUMO levels to allow easy charge injection. The

remaining concepts are essentially identical.

1.4. Improving Active Material Performance

In this part, I will examine selected applications to see what properties are

necessary to obtain high performance, focusing on the active materials. Still, device

engineering plays a significant role in improving the efficiency of conjugated polymer

devices. I will later discuss how synthetic changes in CPs can achieve these desired

properties. Each application requires specific structural changes to obtain maximum

performance. This is the advantage of CPs and their unique synthetic versatility.

1.4.1. OFETs

As described previously, the efficiency of organic field-effect transistors depends

mainly on the charge mobility of the semiconducting material. In conjugated polymers,

the charge mobility is limited by the ability of charge carriers to hop between neighboring

localized states on polymer chains. With this, a high degree of interchain order is required

in the polymer. As a result, conjugated polymers with a typically high amorphous content

yield lower mobilities than small molecules. To obtain high mobility, polymers with a

high degree of crystallinity and long range order must be synthesized. P3HT, a semi-

crystalline polymer, has led to p-type mobilities up to 0.1-0.2 cm2 V-1 s- .13 The

crystalline regions consist of lamellar organized interchain stacks, possessing a high

degree of interchain interaction. For most ordered films, it is believed that there is two-

dimensional interchain charge transport. More recent work on liquid crystalline polymer

yield the highest mobility reported to date with a value of 0.7 cm2 V-1 s-1.14

To some extent, the mobility can be increased by careful deposition of the films. In

P3HT, the polymer can be processed easily from solution. The conditions of processing









(solvent, temperature, concentration, etc.) can be tuned to obtain the highest amount of

order within the polymer films.15 But this method requires a soluble polymer. Most

conjugated polymers, due to 7t-stacking interactions, are insoluble.

The mobility is also dependent on the molecular weight. Studies show that

increased molecular weights lead to dramatically higher mobilities.16'17 This can be

explained by higher planarity of the polymer chains leading to increased interchain order

and the ability of charge carriers to travel further along the chains before hopping to

neighboring chains. 16 Other authors have argued that the improvement observed with

increasing molecular weight is due to a difference in morphology. The higher molecular

weight polymers form large interconnected domains while the lower molecular weight

polymers forms small crystalline domains separated by the amorphous matrix.17

It was also shown that impurities or defects must be avoided. For example, partial

doping, although it leads to higher mobilities, is detrimental to field-effect transistors as it

yields poor "On-Off" ratios, meaning that even when no voltage is present at the gate the

transistor still conducts current.

1.4.2. Photovoltaic Application

To be a commercially interesting alternative to inorganic materials, it is estimated

that a power-conversion efficiency of at least 10% is required for photovoltaic devices. 18

Much work has already been performed in the last few years towards this objective.

Power-conversion efficiencies up to 3-5% have now been obtained.19 However, it is clear

that new concepts and new materials are needed to improve this value even further.

Several factors can be tuned synthetically to increase photovoltaic power-

conversion efficiency. 1) The absorption of photons can be improved. The polymers used

so far have too high bandgap and most of the solar energy is not absorbed. Therefore, a









low band-gap polymer able to absorb the intense NIR emission (700 nm, 1.4 eV) of the

sun must be synthesized. Blends of conjugated polymers can also be used to broaden the

absorption profile of the devices.20 2) Increase the interfacial surface area. This has

already been accomplished by replacing the bilayer device configuration with a

bicontinuous bulk heterogenous junction configuration in donor-acceptor photovoltaic

devices. In bulk heterojunction devices, both donor and acceptor are intimately mixed,

resulting in a significant improvement of the efficiency.21 Further improvement can be

obtained by decreasing the domain size in the blend layers. However, the domain size

must be large enough so that recombination is prevented and the charges are carried

efficiently to the electrodes. It is estimated that an exciton can travel an average of 10 nm

before returning to the ground state implying an optimum distance of 20 nm for the size

of the layers, so that the acceptor is within reach of all excitons generated in the donor

materials. This morphology control can possibly be obtained in block copolymers. By

maintaining a low polydispersity, controlling the nature and size of the blocks, precise

control of the morphology is achieved. 3) Control of the active materials' HOMO and

LUMO levels is essential. As fullerene and its derivatives have proven to be the best

acceptors, I will look only at the donor HOMO and LUMO levels. Control of the LUMO

level plays a decisive role in the charge separation process. It is estimated that the value

of the donor HOMO must be at least 0.3 eV above the LUMO of the fullerene LUMO

level to enable efficient charge separation by overcoming the exciton binding energy.22

The HOMO of the donor is important too, as it is believed to control the open-circuit

voltage and the power-conversion efficiency. 4) In addition, the materials used in

photovoltaic devices must have high mobility values. High electron and hole mobilities









will afford fast transport of charges to the electrodes and avoid recombination. Low

mobility of either holes or electrons will result in an increase of the series resistance,

decreasing the current generated by the device.19 Therefore, a material having significant

interchain interactions and some crystallinity should improve the charge transport in the

photovoltaic cells.

1.4.3. Polymer Electroluminescent Diodes (PLEDs)

Essential to PLEDs is to control the bandgap. By modifying the bandgap, albeit is

possible to change the color emitted by the polymer. Obtaining blue, red and green

emitting polymers opens the way for full-color display applications. In Figure 1-9,

several conjugated polymer along with their emitted colors are introduced. These

materials afford access to every color required for display applications.













nn -nn S n
/ \ 0-
S
PFO-BT PFO MEH-PPV POPT
Green Blue Red-orange Red I near-IR

Figure 1-9. Representative luminescence colors of some conjugated polymers.

Netherveless, if any colors can be obtained, the efficiency of the light-emission

process and the brightness are not satisfying. Part of the limited efficiency comes from a

theoretical limit inherent to the electroluminescence process in conjugated polymers. In

PLEDs, electrons and holes are injected at both electrodes. When an electron-hole pair is









formed, simple spin-statistics predicts that 25% of the excited states are singlet states, and

75% are triplet states. It is believed that 25% percent is the theoretical maximum

efficiency achievable in polymer light-emitting diodes. However, more recent theoretical

studies have since suggested that this might not apply to all polymers.22

To estimate the efficiency of the emission once a singlet excited state is formed, it

is necessary to look at the photoluminescence quantum efficiency. Film

photoluminescence quantum yield, the ratio of the amount of emitted photons to the

absorbed photons, gives us a good gauge of whether a polymer is a good candidate for

OLED applications. The quantum yield is highly dependent on the extent of interchain

interactions. After recombination the presence ofl -stacking interactions in conjugated

polymers leads to efficient interchain energy transfer to non-emissive, low energy traps.

The excitation energy is thus lost through non-radiative decay. In highly ordered

materials, although the solution quantum yields are often very high, the film quantum

yields are very low. To obtain higher quantum yield values, interchain interactions must

be prevented. Poly(2- methoxy-5-(2-ethylhexyl)oxy-paraphenylenevinylene) (MEH-

PPV), shown in Figure 1-9 is one of the most efficient polymers reported to date in

PLEDs. It displays high quantum yield in the solid-state due to several factors: 1)

presence of bulky and flexible 2-ethylhexyloxy side chains, 2) main chain disorder due to

the presence of both syn and trans substituted double bonds, 3) interchain disorder

induced by the asymmetry of the monomer with methyloxy and ethylhexyloxy side

chains, and 4) presence of tetrahedral defects due to incomplete conversion from the

saturated precursor to the unsaturated polymer.









Low mobilities are an advantage as charges spend more time within the active layer

and chances of recombination increase. But the mobilities of electrons and holes also

need to be balanced so that recombination occurs within the active materials, not at the

electrode interface. This is difficult as there are few polymers having similar electron and

hole mobilities. Introducing additional layers at the electrodes to transport or block

charges solves the problem. Solubility of the polymers is of course required for

inexpensive, easy processing of the polymers.

1.4.4. Electrochromic Devices

As mentioned before, the redox process in electrochemical devices is very different

as counterions balance the doped states. This implies that for efficient switching of an

electrochromic device, the dopant ion must be able to penetrate the polymer film

efficiently and the electrons must be able to move from the electrode inside the polymer

films.23 Highly ordered polymers dope slowly since they possess crystalline regions,

where the dopant ions cannot penetrate easily. Amorphous materials are therefore

excellent candidates for these applications. However, some interchain interactions are

necessary for electron transport between the electrode and the polymer bulk. PEDOT,

used in electrochromic windows, switches from a dark blue absorptive color to a highly

transmissive sky blue color with a switching speed of -2s. This is much shorter than most

inorganic electrochromic materials. Increasing amorphous domains and decreasing

interchain interactions is expected to improve switching speeds. This should increase the

doping level resulting in better contrast between neutral and doped state.24

Moreover, the control of both the neutral and oxidized state colors must be

obtained. By tuning the bandgap, a variety of colors are now available.25 Large bandgap

polymers, with absorptions in the UV region of the electromagnetic spectrum, are clear in









the neutral state but colored in the doped state, as polaron and bipolaron intragap optical

transitions are shifted to lower energies in the visible spectrum range. Polymers with

absorptions in the visible region will display a bathochromic shift in the doped state and

can be colorless. This is the case for PProDOT-Me2 and PEDOT, which absorb in the red

and have a dark blue color in the neutral state. When doped, the polymers absorb in the

infra-red and are mostly transparent.

Polymer solubility is also essential for inexpensive processing, as electrochemical

polymerization is problematic when considering large area applications.

1.5. Synthetic Control in Conjugated Polymers

This section will highlight how synthetic changes can affect the properties of

conjugated polymers.

Discussing bandgap modification through synthetic changes, Roncali has shown

that the bandgap is determined by the sum of several contributions: Peirls distortion (or

bond-length alternation (BLA)), substituents effects, intrachain interactions, interchain

interactions and resonance effects.26 A donor-acceptor contribution can be added to

provide a more complete description, as this effect does not obviously fit in the above. It

must be noted that all contributions are connected and that tuning the individual

contributions will result in changing the others.

All the parameters described above are not only defining the bandgap value, but

also the properties of the conjugated polymers. In this section, only the substituents

effects, and inter- and intrachain interactions will be detailed as they are most relevant to

the work presented in this dissertation. More information on donor-acceptor systems can

be found elsewhere.27









1.5.1. Substituent Effects

By introducing substituents on the conjugated polymer backbone, HOMO and

LUMO levels can be controlled precisely. By attaching electron-donating or electron-

withdrawing chains in direct conjugation with the conjugated backbone, the HOMO and

LUMO will be increased and decreased, respectively. Poly(3,4-alkylenedioxythiophenes)

(PXDOTs) are examples of a donor substituent effect. By introducing the oxygen at the

3- and 4- positions of the thiophene, 7t-donation of the lone pairs into the thiophene ring

occurs. As a result, the HOMO level is raised (-4.1 eV for neutral PEDOT, -5.3eV for

P3HT) and the bandgap is decreased (1.6 eV for PEDOT, 2.35eV for P3HT). PXDOTs

are therefore much easier to oxidize than polythiophenes and a bathochromic shift is

observed in their absorption spectrum (polymers are more blue). If electron-withdrawing

species are introduced in conjugation with the conjugated backbone, the result is a lower

LUMO level and a smaller bandgap. The oxygens have also an inductive electron-

withdrawing effect but it is overwhelmed by the resonance donating effect. But if a

methylene spacer is introduced between the backbone and the oxygen, then the resonance

effect no longer occurs. The inductive effect is dominant and the oxidation potential is

raised. Compared to poly(thiophenes), it was shown that poly(3-

alkyloxymethylthiophenes) have 100mV higher oxidation potential, corresponding to 0.1

eV lower HOMO levels.28

1.5.2. Intrachain Interactions

When the backbone of a conducting polymer is twisted out of planarity, the 7t

orbital overlap decreases, resulting in a decrease of the effective conjugation length.29

The bandgap will be much higher in twisted polymers than in planar polymers. This leads

to blue-shifted absorption and emission spectra.









Internal twisting has a dramatic effect on conductivity and charge transport in the

solid state. With increased twisting, intrachain charge transport along polymer chains will

decrease strongly. This results also in changes in interchain ordering which is highly

dependent on the individual chains conformations. Normally, polymers chains with a

strongly twisted backbone cannot order easily in the solid state. One exception is

possible where the twisting is regular leading to a formation of a helical structure.30

Polyfluorenes and polycarbazoles are good examples of highly twisted materials.

They are transparent in the neutral state, and emit blue light. Steric repulsions from

neighboring hydrogens on adjacent aryl rings prevent a planar conformation. Since

interchain ordering is strongly hindered, these two polymers are excellent candidates for

light-emitting applications having high fluorescence quantum yield efficiencies.31 In

addition, these polymers are cathodically coloring polymers. When oxidized, they absorb

in the visible range and are colored. When neutral, the polymers are highly transmissive,

as they mostly absorb UV radiations. Drawbacks of these polymers include high turn-on

voltages in PLEDs, high oxidation potential in electrolytes, and problems of degradation

over time leading to color changes.

Another striking example of the importance of intrachain order is found in poly(3-

alkylthiophenes). The monomer is not symmetric and can lead to Head-to-Tail (HT),

Head-to-Head (HH) and Tail-to-Tail (TT) arrangements during polymerization (Figure 1-

10A). When the polymer is obtained from electropolymerization (see chapter 2) or FeCl3

mediated chemical polymerization, the polymer is regiorandom and contains significant

amounts of HH and TT couplings. This creates steric interactions between every other

thiophene unit, as shown in Figure 1-10B, forcing twisting of the conjugated backbone.

































Figure 1-10. Effect of structural regularity on poly(3-octylthiophene) chain conformation.
(A) Regioregular P30T; (B) Regioirregular P30T; twisting arises from steric
interaction at the H-H site. Adapted from ref 32.

This torsion results in low interchain interactions, low mobilities and low

conductivities. On the other hand, if the polymer is obtained by Rieke polymerization or

Grignard metathesis polymerization, then a high degree of regioregularity (HT >95%) is

obtained.32 These polymers can adopt a planar conformation with higher conjugation

lengths. The planarity enables a high degree of interchain interactions in the solid state,

leading to an increase of conductivity and mobility of several orders of magnitude.33 In

solution, the regioregular samples absorption displays a bathochromic shift (20-30 nm),

indicating a more planar (rod-like) conformation and longer conjugation length.34 This is

much less than the shift observed in the solid state (140 nm), which implies that alkyl

poly(thiophene) chains have a significant degree of conformational freedom in solution,









and therefore display smaller regioregularity dependence. Because of the increased

planarity, P3ATs are strongly colored in the neutral states, with a bandgap around 2.3 eV.

When oxidized, the absorption is shifted to longer wavelengths and the polymer is blue

colored.

Intrachain twisting also leads to changes in emission colors. Figure 1-11 shows a

series of different substituted polythiophenes with their emission colors.39 Disubstitution

of thiophene leads to a high degree of twisting arising from steric repulsions between side

chains on adjacent thiophenes, and also steric interactions between side chains and the

large sulfur atom. The polymers then have shorter conjugation lengths, and their emission

shifts to higher energy (blue-shift) as the twisting increases.













S n S n S n S n S n
Blue Blue Green Green Red / near-IR

Figure 1-11. Color tuning of film luminescence though intrachain twisting. The driving
force is steric repulsion between bulky groups.

1.5.3. Interchain Interactions

As seen above, intrachain planarity favors interchain interactions. Another

important parameter is the regularity of the chains. In poly(m-phenylene) polymers,

strong intermolecular order is observed despite that the chains having a helical, nonplanar

backbone.30 The same regularity in the side chains is needed to allow interchain order.









The density and the nature of side chains also play a role in the solid state ordering of the

chains, as shown by Wegner et al. on substituted poly(p-phenyleneterephthalate) rigid-

rod polymers.35 When a high density of identical side chain is used, the polymer yields

two-dimensional lamellar packing. When a spacer without side chains is used between

terephthalic units bearing linear alkyl side chains, the side chains on neighboring lamellar

stacks are interdigitated. With higher side chain density, interdigitation is not possible.

The packing described above is general to rigid-rod polymers and applies to most

regioregular conjugated polymers. Winokur et al. demonstrated that poly(3-

hexylthiophenes) form non-interdigitated stacks.36 The side chains are essential to the

solid state packing as in planar alkyl polythiophenes, side chains extend into the plane of

the backbone, and do not present any hindrance to the chains stacking. Since the tendency

of the side chains to crystallize increases with the number of carbons, more order is

observed in poly(thiophenes) with longer side chains. This leads to significant

improvements in conductivity.33

Introduction of bulky groups instead of linear considerably decrease the interchain

interactions, as steric hindrance is introduced in the stacking direction. Poly(3-(2S-

methylbutyl)thiophene) displays much lower mobility (10-3 cm2V- s-1), even though the

branched group is small.37 By introducing larger branching, interchain interactions can be

decreased further. This has proved a very efficient method for the synthesis of highly

luminescent polythiophenes.39'71 The presence of the heavy sulfur atom helps inter-

system crossing to the triplet state, resulting in limited solution fluorescence quantum

yields (0.2-0.4).38 A much bigger issue is that poly(thiophenes) have a high degree of

interchain order in the solid state resulting in low film quantum yields. By introducing









steric bulk in the side chains, interchain interactions are strongly decreased and the

photoluminescence quantum yield can be greatly improved (Figure 1-12).39 Poly(3-(2,5-

dioctylphenyl)thiophene), which has the phenyl ring perpendicular to the poly(thiophene)

backbone, has a high film quantum yield of 0.24 (0.37 in CHCl3).












S n S n S n S n
QY (CHCI3)= 0.27 QY (CHCI3)= 0.26 QY (CHCI3)= 0.18 QY (CHCI3)= 0.37
QY (film)= 0.04 QY (film)= 0.09 QY (film)= 0.09 QY (film)= 0.24
HT=70% HT=70% HT=94% HT=90%

Figure 1-12. Fluorescence quantum yield dependence on substituents bulk. Both solution
and film fluorescence quantum yield are provided. The regioregularity is
provided as some polymers have limited HT content, which might result in
higher film quantum yield. All polymers are red-emitters. Adapted from ref.
39.

Interchain interactions also have a strong effect on the bandgap and the

absorption/emission properties of conjugated polymers. Strong t-stacking interactions

lead to significant shifts of the bandgap. The shift depends heavily on the relative

orientation of neighboring chains, as shown in Figure 1-13.40,41 For H-aggregates, formed

when two chromophores are in cofacial arrangement, the transition from the ground state

to the lower level of the excited state is forbidden but the transition from the ground state

to the upper level is allowed, leading to a blue-shifted absorption. For the same reason,

the emission for such aggregates is expected to be strongly quenched. 42 For J-aggregates,

formed when two chromophores are in a staggered ("brick-work") arrangement, there is a










bathochromic shift, as the transition from the ground state to the upper level of the dimer

excited state is forbidden and the transition from the ground state to the lower level is

allowed. In this type of aggregate, strong emission is seen.43 A third type of aggregate,

where each chromophores is tilted relative to its neighbors, leads to little or no shift of the

absorption since both transitions to the excited state are allowed. Only if the Davydov

splitting is large enough, it is possible to observe splitting in the absorbance spectrum.

J-aggregate Oblique Arrangement H-aggregate












J-aggregales H-aggregates
Eb S S S
















S---- G -
S












MONO BICHROMOPHORE MONO 8ICHROMOPHORE MONO BICHROMOPHORE
REIND-LINE OBLIQBANO 8ROA UE PARALLEL-S






Figure 1-13. Davydov splitting in interchain aggregates. The resulting energy levels and

absorption spectrum are also shown. Solid Lines: allowed transition; dashed
lines: forbidden transitions. Adapted from reference 77.

Oblique chromophores arrangement has been reported by Swager et al.44 Using a

poly(phenylene ethynylene) (PPE) copolymer with alternated pentiptycene and chiral
-7k























poly(phenylene ethynylene) (PPE) copolymer with alternated pentiptycene and chiral









dimethyloctyl side chains, they showed that the film fluorescence quantum yield is 0.65,

one of the highest reported to date.

1.6. Towards Soluble Conjugated Polymers

Unsubstituted polythiophene, polypyrrole, polyphenylene and other CPs are

insoluble, intractable and infusible. This makes them practically useless for most

applications. On the other hand, soluble organic conjugated polymers can be spray-

coated, spin-coated, or even printed. Obtaining solubility in conjugated polymers is,

however, a difficult task due to their propensity to form interchain 7t-stacks. The

individual 7t-7t interactions are weak, but they add up to a strong interaction. To induce

solubility, it is necessary to decrease interchain interactions, and to make the solvent-

polymer interactions more favorable. Substituents increase the entropy of the polymer

chains, and increase the solvent-polymer interactions. By selecting polar or ionic

substituents (oligoethers chains, phosphate, carboxylate, sulfonate, ammonium, etc.),

solubility in polar solvents (including water) can be achieved.45 With nonpolar

substituents alkyll chains for example) solubility in organic solvents can be obtained.

Bulky substituents create a larger increase in entropy, and prevent a close chain packing.

But as discussed earlier, this will decrease mobility and conductivity of the materials. For

applications where high mobility or conductivity is required, substitution with linear

substituents is then a better approach. Another possibility is to introduce regioirregularity

in the backbone or induce intrachain twisting but this often leads to decreased interchain

interactions. It is therefore important to consider the application when choosing which

method will be the most appropriate to obtain solubility.

Soluble polymers can be obtained through a wide variety of polymerization

methods.46 The most used is FeCl3 polymerization. It directly uses the









electropolymerizable monomer and does not require further functionalization. The

polymerization mechanism proceeds through formation of the radical cation of the

monomer that propagates through coupling with other monomer units. The polymer is

obtained in the oxidized state, and reduction of the polymer back to the neutral state as

well as removal of the iron catalyst is difficult. Also, the high reactivity of the cation

radical leads to numerous side reactions (in the case of alkyl poly(thiophene)s

crosslinking through the 3 position of thiophene can occur), leading to high

polydispersity. In addition, this method yields highly regioirregular polymers. By using

metal-mediated polymerization, side reactions can be eliminated. The process requires

functionalization of the monomer with halogen or organometallic groups

(organomagnesium, organotin or organoborates). Introduction of the metal catalyst yields

the neutral polymer, removing the chemical reduction step. Regioregularity can be

obtained if the functionality of the monomer, catalyst and reaction conditions are well

chosen. Figure 1-14 presents polymerization conditions leading to regioregular polymers.

One drawback of this polymerization conditions is that they require cryogenic conditions.

A new method developed by the McCullough group, Grignard Metathesis (GriM)

polymerization removes that constraint, providing a simple and convenient way to

prepare regioregular, neutral conjugated polymers.32'33'46'47'48'49'85 It requires preparation

and purification of a dibrominated analog of the electropolymerizable monomer. For the

polymerization step, the halogenated monomer is reacted with one equivalent of

methylmagnesium bromide, converting one bromine to an organomagnesium

functionality. After the conversion is complete, a coupling catalyst such as Ni(II)dpppCl2

is introduced, leading to a fast polymerization.











alkyl alkyl alkyl
1st Step 2nd Step

X SY M- Y As

Method X Y st Stp M2ndtp

1 a -H -Br 1) LDA, THF, -78C -MgBr Ni(dppp)Cl2
2) MgBr2 OEt2, -780C to rt
2 b -Br -Br 1) Zn* -ZnCI Ni(dppe)C1l2
3 -H -I 1) LDA, THF, -78C -SnBu3 [Pd(Ph3)4]
2) Bu3Sn-CI, -78C
4 -H -I 1) LDA, THF, -40C 1-0 Pd(OAc)2, K2CO3
2) B(OMe)3, -780C -B THF, EtOH, H20
3) H+ O
4) R-OH, Na2SO4
yields 60-75%, Mw=20K-40K, PDI=I.12-1.4. b yields 67-82%, Mw=37K-49K, PDI=1. 13-1.48. c dppe=
diphenylphosphinoethane.

Figure 1-14. Polymerization method leading to regioregular Poly(3-alkylthiophene)s.
Adapted from reference 47j.

The mechanism of the reaction is still under investigation. It may proceed through a

chain growth process (Figure 1-14).48 During initiation and reduction of the Ni(II)

catalyst to Ni(0), the Ni(0) forms an associated pair with the coupling product. Following

a cycle of oxidative addition, transmetalation and reductive elimination, a monomer unit

is added to the chain, and the associated pair is reformed. This implies that the

polymerization is controlled not by stoichiometry of bromide to organomagnesium

functionalities as would be expected in a condensation polymerization, but by the

monomer to catalyst concentration ratio. The McCullough group also demonstrated that

Grignard Metathesis is a "quasi-living" polymerization, with the chain end remaining

active at the end of the polymerization process,49 allowing for the functionalization of the

chain ends and the synthesis of block copolymers.









Br

C fn _Br Ni(dppp)CI2 N/RL-Ni

1 2 / Br
R


R
reductive Ni(O) + Br Br
elimination L /

Associated pair [3*4]

oxidative addition
after several catalytic cycles


CIZnJIsl\Br


Associated pair [3.7]

reductive elimination


Figure 1-15. Proposed chain growth mechanism for Grignard Metathesis Polymerization.
Adapted from ref 48.

Grignard metathesis is therefore a very promising method for obtaining tailored

block copolymers with controlled morphology, crucial in photovoltaic devices and light-

emitting applications. However, it must be pointed out that chain termination still occurs

at high conversion, and the polymerization is therefore not yet "controlled". The

polydispersity, although quite low, is still much higher than anionic or cationic living

polymerizations. It is also not obvious that the study for poly(3-hexylthiophene) can be

transferred to other monomers such as more electron-poor or electron-rich monomers, or

that the molecular weights can be obtained reproducibly. Much work must still be carried

out to achieve true living polymerization but initial reports so far are truly exciting.









In this dissertation, after giving a general experimental overview in Chapter 2 and a

detailed introduction to dioxythiophene-based polymers in Chapter 3, I will discuss how

electrochromic properties of disubstituted poly(3,4-propylenedioxythiophenes)

(PProDOT) are greatly improved by introducing branched substituents that decrease

interchain interactions and yield more amorphous polymers. The branched alkyl

substituted PProDOTs, presented in Chapter 3, yield polymers that self-assemble during

processing and give ordered aggregates of stacked chains. Alkoxy substituted PProDOTs,

described in Chapter 4, yield more disordered aggregates. This leads to Chapter 5 which

describes the synthesis and properties of chiral branched PProDOTs along with the use of

circular dichroism (CD) to investigate the aggregation and ordering behavior in

PProDOTs. Finally, Chapter 6 shows the synthesis and properties of the first soluble

poly(3,4-phenylenedioxythiophene)s (PPheDOTs). Regiosymmetric didodecyl

PPheDOTs with linear substituents have a high degree of order and provide an excellent

platform for the development of high mobility and high conductivity materials, while

asymmetric disubstituted PPheDOTs containing dodecyl and ethylhexyl substituents are

highly disordered and provide an excellent platform for the development of light-emitting

materials.














CHAPTER 2
EXPERIMENTAL METHODS

In Chapter 1, the theory and concepts which control the chemistry and properties

behind conjugated polymers were presented. Some areas where CPs find applications and

what can be done synthetically to improve the performance of the materials were also

described. In this chapter, all of the experimental methods used to characterize the

structure as well as the electronic and optical properties of the molecules and polymers

presented in this dissertation will be introduced.

2.1. General Synthetic Methods

All chemical and solvents were purchased from Aldrich or Acros and used without

further purification unless otherwise noted. Dry THF and dry diethyl ether were obtained

by distillation from Na/benzophenone ketyl. Dry dichloromethane and dry acetonitrile

were obtained by distillation from CaH2. All reactions were performed under argon

atmosphere using standard Schlenk techniques. Detailed synthesis of each compound

presented in this dissertation can be found at the end of each chapter.

2.2. Molecular Characterization

All the new molecules presented in this dissertation were structurally characterized

by 1H NMR and 13C NMR, High Resolution Mass Spectrometry. 1H, 13C NMR were

obtained from a Gemini 300 FT-NMR, Mercury 300 FT-NMR, or VXR 300 FT-NMR.

HRMS was obtained on a Finnigan MAT 95Q mass spectrometer. The purity was

evaluated using elemental analysis carried out by the elemental service at the University

of Florida (C, H, N) or Robertson Microlit Laboratories, Michigan (C, H, N, S, Br). IR









spectroscopy was also used for functional group identification and was recorded on a

Perkin-Elmer Spectrum One FT-IR spectrophotometer.

2.3. Electrochemical Characterization

Monomer electrochemistry, polymer electrodeposition and polymer

electrochemistry were performed using a standard three electrodes configuration: a

platinum button working electrode (area= 0.02 cm2), a platinum foil counter-electrode

(S-1 cm2>>0.02 cm2) and a silver wire pseudo-reference (Figure 2-1). The potential is

applied from an EG&G Potentiostat/Galvanostat 273A. The Pt counter-electrode was

cleaned by Bunsen-burner flaming. The silver quasi-reference was polished using sand

paper. The Pt button working electrode was cleaned by rubbing gently with a kimwipe

wetted with toluene. The silver wire was systematically calibrated with a ferrocene

solution following experiments. To determine with precision the monomer and polymer

oxidation potential, an immediate calibration with ferrocene is performed following each

experiment. A solution of 0. M tetrabutylammonium perchlorate (TBAP, prepared from

tetrabutylammonium bromide and perchloric acid solution, recrystallized in methanol) in

dry acetonitrile (from CaH2) was used as electrolyte.

Pt Button
Working Electrode


Pt foil
Counter electrode Ag wire
Reference electrode







Figure 2-1. Three electrodes (Pt button, large Pt foil counter, Ag wire reference)
electrochemical setup.









2.4. Polymer Characterization

2.4.1. Structural Characterization

The polymers were characterized by 1H NMR, 13C NMR (if polymer soluble), and

elemental analysis. Due to the fast relaxation from the polymers, up to 20,000 scans were

often needed. Either CDCl3 or C6D6 was used depending on the polymers solubility. GPC

was performed on two 300 x 7.5 mm Polymer Laboratories PL Gel 5 PM mixed-C

columns with a 2996 photodiode array detector at the Xmax of the polymer solution. A

constant flow rate of 1 mL/min was used. Molecular weights were obtained relative to

polystyrene standards. Polymer solutions (0.5 mg/mL) were prepared in THF and filtered

through a 450 nm GPC filter before injection. In the case of PPheDOT(C12)2 described in

Chapter 7, which is only soluble in chlorinated or aromatic solvent above 800C, the NMR

was carried out in 1,1,2,2-tetrachloroethane-d2 at 1200C. GPC analysis on

PPheDOT(C12)2 (Chapter 6) was carried out by Dr Steve Eyles at the University of

Massachusetts, Amherst. It was performed on a PL220 high temperature GPC (Polymer

Laboratories, Inc., Amherst MA). The sample was injected at 5 mg/mL concentration

using 1,2,4-trichlorobenzene at 135 C, 1 mL/min as mobile phase. Separation was

achieved using a set of four Polymer Labs Mixed A columns (7.5 x 300 mm). The

polymer was detected by differential refractive index. Molecular weights were obtained

relative to polystyrene standards.

2.4.2. Thermal Characterization

All polymers were characterized by thermogravimetric (TGA) and differential

scanning calorimetry (DSC) analysis. TGA was carried out on a Perkin-Elmer TGA7

thermogravimetric analyzer. DSC was carried out on a TA Instrument DSC Q1000

calorimeter.









2.4.3. Morphology Characterization

This work was carried out in collaboration with Dr Wojciech Pisula, Nok Tsao and

Pr Klaus Mullen of the Max Planck Institute for Polymer Science, Mainz, Germany. The

2D-WAXS experiments were performed by means of a rotating anode (Rigaku 18 kW)

X-ray beam with a pinhole collimation and a 2D Siemens detector. A double graphite

monochromator for the Cu-Ka radiation (X=0.154 nm) was used. For this experiment,

fibers were extruded using a home-built mini-extruder.50 A photograph of a

poly(paraphenyleneethynylene) extruded fiber can be found in the literature.51

AFM work was done in collaboration with Thomas Joncheray. AFM imaging was

carried out in tapping mode with a Nanoscope III AFM (Digital Instruments, Inc., Santa

Barbara, CA) using silicon probes (Nanosensor dimensions: T = 3.8-4.5[tm, W = 26-27

|tm, L = 128 [tm). The images were processed with a second-order flattening routine.

2.4.4. Solution Optical Characterization

Polymer solutions were prepared using spectrophotometric grade solvents. New

bottles were used, especially with chlorinated solvents, as old bottles develop acidity

leading to oxidation of the polymers. All absorption spectra were obtained using a Varian

Cary 500 scan UV-vis-NIR spectrophotometer. Thermochromism studies were performed

using a SPV 1*1 Varian Cary dual-cell Peltier accessory.

Solution fluorescence spectra of the polymers and fluorescence solvatochromism

were recorded on a Fluorolog 3. Solution fluorescence quantum yields were measured

relative to a standard. The standard was chosen by analyzing the absorbance and

fluorescence spectra of many possible candidates listed on the Oregon Medical Laser

Center website under the Alphabetical Index of Photochem CAD Spectra.52 Either









Rhodamine 6G (ethanol, Xx=480 nm, Of= 0.95) or sulforhodamine (ethanol, Xex=550 nm,

Of= 0.9) were found appropriate as standard, depending on the absorption spectrum of the

specific polymer considered. The integration time and the slits (excitation and emission)

were respectively set at 0.5s and 2mm. When doing a quantum yield measurement, it is

necessary to record the standard and the fluorescence with the same slits and integration

value. The slit size should be increased if the fluorescence signal is low and noisy.

However, the signal intensity at Xmax should always be kept well under 107 counts s-1 as

the response of the detector is not proportional to the emission intensity at such high

value, resulting in large errors in quantum yields. Integration time can be increased to

improve the signal-to-noise ratio (it does not change the signal intensity though). Only

spectrophotometric grade solvents were used. Unless specified, absorption of the samples

was kept under 0.1 (at Xmax) to prevent intermolecular quenching due to aggregation

excessive concentration. The following equation was used to calculate the solution

fluorescence quantum yield:

(1 10 Astandard ( m ) (m)
Equation 2-1: sample standard X Astapample ) X (sample
(1 10 sampe standard) (standard
A is the absorbance at the excitation wavelength, n is the refractive index of the

solvent used to take the fluorescence spectrum, and I is the number of emitted photons

(obtained by integrating the fluorescence spectrum).

2.4.5. Solution Processing Techniques

The processing of conjugated polymers from solution is an extremely important

step in their characterization and application. Different methods are available that lead to

various film qualities, control of thickness, and different ease of processing. In this









section, a description of the processing techniques used in this dissertation is given: drop-

casting, spin-coating and spray-coating.

2.4.5.1. Drop-casting

Drop-casting is the easiest technique to make a film. But it is also the technique

leading to the poorest film quality. The polymer solutions are generally deposited on

polar materials (mica, glass, ITO, and most metals). The wettability of the polymer

solutions on polar substrates is very low, as all polymers presented in this dissertation are

hydrophobic. As a result, the solution tends to concentrate at specific spots and poor film

quality is obtained. To improve film quality, it is possible to use a razor blade to spread

the solution on the surface as the solvent dries up but the resulting films still have poor

quality. The concentration used is usually 5mg/mL in toluene.

2.4.5.2. Spin-coating

Spin-coating leads to the best film quality of all the film deposition techniques. In

this method, a substrate is placed in the middle of the spin-coater and vacuum is applied

underneath. The polymer solution is deposited with a pipette all over the surface of the

substrate. The substrate is then rotated at the desired rate and after solvent evaporation, a

uniform film is formed on the surface.

Many factors contribute to the quality of the spin-coated films, as well as the

thickness of the deposited layer. The main factors are rotation speed, solvent, evaporation

rate, concentration of the polymer solution and polymer molecular weight. Below is the

AFM of a spin-coated film on glass.

For AFM imaging, a concentration of 0.2 mg/mL was used. The best solvent,

leading to the most ordering was found to be ortho-dichlorobenzene for all polymers. The

spin-coating rate used was 2000 rpm. This typically led to the formation of homogenous









monolayer thick films. For film fluorescence, thicker films are needed, so a higher

concentration of 5-10 mg/mL was used, with a spin-coating rate between 1000-2000 rpm.

Toluene was used as the solvent since it is a good solvent for all of the polymers analyzed

for film fluorescence in this dissertation. To increase film thickness, higher solution

concentrations or lower spin rates can be used, but using excessive concentration or too

low a spin-rate can lead to polymer aggregation, which leads to poor film quality.

Spin-coating is the preferred method for making LEDs, LECs or OFETs where

high film quality is a requirement. Drawbacks of the methods include the loss of

materials since most of the deposited solution is ejected off the subtrate (it is possible to

recover part of this lost material but it is very tedious), the fact that only thin films (<300

nm) can be deposited and that a symmetrical substrate must be used (disc, square). Also,

the method is hard to apply to large surface areas.

2.4.5.3. Spray-coating

The spray-coating method is a very practical method to form uniform films on any

kind of surface and applicable to large surface areas. In this method, the polymer solution

is placed in a reservoir cup of a spray-brush (Aztek A470), and sprayed through a nozzle

using compressed air. The resulting films are very homogenous to the eyes as seen in

Figure 2-2. However, a closer look by profilometry reveals that the roughness is much

higher than observed in spin-coated films, although it is clear that the films are fully

covered. Thick films (1-24m) can be obtained through this method. If the conditions are

well controlled, the solvent evaporates rapidly and does not have enough time to dissolve

the lower deposited layers. These conditions are pressure (it was found 12 psi to be

appropriate for our films), polymer concentration (often 5mg/mL, but higher

concentration must be used for low molecular weights polymers), solvent (highest quality









films with toluene for all polymers studied) and distance from the substrate (at least 10-

20 cm distance from the substrate is needed, to allow the dispersion of thin droplets from

the spray-brush nozzle). For colored films, the film thickness can be simply controlled by

eye during spray-coating, as 50nm differences in film thickness are easily seen.









Figure 2-2. Spray-coated films of PProDOT-(CH20(2-ethylhexyl))2 and PProDOT-
(CH20C18H37)2. Films are sprayed from a 5mg/mL solution in toluene at an
air pressure of 12 psi.

This is a method of choice for electrochromism characterization and electrochromic

devices.

2.4.6. Film Fluorescence Characterization

Film quantum yield were obtained using a PTI MOD A1010 white light

illumination and an Instruments SA, Inc. monochromator. The light from the source or

fluorescence was collected using an ORIEL 70451 integrating sphere and a Spectrum-

One CCD detector. The fluorescence quantum yield is then calculated following a

published method.53

2.4.7. Spectroelectrochemical Characterization

The properties of conjugated polymers, as discussed earlier depend heavily on the

redox state. The spectroelectrochemistry experiment (see Chapter 1) is used to monitor

the variation of optical spectrum with applied potential. This experiment follows the

fundamental optical changes of a polymer as a function of the doping levels, as described

in Chapter one. The films' absorption spectra were obtained using a Varian Cary 500









scan UV-vis-NIR spectrophotometer. The optical bandgap is obtained from the onset of

the neutral polymer 7t-t* transition. A three electrode setup connected to an EG&G

Potentiostat/Galvanostat 273 was used to change the potential applied to the films.

Another measurement, allowing one to follow the color with doping, is in-situ

colorimetry analysis.54 According to the Yxy color system developed by the Commission

International de l'Eclairage (CIE) in 1931, the color is defined by its chromaticity (x,y)

and by its luminance (Y). These parameters were defined based on the "standard

observer", meaning that they were designed based on how colors are perceived by an

average of multiple people. The luminance parameter Y can be thought to be the

brightness of a color as perceived by the human eye. For example, white is perceived as a

very bright color where grey is perceived as less bright, although they have the same

chromaticity. The chromaticity is defined by the two parameters x and y, which

characterized the color itself, independently of its brightness. They represent two

variables defining the color perceived and are a mathematical combination of what is

detected by the three receptors present in our eyes (often referred to as blue, green, red

receptors), each detecting a range of the visible light wavelength.

In this dissertation, x,y and Y values were recorded by a Minolta Chromameter CS-

100. Y is given in Cd/m2 (x,y have no units). Sample was illuminated from behind using

a D50 (500K) light source. A background measurement was recorded using a blank ITO

slide in the appropriate electrolyte solution in a quartz cuvette. The colorimetry was

recorded using the following settings: calibration set at "PRESET", measuring mode set

at "Abs". And response set at "SLOW". These settings must be used as other settings

will lead to erroneous data. All films (except PPheDOT(C12)2) used in









spectroelectrochemistry, luminance and CE experiments were prepared by spray-coating

onto Indium Tin Oxide (ITO) coated glass slides (Delta Technologies, 8-12 Q/I).

PPheDOT(C12)2 films were prepared by drop-casting on ITO-coated glass slides from a

hot (1000C) solution in xylenes, as it is insoluble at room temperature and cannot be

spray-coated.

Another useful tool in electrochromic materials characterization is the composite

coloration efficiency.24 In this measurement, the transmittance of the film at Xmax and the

charge injected into the film are recorded as a function of time during a potential step

from a potential where the polymer is fully neutral to a potential where the polymer is

fully oxidized. As shown in Figure 2-3 for PProDOTMe2, as the potential is stepped from

-0.5V to 1.2V, the transmittance at 585 nm increases strongly as the polymer is oxidized

and the visible t-7* optical transition is bleached, reaching a plateau when it is fully

oxidized. The time required to obtain 95% of the optimum contrast is taken as the

switching time of the polymer and is a critical parameter to characterize a material

designed for an electrochromic application. The coloration efficiency is calculated from

the following equations:

Equation 2.2: AOD= log[T(ox at 95%)/Tred]

Equation 2.3: CE= AOD/Qd

Qd is the charge required to obtain 95% of the total optical contrast. T(ox at 95%) is

the film transmittance at 95% of the total contrast. Tred is the film transmittance in the

neutral state.










1 0
(a)
100%&T (a)
0.2
80.5 >
cm0 05.4)
E
0.6 8
0.2 -0
0 0.8


(b)
4 100

E 3- 98
3 95
9592 90
E 2 O80



0
o --

0 2 4 6 8 10 12 14 16
Time (seconds)

Figure 2-3. Time evolution of transmittance and injected charge for an
electropolymerized film of PProDOT-Me2. Adapted from ref. 24.

The CE value provides a practical way of comparing color change charge

efficiency between different materials. For example, our research group showed that

PEDOT, PProDOT and PProDOT-Me2 have increasing CE values: 183 cm2/C,

255cm2/C, 375cm2/C.64 This trend correlates well with PProDOTs having a higher

contrast than PEDOT (51% A%T at Xmax of 585 nm for PEDOT, 63% A%T at Xmax of 578

nm for PProDOT, 72% A%T at Xmax of 585 nm for PProDOTMe2). PProDOTs also

requires less charge to obtain full doping of the polymer. This is explained by PEDOT

having more ordered, packed morphology than PProDOT, as the more flexible seven-

membered ring provides steric hindrance to chain packing and allows for easier

penetration of the dopant ion. Substitution of the seven-membered ring with methyl

groups hinders interchain interaction. This could result in more capacitive contributions









to the current (not contributing to polymer doping) for PEDOT, than PProDOT and

PProDOT-Me2.

2.4.8. Circular Dichroism

The method will be discussed in details in Chapter 5 concerning chiral PProDOTs.

CD spectra were measured on a JASCO J-815 CD spectrometer, with a Peltier

Temperature Programmer model JASCO PTC-348WI.

2.4.9. Conductivity Measurements

In this work, most conductivity values were measured using the four-point probe

method. The experimental setup is shown in Figure 2-4.


+ AV


1 2 3 4













Figure 2-4. Four-point probe conductivity method.

This method has several advantages. If the voltmeter has a high impedance, then

problem of contact resistance met in two points measurements is avoided. This method

also allows the conductivity to be measured at several locations in the films. An average

measurement is then obtained, which is useful since the presence of cracks or

morphology defects will alter the measured conductivity. This cannot be done in methods









involving thermal evaporation of metal electrodes onto the film, used for

PPheDOT(C12)2.

The films used for this measurement were all spray-coated onto glass slides (1

square inch), except for PPheDOT(C12)2 which cannot be spay-coated (a procedure is

described later for this polymer). The spray-coated films were exposed to iodine vapor in

an iodine chamber overnight and then quickly brought to the Signatone S-301-4 four-

point probe apparatus for conductivity measurement. As seen in Figure 2-5, a constant

current I (between 1tA and 100 ptA) is applied between electrode 1 and 4 using a

Keithley 224 current generator (voltage threshold was set at 30 V, intensity threshold was

set at 5 x 103 A), and the voltage drop between electrodes 2 and 3 (AV) was monitored

using a Keithley 197 voltammeter. After obtaining the film thickness t from a Sloan

Dektak 3030 profilometer, the conductivity is then calculated by the following equation:

Equation 2.4: p = (AV/I) (t 7 /ln2) F

where F(t/d) is a correction factor approaching zero when t<
films used in our study are very thin compared to the distance between electrodes, F-1.

If the electrodes make good contact with the oxidized polymer, the Vthreshold light on

the current generator should be solid. If a poor contact is made with the films (caused by

holes, cracks in the film between the electrodes) then the Vthreshold light will blink. To

verify that a valid conductivity measurement will be obtained, the voltage drop is

monitored as the applied current is modified. If the conductivity measurement is good,

the voltage drop change is directly proportional to the current change (Ohm's law). For

every measurement, the voltage drop and film thickness were measured at several

locations and an average value is then calculated, yielding an average value of







conductivity for the polymer film. Usually, the current applied to electrodes 1 and 4 is set
at 100 [tA. However, it was discovered that for the lower conductivity films, the voltage
needed to obtain this current quickly rose above the threshold of 30V after the four-point
probe is applied on the film. In this case, the current was decreased to down to 10 utA or
1-2 paA.
In the case of PPheDOT(C12)2, films could not be spray-coated. Spin-coating from
hot toluene solutions (100 C) afforded homogenous thin films. Four gold electrodes
were thermally evaporated onto the spin-cast films (Figure 2-5). Copper wires were
soldered to the 4 electrodes and connected to the current generator and voltmeter
described above for the 4 point conductivity measurement. The films were placed in a
specially designed chamber, and sealed under vacuum. Bromine was introduced through
a septum via syringe and the voltage drop was measured. After measurement of the film
thickness, conductivity was calculated using Equation 2.4.


t
Y


AV

2 3


Figure 2-5. Four-point conductivity measurement. Gold electrodes are thermally
evaporated on spin-coated polymer film.


4














CHAPTER 3
SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKYL POLY(3,4-
PROPYLENEDIOXYTHIOPHENES) (PPRODOT-R2)

3.1. Introduction

Chapter 1 described the properties of soluble alkyl poly(thiophene)s. These

polymers have good solubilities, but high oxidation potentials. By introducing two

electron-donating oxygens onto the 3- and 4-positions of the thiophene ring, the oxidation

potential is considerably lowered, and the polymers become stable in their oxidized state.

It also prevents crosslinking at the 3-and 4- positions of the thiophene ring, as observed in

alkyl poly(thiophene)s. Poly(3,4-ethylenedioxythiophene) (PEDOT) is an electron-rich,

highly conductive polymer that has been used in many applications, including anti-static

coatings, capacitors, and "smart windows".56 PEDOT has conductivities up to 200-

500 S cm-1 in the oxidized form.8 The polymer is highly insoluble because of the high

degree of interchain interactions due to a more planar intrachain conformation. This was

shown by studies on EDOT oligomers and theoretical calculations.57 Multiple factors

contribute to the planarization of the backbone: mesomeric effect induced by the

electron-donating oxygens, low steric interactions between the sulfur atom and the small

oxygen atoms (much smaller than methylene), and attractive sulfur-oxygen interactions.58

Also, the two alkoxy substituents are tied together in the six-membered ring. The ring

structure is critical since poly(3,4-dialkoxythiophenes) have been shown to exhibit much

lower conductivities,59 attributed to the flexibility of the alkoxy substituents generating

intrachain steric repulsion between substituents on adjacent thiophenes. As discussed









earlier, this steric repulsion results in intrachain twisting and decreased interchain

interactions.

Substitution of the six-membered rings of PEDOT with linear tetradecyl alkyl chain

induces solubility in organic solvent.60 Shorter linear alkyl chains (Ci-Cio) do not create

sufficient steric hindrance to overcome the 7t-stacking, leading to insoluble polymers. The

introduction of such long linear alkyl chains does not disturb the packing of the chains.

This is a bit surprising given as inter and intrachain would be expected (the polymer is

regioirregular) side chain repulsion. Theoretical calculations in our group by Alejandro

Perdomo (in collaboration with the Bredas research group) show the six-membered ring

adopts a twisted chair conformation, in which the substituent lies in an equatorial position

within the polythiophene backbone plane (Figure 3-1).


(a)


0 0 0 0 0 0 0



350 S cm-1 200 S cm-1 550 S cm-1 850 S cm-1

Conformational and substituents effects on 3,4-ethylenedioxythiophenes. (a)
side view and (b) back view of EDOT in the "twisted" conformation,
calculated to be the most stable conformer using ANNEALING method as
implemented in AMPAC and optimized at the B3LYP/6-3 1G* level of
theory. (c) Structures and conductivities for a series of alkylated PEDOTs.
The conductivities were all obtained by in-situ conductivity on
electropolymerized films.62


(c)

0 0



650 S cm-1

Figure 3-1









As a result, crystallization of the long linear alkyl chains yields an improvement of

the stacking of the polymer chains and allows for higher conductivities.61 With shorter

chains that do not order easily, the regioirregularity of the side chains dominates and

lower conductivities are observed compared to PEDOT.62 This trend is also illustrated in

Figure 3-1. One drawback of neutral PEDOT based polymers is their instability to

ambient conditions (air, light and water). The polymers easily oxidize in air and degrade

over time. This is different with the neutral form of the poly(3,4-

propylenedioxythiophenes) (PProDOT) based polymers. Although the only difference

lies in the presence of the larger 7-membered ring in place of the six-membered ring,

PProDOTs are much more stable to ambient conditions and can be stored in air for

extended periods of time without oxidizing. Theoretical calculations (by Alejandro

Perdomo) show that this increased stability may originate from the greater flexibility of

the seven-membered ring with two stable conformations: the "twisted" conformation,

similar to PEDOT (both in conformation and in energy), and a lower energy chair type

conformation (Figure 3-2). The predominant form depends heavily on the substitution of

the seven-membered ring. X-ray crystal structure on crystalline ProDOT derivatives have

confirmed the existence of these two conformers.63 To induce solubility, alkyl chains can

be introduced at the 2-position of the propylene bridge. This substitution leads to a

regiosymmetric monomer; therefore regioregularity of the side chains in the polymer is

induced. Also, interactions between substituents of adjacent thiophenes are minimized at

this position. Early attempts using methyl (PProDOT-Me2) and ethyl (PProDOT-Et2)

substituents yielded insoluble polymers. 24,64 Electropolymerized films of PProDOT-Me2,









PProDOT-Et2 displayed enhanced properties, with higher coloration efficiency, and

shorter switching times than PProDOT and PEDOT



A) B)
















Figure 3-2. Two most stable conformations of ProDOT. A) The "chair" conformation; B)
The "7ii /vwe conformation. Calculations were performed using
ANNEALING method as implemented in AMPAC. Each conformer found
was subsequently optimized at the B3LYP/6-31G* level of theory. Hydrogens
are white; carbons are grey; oxygens are red; sulfurs are yellow.

To induce solubility, longer alkyl chains were required. The synthesis of PProDOT-

Bu2 indeed provided the first soluble PProDOT,63a but the solubility was limited to the

lower molecular weight fractions (Mn= 3000 g mol-1). To further increase the solubility,

the first approach employed was to increase the length of the linear alkyl side chains. The

second was to introduce steric bulk and branched substituents. In this chapter are

introduced PProDOTs symmetrically substituted with various branched alkyl groups and

the effect of substitution on the properties of the conjugated polymers is discussed

thoroughly. The family of polymers synthesized and described in this Chapter is shown in

Figure 3-3.
















0 0


n


OS
n


PProDOT(2-methylbutyl)2 PProDOT(2-ethylbutyl)2 PProDOT-hexyl2 PProDOT-(2-ethylhexyl)2
(only electrodeposited)

Figure 3-3. Family of branched dialkyl PProDOTs. PProDOT-Hexyl2 was synthesized for
comparison and discussion of branching effects.

3.2. Electropolymerized PProDOT-R2

3.2.1. Electropolymerizable Monomer Synthesis

The electropolymerizable monomers were synthesized by transetherification of 3,4-

dimethoxythiophene and 2,2-dialkyl-propane-1,3-diol, as shown in Figure 3-4. All diols

used in this dissertation were synthesized by malonic ester synthesis followed by lithium

aluminum hydride reduction as indicated in Figure 3-4.65 The synthesis is easily scalable

and the starting materials are inexpensive. In the case of 2,2-dihexylpropane-1,3-diol, the

synthesis was scaled up to a several hundred grams scale in a collaborative work with

Benjamin Reeves and Barry Thompson. The key intermediate, 3,4-dimethoxythiophene,

was prepared from a copper-mediated Ullmann ether reaction of 3,4-dibromothiophene.

The preparation of 3,4-dibromothiophene from thiophene is also included since much of

the 3,4-dibromothiophene used for this dissertation work was obtained by this method.

This product is now commercially available at a competitive price, avoiding large scale,

tedious and potentially dangerous steps. These steps include tetrabromination of

thiophene (with a large amount of HBr released), followed treatment of










tetrabromothiophene with either two equivalents of n-butyllithium or Zn metal in acetic

acid.

Br Br Br Br MeO OMe
Br2 Br 2 eq. n-BuLi, -780C ,, NaOMe, CuO, KI
SCHCl3 Br S r or Zn dust, S MeOH S
90% AceticAcid 70-85%
80%

0 1) NaH j 0 LAH OH OH
EtO OEt 2)R-Br EtO OEt Et20 R R 25-50% from diethylmalonate


R R

MeO OMe 0 0 R= -(2-methylbutyl)
OH OH pTSA -(2-ethylbutyl)
+ -hexyl
Toluene -(2-ethylhexyl)
S R R 60-80% s

Figure 3-4. Synthesis of electropolymerizable alkyl substituted ProDOTs. Branched 2-
methylbutyl and 2-ethylhexyl derivatives are prepared from racemic reagents.

3.2.2. Electrodeposition and Electrochemistry

After thorough purification of the electropolymerizable monomers, polymer films

were electrodeposited onto platinum button electrodes. As seen in Table 3-1, the

monomer oxidation depends little on the substitution.

Table 3-1. ProDOT-R2 monomer oxidation onset and peak potentials. Scan-rate is 50
mV/s.
R Eonset (V) Epeak (V)
-butyl 0.99 V 1.10 V
-hexyl 0.97 V 1.11 V
-2-methylbutyl 0.88 V 1.08 V
-2-ethylbutyl 0.98 V 1.11 V
-2-ethylhexyl 1.03 V 1.11 V

All onsets of oxidation or peak potentials are within a range of less than 100mV

from each other, consistent with the fact that the substituents are remote from the

dioxythiophene ring and do not affect significantly the electronic properties of the

thiophenes. All PProDOT-R2 polymers are easily electrodeposited in a polar,










electrochemically stable solvent such as acetonitrile. The monomers used in this study are

soluble in this solvent, but the polymers are not, allowing a smooth deposition of films

with various thicknesses. Figure 3-5 illustrates the deposition of a PProDOT-(2-

ethylhexyl)2 film on a platinum button.



20-

15-

10- O O

H H
E 05-

00-

05-

-10* IIIII0
-10 -05 00 05 10
E(V) vs. Fc/Fc



Figure 3-5. Electrodeposition of PProDOT-(2-ethylhexyl)2 on platinum button electrode.
The film was deposited from a 0.01M monomer solution in 0.1M
TBAP/ACN, at a scan rate of 50 mV/s.

After deposition of the polymers from each of the monomers, the films were rinsed

and studied in monomer-free 0.1M TBAP/ACN solution. In contrast to the monomer

oxidation, significant differences are observed in polymer oxidation as the side chains are

modified. Figure 3-6 presents the overlayed cyclic voltammetry of all PProDOT-R2

polymers studied. In the butyl substituted series, as methyl and ethyl branching are

introduced on the 2-position of the butyl side chains, the oxidation peaks are shifted to

higher oxidation potentials. In addition, the redox waves become narrower as steric bulk

is introduced. In the hexyl series, the same trend is observed going from PProDOT-

Hexyl2 to PProDOT-(2-ethylhexyl)2. As the chains with the stronger interchain










interactions are expected to have lower oxidation potential, this trend is consistent with

decreased interchain interactions as the steric bulk of substituents increases. The

narrowing of the redox waves may possibly be explained by the increasing open

morphology of the polymer films as steric bulk is increased.



PProDOT-Bu.
PProDOT-Hx2
PProDOT-i2-metnyl Dtyl),
PProDOT-(2-ethylbutyl
-- PProDOT-(2-ethylhexy 1).

X 0.4-
E 0.2-

-0.2-

-0.6-
-0.8-
-1.0-
-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4
E vs Fc/Fc* (V)



Figure 3-6. Polymer oxidation in the PProDOT-R2 series. All the polymers were
deposited by cyclic voltammetry at 50mV/s scan rate from 0.01M monomer
solution in 0.1M TBAP/ACN. The polymer oxidation curves were recorded in
monomer-free electrolyte at 50mV/s.

Comparing the oxidation curves of PProDOT-(2-ethylhexyl)2 and PProDOT-(2-

ethylbutyl)2, it seems that although the steric bulk of ethylhexyl is greater than ethylbutyl,

PProDOT-(2-ethylbutyl)2 has the higher oxidation potential. Examining the onset of

polymer oxidation, PProDOT-(2-ethylhexyl)2 has a higher onset potential, consistent with

a decrease of interchain interactions. The higher oxidation peak for PProDOT-(2-

ethylbutyl)2 is explained by considering the penetration of dopant ions into the polymer

film. We speculate that cyclic voltammetry is not only probing thermodynamic behavior

of the polymer but also the kinetic diffusion of the dopant ion inside the polymer film. In









the lower potential region of the oxidation wave, the oxidation of the polymer is

thermodynamically controlled and the chains with the lowest oxidation potentials will

oxidize first. At higher potential the current is limited by the penetration of the dopant

ions into the film, which is diffusion limited. In the case of PProDOT-(2-ethylhexyl)2, the

bulkier side chains provide more distance between chain stacks (different from the

interchain 7t-stacking distance) and the diffusion of the dopant ion is easier, resulting in a

lower peak potential.

3.3. Chemically Polymerized Soluble PProDOT-R2

3.3.1. Synthesis and Polymer Characterization

After bromination of the electropolymerizable monomer, the polymer is prepared

by Grignard Metathesis polymerization (Figure 3-7).47 In this method, the chemically

polymerizable monomer is reacted in THF at reflux temperature with one equivalent of

methylmagnesium bromide titratedd by a published method66). After the halogen-metal

exchange is complete, Ni(dppp)C12 is added in one portion, initiating the polymerization.

Within a few seconds, the yellow color of the catalyst turns red or purple as polymer is

formed. The polymerization is complete a few hours following introduction of the

catalyst.



Y0 ( NBS 0 0 1. MeMgBr, THF 0 0
DMF B /\Br 2. Ni(dppp)C1I2
S Br BrS
n

Figure 3-7. Grignard Metathesis polymerization of soluble PProDOT-R2.

After purification by Soxhlet extraction in MeOH (to remove magnesium salts,

polar impurities) and Soxhlet extraction with hexanes (to remove low molecular weight










polymer), the polymer is extracted with dichloromethane, chloroform or toluene. All

polymers show high solubility in many organic solvents (e.g. toluene, chloroform, THF).

Proton and carbon NMR confirmed the structure (see Experimental Section). Molecular

weights were estimated by GPC analysis in THF and are shown in Table 3-2. PProDOT-

Hx2 could be obtained in 5-10 g quantity, demonstrating that the synthesis is scalable.

Table 3-2. Molecular weight analysis of GriM polymerized PProDOT-R2. Molecular
weights are estimated vs. polystyrene standards.
Mn (g mol ) Xn Mw (g mol 1) PDI
Butyl 6,000 22 n/a n/a
Hexyl 27,000 83 47,600 1.73
2-methylbutyl 17,000 57 40,000 1.76
2-ethylhexyl 43,000 113 62,600 1.6

It is important to point out that the number-average molecular weight is well above

the effective conjugation length, and the optical and electronic properties are saturated.

Figure 3-8 shows the evolution of UV-Vis absorption spectrum as it is eluted out of the

GPC columns. Up to a number-average molecular weight of 5,700 g mol-1, there is a

significant shift of the Xmax. Above this molecular weight, the maxima of absorption

remain constant, suggesting an effective conjugation length of ca. 15 repeat units.


0.08- 008-
Mn X 539 539
0.07- -14,300(46) 576 007- M X 576
10,700(28) 14,300 (37)
0.06- 8,600 (23) 006- 17,600(46)
0.05 -7,500 (19) --21,100(55)
--5,700 (15) 005- --27,000(71) 539
0.04- 4,000 (10) 28,800(75) 578
S04 --2,800 (7) 57 004- -29,500(77)
0.03- 572 03 -32,200 (84) 540 579
< 37 570 <0
536 567 0 02-
0.01 2 001 540 6
0.00 526 000 53 576

200 300 400 500 600 700 800 200 300 400 500 600 700 800
% (nm) X (nm)

Figure 3-8. Evolution of UV-Vis absorption spectrum with molecular weight for
PProDOT(2-ethylhexyl)2. Number-average molecular weights are estimated
vs. polystyrene standards.







53


The thermal properties of the bulk polymers were studied by TGA and DSC


analysis. TGA indicates that the polymers have good thermal stability, reaching 5%


weight loss at ca. 3500C. For each polymer, the weight loss corresponds to the loss of the


2,2-dialkylpropyl unit. DSC analysis revealed no transition in the -150 to 2500C range


suggesting the polymers are amorphous, as expected from introducing bulky branched


substituents.


3.3.2. Solution Properties

The solution properties were studied by UV-Vis absorbance and fluorescence


spectroscopy. Figure 3-9 shows the spectra for PProDOT-Hexyl2 and PProDOT(2-


ethylhexyl)2.


012 012/ -12
PProDOT-Hexyl PProDOT-EtHx
SPPr T-Hexy2 -1 2 PPrDOT-EtH2 Stokes shift= 652 cm
010- Stokesshift= 860cm 010 595 m 619 nm 10
548 nm 585 nm 616 nm -1 0
553 nm
008- 008- -08
a o 006
006- 0 006- -06
/ 672 nm < 677 nm
004- 7 n 04 2D 004- 07 n 04 o

002- 740nm -02 002- 747 nm 02

000 00 000 -- 0
400 500 600 700 800 400 500 600 700 800
.(nm) .(nm)



Figure 3-9. Absorption and photoluminescence spectrum of PProDOT-Hexyl2 and
PProDOT(2-ethylhexyl)2. The polymers were excited at 550 nm.

The striking features of the solution optical properties are the presence of well-


resolved vibronic features, and the small stokes shifts (<700 cm-1). Some controversy still


exists on the origin of vibronic coupling and whether it is an interchain or intrachain


phenomenon as reviewed in our research group.67 Overall, there is overwhelming support


that vibronic features in CPs absorption and emission spectra arise from the coupling of


electronic absorption with vibrational modes of the polymer backbone and have an







54


intramolecular origin.69 In the spectra shown above, the polymer solutions are diluted but

still have well-resolved vibronic features, also suggesting an intramolecular, not

intermolecular origin of vibronic coupling. This was confirmed by dilution studies

showing no dependence of the peak wavelengths on the absorption on concentration.

As described by Bredas et al.,69 vibronic coupling depends on the respective

geometries of the ground and excited state (Figure 3-10). In a molecule where ground

state and excited state have identical geometries, such coupling is forbidden. The result is

that a single identical peak should be observed for absorption and emission. But when the

ground state and the excited state geometries are different, then vibronic coupling can be

68
seen.

C)

















tQ










Figure 3-10. Evolution of absorption spectrum with increasing distortion between the
ground state and the excited state. Adapted from ref. 69.









According to Kasha's rule,70 the fluorescence will occur from the lowest vibrational

state of the excited state resulting in a bathochromic shift of the emission compared to the

absorption. This is the origin of the Stokes shift, defined as the energy difference between

the energy at the maximum of absorption and the energy at the maximum of emission.

The larger the Stokes shift, the more distortion exists between the ground and the excited

states. As a quinoidal planar form is predicted in the excited state, it follows that a small

Stokes shift indicates a planar arrangement of the chain in the ground state.

In the case of PProDOT-R2 polymers, the presence of two clear vibronic peaks in

absorption and three in emission, assigned to the 0-0, 0-1 and 0-2 (only in emission)

vibronic transitions, along with a small Stokes shift indicate a small displacement of

geometry between the ground and the first excited state along with a planar conformation

of the chains. In poly(3-alkylthiophene)s, which have much higher intrachain

conformational flexibility in solution, the absorption is broad and featureless and the

Stokes shift is much higher at 5500 cm1. 71 Table 3-3 shows the solution properties for all

alkyl substituted PProDOTs studied here.

Table 3-3. Optical properties of alkyl substituted PProDOTs in toluene solution. Also
indicated is the relative intensity of the vibronic bands.
Stokes
R nmax absorption Shift Fsol.a
(nm) nmax emission (nm) (cm-1)
Hexyl 585 (1), 548 (0.96) 616 (1), 672 (0.46), 740 (0.13) 860 0.35
2-methylbutyl 602 (1), 556 (0.74) 621 (1), 677 (0.40), 746 (0.10) 482 0.36
2-ethylhexyl 595 (1), 553 (0.82) 619 (1), 677 (0.44), 747 (0.11) 652 0.37
(a) Quantum yield was calculated using sulforhodamine excited at 550 nm as standard.

From the solution optical data above, it is clear that branched substituted

PProDOTs have a more planar backbone and less conformational freedom than linear

substituted PProDOTs, as indicated by a smaller Stokes shift and more resolved vibronic









features. As expected, such differences are not seen in the fluorescence spectrum as there

is vibrational relaxation to the more stable, planar quinoidal conformation before

emission. The quantum yield remains mostly unaffected by the increasing steric bulk,

suggesting interchain interactions are not involved in toluene solution and that the chains

are molecularly dissolved.

3.3.3. Optoelectronic Properties of Solution Processed Films

To characterize the optical properties of the PProDOT-R2 polymers in the solid

state, films were spray-cast from toluene solution. The solutions were all red-colored. For

branched alkyl polymers, as the solvent dried out on the substrate, the red color changed

to a blue-purple color in the solid state. The corresponding absorption spectrum, shown in

Figure 3-11 for PProDOT(2-methylbutyl)2, shows a 20 nm bathochromic shift in

absorption between the toluene solution and the film as cast, indicating that the polymer

chains order during solvent evaporation and that there is significant interchain

interactions between polymer chains in the solid state. The vibronic coupling of the

spray-coated films becomes more resolved, consistent with planarization of the chains

induced by the aggregation process. When the films are oxidized and reneutralized

electrochemically, no further changes of optical absorption are observed.

PProDOT-Hx2 behaves differently. The red color of the solution is maintained in

the film state. As seen in Figure 3-11, the absorption spectra of solution and spray-coated

films have identical Xmax. This indicates that the polymer chains retain a solution

conformation upon casting. The broader absorption of the film state suggests that

aggregation does occur, but that the aggregates are ill-defined. Upon redox switching of

PProDOT-Hx2 spray-coated films, the color changes to blue-purple and the absorption

spectrum undergoes a 20 nm bathochromic shift. This behavior was also observed in











PProDOT-Bu2.63a The absorption shift is attributed to a doping-induced rearrangement of


the polymer chains. In the oxidized state, the chains adopt the more planar quinoidal


structure, forcing intrachain but also interchain rearrangements. These changes are


preserved upon reduction to the neutral polymer and no further shift is observed upon


further redox cycles.


Doping-induced rearrangement of PProDOT-Hx2 cast from toluene
Doping induced shift PProDOT-(2-methylbutyl)2 racemic
1Film as cast
10- -- Oxidized and reneutralized
Film as cast Toluene Solution
09 After Switching
Toluene Solution
08- 58 557
0 .8: 625 d 598
07- 571 623 As cast Oxidized and
S 5 reneutrazed585
06- o8-
o -533
04-

03-
01

400 500 600 700 0 5 60 70
.(nm) (nm)



Figure 3-11. Doping/Casting induced rearrangement in linear vs. branched alkyl
substituted PProDOTs. (left) PProDOT(2-methylbutyl)2; (right) PProDOT-
Hx2.

A possible explanation for the different behavior is that PProDOT-Hx2, is that the


linear substituted seven-membered ring can adopt both chair and twisted conformations


discussed above. This is supported by X-ray structures carried out on BisProDOT-(Et)2,


presented in Figure 3-12, and also theoretical calculations predicting a very small


difference of energy between the two conformers, in favor of the chair conformation.63a


In the case of branched substituents, theoretical calculations predict the twisted (more


planar) conformer to be significantly lower in energy than the chair conformer. As a


result, the branched polymer chains would have a much higher planarity and regularity.


This would favor strong interchain interactions and spontaneous organization during









casting. In the case of PProDOT-Hx2, the irregular distribution of the two conformers

within a polymer chain is expected to prevent efficient packing in the solid state.















Figure 3-12. X-ray crystal structure of BisProDOT-Et2 showing that a mixture of chair
and twisted conformations are present.7 Theoretical calculation (A. Perdomo)
shows the difference of energy between the two conformers to be less than
2.5kJ/mole (kBT at room temperature).

As demonstrated from the solution properties, the linear substituted PProDOTs are

more twisted than branched PProDOTs. This intrachain twisted conformation is expected

to easily hinder solid state packing and can also explain why linear PProDOTs form

disordered aggregates. Oxidation during electrochemical switching will force a more

planar conformation. Also, some authors suggest that in the oxidized state, t-dimers

might form to stabilize the polaron and bipolaron state.72 These two effects would allow

the reordering observed during switching. Table 3-4 displays the absorption maximum

for all polymers freshly cast from toluene, and following electrochemical doping.

Table 3-4. Solution, cast films and electrochemically oxidized and reneutralized films
absorption properties (a) (sh)= shoulder
R= Xnax Eg Xmax (cast) Eg (eV) Xmax (nm) Eg (eV)
(nm) (eV) (nm) (cast) (switched) redoxx)
Hexyl 552, 585 2.01 548, 585 1.97 576 1.85
2-methylbutyl 602, 556, 1.98 623,571,533 1.88 625, 572, 533 1.88
517 (sh)a
2-ethylhexyl 552, 595 1.99 612, 559, 525 1.94 618, 564, 523 1.93







59


Films spray-cast onto ITO were studied by spectroelectrochemistry. The behavior

is highly dependent on the type of substituents. As the steric bulk is increased, the optical

changes with increasing potential become more abrupt. PProDOT-Hx2 switches within

600mV potential increase, but PProDOT(2-methylbutyl)2 and PProDOT(2-ethylhexyl)2

switch within 350mV and 250mV, respectively (Figure 3-13). It was also observed that

the absorption of PProDOT-Hx2 does not exhibit a well defined vibronic structure, in

contrast to the branched derivatives indicating that the hexyl polymer retains

conformational disorder in the solid state, even following doping-induced rearrangement.

Consistent with electrochemical results suggesting decreasing interchain interactions with

steric bulk, the bandgap is increased from 1.85 eV for the hexyl polymer to 1.92eV for

the ethylhexyl polymer.




-03V
14 -V0 30V 0
0 00 3V 1V 12-. An
4 09V 0F-09V
08V -08V
-06V 07V
1 -03V 1V 04V -03V 1V 05V
0u 0 3V 0-0 4V
0 2V OV










This trend is also reflected in the potential dependence of the luminance seen in
01. 0 0V 02
-03V0 3V 0 0 0 1 l 0 53V




Figure 3-13. Spectroelectrochemistry experiment for PProDOT-Hx2 (left) and PProDOT-
(2-ethylhexyl)2 (right) in 0. 1M TBAP/ACN.

This trend is also reflected in the potential dependence of the luminance seen in

Figure 3-14. The luminance of PProDOT-Hx2 changes gradually (600mV) but the

luminance of the branched polymers varies abruptly (<300mV). To compare the

polymers electrochromic efficiency, coloration efficiency experiments were carried out

on the polymers. The results are summed up in Table 3-5. All spray-cast alkyl substituted







60


PProDOTs films display high color contrast, but the charge required to achieve 95% of


this contrast is higher in the linear polymers than the branched polymers, yielding higher


coloration efficiencies for the branched polymers. This can be explained by the


amorphous character of the branched polymers, with the bulky substituents providing


more open volume for the dopant ions to penetrate the films, effectively decreasing the


amount of capacitive currents contributions to the overall current during the polymers


oxidation.



PProDOT-(Hx)2
m PProDOT-(2-methybutyl)2
PProDOT-(2-ethylhexyl)2
90-

80- i
*
) 70-
c f
*
S*
0 50- O
1
40-

30-

20- *

-06 -04 -02 00 02 04 06
E (V) vs. Fc/Fc'



Figure 3-14. Luminance change with applied potential. All films were spray-coated from
toluene solution switched between -0.5V and 1V to eliminate any doping-
induced rearrangement effect. All films were -150-200 nm thick as
determined by profilometry.

Table 3-5. Coloration Efficiency study on PProDOT-R2 spray-coated films.
Substituent Switching AY AT AOD Qd CE
Time (s) (%) (%) (mC/cm2) (cm2/C)
Hexyl 0.37 58 65 0.52 0.61 850
2-methylbutyl 0.40 64 70 0.6 0.38 1020
2-ethylhexyl 0.73 70 79 N/A 0.87 1050









3.3.4. Conductivity Measurements

The conductivity of spray-coated PProDOT-R2 polymer films was determined by

the four-point probe method and the experimental parameters are reported in Table 3-6..

The measurements are taken as an average of multiple locations of the films, and

reproducibility was checked by measuring conductivity on several films, leading to

statistically consistent results.

Table 3-6. Conductivity measurements on spray-coated films gas phase doped with
iodine. Measurements are average values of at least two films, taken at
multiple locations of the films.
R= I (pA) AV (mV) Average a (S cm1)
Thickness (nm)
Hexyl N/A N/A N/A 5-10
2-methylbutyl 100 203, 185 286, 251 3.8, 4.2
2-ethylhexyl 10 300, 194 222, 234 0.3, 0.5

The conductivity decreases by an order of magnitude with increasing steric bulk,

going from hexyl to the ethylhexyl side chains. The methyl butyl derivative surprisingly

gives a similar conductivity to the linear hexyl substituted polymer. This can be explained

by considering both inter and intrachain interactions. PProDOT-(2-methylbutyl)2 has less

interchain interactions but has a more planar chain conformation. It is therefore expected

to have lower interchain charge transport through the polymer stacks than PProDOT-Hx2,

but higher intrachain charge transport along the polymer chains. Also, as discussed for

the polymer electrochemistry, the inter-stack distance is expected to be shorter in the

butyl polymers corresponding to a higher charge transport and conductivity between

stacks. Overall, introducing larger substituents prevents efficient charge transport in the

bulk material. This is the drawback of using branched substituents instead of longer alkyl

chains to induce solubility.









3.4. High Performance Electrochromic Devices

Because of the properties described above, the dialkyl substituted PProDOTs, and

in particular the branched compounds, seem ideal materials for high contrast

electrochromic materials. This section describes the application of these polymers in an

absorptive/reflective electrochromic device. The devices made with PProDOT-R2 were

prepared by Aubrey Dyer and Harun Turkcu. Figure 3-15 gives a schematic

representation of the device construction.

Spray-Cast Gold-coated substrate
PProDOT(2-ethylhexyl)2 (e.g., Mylar)
Gold-coated
porous membrane r


\Copper Contact


'Gel Electrolyte-soaked
porous separator
Spray-Cast
Transparent/ PProDOT(2-ethylhexyl)2
Cover

Figure 3-15. Schematic representation of a reflective/absorptive EC device using spray-
coated PProDOT(2-ethylhexyl)2 as the active and storage layer.

A porous gold membrane is coated with an electrochromic polymer (spray-coated

PProDOT(2-ethylhexyl)2), which constitutes the active layer of the device. The polymer

is oxidized electrochemically prior to building the device. The device is assembled by

placing the coated membrane on another layer of electrochromic polymer coated with gel

electrolyte serving as a charge storage layer. Upon applying a negative bias to the device,

the active polymer layer is reduced to the neutral form, and the device is absorptive to










visible light but highly reflective to NIR light, as shown in Figure 3-16.


110
-800mV
100-
90-
80 8
E 70
0
60 -
S50
S40-
S30 -
20 800mV
10-
200 400 600 800 1000 1200 1400 1600 1800 2000 2200
Wavelength(nm)



Figure 3-16. Reflectance plot for a reflective/absorptive EC device using spray-coated
PProDOT(2-ethylhexyl)2 as the active and storage layer.

3.5. Conclusion

A series of soluble, regiosymmetrically substituted branched alkyl PProDOTs were

synthesized by Grignard Metathesis. Introduction of branching results in significant

improvement in solubility and electrochromic properties, leading to faster switching

rates, higher contrasts and significantly higher coloration efficiencies. The improvement

is attributed mainly to a decrease of interchain interactions promoted by the bulkiness of

the branched substituents, resulting in the highest coloration efficiencies, but also the

lowest conductivities for PProDOT-(2-ethylhexyl)2 polymer. In addition, the branched

polymers display unusual spectroelectrochemical properties, with most optical changes

obtained in a narrow optical window (<350mV), in contrast to linear substituted

polymers, requiring much larger potential increase (>600mV). This behavior is attributed









to a more open morphology of the polymer films substituted with the bulky side chains,

allowing easier penetration of dopant ions.

The introduction of branched alkyl substituents also affects the intrachain

conformation of the chains. Optical absorption studies on solutions indicate small Stokes

shift, well-resolved vibronic features with a dominant 0-0 transition, pointing to a mostly

planar conformation of the polymer chains. The chains planarity allows easy interchain

ordering of the polymer chains in the solid state, evidenced from the large bathochromic

shift in absorption and a significant change of color observed during spray-casting of the

polymers.

In Chapter 5, the synthesis of chiral equivalents of these polymers will be

described. These polymers can be studied using chiroptical techniques which are

powerful tools to examine interchain and intrachain interactions, affording better

understanding on how the branched substituents affect the electrochromic properties.

3.6. Chapter Synthetic Details

3,4-dimethoxythiophene: In a 250 mL 3-neck round bottom flask equipped with a

reflux condenser 6.2 g (0.27 mol) of sodium was slowly dissolved in 90 mL of methanol

under argon. Then 4.2 g (0.053 mol) of CuO, 0.9 g (0.0053 mol) of KI, and 13 g (0.053

mol) of 3,4-dibromothiophene were added. The black mixture was refluxed for 3 days.

0.9 g (0.0053 mol) of KI was added and the mixture was refluxed for an additional 24

hours. The dark mixture was cooled, filtered through Btichner, diluted with 150 mL of

water, and extracted 3 times with ether. The combined ether layers were washed with

water and dried with magnesium sulfate. The ether was removed under vacuum, and the

crude product was purified by vacuum distillation (80-82 C / 1.0 mm Hg), (lit. 59-65 C









/ 0.5 mm Hg) to yield 5.0 g (65 %) of product. 1H NMR (300 MHz, CDCl3) 6 6.2 (s, 2H),

3.8 (s, 6H).

General Procedure for the synthesis of alkylated diethyl malonate: In a 5 L flame

dried 3 neck round bottom flask equipped with an argon inlet, a condenser, and an

addition funnel were combined 2L of dry THF, 3.5 mol of alkyl bromide (3eq), and 3.5

mol of NaH. The flask was cooled to 0 C and 1.15 mol of freshly distilled diethyl

malonate was added dropwise through the addition funnel. When the addition of the

malonate was completed, the mixture was refluxed overnight. The flask was then cooled

at 0 C and the remaining sodium hydride was quenched by adding water dropwise. The

mixture was then poured into brine (2 L), extracted two times with ether, and washed

with brine. The solvent and the alkyl bromide were removed under vacuum. The crude oil

obtained was then used in the next step without further purification.

General Procedure for the synthesis of diols: In a 5 L flame dried 3 neck round

bottom flask equipped with an argon inlet, a condenser, and an addition funnel, were

combined 2 L of dry ethyl ether and 1.7 mol of LiAlH4 powder. The crude dialkyl

malonate (1.13 mol) was added dropwise at 0 C. When the addition was completed, the

mixture was allowed to warm to room temperature. The reaction mixture was stirred

under argon for 20 hr. The excess LiAlH4 was SLOWLY quenched with one liter of 1M

HCI at 0C. The aqueous phase was extracted with 2x500 mL ether and the combined

organic phases were washed with water (4x500 mL). The organic phase was dried with

magnesium sulfate and the solvent was evaporated under vacuum. The resulting product

is purified by column chromatography (90% DCM/10% acetonitrile, product revealed









with vanillin dip as black spots). After purification, yield obtained is 25-50% for

branched derivatives, 65-80% for the linear derivatives.

2,2-Dihexylpropane-1,3-diol: White crystalline solid. 1H NMR (300 MHz, CDC13)

6 3.59 (d, 4H, J= 5.3 Hz), 2.39 (t, 2H, J= 5.3 Hz), 1.40-1.10 (m, 20H), 0.90 (t, 6H, J= 7.3

Hz); 13C NMR (75 MHz, CDCl3) 6 69.7, 41.2, 32.0, 31.1, 30,5, 29.9, 23.1, 22.9, 14.3;

HRMS calculated for C15H3202: 245.2481 Found: 245.2475 Elemental Anal. Calcd for

C15H3202: C 73.71; H 14.20. Found: C 74.12; H 14.18.

2,2-Bis-(2-methylbutvl)-propane-1,3-diol: white amorphous solid. 1H NMR (300

MHz, CDCl3) 6 0.73-0.97 (m, 12H), 1.05-1.26 (m, 4H), 1.26-1.51 (m, 6H), 2.21-2.32 (br,

2H), 3.51-3.66 (br, 4H); 13C NMR (75 MHz, CDCl3) 6 11.73, 21.92, 29.56, 32.21, 39.18,

42.82, 70.21.

2,2-Bis-(2-ethylhexyl)-propane-1,3-diol: clear oil. H NMR (300 MHz, CDCl3) 6

3.65 (s, 4H), 2.41 (s, 2H), 1.40-1.10 (m, 22H), 0.95-0.80 (m, 12H); 13C NMR (75 MHz,

CDCl3) 6 70.1, 42.8, 37.1, 34.9, 33.7, 29.0, 27.9, 23.4, 14.4, 10.8 HRMS Calcd for

C19H4102 (M+H)+ 301.3106 Found 301.3103; Elemental Anal. Calcd for C19H4002 C

75.94; H 13.42. Found C 75.95 H 12.35.

General procedure for the transetherification of 3,4-dimethoxythiophene with diols:

21 mmol of 3,4-dimethoxythiophene, 22 mmol of diol, 2.1 mmol ofp-toluenesulfonic

acid, and 200 mL toluene were combined in a 500 mL flask equipped with a soxhlet

extractor with type 4A molecular sieves or CaCl2 in a cellulose thimble. The solution was

refluxed overnight. The reaction mixture was cooled and washed once with water. The

toluene was removed under vacuum, and the crude product was purified by column

chromatography on silica gel with 3:2 hexanes / methylene chloride.









3,3-Dihexvl-3,4-dihydro-2H-thieno[3,4-bl[1,4]dioxepine (ProDOT(Hx)2): clear

oil (95 % yield); 1HNMR (300 MHz, CDCl3) 6 6.42 (s, 2H), 3.88 (s, 4H), 1.45-1.20 (m,

20 H), 0.95-0.82 (m, 6H). 13C NMR (75 MHz, CDCl3) 6 149.9, 104.9, 77.8, 43.9, 32.0,

32.0, 30.4, 23.0, 22.9, 14.3. HRMS calculated for C19H3202S: 324.2123 Found: 324.2120.

Elemental Anal. Calcd for C19H3202S: C 70.32; H 9.94; S 9.88 Found: C 70.48; H 10.48;

S 9.78.

3,3-bis(2-methylbutvl)-3,4-dihydro-2H-thieno[3,4-bl[1,41dioxepine

(ProDOT(2-methylbutvl),): clear oil (70% yield); 1H NMR (300 MHz, CDCl3) 6 0.77-

1.01 (m, 12H), 1.07-1.63 (m, 10H), 3.79-4.05 (m, 4H), 6.42 (s, 2H); 13C NMR (75 MHz,

CDCl3) 611.69, 22.06, 22.08, 29.66, 29.68, 32.17, 32.21, 40.85, 40.88, 45.57, 78.24,

78.35, 78.39, 104.65, 149.92.

3,3-Bis-(2-ethylbutvl)-3,4-dihydro-2H-thieno[3,4-bi[1,4]dioxepine (ProDOT(2-

ethylbutyl)h): The crude oil obtained was purified by column chromatography (3:2)

hexanes/dichloromethane followed by another column using 3:1

hexanes/dichloromethane to afford a clear oil (66% yield). 1H NMR (300MHz, CDCl3) 6

0.78-0.95 (t, 12H), 1.21-1.47 (m, 14H), 3.93 (s, 4H), 6.42 (s, 2H); 13C NMR (75MHz,

CDCl3) 6 10.94, 27.57, 35.17, 38.23, 45.44, 77.98, 104.66, 149.97.

3,3-Bis-(2-ethylhexvl)-3,4-dihydro-2H-thieno[3,4-bl[l,4]dioxepine (ProDOT(2-

ethylhexyl)z): The crude oil obtained was purified by column chromatography (3:2)

hexanes/dichloromethane followed by another column using 3:1

hexanes/dichloromethane to afford 6.0 g of clear oil (57%). 1H NMR (300MHz, CDCl3) 6

6.43 (s, 2H), 3.93 (s, 4H), 1.2-1.5 (m, 22H), 0.75-1.0 (m, 12H); 13C NMR (75MHz,

CDC13) 6 150.0, 104.61, 78.0 (t), 45.5, 38.7, 35.0, 33.8, 29.0, 28.0, 23.3, 14.4, 10.8.;









HRMS Calcd for C23H4002S 380.2749. Found 380.2753; HRMS calculated for

C23H4002S: 380.2749 Found: 380.2753. Elemental Anal. Calcd for C23H4002S: C 72.58;

H 10.59; 0 8.41; S 8.42. Found: C 72.78; H 10.30; 0 8.68; S 8.24.

General procedure for the bromination of ProDOT-R2: In a 2-neck 250 mL round

bottom flask filled with 80 mL chloroform, 1.5g (2.1 mmol) of ProDOT was added and

the solution was bubbled under argon for 60 minutes. Then 1.12 g (6.24 mmols) N-

bromosuccinimde was added and the solution was stirred for 20 hr. After completion, the

solvent was removed by rotary evaporation under reduced pressure and the resulting

residue was purified by column chromatography on SiO2 with (4:1)

hexanes/dichloromethane .

6,8-Dibromo-3,3-Dihexvl-3,4-dihvdro-2H-thieno[3,4-bi [1,41dioxepine

(ProDOT(Hx)2Br2): clear oil obtained (91% yield).1H NMR (300MHz, CDCl3) 6 3.93

(s, 4H), 1.45-1.15 (m, 20H), 0.90 (t, 6H, J= 7.0 Hz); 13C NMR (75MHz, CDCl3) 6 147.4,

104.8, 90.8, 78.3, 44.2, 31.9, 30.3, 22.9, 14.3; HRMS calculated for C19H3002SBr2:

480.0333 Found: 480.0334. Elemental Anal. Calcd for C19H3002SBr2: C 47.31; H 6.27; S

6.65; Br 33.13. Found: C 47.83; H 6.79; S 6.88; Br 32.79.

6,8-Dibromo-3,3-bis(2-methylbutyl)-3,4-dihydro-2H-thieno[3,4-

bl [1,41dioxepine (ProDOT(2-methylbutvlh)Br2): product obtained as a clear oil

(86%).1H NMR (300MHz, CDC13) 6 0.8-1.0 (m, 12H), 1.08-1.27 (m, 2H), 1.27-1.59 (m,

8H), 3.86-4.10 (m, 4H); 13C NMR (75MHz, CDC13) 6 11.67, 21.93, 21.96, 29.67, 29.70,

32.08, 32.13, 40.81, 40.83, 40.85, 45.87, 78.98, 79.07, 79.11, 90.64, 147.31.

6,8-Dibromo-3,3-Bis-(2-ethylbutvl)-3,4-dihydro-2H-thieno[3,4-bi [1,41dioxepine

(ProDOT(2-ethylbutvl)2Br2): The crude oil obtained was purified by column









chromatography (4:1) hexanes/dichloromethane to afford 1.2 g of clear oil ( 81%). 1H

NMR (300MHz, CDCl3) 6 0.77-0.92 (t, 12H), 1.2-1.45 (m, 14H), 4.0 (s, 4H); 13C NMR

(75MHz, CDCl3) 6 10.92, 27.48, 35.19, 38.27, 45.72, 78.59, 90.65, 147.30; HRMS Calcd

for C23H3802SBr2 483.0386. Found 483.0380; Elemental Anal. Calcd for C19H3002SBr2:

C 47.31; H 6.27 Found: C 47.43; H 6.40.

6,8-Dibromo-3,3-Bis-(2-ethylhexvl)-3,4-dihydro-2H-thieno 13,4-bl [1,41 dioxepine

(ProDOT(EtHx)2Br2): The crude oil obtained was purified by column chromatography

(4:1) hexanes/dichloromethane to afford a clear oil (80 %). 1H NMR (300MHz, CDCl3) 6

4.00 (s, 4H), 1.15-1.5 (m, 22H), 0.8-1.0 (m, 12H); 13C NMR (75MHz, CDCl3) 6 147.3,

90.5, 78.6, 45.8, 38.8, 35.0, 29.0, 28.0, 23.3, 14.4, 10.8; HRMS Calcd for C23H3802SBr2

538.0940. Found 538.0944; Elemental Anal. Calcd for C23H3802SBr2: C 51.31; H 7.11; S

5.96 Found: C 51.28; H 7.00; S 6.04.

General Procedure for Grignard metathesis polymerization of ProDOT-

RzBr2: In a flame dried 250 mL round bottom flask, dry THF (150 mL) and 3.0 g (0.34

mmol) of ProDOT(R)2Br2 was added under argon. Then methyl magnesium bromide

(3.75 mL, 3.45 mmol, 0.918 M) was slowly added by syringe. The mixture was then

refluxed for 2 hrs. After, the flask was cooled and Ni(dppp)C12 (18.4 mg, 0.0341 mmol)

was added and the reaction was heated at reflux overnight under argon. The solution was

then cooled and the polymer was precipitated by pouring the solution in 400 mL

methanol. The dark purple solid was purified by soxhlet extraction with methanol for 24

hr, hexanes for 48 hr, and finally chloroform for 24 hr. The chloroform was evaporated

under reduced pressure to afford purple solid.









Polv(3,3-Dihexvl-3,4-dihydro-2H-thieno[3,4-b] [1,41dioxepine)

(PProDOT(Hexvl)2): shiny brown solid obtained (66 %). 1H NMR (300 MHz, CDCl3) 6

3.95 (bs, 4H), 1.62-1.2 (m, 20H), 0.97-0.80 (m, 6H); 13C (75 MHz, benzene-d6) 6 146.4,

115.3, 78.0, 44.3, 32.6, 31.0, 23.5, 14.8; Elemental Anal. Calcd for (C19H3002S)164HBr: C

70.65; H 9.38; S 9.91, Br 0.15 Found: C 69.87; H 9.99; S 9.52; Br 0.15; Ni <0.01. GPC

analysis: Mn= 38,100, Mw=65,900 PDI=1.73.

Polv(3,3-bis(2-methvlbutvl)2-3,4-dihvdro-2H-thieno [3,4-b] [1,41 dioxepine)

(PProDOT(2-methvlbutvl)2): shiny brown solid obtained (60%). 1H NMR (300 MHz,

CDCl3) 6 0.82-1.16 (br, 12H), 1.16-1.3 (br, 4H), 1.3-1.5 (br, 4H), 1.5-1.65 (br, 2H), 3.9-

4.15 (br, 4H); 13C (75 MHz, benzene-d6) 6 12.15, 22.61, 30.10, 32.67, 32.77, 41.22,

45.93, 78.72, 114.98, 145.87; GPC analysis: M,=17,000, Mw=30,000 PDI= 1.76.














CHAPTER 4
SYNTHETIC CONTROL OF ORDER IN BRANCHED ALKOXYMETHYL
POLY(3,4-PROPYLENEDIOXYTHIOPHENES) (PPRODOT-(CH20R)2)

4.1. Introduction

The previous chapter demonstrated that increasing the steric bulk in branched alkyl

PProDOT polymers, these having all carbon based substituents, results in a decrease of t-

stacking interactions and possibly an increase of the distance between R-stacks as well.

This leads to polymers with higher solubility in organic solvents, higher contrast and fast

switching electrochromic devices due to the fast diffusion of dopant ions into the polymer

films being facilitated. To enhance the polymer solubility and further optimize the

electrochromic properties, alkoxymethyl spacers were placed between the 2- position of

the ProDOT propylene bridge and the branched alkyl side chains to provide ether linked

substituents. The presence of this spacer in the side chains will provide more steric

hindrance and prevent ordering due to the conformational flexibility of the alkoxy chains.

Combined with the steric bulk of the branched side chains should lead to a strong

decrease in interchain interactions, and more disorder in solution and solid state. On the

other hand, as the branching groups are further away from the seven-membered ring and

have more flexibility than the rigid alkyl group, less effect of the branching group on the

ring conformation could be expected, leading to important intrachain and interchain

changes. Figure 4-1 displays the structures described and studied in this Chapter.

PProDOT-(CH20C18H37)2, synthesized by Ben Reeves, is used to demonstrate the

differences between branched and linear polymers.






















PProDOT-(CH20-2-methyl b



o o


O 0


n


O o


O o


n
PProDOT-(CH20-2-ethy


PProDOT-(CH20-2-ethylhexyl)2




0 0





S n
F

W


n
~ProDOT-(CH2OC1 8H37)2


Figure 4-1. Family of branched dialkoxymethyl substituted PProDOTs. PProDOT-
(CH20C18H37)2 was synthesized by Ben Reeves and will be used for
comparison and discussion of branching effects.

4.2. Electropolymerized PProDOT-(CH2OR)2

4.2.1. Electropolymerizable Monomer Synthesis

An advantage of the synthesis of dialkoxymethyl substituted ProDOTs, compared

to the alkyl substituted polymers, is their ease of synthesis. As shown in Figure 4-2, the

substituents are placed in the last step of the synthesis using a simple Williamson

etherification between the corresponding alcohol and PProDOT-(CH2Br)2. PProDOT-

(CH2Br)2 is prepared by transetherification between 3,4-dimethoxythiophene and 2,2-

bis(bromomethyl)-propane-1,3-diol, both commercially available. The alkyl substituted


lbutyl)2


F







73


ProDOTs, described in Chapter 3 are more difficult to synthesize, as the disubstituted

2,2-propane-1,3-diol must be prepared. On the contrary, many linear and branched

alcohols are commercially available. Also, in the case of branched derivatives, the diol

synthesis has a low overall yield, which is a problem when the starting materials are

expensive or difficult to obtain.




OH OH R= -2-methylbutyl
MeO OMe pTSA 0 _O ROH, NaH. 0 0 -2-ethylbutyl
+ Toluene /\ DMF -2-ethylhexyl

S Br Br 60-80% S S -C18H37

Figure 4-2. Synthesis of electropolymerizable alkoxymethyl substituted ProDOTs.
Branched 2-methylbutyl and 2-ethylhexyl derivatives are prepared from
racemic reagents.

4.2.2. Electrodeposition and Electrochemistry

The alkoxymethyl substituted ProDOT electropolymerizable monomers were

electrodeposited on a platinum button from a 0.01M monomer solution in 0.1M

TBAP/ACN. Figure 4-3 shows the electrodeposition of PProDOT-(CH20-2-ethylhexyl)2.


5-




0 0.
E 2-
E 1

0-


2-
-1-



-10 -05 00 05 10 15
E(V) vs Fc/Fc



Figure 4-3. Electrodeposition of PProDOT(CH20-2-ethylhexyl)2 on Pt Button. The film
was deposited from a 0.01M monomer solution in 0.1M TBAP/ACN, at a
scan rate of 50 mV/s.










After electrodeposition on platinum button electrodes, the polymers oxidations in

monomer-free electrolyte were compared (Figure 4-4). A similar trend to the alkyl

derivatives was observed, where increasing the steric bulk of the side chains results in an

increase of the onset and peak oxidation potentials. This shift is consistent with less

interchain interactions when the substituents are bulkier. Again, as seen with the alkyl

substituted PProDOT, the ethylhexyloxymethyl derivative has a lower peak oxidation

potential than PProDOT-(CH20-2-ethylbutyl)2, although the ethylhexyloxy chains are

bulkier. This behavior might be explained by easier diffusion of the dopant ions between

polymer stacks.


ethylhexyloxy
ethylbutyloxy
-- methylbutyloxy
10-







Z -05-

-1 0-

-08 -06 -04 -02 00 02 04
E(V) vs. Fc/Fc+


Figure 4-4. Polymer oxidation in the PProDOT-(CH20R)2 series. All the polymers were
deposited by cyclic voltammetry at 50mV/s scan rate from 0.01M monomer
solution in 0.1M TBAP/ACN. The polymer oxidation curves were recorded in
monomer-free electrolyte at 50mV/s.

Table 4-1 compares the polymer oxidation values of the PProDOT-R2 and

PProDOT-(CH20R)2 series. Overall, introduction of the oxygens does not seem to have a

strong effect on the polymer oxidation, except in the case of the methyl branched

polymers. PProDOT-(2-methylbutyloxymethyl)2 has a significantly poorer reversibility in









oxidation than PProDOT-(2-methylbutyl)2. In the case of the bigger branching ethyl

group, the oxidation peaks are all quasi-reversible. This trend indicates that the branching

groups are mainly responsible for the increase in polymer oxidation due to steric bulk.

The introduction of the oxymethyl spacer seems to have a minor effect, especially with

small branching groups, where a broad two-peak reduction suggests different chain

conformations or aggregates exist in the oxidized state.

Table 4-1. Comparison of alkyl and alkoxymethyl substituted PProDOTs polymer
oxidation. Potentials are vs. Fc/Fc+.
PProDOT Eonset E1/2 (mV) AEp (mV) I[ox], p / I[red], p
Substituents monomer Polymer Polymer Polymer
Butyl 0.99 V -65 (-180a) 129(281) 2.15
Hexyl 0.97 V -66(-165 a) 54 (252) 1.12
2-methylbutyl 0.88 V -3 135 1.14
2-methylbutyloxymethyl 1.02V 0 (-269) 50 (295) 3.51
2-ethylbutyl 0.98 V 155 107 1
2-ethylbutyloxymethyl 0.97V 52 124 1
2-ethylhexyl 1.03 V 28 34 1.3
2-ethylhexyloxymethyl 1.01V 75 139 1

4.3. Chemically Polymerized Soluble PProDOT-(CH2OR)2

4.3.1. Synthesis and Polymer Characterization

After bromination of the electrochemically polymerizable monomer with N-

bromosuccinimide, the soluble polymers were obtained by Grignard Metathesis (Figure

4-5).

OR OR OR OR OR OR


0 NBS 0 1. MeMgBr, THF
DMF Br I \ Br 2. Ni(dppp)C12 /
S Br S Br S
n
Figure 4-5. Polymerization of PProDOT-(CH20R)2 by Grignard Metathesis.

After purification by Soxhlet extraction with MeOH and hexanes, the polymers

were extracted with chloroform, and obtained as shiny brown solids after solvent










evaporation. The polymers are highly soluble in chloroform, toluene, and THF. For

PProDOT-(CH20-2-methylbutyl)2, heat was required to obtain dissolution of the polymer

chains. The polymer chains remained in solution but a change of color from red to purple

suggests aggregation might occur as the solutions are cooled to room temperature. The

polymer structures were confirmed by 1H and 13C NMR. GPC analysis of the polymers

show molecular weights between 10,000 and 20,000 g mol-1 (Table 4-2), corresponding

to a molecular structure of more than 30 repeating units.

Table 4-2. Molecular weight analysis of GriM polymerized PProDOT-(CH20R)2. The
molecular weights are determined vs. polystyrene standards.
R Mn (g mol ) Xn Mw (g mol ) PDI
CH20-2-methylbutyl N/A N/A N/A N/A
CH20-2-ethylbutyl 12,400 33 17,500 1.4
CH20-2-ethylhexyl 13,000 30 22,200 1.7



4.3.2. Solution properties

The solution properties were studied by UV-Vis absorbance and fluorescence

spectroscopy. Figure 4-6 shows the spectrum for PProDOT-(CH20-2-methylbutyl)2 and

PProDOT-(CH20-2-ethylhexyl)2 in xylenes solutions.


PProDOT-(CH 0-2-methylbutyl) 2PProDOT(CH 0-2-ethylhexyl)2
548 1611 545 604
^ /\ *20x106 008- -5x106
006- 845cm-1 3 8 744cm -4x10o m
S.15x106 006- 659 3
84 o3- o
-10xlO6 004- -2x10

721
0 02- -50x10' 002- -1x 0

=I000- --0-0
400 500 600 700 800 400 500 600 700 800
.(nm) .(nm)


Figure 4-6. Absorption and photoluminescence spectrum of PProDOT(CH20-2-
methylbutyl)2 and PProDOT(CH20-2-ethylhexyl)2. For fluorescence,
Xex=550nm.









UV-Vis absorption and fluorescence results for PProDOT(CH20-2-methylbutyl)2,

PProDOT(CH20-2-ethylbutyl)2 and PProDOT(CH20-2-ethylhexyl)2 are summarized in

Table 4-3. The alkoxymethyl substituted polymers have clear vibronic features, attributed

to the 0-0 and 0-1 vibrational transitions. The 0-1 vibronic transition is the dominant

vibronic feature, in contrast with branched alkyl substituted PProDOTs, where the 0-0

transition is dominant. In PProDOT-Hx2, the two vibronic transitions have similar

intensities. As described in Figure 3-12, stronger higher energy vibronic transitions for

alkoxymethyl substituted polymers (and PProDOT-Hx2) suggest these polymers have

more intrachain conformational disorder.

Table 4-3. Optical properties of alkoxymethyl substituted PProDOTs in toluene solution.
Also indicated in parenthese is the relative intensity of the vibronic bands
Stokes
R Xmax absorption Xmax emission Shift Fsol.a
(nm) (nm) (cm-1)
2-methylbutyl 548 (1), 581 (0.92) 611 (1), 663 (0.71) 845 0.18
2-ethylbutyl 545 (1), 584 (0.99) 605 (1), 658 (0.55), 721 (0.17) 595 0.37
2-ethylhexyl 545 (1), 578 (0.98) 604 (1), 659 (0.62), 721 (0.25) 744 0.34
(a) Quantum yield was calculated using sulforhodamine excited at 550 nm as standard.
PProDOT(CH20-2-ethylbutyl)2 and PProDOT(CH20-2-ethylhexyl)2 in solution

have quantum yields of 0.34 and 0.37, similar to values obtained for PProDOT-R2. The

minimal dependence of the quantum yields on the polymer structure suggests that

interchain interactions are not involved and the chains are molecularly dissolved. If

interchain interactions were involved in solution, significant differences of quantum

yields would be expected as interchain distance varies with steric bulk. PProDOT-

(CH20-2-methylbutyl)2, on the other hand, has a lower quantum yield of 0.18. The

decreased quantum yield is consistent with interchain quenching in solution as the

polymer has low solubility at room temperature and required heating to dissolve. Another

possible explanation is that the more twisted polymer conformation allows for intrachain







78



folding. Intrachain quenching between chromophores within a single chain will lead to


energy transfer to traps, leading to a decrease in quantum yield.


4.3.3. Optoelectronic Properties of Solution Processed Films

Films were spray-cast from either toluene or chloroform solution (5mg/ mL, 12 psi)


onto ITO-coated glass slides. Absorbance was recorded after casting and following redox


switching of the films. Results for the alkoxymethyl substituted PProDOTs are presented


in Table 4-4, and in Figure 4-7 for PProDOT(CH20-2-methylbutyl)2 and PProDOT-


(CH20-2-ethylhexyl)2.


PProDOT-(CH20EtHx)2 cast film (from toluene) before and after switching
PProDOT(CH0-2- methylbutyl) Film as cast
--Oxidized and reneutralized --film as cast
11 CHCI solution oxdized and reneutrahzed
S2- toluene solution
S0 544 electrochemically polymezed film
09- 10- 555-. 582 -604
S08- o
0 7- o08-
< 06 <
05. 06-
S 04- E
S 03- 04-
0202-
01-
00- 00
400 500 600 700 400 500 600 700
(nm) (nm)



Figure 4-7. Doping/Casting induced rearrangement in linear vs. branched alkyl
substituted PProDOTs. (left) PProDOT(CH20-2-methylbutyl)2; (right)
PProDOT-(CH20-2-ethylhexyl)2.


The behavior of PProDOT-(CH20-2-ethylhexyl)2 and PProDOT-(CH20-2-


ethylbutyl)2 is similar to the one observed in PProDOT-Hx2. Upon casting, the polymer


films retain a solution conformation, as they have similar absorption spectrum.


PProDOT(CH20-2-methylbutyl)2 spray-cast film, although its absorbance maxima are


identical for both cast film and solution, has a broader absorption spectrum dominated by


the 0-1 vibronic transition, different from chloroform solution where the 0-0 vibronic









features dominate. This suggests that the polymer forms disordered aggregates with

limited interchain interactions and that the individual chains are highly twisted.

Upon switching the polymer film electrochemically, the absorption spectra of the

spray-cast films undergo a bathochromic shift, the optical bandgap is lowered, and the

vibronic features become better resolved. The well-resolved vibronic structure supports a

planar intrachain conformation of the polymer chains, which can also explain the

absorption bathochromic shift and lower bandgap. An increase of interchain interactions

after redox switching is also likely, as the planarity favor interchain ordering of the

polymer chains.

Table 4-4. Optical properties of PProDOT(CH20-2-alkyloxymethyl)2 polymers in
solution, films as cast and films following electrochemical
oxidation/reneutralization cycle.
R= )max Eg kmax Eg )max Eg
(toluene) (Toluene) (cast) (cast) (switched) (switched)
2-methylbutyl 588, 549 2.0 586, 544 1.96 612, 561, 1.91
528 (sh)
2-ethylbutyl 579, 545 2.01 581, 544 1.98 607, 556, 1.95
520
2-ethylhexyl 575, 544 2.01 582, 544 2.0 604, 555, 1.97
520

The spray-cast films were then analyzed by spectroelectrochemistry. For the

branched ethylhexyloxymethyl polymer, shown in Figure 4-8, a similar effect to the

branched alkyl analogs is observed, with sharp optical changes as the potential is

increased. For PProDOT-(CH20-2-ethylhexyl)2, most optical changes are obtained with

less than 150 mV potential increase. This is sharper than the ethylhexyl alkyl substituted

polymer, possibly indicating a synergistic effect between the steric bulk from the ethyl

branching group and the flexibility provided by introduction of the oxygens. In contrast

the linear octadecyloxymethyl substituted polymer, also shown in Figure 4-8, switches











gradually and requires 600mV potential increase to obtain similar optical changes. These


differences can be rationalized in terms of morphology of the polymer films. In the case


of the octadecyloxy methyl substituted polymer, crystallization of the side chains,


evidenced by melting and crystallizations transitions in the DSC thermal analysis, hinders


the penetration of the dopant ions inside the polymer film.73 In the case of the bulky


substituents, the interchain and interstack distance increase, leaving more space for the


dopant ions to penetrate.




1 o PProDOT-(CH2OC18H37)2
10-
10 08- -075V
08- -055V
+1 20V 035V
0 -+100V 06- -025V
06- +080V 0 15V

S04- +040V 04 005V
+0 10V -015 V
02-50V --025V
002- --045 V

00- -095V
400 600 800 1000 100 1400 1600 400 600 800 1000 1200 1400 1600
(nm) Wavelength (nm)



Figure 4-8. Spectroelectrochemistry experiment for PProDOT-(CH20-2-ethylhexyl)2
(left) and PProDOT-(CH20C18H37)2 (right).

Luminance studies on spray-cast films confirm the trend observed in the


spectroelectrochemistry experiment. Figure 4-9 shows the overlayed luminance plot as a


function of potential of alkoxymethyl PProDOT polymers. The alkyl substituted


PProDOT-(2-ethylhexyl)2 is added for comparison. As expected, as the steric bulk is


increased by introducing larger branching, the optical changes with potential are sharper.


This demonstrates that the branching group is responsible for these unusual optical


changes. The introduction of alkoxy in place of alkyl substituents seems to reinforce this











effect as the ethylhexyloxymethyl polymer display sharper optical changes than the

ethylhexyl polymer.


PProDOT-(2-ethylhexyl)
-*-PProDOT-(CHOC H35)2
-m-PProDOT-(CH 20-2-ethylhexyl)2
90- -.- PProDOT-(CH 20-2-ethylbutyl)2
80-
S70-
60-
S50-
40-
30-
20-
-06 -04 -02 00 02 04 06
E (V) vs Fc/Fc'



Figure 4-9. Luminance change vs. applied potential in PProDOT(CH20R)2 polymers. All
films were spray-coated from toluene solution switched between -0.5V and
IV to eliminate any doping-induced rearrangement effect. All films were
-150-200 nm thick as determined by profilometry.

To evaluate the efficiency of the electrochromic transition, coloration efficiency

experiments on the spray-cast films were carried out (Table 4-5).

Table 4-5. Coloration Efficiency of PProDOT-(CH20R)2 films sprayed on ITO-coated
glass slides.
Substituent Switching AT AOD Qd CE
Time (s)a (%) (mC/cm2) (cm2/C)
2-methylbutyl 0.7 72 1.1 1.2 923
2-ethylbutyl 0.4 70 0.8 0.65 1240
2-ethylhexyl 0.6 80 1.12 0.9 1235
a time to achieve 95% of total color contrast; b color contrast between fully oxidized and
neutral states; c log(Tox(95%)/Tred)

The results indicate that as the branching size increases, the coloration efficiency

increases as well. PProDOT-(CH20-2-methylbutyl)2, compared to PProDOT-(CH20-2-

ethylhexyl)2, requires more charges to obtain a similar change of optical density. The

switching time is also smaller for ethylhexyl polymer. The increasing coloration









efficiency trend can therefore be explained by the increased interchain and interstacks

distance, allowing more efficient penetration of the dopant ions into the polymer films.

4.3.4. Conductivity Measurement

The conductivity of spray-coated PProDOT-CH2OR2 polymer films was

determined by the four-point probe method. The measurements are taken as an average of

multiple locations of the films, and reproducibility was checked by measuring

conductivity on several films, leading to consistent results. The value obtained for the

alkoxymethyl substituted PProDOTs are given in Table 4-6, along with the voltage drop

obtained for a constant intensity applied to the doped spray-coated films. The

conductivity decreases sharply with increasing size of the branching group. Interestingly,

increasing the size of the main chain from butyl to hexyl does not appear to affect

significantly the film conductivity.63a This correlates well with our assumption that the

branching size, not the main chain size, is controlling the interchain distance.

Table 4-6. Conductivity measurement for PProDOT(CH20R)2 spray-coated films. Films
were gas phased doped for 12 hours in an iodine chamber prior to measuring
conductivity.
R= I (pV)" AV (mV) b Thicknessc(nm) a (S cm1)
2-ethylbutyloxymethyl 2 83 658 0.08
2-ethylhexyloxymethyl 1 246 367 0.07
2-ethylhexyl 10 300, 194 222, 234 0.3, 0.5
2-methylbutyloxymethyl 10 148, 165 233,246 0.54, 0.64
2-methylbutyl 100 203, 185 286, 251 3.8, 4.2
Hexyl N/A N/A N/A 5-10
(a) Intensity setting; (b) Average voltage drop; (c) Average thickness obtained by
profilometry.

Comparing the properties of alkyl and alkoxy polymers, the conductivity of the

alkoxymethyl substituted polymers is one order of magnitude lower than their alkyl

analogs. Given the electronic and optical results presented above, a possible explanation

is that the alkoxymethyl substituted polymers have a higher degree of intrachain and









interchain disorder. Further studies on the chiral equivalents of these polymers, presented

in Chapter 5, will provide additional data supporting it. The lower conductivities of

branched polymers are further evidence that the coloration efficiency of these polymers is

limited by the diffusion of dopant ion into the films, not the electronic conductivity.

4.4. High Performance Electrochromic Devices

Figure 4-10 shows a schematic representation of the construction of a dual-window

electrochromic device.




bsle ITO caly Cdig




(b)






PBEDOT-NMeCz* PBEDOT-NMeCz




Colored state Bleached state
Figure 4-10. Electrochemical device using spray-coated PProDOT(CH202-ethylhexyl)2 as
the anodically coloring polymer and Poly(BisEDOT-N-methylcarbazole)
electropolymerized film as the cathodically coloring polymer. (a) Schematic
diagram of the dual-window electrochromic device; (b) Polymer colors for an
applied bias of-1V (colored state) and +1V (bleached state).

The electrochromic device is built from two ITO-coated glass slides, one coated

with an anodically coloring polymer (in our case spray-cast PProDOT-(CH2OEtHx)2) and

a second coated with an electrochemically oxidized, cathodically coloring polymer (in









this work, the polymer used is (Poly(BisEDOT-N-methylcarbazole)). The two ITO slides

are then combined, facing each other, with a layer of gel electrolyte. When a negative

bias (-1V) is applied to the device both polymers are colored, giving a dark absorptive

color to the film (Figure 4-10). When a positive potential of +1V is applied then

PProDOT-(CH2OEtHx)2) is fully oxidized in its highly transmissive, sky blue color state

while Poly(BisEDOT-N-methylcarbazole)2 is reduced to its neutral, highly transmissive

yellow color state. As presented in Figure 4-11, PProDOT(CH20-2-ethylhexyl)2 yields an

electrochromic device with high luminance contrast and high coloration efficiency (4800

cm2/C). The device can be fully switched up to rates of 2Hz.










Cathodically cor






Figure 4-11. Luminance plot of a dual-window EC device using spray-coated
S n 9 I Anodically

Cathodically OT((CH20-2-ethylhexyl)2) the anodically coloring coloring
coloring polymer.Polymer
Polymer 0 (electrochemic
(spray-cast) -1.2 -10 -Q8 46 -0a41-02 GO G2 o04 06 OJR 10'12 ally deposited)
E(V)


Figure 4-11. Luminance plot of a dual-window EC device using spray-coated
PProDOT((CH2O-2-ethylhexyl)2) as the anodically coloring polymer and
electrolpolymerized Poly(BisEDOT-N-methylcarbazole) as the anodically
coloring polymer.

Similar devices, using a spray-coated PProDOT(CH20-C18H37)2, led to CE values

of only 1300 cm2 C-1. This work was carried out by Ali Cirpan and Avni Argun. It

demonstrates nicely the difference of properties obtained between branched and long

linear alkyl chains, both displaying high solubility.