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Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2011-05-31.

Permanent Link: http://ufdc.ufl.edu/UFE0024404/00001

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Title: Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2011-05-31.
Physical Description: Book
Language: english
Creator: Steckler, Timothy
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

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Subjects / Keywords: Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
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theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
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Electronic Thesis or Dissertation

Notes

Statement of Responsibility: by Timothy Steckler.
Thesis: Thesis (Ph.D.)--University of Florida, 2009.
Local: Adviser: Reynolds, John R.
Electronic Access: INACCESSIBLE UNTIL 2011-05-31

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Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024404:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024404/00001

Material Information

Title: Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2011-05-31.
Physical Description: Book
Language: english
Creator: Steckler, Timothy
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Statement of Responsibility: by Timothy Steckler.
Thesis: Thesis (Ph.D.)--University of Florida, 2009.
Local: Adviser: Reynolds, John R.
Electronic Access: INACCESSIBLE UNTIL 2011-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024404:00001


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1 MANIPULATING THE BAND GAP OF DONOR-ACCEPTOR LOW BAND GAP POLYMERS By TIMOTHY THOMAS STECKLER 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 2009

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2 2009 Timothy T. Steckler

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3 To my mom and dad

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4 ACKNOWLEDGMENTS I would like to thank m y advisor, Dr. John Re ynolds, for being the best teacher/mentor a graduate student could ever ask for. It was his sharing of knowledge and guidance that have molded me into the person I am today, both scientifically and personally, and for that I will never be able to give enough thanks. I am very thankful to the numerous professors who have contributed to my education here at the University of Florida. I thank my co mmittee: Dr. Ken Wagener, Dr. Ron Castellano, Dr. Randy Duran and Dr. Anthony Brennan. They have been a significant part of my educational development. Many contributions from others at the university have been paramount to the work presented in this dissertation. I thank Dr. Kh alil Abboud for his work on solving x-ray crystal structures; James Leonard for getting me in the door for x-ray analysis and his GPC work; Erik Berda, Jianguo Mei, Kate Opper for thermal anal ysis; Aburey Dyer, Merv e Ertas, and Svetlana Vasilyeva for their wonderful insights into elec trochemistry; Stefan Ellinger for his work on collaborative synthesis. Numerous people in the Reynol ds group have contributed to my development as a synthetic chemist, and for that I thank Stefan Ellinger, Ryan Walczak, Ben Reeves, Christophe Grenier, Emilie Galand, Barry Thompson, Genay Jones, Pierre Beaujuge, Jianguo Mei, Dan Patel, C.J. DuBois and David Whitker. I also thank the many members of the Geor ge and Josephine Butler Polymer Research Laboratory who have had signifi cant influences on me both pr ofessionally and personally; George and Josephine Butler; Travis Baugh man, Tim Hopkins, Sophie Bernard, and Andrew Skolnik (SLS, Inc.).

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5 I would like to give a special thanks to Bob Brookins, not only for many shared failures in collaborative work, but also for many successes in knowledge gained. He was a great friend to have around and I enjoyed the numerous cookie dews. I also thank Stefan Ellinger for showing me not only how to work hard, but also how to enjoy a small one. I bestow a special thanks to Merve Ertas for her friendship and support both in and outside of the lab. Finally, I would like to thank my family fo r their support throughout my whole graduate school career. My parents, Tom and Lil Steckle r, have always supported me and given me sound advice. My brother, Steve Steckle r, has always been there for me and is a driving force for me to continue on in my career.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ............................................................................................................... 4LIST OF TABLES ...........................................................................................................................8LIST OF FIGURES .........................................................................................................................9ABSTRACT ...................................................................................................................... .............13 CHAP TER 1 INTRODUCTION .................................................................................................................. 16History of Conjugated Polymers ............................................................................................ 16Electronic Properties ...............................................................................................................17Controlling the Band Gap Towards Low Gap Systems .......................................................... 20Polymerization Methods for DA Conjugated Polymers ......................................................... 24Electrochemical Polymerization ......................................................................................25Chemical Oxidative Polymerization ................................................................................26Metal Mediated Polymerizations ..................................................................................... 27Acceptors in DAD Oligomers/CPs ................................................................................ 29Design Principles of DAD Architectures for CPs .......................................................... 312 EXPERIMENTAL .................................................................................................................. 34Overview ...................................................................................................................... ...........34Molecular Characterization .................................................................................................... 34X-Ray Crystallography ...........................................................................................................34Polymer Characterization ...................................................................................................... .36Electrochemical Methods ....................................................................................................... 36General Set-Up ................................................................................................................37Preparation of DAD Mono mer Solutions for Electrochemicalpolymerization ............... 37Deposition of Polymers ................................................................................................... 38Cyclic Voltammetry/Differen tial Pulse Volatmmetry ..................................................... 39Optical Characterization .........................................................................................................41Materials for Optical Characterization ............................................................................41Spectroelectrochemistry .................................................................................................. 423 P(BEDOT-PYRIDOPYRAZINE): PROBING THE PROPERTIES OF A MULTIPLE REDOX STATE POLYMER ................................................................................................. 43Introduction .................................................................................................................. ...........43Monomer Synthesis and Characterization .............................................................................. 46Electrochemical Polymeri zation/Characterization ................................................................. 48Electropolymerization ..................................................................................................... 48

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7 Cyclic Voltammetry ........................................................................................................50Spectroelectochemistry .................................................................................................... 52Conclusions .............................................................................................................................56Experimental .................................................................................................................. .........574 BXDOT DONOR-ACCEPTOR-DONOR LOW BAND GAP POL YMERS ........................ 63Background .................................................................................................................... .........63Monomer Synthesis and Characterization .............................................................................. 64Electrochemical Polymerizat ion and Characterization ........................................................... 68Electrochemical Polymerization of Monomers ............................................................... 68Polymer Electrochemistry ........................................................................................ 71Optical Characterization ..................................................................................................79Oxidative Spectroelectrochemistry .......................................................................... 80Reductive Spectroelectrochemistry .......................................................................... 88Conclusions .............................................................................................................................93Experimental .................................................................................................................. .........945 DTP BASED SOLUBLE DONOR ACCEPTOR POLYMERS .......................................... 101Introduction .................................................................................................................. .........101Monomer/Polymer Synthesi s and Characterization ............................................................. 103Electrochemical and Spectroelect rochemical Characterization ............................................112Polymer Electrochemistry ...................................................................................... 112Polymer Spectroelectrochemistry .......................................................................... 118Conclusions ...........................................................................................................................126Experimental .................................................................................................................. .......128 APPENDIX A X-RAY CRYSTALLOGRAPHIC DATA ...........................................................................134B ELECTROCHEMICAL POLYME RIZATION OF MONOMERS FROM CHAPTER 4 .. 142LIST OF REFERENCES .............................................................................................................146BIOGRAPHICAL SKETCH .......................................................................................................156

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8 LIST OF TABLES Table page 4-1 UV-VIS absorption data for monomers 6a-c, 7a-c and 8a-c. ........................................... 674-2 Summary of electrochemical data (CV) for polymers P6-8a-c. ........................................ 724-3 Summary of the observed onsets for oxidation and reduction by DPV for polymers P6-8a-c ...............................................................................................................................725-1 GPC estimated molecular weights (THF as mobile phase, relative to polystyrene standards) and yields of the Stille polymerization ...........................................................1075-2 Summary of electrochemical data for P(DTP-Acceptors) investigated ........................... 118A-1 Crystal data and st ructure refinement for 6a (Chapter 4). ...............................................134A-2 Crystal data and st ructure refinement for 6b (Chapter 4). ...............................................136A-3 Crystal data and stru cture refinement for 7 a (Chapter 4). ...............................................138A-4 Crystal data and st ructure refinement for 7c (Chapter 4). ...............................................140

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9 LIST OF FIGURES Figure page 1-1 Common conjugated polymers: poly(acetylene) PA, poly( -phenylene) PPP, poly(an iline) PANI, poly(thiophene) PTh, poly(pyrrole) PPy, and poly(3,4ethylenedioxythiophene) PEDOT. ..................................................................................... 161-2 The different ground state energies for degenerate PA and non-degenerate PTh ............. 171-3 p-Doping of PPy ................................................................................................................201-4 Resonance structures of the aromatic (l eft) and quinoid (rig ht) forms of PITN ................ 211-5 Increase in planarity for poly(pyrrole-benzothiadiazole) relative to the N-Boc protected precursor.............................................................................................................221-6 Demonstration of interchain effects in poly(3-hexylthiophene) ........................................221-7 Donor-acceptor band gap compression ..............................................................................231-8 General mechanism for the oxidative (electrochemical & chemical) polymerization of thiophene. ......................................................................................................................251-9 Outline of the Stille reacti on and the Carothers equation .................................................. 291-10 Reduction potentials of various nitrogen containing heterocycles measured in anhydrous DMF ( V vs. Hg pool) ...................................................................................... 301-11 Reduction potentials of fused heterocyclic quinoid type acceptors incorporated into DAD oligomers/polymers with thiophene as the donor .................................................... 312-1 Example of DPV waveform relative to CV waveform ...................................................... 413-1 Structure of PBEDOT-PyrPyr-Ph2 .....................................................................................453-2 Synthesis of 5,8-dibromo-2,3dihexyl-pyrido[3,4-b]pyrazine ........................................... 463-3 Synthesis of 5,8-dibromo-2,3didodecylpyrido[3,4-b]pyrazine ........................................ 473-4 Synthesis of monomers 11 and 12 and their respective polymers P1 and P2 ...................483-5 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/1:1 DCM:ACN solution ...............................................................................493-6 Cyclic voltammetry of polymers P1 and P2 and the associated colored states .................513-7 Proposed structure for the radi cal anion of the first reduction ...........................................51

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10 3-8 Oxidative spectroelectrochemistry of P1 and P2 on ITO in 0.1 M TBAP/ ACN ..............533-9 Reductive spectroelectrochemistry of P1 on an ITO coated glass slide in monomer free electrolyte solution (0.1 M TBAP in ACN) at applied potentials of (a) -1.15 V to (j) -2.05 V in 100 mV increments ...................................................................................... 553-10 Reductive spectroelectrochemistry of P2 on an ITO coated glass slide in monomer free electrolyte solution (0.1 M TBAP in ACN) at applied potentials of (a) -1.14 V to (i) -1.94 V in 100 mV increments ...................................................................................... 553-11 Photograph of a film of P2 after reductive spectroelectrochemistry ................................. 564-1 The different dioxythiophe ne based donors and thiadiazole based acceptors used to make a new family of DAD monomers and polymers. ..................................................... 644-2 Synthesis of DAD monomers where (a) = EDOT, (b) = ProDOT, and (c) = ProDOTMe2. ......................................................................................................................654-3 Crystal structure of Monomer 6a showing a torsion angle of 53 between the EDOT donor and the benzobis(th iadiazole) acceptor .................................................................... 664-4 UV-VIS spectra of monomers ........................................................................................... 684-5 Electrochemical poly merization of monomers 6-8a-c to yield polymers P6-8a-c ............694-6 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/DCM solution of 6b yielding P6b ...............................................................704-7 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of polymers P7a-b on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .........734-8 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of polymer P7c on a Pt button working electrod e in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .........744-9 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of polymers P8a-b on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .........754-10 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of polymer P8c on a Pt button working electrod e in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .........764-11 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of polymers P6a-b on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .........77

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11 4-12 CV (scan rate = 50 mV/s) and DPV (step size of 2 m V and step time of 0.1 seconds) of polymer P6c on a Pt button working electrod e in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .........784-13 Oxidative spectroelectrochemistry of P6a-c on ITO in 0.2 M TBAP-PC ......................... 824-14 UV-VIS-NIR absorption of the electrodes used and P6a on a SWCNT electrode ........... 834-15 Oxidative spectroelectrochemistry of P7a-c on ITO in 0.2 M TBAP-PC ......................... 864-16 Oxidative spectroelectrochemistry of P8a-c on ITO in 0.2 M TBAP-PC ......................... 874-17 Reductive spectroelectrochemistry of P6a-c on ITO in 0.2 M TBAP-PC ........................ 904-18 Reductive spectroelectrochemistry of P7a-c on ITO in 0.2 M TBAP-PC ........................ 914-19 Reductive spectroelectrochemistry of P8a-c on ITO in 0.2 M TBAP-PC ........................ 925-1 Targeted DTP based DA polymers .................................................................................. 1025-2 Synthesis of 4,9-bis(5-bromothiophe n-2-yl)-6,7-dihexyl-[ 1,2,5]thiadiazolo[3,4g]quinoxaline and 4,9-dibromo-6,7-dihexyl -[1,2,5]thiadiazolo[3,4-g]quinoxaline ........ 1035-3 General synthesis of DTP based DA polymers via Stille Polymerization ....................... 1045-4 GPC chromatograms of P(DTP-acceptor) polymers ....................................................... 1065-5 UV-VIS-NIR of neutral pol ymers spray cast onto ITO ...................................................1085-6 Pictures of spray cast neutral polymers on ITO ............................................................... 1085-7 UV-VIS-NIR analysis of P(DTP-BThBBT) and P(DTP-TQHx2) on SWCNTs and reflectance of P(DTP-BThBBT) on gold ......................................................................... 1105-8 Solution thermochromism and concentr ation dependence UV-VIS-NIR analysis of P(DTP-BTD) in toluene ...................................................................................................1125-9 CV (scan rate = 25 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of P(DTP-BThBTD) and P(DTP-BTD) on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution ......................................................................................... 1155-10 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of P(DTP-BThTQHx2) and P(DTP-TQHx2) on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution .....................................................................................1175-11 CV (scan rate = 50 mV/s) and DPV (step size of 2 mV and step time of 0.1 seconds) of P(DTP-BThBBT) on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution ...................................................................................................................... .......118

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12 5-12 Spectroelectochemistry of P(DTP-BThB TD) in 0.1 M TBAP/PC and the associated colored states ....................................................................................................................1205-13 Spectroelectochemistry of P(DTP-BTD) in 0.1 M TBAP/PC and the associated colored states ....................................................................................................................1215-14 Spectroelectochemistry of P(DTP-BThTQHx2) in 0.1 M TBAP/PC and the associated colored states ..................................................................................................1225-15 Spectroelectochemistry of P(DTP-TQHx2) in 0.1 M TBAP/PC and the associated colored states ....................................................................................................................1245-16 Spectroelectochemistry of P(DTP-BThBBT) in 0.1 M TBAP/PC and the associated colored states ....................................................................................................................126A-1 Crystal Structure for compound 6a (Chapter 4) ..............................................................134A-2 Crystal Structure for compound 6b (Chapter 4) .............................................................. 136A-3 Crystal Structure for compound 7a (Chapter 4) ..............................................................138A-4 Crystal Structure for compound 7c (Chapter 4) ...............................................................140B-1 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/DCM solution of 6a yielding P6a ..............................................................142B-2 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 7a yielding P7a ...............................................142B-3 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 8a yielding P8a ...............................................143B-4 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 7b yielding P7b .............................................. 143B-5 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 8b yielding P8b .............................................. 144B-6 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/DCM solution of 6c yielding P6c ..............................................................144B-7 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 7c yielding P7c ...............................................145B-8 Repetitive scan electropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 8c yielding P8c ...............................................145

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13 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 MANIPULATING THE BAND GAP OF DONOR-ACCEPTOR LOW BAND GAP POLYMERS By Timothy T. Steckler May 2009 Chair: John R. Reynolds Major: Chemistry The work presented herein focuses on design of low band gap polymers via the donoracceptor methodology. One of the advantages of lo w band gap polymers is their ability to reach multiple redox states in a small potential window. These different redox states are usually accompanied by color change. The use of stronger acceptors, with more positive reduction potentials, will ultimately lead to improved stability in the reduced state, for possible applications in charge storage and electrochromic s. The goal of this study is to examine the structure-property relationships between the dono r-acceptor connectivity and their control of the optical and electronic properties. Initial investigation into the pyrido[3,4b]pyrazine acceptors involved the electrochemical polymerization of 5,8-bis-(2,3dihydrothieno[3,4-b][1,4]dioxi n-5-yl)-2,3-dihexyl-pyrido[3,4b]pyrazine (BEDOT-PyrPyr-(C6H13)2) and 5,8-bis-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)2,3-didodecyl-pyrido[3,4-b]pyrazine (BEDOT-PyrPyr-(C12H25)2) to yield P(BEDOT-PyrPyr(C6H13)2) and P(BEDOT-PyrPyr-(C12H25)2). Both polymers were dark blue and exhibited optical band gaps of 1.4 eV with a first reduction potential of Ep = ~ -1.6 V vs. SCE. The second reduction seen in the previously synthesized BEDOT-PyrPyr-Ph2 polymer was either not observed or seen for only one to two cycles due to stability issues.

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14 The next generation of DAD monomers deve loped for electrochemical polymerization involved 3,4-ethylenedioxythiophene (EDOT), 3,4-propylenedioxythiophene (ProDOT), and 2,2dimethyl substituted ProDOT (ProDOTMe2) donors. These donors were combined with either thiadiazolo[3,4-g]quinoxaline (TQ) or benzo[1,2c ;4,5c ]bis[1,2,5]thiadiazole (BBT) acceptors. The lowest band gap in the family was ~0.5 to 0.7 eV for P(BEDOT-BBT) corresponding to a dark olive green neutral state while the highest optical band gap was ~ 1.5 eV for P(BProDOTMe2-TQMe2) yielding a light grey/blue neutral stat e. Due to the low band gaps in this family, new spectroscopic materials were needed to replace ITO, which absorbs strongly beyond 1600 nm. This lead to the use of singl e walled carbon nanotube (SWCNTs) electrodes, which have a high degree of transparency in th e NIR, for improved optic al characterization at longer wavelengths. All BBT based polymers showed two reductions with onsets near -0.4 V and -1.2 V vs. SCE while TQ based polymers show ed reductions onsets n ear -0.7 V and ~ -1.4 V vs. SCE. The onset of oxidation for the BBT based polymers could be controlled over a ~300 mV window from ~ 0.2 V for EDOT to ~ 0.5 V vs. SCE for ProDOTMe2. Meanwhile the onset of oxidation in the TQ based polymers ranged from ~ 0.4 V to ~ 0.65 V vs. SCE. A final project focused on the synthesis of soluble DA polymers via Stille polymerization using dibromo based acceptors; benzo[2,1,3]thiadi azole (BTD), TQ, and BBT based combined with N-(3,4,5-trin-dodecyloxyphenyl)-dithieno[3,2-b:2 ,3 d ]pyrrole (DTP) based donor. The tri-alkoxyphenyl group allows for good solubility wh ile the DTP core allows for planarity along the conjugated backbone, resul ting in low band gap, soluble DA polymers. P(DTP-BThBBT) has an optical band gap of ~ 0.5 to 0.6 eV, which is the lowest reported band gap for a soluble spray-processable polymer to date. With th is polymer showing both pand n-type doping

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15 characteristics at relatively low potentials, am bipolar charge-transport was investigated and confirmed.

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16 CHAPTER 1 INTRODUCTION History of Conjugated Polymers The discovery that -conjugated polym ers (CPs) could be conducting in th e late 1970s by Heeger, MacDiarmid, and Shirakawa when they found that polyacetylene (PA), when chemically doped, became highly conductive, stimulated immense interest and research efforts.1,2 However, due to poor solubility, a nd stability issues in the doped state, other avenues were pursued to solve these problems. This lead to the investigation of other CPs such as polyaniline, polythiophene, poly( -phenylene) and polypyrrole to name a few (Figure 1-1). Though none of these materials have the ideal properties for re placing metals such as copper (as related to conductivity), numerous other uses have surfaced. Based on a polymers material adva ntages such as light weight, flexibility, and ease of processabilit y, CPs are now used in polymer light emitting diodes (PLEDs),3-6 electrochromic devices,7-11 photovoltaic devices,12-19 charge storage20-25 and organic field-effect transistors (OFETs).26-30 The inherent properties of the -conjugated backbone in CPs play an important role in de termining the material characteristics, and thus applications. S H N H N S O O n n n nn n Figure 1-1. Common conjugated po lymers: poly(acetylene) PA, poly( -phenylene) PPP, poly(aniline) PANI, poly(thiophene) PTh, poly(pyrrole) PPy, and poly(3,4ethylenedioxythiophene) PEDOT. In order to optimize new conjugated polymers for the various app lications mentioned previously, it is important to understand the st ructure-property relationships relative to the materials optical and electronic properties. By using more complex molecules such as donoracceptors, it is possible to tailor these prope rties for multiple applications beginning from a

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17 similar core structure. To develop such system s, it is important to understand how the individual fragments properties will morph together to yield a new set of final properties. The remainder of this chapter will deal with th e electronic and optical properties of conjugated polymers along with the design and synthesis of low band gap polymers. Electronic Properties In a CP there is a delocalized -electron system along the polymer backbone involving the overlap of p-orbitals. As more and more mono mer units are connected, th e orbitals of similar energy combine to form more levels until a saturation point is reached and they become bands. These bands can be divided into the highest occupied molecular or bital (HOMO) or valence band and the lowest unoccupied molecular orbital (L UMO) or conduction band. The difference in energy between the HOMO and LUMO le vels is known as the band gap, Eg.31,32 There are two different types of CPs relative to their conjugated backbones, degenerate and non-degenerate. PA is the exception for a degenerate polymer becau se it has two energetically equivalent forms in the ground state (Figure 1-2). All other co njugated polymers can be classified as nondegenerate polymers, since the different ground stat es are not energetically equivalent as can be seen for the aromatic form relative to the quinoid form for PTh (Figure 1-2).33 Relative Energy PTh PTh PA PA Figure 1-2. The different ground state energies for degenerate PA and non-degenerate PTh.

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18 One can picture a CP, such as PA, as an in finite chain of alternating single and double bonds with each carbon being sp2 hybridized, thus the chain would be a continuum of overlapping p orbitals each contai ning one electron. This type of structure should lead to a highly conductive material along the axis of the conjugated backbone since the valence band would be half filled and delocali zed like that of a metal conductor. However, CPs suffer from Peierls distortion,31 which is an electron-phonon coupling th at leads to a symmetry lowering effect resulting in a less delocali zed system. This results in an increase in stability for the bonding orbitals and a decrease in stability for the anti-bonding orbita ls due to the lengthening of single bonds and the shortening of double bonds. Th e Peierls distortion in PA results in the opening up of a band gap, which is ~ 1.5 eV.34,35 The band gap plays an important role in determining a polymers optical and electronic properties. Since most neutral CPs are usually considered semi-conductors (0.3 eV < Eg < 3-4 eV, Eg > 3-4 eV are considered insulators), they must be doped in order to s ee a change their optical or electronic properties.36 The different ways to dope a polymer include chemical, electrochemical, metal-polymer interfacial, and p hotochemical. Detailed explanations of these processes and applications can be obtained from various Rey nolds group dissertations and the literature.33,37-40 Electrochemical doping will be discussed briefly since that is the foundation of characterization throughout this dissertation. The doping of PA is unique compared to the re st of CPs, due to its degenerate ground state. In neutral trans -PA with an odd number of re peat units, there is a single -electron (radical) that is delocaliz ed over several repeat units known as a neutral soliton, which is located mid gap between the HOMO and LUMO levels with a spin of .41,42 Upon oxidation (or reduction) an electron is removed (or added) leaving an empty (or doubly occupied) mid gap

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19 state which is spinless and charged positively or negatively. Due to PAs degeneracy, these solitons can migrate along the backbone without an increase in the distortion energy, thus allowing for higher conductivity compared other CPs. Oxidation (p-type doping) or reduction (n-type doping) of a non-degenerate CP causes the removal or addition of an electr on to create a charged state know n as a polaron (radical cation or anion), which has a spin of Oxidative doping of PPy can be seen in Figure 1-3. Single oxidation of a polymer is usually accompanied by a change in the polymer backbone from the neutral aromatic structure to th e polaronic quinoid like structure. Along with the change in the backbone there is the formation of intr agap states known as the polaron bands.43 The polaron is delocalized over ~ 4 rings for PPy.43,44 If the procedure is repeated again an electron may be removed from somewhere else along the polymer backbone to produce another polaron, or an electron could be removed from the polaron to create a bipolaron (a spinless state). As a polymer becomes more heavily doped, usually th e bipolaron state starts to become more dominant as was shown for PPy.43 These energy states are locat ed within the polymer band gap, with the polaron bands located closer to the or iginal HOMO and LUMO levels compared to the bipolaron bands, which are compressed more. It is these bands that cause the optical changes associated with the different re dox states in a CP (Figure 1-3).33,45 It is through the synthetic chemists ability to design and assemble new molecules and polymers that allows control over the desired electronic an d optical properties.

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20 H N N H H N N H H N N H H N N H N N H H N N H H N N H N N H N N H -e-e-H H H Neutral Polaron Bipolaron HOMO HOMO HOMO LUMO LUMO LUMO Eg Polaron BipolaronAB Figure 1-3. p-Doping of PPy. A) Successive one eoxidations of PPy. B) Polaron and bipolaron band formation. Controlling the Band Gap Towards Low Gap Systems Low band gap polym ers are usually considered to be polymers that have a band gap below 1.5 eV (corresponding to an onset of the lowest energy absorption of the neutral polymer greater than or equal to ~800 nm) and have been the focus of many studies and reviews.46-52 These polymers are colored in the neutral state due to the transition located at low energies, and become more transparent upon dopi ng with a decrease of the transition and development of lower energy transitions. By having a low band gap, the conduction band can be reached easier, allowing for the possibility of ntype doping. Thus, low band gap polymers could lead to dual ptype and n-type devices with a sing le polymer such as ambipolar OFETs27,30,53 and supercapacitors.54-56 Through the careful choice and modifi cation of various building blocks in different configurations allows for fine control over absorption (color), emission, oxidation/reduction potentials (for both tunab ility and stability in applications), and mobility/conductivity. Some of the methods used for the design and control of properties in low band gap polymers include, but are not limited to, minimizing bond-length alternation (BLA),

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21 planarity, aromaticity (resonance), interchain effects and donor-acceptor (DA) effects.47,48 It can be very hard to look at these methodologies indi vidually because they of ten interrelate to each other. As was discussed earlier, we found that PA along with other CPs suffer from a Peierls distortion, that result s in BLA with the single bonds becoming longer and the double bonds becoming shorter, thus opening up a band gap. The classic example of minimizing BLA in heteroaromatic CPs is polyisothianaphthene (PITN) (Figure 1-4). This relates to both aromaticity (resonance) and BLA. As was discussed previously for non-degenerate CPs, the aromatic form is usually more stable in the ground state relative to the quinoid form (Figure 1-2). It is possible to minimize BLA by gaining a resonance contribution from the higher energy quinoid form in the ground state, since this would increase the double bond character between adjacent thiophene rings. Since PTh has a band gap of ~2.0 eV, it was thought that if one could force more quinoid character in the ground st ate of PTh, one could reduce BLA and the band gap. To demonstrate this, Wudl et. al.synthesized PITN, and they found that because the benzene ring has a higher energy of aromaticity than thiophene, the polymer in the ground state has a significant contribution from the quinoid re sonance form. This produced a polymer with a band gap of ~1.0 eV, which is a pproximately half that of PTh.57,58 S n S n Figure 1-4. Resonance structures of the aromatic (left) and quinoid (right) forms of PITN. Another way to control the band gap is through planarity. This involves the overlap of the p-orbitals along the conjugated polymer backbone. In a normal conjugated polymer, there is the ability for neighboring units to rotate out of plan arity, thus diminishing the overlap of p-orbitals

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22 and conjugation. This results in a higher ba nd gap. By inducing the polymer backbone into a more planar structure, better ove rlap occurs amongst the p-orbita ls so conjugation is increased and a smaller band gap can be obtained. One simp le example is poly(pyrrole-benzothiadiazole) (Figure 1-5). When the soluble precursor polymer is in its nonplanar Boc protected state, the max is at 434 nm in chloroform, but when a sp in coated film was deprotected, the polymer planarizes and we s ee a red shift in the max to 704 nm.59 With careful choi ce of where to add substituents to the monomers or the choice of certain monomers, the final planarity of the polymer can be controlled. Figure 1-5. Increase in plan arity for poly(pyrrole-benzothiadiazole) relative to the N-Boc protected precursor. Interchain effects have best been shown with poly(3-alkylthiophenes). The 3-alkyl thiophenes in the polymer can be connected in a head-to-tail (HT), head-tohead (HH), or a tailto-tail fashion (TT). Depending on the polymerization method, different amounts of HT, HH, and TT connections are observed. A HH connecti on leads to defects causing a severe twist along the backbone. This results in a higher band gap and dimi nished conductivity. Certain polymerization methods allow for the forma tion of 98-99 % HT poly(3-alkylthiophene). Regioregular HT poly(3-alkylthi ophenes) (Figure 1-6) have im proved electronic properties due to a more planar backbone and the ability to self assemble into highly ordered polymer films.60-62 S S S C6H13 C6H13 C6H13 n Figure 1-6. Demonstration of intercha in effects in poly(3-hexylthiophene).

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23 Low band gap DA polymers are of interest becau se of the accessibility to reach multiple redox states (p-type or n-type doping) in a small potential window. This is due to the placement of the valence band relative to the conduction band. The goal is to select a strong donor with a high HOMO level and a strong acceptor with a lo w LUMO level. When the donor and acceptor are coupled, the orbita ls mix forming a new set of orbitals with a much smaller band gap compared to its individual parts (Figure 1-7), and upon polymerization can yield very small band gaps, as was demonstrated early on by Havinga et. al .63 With the proper choice of donor and acceptor, the band gap can be modified and thus the final properties can be adjusted.48 Band Gap, EgHOMO HOMO LUMO LUMO Donor Acceptor Donor-Acceptor Energy Figure 1-7. Donor-acceptor band gap compression. [Modified from van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Havinga, E. E.; Meijer, E. W. Mater. Sci. Eng. 2001 32, 140].48 This idea for DA oligomers/polymers has been called into question over the last few years in theoretical work done by Salzner et. al .64-66 The general assumption is that since the ionization potentials (IPs)/HOMO of the donor and the acceptor are closer in energy, they tend to mix better and result in an increase in the IP /HOMO of the polymer. However, the electron affinities (EAs)/LUMO of the donor and the accept or are too energetically different to have significant mixing, thus you end up with a narrow LUMO band that is localized mostly on the

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24 acceptor with an EA similar to that of the accep tor. The true conduction band is located at a higher energy. So, even though the band gap is low, one still does not observe a substantial increase in conductivity upon reduction. This wa s demonstrated by the study of PBEDOT-Pyr and PBEDOT-PyrPyr-Ph2,67,68 which measured in-situ conductivit y associated with the different redox states. It was found that the conductivity in the n-doped state for PBEDOT-Pyr was 30 times less than when in the p-doped state, while the conductivity for PBEDOT-PyrPyr-Ph2 was even less in the n-doped state relati ve to the p-doped state. No capacitive effects were seen in the n-type conductivity profile fo r either polymer, indicating a highly localized anionic state. So while the famous orbital mixing diagram in Figure 1-7 has been questioned, that does not mean the DA approach does not work. It ju st means that getting a highly delocalized conduction band might be difficult. Perhaps a better way to think of the DA approach is to picture the mesomerism of D A D+=A-. This can be thought of as the often used term intramolecular charge transfer (ICT). The str onger the donor and the accep tor are, the increased amount of ICT there is, thus resu lting in increased quinoid charac ter in the ground state, leading to a small band gap.69 The stronger the DA interaction, th e more red shifted the absorption becomes. This ICT band can be thought of as the gap between the HOMO and the low lying LUMO that is isolated more on the acceptor as explained above. It is these principles that become important factors for the design and appli cation of new DA CPs, es pecially as it relates to electrochromic applications.7,9,70,71 Polymerization Methods for DA Conjugated Polymers Though there are m any different polymerizati on methods used to synthesize DA CPs, such as electrochemical, oxidative, and metal me diated couplings, this section will focus on the

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25 methods used throughout the work done in this dissertation. The main focus will be on the design of donor-acceptor-donor (DAD) compounds fo r applications in oxi dative polymerization. Electrochemical Polymerization Electropolym erization allows for the deposit ion of polymers onto different electrode surfaces (i.e. Pt button or ITO coated glass) for immediate characteri zation of optical or electronic properties. The mechanism for the electrochemical polymerization of heterocycles can be seen in Figure 1-8, which is thought to be very similar to the mechanism for chemical oxidative polymerization. For electrochemical polymerization, initially a monomer such as thiophene is dissolved in a monomer/supporting electrolyte so lution. The solution is then subjected to an oxidizing potenti al for the given monomer, lead ing to radical cation formation (Figure 1-8). The radical cation can then c ouple to monomer, undergo oxidation again followed by the loss of two protons to yield the neutral dimer. This process can then be repeated multiple times to deposit polymer on the electrode surface. Another path is for the radical cation to couple with another radical cation, followed by the lo ss of two protons to yiel d the neutral dimer. Again, repetition of this procedure numerous times will yield polymer.72 S -e-S S S S S S + S S radical-radical coupling S S + radical-monomer coupling S S H H -e-2H+S S multiple repetitions S n Figure 1-8. General mechanism for the oxidative (electrochemical & chemical) polymerization of thiophene.

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26 One of the major drawbacks of electrochemical polymerization is the fact that it yields insoluble polymers which do not have the ability to be characterized by traditional methods such as NMR and GPC. An even more important draw back is the electrochemical polymerization of unsubstituted monomers like thiophene or pyrrole, which have the ab ility to couple at the 3and 4-positons along with the 2and 5-positions. Th ese defective couplings lead to a decrease in conjugation, cross-linking, and diminished electronic properties.73,74 This can be avoided through substitution of the 3and 4positions with blocking groups. 3,4-Dioxythiophene based monomers (XDOT) are a good example of this strategy.11 Not only does the dioxythiophene bridge on the XDOT monomers block the deleterious couplings during electropolymerization, but they also increase the el ectron density of the monomer. By using a donor that is more electr on rich such as EDOT, the advantage of a low oxidation potential for ease of elect rochemical synthesis is gained.75,76 This avoids side reactions that can occur at higher potentials such as over oxidation of the re sulting polymer film due to the high monomer oxidation potential. Dioxythiophene based donors are one of the few donor units that offer the chemical robustness for multi-step synthesis similar to that of thiophene and the advantage of being more electron rich for easier electrochemical polymerization. Chemical Oxidative Polymerization While chemical oxidative polym erizations are sim ilar to electropolymerizations, this method allows for the synthesis of CPs on a la rge scale in a fairly inexpensive fashion along with high yields. The mechanism of polymerizati on follows the same principle as described in Figure 1-8, however a chemical oxidant such as FeCl3 is used instead of an electrode.77 An important note is that as the polymer chain forms, it stays in an oxidized state, so when complete, the polymer has to be isolated and dedoped w ith strong reducing agents such as ammonium hydroxide or hydrazine. Since the polymer is in an oxidized state as it is growing, it becomes

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27 more rigid relative to the neutra l form, and could precipitate out of solution. If the monomer is not properly substituted with flexible substituen ts to increase solubility, the molecular weight and thus the optical and electroni c properties could suffer. Besides suffering from the same side reactions as mentioned for elec trochemical polymerization, chemi cal oxidative polymerizations also suffer from the fact that they can leave residual oxidant trapped in the polymer, which can lead to poor device performance, and they are performed under very harsh conditions. During the polymerization, large amounts of HCl are pro duced and upon neutralization strong reducing agents are used. This can severely limit the t ypes functional monomers used for polymerization, and thus alternative methods such as metal mediated couplings are desired.78 Metal Mediated Polymerizations While there are num erous different ways to synthesize chemically polymerized polymers, the main methods used today are Grignard metathesis (GriM),60,79 Yamamoto (Ni(COD)2 ),80-82 Suzuki83-89 and Stille90,91 coupling chemistries. While all have their advantages; GriM can produce highly regioregular poly(3-alkylthiophe nes) along with high molecular weight polymers with narrow polydispersities,92,93 Yamamoto polymerizations are good for the coupling of electron poor aryl halides,80,94 Suzuki polymerizations are fairly tolerant of functional groups and can produce high molecular weight polymers along with AB monomers.95-97 One of the set backs of the GriM polymerization method is that they are performed under strongly basic conditions, which can be problematic for strong acceptors that are base sensitive. There is also very few examples for multi-ring systems being polymerized successfully.98,99 While the Yamamoto polymerization has been used successfully for the synthesis of DA CPs,16,100,101 some of the draw backs are the use of stoichiometric amounts of expensive nickel catalyst along with the reaction being highly air and moisture sensitive. Suzuki polymerizations are also performed under basic conditions, but they are not near ly as strong and can tolerate some of the stronger acceptors,

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28 however most of the reported cases involve copolymers with phenylene, fluorene, or carbazole.12,102-105 For the DA polymers seen in the literature today that are thiophene or dioxythiophene based, the work horse polymerization methodology has been the Stille reaction.17,26,53,69,106-109 The Stille reaction/polymerization offers many benefits, as one of the most mild reactions that is very tolerant of many different functional groups such as amines, esters, aldehydes, ethers, and nitro groups.110 It is its tolerance to many functionalities that make it useful not only in polymerization but also in the synthesis multi-ring systems for conjugated polymers/oligomers.111-113 The stannyl compounds are stable to air and moisture, which allows for the easy purification and storage of the monomers. While palladium (0) is the active species in the catalytic cycle, this can be generated in-situ from palladium (II) catalysts by the homo-coupling of the stannyl reagent (Figure 19).114 This allows for the use of inexpensive air stable catalysts such as Pd(II)Cl2(PPh3)2. The palladium (0) species then reacts with an aryl halide or triflate and undergoes oxidative addition to the organopalladium halide Then transmetalation of the stannyl compound occurs followed by reductive elimination to produce palladium (0) and the product. The most important part of this mechanistic cycle to the polymer chemist using a palladium (II) catalyst is the beginning. It is important to account for the loss of the appropriate amount of stannyl reagent required to make the palladium (0) active catalyst. While this is not as important for small molecule synthesis, if not accounted for, this would cause a stoichiometric imbalance and lead to lower molecular weights, as expected for a step growth polymerization modeled by the Carothers equation (Figure 1-9). The Stille reaction/polymerization is one of the easiest c oupling reactions to set up due to the air stability of all the components. However, one major draw back is the toxicity of tin. While the trimethyl stannyl derivatives are more reactive than the tributyl version, the tributyl version is less toxic, however both are still very toxic.

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29 A BXn= 1 1-p p = (N0-N) N0 Figure 1-9. Outline of the Stille reaction and the Carothers equati on. A) Mechanism of the Stille reaction. B) Carothers equation fo r step growth polymerization, Xn = degree of polymerization, p = reaction conversion, N0 = number of monomers present initially, and N = number of monomers reacted. Acceptors in DAD Oligomers/CPs As was discussed earlier, the use of the DA m ethodology to control the band gap is a useful tool to the synthetic chem ist. It has been demonstrated that by increasing the amount of imine nitrogens (C=N) in heterocycles, the re duction potential becomes more positive, thus making the system easier to reduce.115 A simple example of this is shown in six-membered ring heterocycles. Going from pyridine (1 C=N)) to pyr azine (2 C=N) all the way up to s-tetrazine (4 C=N) there is an increase in reduction potential by ~ 1.85 V (Figure 1-10). The same trend is shown for fused-ring heterocycles, in going from quinoline (-1.59 V) to pter idine (-0.52 V), there is a ~ 1 V shift to more positive reduction potentials. We also see the arrangement of the imine nitrogens affect the reducti on potential shifting it 200 mV more positive in going from pyrimidine (1.78 V) to pyrazine (1.57 V).

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30 Figure 1-10. Reduction potential s of various nitrogen containing heterocycles measured in anhydrous DMF ( V vs. Hg pool).115 These trends can be applied to a new set of acceptors known as o-quinoid type acceptors. These acceptors usually involve the incorporation of thiadiazole ring(s) and or imine nitrogens into the heterocycle. The advant age of the thiadiazole ring is that the hypervalent sulfur atom can help stabilize negative charge.116 These are some of the str ongest two or three-ring fused heterocycle acceptors known to date and domin ate most of the research being done in DA oligomers/polymers (Figure 1-11).7,12,16,17,26,49,71,101,102,105,107-109,117-119 The acceptors offer wide range of band gap control with peak (Ep,c) reduction potentials ranging from -1.51 V all the way down to -0.19 V for DAD oligomers and -1.74 V to ~ -0.4 V vs. SCE for the electrochemically polymerized polymers. It is important to note th at the thiadiazole rings are much more electron withdrawing compared to their imine (C=N) count erpart. There is a +300 mV positive shift in going from quinoxaline to 2,1,3-benz othiadiazole. An important note is that while the thiadiazole rings increase the acceptor strength, they do not allow for synthetic flexibility towards solubility like the quinoxaline and pyrazine based acceptors do. Through various combinations of imine nitrogens and thiadiazole rings, one can control the reduction potential

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31 and thus the band gap of a desired DAD olig omer/polymer. These acceptors have been incorporated into very low band gap polymers, with an electropolymerized BTh-TTP polymer having a band gap of 0.3 eV120 and a soluble polymer, P(DTPBThBBT), which has a band gap of ~0.5 eV will be discussed in chapter 5.53 NN S N S N S NN S NN N S N N S N N S N NN R R N S N N S N NN NN N NN Ph Ph Ar S S Ar= BTD Monomer:-1.22V Polymer:-1.38V PQ Monomer:-1.17V Polymer:-1.19V TQ Monomer(R=H):-0.72V Polymer(R=H):-0.78V Monomer(R=CH3):-0.85V TTD Monomer:-0.93V TP Monomer(R=H):-1.05V Polymer(R=H):-1.33V Monomer(R=CH3):-1.36V BBT Monomer:-0.53V Polymer:-0.68V TTP Monomer:-0.19V Polymer:~-0.4V*QU Monomer:-1.51V Polymer:-1.74V PyrPyr Monomer:-1.28V Polymer:-1.31V Ar S S n E-chemPolym R R Figure 1-11. Reduction potentials of fused heterocyclic quinoid type acceptors incorporated into DAD oligomers/polymers with thiophene as the donor. The acceptors are quinoxaline (QU); pyrido[3,4b]pyrazine (PyrPyr); 2,1,3-benzothiadiazole (BTD); pyrazino[2,3g]quinoxaline (PQ); thieno[3,4b]pyrazino (TP); thieno[3,4c ][1,2,5]thiadiazolo (TTD ); [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ); benzo[1,2c;3,4-c ]bis[1,2,5]thiadiazolo (BBT); [1,2,5]thiadiazolo[3,4b]thieno[3,4e ]pyrazine (TTP). All potentials (Ep,c) are relative to SCE and taken from the literature.* polymer reduction potential was estimated from the CV shown.111,112,120 Design Principles of DAD Architectures for CPs One of the m ajor advantages of the DAD architecture is its ability to undergo electrochemical polymerization quite easily when designed properly. It is in the choice of the donors and acceptors that allows one to control the final properties of the polymers via the DAD monomer structure. While the structure prope rty relationships between the DAD architecture

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32 and the optoelectronic properties of the polymers will be examined throughout this dissertation, a few desirable properties will be highlighted. The most important issue in the synthesis of DAD compounds is solubility. The nature of the DAD concept leads to at least a minimum of a three ring system, and usually many more. The more solublizing groups (i.e alkyl, branch ed alkyl, bulky substituents) there are on the compound, the easier it is to handle and purify duri ng synthesis. If the DAD compound is to be used in a chemical polymerization (oxidative, me tal mediated), then the more soluble it is, the better. Depending on the choice of donor and a cceptor, one might be able to place the solublizing groups on the donor, the acceptor, bot h, or none. Usually stronger acceptors like, benzothiadiazole (BTD), benzobisthiadiazo le (BBT), thienylthiadiazole (TTD), and thienylthiadiazolopyrazine (TTP) do not allow for incorporation of solublizing groups, so they must be incorporated onto the donor if re quired (depending on whether making a DAD homopolymer or copolymerizing with a different monomer). There are a myriad of acceptors that allow for incorporation of solubility su ch as quinoxaline (QU) pyridopyrazine (PyrPyr), thienylpyrazine (TP), and thiadiazoloquinoxaline (TQ). In these accep tors, the solublizing groups are located far enough away from the conjuga ted backbone not to cause steric interactions interfering with the planarity of the CP, but will influence the in terchain interactions. If the acceptor chosen is a three ring a cceptor system where the donors are attached to the middle ring, only small five-membered ring heterocyclic donors like thiophene, N-H pyrrole, and their fused analogs will be highly planar. Bulkier sixmembered ring heterocyclic donors such as phenylenes, fluorenes, carbazoles, substituted pyrroles, and dioxythiophenes will be twisted out of plane, thus blue-shifting the band gap. An ex ample of this is the comparison of BTh-BBT to BEDOT-BBT, and will be discussed in chapter 4. If the donor is att ached to a multi-ring

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33 acceptor at one end, then five-membered ring he terocyclic donors such as thiophene, N-H pyrrole, their fused analogs, and dioxythiophene donors can be nearly planar. BEDOT-PyrPyrPh2 is a good example of this.67 It is through these multiple interactions along with donor and acceptor strength that the chemist can design th e DAD monomers for fine control over the polymers optical and elec tronic properties. The remainder of this dissertation will deal with the structure-prope rty relationships of various donor acceptor polymers starting from the DAD architecture. The DAD architecture lends itself to electropolymeri zation, which allows for easy a nd quick characte rization of the optical and electronic properties. Chapter 3 ex plores the initial foray into the DAD polymer synthesis and characterization i nvolving pyridopyrazine chemistry. Upon realizing the faults of the initial system, Chapter 4 explores increasi ng the acceptor strength to stronger TQ and BBT based acceptors. Multiple dioxythiophene based donors were also investigated, to come up with a family of polymers capable of fine control ove r the optical and electronic properties with hopes of improved stability. Finally, Chapter 5 will de al with incorporating th ese types of acceptors into new soluble, very low band gap polymers. The goal was to find a strong donor with the proper connectivity to these strong acceptors in order to create even lower band gap polymers that are solution processable. Through collaboration with Seth Ma rder at Georgia Tech, a strong dithienylpyrrole (DTP) based donor was coupled to the various thiadiazole based acceptors discussed previously, yielding the lowest band gap, soluble, conjugated polymers to date.

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34 CHAPTER 2 EXPERIMENTAL Overview This chapter provides an overview of the expe rimental m ethods and analytical techniques used to prepare and characterize the monomers and polymers in this dissertation. These methods and techniques will only be highlighted sin ce previous Reynolds group dissertations have exhaustively explained these techniques. The sy nthetic details for the specific compounds can be found in Chapters 3-5. Molecular Characterization Com pounds were characterized by 1H and 13C NMR using a Mercury 300 FT-NMR, VXR300 FT NMR, and a Gemini 300 FT-NMR. High resolution mass spectrometry was performed at the University of Florida, Department of Ch emistry using either an Agilent 6210 time-of-flight mass spectrometer, a Bruker Apex II FTICR mass spectrometer, or a Finnigan MAT 96Q mass spectrometer. Elemental (CHN) analysis was performed at the University of Florida, Department of Chemistry, Atlantic Microlabs, and Robertson Microl it labaoratories. X-Ray Crystallography X-ray quality crystals w ere obtained from slow evaporation/diffusion of solutions in the following manner. The compounds were dissolved in good solvent, such as dichloromethane or chloroform, and placed inside a test-tube. Then heptane, a poor solvent for the compound, was added carefully to form a layer on top of the good solvent. The test-tube was then covered with aluminum foil and the solution was allo wed to diffuse and evaporate slowly. Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphe re of data (1850 frames) was

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35 collected using the -scan method (0.3 frame width). The first 50 frames were re-measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integrat ion were applied based on measured indexed crystal faces. The structure was solved by the Direct Me thods in SHELXTL6, and refined using fullmatrix least squares. The non-H atoms were tr eated anisotropically, wh ereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. For 6a (Chapter 4), the asymmetric unit consists of two half molecule s (each located on an inversion center). One of the molecules has a di sorder in the C18-C19 unit and was refined in two parts (minor part is labeled C18-C19). Their site occupation factors were dependently refined. A total of 270 parameters were refine d in the final cycle of refinement using 3205 reflections with I > 2 (I) to yield R1 and wR2 of 3.74% and 9.23%, respectively. Refinement was done using F2. For 6b (Chapter 4), the asymmetric unit consis ts of two chemically equivalent but crystallographically independent molecules. A to tal of 289 parameters were refined in the final cycle of refinement using 1990 reflections with I > 2 (I) to yield R1 and wR2 of 6.76% and 15.26%, respectively. Refinement was done using F2. For 7a (Chapter 4), a total of 298 parameters were refined in the final cycle of refinement using 3658 reflections with I > 2 (I) to yield R1 and wR2 of 4.07% and 9.74%, respectively. Refinement was done using F2. For 7c (Chapter 4), a total of 352 parameters were refined in the final cycle of refinement using 4962 reflections with I > 2 (I) to yield R1 and wR2 of 4.00% and 10.48%, respectively. Refinement was done using F2.

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36 Polymer Characterization Polym ers were characterized by 1H NMR using a Varian Mercury 300 MHz spectrometer. Elemental analyses were carried out by Atlantic Microlabs. Thermal gravimetric analysis (TGA) measurements were performed on NETZSCH thermogravimetric analyzer (model STA 449C) under a nitrogen flow at a heating rate of 10 C/min or on a TA Instruments TGA Q5000 thermogravimetric analyzer under an air flow at a heating rate of 30 C/min. Differential scanning calorimetry (DSC) was performed on a TA instruments DSC Q1000 equipped with liquid nitrogen cooling accessory calibrated with sapphire and indium standards. All samples (25 mg) were prepared in hermetically sealed pans and referenced to an empty pan. Gel permeation chromatography (GPC) was performe d using a Waters Asso ciates GPCV2000 liquid chromatography system with its internal differential refractive index detector (DRI) at 40 C, using two Waters Styragel HR-5E columns (10 m PD, 7.8 mm i.d., 300 mm length) with HPLC grade THF as the mobile phase at a flow rate of 1.0 mL / min. Injections were made at 0.05 0.07 % w/v sample concentration using a 220.5 L injection volume. Retention times were calibrated against a minimum of nine narrow mol ecular weight polystyrene standards (Polymer Laboratories; Amherst, MA). Electrochemical Methods Electrochemistry allows one to probe the electronic redox properties of conjugated polym ers in order to determine the band gap a nd position of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels. The HOMO level is usually taken as the onset of oxi dation, while the LUMO level is taken as the onset of reduction as determined by cyclic voltammetry (CV) or differential pulse volatmmetry (DPV).

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37 All potentials reported in this dissertati on were measured relative to the Fc/Fc+ redox couple, and then converted to volts verses the sa turated calomel electrode (SCE), since most of the literature reports potentials relative to SCE. In this work, E(SCE) = E(Fc) + 0.38 V.121 To determine the HOMO/LUMO levels relative to vacuum, E(VAC) = E(SCE) + 4.7 V.37 General Set-Up Electrochemical experiments were p erformed in a three electrode cell consisting of a platinum button (0.02 cm2) working electrode, a platinum flag counter electrode and a Ag wire pseudo reference electrode or a Ag/Ag+ reference electrode calib rated using a 5 mM Fc/Fc+ in 0.1 M supporting electrolyte soluti on. Spectroelectrochemical experiments were performed on ITO-coated glass work ing electrodes (~ 1.5 cm2) using a Ag wire pseudo reference electrode and a platinum wire counter electrode. The supporting electrolyte used in all of the experiment s was tetrabutylammonium perchlorate (TBAP) dissolved in freshly distille d methylene chloride (D CM), acetonitrile (ACN) or propylene carbonate (PC). All electrochemical and spectroelectrochemical measurements were made with an EG&G PA R model 273A potentiostat/ galva nostat, and optical data was measured with a Cary 500 UV-VIS-NIR spectro photometer or a StellerNet Diode Array UVVIS-NIR. Preparation of DAD Monomer Solutions for Electrochemicalpolymeriz ation In general, monomer concentrations used in elecrochemcial polymerization are in the range of 5 to 10 mM. Sometimes it is possible to depo sit polymer films from lower concentrations. The most common used solvents for polymer de position are DCM, ACN and PC. The goal is to synthesize a DAD compound with just enough solubility to dissolve in one or a mixture of these solvents, but yet still be able to handle on the synthetic end.

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38 The choice of solvents can be troublesome, a nd usually involve a lo t of trial and error depending on the molecule you are trying to polymerize. Ideally, there should be enough solubility for the monomer (5-10 mM), but poor solubility for the polymer (to prevent dissolution and increase deposition). For DAD monomers wit hout any solublizing groups, usually straight DCM works quite well. For DAD monomers with solublizing groups, usually straight PC or ACN will work depending on solu bility. More often than not a mixture of DCM/PC or DCM/ACN will be needed. The best way to make up solutions of mixed solvents is to use a minimum amount of good solvent to di ssolve the monomer, and then add the poor solvent until the desired volume is reached. If the DAD compound crashes out during addition of the poor solvent, it may be necessary to add a little more of the good solv ent to re-dissolve the DAD monomer. This is analogous to the recrystallization of compounds from acetone/water, and works quite well. Deposition of Polymers For soluble polym ers, films were deposited on to the working electr ode by drop-casting or spray-casting from 2 to 5 mg/mL toluene or ch loroform solutions. However, most of the polymers studied in this dissert ation were prepared by electroc hemical polymerization. Polymer deposition onto the working electrode was perfor med potentiostatically or by repetitive scan cyclic voltammetry. In both cases, 5 mM m onomer in 0.1 M TBAP supporting electrolyte solution was used. For repetitive scan cyclic voltammetry, the monomer was scanned from a neutral potential to a point just past the monome r oxidation potential. Potentiostatic deposition was done by holding the potential constant, just beyond the monome r oxidation potential, until a certain amount of charge (~0.04 C) had passed. Th e films were then rinsed with DCM or ACN and characterized in monomer free electrolyte solution.

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39 Cyclic Voltammetry/Differential Pulse Volatmmetry The m ajority of the work in this dissertation centers around cyclic voltammetry (CV) and differential pulse voltammetry (DPV) characterization of pol ymer films drop cast or electrodeposited onto platinum button or ITO coated glass working electrodes. Detailed explanations of these techniques in various Reynolds group dissertations have been quite extensive and serve as a good reference point.39,78,122 In CV, usually the potential of the working electrode is scanned from a neutral potentia l (the polymer is in it s insulating form), to a vertex potential (oxidizing or reduc ing potential of the polymer) back to the neutral potential at a constant rate while the current is monitored. As the potential approaches the polymers oxidation potential, electrons are removed from the polymer and the charge is counter balanced by the supporting electrolyte. This results in a current flow and is measured as a function of change in potential relative to time (scan rate). For pol ymer films adhered on an electrode surface which are not under diffusion control, th e relationship between peak current and scan rate can be seen in equation 2-1. Ip=(n2F2/4RT) O Equation (2-1) Here, n = the number of electrons, F = Farada y constant (96,485 C/mol), R = the universal gas constant, T= temperature, = scan rate (V/s), = area of the electrode (cm2, and O = concentration of adsorbed O (mol/cm2). For well adhered films, the peak current varies linearly with scan rate, and the film is not under diffusion control. For reversible systems, the peaks on the forward and reverse scans should be symmetri cal in shape and intensity, but with equal and opposite signs for the current. For polymers t hough, the forward and reverse scans are usually not symmetrical due to different adsorption strengths or O and R, double layer charging, different film morphologies, charge transport, and various cha nges in the film during the process (swelling & contracting).

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40 The best way to minimize the factors that co ntribute to the asymmetry of the CV curve (especially charging currents) is through the use of DPV. Comp aring CV to DPV, CV uses a saw tooth wave form while DPV utilizes a potential square wave form (Fi gure 2-1). In the CV waveform, the current is being measured constan tly, so background currents (such as charging of the double layer) are included in the measurement along with the current associated with the oxidation or reduction. In DPV, th e potential is held constant for certain amount of time while the background current is monitored, and then righ t before the pulse, the current is measured at io. Then a pulse is applied (amplitude is usually 10 -100 mV), and the current is measured again immediately after the pulse i Then the potential comes back down to a slightly higher potential, depending on the step size (usually 1-2 mV). The advantage of DPV is by measuring the differential current ( i io), it allows for the background charging currents to reach equilibrium before the pulse is applied, and if the pulse is no t close to the E0 of the system, no faradaic current is measured, thus yielding no real current response. Only when the pulse approaches the E0 of the system and oxidation or reduction begins to occur will a faradaic current be measured.123 The longer the step time the better the sensitivity you will have since the charging currents will be minimized. The increased sensitivity of DPV allows for improved accuracy for measuring the onsets for oxidation and reduction, and thus determining the HOMO/LUMO values. This also can be a good indication of how re versible a system really is. For a reversible system, the peaks should be highly symmetrical a nd sharp with minimal peak to peak separation (less than 100 mV for c onjugated polymers).

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41 Potential TimeCV Waveform Potential Time Amplitude Step size Step timeDPV Waveformioi Figure 2-1. Example of DPV wavefo rm relative to CV waveform. Optical Characterization Materials for Optical Characterization Most often polym er optoelectronic properties are investigated using ITO coated glass working electrodes. These electrodes are highly tr ansparent in the visible region of the spectrum, allowing for optimum characterization for the di fferent colored states (redox states) of a conjugated polymer. This electrode is well suited for polymers with band gaps (defined as the onset of the lowest energy absorption) 1 eV. However, when working with donor-acceptor systems with low band gaps, ITO can be a problem due to a strong absorption beyond 1600 nm. This makes it hard to determine the optical band gap due to poor baseli ne resolution. Switching to single walled carbon nanotube electrodes (SWCNTs), which are highly transparent into the NIR, allow for increased accura cy in bad gap determination.124 This electrode material has played an important role in the characterization of some of the low band gap polymers in this dissertation, and has proven to be a valuable commodity in the band gap determination for very low band gap polymers.

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42 Spectroelectrochemistry To develop a m ore complete understanding of the systems st udied in this dissertation, spectroelectrochemistry was performed on thes e systems. Typically, the polymers were electrodeposited potentiostatically onto ITO coated glass working electrodes from 5 mM monomer 0.1 M TBAP solutions containing va rious amounts of DCM, ACN, or propylene depending on monomer solubility. For soluble po lymers, films were spray cast from 3-5 mg/mL polymer solutions in chloroform or toluene. The films were then placed in a cuvette equipped with a platinum wire counter elec trode and a silver wire pseudo reference electrode. The cuvette was then filled with degassed monomer free elect rolyte solution (usually 0.1 M TBAP-PC for most of the work in this dissertation), and the fi lms were then broken in by repetitive scanning in a potential window containing the desired redox couple until a re producible trace was attained ( ca. 20 times). Characterization of a polymers neutral to oxidi zed state was performed on the bench top using a Carry 500 UV-VI S-NIR spectrophotometer. It is important to note that all bench top experiments were performed under an argon blanket. For characterization of a polymers neutral state to the re duced state(s), the us e of the glove box was required due to the high sensitivity of radical anions towards water and air. These measurements were recorded on a Stellarnet Photodiode Array spectr ophotometer connected to the glove box via fiber optic cables. In certain cases, the reductiv e characterization was done on the bench top under stringent air and moisture free conditions. Spect roelectrochemistry allows one to monitor the change in the absorption profile of a polymer as it is switched between different redox states. This gives insight into the optical band ga p, how to control the polymers colored states through structural modification, and the nature of charge carriers formed upon oxidation or reduction.

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43 CHAPTER 3 P(BEDOT-PYRIDOPYRAZINE): PROBING TH E PROPERTIES OF A MULTIPLE REDOX STATE POLYMER Introduction Low band gap polym ers have been the focus of many studies, and were reviewed briefly in Chapter 1. These polymers are colore d in the neutral state due to the transition located at low energies, and become more transp arent upon doping with a decrease of the transition and development of lower energy transitions. By having a low band gap, the conduction band can be reached easier, allowing for the possi bility of n-type doping. Thus, low band gap polymers could lead to dual p-t ype and n-type electrochromic devices with a single polymer. Some methods for obtaining these polymers were discussed earlier in Chapter 1, including, but not limited to, minimizing bond-length alternation, interchain effects, planarity, and donoracceptor effects. Donor-acceptor polymers are of interest because they possess multiple redox states (p-type or n-type doping) in a small pot ential window. This is due to the placement of the valence band (highest occupied molecular or bital, HOMO) relative to the conduction band (lowest unoccupied molecular orbital, LUMO). The goal is to sel ect a strong donor with a high HOMO level and a strong acceptor with a low LUMO level. When the donor and acceptor are coupled, the orbitals mix forming a new set of orbitals, with the ne wly formed HOMO taking on a similar energy to the donor while the LUMO will be similar in en ergy to the acceptor. As was discussed in Chapter 1, the LUMO is thought to be isolated on the acceptor instead of being a true conduction band, and the small gap is attributed to intramolecu lar charge transfer (ICT). Nonetheless, the new donor-acceptor material now has a much smaller HOMO-LUMO gap compared to its

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44 individual parts. With the proper choice of donor and acceptor, the band gap can be modified and thus the final properties can be adjusted. Some previously investigated donor-accep tor systems involved cyano and nitro functionalized acceptors,125-127 polysquaraines,63,128 cyanovinylenes10,38,129 and fused ring aryl acceptors such as pyridopyrazine and thiadiazole rings.59,112,130 One of the more interesting systems involves the pyridopyrazine acceptor moiety. This structure allows access to multiple redox states, which can lead to more complex devices.67,68,112,131 Instead of just having two colored states associated with the neutral a nd oxidized species of a polymer, there is the possibility of having three to four different co lored states depending if the polymer has one or two reductions. One of the benefits of using this acceptor for an initial st udy is the synthetic ease by which these acceptors can be prepared. The pyridopyrazine acceptor is capable of stabilizing two negative charges. When this unit is coupled to a donor that is easily oxidized, there is now the possibility of four electronic states. A polymer of this structure can be cycled electrochemically (in a suitable solvent/electrolyte system) from the neutral state to reveal the two possible reduced states and th e oxidized state. These states can lead to different colors associated with the electrochromic properties of the polymer system. It is also possible to add solublizing groups to the pyri dopyrazine acceptor unit via the in stallation of the pyrazine ring.132 Poly[5,8-bis-(3-dihydro-thie no[3,4-b][1,4]dioxin-5-yl)-2,3diphenyl-pyrido[3,4-b]pyrazine (PBEDOT-PyrPyr-Ph2) (Figure 3-1), which was synthe sized previously in our group,68 shows four distinct electronic states; th e neutral form is lime green, the oxi dized state it is light gray, the first reduced state is a bu rgundy red, and the second reduced state it is a dark gray.

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45 Figure 3-1. Structure of PBEDOT-PyrPyr-Ph2. Choosing the proper donor for the donor-ac ceptor-donor (DAD) mono mer structure is important. By choosing EDOT as the donor, one can take advantage of its low oxidation potential for ease of el ectrochemical synthesis.75,76 This allows for electrochemical deposition of polymers onto platinum button or ITO coated gl ass working electrodes for characterization of their electronic and optical properties. The DAD architecture can be accessed by different transition metal cross-coupling reactions. The Reynolds group and the Yamamoto group have demonstrated the effectiveness of the Stille and Negishi coupling reactions towards the DAD architecture.112,133-135 Yamamoto et. al. have used the Stille method for the coupling of thiophene to various quinoxaline and pyridiopyrazine derivatives to make donor-acceptor polymers. Reynolds et. al. have used the Stille and Negishi couplings of EDOT to carbazole, pyridine, and pyridopyrazine.67,68,136 This work will investigate the differences in th e optical and electronic properties relative to having solublizing alkyl groups verses phenyl gr oups located on a pyridopyrazine acceptor in the DAD architecture with 3,4-ethylene dioxythiophene as the donor. F unctionalized acceptor targets of 5,8-dibromo-2,3-dihexyl-pyrido[3,4-b]pyrazine and 5,8-di bromo-2,3-didodecylpyrido[3,4b]pyrazine were chosen since long alkyl chains have been shown to increase solubility, allowing for easier purification and handli ng of solutions. The polymers ha ve been analyzed by cyclic voltammetry and spectroelectrochemistry to investigate their electr onic and optical properties. A comparison of the electronic and optical data to that of the previously made phenyl derivative

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46 will be used to establish structure-property relationships. These polymers might also be interesting for supercapacitor appl ications since previous inves tigations have shown PEDOT and its derivatives to have high stability, fast switching kine tics and high charge storage capacity.137,138 Monomer Synthesis and Characterization The synthesis of 5,8-dibrom o-2,3-dihexylpyrido[3,4b]pyrazine ( 5) is outlined in Figure 32. First, 3,4-diamino pyridine was brominated at the 2 and 5 positions with bromine in 48 % HBr to yield 3,4-diamino-2,5-dibromopyridine ( 2 ).112 This provides the base of the acceptor unit which can then be functionalized with -diones. Second, tetradecane-7,8-dione ( 4 ) was prepared by the oxidation of 7-tetradecyne with KMnO4 in acetone/H2O.139 Finally, ( 5) was obtained by the condensation between 2 and 4 in refluxing butanol.112 Figure 3-2. Synthesis of 5,8-dibr omo-2,3-dihexyl-pyrido[3,4-b]pyrazine. The synthesis of 5,8-dibr omo-2,3-didodecylpyrido[3,4b]pyrazine ( 9 ) (Figure 3-3), began with the formation of the internal alkyne. Lithiation of 1-tetradecyne ( 6 ), followed by the addition of 1-bromododecane, yielded hexacos-13-yne ( 7).132 Subsequent KMnO4 oxidation of 7

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47 yielded hexacosane-13,14-dione (8 ).140,141 Finally, the condensation reaction between 2 and 8 in refluxing butanol yielded 9.112 Figure 3-3. Synthesis of 5,8-dibr omo-2,3-didodecylpyrido[3,4-b]pyrazine. With the acceptor units in hand, the prepara tion of the DAD monomers and polymers were carried out (Figure 3-4). The DAD structure was chosen because it allows for the deposition of polymer directly onto working electrodes, such as platinum or ITO, for further electronic and optical characterization. (2,3-Dihydrothie no[3,4-b][1,4]dioxin-5-yl)trimethylstannane ( 10) was chosen as the donor due to the ability to is olate and purify it before coupling.39,98,142 A Stille cross-coupling reacti on between the donor ( 10) and the acceptors 5 and 9 yielded 5,8-Bis-(2,3dihydrothieno[3,4-b][1,4]d ioxin-5-yl)-2,3-dihexylpyrido[3,4-b]pyrazine ( 11) and 5,8-Bis-(2,3dihydro-thieno[3,4-b][1,4]dioxin-5-yl)2,3-didodecyl-pyri do[3,4-b]pyrazine ( 12) in moderate yields.

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48 Figure 3-4. Synthesis of monomers 11 and 12 and their respective polymers P1 and P2 Electrochemical Polymerization/Characterization Electropolymerization One of the reasons for the m onomers being functionalized with alkyl ch ains was to obtain continuous, optically clear films (due to the film forming properties of alkyl chains) relative to the previously studied phenyl derivative, whic h would sometimes crack. Electropolymerization of the monomers was carried out via repeated sc an cyclic voltammetry in an electrochemical cell, consisting of a platinum button working electrode, a platinum (flag or wire) counter electrode, and a silver wire ps eudo reference electrode. The pseudo reference electrode was calibrated with the ferrocene redox couple (Fc/Fc+) from a solution containing 5 mM ferrocene and 0.1 M TBAP (tetrabutylammonium perchlorate) in acetonitrile. All of the potentials in this chapter are reported as V vs. SCE (as discusse d in Chapter 2) for easy comparison throughout this dissertation and to literat ure values. The polymers were deposited from a 5 mM monomer,

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49 0.1 M supporting electrolyte (TBAP) solution in 1:1 dichlorometh ane:acetonitrile (DCM:ACN). The formation of P1 and P2 from 11 and 12 can be seen in Figure 3-5. During the first scan in Figure 35 A, there is a large peak at 0.88 V. This is due to the oxidation of monomer 11 at the electrode. On the reverse part of the first scan there is a slight reduction peak associated with the reduction of the deposited oligomers/polymer on the electrode. Subsequent cycling shows a broad oxid ation and reduction that increases in intensity and develops at lower and lower potentials. This is due to the fact that as the monomer couples to form oligomers and polymer, the conjugation in these chains is extended and the oxidation of longer oligomers and polymer chains take place at lower potentials than the monomer. The increase in current density of these lower oxi dation and reduction peak s is a good indication of polymer film formation on the electrode. This is similar to the electrochemical polymerization of monomer 12, which has its monomer oxidation potenti al at 0.86 V (Figure 3-5 B). Both monomers gave smooth polymer films. The elec trodes and attached polym er films were then rinsed with monomer free electrolyte to remove any residual monomer and the films were inspected before furt her characterization. -0.20.00.20.40.60.81.01.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 Current Density (mA/cm2)Potetnial (V vs. SCE)-0.20.00.20.40.60.81.01.2 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Current Density (mA/cm2)Potenetial (V vs. SCE)AB Figure 3-5. Repetitive scan electropolymerization (50 mV/s, 10 cycles ) from a 5 mM monomer 0.1 M TBAP/1:1 DCM:ACN solution. A) Monomer 11 yielding P1 B) Monomer 12 yielding P2

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50 Cyclic Voltammetry The electrod eposited polymer f ilms were then transferred into an electrochemical cell set up as described previously, except a Ag/Ag+ reference electrode was us ed, and characterized in monomer free electrolyte solution (0.1 M TBAP in ACN). The polymers were scanned using cyclic voltammetry (50 mV/s) until a reproducible CV was obtained (ca. 20 times) in order to investigate the electr onic properties. P1 (Figure 3-6 A) shows an onset of reduction at -1.38 V (E1/2 = -1.49 V). The first reduction peak of the polymer is quite stable (over 50 to100 cycles) and quasi-reversible with adequa te charge compensation on the reverse scan. However, the second reduction (not shown) is highly unstable and leads to film degradation and loss of electroactivity. The second reduction peak has been observed when a film of P1 on ITO was switched, however the reduction is ne arly irreversible and leads to film degradation. This could be due to the instability of the film at such a low potential and the high reactivity of the radical anions formed. The polymer shows a broad oxidati on peak with the main onset of oxidation at ~ -0.03 V. The oxidation of the film is interesting because it shows both a faradaic (oxidation with charge transfer involving el ectroactive species from -0.03 V to 0.35 V) and non-faradaic response (no further oxidation or charge transfer reactions of electroac tive species from ~ 0.35 V to 0.80 V) indicative of capaciti ve and pseudo capacitive behavior.143-145 The polymer has an electrochemical band gap of 1.35 eV. The colors for P1 (Figure 3-6 C) go from a neutral light navy-blue to an oxidize d more transparent greenish grey. Upon reduction the film becomes a light greyish pink. CV analysis of P2 (Figure 3-6 B) shows an ons et for reduction at -1.43 V (E1/2 = -1.50 V) establishing similar behavior to P1. While the first reduction has adequate charge compensation on the reverse scan, the peak to peak separation in P2 is much larger than in P1 indicating the reduction of P2 is not as reversible as it is for P1 The long alkyl chains in P2 may result in a

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51 more compact film making it harder for the supporting electrolyte to move in and out of the film. The first reduction has good stability over the 50 to 100 cycles used for characterization. The second reduction for this polymer was highly unsta ble and could only be seen for a few cycles, as described for P1 The onset for oxidation of P2 was observed at -0.04 V, and has both a faradaic and non-faradaic response similar to that of P1 The electrochemical band gap for P2 is estimated at 1.39 eV. -1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -2 -1 0 1 2 Current Density (mA/cm2)Potential (V vs. SCE)-2.0-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.8 -2 -1 0 1 2 3 Current Density (mA/cm2)Potential (V vs. SCE)AB C NO R Figure 3-6. Cyclic voltammetry of polymers P1 and P2 and the associated colored states. Cyclic voltammetry was performed on a Pt button working electrode in 0.1 M TBAP/ACN at a scan rate of 50 mV/s. Individual films for oxidation and reduc tion were used. A) CV of P1 B) CV of P2 C) Pictures of the 1st re duction (R), neutral (N), and oxidized (O) states of P1 N NN S S O O O O n R R N NN S S O O O O n R R Figure 3-7. Proposed structure for the ra dical anion of the first reduction.

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52 The key note here is that while both P1 and P2 have their first reductions at E1/2 = ~ -1.5 V for the first reduction, these valu es are 400 mV more negative than the previously reported reduction value of E1/2 = -1.1 V for P(BEDOT-PyrPyr-Ph2. One possible reason for this is the electron donating nature of alkyl groups making it more difficult to reduce these polymers. Also, the phenyl groups could extend the conjugation in the solid state resulting in lower reduction poteentials.146 When looking at the second reduction, the stability is greatly decreased compared to the phenyl derivative. So while we do gain better solubility of the monomers in terms of synthetic work, we lose the electrochemical advantages of having the phenyl groups. This demonstrates another possibility for controlling the band gap. Spectroelectochemistry Polym er films of P1 and P2 were deposited potentiostatic ally from 5 mM monomer 0.1 M TBAP/(DCM/ACN) solution onto IT O coated glass working electr odes in order to characterize their optical properties. The films were placed in a cuvette containing 0.1 M TBAP/ACN with a platinum wire counter electrode and a silver wire pseudo referen ce electrode calibrated to Fc/Fc+. The films were then neutralized and cycled by CV until a reproducible CV was attained for oxidative spectroelectrochemistry. Neutral P1 has a max at 689 nm and a high energy peak at 404 nm (Figure 3-8 A). The peak at 689 is attributed to intramolecular charge transfer interactions while the peak at 404 nm is associated with the transition.27,147 The max covers most of the visible region tailing off to minimum around 470 nm before rising back up. Thus the polymer is a blue/navy blue in the neutral state. The onset of ab sorption is at ~850 nm correspondi ng to an optical band gap of about 1.45 eV. Almost identical absorptions are seen for P2 (Figure 3-8 B), which has a max at 691 nm and a high energy peak at 401 nm. The same tail of the max is seen from the red down

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53 to the blue resulting in a blue/navy blue neutral polymer. The onset of absorption is also at ~ 850 nm corresponding to the same op tical band gap of 1.45 eV. Thes e values are in good agreement with the electrochemical gap of 1.35 eV for P1 and 1.39 eV for P2 In comparison to the optical band gap of the previously studied P(BEDOT-PyrPyr-Ph2, (Eg = ~1.2 eV), there is a ~ 0.25 eV increase in the band gap in going from phenyl substituted PyrPyr to the alkyl substituted PyrPyr. Though the difference is not as large as was in the electrochemical data the trend is observed. Upon oxidation, there is a bleaching of the both neutral absorptions in P1 and P2 with the decreases beginning around -0.1 to 0.0 V, which matches up well with the CV data for the onset of oxidation. As the oxidation potential is increased, there is the development of a peak around 900 nm along with a tail from the NIR, indicating the formation of polaron charge carriers. In the oxidized state, both polymers now have a sha llow v-shape with the tail from the peak at 900 nm reaching a minimum around 500-550 nm with a slight increase in absorption in going to shorter wavelengths yielding a lighter more transpar ent greenish grey color in the oxidized state. 4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 n n n a a a Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 l l l a a a Absorbance (A.U.)Wavelength (nm)A B Figure 3-8. Oxidative spect roelectrochemistry of P1 and P2 on ITO in 0.1 M TBAP/ACN. (A) P1 at potentials of (a) -0.49 V to (n) 0.81 V in 100 mV increments; (B) P2 at potentials of (a) -0.49 V to (n) 0.61 V in 100 mV increments.

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54 Due to the high reactivity of a polymer in th e n-doped state to air and water, reductive spectroelectrochemistry was performed in the glove box.148 This was done using a Stellarnet Diode Array VIS-NIR spectrophoto meter which was connected via fiber optic cables into the glove box. This allows for characterization without the worries of water or oxygen contamination from the atmosphere. Application of reducing potentials to neutral P1 (the small peak in neutral spectrum around 970 nm is due to trapped charges, and disappears upon more ne gative potentials) (Figure 3-9) shows a bleaching of the ICT band and the high energy band up to the first reduction (-1.55 V). As these bands bleach, a band develops around 1200 nm tails into the visible region This band in the NIR is indicative of charge carrier forma tion involving a true n-dop ed state and matches up well with the first reduction seen by CV.67 There is also a peak that evolves at ~470 nm during this reduction process that yields a polymer that is grayish pink in color. In going to more negative potentials, there is almost a complete lo ss of intensity for the charge carrier band at 1200 nm, along with an increase in intensity of th e high energy peak at 470 nm with concurrent formation of a shoulder at 630 nm. This peak is probably due to film degr adation, as can be seen for a typical film after reductive spectroelectrochemistry (Figure 3-11). Upon reducing P2 through the first reduced state, we see similar changes to the absorption spectrum as for P1 There is a bleaching of the ICT band and the high energy peak with the concurrent development of a fairly intense ba nd peaking around 1400 nm ta iling through the NIR into the visible region, indicative of the formation of an n-doped state. The intensity for this NIR band peaks at -1.75 V, which corresponds with the first reduced state for P2 as seen by CV.

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55 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 d e j j j j a a a a Absorbance (A.U.)Wavelength (nm) Figure 3-9. Reductive spect roelectrochemistry of P1 on an ITO coated glass slide in monomer free electrolyte solution (0.1 M TBAP in ACN) at applied potentials of (a) -1.15 V to (j) -2.05 V in 100 mV increments. Bold bl ack line = neutral (1.15 V), dashed line = first reduction (-1.55 V), a nd bold dotted line = (-2.05 V) 400600800100012001400 0.0 0.2 0.4 0.6 0.8 1.0 i i a a i a Normalized Absorbance (A.U.)Wavelength (nm) Figure 3-10. Reductive spect roelectrochemistry of P2 on an ITO coated glass slide in monomer free electrolyte solution (0.1 M TBAP in ACN) at applied potentials of (a) -1.14 V to (i) -1.94 V in 100 mV increments. Bold bl ack line = neutral (-1.14 V), bold yellow = first reduction (-1.75 V), and bold navy = (-1.94 V).

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56 Figure 3-11. Photograph of a film of P2 after reductive spectroelec trochemistry. The same observations were seen for P1. Conclusions In this chapter, DAD conjugated poly me rs with solublizing alkyl groups (C6H13 and C12H25) were synthesized, electrochemically polymerized, and characterized. Electropolymerization allows for quick characte rization and possible conc lusions of structure property relationships. The neutra l polymers are navy blue in colo r with a band gap of ~1.45 eV. The oxidation of these polymers by cyclic voltammetry shows the possibility for use in capacitors due to their faradaic and non-faradaic characteristics. Both polymers show access to multiple electronic and optical states via cyclic voltammetry and spectroelectrochemistry. Their optical properties change in accordance with the electronic st ates. It should be noted that the second reduction of these polymers were high ly unstable upon repeat ed reductive cycling, where as the first reduction was quite stable. Th e stability issues seen with the second reduction thus only allows for three different colored stat es in these polymers compared to the diphenyl derivative, which had four colored states. It is not clear if the loss in stability of the second reduction for these alkyl derivativ es is solely due to the more negative reduction potentials compared to the diphenyl derivative, or if it has to due with the nature of the alkyl groups, which have -protons. These protons could be highly react ive to the radical anions formed during the second reduction. It is unclea r right now what causes these stability issues, and further investigation is needed.

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57 Another important aspect of this study shows th e ability to fine tune the properties of these DA systems. We saw that in going from the pr eviously reported diphenyl derivative to the alkyl derivatives, there is ~0.2 eV increase in the band gap. This corresponds to a neutral navy blue colored polymer for the alkyl de rivative compared to a gree n color for the neutral phenyl derivative. We also saw a 200-300 mV negative sh ift in reduction poten tials compared to the phenyl derivatives. These proper ties demonstrate another useful tool for the synthetic organic chemist to fine tune the voltage window of these polymers for possi ble applications in supercapacitors. The ability to functionalize the acceptor, vi a the condensation reacti on of the dicarbonyl moiety, is an important feature of these polymers. This could not only lead to solubility, but also to the tailoring of desired pr operties depending on the applica tion. By synthesizing a dicarbonyl moiety containing different functionalities such as organic dyes instead of alkyl chains, one could access different colors for electrochromic devices. Experimental 3,4-diamino-2,5-dibromopyridine (2).112 3,4-Diaminopyridine (4.99 g, 0.0457 mol) and 110 mL of 48 % HBr was placed into a 250 mL 3-neck round bottom flask equipped with a reflux condenser, addition funnel, and vented to a NaOH scrubber. The solution was then heated to reflux. Bromine (4.73 mL, 0.0293 mol) was a dded drop wise over ~1 h. The solution was then heated at reflux for 5 h. Upon cooling, a pr ecipitate was collected by filtration and washed with an aqueous solution of saturated Na2S2O3, K2CO3, and then distilled water. After drying under vacuum 9.37g (77 %) of a cream-colored solid was obtained. 1H NMR (300 MHz, DMSOd6) 7.53 (s, 1H), 5.99 (s, 2H), 5.05 (s, 2H); 13C NMR (75 MHz, DMSO-d6) 104.47, 125.90, 128.80, 138.39, 139.17 HRMS calcd. For C5H5N3Br2 264.8850 Found 264.8851.

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58 Tetradecane-7,8-dione (4).139 A 3 L Erlenmeyer flask equi pped with a magnetic stir bar was charged with 7-tetradecyne (5.25g, 0.027 mol) and 1.05 L of reagent grade acetone. In a separate flask, 1.36 g of NaHCO3, 13.6 g of MgSO4, and 600 mL of H2O were combined to form a buffer solution, which was added to the 3 L Erlenmeyer flask. KMnO4 (16.6 g, 0.105 mol) was added and the solution was stirred for 4 h. Th e unreacted permanganate and precipitated MnO2 were converted to soluble Mn2+ by adding ~ 21 g of NaNO2 and ~140 mL of H2SO4. The solution was then saturated with sodium chlo ride and extracted (3 x 200 mL) with a 1:1 hexane:ether mixture. The organic solvent was removed under reduced pressure and the residue was dissolved in 50 mL of ether and extracted (4 x 50 mL) with 5 % NaOH. After washing the solution with brine, and drying over MgSO4, the solvent was removed under reduced pressure to yield a yellow solid. After recrystallization from MeOH, 3.56 g (58 %) of yellow plates were obtained. mp 40 oC (lit. 38-39 oC).27 1H NMR (300 MHz, CDCl3) 0.88 (t, 6H), 1.29 (m, 12H), 1.57(p, 4H), 2.73 (t, 4H) HRMS calcd. For C14H26O2 226.1933 Found 226.1927. Hexacos-13-yne (7).132 Under an argon atmosphere, 125 mL of dry THF was transferred into a dry 500 mL 3-neck round bottom flask e quipped with a stir bar, reflux condenser, and addition funnel. 1-Tetradecyne (10.0 mL, 0.041 mol) of was adde d via syringe and the solution was cooled to 0 oC. Then n-BuLi (16.2 mL, 2.5 M) was ad ded drop wise. The solution was then allowed to warm up to room temperature a nd 1-bromododecane (9.82 mL, 0.041 mol) was added drop wise. The solution was then heated to re flux for 3 days. After cooling, the solution was extracted (3 x 65 mL) with Na2SO4 and (3 x 75 mL) H2O. The solution was dried over MgSO4 and the solvent was removed under reduced pressure to yield 14.33 g (97 %) of a white solid. mp 29-33 oC. 1H NMR (300 MHz, CDCl3) 0.88 (t, 6H), 1.2-1.5 (m, 40H), 2.14 (t, 4H); 13C NMR (75 MHz, CDCl3) 14.11, 18.76, 22.69, 28.87, 29.18, 29.36, 29.57, 29.64, 29.68, 31.93, 80.25.

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59 Hexacosane-13,14-dione (8).140,141 A 500 mL Erlenmeyer flask equipped with a reflux condenser and stir bar was charged with KMnO4 (5.85 g, 0.037 mol) and 100 mL H2O. In a separate flask, hexacos-13-yne (3.26 g, 0.009 mol) of, 100 mL of CH2Cl2, 1.5 mL aliquot 336 (Aldrich), and 1.5 mL of acetic acid were comb ined. This solution was then added to the KMnO4/H2O solution and heated to reflux for 6 h. Af ter cooling, 2 g of sodium bisulfite was added and the solution allowed to stir for 15 mi n. Next the solution was acidified with conc. HCl, and 4 g of sodium bisulfite was added in small portions. The aque ous layer was separated and saturated with NaCl, followed by extraction (3 x 75 mL) with CH2Cl2. The organic layers were combined and extracted (3 x 75 mL ) with 5 % NaOH. After drying over MgSO4, the solvent was removed under reduced pressure to yi eld a light yellow solid. Recrystallization from MeOH yielded 1.45 g (41 %) of light yellow plates. mp 73-75 oC (lit. 76-78 oC).30 1H NMR (300 MHz, CDCl3) 0.88 (t, 6H), 1.25 (m, 36H), 1.57 (p,4H) 2.72 (t, 4H); 13C NMR (75 MHz, CDCl3) 14.11, 22.68, 23.07, 29.14, 29.33, 29.43, 29.58, 29.62, 31.91, 36.09, 200.22. HRMS calcd for C26H50O2 394.3811 Found 394.3813. 5,8-dibromo-2,3-dihexyl-pyrido[3,4-b]pyrazine (5).112,132 3,4-Diamino-2,5dibromopyridine (1.31 g, 0.0049 mol), te tradecane-7,8-dione (1.14 g, 0.0050 mol), ptoluenesulfonic acid monohydrate (0.02 g, 0.00010 mo l) of, and 20 mL of 1-butanol were combined in a 100 mL 3-neck round bottom flask e quipped with a reflux condenser and stir bar. The solution was then heated to reflux for 5 h. After cooling, a prec ipitate was collected by filtration. Recrystallization from EtOH yiel ded 1.46 g (65 %) of an off-white solid. mp 71.572.8 oC. 1H NMR (300 MHz, CDCl3), 0.92 (t, 6H), 1.3-1.5 (m, 12H), 1.92 (m, 4H), 3.10 (m, 4H), 8.68 (s, 1H); 13C NMR (75 MHz, CDCl3) 14.06, 22.56, 22.57, 27.43, 29.06, 29.10, 31.65, 31.69, 34.85, 35.12, 120.08, 135.97, 142.49, 145.70, 146.40, 160.51, 163.16. Elemental Anal.

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60 Calcd. For C19H27N3Br2: C, 49.91; H, 5.95; N, 9.19; Br, 34.95. Found: C, 50.03; H, 5.99; N, 9.06. HRMS calcd. for C19H27N3Br2 457.0551 Found 457.0556. 5,8-Dibromo-2,3-didodecyl-pyrido[3,4-b]pyrazine (9).112,132 3,4-Diamino-2,5dibromopyridine (1.32 g, 0.0049 mol), hexacosane-13,14-dione (1.99 g, 0.0050 mol), ptoluenesulfonic acid monohydrate (0.02 g, 0.00010 mol) and 23 mL of 1-butanol were combined in a 100 mL 3-neck round bottom flask equipped w ith a reflux condenser and stir bar. The solution was heated to reflux for 5 h. Upon cooling, a light yellow solid was collected by filtration. Column chromatography (7:3 CH2Cl2:Hexane) yielded 1.63 g (53 %) of a white solid. mp 58-59.5 oC. 1H NMR (300 MHz, CDCl3) 0.88 (t, 6H), 1.22-1.54 (m, 36H), 1.86-1.98 (m 4H), 3.06-3.12 (m, 4H), 8.68 (s, 1H); 13C NMR (75 MHz, CDCl3) 14.10, 22.67, 27.50, 29.34, 29.39, 29,43, 29.46, 29.48, 29.54, 29.63, 31.91, 34.86, 35.13, 120.09, 135.98, 142.50, 145.72, 146.40, 160.54, 163.18. Elemental Anal. Calcd. for C31H51N3Br2: C, 59.52; H, 8.22; N, 6.72; Br, 25.55. Found: C, 60.15; H, 8.66; N, 6.61. HRMS calcd. for C31H51N3Br2 (M+H) 624.2528 Found 624.2547 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin5-yl)-2,3-dihexylpyrido[3,4-b]pyrazine (11).142 Under an argon atmosphere, 5,8-dibromo-2,3-dihexyl-pyrido[3,4-b]pyrazine (0.42 g, 0.00092 mol), (2,3-dihydrothieno[3,4b][1,4]dioxin-5-yl)trimethyl stannane (0.66 g, 0.0020 mol), and 25 mL of anhydrous DMF were combined in a dry 100 mL 3-neck round bottom flask with a stir bar. The mixture was degassed under argon for 1 h. Then Pd(II)Cl2(PPh3)2 (0.07 g, 11 mol %) was added, the solution was heated to 75 oC, and allowed to react for ~18 h. After cooling, the reaction mixture was poured into 200 mL of H2O and extracted repeatedly with ether. The organic solution was then concentrated and extracted repeatedly with brine. After drying over MgSO4, removal of ether under reduced pressure gave an orange-red solid. Column

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61 chromatography (1:1 DCM:EtOAc) yielded 0.21 g ( 40 %) of an orange crystalline powder. mp 167-168 oC. 1H NMR (300 MHz, CDCl3) 0.91 (t, 6H), 1.3-1.55 (m, 12H), 1.95-2.1 (m, 4H), 3.00-3.15 (m, 4H), 4.25-4.50 (m, 8H), 6.55 (s 1H), 6.63 (s, 1H), 9.72 (s, 1H); 13C NMR (75 MHz, CDCl3) 14.06, 22.59, 27.57, 27.72, 29.20, 31.75, 34.90, 35.18, 64.21, 64.29, 64.77, 65.29, 103.15, 105.21, 110.89, 114.05, 122.30, 132.52, 139.46, 140.38, 141.29, 141.73, 142.50, 144.30, 149.82, 156.10, 159.20. Elemental Anal. Calcd. for C31H37N3O4S2: C 64.22, H 6.47, N 7.25. Found C 64.21, H 6.68, N 7.19; HRMS calcd. for C31H37N3O4S2 579.2225 Found 579.2210. 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin5-yl)-2,3-didodecylpyrido[3,4-b]pyrazine (12).142 Under an argon atmosphere, 5,8-Dibromo-2,3-didodecyl-pyrido[3,4-b]pyrazine (0.77 g, 0.0012 mol), (2,3-dihydrothieno[3,4b][1,4]dioxin-5-yl)trimet hylstannane (0.79 g, 0.0026 mol), and 25 mL of anhydrous DMF were combined in a dry 100 mL 3-neck round bottom flask with a stir bar. The mixture was then dega ssed under argon for 1 h. Next, Pd(II)Cl2(PPh3)2 (0.09 g, 10 mol %) was added, the solution was heated to 75 oC, and allowed to react for ~19 h. After cooling, the solution was poured into 250 mL of H2O and then extracted repeatedly with ether. The organic phase was then extracted repeatedly with brine. The solution was dried over MgSO4 and the solvent was removed under reduced pr essure to yield a red solid. Column chromatography (4:1 CH2Cl2:EtOAc) and then (EtOAc) yielded 0.57 g (62 %) of an orange solid. mp 108.5-109 oC. 1H NMR (300 MHz, CDCl3) 0.88 (t, 6H), 1.2-1.5 (m, 36H), 1.95-2.1 (m, 4H), 3-3.15 (m, 4H), 4.25-4.5 (m, 8H), 6.54 (s, 1H), 6.62 (s, 1H), 9.71 (s, 1H); 13C NMR (75 MHz, CDCl3) 14.09, 22.67, 27.62, 27.78, 29.34, 29.54, 29.58, 29.64, 29.67, 29.70, 31.90, 34.93, 35.21, 64.24, 63.32, 64.79, 65.31, 103.17, 105.23, 110.92, 114.08, 122.32, 132.55, 139.48, 140.39, 141.30, 141.74, 142.52, 144.32, 149.84, 156.13, 159.23. Elemental Anal. Calcd. for

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62 C43H61N3O4S2: C 69.04, H 8.22, N 5.62. Found C 69.16, H 8.20, N 5.61; HRMS calcd. for C43H61N3O4S2 747.4103 Found 747.4122.

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63 CHAPTER 4 BXDOT DONOR-ACCEPTOR-DONO R LOW B AND GAP POLYMERS Background As was discussed in the gene ral introduction and Chapter 3, by com bining strong donors with strong acceptors, it is possible to compre ss the band gap and tune the HOMO/LUMO levels of the final polymer. Through the proper choice of the donor and acceptor, one can tailor the properties of the final polymer for applications such as electrochromics, OLEDs, OFETs and charge storage. One of the major draw backs of n-type polymers is their stability in the reduced state. As we saw in Chapter 3, the second reduction of the pyridopyrazine DAD polymers was highly unstable and could only be seen for a few cycles. Stability issues have also been seen for some pyridopyrazine vinylene polymers.132,146 By using stronger acceptors with more positive reduction potentials, it should be possible to improve the stability of n-type polymers to repetitive cycling in the reduced state.148 To circumvent the stability issues seen in Ch apter 3, and still maintain the advantages of dioxythiophene based systems for ease of electrochemical polymerization and characterization, the goal was to synthesize DAD monomers and pol ymers incorporating the highly electron poor [1,2,5]thiadiazolo[3,4g]quinoxaline (TQ) a nd benzo[1,2-c;3,4-c ]bis[1,2,5]thiadiazole (BBT) based acceptors. One of the advantages of usi ng these acceptors is that both are synthesized from the same intermediate.111 Also, by broadening our donor se lection from EDOT to include ProDOTs, we should be able to induce fine control over the band gap by varying the degree of intramolecular charge transfer for a family of DAD polymers.

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64 Monomer Synthesis and Characterization The synthesis of a fa mily of 9 different DAD monomers and polymers involving three different donors and two different acceptors were investigated. The donors range from the most electron rich 3,4-ethylenedioxythiophene (EDOT) to th e less electron rich 3,4propylenedioxythiophene (ProDOT) and 2,2-dimethyl substituted ProDOT (ProDOTMe2) (Figure 4-1). The two acceptors studied incl ude thiadiazoloquinoxaline (TQ) and the more electron poor benzobis(thiadiazole) (BBT) (Figure 4-1). Through the various combinations of the donors and acceptors, we should be able to ex ert fine control over the band gap and voltage window between polymer oxidation and reduction. Figure 4-1. The different dioxythiophene based donors and thia diazole based acceptors used to make a new family of D AD monomers and polymers. The synthesis of the nine monomers starts with the bromination of 2,1,3-benzothiadiazole ( 1)149 followed by nitration to yield 4,7-dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole ( 3)150 as illustrated in Figure 4-2. Although the yield of 3 is low, it is early on in the synthesis and can be scaled up. Next, a Stille c oupling was performed between 3 and the stannyl compounds of

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65 EDOT, ProDOT, and ProDOTMe2 to yield 4a-c .98 This was followed by reduction with iron in acetic acid to yield compounds 5a-c Ring closing with N-thionylaniline in pyridine gave the BBT derivatives 6a-c. Ring closing in acetic acid with 2,3-butanedione or 7-tetradecanedione gave the TQ derivatives 7a-c and 8a-c respectively.111 Figure 4-2. Synthesis of DAD monomers wh ere (a) = EDOT, (b) = ProDOT, and (c) = ProDOTMe2. It was originally thought that by using a stronger donor like EDOT rather than thiophene, that 6a would observe a red shift in absorbance relative to the bisthienylBBT derivative.

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66 However, the max for 6a is 643 nm, which is significantly blue shifted relative to the bisthienylBBT derivative, which has a max of 703 nm.151 The cause of this was revealed by examining the crystal structure of 6a (Figure 4-3) relative to that of the previously reported BTh-BBT derivative. The torsion angl e between the EDOT donor and th e BBT acceptor is 53 compared to 0 for the thiophene relative to the BBT acceptor.151 The large dihedral angle in 6a is caused by the steric interactions of the nitrogens on the BBT acceptor and the oxygens on the EDOT donors. This hinders the overlap of the p-or bitals and thus limits the amount of ICT and conjugation. Since 6a has a large dihedral angle, it can be assumed that all of the other dioxythiophene derivatives are also highly twisted. Crysta l structures of compounds 6b 7a, and 7c were obtained and also show large dihedral angles ranging from 47 to 56 (Appendix A). These large dihedral angles result in poor orbital overlap. Howeve r, we should still be able to exude fine control over the properties by varying the donor, the acceptor, or both. 53 Figure 4-3. Crystal st ructure of Monomer 6a showing a torsion angle of 53 between the EDOT donor and the benzobis(thiadiazole) accepto r. Selected bond lengths: C1-C3A, 1.405 ; C1-C2, 1.447 ; C2-C3, 1.412 ; C3-C4, 1.463 ; C4-C5, 1.372 ; C5-C6, 1.420 ; C6-C7, 1.356 ; S1-N2, 1.603 ; N2-C2, 1.365

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67 A UV-VIS study of the monomers was performe d to examine the effects of the donor and acceptor strengths on the intramolecular charge tr ansfer (ICT) band absorbance. A summary of their properties can be seen in Table 4-1. Comparing monomers 7a-c (Figure 4-4 A), 7a has the greatest red shift with a max at 538 nm, compared to 7c which is in the middle at 527 nm, while 7b is the lowest at 522 nm. This suggests that EDOT ProDOTMe2 ProDOT in donor strength. This trend is also seen for compounds 8a-c (Figure 4-4 B). For compounds 6a-c (Figure 4-4 C), the trend is similar, except that the ProDOT and ProDOTMe2 derivatives are almost identical with max at 626 nm and 627 nm respectively compared to 6a with a max at 643 nm, resulting in EDOT > ProDOTMe2 ProDOT. Monomers 6a-c have broad absorptions starting from 750 nm extending through the visible to 500 nm, while having minimal absorption from 500 to 400 nm. This results in blue colored solutions. Meanwhile monomers 7a-c and 8a-c have broad absorptions starting around 625 nm for 7a & 8a and 600 nm for 7b-c & 8b-c and ending around 450 nm to 430 nm respectively, resulting in dark pink solutions. Table 4-1. UV-VIS absorp tion data for monomers 6a-c, 7a-c and 8a-c. Monomer max/Molar Absorptivity, (cm-1M-1) max/Molar Absorptivity, (cm-1M-1) 6a 643 nm / 30,000 353 nm / 66,000 6b 626 nm / 10,000 354 nm / 21,000 6c 627 nm / 11,000 354 nm / 24,000 7a 538 nm / 16,000 371 nm / 23,000 7b 522 nm / 14,000 371 nm / 22,000 7c 527 nm / 13,000 371 nm / 19,000 8a 536 nm / 13,000 372 nm / 23,000 8b 523 nm / 8,000 373 nm / 14,000 8c 527 nm / 10,000 373 nm / 18,000 UV-VIS analysis has shown that monomer 6a has a molar absorptivity of almost three times that of 6b-c (Table 4-1). However, when looking at compounds 7a-c and 8a-c compounds 7a and 8a have molar absorptivities that are only 2,000-5,000 cm-1M-1 higher than the other

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68 derivatives. While this still s uggests that the EDOT compounds ab sorb more strongly than the ProDOT or ProDOTMe2 derivatives, this is much less pronounced for the TQ monomers. 350400450500550600650700750800 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 max = 538 nmmax = 527 nmmax = 522 nmNormalized Absorbance (A.U.)Wavelength (nm)A350400450500550600650700750800 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 max = 523 nmmax = 527 nmmax = 536 nmNormalized Absorbance (A.U.)Wavelength (nm)B3504004505005506006507007508008509009501000 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 max = 643 nmmax = 627 nmmax = 626 nmNormalized Absorbance (A.U.)Wavelength (nm)C Figure 4-4. UV-VIS spectra of monomers. A) 7a (solid: max = 538 nm and 371 nm and 357 nm sh), 7b (dotted: max 522 nm and 371 nm and 357 nm sh) and 7c (dashed: max 527 nm and 371 nm and 357 nm sh). B) 8a (solid: max = 536 nm and 371 nm and 357 nm sh), 8b (dotted: max = 523 nm and 371 nm and 357 nm sh) and 8c (dashed: max = 527 nm and 371 nm and 357 nm sh). C) 6a (solid: max = 643 nm and 353 nm), 6b (dotted: max = 626 nm and 354 nm) and 6c (dashed: max 627 nm and 354 nm). Electrochemical Polymerization and Characterization Electrochemical Polymerization of Monomers Electrochemical po lymerization of monomers 68a-c (Figure 4-5) were carried out from 5 mM monomer 0.1 M TBAP (supporting electrolyte) solutions in ei ther pure dichloromethane

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69 (DCM) for monomers 6a-c, or in a mixture of propylene carbonate (PC):DCM (~9:1) for monomers 7-8a-c (Figure 4-7). Pure DCM had to be used for monomers 6a-c due to poor solubility. Even for monomers 7-8a-c ~ 10% DCM was needed to at tain substantial solubility for electrochemical polymerization. Polymer f ilms were deposited by repetitive scan cyclic voltammetry or potentiostatically in an electrochemical cell consisting of a platinum button or ITO working electrode, a platinum (flag or wire ) counter electrode, and a silver wire pseudo reference electrode. The reference electrode was calibrated with the ferrocene redox couple (Fc/Fc+) from a solution containing 5 mM ferro cene and 0.1 M TBAP (tetrabutylammonium perchlorate) in PC. All potential va lues were measured relative to Fc/Fc+, and then converted to SCE (ESCE = EFc/Fc+ + 0.38 V)121 to be consistent with the most frequently reported values in the literature. Figure 4-5. Electrochemical polymerization of monomers 6-8a-c to yield polymers P6-8a-c.

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70 A representative electrochemical polymerization of monomer 6b is shown in Figure 4-6. Upon increasing the po tential, monomer 6b oxidizes at an Ep of 1.06 V vs. SCE. Upon the reverse of the first scan, there is a broad reduction peak due to the deposition of oligomers and polymers. Repetitive cycling shows broad oxida tion and reduction peaks th at evolve at lower potentials. This is due to the coupling of monomers to produce oligomers and polymers that oxidize at lower potentials due to the increase in conjugation. The increase in intensity of these peaks with repeated scans is associat ed with deposition of the polymer ( P6b ) on the electrode. The remaining electrochemical polymerizations of monomers 6-8a-c can be seen in Appendix B. In general, all of the monomers oxidize near the same potential around 1.0 to 1.1 V. This is due to the experimental error associated with the use of the silver wire pse udo reference electrode. -0.4-0.20.00.20.40.60.81.01.2 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Ep = 1.06 V Current Density (mA/cm2)Potential (V vs. SCE) Figure 4-6. Repetitive scan electropolymerization (50 mV/s, 10 cycles ) from a 5 mM monomer 0.1 M TBAP/DCM solution of 6b yielding P6b

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71 Polymer Electrochemistry In order to evaluate a polym er s potential use in applications such as charge storage, electrochromics, and OFETs, it is important to understand the redox properties, magnitude of the band gap, and the position of the HOMO/LUM O levels. These properties were probed electrochemically by cyclic voltammetry (CV) an d differential pulse voltammetry (DPV) as was discussed in Chapter 2. The difference between the onsets of oxidati on and reduction correspond to the polymers electrochemical band gap with the values of the onsets rela ting to the position of the HOMO/LUMO levels. The electrodeposited polymers P6-8a-c were rinsed with monomer free electrolyte and characterized in 0.1 M TBAP-PC using the sa me set up as described earlier, except instead of a silver wire pseudo refe rence electrode used during growth, a Ag/Ag+ reference electrode was used. Th is is a highly stable reference electrode which is not subjected to the extreme potential drifts that are sometimes seen with the silver wire pseudo reference electrode. The electrode was calibrated relative to Fc/Fc+, and all measured potentials were then converted to SCE for consis tency with the literature.121 Polymer films were switched by repetitive potential scanning from the neutral stat e to either the oxidized or reduced state until a reproducible CV was obtained. DPV was also pe rformed on the polymer films after they were conditioned to a reproducible redox response ( i.e. broken in). Individual films were used for oxidation and reduction. This was done because upon full CV scans (oxidation and reduction), the evolution of prepeaks, attrib uted to trapped charges, made characterization of the onsets difficult.152,153 Film stability was also an issue for full CV scans in some instances, as the film would degrade rapidly with a loss of electroactivity af ter only a few cycles. A summary of the electrochemical data as determined by CV can be seen in Table 4-2 and as determined by DPV can be seen in Table 4-3.

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72 Table 4-2. Summary of electrochemical data (CV) for polymers P6-8a-c. All data is V vs. SCE. Eg is taken as Eonset ox Eonset red. Polymer Eox onset Ep ox E1/2 HOMO ( eV) Ered 1 onset Ep E1/2 LUMO (eV) Ep red 2 E1/2 Eg (eV) P6a 0.23 0.63 0.53 4.93 -0.41-0.68-0.524.29 -1.37 -1.28 0.64 P6b 0.43 0.84 0.66 5.13 -0.36-0.67-0.554.34 -1.41 -1.30 0.79 P6c 0.5 0.76 0.68 5.20 -0.35-0.66-0.514.35 -1.37 -1.27 0.85 P7a 0.41 0.61 0.57 5.11 -0.72-0.95-0.893.98 -1.58 -1.54 1.13 P7b 0.55 0.76 0.69 5.25 -0.71-0.93-0.843.99 -1.53 -1.52 1.26 P7c 0.63 0.77 0.73 5.33 -0.71-0.87-0.824.00 -1.45 -1.46 1.33 P8a 0.43 0.64 0.57 5.13 -0.74-0.95-0.893.96 -1.58 -1.55 1.17 P8b 0.59 0.76 0.72 5.29 -0.72-0.92-0.843.98 -1.51 -1.50 1.31 P8c 0.63 0.78 0.74 5.33 -0.72-0.90-0.853.98 -1.50 -1.50 1.35 Table 4-3. Summary of the observed onsets for oxidation an d reduction by DPV for polymers P6-8a-c. All data is V vs. SCE. Eg is taken as Eonset ox Eonset red. Polymer Eox onset HOMO ( eV) Ered 1 onset LUMO (eV) Eg (eV) Eg DPVE g CV P6a 0.03 4.73 -0.23 4.47 0.26 -0.38 P6b 0.36 5.06 -0.25 4.45 0.61 -0.18 P6c 0.44 5.14 -0.23 4.47 0.67 -0.18 P7a 0.25 4.95 -0.63 4.07 0.98 -0.15 P7b 0.50 5.20 -0.63 4.07 1.13 -0.13 P7c 0.60 5.30 -0.65 4.05 1.25 -0.08 P8a 0.36 5.06 -0.65 4.05 1.01 -0.16 P8b 0.54 5.24 -0.64 4.06 1.18 -0.13 P8c 0.59 5.29 -0.66 4.04 1.25 -0.10 By switching to the stronger TQ based acceptors in P7a-c relative to the PyrPyr based acceptors studied in Chapter 3, there is an increa se to more positive reduction potentials with an onset of reduction ~600 mV more positive. Application of reducing potentials to P7a-b (Figure 4-7) and P7c (Figure 4-8) shows two sharp quasi-reversib le reductions by CV with onsets for the first reduction at -0.71 to -0.72 V. The ons ets for reduction observe d by DPV were ~70 mV more positive at -0.63 to -0.65 V. While the first reduction for polymers P7a-c was very stable over the 50 to 100 cycles required for break in and analysis, it should be noted that the stability of the second reduction for P7a was poor with almost complete loss of electroac tivity of the second reduction over several cycl es leading to film degradation, thus only the second CV scan

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73 of the full reduction after break in for the first reduction is shown (Figur e 4-7 A). The full DPV reduction of P7a was obtained after break in for the first reduction, and only the first set of DPV experiments are shown (Figure 4-7 C) Different films had to be used in order to obtain the CV and DPV results for both reductions in P7a. -1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Current Density (mA/cm22)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Current Density (mA/cm2)Potential (V vs. SCE)A C D B Figure 4-7. CV (scan rate = 50 mV/s) and DPV (s tep size of 2 mV and step time of 0.1 seconds) of polymers P7a-b on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P7a. B) CV of P7b C) DPV of P7a. D) DPV of P7b Upon application of anodic potentials to P7a-b (Figures 4-7) and P7c (Figure 4-8), fairly sharp oxidation peaks with a decrease in current after the Ep are observed, indicative of redox type conductivity. The onsets of oxidation for P7a-c range from 0.41 V, to 0.55 V, to 0.63 V as determined by CV (Table 4-2). This is in accord with EDOT ( P7a) being a stronger donor than

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74 ProDOT ( P7b ) and ProDOT being a slightly stronger donor than ProDOTMe2 ( P7c ). DPV analysis of the onsets gives slig htly lower values for oxidation (T able 4-3). This results in electrochemical band gaps of 1.13, 1.26, and 1.33 eV for P7a-c respectively as determined by CV and 0.98, 1.13, and 1.25 eV by DPV. -1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 Current Density (mA/cm2)Potential (V vs. SCE)AB Figure 4-8. CV (scan rate = 50 mV/s) and DPV (s tep size of 2 mV and step time of 0.1 seconds) of polymer P7c on a Pt button working electrod e in 0.1 M TBAP-PC electrolyte solution. A) CV of P7c B) DPV of P7c Analysis of polymers P8a-b (Figure 4-9) and P8c (Figure 4-10) by CV and DPV were performed and show similar results to P7a-c. CV oxidation shows sharp peaks typical of site limited redox conductivity with onsets at 0.43 V, 0.59 V, and 0.63 V for P8a-c respectively. DPV estimation of the onsets for oxidation of P8a-c are 0.36 V, 0.54 V, and 0.59 V, which again is 40 to 80 mV less than estimated by CV. With the application of cathodic potentials to P8a-c, there are two sharp quasi-reversible reductions with onsets at -0.74 V, -0.72 V, and -0.72 V respectively. Reduction onsets estimated by DVP for P8a-c are at -0.65 V, -0.64 V, and -0.66 V accordingly. The first reductions for polymers P8a-c are very stable as described for P7a-c, but again it should be noted th at the second reduction for P8a was highly unstable and a loss of electroactivity over a few cycles was observed, thus the first s can is shown for reduction. DPV

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75 analysis of the second reduction of P8a (Figure 4-9 C) shows very little charge compensation on the reverse scan, and some film degradation is ob served. Separate films were used to obtain the CV and DPV results as was done for P7a. The band gaps determined by CV for P8a-c were 1.17 eV, 1.31 eV, and 1.35 eV, while DPV gave 1.01 eV, 1.18 eV, and 1.25 eV respectively. -1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 Current Density (mA/cm22)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Current Density (mA/cm2)Potential (V vs. SCE)AB C D Figure 4-9. CV (scan rate = 50 mV/s) and DPV (s tep size of 2 mV and step time of 0.1 seconds) of polymers P8a-b on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P8a. B) CV of P8b C) DPV of P8a. D) DPV of P8b

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76 -1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 Current Density (mA/cm2)Potential (V vs. SCE)A-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 Current Density (mA/cm2)Potential (V vs. SCE)B Figure 4-10. CV (scan rate = 50 mV/s) and DP V (step size of 2 mV and step time of 0.1 seconds) of polymer P8c on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P8c B) DPV of P8c Finally, CV and DPV analysis of P6a-b (Figure 4-11) and P6c (Figure 4-12) were performed. Applying an anodic potential to P6a (Figure 4-11 A) shows a normal faradaic response yielding a singl e oxidation at an E1/2 of 0.53 V with an onset of oxidation at 0.23 V. However, the oxidation does not fall off sharply after reaching the peak oxidation potential as was observed for P7-8a-c, which is indicative of capacitive behavior.143-145 This is demonstrated clearly in the DPV of P6a (Figure 4-11 C) where after the peak oxida tion potential from CV is reached (~0.63 V), the current stays relatively constant. Reduction of P6a (Figure 4-11 A) shows two reductions at an E1/2 of -0.52 V and -1.28 V respectively, with an onset for the first reduction at -0.41 V. Both reduc tions are quasi-reversible with adequate charge compensation on the reverse scans. This demonstrates the hi gh electron accepting abil ity of the polymer and that it can stabilize two negativ e charges due to having two thia diazole rings on the acceptor. The electrochemical band gap is taken as the ons et of oxidation minus th e onset of reduction. Thus, P6a has an electrochemical band gap of 0.64 eV estimated by CV. One of the advantages of DPV is the increased sensitivity allowing for a more accurate estimation of the onsets of

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77 oxidation and reduction. DPV was performed on P6a (Figure 4-11 C) and shows an onset for reduction at -0.23 V, and an onset fo r oxidation at 0.03 V. It is inte resting to note that there is a slight shoulder peak around 0.2 V in the DPV oxida tion. This peak makes it hard to draw an accurate tangent line and to determine the onset but the change is not expected be that significant. While the band gap estimated by DPV was found to be 0.26 eV (~0.3 eV), it is unlikely that the band gap is 0.3 eV. Determination of the band gap for very low band gap polymers will be discussed in more detail later in this chapter, especially in reference to the optical data. -1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Current Density (mA/cm2)Potential (V vs. SCE)-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -2 -1 0 1 2 3 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Current Density (mA/cm2)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Current Density (mA/cm2)Potential (V vs. SCE)-4 -3 -2 -1 0 1 2 3 4 5 Current Density (mA/cm2) AB C D Figure 4-11. CV (scan rate = 50 mV/s) and DP V (step size of 2 mV and step time of 0.1 seconds) of polymers P6a-b on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P6a. B) CV of P6b. C) DPV of P6a. D) DPV of P6b

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78 -1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Current Density (mA/cm22)Potential (V vs. SCE)-1.8-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Current Density (mA/cm22)Potential (V vs. SCE)AB Figure 4-12. CV (scan rate = 50 mV/s) and DP V (step size of 2 mV and step time of 0.1 seconds) of polymer P6c on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P6c B) DPV of P6c CV analysis of P6b (Figure 4-11 B) shows a si ngle oxidation with an E1/2 of 0.66 V with an onset of oxidation at 0.43 V. Agai n the behavior is quite similar to P6a with the capacitive nature of the oxidation around the Ep ox (as determined by CV) as shown in the DPV (Figure 4-11 D). The onset for oxidation increased by 200 mV while the E1/2 increased by 130 mV relative to P6a. This reflects the diminished electron dona ting ability of ProDOT relative to EDOT. P6b has an onset of reduction at -0.36 V and shows two reductions at E1/2 of -0.55 V and -1.30 V. These values are quite similar to the reduction potentials for P6a and P6c The electrochemical band gap determined by CV for P6b is 0.79 eV, which is 0.15 eV higher than P6a, due to the decreased donor strength. In looking at the DPV (Figure 4-13d), the onset for reduction is around -0.25 V while the onset for oxidation is ne ar 0.35 V, corresponding to an electrochemical band gap of 0.6 eV. CV analysis of P6c (Figure 4-12 A) shows very similar reductive behavior to P6a-b with two quasi-reversible reductions at E1/2 of -0.51 V and -1.27 V and an onset of reduction at -0.35 V. Application of an oxidizing potential to P6c shows an onset of oxidation at 0.50 V (E1/2 ox =

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79 0.68 V), which is slightly higher (70 mV) than for P6b yielding a band gap of 0.85 eV. This is due to a slight decrease in the donor strength in going from ProDOT to ProDOTMe2. The oxidation of P6c is much sharper and shows an increase in loss of current after the Ep relative to P6a-b which is indicative of a greater contribution of site limited redox conductivity to the overall current. The onsets for oxidation, re duction, and the electrochemical band gap, as determined by DPV (Figure 4-12 B) for P6c are 0.44 V, -0.23 V, and 0.67 eV respectively. This is consistent with CV data with an increase in the band gap by 0.06 eV. The general trend so far is that the DPV determined band gap is about 0.1 to 0.2 eV smaller than what is estimated by CV for P6-8a-c. P6a, which has a DPV band gap almost 0.4 eV smaller than what was determined by CV, is an outlier from this trend probably due to trapped charges. It can be seen that within a sub-family of polymers (i.e. P7a-c) the LUMO remains relatively unchanged while the HOMO is changing with the different donors, demonstrating the donor control on the band gap. The difference in band gaps of EDOT donors ( P6-8a ) relative to ProDOT donors ( P6-8b ) is ~ 0.13 to 0.15 eV, while the difference between the ProDOT donors ( P6-8b) relative to the ProDOTMe2 ( P6-8c ) donors is only 0.04 to 0.07 eV. Comparison of the electrochemical band gaps to th e optical band gaps will be discussed in the next section. Optical Characterization The electro-optical properties of this fa m ily of polymers was investigated via spectroelectrochemistry. Polymer films were elec trodeposited potentiostatic ally onto ITO coated glass working electrodes. The pol ymer films were then placed in a cuvette with a platinum wire counter electrode and a silver wire pseudo reference electr ode (calibrated to the Fc/Fc+ redox couple) and switched by cyclic voltammetry in a 0.1 M TBAP/P C solution until a reproducible CV was attained before spectroelectrochemical measurements were performed. While oxidative

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80 spectroelectrochemistry can usually be performed on the bench top, reductive spectroelectrochemistry is normally done in a gl ove box due to stability issues of the reduced polymers in regards to water and air. Howe ver, due to instrument problems, reductive spectroelectrochemistry was performed on the bench top using stringent conditions to prevent moisture and oxygen contamination. Due to stabili ty issues of the films to repetitive reductive cycling on ITO, especially outside the glove box, the electrodeposited films were neutralized and then subjected to reductive spectroelectrochemistry. The optical band gaps for P6-8a-c were taken as the onset of absorption of the ne utral polymer after break in for oxidative spectroelectrochemistry. Oxidative Spectroelectrochemistry Figure 4-13 shows the oxidative spec troelectrochem ical series for P6a-c P6a-c have max at 985 nm ( P6a), 874nm ( P6b ), and 858 nm ( P6c ) respectively. The higher energy peaks associated with these polymers can be attributed to transitions ( -transition band) while the lower energy peak is attributed to intramolecular charge transfer (CT band), as has been seen in similar DA polymers and theoretical work.30,64,105,112,135,154,155 The blue shift in the CT band for P6a to P6c correlates with the decreasi ng strength of the donors. P6a absorbs in both the red and the blue portions of the spectrum, while th ere is a very little absorption around 600 nm, corresponding to a neutral olive green color (Figure 4-13 D). P6b follows a similar absorption pattern as P6a however, the gap around 600 nm is more fl at and slightly wider, yielding a light green colored polymer. P6c is similar in absorption profile to P6b with just a slight blue shift of the gap in the two band absorption leading to a more grey/green neutral polymer. The optical band gap for P6c was measured to be 1.09 eV while P6b was observed at 1.04 eV. These values are about 0.25 eV higher than the electrochemical band gap determined by CV (0.85 eV and 0.79

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81 eV) and 0.4 eV higher by DPV (0.67 eV and 0.61 eV). The band gap for P6a is too low for the scope of traditional characterization on ITO. This is because ITO absorbs strongly beyond 1600 nm (Figure 4-14 A), making baselin e absorption hard to quantif y. By switching to the more transparent single walled carbon nanotube (SWC NT) electrodes, which have a high degree of transparency into the IR (Figure 4-14 A), allo ws for a more accurate optical band gap to be measured.124 P6a was deposited electrochemically on a SWCNT electrode, broken in, neutralized, and analyzed by UV-VIS-NIR under solvent free conditions as described previously.156 Figure 4-14 B shows neutral P6a on a SWCNT electrode. The optical band gap was observed to be between 0.53 and 0.68 eV depending upon which method is used to determine the onset of absorpti on. This value is in good agreem ent with the electrochemical band gap of 0.64 eV determined by CV. Upon application of oxidizing potentials to P6a, a bleaching of both the CT band (985 nm) and the -transition band (359 nm) start around +0.2 V (c omparable to CV onset for oxidation), with formation of polaron charge carriers (Figure 4-13 A). Upon reaching higher potentials, bipolaron charge carriers are form ed as seen by the peak at ~1300 nm. The intense absorptions in the NIR are indicative of the polymer bei ng in a more conducting p-doped state. The absorption band of P6a in the fully p-doped state extends back through the visible region (decreasing in intensity down to 430 nm) with slightly increased in tensity relative to the neutral state. This results in a grey colored film in the oxidized state. The same transitions seen in P6a are also seen in P6b-c (Figure 4-13 B and C) upon application of oxidizing potentials. The only difference is that in P6b the bleaching of the CT band (874 nm) and the -transition band (359 nm) starts around +0.3 to +0.4 V, while in P6c the CT band (858 nm) and the -transition band (358 nm) start to bleach around +0.4 to +0.5 V. Th ese values are in good agreement with onsets

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82 for oxidation in the CV data. When P6b is in the fully oxidized state, there is a noticeable shoulder peak around 560 nm on the tail from the NIR, followed by a sharper decrease down to 460 nm where the change in P6a is more gradual. This results in a darker grey/blue film. P6c shows an even larger shoulder peak at ~ 570 nm decreasing shar ply down to 450 nm, resulting in a lighter grey/blue oxidized film. 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 l a l l l a a aEg = 1.04 eVmax = 359 nmmax = 874 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 a n n a n n a a n amax = 359 nm max = 985 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 i i i i a a a a max = 358 nmmax = 858 nm Eg = 1.09 eV Absorbance (A.U.)Wavelength (nm)Neutral Ox P6a P6b P6c AB CD Figure 4-13. Oxidative spectroelectrochemistry of P6a-c on ITO in 0.2 M TBAP-PC. All potentials reported vs. SCE. A) P6a at potentials of (a) 0.24 V to (n) +1.06 V in 100 mV increments. B) P6b at potentials of (a) 0.0 V to (l) 1.0 V in 100 mV increments. C) P6c at potentials of (a) 0.06 V, (b) 0.26 V to (i) 0.96 V in 100 mV increments. D) Pictures of P6a-c in their neutral and oxidized states.

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83 0.40.60.81.01.21.4 0.0 0.5 1.0 1.5 0.40.50.60.70.8 0.2 0.4 0.6 0.8 Eg = ~ 0.53 eV Absorbance (A.U.)Energy (eV) max = 974 nm (1.27 eV)Eg = ~ 0.68 eV Absorbance (A.U.)Energy (eV)30060090012001500180021002400270030003300 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Absorption (A.U.)Wavelength (nm)AB Figure 4-14. UV-VIS-NIR absorpti on of the electrodes used and P6a on a SWCNT electrode. A) UV-VIS-NIR absorption of ITO (solid) and SWCNT (dashed) relative to air. B) UV-VIS-NIR of neutral P6a on SWCNT electrode under solvent free conditions. The oxidative spectroelectrochemistry for P7a-c can be seen in Figure 4-15. P7a-c have CT bands and the -transition bands at 738 nm and 374 nm (P7a), 673nm and 371 nm ( P7b ) and 657 nm and 369 nm ( P7c ) respectively. It can be seen that by going from the strong BBT based acceptor in P6a-c, there is a blue shift of the CT bands of P7a-c due to the weaker TQ acceptor. The CT band of P7a is blue sifted ab out 250 nm relative to P6a while the CT band for P7b-c are blue shifted about 200 nm each. The CT band for P7a at 738 nm tails off sharply through the visible region to a minimum at about 500 nm, upon which there is a sharp increase in absorbance up to 374 nm. This sharp two band absorption of th e red and blue regions results in an emerald green neutral polymer (Figure 4-15 A). Wh en looking at into the NIR of neutral P7a, there is a slight shoulder around 900 nm, which depending on what tangent is used for determining the onset, gives a band gap of 1.18 eV to 1.26 eV. This shoulder seems to have come from continued cycling from the neutral state to the oxidized state duri ng break in. This can be seen relative to the neutral polymer film used for reduction (Figure 4-18 A), which after electropolymerization, was held at a neutralizing potential with no cycling before doing reductive spectroelectrochemistry, a nd the shoulder peak is almost completely gone. It is unclear

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84 whether this shoulder is a result of trapped charges or if it could be the result of some change in morphology from repetitive cycling (which could be solvent/electrolyte dependent), possibly some kind of induced aggregation. Film neut ralization with hydrazine would be the first experiment to do to make sure it is not due to tr apped charges. If this does not prove to be the case, future studies could include switching the solvent/electrol yte system used for polymer deposition and break in, or performing temperat ure dependent spectroelectrochemistry. These experiments could provide insight in to what is causing this shoulder. If 1.26 eV is taken as the optical band gap, the value is 0.13 eV higher th an the electrochemical band gap determined by CV, or 0.05 eV higher if the shoulder peak is used. Based upon the results for the neutral polymer used for reductive spectroelect rochemistry, the op tical band gap for P7a will be assumed to be 1.26 eV for future discussion. P7b, with a weaker donor, has a CT band that is blue shifted ~75 nm relative to P7a (Figure 4-15 B). The CT band tails through the visible region down to 460 nm, with not nearly as sharp of an increase going up to the high energy peak at 371 nm, resul ting in a light grey/blue film in the neutral state. The optical band gap was determined to be 1.5 eV. These results are quite similar to P7c (Figure 4-15 C), with a slight blue shift in th e CT band of about 16 nm relative to P7b resulting in a slightly darker grey/blu e neutral film. The optical band gap for P7c was 1.48 eV, which is almost identical to the 1.5 eV of P7b. The optical band gaps range from 0.13 eV above the electrochemical band gap for P7a to 0.24 eV for P7b and 0.15 eV for P7c Application of an oxidizing potential to P7a results in the bleaching of the -transition band along with a slight bleaching of the CT band starting around +0.4 to +0.5 V. Only a slight bleaching of the CT band occurs compared to the -transition band when fully oxidized. This is

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85 due to the tail from the NIR absorbing through the visible region as a result of the formation of polaron and bipolaron charge carriers (Figure 4-15). This results in a darker greenish grey film in the oxidized state. The same effect of the pa rtial bleaching of the CT band due to the tail from the formation of polaron and bipolaron char ge carrier bands is also seen in P7b-c These transitions start to occur at +0.6 to +0.7 V in P7b-c respectively. The absorption tail from the NIR through the visible portion for P7b is not quite as intense as in P7a, resulting in a light grey color in the oxidized state. The ta il from the charge carrier band in P7c has a slight increase in relative intensity to P7b and a sharper absorption well at 48 0 nm resulting in a darker grey oxidized film (Figure 4-15 C). When comparing P7a-c and P8a-c, the only structural change is of the methyl group on the TQ acceptor to the longer hexyl group. Examining the neutral polymers (Figure 4-16), there is little change in the -transition bands ( 4 nm red shift for P8a vs. P7a and 2 nm red shift for P8bc vs. P7b-c ), however the CT bands shift by 50 nm ( P8a), 28 nm ( P8b ), and 33 nm ( P8c ) respectively. The general profile s of the neutral absorptions are quite similar to their analogous counter parts. The red shift in the CT band for P8a to 778 nm results in a slight change in color to lighter more pastel green. For P8b the red shift of the CT band to 701 nm gives more of a navy blue color in the neutral state. P8c has a CT band at 690 nm and is very similar in color to P7c with a small change to more of a past el grey/blue. The optical band gaps for P8a-c were measured to be 1.27 eV ( P8a) and 1.42 eV ( P8b-c ). While the band gap for P8a is almost identical to P7a (unless the shoulder of P7a is taken into account), the optical band gaps for P8bc are about 0.08 to 0.06 eV lower relative to P7b-c possibly due to inte rchain interactions.

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86 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 g a g g a aEg = 1.48 eV max = 369 nmmax = 657 nmAbsorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 i i a a i amax = 371 nm Eg = 1.5 eVmax = 673 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 j j a a j aEg = 1.26 eV Eg = 1.18 eV max = 374 nm max = 738 nm Absorbance (A.U.)Wavelength (nm)Neutral Ox P7a P7b P7c A B D C Figure 4-15. Oxidative spectroelectrochemistry of P7a-c on ITO in 0.2 M TBAP-PC. All potentials reported vs. SCE. A) P7a at potentials of (a) 0.04 V, (b) 0.24 V to (j) 1.04 V in 100 mV increments. B) P7b at potentials of (a) 0.1 V, (b) 0.3 V to (i) 1.0 V in 100 mV increments. C) P7c at potentials of (a) 0.4 V to (g) 1.0 V in 100 mV increments. D) Pictures of P7a-c in their neutral and oxidized states. When a potential of about +0.45 V is applied to P8a (Figure 4-16 A), a bleaching of both absorptions begin (correlates well with CV data), and by +0.65 V, th e film is quite bleached with the formation of polaron charge carriers. Upon app lication of higher potentia ls, there is a shift in the low energy transition to ~1250 nm, indicative of bipolaron formation. This peak tails down through the visible region bottoming out around 500 nm with little increase in intensity in moving past 400 nm, resulting in a pastel grey colored film with a hint of green.

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87 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 h h h a a a max = 371 nm Eg = 1.42 eVmax = 690 nmAbsorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 h a a a h h max = 373 nm Eg = 1.42 eVmax = 701 nmAbsorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 j j j a a aEg = 1.27 eV max = 778 nmmax = 378 nm Absorbance (A.U.)Wavelength (nm)NeutralOx P7a P7b P7c AB CD Figure 4-16. Oxidative spectroelectrochemistry of P8a-c on ITO in 0.2 M TBAP-PC. All potentials reported vs. SCE. A) P8a at potentials of (a) -0.15 V, (b) 0.05 V, (c) 0.25 V to (j) 0.95 V in 100 mV increments. B) P8b at potentials of (a) 0.26 V, (b) 0.46 V to (h) 1.06 V in 100 mV increments. C) P8c at potentials of (a) 0.4 V to (h) 1.1 V in 100 mV increments. D) Pictures of P8a-c in their neutral and oxidized states. P8b shows a similar trend, with bleaching of the neutral absorptions begi nning at a slightly higher potential, comparable to the CV data, around +0.66 V (Fi gure 4-16 B). The bleaching occurs over a small potential range, and by +0.76 V both absorptions are highly bleached with a strong absorption throughout the NIR. Upon higher potentials, a peak attenuates at ~ 1100 nm that tails through the visible reaching a mi nimum around 490 nm with little increase in absorption moving to 400 nm. This results in a grey colored film.

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88 The bleaching of the neutral absorptions in P8c starts at +0.7 V (good CV correlation), and by +0.8 V the film is highly bleached (Figure 416 C). Applying higher potentials results in charge carrier peak attenuation just beyond 1000 nm which tails through visible very similar to P8b reaching a minimum around 490 nm. This results in a similar colored, but slightly lighter grey film. Reductive Spectroelectrochemistry To gain a better understanding of how these polym ers behave optically and electronically when they are reduced, reductive spec troelectrochemistry was performed on P6-8a-c. Previous work done in our group on PBEDOT-PyrPyr-Ph2 has demonstrated that even though a polymer may show an electrochemical reduction, that does not mean it can be attributed to true n-type doping.67,68,142 It was demonstrated that charge carri er band formation should be seen optically via spectroelectrochemistry and th ere should be an increase in conductivity associated with the reduction as measured by in-situ conductivity.67 The nature of the whether the conductivity measured is truly electronic or redox based was debatable. When looking at the nand p-type conductance profiles for PBEDOT-PyrPyr-Ph2, they were quite different. In the p-type doping, the conductivity remained high and showed capacitive behavior upon increasingly applied potentials past the E1/2 (indicative of a highly conductive mate rial), and also had a very intense absorption in the NIR. However, the n-type doping showed a drop off in conductivity (no capacitive behavior) mirroring the electrochemical reductions seen by CV/DPV. Also, the absorptions seen in the NIR upon reduction were not as intens e as there were for p-doping, suggesting more of a redox type conductivity instead of a highly delocalized state. While definitions may vary from person to person, I th ink in order to be tr uly n-type doped, you must have the formation of intense absorption bands in the NIR upon reduction equivalent to p-type doping, along with a conductivity pr ofile that is capacitive in nature. None the less, reductive

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89 spectroelectrochemistry can give us insight into the n-doping process, while conductivity experiments would need to be performe d to gain a complete understanding. Examining spectral changes upon reduction for P6a-c (Figure 4-17) the general trend is for a steady decrease in the intensity of the CT band throughout the whole reduction process. Comparing P6a and P6c there is the concurrent development of a small peak that grows in just beyond 1000 nm during the first reduction process, which heavily overlaps with the CT band, but with much lower intensity, making it hard to characterize. P6b does not show this slightly red shifted peak at 1000 nm, but does show a small fl at increase in the NIR which then disappears upon full reduction. There is also the develo pment of some small sharp peaks between 600-800 nm during the first reduction process for P6a-c which remain throughout the second reduction process. Examining the higher energy portion of the spectrum during the first reduction process reveals a decrease in the -transition band at 359 nm is along with the formation of a new high energy band at 393 nm ( P6a,c ) and 396 nm ( P6b ). This is followed by a decrease in intensity of these newly formed bands during the second reducti on process. The important thing to note here is that unlike oxidation, where th ere was a large increase in abso rbance in the NIR associated with polaron and bipolaron charge carrier formati on, very little change is occurring in the NIR for P6a-c. This is indicative of an isolated reduc tion that is not deloca lized along the conjugated backbone, but highly localized on the acceptor. A ll of the films showed signs of degradation after the measurements were performed, especially P6a and P6b as is evident by the sharp peaks around 500 nm developing during the second redu ction process which would not go away upon returning to the neutral state. This is not surprising cons idering how negative the applied potentials were at the end of the experiment (-1 .5 to -1.7 V) along with this being performed on the bench top with caution taken to pr event air and moisture exposure.

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90 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 a n n a n amax = 977 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 o m a o a o amax = 867 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 q f a q amax = 834 nm Absorbance (A.U.)Wavelength (nm)A B C Figure 4-17. Reductive spect roelectrochemistry of P6a-c on ITO in 0.2 M TBAP-PC. Solid lines = neutral polymer, dashed lines = 1st red., and dotted lines = 2nd red. All potentials reported vs. SCE. A) P6a at potentials of (a) 0.2 V to (n) -1.5 V in 100 mV increments. B) P6b at potentials of (a) -0.1 V to (o) -1.5 V in 100 mV increments. C) P8c at potentials of (a) -0.07 V to (q) -1.67 V in 100 mV increments. Analysis of P7a-c (Figure 4-18) shows similar results to P6a-c There is a steady decrease in the CT band through out the reduction process. The -transition band in the neutral polymers at 373 nm ( P7a) and 370 nm ( P7b-c ) decrease during the first reduction process while new high energy bands forms at 399 nm ( P7a, -1.1 V), 399 nm (P7b -1.44 V), and 400 nm (P7c -1.1 V) respectively. There is also the formation of a sharp peak where the CT band is decreasing during the first reduction process at 754 nm ( P7a, -1.1 V) and 759 nm (P7b -1.44 V, P7c -1.1 V). It is unclear what these sharp peaks are from, but it is probably related to the change in the acceptor

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91 structure upon stabilization of an added electron during the reduc tion process. Upon application of increased reducing potentials, all of the aforementioned peaks decrease in intensity. Again, the key is that there is no formation of any charge carrier bands in the NIR, indicating an isolated reduction of the polymer. 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 n q q a a q amax = 669 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 q q q j a a a max = 728 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 j o o o o a a a amax = 657 nm Absorbance (A.U.)Wavelength (nm)A B C Figure 4-18. Reductive spect roelectrochemistry of P7a-c on ITO in 0.2 M TBAP-PC. Solid lines = neutral polymer, dashed lines = 1st red., and dotted lines = 2nd red. All potentials reported vs. SCE. A) P7a at potentials of (a) 0.2 V to (q) -1.8 V in 100 mV increments. B) P7b at potentials of (a) -0.34 V to (o) -1.74 V in 100 mV increments. C) P8c at potentials of (a) -0.4 V to (o) -1.8 V in 100 mV increments.

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92 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 i q q q q a a a amax = 377 nmmax = 775 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 q q q a a amax = 693 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 a j j q q q q a a amax = 701 nm Absorbance (A.U.)Wavelength (nm)A B C Figure 4-19. Reductive spect roelectrochemistry of P8a-c on ITO in 0.2 M TBAP-PC. Solid lines = neutral polymer, dashed lines = 1st red., and dotted lines = 2nd red. All potentials reported vs. SCE. A) P8a at potentials of (a) 0.25 V to (q) -1.85 V in 100 mV increments. B) P8b at potentials of (a) 0.0 V, (b ) -0.20 V, (c) -0.40 V to (q) -1.80 V in 100 mV increments. C) P8c at potentials of (a) 0.0 V, (b) -0.20 V, (c) -0.40 V to (q) -1.80 V in 100 mV increments. Reductive spectroelectrochemistry is shown for P8a-c in Figure 4-19. The low energy CT band decreases in intensity th roughout the reduction process co mparable to the previous polymers. During the first reductio n process, there is the same sh arp peak that develops on the decreasing CT band at 753 nm ( P8a, -1.05 V), 754 nm (P8b -1.10 V), and 748 nm (P8c -1.10 V) as was seen for P7a-c This can be attributed to the TQ acceptor. Meanwhile, the neutral transition bands at 377 nm ( P8a), 373 nm (P8b ), and 372 nm ( P8c ) start to bleach out with the

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93 formation of a new high energy peak at 403 nm ( P8a-b -1.05 V and -1.10 V respectively) and 402 nm (P8c -1.1 V, very small shoulder). In movi ng on to the second reduction, all the peaks decrease in intensity for P8a-b while in P8c the shoulder at 402 nm develops into a tiny peak during the second reduction up to -1 .8 V, but all the other peaks c ontinue to lose intensity. Again, no charge carrier band formation was seen indicating an isolated reduction process is going on. Conclusions The data presented in this chapter has brought a f ew things to light relative to characterization methods needed for low band gap pol ymers and their stability issues. In relation to reductive stability, it was noted that for the TQ derivatives P7a and P8a, the second reduction was not that stable in the solvent/electrolyte system used for this study. While the other polymers were fairly stable, this stability issue with the second reduction has put up a red flag. The structure of the TQ derivatives in this ch apter is similar to the PyrPyr acceptor used in Chapter 3, in that both polymers have alkyl chai ns attached to a pyrazine ring in the acceptor, and both have stability issues w ith the second reduction. It is po ssible that the anion radicals created during reduction in the presence of benzylic protons could lead to degradation. Perhaps by changing the alkyl groups on the acceptor to phenyl or phenoxy groups, one could see improved stability. While stability issues were seen for some of the TQ derivatives, the BBT systems proved to be quite stable, and reduced at even more positive potentials than the TQ derivatives, thus enhancing the st ability in the reduced state. Both systems have shown the ability to stabilize multiple reductions, however op tical characterization of the reduced states in these systems indicate a highly localized state with no delocalized char ge carrier formation. While the systems studied here are not truly n-type doping systems, th ey can serve as redox active materials for applications in el ectrochromics or charge storage.

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94 Another point is that for very low band gap polymers such as P6a, it was shown that determination of the optical band gap using tradit ional ITO electrodes for optical characterization is not necessarily the best method. The useful ness of SWCNTs has been shown, estimating a band gap of 0.53 to 0.68 eV, which was in good agreem ent with the CV data. This supports the use of SWCNTs for characterization of very low band gap polymers. Experimental Com pounds 2,149 3,150 7,8-tetradecanedione,139 ProDOT157 and ProDOTMe2 158 were made according to literature procedure. 2,3-butanedione, TMS-Cl, anhydrous pyridine, and Nthionylaniline was purchased from Aldrich and used as received. Glacial acetic acid was purchased from Fisher and used as recei ved. (2,3-dihydrothi eno[3,4-b][1,4]dioxin-5yl)trimethylstannane,98 (3,4-dihydro-2H-thieno[3,4-b][1,4]di oxepin-6-yl)trim ethylstannane,98 and (3,3-dimethyl-3,4-dihydro2H-thieno[3,4-b][1,4]dioxepi n-6-yl)trimethylstannane98 were made according to literature procedur e and used with out purification. General procedure for the Stille couplin g of stannylated dioxythiophenes with compound 3 to synthesize 4a-c: To a flame dried 100 mL 3-neck round bottom flask was added 6.7 mmol of 3 and 14 mmol trimethyltin-XDOT. Then 25 mL of dry THF was added and the solution was degassed for 30 minutes. Then 0.33mmol of Pd(II)Cl2(PPh3)2 was added and the solution was refluxed for 3-4 hours. The solution was cooled and the solvent was removed under reduced pressure followed by column chromatography. 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin5-yl)-5,6-dinitrobenz o[c][1,2,5]thiadiazole (4a) Column chromatography (CHCl3, SiO2) yield 68 % of a red solid. mp 255-257 C. 1H NMR (300 MHz, DMSO) 4.17-4.23 (m, 8H), 7.15 (s, 2H); 13C NMR (75 MHz, DMSO) 64.15, 64.64, 104.02, 105.94, 119.97, 140.72, 141.67, 142.28, 152.09. Elemental Anal. Calcd. for

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95 C18H10N4O8S3: C, 42.68; H, 1.99; N, 11.06; O, 25.27; S, 18.99. Found: C, 42.89; H, 1.88; N, 10.84. HRMS Calcd. for C18H11N4O8S3 (M+H) 506.97335 Found 506.97328. 4,7-bis(3,4-dihydro-2H-thieno[ 3,4-b][1,4]dioxepin-6-yl)-5,6dinitrobenzo[c][1,2,5]thiadiazole (4b). Column chromatography (CHCl3, SiO2) yield 49 % of a red solid. 1H NMR (300 MHz, CHCl3) 2.22 (p, 4H), 4.08 (t, 4 H), 4.16 (t, 4H), 6.94 (s, 2H). Elemental Anal. Calcd. for C20H14N4O8S3: C, 44.94; H, 2.64; N, 10.48; O, 23.94; S, 18.00. Found: C, 44.96; H, 2.67; N, 10.16. HRMS Calcd. for C20H15N4O8S3 (M+H) 535.0047 Found 535.0017. 4,7-bis(3,3-dimethyl-3,4dihydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)-5,6dinitrobenzo[c][1,2,5]thiadiazole (4c). Column chromatography (CHCl3/Hex 4:1, SiO2) yield 67 % of a red/orange solid. 1H NMR (300 MHz, CHCl3) 1.01 (s, 12H), 3.74 (s, 4 H), 3.82 (s, 4H), 6.88 (s, 2H). Elemental Anal. Calcd. for C24H22N4O8S3: C, 48..80; H, 3.75; N, 9.49; O, 21.67; S, 16.29. Found: C, 48.93; H, 3.71; N, 9.49. HRMS Calcd. for C24H22N4O8S3Na (M+Na) 613.0492 Found 613.0492. General procedure for the synthesis of co mpounds 5a-c via iron mediated reduction of compounds 4a-c. To a dry 100 mL 3-neck round bottom fl ask equipped with a condenser was added 2.0mmol of compound 4 and 24 mmol of iron powder. To this was added 40 mL of degassed AcOH. The reaction was heated to 100 C for 3 hours and then allowed to cool. A golden yellow color solid was collected by filtra tion and washed with water, saturated sodium bicarbonate, and water in this order. Purified by column chromatography. 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]di oxin-5-yl)benzo[c][1,2,5]thiadiazole-5,6diamine (5a) Column Chromatography (7:1 CH2Cl2:EtOAc, SiO2) yield 87 % of a yellow solid. mp decomp. >260 C. 1H NMR (300 MHz, DMSO) 4.22 (s, 8H), 5.70 (s, 4H), 6.73 (s, 2H); 13C

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96 NMR (75 MHz, DMSO) 64.13, 64.32, 98.62, 99.65, 109.14, 138.96, 140.67, 141.48, 152.62. Elemental Anal. Calcd. for C18H14N4O4S3: C, 48.42; H, 3.16; N, 12.55; O, 14.33; S, 21.54. Found: C, 48.52; H, 3.04; N, 12.12. HRMS Calcd. for C18H15N4O4S3 (M+H) 447.0255 Found 447.0252 4,7-bis(3,4-dihydro-2H-thieno[3,4-b][1,4]di oxepin-6-yl)benzo[c][1,2,5]thiadiazole-5,6diamine (5b). Column chromatography (5 % EtOAc/CH2Cl2, SiO2) yield 72 % of a golden yellow solid. 1H NMR (300 MHz, CHCl3) 2.23 (p, 4H), 4.11 (t, 4 H), 4.18 (t, 4H), 4.27 (s, 4H), 6.81 (s, 2H). Elemental Anal. Calcd. for C20H18N4O4S3: C, 50.62; H, 3.82; N, 11.81; O, 13.49; S, 20.27. Found: C, 50.38; H, 3.72; N, 11.42. HRMS Calcd. for C20H19N4O4S3 (M+H) 475.0563 Found 475.0605. 4,7-bis(3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-6yl)benzo[c][1,2,5]thiadiazole-5,6-diamine (5c). Column chromatography (CH2Cl2, SiO2) yield 91 % of a golden yellow solid. 1H NMR (300 MHz, CHCl3) 1.03 (s, 12H), 3.77 (s, 4 H), 3.82 (s, 4H), 4.29 (s, 4H), 6.76 (s, 2H). Elemental Anal. Calcd. for C24H26N4O4S3: C, 54.32; H, 4.94; N, 10.56; O, 12.06; S, 18.31. Found: C, 54.09; H, 4.88; N, 10.34. HRMS Calcd. for C24H27N4O4S3 (M+H) 531.1189 Found 531.1254. General procedure for the synthesis of BXDOT-benzobis(thiadiazole) monomers 6a-c. To a flame dried 25 mL 3-neck round bo ttom flask was added 1.2 mmol of compound 5, 7 mL of anhydrous pyridine, 2.6 mmol of N-thionylaniline, and 2.2 mmol of TMS-Cl. The solution was heated to 80 C overnight. The reaction was allowed to cool, poured into water, and collected by filtration. Purified by column chromatography. 4,8-bis(2,3-dihydrothieno[3,4-b][1 ,4]dioxin-5-yl)benzo[1,2-c;4,5c ]bis[1,2,5]thiadiazole (6a). Column chromatography (CH2Cl2, SiO2) yield 84 % of a dark

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97 purple solid. decomposition > 292 C. 1H NMR (300 MHz, DMSO) 4.22-4.29 (m, 8H), 7.05 (s, 2H). Elemental Anal. Calcd. for C18H10N4O4S4: C, 45.56; H, 2.12; N, 11.81; O, 13.49; S, 27.03. Found: C, 45.52; H, 1.96; N, 11.62. HRMS Calcd. for C18H10N4O4S4 (M+) 473.9585 Found 473.9604 4,8-bis(3,4-dihydro-2H-thieno[3,4-b ][1,4]dioxepin-6-yl)benzo[1,2-c;4,5c ]bis[1,2,5]thiadiazole (6b). Column chromatography (CH2Cl2, SiO2) yield 85 % of a dark purple solid. 1H NMR (300 MHz, CDCl3) 2.28 (p, 4H), 4.24 (t, 4H), 4.29 (t, 4H), 6.98 (s, 2H). Elemental Anal. Calcd. for C20H14N4O4S4: C, 47.79; H, 2.81; N, 11.15; O, 12.73; S, 25.52. Found: C, 47.80; H, 2.71; N, 10.76. HRMS Calcd. for C20H15N4O4S4 (M+H) 502.9976 Found 502.9920. 4,8-bis(3,3-dimethyl-3,4-dihy dro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)benzo[1,2-c;4,5c ]bis[1,2,5]thiadiazole (6c). Column chromatography (CH2Cl2, SiO2) yield 71 % of a dark purple solid. 1H NMR (300 MHz, CDCl3) 1.06 (s, 12H), 3.89 (s, 4H ), 3.97 (s, 4H), 6.93 (s, 2H); 13C NMR (75 MHz, CDCl3) 21.80, 39.34, 80.28, 80.60, 109.34, 114.21, 115.82, 149.49, 150.69, 152.99. Elemental Anal. Calcd. for C24H22N4O4S4: C, 51.59; H, 3.97; N, 10.03; O, 11.45; S, 22.96. Found: C, 51.64; H, 3.91; N, 9.71. HRMS Calcd. for C24H23N4O4S4 (M+H) 559.0597 Found 559.0598. General procedure for the synthesis of BXDOT-dialkylthiadiazoloquinoxalines (7a-c and 8a-c). 0.47 mmol of compound 5 was placed in a 100 mL round bottom flask followed by 35 mL of acetic acid. Then 0.94 mmol of either 2,3-butane dione or 7,8 -tetradecanedione was added and the soln was stirred for 2-12 h. Th e reaction was then poured into 40 mL of 5 % NaOH and extracted with dichloromethane. The organic layer was then washed with saturated

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98 NaHCO3,water, and dried over MgSO4. Removal of solvent under reduced pressure followed by column chromatography gave the desired compounds. 4,9-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-6,7-dimethyl[1,2,5]thiadiazolo[3,4g]quinoxaline (7a). Column chromatography (CH2Cl2, SiO2) yield 99 % of a dark red solid. 1H NMR (300 MHz, CDCl3) 2.74 (s, 6H), 4.22-4.25 (m, 4H), 4.30-4.32 (m, 4H), 6.72 (s, 2H); 13C NMR (75 MHz, CDCl3) 24.04, 64.72, 102.76, 110.15, 121.43, 137.93, 141.09, 141.67, 152.55, 155.15. Elemental Anal. Calcd. for C22H16N4O4S4: C, 53.21; H, 3.25; N, 11.28; O, 12.89; S, 19.37. Found: C, 53.38; H, 3.28; N, 11.12. HRMS Calcd. for C22H17N4O4S4 (M+H) 497.04064 Found 497.03902. 4,9-bis(3,4-dihydro-2H-thieno[3,4-b ][1,4]dioxepin-6-yl)-6,7-dimethyl[1,2,5]thiadiazolo[3,4-g]quinoxaline (7b). Column chromatography (CH2Cl2, SiO2) yield 83 % of a dark red solid. 1H NMR (300 MHz, CDCl3) 2.23 (p, 4H), 2.73 (s, 6H), 4.20-4.25 (m, 8H), 6.92 (s, 2H); 13C NMR (75 MHz, CDCl3) 23.94, 34.31, 71.12, 71.64, 108.91, 116.09, 121.96, 138.21, 149.40, 150.58, 152.82, 155.17. Elemental Anal. Calcd. for C24H20N4O4S3: C, 54.94; H, 3.84; N, 10.68; O, 12.20; S, 18.34. Found: C, 55.19; H, 3.82; N, 10.68. HRMS Calcd. for C24H21N4O4S3 (M+H) 525.0725 Found 525.0673. 4,9-bis(3,3-dimethyl-3,4-di hydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)-6,7-dimethyl[1,2,5]thiadiazolo[3,4-g]quinoxaline (7c). Column chromatography (CH2Cl2, SiO2) yield 70 % of a dark red solid. 1H NMR (300 MHz, CDCl3) 1.03 (s, 12H), 2.73 (s, 6H), 3.89 (m, 8H), 6.88 (s, 2H); 13C NMR (75 MHz, CDCl3) 21.88, 23.92, 39.30, 80.10, 80.43, 108.27, 115.35, 121.85, 138.11, 149.08, 150.15, 152.74, 155.11. Elemental Anal. Calcd. for C28H28N4O4S3: C, 57.91; H, 4.86; N, 9.65; O, 11.02; S, 16.56. Found: C, 58.43; H, 5.00; N, 9.29. HRMS Calcd. for C28H29N4O4S3 (M+H) 581.1351 Found 581.1354.

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99 4,9-bis(2,3-dihydrothieno[3,4-b][1,4]dioxi n-5-yl)-6,7-dihexyl-[1,2,5]thiadiazolo[3,4g]quinoxaline (8a). Column chromatography (CH2Cl2, SiO2) yield 66 % of a dark purple solid. 1H NMR (300 MHz, CDCl3) 0.91 (t, 6H), 1.32-1.48 (m,12H), 1.92 (p, 4H), 3.00 (t, 4H), 4.214.24 (m, 4H), 4.30-4.33 (m, 4H), 6.72 (s, 2H); 13C NMR (75 MHz, CDCl3) 14.32, 22.87, 27.15, 29.44, 32.07, 35.54, 64.75, 64.81 102.61, 110.38, 121.38, 137.74, 140.84, 141.55, 152.57, 158.04. Elemental Anal. Calcd. for C32H36N4O4S3: C, 60.35; H, 5.70; N, 8.80; O, 10.05; S, 15.10. Found: C, 60.33; H, 5.63; N, 8.77. HRMS Calcd. for C32H37N4O4S3 (M+H) 637.19714 Found 637.19873. 4,9-bis(3,4-dihydro-2H-thieno[3,4-b ][1,4]dioxepin-6-yl)-6,7-dihexyl[1,2,5]thiadiazolo[3,4-g]quinoxaline (8b). Column chromatography (CH2Cl2, SiO2) yield 71 % of a dark purple solid. 1H NMR (300 MHz, CDCl3) 0.90 (t, 6H), 1.30-1.42 (m,12H), 1.87 (p, 4H), 2.27 (p, 4H), 2.98 (t, 4H), 4.22 (m, 8H), 6.90 (s, 2H); 13C NMR (75 MHz, CDCl3) 14.29, 22.77, 27.06, 29.32, 31.92, 34.23, 35.46, 71.06, 71.59 108.81, 116.18, 121.84, 138.02, 149.10, 150.34, 152.60, 158.14. Elemental Anal. Calcd. for C34H40N4O4S3: C, 61.42; H, 6.06; N, 8.43; O, 9.63; S, 14.47. Found: C, 61.30; H, 6.06; N, 8.35. HRMS Calcd. for C34H41N4O4S3 (M+H) 665.2290 Found 665.2258. 4,9-bis(3,3-dimethyl-3,4-dihy dro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)-6,7-dihexyl[1,2,5]thiadiazolo[3,4-g]quinoxaline (8c). Column chromatography (CH2Cl2, SiO2) yield 33 % of a dark purple solid. 1H NMR (300 MHz, CDCl3) 0.90 (t, 6H), 1.03 (s, 12H), 1.25-1.43 (m, 12H), 1.88 (p, 4H), 2.98 (t, 4H), 3.88 (s, 8H), 6.86 (s, 2H); 13C NMR (75 MHz, CDCl3) 14.31, 21.86, 22.84, 27.22, 29.43, 31.97, 35.60, 39.27, 80.12, 80.44, 108.17, 115.54, 121.78, 138.03, 148.83, 149.98.152.62, 158.18. Elemental Anal. Calcd. for C38H48N4O4S3: C, 63.30; H, 6.71; N,

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100 7.77; O, 8.88; S, 13.34. Found: C, 63.13; H, 6.79; N, 7.68. HRMS Calcd. for C38H49N4O4S3 (M+H) 721.2916 Found 721.2928.

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101 CHAPTER 5 DTP BASED SOLUBLE DONOR-ACCEPTOR POLYMERS Introduction As discussed in Chapter 1, the DA approach tow ards low band gap polymers has proven to be an effective strategy towards controlling th e band gap and thus the electronic properties of conjugated materials. However, the importance of planarity in the conjugated back bone cannot be forgotten. As was demonstrated in Chapter 4, the use of stronger donors such as EDOT and ProDOT relative to thiophene in these DAD monomers and polymers did not necessarily give lower band gap polymers. This was explained by the high degree of torsion between the donor and the acceptor. The max for BEDOT-BBT (643nm) is blue shifted about 60 nm compared to BTh-BBT (702 nm). A high torsion angle was also seen in the TQ derivatives. While the TQ and BBT acceptors have generated low band gap materials for use in electroluminescence5,118,159,160 and photovoltaic applications,13,16,17,28,50,161 the most promising donor molecule so far has been thiophene, due to its synthetic flexibility a nd its ability to form a highly planar structure with the acceptor. In keeping with this strategy, an ideal donor would be stronger than thiophene, have the planarity of thiophene, and improved synthetic fl exibility towards solubility. Fused donors such as fluorene and carbazole have been used with similar acceptors, and while they give solubilities of ~10 mg/mL, they are not as strong of a donor as thiophene.5,12,103,162 Two candidates that can provide solubility, planar ity, and be stronger donors are cyclopentadithiophene163-165 and dithienopyrrole (DTP).166-168 While some work has been done using cyclopentadithiophene as a donor in DA oligomers/polymers,117,169-171 little work has been done using DTP as a donor in DA oligomers/polymers.17,26,166

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102 This work entails the polymerization of a strong soluble donor, 2,6-bi s(tributylstannyl)-N(3,4,5-tris(dodecyloxy)phenyl)-dithieno[3,2-b:2',3'd]pyrrole,53,172 polymerized with five different dibromo acceptors: Br2BThBTD, Br2BTD, Br2BTh-TQHx2, Br2TQHx2, Br2BThBBT. The targeted polymers can be seen in Figure 51. A comparison of the acceptor strength on the optical and electronic properties were investigated along with a focus on the connectivity of the acceptor cores, whether it is the DTP donor conne cted directly to the acceptor or with a thiophene spacer. These polymers were char acterized by NMR, GPC, UV-VIS, elemental analysis, electrochemistry, a nd spectroelectrochemistry. Figure 5-1. Targeted DTP based DA polymers.

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103 Monomer/Polymer Synthesis and Characterization The following donor, dibrom o acceptors, and in termediates: 2,6-bis(tributylstannyl)-N(3,4,5-tris(dodecyloxy)phenyl)-dithieno[3,2-b:2',3'd]pyrrole,53 4,7dibromobenzo[c][1,2,5]thiadiazole (Br2BTD),149 4,7-bis(5-bromothiophen-2yl)benzo[c][1,2,5]thiadiazole (Br2BThBTD),103 4,7-bis(5-bromot hiophen-2-yl)-2 42-benzo[1,2c;4,5-c ]bis[1,2,5]thiadiazole (Br2BThBBT),173 6,7-dihexyl-4,9di(thiophen-2yl)[1,2,5]thiadiazolo[3,4g]quinoxaline (BThTQHx2)111 and 4,7-dibromobenzo[ c][1,2,5]thiadiazole5,6-diamine174 were prepared according to literature procedures. 4,9-bis( 5-bromothiophen-2-yl)6,7-dihexyl-[1,2,5]thiadiazolo [3,4-g]quinoxaline (Br2BThTQHx2), and 4,9-dibromo-6,7dihexyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline (Br2TQHx2), were prepared via bromination in DMF and condensation in acetic acid respectively (Figure 5-2). Figure 5-2. Synthesis of 4,9-bis(5-bromot hiophen-2-yl)-6,7-dihexyl -[1,2,5]thiadiazolo[3,4g]quinoxaline and 4,9-dibromo-6,7-dihexyl -[1,2,5]thiadiazolo[3,4-g]quinoxaline.

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104 Figure 5-3. General synthesis of DTP based DA polymers via Stille Polymerization. = Br. The advantage of the DTP donor is the ability to functionalize the pyrrole nitrogen. In this case, a trisdodecyloxyphenyl substituent was inco rporated to maximize solubility. Polymers were made via Stille polymerization due to its mild reaction conditions, toleration of functional groups, and high yields.110 A general polymerization can be seen in Figure 5-3. Usually the donor and the catalyst were placed in a dry 3neck round bottom flask and subjected to 5 vacuum/argon backfill cycles. Then dry THF was added and the solution was degassed for ~1 h. This extra degassing was done to make sure all of the oxygen was removed since the donor is an oil and could still have oxygen trapped in it. Fi nally the acceptor was added and the solution was heated to reflux for ~2 days. After cooling, the solution was concentr ated, precipitated into methanol, and collected by filtration. The crude polymer was then placed in a thimble and purified by Soxhlet extraction with methanol, acetone hexane, and chloroform in that order with each one running ~1day. The volume of the chloro form fraction was then reduced, precipitated

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105 into methanol, and collected by filtration yielding a black solid. It should be noted that, while the order of addition was not important for making P(DTP-BThBTD), it was very important for making P(DTP-BThBBT). When the donor and accepto r were combined in the same flask with THF and degassed, the reaction turned dark blue in color before any addition of catalyst. Upon subsequent addition of catalys t and polymerization, no polymer was isolated. Thus for the stronger TQ and BBT based polymers, the acceptor was always added last. The yield of the polymerization ranged from 83-95 % (Table 51) with the exception of P(DTP-BThTQHx2) (46 %). Polymer molecular weights were determined by GPC relative to polystyrene standards with THF as the mobile phase. Molecular weights ranged from 9,600 g/mol (satisfactory) for P(DTP-BThTQHx2) up to 106,000 g/mol (excellent) for P(DTP-BThBTD) (Table 5-1). Examination of the GPC chromatograms show nice monomodal distributions for P(DTPBThBTD), P(DTP-BTD), and P(DTP-TQHx2) with low PDIs (~ 2). However, P(DTPBThTQHx2) and P(DTP-BThBBT) have bimodal distri butions and high polydispersities (>3), indicating the presence of oligomers. One of the main c ontributing factors that could have resulted in low molecular weights is stoichiometr ic imbalance. Since all of the polymerizations were carried out using Pd(II)Cl2(PPh3)2, it is known that to go to the active Pd(0) species, the Pd(II) species must get reduced by the stannyl compound to form the active Pd(0) species, which results in homo coupled product.114 Thus it is necessary to ad just the amount of the stannyl monomer relative to the amount of catalyst being used in or der to obtain higher molecular weights. There is also the issue of weighing out an exact amount of monomer when it is a viscous oil. The best way to approach this is to obtain the weight of the empty reaction flask, then add the monomer via pipette or by solution followed by evapora tion of the solvent. Finally,

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106 weigh the flask again and base al l calculations for cat alyst and the other m onomer off the weight of the oil in the reaction flask. Another source of error is incomp lete dryness of the oil, which would again result in a stoichiometric imbalance and reduce molecular weight. P(DTP-BThBTD) P(DTP-BTD) P(DTP-BThTQHx2) P(DTP-TQHx2) P(DTP-BThBBT) Figure 5-4. GPC chromatograms of P(DTP-acceptor) polymers.

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107 Table 5-1. GPC estimated molecular weights (T HF as mobile phase, relative to polystyrene standards) and yields of the Stille polymerization. Polymer Mn (g/mol) PDI DP % Yield P(DTP-BThBTD) 106,000 1.4 96 95 P(DTP-BTD) P(DTP-BThTQHx2) 24,000 9,600 2.2 2.9 25 7 95 46 P(DTP-TQHx2) P(DTP-BThBBT) 19,000 14,000 2.0 3.6 16 12 83 89 All polymers are soluble in chloroform, THF a nd toluene. Polymers were spray-cast from either chloroform or toluene solutions (3-4 mg/mL) onto ITO coated glass and dried under vacuum overnight. The neutral polymers we re then analyzed by UV-VIS-NIR spectroscopy (Figure 5-5) and photographed (Fig ure 5-6). The neutral polymers all show a characteristic two band absorption, which is attributed to an ICT ba nd that occurs at long wa velengths (low energy) and a transition at the shorter wavelengths (hi gher energy) as has been discussed in the previous chapters. P(DTP-BThBTD) has a max of 673 nm, a higher energy shoulder peak at 464 nm, and an optical band gap of 1.45 eV. Because the max absorbs strongly through the whole visible spectrum, but tails off towards the higher energy peak with a slight dip at 500 nm, the polymer appears to be a dark greeni sh/blue in color. P(DTP-BTD) has a max of 699 nm (low energy shoulder at ~1000 nm), a higher energy peak at 427 nm, and an optical band gap of 0.98 eV (the nature of this shoulder peak, possibl e aggregation, and the ba nd gap will be discussed later in the chapter, but the band gap of 0.98 eV is doubtful). Due to the deeper trough just beyond 500 nm, and the ICT band and higher energy p eak intensities almost being equivalent, yields an emerald green neutral polymer. P(DTP-BThTQHx2) has a max of 975 nm, an almost equally intense higher energy peak at 512 nm, an d an optical band gap of 0.95 eV. Having this lower band gap means the ICT band is almost comp letely out of the visible spectrum leaving the higher energy peak absorption in the green part of the spectrum at 512 nm. This results in a light pink colored film. P(DTP-TQHx) has an ICT band at 1252 nm along with a less intense higher

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108 energy peak at 476 nm. The profile of the absorp tion in the visible is quite similar to P(DTPBThTQHx2), but nearly as intense, resulting in a golden brown neutral polymer. The last polymer in the family, P(DTP-BThBBT) has a max of 1219 nm and a higher energy peak with a slightly higher intensity at 533 nm. This highe r energy peak absorbs strongly in the green and yellow portions of the spectrum, resulting in a light purple colored film. 400600800100012001400160018002000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 c b a Polymer Films sprayed on ITOmax = 699 nmmax = 673 nmmax = 975 nmmax = 1219 nmmax = 1252 nmNormalized Absorbance (A.U.)Wavelength (nm) P(DTP-BThBTD) P(DTP-BTD) P(DTP-BThTQHx2) P(DTP-BThBBT) P(DTP-TQHx2) Figure 5-5. UV-VIS-NIR of ne utral polymers spray cast onto ITO. (a) P(DTP-BThBTD) Eg = 1.45 eV, (b) P(DTP-BTD) Eg = 0.98 eV, (c) (PDTP-BThTQHx2) Eg = 0.95 eV. Figure 5-6. Pictures of spra y cast neutral polymers on ITO. From left to right: P(DTPBThBTD), P(BThBBT), P(DTP-BTD), P( DTP-BThTQHx2), and P(DTP-TQHx2).

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109 There are a few trends to be observed. In staying in the bisthienyl (BTh) family of polymers, we see that in going from the weakest acceptor P(DTP-BThBTD) to the intermediate acceptor P(DTP-BThTQHx2) there is a red shift in the max by 302 nm from 673 nm to 975 nm respectively. Then, by moving on to the stronge st acceptor in the family, P(DTP-BThBBT) there is a 244 nm red shift in max relative to the intermediated acceptor P(DTP-BThTQHx2) from 975 nm to 1219 nm. This red shifting of the max suggests an increasing amount of ICT in going from BTD to TQ to BBT. This follows the trend of increased acceptor strength (due to increased amounts of electron accepting imine nitrogens) as discussed in chapter 1. The optical band gap also decreases by 0.5 eV in going from P(DTP-BThBTD) (1.45 eV) to P(DTP-BThTQHx2) (0.95 eV). Comparing the connectivity of the same co re acceptor to the donor, we see that in going from P(DTP-BThTQHx2), which has a max of 975 nm and a thiophene spacer between the DTP donor and the TQ acceptor, P(DTP-TQHx2), has a max of 1252 nm and no thiophene spacer. Removal of the thiophene spacer has re sulted in a 277 nm red shift in the max. This demonstrates an increase in ICT between the donor and the acce ptor relative to the a ddition of a thiophene spacer, which blue shifts the max and the band gap. These effects have been seen before and are attributed to a decrease in the amount of ICT.70,105,154 For the two lowest band gap (long wavelength absorbing) polymers studied at present, P(DTP-BThBBT) and P(DTP-TQHx2), it is hard to determine an optical band gap using ITO since these polymer begin to absorb well beyond th e useful range of ITO. This is because ITO has a strong absorbance beyond 1600 nm, which makes baseline absorption hard to quantify for determining an onset of absorption.53,156 By switching to single walled carbon nanotube (SWCNTs) electrodes, which are highly transparent into the IR,124 we can overcome the

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110 deficiencies of ITO for a more accurate determ ination of the optical band gap. To probe the optical band optical band gap even further, reflectance measurements on gold were performed which allows for improved characterization of th e baseline deeper into the mid-IR. For these measurements, the polymers were spray-cast onto SWCNT or gold and analyzed. P(DTPBThBBT) has a max of 1208 nm and an estimated ba nd gap of 0.63 eV while P(DTP-TQHx2) has a max of 1243 nm, but still has significant absorption beyond the range of the spectrophotometer, thus only a rough estimate of ~ 0.5 eV can be made for the band gap. Reflectance analysis for P(DTP-BThBBT) on gold estimates a band gap of ~ 0.5 eV. These band gaps are the lowest values for a soluble polymer to date. 50010001500200025003000 0.0 0.2 0.4 0.6 0.8 1.0 1.2 max = 1243 nmmax = 1208 nmNormalized Absorbance (A.U.)Wavelength (nm)4000800012000160002000024000 0 20000 40000 60000 80000 100000 Absorption Coefficient (cm-1)Wavelength (nm)AB Figure 5-7. UV-VIS-NIR analysis of P(DTP-BT hBBT) and P(DTP-TQHx2) on SWCNTs and reflectance of P(DTP-BThBBT) on gold. A) UV-VIS-NIR of P(DTP-BThBBT) (solid) and P(DTP-TQHx2) (dash) on SWCNTs. B) Re flectance spectrum of P(DTPBThBBT) on gold. It is important to note that throughout all of the UV-VIS-NIR spectra for this family of polymers (Figures 5-5, 5-6, and 57), there is a scattering effect on the base line absorption. Instead of the baseline being flat and having an absorbance at or near zero until the onset of absorption, we see a baseline that increases slowly up until the onset of absorption. It was not until doing the reflectance measurement on gold that we see a true baseline. The reason for this

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111 is unknown, but might have to do with the resu lting film morphology from spray casting. The films look speckled and rough to th e eye, which might be the cause of the scattering. Further investigation is needed to look into this, such as a comparison of the sp ray-cast films to films made by drop casting or spin-coating. In looking at the comparison of P( DTP-BThBTD) to P(DTP-BTD) the max red shifts only 26 nm, from 673nm to 699 nm. In order to make a comparison of the band gaps between the two polymers, it has to be determined if the shoul der peak at 1000 nm is due to aggregation. UVVIS-NIR of a P(DTP-BTD)/toluene polymer solu tion was measured over a broad range from 10 C up to 90 C. At 10 C the max is at 683 nm with the shou lder peaking at 1051 nm. Upon increasing the temperature, we see an in itial decrease in the intensity of the max followed by an increase and a blue shifting to 669 nm at 90 C More importantly, the shoulder peaking at 1051 nm is steadily decreasing a nd blue shifting over the whole temperature range, indicating aggregation. However, the shoulder does not comp letely disappear even at 90 C. In order to look at this further, the soluti on was subjected to three consecu tive 1:2 dilutions and a UV-VIS at each concentration was measured at 90 C (Figure 5-9). Even at very dilute concentrations, it can be seen that the shoulder peak does not go away, indica ting that the polymer is still aggregated and not mol ecularly dissolved.

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112 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 411 nm 423 nm 1051 nm 669 nm 683 nm Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (A.U.)Wavelength (nm)AB Figure 5-8. Solution thermochro mism and concentration dependence UV-VIS-NIR analysis of P(DTP-BTD) in toluene. A) Thermochromism of a 5.32 x 10-5 M P(DTPBTD)/toluene solution from 10 C to 90 C in 5 C increments (solid line = 10 C, dashed bold line = 90 C). B) Concentra tion dependence of UV-VIS-NIR spectra for a P(DTP-BTD)/toluene solution at 90 C (solid line = 5.32 x 10-5 M, dashed line = 2.66 x 10-5 M, dotted line = 1.33 x 10-5 M, and dash dot line = 6.65 x 10-6 M). Electrochemical and Spectroelect rochemica l Characterization Polymer Electrochemistry W e have just talked about the very noticeable changes in the optical data for the polymers in moving from the weaker BTD, to the intermed iate TQ, to the strongest BBT based acceptors. We have also noticed significant changes relative to having a thiophene sp acer present or not. It is important to understand how the optical trends seen here initially will relate to the redox properties of the polymers. The polymers we re analyzed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) to determine the elec trochemical band gap, and the position of the HOMO/LUMO levels. Polymers were characterized as drop cast films on a platinum button working electrode in a three electrode cell with a platinum flag counter electrode and a Ag/Ag+ reference electrode (calibrated to Fc/Fc+). All potentials reported are adjusted relative to SCE to be consistent with the literature va lues and the rest of this dissertation. Polymers were drop cast from either toluene or chloroform solutions onto platinum button

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113 working electrodes. All polymers were sca nned by CV until a reproducible CV was obtained ( ca. 20-30 times). The onsets for oxidation and re duction were taken as the tangent of oxidation or reduction relative to the baseline. All experime nts were carried out in 0.1 M tetrabutylammonium perchlorate/ propylene carbonate (TBAP/PC) el ectrolyte solutions inside an argon filled dry box. In order to better understand these systems, CV and DPV analysis of P(DTP-BThBTD) and P(DTP-BTD) can be seen in Figure 5-9. To avoid trapped charge s and stability issues associated with full CV scans, separate film s were used for oxidation and reduction. P(DTPBThBTD) (Figure 5-9 A) shows a single reduction with an onset of ~ -1.3 V, however, no peak reduction potential could be obtained. The onset for oxidation is observed at 0.6 V, and increases until about 0.8 V, where upon further ox idation gives a very flat current response making it hard to determine the E1/2. This can be attributed to the capacitive charging of the polymer film in its conducting state. If the f ilm was not conducting, ther e should be a drop in the current response at po tentials past the E1/2 due to a site limited redox conductivity mechanism. This type of behavior has b een studied by past group members, however, in-situ conductivity was performed to substantiate this.38,67,68 The difference between the onset of oxidation and reduction corresponds to an electrochemical band gap of 1.9 eV, which is substantially higher than the optical band gap of 1.45 eV. A comple te summary of all the onsets and HOMO/LUMO values for all of the polymers can be found in tabl e 5-2. It can be seen that the current density observed for oxidation is almost 100 times more than is observed for reduction. This is probably due to the dense nature of the drop cast film, making it hard for the supp orting electrolyte (i.e. the TBA+) to flow in and out of the polymer film during reduction. This is a trend that can be seen throughout the CV and DPV analysis in the remainder of this chapter, however, for the non

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114 BTD based polymers (Figures 510 and 5-11), the difference in currents between oxidation and reduction is only by a factor of ten. When looking at the CV for P(DTP-BTD) (Figure 5-9 B), we see a very similar CV to that of P(DTP-BThBTD). The onset for reduction oc curs at -1.25 V with no discernable peak reduction potential. Meanwhile, the oxidation pr oduced a slightly sharper CV, where a peak oxidation at 1.04 V and an E1/2 of 0.92 V could be observed. Th e onset for oxidation occurs at 0.55 V, yielding an electrochemical band gap of 1.8 eV, which is only 0.1 eV smaller relative to P(DTP-BThBTD). DPV, which is a more sensitive technique than CV and gives more accurate onsets and sharper peaks, was attempted to resolve some of the peak potentials and increase the accuracy of the onsets. DPV analysis of P(DTP-BThBTD) (F igure 5-9 C) shows a reduction peak with an Ep at -1.47 V and an E1/2 of -1.34 V. The reduction is quasi-reversible with adequate charge compensation on the reverse scan. This dem onstrates the usefulne ss of DPV (increased sensitivity) relative to CV. Note the reducti on onset occurs at -1.17 V and shows the typical faradaic response with no capacitive behavior. Meanwhile the oxidation is broad process and shows both faradaic and capacitive behavior, w ith an onset of oxidation at 0.46 V. This corresponds to a band gap of 1.65 eV, which is a lot closer to the optic al band gap of 1.45 eV relative to CV. DPV analysis of P(DTP-BTD) (Figure 5-9 D) shows a very similar reduction, with an Ep at -1.45 V and an identical E1/2 at -1.34 V. The reduction peak shows the typical faradaic response with an onset at -1.17 V. Fo r oxidation, we see both faradaic and capacitive behavior with an onset of 0.37 V. This corresponds to an electrochemical gap of 1.54 eV. Based on the electrochemical data and the solution thermochromism, it is likely that the true band gap of P(DTP-BTD) is somewhere a lot clos er to that of P(DTP-BThBTD).

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115 Moving to the TQ family, CV analysis of P(DTP-BThTQHx2) (Figure 5-10 A) shows an oxidation with an E1/2 at 0.7 V and an onset of oxidation at 0.3 9 V. Again there is little current loss after the Ep, indicating capacitive behavior. The re duction CV shows two quasi-reversible reductions at an E1/2 of -0.88 V and -1.28 V with a drop in current after the Ep, indicating a localized state. The onset for the first reduction is at -0.84 V, which is almost a 400 mV increase in reduction potential by switching fro m the BTD based polymers to BThTQHx2 and can be attributed to the increased acceptor strength. The electrochemical band gap by CV is determined to be about 1.43 eV. This is still si gnificantly higher than th e optical band gap of ~ 0.95 eV. -1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.16 -0.14 -0.12 -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Ep = -1.21 V Ep = -1.47 V E1/2 = -1.34 V Current Density (mA/cm2)Potential (V vs. SCE)-6 -4 -2 0 2 4 6 Current Density (mA/cm2) -1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.16 -0.14 -0.12 -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.80 V 1.04 VCurrent Density (mA/cm2)Potential (V vs. SCE)-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Current Density (mA/cm2) E1/2 = 0.92 V -1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.15 -0.10 -0.05 0.00 0.05 0.10 Current Density (mA/cm2)Potential (V vs. SCE)-4 -2 0 2 4 6 Current Density (mA/cm2) -1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.14 -0.12 -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 E1/2 = -1.34 V -1.23 VCurrent Density (mA/cm2)Potential (V vs. SCE)-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Current Density (mA/cm2) -1.45 V A C B D Figure 5-9. CV (scan rate = 25 mV/s) and DPV (s tep size of 2 mV and step time of 0.1 seconds) of P(DTP-BThBTD) and P(DTP-BTD) on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P( DTP-BThBTD). B) CV of P(DTP-BTD). C) DPV of P(DTP-BThBTD). D) DPV of P(DTP-BTD).

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116 Analysis of P(DTP-TQHx2) by CV (Figure 10 B) shows some very interesting behavior. Only the first reduction is seen by CV. There are no recognizable peaks associated with the second reduction. This is unexpected. Perhaps th e film is too dense to allow for the movement of the electrolyte in for the second reduction. Or maybe it might be a stability issue. Since the peaks are not well defined, only the onset could be attained, which is -0.70 V for reduction. The oxidation P(DTP-TQHx2) shows an onset at 0.44 V, an E1/2 at 0.79 V, and an Ep at 0.98 V. Upon further oxidizing potentials there is little current loss indicating some capacitive behavior. The electrochemical band gap is estimated to be 1.16 eV Again, this is much higher than the optical band gap. DPV analysis of P(DTP-BThTQHx2) (Figure 10 C) shows two quasi-reversible reductions at E1/2 = -0.86 and -1.30 V, with a large decrease in current after going to potentials increasingly cathodic of the E1/2 implicating a localized charge state. The oxidation of the polymer shows some capacitive behavior beyond the E1/2. The onset for reduction is located at -0.7 V, meanwhile the onset of oxidation occurs at 0.39 V, giving an electrochemical band gap of 1.09 eV. This value is fairly close to optical band gap of 0.95 eV. Application of cathodic potentials by DPV to P(DTP-TQHx2) (Figure 10 D) shows a quasireversible reduction at E1/2 = -0.84 V with an onset at -0.65 V. This is in fairly good agreement to the bisthienyl derivative, however, unlike P(DTP-BThTQHx2), the onset of oxidation is seen at 0.28 V, yielding an electrochemical band gap of 0.93 eV, which is much higher than the estimated 0.5 eV optical band gap.

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117 -1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.21.4 -0.2 -0.1 0.0 0.1 0.2 E1/2 = -0.84 V Ep = 0.77 V Ep = 0.90 V Current Density (mA/cm2)Potential (V vs. SCE)-4 -3 -2 -1 0 1 2 3 4 Current Density (mA/cm2) -1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.12 -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 E1/2 = 0.79 V Ep = 0.61 V Ep = 0.98 V Current Density (mA/cm2)Potential (V vs. SCE)-2 -1 0 1 2 3 Current Density (mA/cm2) -1.6-1.4-1.2-1.0-0.8-0.6-0.4 -0.20.00.20.40.60.81.01.2 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 Ep = 0.59 V Ep = 0.81 V Current Density (mA/cm2)Potential (V vs. SCE)-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 E1/2 = ~ -0.88 V E1/2 = -1.28 V Ep = -0.77 V E1/2 = 0.70 V Ep = ~ -1.0 V Ep = -1.37 V Ep = -1.19 V Current Density (mA/cm2)-1.6-1.4-1.2-1.0-0.8-0.6-0.4 -0.20.00.20.40.60.81.01.2 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Current Density (mA/cm2)Potential (V vs. SCE)-5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Ep = -1.35 V Ep = -1.24 V E1/2 = -1.30 V E1/2 = -0.85 V Ep = -0.81 V Ep = -0.90 V Current Density (mA/cm2) A B C D Figure 5-10. CV (scan rate = 50 mV/s) and DP V (step size of 2 mV and step time of 0.1 seconds) of P(DTP-BThTQHx2) and P(DTP-TQHx2) on a Pt button working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P(DTP-BThTQHx2). B) CV of P(DTP-TQHx2). C) DPV of P(DTP-BThTQHx2). D) DPV of P(DTP-TQHx2). Finally, P(DTP-BThBBT) was analyzed by CV and DVP. CV analysis (Figure 5-11 A) shows two quasi-reversible reductions at E1/2 = -0.69 V and -1.08 V, with an onset for the first reduction at -0.51 V. The onset for oxidat ion was at 0.45 V with the oxidation having a capacitive nature beyond the Ep. DPV analysis (Figure 5-11 B) also shows two quasi-reversible reductions, at E1/2 of -0.57 V and -1.08 V. The onset fo r the first reduction occurs at -0.39 V while the onset for oxidation occurs at 0.26 V, giving an electrochemical band gap of 0.65 eV. This estimate is very close to th e optical band gap of 0.5 to 0.6 eV. The general trend shown in going from the weaker BTD based acceptors to the stronger TQ and BBT based acceptors is the decrease in the HOMO/LUMO gap by a significant lowering

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118 of the LUMO value relative to the HOMO le vel. When comparing the polymers, the electrochemical data estimates a larger band gap than is determined optically. -1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 Current Density (mA/cm2)Potential (V vs. SCE)-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 E1/2 = -0.59 V Ep = -0.48 V E1/2 = -1.06 V Ep = -1.01 V Ep = -1.12 V Ep = -0.71 V Current Density (mA/cm2) -1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 Current Density (mA/cm2)Potential (V vs. SCE)-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 E1/2 = -0.57 V E1/2 = -1.08 V Ep = -1.05 V Ep = -1.11 V Ep = -0.62 V Ep = -0.52 V Current Density (mA/cm2) AB Figure 5-11. CV (scan rate = 50 mV/s) and DP V (step size of 2 mV and step time of 0.1 seconds) of P(DTP-BThBBT) on a Pt butt on working electrode in 0.1 M TBAP-PC electrolyte solution. A) CV of P(DTP-BThBBT). B) DPV of P(DTP-BThBBT). Table 5-2. Summary of electroc hemical data for P(DTP-Accepto rs) investigated. All onset values are Volts vs. SCE. All HOMO/LUMO values were calculated by E(VAC) = E(SCE) + 4.7.37 (* = aggregate). Acceptor Eox (CV) onset HOMO (CV) eV Ered (CV) onset LUMO (CV) eV Eox (DPV) onset HOMO (DPV) eV Ered (DPV) onset LUMO (DPV) eV Eg (optical) BThBTD 0.6 5.3 -1.3 3.40 0.46 5.16 -1.17 3.53 1.45 BTD 0.55 5.25 -1.25 3.45 0.37 5.07 -1.17 3.53 0.98 BThTQHx2 0.39 5.09 -0.84 3.86 0.39 5.09 -0.70 4.00 0.95 TQHx2 0.44 5.14 -0.70 4.00 0.28 4.98 -0.65 4.05 ~ 0.5 BThBBT 0.45 5.15 -0.51 4.19 0.26 4.96 -0.39 4.31 0.5-0.6 Polymer Spectroelectrochemistry The techniq ue of spectroelectrochemistry was us ed to probe the electro-optical properties of this family of polymers. Polymer films were spray cast from chloroform or toluene solutions on to ITO coated glass working electrodes. Th e polymer films were then placed in a cuvette with a platinum wire counter elec trode and a silver wire pseudo re ference electrode (calibrated to

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119 the Fc/Fc+ redox couple and converted relative to SC E) and switched by repetitive potential scanning from a neutral potential to the desired charged state in a 0.1 M TBAP/PC solution until a reproducible CV was seen before spectroelectrochemical measurements were performed. The polymers were analyzed in both oxidation and re duction with reductive sp ectroelectrochemistry performed in an argon filled glove box using a Stellarnet photodiode array detector. Oxidative spectroelectrochemistry was perf ormed on P(DTP-BThBTD) (Figure 5-12 A). As discussed in Chapters 3 and 4, the long wavelength absorption in these donor-acceptor polymers is due to intramolecular charge transfer (CT), while the high energy peak is considered to be the transition ( -transition). For neutral P(DTPBThBTD), we see a strong CT band at 660 nm that tails off through the visible region down to the -transition band (shoulder) at 473 nm, which then falls off abruptly. This leaves the green and blue por tions of the spectrum partially open resulting in a dark greenish/blue neutral film. Th e optical band gap is determined by the onset of absorption in th e neutral polymer, which for P(DTP-BThBTD) occurs at ~ 870 nm, or 1.4 eV. Upon oxidation, the bleaching of both neutral transitions starts to occur around 0.5 V, which coincides nicely with the CV oxida tion data. As the polymer is oxidized, polaron and bipolaron charge carriers are formed, resu lting in an intermediate peak around 800 nm along with a low energy peak at a wavelength beyond 1 600 nm. Upon full oxidation there is an intense charge carrier band 1600 nm, which is indicative of the polymer being in a more conducting state. The band then tails off as it passes in to and all the way thr ough the visible region, resulting in a more transmi ssive grey blue film. Upon reduction of P(DTP-BThBTD) (Figure 5-12 B), a decrease in the CT band at applied potentials of -1.2 to -1.3 V is observed, which ag rees well with the electrochemical data for reduction. At intermediate reduction levels th ere is the bleaching of the CT band and the

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120 development of a broad absorption across the NI R and two new absorption bands at 500 nm and 800 nm, which upon further reduction disappear w ith the formation of a small band at 620 nm and an intense band in the NIR around 1300 nm. It ha s been demonstrated in the past with in the Reynolds group (PBEDOT-PyrPyr-Ph2 in 0.1 M TBAP-ACN/DCM) that the formation of charge carriers bands in the NIR upon reduction were indeed n-type doping. This was confirmed with in-situ conductivity measurements.67,68 In the reduced state we s ee a light purple colored film, that is indicative of n-type dopi ng due to the strong charge carri er band formation in the NIR, however in-situ conductivity would have to be measured to confirm these suspicions. NO R C400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 max = 659 nmAbsorbance (A.U.)Wavelength (nm)B4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Eg = ~1.42 eV max 473 nmmax 660 nmAbsorbance (A.U.)Wavelength (nm)A Figure 5-12. Spectroelectochemistry of P(DTP-BThBTD) in 0.1 M TBAP/PC and the associated colored states. A) Oxidative switching of a film from -0.16 V (bold) to 1.24 V (dashed) vs. SCE in 100 mV increments. B) Reductive switching of a film from -0.92 V (bold) to -1.72 V (dashed) vs. SCE in 100 mV increments. C) Pictures in the reduced (R), neutral (N) and oxidized (O) states. Sticking with the same acceptor, but removing the thiophene spacer, oxidative spectroelectrochemistry was performed on P(DTP-BT D) (Figure 5-13 A). In the neutral polymer

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121 the CT band is located at 676 nm (with a shoulder peak at 1020 nm attributed to aggregation), while the transition band is at 427 nm and of equa l intensity. The nice trough over the 500 nm region in the neutral state result s in a deep emerald green neutral polymer. In comparison to P(DTP-BThBTD), the -transition band in P(DTP-BTD) is blue shifted 46 nm and is now of equal intensity to the CT band, while the CT band is only sligh tly red shifted, but broadened by the aggregation peak. Upon oxidation there is a disappearance of the shoulder at 1020 nm with a slight red shifting of the CT ba nd. Upon full oxidation there the charge carrier peaks can be seen at ~ 800 nm and ~1600 nm, while the -transition band is bleached, re sulting in a slightly more transparent grey/green film. 400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 max = ~457 nm max = ~683 nmAbsorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 max 676 nm Eg = ~0.98 eV max shoulder ~1020 nmmax 427 nmAbsorbance (A.U.)Wavelength (nm)C NO R A B Figure 5-13. Spectroelectochemistry of P(DT P-BTD) in 0.1 M TBAP/PC and the associated colored states. A) Oxidative switching of a film from -0.31 V (bold) to 1.09 V (dashed) vs. SCE in 100 mV increments. B) Reductive switching of a film from -1.16 V (bold) to -1.86 V (dashed) vs. SCE in 100 mV increments. C) Pictures in the reduced (R), neutral (N) and oxidized (O) states.

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122 Upon reduction of P(DTP-BTD) (Figure 5-13 B) a slight decrease in the CT band is observed, while concurrently the -transition band and the aggregat e peak are increasing. There is also the development of a broad charge carrier absorption across the NIR, peaking around 1070 nm, but the intensity is not ne arly as strong as it was in P(DT P-BThBTD). This results in a relatively flat absorption acro ss the visible region down to a bout 500 nm, where the absorption falls off. This yields a dark greenish grey polymer in the reduced state. 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Eg = ~0.95 eV max = 511 nmmax = 963 nmAbsorbance (A.U.)Wavelength (nm)400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 max = 511 nmmax = 951 nmAbsorbance (A.U.)Wavelength (nm)C NO R2R1 A B Figure 5-14. Spectroelectochemistry of P(DTP-BThTQHx2) in 0.1 M TBAP/PC and the associated colored states. A) Oxidative switching of a film from -0.33 V (bold) to 1.07 V (dashed) vs. SCE in 100 mV increments. B) Reductive switching of a film from -0.54 V (bold) to -0.85 V (dashed) to -1.94 V (Dotted) vs. SCE in 100 mV increments. C) Pictures in the 2nd reduced (R2), 1st reduced (R1), neutral (N) and oxidized (O) states. In switching to the stronger TQ based acceptor, the CT band has red shifted about 303 nm relative to P(DTP-BThBTD), while the -transition band has red shifted 38 nm. Both bands (511 nm and 963 nm) are approximately the same intensity, with the gap between them centered

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123 at 670 nm. This results in a light maroon co lored neutral film. Upon oxidation of P(DTPBThTQHx2) (Figure 5-14 A), spectral changes start to occur at about +0.4 V, which corresponds well to the onset of oxidation from the electroche mistry data. As the polymer becomes oxidized the CT band and the -transition band bleach completely, with formation of an intense charge carrier band that tails off th rough the near IR, with minima l absorption through the visible region. This results in a highly transparent, light grey colore d film in the p-doped state. Application of reducing pot entials to P(DTP-BThTQHx2) (Figure 5-14 B) through the first reduced state, results in a bleach ing of the CT band with a concu rrent red shift and increase in absorbance of the -transition band (540 nm). There is also the formation of a possible charge carrier absorption band at 1300 nm, however, it is not that intense, indicating a more localized state. The resulting increased -transition band declines very quick ly through the blue and violet part of the spectrum while it tails off more slow ly through the visible part of the spectrum into the NIR. This results in a bright deep purple colored film. Upon reaching the second reduction, the NIR band has completely bleached while the high energy band has red shifted and increased in intensity (570 nm). The formation of a new ba nd at 900 nm was also observed. This results in a brilliant indigo colored film. With the lack of any intense bands in the NIR, it is likely that these reduced states are highl y localized on the acceptor. Examination of P(DTP-TQHx2) allows one to probe the eff ect of removing the thiophene spacer. For Neutral P(DTP-TQHx2), we see a 34 nm blue shift in the -transition band (477 nm) along with a 276 nm red shift in the CT band (1239 nm) relative to P(DTP-BThTQHx2) (Figure 5-15 A). The large shift in the CT band and increased intensity relative to the -transition band can be attributed to the increased donor-acceptor interact ions due to the removal of the thiophene spacer as discussed in the beginning of this chapter. With the -transition band being the only

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124 major absorption in the visible part of the sp ectrum, this leaves a gap from the yellow through the red parts in the visible spectrum, resul ting in a golden brown ne utral polymer. Upon oxidation there is a bleaching of the -transition band and an increa se in absorption in the NIR due to charge carrier formation. The new charge carrier band also tails ba ck into the red portion of the visible spectrum, resulting a light olive green oxidized state. Upon reduction (Figure 5-15 B) there is a large increase and red shift in the -transition band out to 520 nm. Meanwhile ther e is a decrease in the CT band with the formation of a new, less intense band just past 1550 nm. This results in a dark brow n colored film in the reduced state. 400600800100012001400 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 max = ~ 472 nm max = ~1211 nmNormalized Absorbance (A.U.)Wavelength (nm)4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 max= 319 nmmax= 477 nmmax= 1239 nmAbsorbance (A.U.)Wavelength (nm)C NO R AB Figure 5-15. Spectroelectochemistry of P(DTP-TQHx2) in 0.1 M TBAP/PC and the associated colored states. A) Oxidative switching of a film from -0.25 V (bold) to 1.15 V (dashed) vs. SCE in 100 mV increments. B) Reductive switching of a film from -0.21 V (bold) to -1.31 V vs. SCE in 100 mV increments. C) Pictures in the reduced (R), neutral (N) and oxidized (O) states.

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125 To complete the series of the variable acceptor DA polymers, P(DTP-BThBBT), containing the strongest acceptor in the family, was analyzed. In the neutral polymer, the only major absorption is from the -transition at 529 nm, which is 18 nm red shifted relative to the transition in P(DTP-BThTQHx2). The CT band is sifted well into the NIR at 1231 nm, which is 276 nm beyond that for P(DTP-BThTQHx2). A strong red shift in the CT band results from the use of the much stronger BBT based acceptor. The visible absorption of the -transition band in neutral P(DTP-BThBBT) at 529 nm results in a purple/maroon colored film (Figure 5-16). Upon application of oxidizing potentials (Figure 5-16 A), there is a bleaching of the -transition along with the concurrent formation of a highly inte nse charge carrier band in the NIR peaking around 1400 nm. As this intense band grows in, it starts to broaden and expand into the visible portion of spectrum with the tail reaching a minimum in the blue portion of the spectrum. This results in more transmissive grey blue film in the oxidized state. Upon application of cathodic pot entials to the polymer through the first reduction (Figure 5-16 B, dashed bold line), we see a red shif t (11 nm) an increase in intensity of the -transition out to 540 nm along with the development of a s light shoulder peak ar ound 700 nm. While this is happening, the CT band is starting to bleach an d there is the formation of a smaller less intense band at ~ 1450 nm. While this could be a true n-doped state, the lack of intensity of the new band suggests it might be more of a localized state. With the -transition absorbing most of the visible portion of the spectrum, tailing off in both the purple and the red portions of the spectrum, the polymer becomes bright purple in color. In moving on to the second reduction, the peak that was developing at 700 nm has now re d shifted out to ~ 775 nm and is now just as intense as the -transition. This increase occurred at the expense of the complete bleaching of

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126 the low energy absorption that formed during th e first reduction, and re sults in a brighter blue/purple film. 4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 max = 529 nmmax = 1231 nmAbsorbbance (A.U.)Wavelength (nm)400600800100012001400 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 max = 524 nm max = 1205 nmAbsorbance (A.U.)Wavelength (nm)C NO R2R1 A D Figure 5-16. Spectroelectochemistry of P(DTPBThBBT) in 0.1 M TBAP/PC and the associated colored states. A) Oxidative switching of a film from -0.13 V (bold) to 0.97 V (dash) vs. SCE in 100 mV increments. B) Reductive switching of a film from 0.05 V (bold) to -1.13 V (dashed) to -1.45 V (dotted) vs. SC E in 100 mV increments. C) Pictures in the 2nd reduced (R2), 1st reduced (R1), neutral (N) and oxidized (O) states. Conclusions When looking at all of the polym ers in this family, a general trend upon oxidation is that the polymers go from a nicely colored neutral state to a more transparent oxidized state. When looking at the polymers with the thio phene spacer, the trend is to a more transparent grey to grey blue color while the others go to a green to blue /green. We also see th at the two bisthienyl polymers capable of two reductions both go to rich purple colors upon the first reduction and then to deeply purple/blue co lors upon the second reduction. This opens up the opportunity for making new copolymers containing two or more of th ese acceptors to contro l the color. Perhaps

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127 an easier option is to make electrochromic devi ces with various blends of these polymers to ultimately control the final colors. Depending on the desired properties for a certain material, we have demonstrated that these acceptors can tune the CT band absorption over ~ 600 nm window from 650 nm to 1250 nm. The interesting note here is the removal of the thiophene spacer from P(DTP-BThTQHx2) resulted in a ~275 nm red shift in the CT band. The next course of action for continuing towards lower gap systems would be to make P(DTP-BBT). In terms of fine control over the absorption spectra and the band gap, the addition of more th iophene spacers could be used to make minor adjustments. We have also demonstrated the use of th e Stille methodology for making soluble donoracceptor polymers with the ability to reach very high molecula r weights in excess of 100 K number average molecular weight (P(DTP-BThBTD)). When the polymers are oxidized, they all show charge carrier band formation into the NIR or farther with increased intensity indicating delocalized bands. Upon reducti on, we see a different story. For P(DTP-BThBTD) we see an intense charge carrier band in the NIR upon reduc tion, indicating delocalized bands indicative of n-type doping. This is the only polymer in th e family that shows a more intense band upon reduction relative to the neutral sp ectrum. All of the other polymers show po ssible charge carrier band formation in the NIR upon first reduction, howeve r, the intensity is much weaker than the neutral spectrum indicating that these bands are probably more localized on the acceptors. For the P(DTP-BThTQHx2) and P(DTP-BThBBT), upon reaching the second reduction, there are no charge carrier bands seen in the NIR with only p eaks in the visible region indicating the charges are localized on the acceptors. These polymers are not a truly n-type doped system in this state.

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128 Experimental 4,9-dibromo-6,7-dihexyl-[1,2,5]thiadiaz olo[3,4g]quinoxaline: 4,7dibromobenzo[c][1,2,5]thi adiazole-5,6-diamine174 (0.257 g, 0.793 mmol) was added to a flame dried 100 mL round bottom flask followed by 30 mL of degassed acetic acid. Next tetradecane7,8-dione139 was added and the solution was stirred overnight under argon in the dark. Then water (~ 50 mL) was added and the solution was extracted with dichloromethane. The organic layer was then washed with water, sodium bicarbonate, and water followed by drying over magnesium sulfate. The solvent was removed un der reduced pressure and the crude solid was purified by column chromatography (3:2 hexanes:dichloromethane) yielding 0.375 g (92 %) of an orange solid. 1H NMR (300 MHz, CDCl3) 0.93 (t, 6H), 1.25-1.55 (m, 12H), 1.99 (p, 4H), 3.10 (t, 4H); 13C NMR (75 MHz, CDCl3) 14.18, 22.75, 26.64, 29.20, 31.89, 35.14, 35.23, 113.26, 137.78, 151.37, 160.28. HRMS Calcd. for C20H26Br2N4S (M+) 512.0245 Found 512.0190; Anal. Calcd. for C20H26Br2N4S: C, 46.71; H, 5.10; Br, 31.07; N, 10.89; S, 6.23. Found: C, 47.05; H, 5.15; N, 10.61. 4,9-bis(5-bromothiophen-2-yl-)-6,7-dihexyl-[1,2,5]thiadiazolo[3,4-g ]quinoxaline: 6,7di-hexyl-4,9-di(thiophen-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (1.09 g, 2.09 mmol) is dissolved in 170 ml DMF and NB S (783 mg, 4.39 mmol) are added in the absence of light. The solution is stirred for 10 h, then methanol is added and the precipitate is filtered off, washed with cold methanol and dried, to obtain 1.08 g ( 76 %) of a blue solid. Mp: 140 C -143 C; Anal. Calcd. for C28H30Br2N4S3: C 49.56, H 4.46, N 8.26 found C 49.64, H 4.44, N 8.23; HRMS (ESI TOF) m/z Calcd. for C28H30Br2N4S3: 676.0049 (M+) found 675.9999 (M+); 1H NMR (C2D2Cl4): 8.82 (d, 2H), 7.23 (d, 2H), 3.01 (t, 4H), 2.02 (t, 4H), 1.60-1.36 (m, 12H) 0.97 (t, 6H); 13C NMR

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129 (C2D2Cl4): 159.27, 152.37, 139.11, 136.09, 134.63, 131.13, 121.93, 121.45, 36.99, 33.31, 30.80, 29.59, 24.09, 15.66. N -(3,4,5-Tri( n -dodecyloxy)phenyl)-2,6-dithieno[3,2b:2',3'd]pyrrole (synthesized by Daniel Sweat and Susan Odom): To an oven-dried 100 mL round-bottomed flask cooled under nitrogen was added dry deoxygenated toluene (4 mL), 3,3-dibromo-2,2-bithiophene (0.21 g, 0.65 mmol), and 3,4,5-tri( n-dodecyloxyphenyl)aniline (0.45 g, 0.70 mmol). A solution of Pd2dba3 (0.030 g, 0.0## mmol) and PtBu3 (0.3 mL, 10% solution in hexane) in dry deoxygenated toluene (2 mL) was added to the r eaction mixture, followed by sodium tert -butoxide (0.175 g, 1.82 mmol). The reaction flask was assembled in a microwave reactor with a reflux condenser, and was heated at 90 Watts for 6 minutes (Tmax = 57 C), then for 19 minutes at 95 Watts (Tmax = 82 C), which was followed by an additional ro und of heating at 100 Watts for 20 minutes (Tmax = 110 C). The reaction mixture was run through a short pad of silica gel, eluting with hexanes / dichloromethane (9:1, then 4:1) and after concentra tion by rotary evapora tion, the product was further purified by column chromatography on sili ca gel using hexanes / dichloromethane (9:1 gradually increasing the ration to 1:1). After co ncentration by rotary ev aporation, a pale yellow oil was obtained, which was precipitated from acetone to give the title compound as an off-white powder (0.38 g, 59%). 1H NMR (500 MHz, CD2Cl2) 7.20 (d, J = 5.0 Hz, 2H), 7.18 (d, J = 5.0 Hz, 2H), 6.76 (s, 2H), 3.98 (m, 6H), 1.84 (quintet, J = 7.0 Hz, 4H), 1.75 (quintet, J = 7.0 Hz, 2H), 1.49 (m, 6H), 1.28 (m, 24H), 0.89 (m, 9H). 13C NMR (75 MHz, CD2Cl2) 154.1, 144.4, 136.5, 135.4, 123.7, 116.7, 112.6, 101.7, 73.9, 69.6, 32.5, 32.1, 30.9, 30.3, 30.2 (2 peaks, 0.6 ppm apart), 29.9 (2 peaks, 0.04 ppm apart) 26.7, 26.6, 23.2 (2 peaks, 0.05 ppm apart), 14.4, 9 peaks missing in alkyl region, presumably due to overlap. EI-MS ( m/z ): 807.6. Anal. calcd. for C50H81NS2O3: C, 74.29; H, 10.10; N, 1.73. Found: C, 74.51; H, 10.19; N, 1.80.

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130 2,6-bis(tributylstannyl)-N-(3,4,5-tris(dod ecyloxy)phenyl)-dithieno[3,2-b:2',3'd]pyrrole (Xuan): A deoxygenated solution of N-(3,4,5tris(dodecyloxy)phenyl)-dithieno[3,2b:2',3'd]pyrrole(0.34 g, 0.42 mmol) in THF (200 mL) was cooled to oC, tBuLi (1.5 mL, 2.4 mmol, 1.7 M in heptane) solution was added, a nd the reaction allowed to warm to room temperature and stirred for 1 h, before cooling to oC again; nBu3SnCl (0.25 mL, 0.8 mmol) was then added and the reaction allowed to warm to room temperature and stir for 3 h. The reaction was quenched with addition of water and extracted with dichloromethane; the extracts dried over MgSO4, concentrated under reduced pr essure and stirred with NEt3 (50 mL) for 2 h. After removal of the volatiles the residue was purified by column chromatography (SiO2, pretreated with NEt3, eluting with hexanes), after whic h a pale yellow oil (0.75 g, 66 %) was obtained.1H NMR (400 MHz, CD2Cl2, ): 7.18 (t, J = 7 Hz, 2H), 6.76(s, 2H), 4.10-3.98 (m, 6H), 1.90-1.80(m, 6H), 1.70-1.12 (m, 80 H), 0.91 (t, J = 7.2 Hz, 27H). 13C-NMR (400 MHz, CDCl3, ): 153.5, 146.7, 135.7 (two peaks separated by ca. 5.0 Hz) 135.5, 122.1, 119.2, 101.5, 73.7, 69.1, 32.0(two peaks separated by ca. 2.3 Hz) 30.5, 29.9, 29.8 (two peaks separated by ca. 5.3 Hz) 29.5(two peaks separated by ca. 2.3 Hz) 29.2, 29.1, 29.0, 27.4, 26.3(two peaks separated by ca. 2.3 Hz) 22.8, 14.3, 13.8, 11.1(4 C missing probably due to overlaps). MS (MALDI): m/z 1385.8 (calcd for C74H133NO3S2Sn2, 1386.4). Elemental Analysis: (C alculated) C: 64.11; H: 9.67: N: 1.01; Found C: 64.16; H: 9.54: N: 0.98. P(DTP-BThBTD)n: To a 100 mL 3-neck round bottom flask were added 4,7-bis(5bromothiophen-2-yl)-[2,1,3]-benzothiadiazole (0.35 g, 0.76 mmol), 2,6-bis(tributylstannyl)-N(3,4,5-tris(dodecyloxy)phenyl)-dithieno[3,2-b:2',3'd]pyrrole (1.11 g, 0.80 mmol) and dry THF (100 mL), vacuum pump filled for 5-6 times, and degassed with Argon for 30 min. PdCl2(PPh3)2(0.027 g, 0.04 mmol) was added, and th e solution was stirred at 60-70 C for 2

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131 days. The solution was dropped in ca 500 mL me thanol, and the solid was filtered. The crude product was purified by Soxhlet washings with methanol, acetone and hexanes each for 1 day, and extraction with chloroform for 1 day. After the second prec ipitation, a black solid (0.80 g, 95%) was obtained. 1H NMR (300 MHz, THF-d8): 8.20-7.80 (br, 4H), 7.51-7.02 (br, 4H), 6.83(br, 2H), 4.11 (br, 6H), 1.94.21 (br, 60 H), 0.91 (br, 9H). Mn =106,000, Mw = 147,000, PDI = 1.4. Elemental Analysis: (Calculated) C: 69.46; H: 7.92; N: 3.80; Found C: 69.72; H: 7.77; N: 3.69. TGA (N2) Td = 368 C. P(DTP-BTD)n: To a 100 mL 3-neck round bottom flask were added 2,6bis(tributylstannyl)-N-(3,4,5-tris (dodecyloxy)phe nyl)-dithieno[3,2b:2',3'-d]pyrrole (0.32 g, 0.23 mmol), PdCl2(PPh3)2(0.008 g, 0.01 mmol) and dry THF (30 mL ), vacuum pump filled for 5 times, and degassed with Argon for 60 min. 4,7dibromobenzo[c][1,2,5]t hiadiazole (0.06 g, 0.22 mmol) was added, and the solution was stirred at 60-70 C for 2 days. The solution was dropped in ca 500 mL methanol, and the solid was filte red. The crude product was purified by Soxhlet washings with methanol, acetone and hexanes each for 1 day, and extraction with chloroform for 1 day. After the second precipitation, a bl ack solid (0.20 g, ca 95 %) was obtained. Mn =24,000, Mw = 53,000, PDI = 2.2. Elemental Analysis: (Calcula ted) C: 71.37; H: 8.88; N: 4.46; Found C: 70.28; H: 8.44; N: 4.27. TGA (N2) Td = 352 C. P(DTP-BThTQHx2)n: To a 100 mL 3-neck round bottom flask were added 2,6bis(tributylstannyl)-N-(3,4,5-tris (dodecyloxy)phe nyl)-dithieno[3,2b:2',3'-d]pyrrole (0.56 g, 0.40 mmol), PdCl2(PPh3)2(0.014 g, 0.02 mmol) and dry THF (50 mL ), vacuum pump filled for 5 times, and degassed with Argon for 60 min. 4,9-Bis(5-bromothiophen2-yl)-6,7-dihexyl[1,2,5]thiadiazolo[3,4g]quinoxaline (0.26 g, 0.39 mmol) was a dded, and the solution was stirred at 60-70 C for 2 days. The solution was dropped in ca 700 mL methanol, and the solid was

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132 filtered. The crude product was purified by Soxhl et washings with methanol, acetone and hexanes each for 1 day, and extraction with chlo roform for 1 day. After the second precipitation, a black solid (0.23 g, ca 50%) was obtained. Mn =9,600, Mw = 28,000, PDI = 2.9. Elemental Analysis: (Calculated) C: 70.59; H: 8.43; N: 5.28; Found C: 70.63; H: 8.30; N: 4.90. TGA (N2) Td = 367 C. P(DTP-TQHx2)n: To a 100 mL 3-neck round bottom flask were added 2,6bis(tributylstannyl)-N-(3,4,5-tris (dodecyloxy)phe nyl)-dithieno[3,2b:2',3'-d]pyrrole (0.57 g, 0.40 mmol), PdCl2(PPh3)2(0.014 g, 0.02 mmol) and dry THF (50 mL ), vacuum pump filled for 5 times, and degassed with Argon for 60 min. 4,9Dibromo-6,7-dihexyl[1,2,5]thiadiazolo[3,4g]quinoxaline (0.20 g, 0.39 mmol) was added, and the solution was stirred at 60-70 C for 2 days. The solution was dropped in ca 600 mL me thanol, and the solid was filtered. The crude product was purified by Soxhlet washings with methanol, acetone and hexanes each for 1 day, and extraction with chloroform for 1 day. After the second pr ecipitation, a black solid was obtained. Mn =19,000, Mw = 38,000, PDI = 2.0 Elemental Analysis: (Calculated) C: 72.30; H: 9.27; N: 6.02; Found C: 71.93; H: 9.07; N: 5.42. TGA (N2) Td = 341 C. P(DTP-BThBBT)n: To a 100 mL 3-neck round bottom flask were added 2,6bis(tributylstannyl)-N-(3,4,5-tris (dodecyloxy)phe nyl)-dithieno[3,2b:2',3'-d]pyrrole (0.66 g, 0.48 mmol), PdCl2(PPh3)2(0.016 g, 0.02 mmol) and dry THF (50 mL ), vacuum pump filled for 5 times, and degassed with Argon for 60 min. 4,7-bis(5-bromothiophen-2-yl)-2 42-benzo[1,2c;4,5-c ]bis[1,2,5]thiadiazole (0.23 g, 0.45 mmol) was added, and the solution was stirred at 6070 C for 2 days. The solution was dropped in ca 600 mL methanol, and the solid was filtered. The crude product was purified by Soxhlet washings with methanol, acetone and hexanes each for 1 day, and extraction with chloroform for 1 day. After the second precipitation, a black solid

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133 (0.47 g, 88%) was obtained. 1H NMR (300 MHz, THF-d8): 9.02 (br, 2H), 7.55-5.78 (br, 6H), 4.15 (br, 6H), 1.94.21 (br, 60 H), 0.91 (br, 9H). Mn =14,000, Mw = 51,000, PDI = 3.6, Elemental Analysis: (Calculated) C: 65.99; H: 7.36; N: 6.01; Found C: 65.23; H: 7.30; N: 5.60. TGA (N2) Td = 331 C.

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134 APPENDIX A X-RAY CRYSTALLOGRAPHIC DATA 53 Figure A-1. Crystal Structure for compound 6a (Chapter 4). Table A-1. Crystal data a nd structure refinement for 6a (Chapter 4). Identification code stec1 Empirical formula C18 H10 N4 O4 S4 Formula weight 474.54 Temperature 173(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 6.2143(7) = 69.407(2). b = 10.8663(12) = 81.976(2). c = 14.9797(16) = 75.468(2). Volume 915.13(17) 3 Z 2 Density (calculated) 1.722 Mg/m3 Absorption coefficient 0.557 mm-1 F(000) 484 Crystal size 0.17 x 0.06 x 0.04 mm3 Theta range for data coll ection 1.45 to 27.49. Index ranges -7 h 8, -8 k 14, -19 l 19 Reflections collected 6248

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135 Independent reflections 4090 [R(int) = 0.0325] Completeness to theta = 27.49 97.7 % Absorption correction Integration Max. and min. transmission 0.9794 and 0.9419 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4090 / 0 / 270 Goodness-of-fit on F2 1.031 Final R indices [I>2sigma(I)] R1 = 0.0374, wR2 = 0.0923 [3205] R indices (all data) R1 = 0.0518, wR2 = 0.0980 Largest diff. peak and hole 0.422 and -0.311 e.-3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

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136 49 Figure A-2. Crystal Structure for compound 6b (Chapter 4). Table A-2. Crystal data a nd structure refinement for 6b (Chapter 4). Identification code stec5 Empirical formula C20 H14 N4 O4 S4 Formula weight 502.59 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P21/n Unit cell dimensions a = 12.4928(16) = 90. b = 10.8585(14) = 98.658(3). c = 15.5644(19) = 90. Volume 2087.3(5) 3 Z 4 Density (calculated) 1.599 Mg/m3 Absorption coefficient 0.493 mm-1 F(000) 1032 Crystal size 0.18 x 0.04 x 0.02 mm3 Theta range for data coll ection 1.95 to 27.49. Index ranges -15 h 16, -14 k 14, -15 l 20 Reflections collected 13942 Independent reflections 4780 [R(int) = 0.1190] Completeness to theta = 27.49 99.7 %

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137 Absorption correction Integration Max. and min. transmission 0.9902 and 0.9164 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4780 / 0 / 289 Goodness-of-fit on F2 0.885 Final R indices [I>2sigma(I)] R1 = 0.0676, wR2 = 0.1526 [1990] R indices (all data) R1 = 0.1736, wR2 = 0.1777 Largest diff. peak and hole 1.181 and -0.371 e.-3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

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138 54 48 Figure A-3. Crystal Structure for compound 7a (Chapter 4). Table A-3. Crystal data and structure refinement for 7 a (Chapter 4). Identification code stec3 Empirical formula C22 H16 N4 O4 S3 Formula weight 496.57 Temperature 173(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 7.4627(8) = 101.290(2). b = 11.0846(12) = 98.186(2). c = 13.0708(14) = 95.442(2). Volume 1041.08(19) 3 Z 2 Density (calculated) 1.584 Mg/m3 Absorption coefficient 0.397 mm-1 F(000) 512 Crystal size 0.18 x 0.11 x 0.04 mm3

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139 Theta range for data coll ection 1.61 to 27.50. Index ranges -4 h 9, -14 k 14, -16 l 16 Reflections collected 7161 Independent reflections 4673 [R(int) = 0.0294] Completeness to theta = 27.50 97.7 % Absorption correction Integration Max. and min. transmission 0.9843 and 0.9319 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4673 / 0 / 298 Goodness-of-fit on F2 1.037 Final R indices [I>2sigma(I)] R1 = 0.0407, wR2 = 0.0974 [3658] R indices (all data) R1 = 0.0564, wR2 = 0.1035 Largest diff. peak and hole 0.371 and -0.222 e.-3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

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140 47 56 Figure A-4. Crystal Structure for compound 7c (Chapter 4). Table A-4. Crystal data a nd structure refinement for 7c (Chapter 4). Identification code stec6 Empirical formula C28 H28 N4 O4 S3 Formula weight 580.72 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P21/c Unit cell dimensions a = 9.3368(5) = 90. b = 22.1015(12) = 108.654(1). c = 14.1452(7) = 90. Volume 2765.6(3) 3 Z 4 Density (calculated) 1.395 Mg/m3 Absorption coefficient 0.310 mm-1

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141 F(000) 1216 Crystal size 0.17 x 0.17 x 0.17 mm3 Theta range for data coll ection 1.78 to 27.50. Index ranges -11 h 12, -28 k 28, -18 l 11 Reflections collected 18666 Independent reflections 6335 [R(int) = 0.0319] Completeness to theta = 27.50 99.7 % Absorption correction Integration Max. and min. transmission 0.9489 and 0.9489 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 6335 / 0 / 352 Goodness-of-fit on F2 1.054 Final R indices [I>2sigma(I)] R1 = 0.0400, wR2 = 0.1048 [4962] R indices (all data) R1 = 0.0543, wR2 = 0.1117 Largest diff. peak and hole 0.392 and -0.251 e.-3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

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142 APPENDIX B ELECTROCHEMICAL POLYMERIZATION OF MONOMERS FROM CHAPTER 4 0.00.20.40.60.81.01.2 -8 -6 -4 -2 0 2 4 6 8 10 Ep = 1.09 VCurrent Density (mA/cm2)Potential (V vs. SCE) Figure B-1. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/DCM solution of 6a yielding P6a. -0.4-0.20.00.20.40.60.81.01.2 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Ep = 0.88 VCurrent Density (mA/cm22)Potential (V vs. SCE) Figure B-2. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 7a yielding P7a.

PAGE 143

143 -0.4-0.20.00.20.40.60.81.01.2 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Ep = 0.97 V Current Density (mA/cm2)Potential (V vs. SCE) Figure B-3. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 8a yielding P8a. -0.4-0.20.00.20.40.60.81.01.21.4 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Ep = 1.04 VCurrent Density (mA/cm2)Potential (V vs. SCE) Figure B-4. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 7b yielding P7b

PAGE 144

144 -0.4-0.20.00.20.40.60.81.01.2 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Ep = 0.97 VCurrent Density (mA/cm2)Potential (V vs. SCE) Figure B-5. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 8b yielding P8b -0.20.00.20.40.60.81.01.2 -6 -4 -2 0 2 4 6 Ep = 1.03 VCurrent Density (mA/cm22)Potential (V vs. SCE) Figure B-6. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/DCM solution of 6c yielding P6c

PAGE 145

145 -0.4-0.20.00.20.40.60.81.01.2 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ep = 0.96 VCurrent Density (mA/cm2)Potential (V vs. SCE) Figure B-7. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 7c yielding P7c -0.4-0.20.00.20.40.60.81.01.21.4 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 Ep = 1.08 VCurrent Density (ma/cm2)Potential (V vs. SCE) Figure B-8. Repetitive scan el ectropolymerization (50 mV/s, 10 cycles) from a 5 mM monomer 0.1 M TBAP/PC:DCM (9:1) solution of 8c yielding P8c

PAGE 146

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156 BIOGRAPHICAL SKETCH Tim othy T. Steckler is the son of Thomas and Lillian Steckler. He was born and raised in Brookfield, WI. He received his bachelors of science degree in chemistry from Winona State UniversityWinona, MN. While at WSU, under the advisement of Dr. Thomas W. Nalli and Dr. Robert W. Koptizke, he was enc ouraged to continue on in his e ducation. Tim then went to the University of Florida to work under the advisement of John R. Reynolds. There, he worked as a synthetic organic chemist of conjugated polymers. He received his Ph.D. from the University of Florida in the spring of 2009