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Increasingly Functional Poly(3,4-alkylenedioxythiophene)s through Facile Substitution

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Increasingly Functional Poly(3,4-alkylenedioxythiophene)s through Facile Substitution
Creator:
JONES, ADOLPHUS GENAY
Copyright Date:
2008

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Colors ( jstor )
Crystals ( jstor )
Electric current ( jstor )
Electrochemistry ( jstor )
Molecules ( jstor )
Monomers ( jstor )
Oxidation ( jstor )
Polymerization ( jstor )
Polymers ( jstor )
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University of Florida
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University of Florida
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Copyright Adolphus Genay Jones. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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11/30/2007
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1 INCREASINGLY FUNCTIONAL POLY(3,4-AL KYLENEDIOXYTHIOPHENE)S THROUGH FACILE SUBSTITUTION By ADOLPHUS GENAY JONES 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 2007

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2 Copyright 2007 by Adolphus Genay Jones

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3 For Rev. Adolphus W. Jones and Mrs. Marion S. Anderson.

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4 ACKNOWLEDGMENTS Having success is a pretty simple formula. A good bit of effort, consistently shrewd decision making, and a little luck are often e nough to overcome any challenge. However, none of the aforementioned occurs without surrounding your self with good people. My time at the University of Florida has done mu ch to support that supposition. Every graduate student has people who are more than peers, but are more closely mentors. Beginning in May of 2002, the following gentle men and scholars of the Butler Polymer Laboratory guided me through the early stumbling block of perf orming synthetic chemistry in the humid and distracting world of Florida. Carl Gaupp and C.J. DuBois showed me how to begin the first steps toward becoming a synthetic chemist. I have tried to demonstrate the same patience and willingness to help younger students th at they showed to me. I cannot forget our postdoctoral student, Shane Waybright. His insight into the Zen of reactions still serves me to this day, when I try to understand what goes wro ng with my synthetic attempts. I must thank John Sworen, a brilliant synthetic mind who taught me how to take synthetic routes from the literature to the reaction vessel. I look forward to following his brilliant career over the decades. If the above are elders, I must recognize those who tread the path immediately before me. Ben Reeves and Barry Thompson did more than se t the standard for synthetic chemists in the Reynolds group. They are two sides of a chemical sword. Barry’s precision and steadfastness taught me how to persevere thr ough both reactions and examinati ons. Ben’s joviality reminded me to enjoy each moment. Though he may never be a professionally comedian, I am sure his current peers enjoy knowing that he “just flew in from Cleveland, Thank You, Goodnight!” There is a familiar saying in my home of Georgia, “Be worthy as you run upon this hallowed sod, for you have dared to tread where ch ampions have trod.” As much as I appreciate those who have come before, I cherish those who j ourneyed with me. Much of the work in this

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5 dissertation belongs in some part to my compatriots in graduate school. My electrochemistry would never have been completed with the unders tanding and intuition of Aubrey Lynn Dyer. I look forward to her being chief technical officer of a company one day, if only to support my own research group. Tim Steckler was a shin ing example that enjoying your life didn’t necessarily prevent you from being a good chemist. If only I could have the arms and abs that cause so many to swoon. One of my favorite as pects of graduate sc hool is the number of international students I have been able to befrie nd. Chief among these is Christophe Grenier. Whether a late night meal, a discussion about soccer, or a critique of someone’s seminar, Christophe provided a welcome perspective on our American sensibilities. I look forward to visiting his home one day, perhaps for a World C up. Finally, my experience would never have been the same without Bob Brookins. It was g ood to have another Georgia Boy nearby. Even better to learn as much about music, as I hope he learned about college football. I look forward to catching up with him and his fam ily during national meetings over my next 30 years. We’ll end every night with Ray Charles’ Georgia on My Mind. I cannot forget the people that continued to shape me from my underg raduate years. These people are more than friends, they are family: Rob Kischuk, and his wife Cheryl, Kevin Lovering – his work life brought much levity to my diffic ult days, and my twin, Jon Jones. I look forward watching his family grow and will enjoy having a reason to regularly “Visit Florida.com” to pay his salary at UF-Tem ple Terrace, er USF. To Kellie Woodling, who knew a simple football tailgate would lead to so many shared experiences? Traveling to watch her beloved Kent ucky Wildcats, in Gainesville, Atlanta, and Lexington has provided much of the highlight of my graduate career. Showing her the joy and

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6 pain of college football was equa lly as thrilling. I hope that bo th of us are there to watch Kentucky get their 8th national championship, our friends hip complicated or otherwise. Progress does not occur without the daily assistance of the Program Assistants in the Department. Most significant to me were Gena Borrero, Lori Clark, Sara Klossner, and Tasha Simmons. Chemistry and classes do not occur without these wonderful people. I must also thank Dr. John R. Reynolds. Ev en though students often ask advisors to be perfect, John has done the very be st at being just right . He has provided support, encouragement, and direction with aspects beyond our wonderful sc ience. I hope that my future students will appreciate my leadership as much as I, and the rest of the group, appreciate his. Finally, absolutely none of this would be possi ble without my dear mother, Patricia Dianne Sheffield Jones. I was told all of my smarts came from her, and her desire to overcome so many odds while giving me everything I could have aske d are a testament to th e strength of AfricanAmerican women. Being able to support her has been a driving fo rce in pursuit of my degree; I look forward to fulfilling that dream.

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7 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ........10 LIST OF FIGURES................................................................................................................ .......11 ABSTRACT....................................................................................................................... ............15 CHAPTER 1 INTRODUCTION................................................................................................................. .18 The Macromolecular Theory and Conjugated Polymers........................................................18 Soluble Conjugated Polymers.................................................................................................20 Chemical and Electrochemical Oxidative Polymerization.....................................................21 Transition Metal-Mediated Polymerization............................................................................22 Polymerization Mechanisms...................................................................................................26 Stille Cross-Coupling......................................................................................................26 Suzuki Cross-Coupling....................................................................................................27 Yamamoto Cross-Coupling.............................................................................................29 Kumada Cross-Coupling.................................................................................................30 Rieke Cross-Coupling.....................................................................................................32 McCullough Cross-Coupling and Grignard Metathesis..................................................33 Electronic Effects in Conjugated Polymers............................................................................36 Doping and Optical Properties........................................................................................37 Electrochromism..............................................................................................................38 2 OVERVIEW OF EXPERIMENTAL METHODS.................................................................42 Monomer Characterization.....................................................................................................42 General Synthesis............................................................................................................42 X-ray Spectroscopy.........................................................................................................42 Polymer Charatcerization....................................................................................................... 44 Gel Permeation Chromatography-UV/VIS.....................................................................44 Differential Scanning Calorimetr y/Thermogravimetric Analysis...................................44 Fluorescence Spectroscopy.............................................................................................44 Polymer Electro chemistry......................................................................................................4 5 Repeated Scan Cyclic Voltammetry................................................................................46 Potentiostatic Deposition.................................................................................................47 Differential Pulse Voltammetry......................................................................................47 Electrochromic Characterization............................................................................................48 Spectroelectrochemistry..................................................................................................48 In situ Colorimetry..........................................................................................................48 Coloration Efficiency......................................................................................................49

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8 3 ALKOXY SUBSTITUTED POLY(3,4PROPYLENEDIOXYTHIOPHENE)S..................51 Dioxythiophene History......................................................................................................... .51 Chemically Polymerized Alkoxy Propylenedioxythiophenes................................................53 Monomer and Polymer Synthesis...........................................................................................54 Electrochemistry............................................................................................................... ......58 Electrochromism................................................................................................................ .....61 Photophysics................................................................................................................... ........65 Conclusion..................................................................................................................... .........67 Experimental Section........................................................................................................... ...68 Materials...................................................................................................................... ....68 Synthesis...................................................................................................................... ....68 4 ARYLOXY SUBSTITUTED POLY( 3,4-PROPYLENEDIOXYTHIOPHENE)S................73 Aryl Substituted Polythiophenes............................................................................................73 Aryl Substituted Propylenedioxythiophenes..........................................................................75 Monomer Synthesis.............................................................................................................. ..77 Electrochemistry............................................................................................................... ......82 Electrochromism................................................................................................................ .....85 Conclusion..................................................................................................................... .........90 Experimental Section........................................................................................................... ...91 Materials...................................................................................................................... ....91 Synthesis...................................................................................................................... ....91 5 REDUCIBLE SIDE GROUP POLY( 3,4-PROPYLENEDIOXYTHIOPHENE)S................94 Literature Review.............................................................................................................. .....94 Monomer Synthesis.............................................................................................................. ..97 Ambient Atmosphere Electrochemistry...............................................................................102 Electrochromism................................................................................................................ ...106 Inert Atmosphere and Reduction Electrochemistry..............................................................110 Conclusion..................................................................................................................... .......116 Experimental Section........................................................................................................... .118 Materials...................................................................................................................... ..118 Synthesis...................................................................................................................... ..118 APPENDIX A CRYSTALLOGRAPHIC DATA.........................................................................................120 B GEL PERMEATION CHROMATOGR APHY WITH PHOTODIODE ARRAY DETECTION...................................................................................................................... ..128 Chromatographic Theory......................................................................................................128 Column Choice..............................................................................................................128 Separation......................................................................................................................129 Calibration.................................................................................................................... .130

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9 Sample Detection...........................................................................................................132 GPC-UV-VIS................................................................................................................134 Operation of the GPC-UV/VIS Instrument..........................................................................135 Pre-Analysis Items.........................................................................................................135 Sample Analysis............................................................................................................136 Data Quantitation...........................................................................................................136 LIST OF REFERENCES............................................................................................................. 138 BIOGRAPHICAL SKETCH.......................................................................................................149

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10 LIST OF TABLES Table page 1-1. Applications and method of doped conjugated polymers......................................................37 3-1. Coloration Efficiency Data for chemically polymerized ProDOTs.......................................65 3-2. Calculated vibronic spacing (cm-1) for chemically polymerized polymers............................66 4-1. Coloration Efficiency Data for Aryloxy Substituted ProDOTs..............................................89 A-1. Crystal data and structur e refinement for ProDOT-EB.......................................................121 A-2. Crystal data and structur e refinement for ProDOT-(CH2OC6H5)2......................................123 A-3. Crystal data and structur e refinement for ProDOT-(CH2OPhMe)2.....................................125 A-4. Crystal data and struct ure refinement for ProDOT-(CH2OC6F5)2......................................127

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11 LIST OF FIGURES Figure page 1-1. Structures of some conjugated polym er classes. Polyacetylene, polypyrrole, polythiophene, polyphenylene, and polyphenylene vinylene are shown...........................18 1-2. Two examples of sol uble conjugated polymers.....................................................................20 1-3. Mechanism of radical-radical coupling in polythiophene......................................................21 1-4. Generalized catalytic cycle for tr ansition metal mediated cross coupling............................23 1-5. Tacticity in generalized pentads.......................................................................................... ...25 1-6. Regioisomers in 3-akylthiophene diads..................................................................................25 1-7. Mechanism of the Stille coupling.......................................................................................... .26 1-8. Mechanism of the Suzuki cross-coupling...............................................................................27 1-9. Generation of AB-type monome r for Suzuki polymerization................................................28 1-10. Yamamoto coupling via ze rovalent nickel catalyst..............................................................29 1-11. Mechanism of the Kumada coupling circa 1980..................................................................30 1-12. Mechanism of the Kumada coupling circa 1987..................................................................31 1-13. Regiospecific oxidative a ddition of activated Zinc in the Rieke coupling...........................32 1-14. Regioregular poly(3-alkylthio phene) via the McCullough method.....................................33 1-15. Diads produced by regioisomers during Grignard Metathesis.............................................34 1-16. YokozawaÂ’s proposed Catalyst Tran sfer Polycondensation mechanism.............................35 1-17. Polythiophenes having multiple color states........................................................................38 2-1. CIE 1931 Chromaticity diagram for PProDOT-EB...............................................................49 3-2. Synthesis of ProDOT-(CH2Br)2 using modified synthesi s of 3,4-dimethoxythiophene........55 3-3. Williamson etherification of ProDOT-(CH2Br)2 followed by bromination and Grignard Metathesis polymerization to give PProDOT-(CH2OC8H17)2 and PProDOT-(CH2OC10H21)2..................................................................................................56 3-4. Thermogravimetric analysis of PProDOT-(CH2OC8H17)2 and PProDOT-(CH2OC10H21)2..................................................................................................58

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12 3-5. Electrochemistry of ProDOT-(CH2OC10H21)2........................................................................59 3-6. Electrochemistry of ProDOT-(CH2OC8H17)2.........................................................................59 3-7. Button electrochemistry of PProDOT-(CH2OC10H21)2 in 0.1 M TBAPF6 and acetonitrile................................................................................................................... .......60 3-8. Spectroelectrochemistry of el ectrochemically deposited films..............................................62 3-9. Spectroelectrochemistry of chemically polymerized films...................................................62 3-10. In situ colorimetry of spray-cast polymer PProDOT-(CH2OC10H21)2.................................63 3-11. In situ colorimetry overlaid onto voltammet ric break-in of spray-cast PProDOT(CH2OC8H17)2....................................................................................................................64 3-12. Photophysical spectra for chem ically polymerized A) PProDOT-(CH2OC8H17)2 and B) PProDOT-(CH2OC10H21)2.............................................................................................66 4-1. Monomer structures for 3-octylth iophene, 3-(4-octylphenyl)thiophene, 3-(4-octyloxyphenyl)thiophene, a nd 3-(1,3-hexyloxyphenyl)thiophene...........................73 4-2. Aryl substituted propylenedioxyth iophene (ProDOT) monomer structures..........................76 4-3. Synthesis of aryloxy propylenedi oxythiophenes by Williamson etherification.....................78 4-4. Unit cell of ProDOT-(CH2OC6H5)2. Viewed along the C* axis.............................................79 4-5. Unit cell of ProDOT-(CH2OPhMe)2.......................................................................................79 4-6. Crystal packing in ProDOT-(CH2OPhMe)2...........................................................................80 4-7. Unit cell of ProDOT-(CH2OC6H5)2 viewed along the b axis.................................................81 4-8. Crystal packing in ProDOT-(CH2OC6H5)2.............................................................................81 4-9. Electrochemistry of ProDOT-(CH2OC6H5)2..........................................................................82 4-10. Electrochemistry of ProDOT-(CH2OPhMe)2.......................................................................83 4-11. Button electrochemistry of PProDOT-(CH2OC6H5)2 in 0.1 M TBAPF6 and acetonitrile....84 4-12. Button electrochemistry of PProDOT-(CH2OPhMe)2 in 0.1 M TBAPF6 and acetonitrile................................................................................................................... .......85 4-13. Spectroelectrochemistry of el ectrochemically deposited PProDOT-(CH2OC6H5)2 from TBAPF6 in ACN................................................................................................................86

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13 4-14. Spectroelectrochemistry of el ectrochemically deposited PProDOT-(CH2OPhMe)2 from TBAPF6 in ACN................................................................................................................87 4-15. In situ colorimetry of PProDOT-(CH2OC6H5)2 and PProDOT-(CH2OPhMe)2....................87 4-16. Tandem chronoabsorptometry/ chronocoulometry for a PProDOT-(CH2OPhMe)2 film.....88 5-1. Synthesis of electron poor aryloxy ProDOT monomers........................................................97 5-2. Synthesis of ProDOT-EB.................................................................................................... ...98 5-3. Unit Cell for ProDOT-(OC6F5)2 viewed along the a axis.......................................................99 5-4. Stacked views of ProDOT-(OC6F5)2....................................................................................100 5-5. Expanded View of Packing of ProDOT-(OC6F5)2 with intermolecular distances shown....100 5-6. Crystal packing for ProDOT-EB..........................................................................................101 5-7. Crystal packing for ProDOT-EB showi ng aryl-aryl distance measurements.......................102 5-8. Ambient atmosphere electrochemistry of ProDOT-(OC6F5)2..............................................102 5-9. Ambient atmosphere electrochemistry of ProDOT-(OPhCN)2............................................103 5-10. Ambient atmosphere electrochemistry of ProDOT-EB......................................................104 5-11. Button electrochemistry of PProDOT-(OC6F5)2 in 0.1 M TBAPF6 and acetonitrile.........105 5-12. Button electrochemistry of PProDOT-(OPhCN)2 in 0.1 M TBAPF6 and acetonitrile.......105 5-13. Button electrochemistry of ProDOT-EB in 0.1 M TBAPF6 and acetonitrile.....................106 5-14. Spectroelectrochemistry of PProDOT-(OC6F5)2................................................................107 5-15. In situ colorimetry of PProDOT-(OC6F5)2.........................................................................107 5-16. Spectroelectrochemistry of PProDOT-EB..........................................................................108 5-17. In situ Colorimetry of PProDOT-EB..................................................................................108 5-18. UV-VIS spectroscopy of PProDOT-(OPhCN)2.................................................................109 5-19. In situ colorimetry of PProDOT-(OPhCN)2.......................................................................110 5-20. Inert atmosphere electrochemistry of ProDOT-(OC6F5)2...................................................111 5-21. Cottrell-type analysis for PProDOT-(OC6F5)2...................................................................111 5-22. Inert atmosphere electrochemistry of ProDOT-(OPhCN)2................................................112

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14 5-23. Cottrell-type analysis for PProDOT-(OPhCN)2.................................................................112 5-24. Inert atmosphere electrochemistry of ProDOT-EB............................................................113 5-25. Differential pulse voltammetry of PProDOT-(OC6F5)2......................................................114 5-26. Differential pulse voltammetry for PProDOT-(OPhCN)2..................................................114 5-27. Differential pulse voltammetry for PProDOT-EB..............................................................115 5-28. Differential pulse voltammetry for PProDOT-(CH2OC6H5)2.............................................116 A-1. Crystal Structure Nu mbering for ProDOT-EB....................................................................120 A-2. Unit Cell for ProDOT-EB................................................................................................... .120 A-3. Crystal Structure Nu mbering for ProDOT-(CH2OC6H5)2...................................................122 A-4. Crystal Structure Nu mbering for ProDOT-(CH2OPhMe)2..................................................124 A-5. Crystal Structure Nu mbering for ProDOT-(CH2OC6F5)2....................................................126

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15 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 INCREASINGLY FUNCTIONAL POLY(3,4-AL KYLENEDIOXYTHIOPHENE)S THROUGH FACILE SUBSTITUTION By Adolphus Genay Jones May, 2007 Chair: John R. Reynolds Major Department: Chemistry This work presents the development of a se ries of poly(3,4-akylened ioxythiophene)s with the potential to be applied in sensors, batteries, capacitors, light emitting devices, and photovoltaic power generation. Both al koxy and aryloxy 3, 4-pr opylenedoxythiophene derivatives were prepared via Williamson ethe rification of the appropriate alcohol and a keystone molecule, 2,2-bis(bromomethyl)-3,4 -propylenedioxythiophe ne. The resulting monomers were purified and fully characterized, then subsequently poly merized via Grignard Metathesis or electrochemical deposition. The optoelectronic properties of the polymers were then studied and compared to similar materials. The first group of polymers stud ied was based on derivatizati on with linear alcohols, Octyl and decyl alcohol were used to produce pol ymer films via electrochemical deposition and soluble polymers via Grignard Metathesis polymerization. After purification by Soxhlet extraction, the chemically synt hesized polymers, PProDOT-(CH2OC8H17)2 and PProDOT(CH2OC10H21)2, gave Mn values of 38 kDa and 57 kDa by gel permeation chromatography in tetrahydrofuran. When compared, the optoelectronic propert ies of PProDOT-(CH2OC8H17)2 showed a maximum absorption at 574 nm, or approximately 2.2 eV, and PProDOT(CH2OC10H21)2 had a higher absorption at 584 nm, equivalent to 2.1 eV. The chemically

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16 polymerized analogues showed similar maximum ab sorptions near 597 nm. Both polymers were electrochromic, switching from deep purple to a transmissive, sky blue upon oxidation. The colorimetrically determined luminance change ( %Y) for these alkoxy substituted PProDOTs is 60%, while the contrast at max ( %T) between colored and transm issive states is 62%. The coloration efficiency of both polymers was determined with PProDOT-(CH2OC10H21)2 giving a maximum value of 1020 cm2/C. Aryl substituted polymers were synthesized to expand the PProDOT family, and to study the influence of aryl groups on ordering. Commerc ial phenol and cresol we re used to obtain the desired monomers which showed interesting pack ing structures by x-ray crystallography. Both ProDOT-(CH2OC6H5)2 and ProDOT-(CH2OPhMe)2 crystals aligned such that the thiophene of one monomer lay between the substituent aryl rings of another monomer. The crystal structure of ProDOT-(CH2OPhMe)2 suggested a much more open spacing, due to the accommodation of the methyl substituents, while ProDOT-(CH2OC6H5)2 took a herringbone order with the sulfur atoms between nearby aryl rings. The monomers were then electrochemically polymerized to give films which were characterized as electrochr omic materials. Both polymers had band gaps near 2.1 eV, oxidize to transmissive, grey films, and had luminance changes smaller than the alkoxy PProDOTs with values of 36% a nd 45% being observed for ProDOT-(CH2OC6H5)2 and ProDOT-(CH2OPhMe)2, respectively. PProDOT-(CH2OC6H5)2 showed a higher composite coloration efficiency of 581 cm2/C than PProDOT-(CH2OPhMe)2 at 377 cm2/C. The final series of polymers was based on electron-poor phenols that could undergo reductive electrochemistry. Synthesized similarly to the previous compounds, pentafluorphenyl, ethyl benzyl, and cyanophenyl derivatives of poly(3,4-propylenedioxythi ophene) were obtained after electrochemical polymerization. These molecules also demonstrated aryl-controlled

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17 ordering in the solid state, especially for PProDOT-(OC6F5)2, where a F-F interaction was observed. Electrochromic properties consistent with the previous aryl substituted PProDOTs were also observed. The reductive electroch emistry was studied using differential pulse voltammetry with only PProDOT-EB showing a reversible electrochemical cycle at E1/2 = -1.8 V versus ferrocene. This work expands the 3, 4-pr opylenedioxythiophene st ructural family of polymers, and provides a foundation for the use of aryl substituents as a means of controlling order in conjugated polymers.

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18 CHAPTER 1 INTRODUCTION The Macromolecular Theory and Conjugated Polymers No material has had a greater impact on mode rn than life than polymers, and synthetic organic chemistry has been a significant compone nt in the growth of polymer science. Prior to the First World War, macromolecular molecules were commercially available, but not fully characterized. Staudinger first propos ed the idea of a macromolecular structure.1 In the 1930’s, Wallace H. Carothers began the work that would lead many to call him the father of synthetic polymer chemistry. He successfully de fined the basic concepts of polymer structure from its starting materials.2,3 He surmised that polymer materials could be obtained from multifunctional monomer molecules through known synthetic organic chemistry, and the unusual stability of macromolecules was due to the primary covalent bonds within the molecule.3 This work led to the commercialization of Nylon-66, which was so successful that it was rationed during the Second World War. Now, one can fi nd polymers in diverse applications such as automotive materials,4 pharmaceuticals,5 coatings,6 and electronics such as semiconductors,7 batteries,8 and devices.9 The importance of these electronics has resulted in the scientific pursuit of conjugated, electroactive polymer materi als, commonly called “conducting polymers.” Conducting polymer research exploded in th e late 1970s due to the discovery of the electronic properties of doped polyacetylene.10 * * * * * * H N S * * * n * n n n n Figure 1-1. Structures of so me conjugated polymer classe s: polyacetylene, polypyrrole, polythiophene, polyphenylene, and polyphenylene vinylene.

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19 That discovery has produced academic research, industrial products, and a Nobel Prize based on the electronic and optical properties of these conjugated organic ma terials (Figure 1-1).11 Conjugated polymer devices such as light em itting electrochemical cells, a combination of luminescent and ion conductive po lymers with a salt between transparent electrodes, have been developed to compete with polym er based light emitting diodes.12 Both assemblies produce light upon application of voltage, however, LECs have lowe r turn-on voltages due to the included salt. This suggests LECs might be more useful in low power applications. Conjugated polymers have also become a foundation for the de velopment of chemical sensors.13 Conjugated polymer sensors respond to analytes based on changes in the polymer’s conductivity, absorption, and fluorescence. Biosensor applications have been studied extensively14 in response to both military and medicinal needs. Another unique application is the development of polymer batteries15,16 and capacitors.17 In these devices, the redox nature of conjugated systems accommodates ion exchange within the solid stat e medium. Conjugated polymers are envisioned as providing both ionic and electr onic transport while reducing the co mplexity in these systems. “Conducting polymers” should have a long research lifespan to provide intense academic and commercial interest. The fundamentals of conjugated polymers have been extensively reviewed in the primary chemical literature. Additionally, the dissertations of Carl Gaupp,18 Dean Welsh,19 Ben Reeves,20 Barry Thompson,21 and Avni Argun22 provide a fascinating examination of the ideas that underpin the field. Here, we will focus on the su b-discipline of solubl e conjugated synthetic methods. The necessary fundamental aspects will be illuminated, but the focus of this chapter will be the synthesis and characterization of soluble conjugated polymers.

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20 Soluble Conjugated Polymers Sustained research effort has b een directed towards increasing the solubility of conjugated polymers (Figure 1-2). The initial discoveries in “conducting polymers” involved insoluble, intractable polymer films, usually obtained in their doped states. The root cause of this insolubility is the inherent extended -conjugation in “conducting” polymers, which results in rigid-rod type polymers.23 Beginning with poly(p-phenylene), significant intellectual capital has been directed towards increasingly sol uble and processable conjugated polymers.24 O O (CH2)2 SO3K O O O O O O 3 3 n n Figure 1-2. Two examples of soluble c onjugated polymers. Poly[2-methoxy-5propyloxysulfonate-1,4-phenylenevinylene]25 and Poly[5-dodecyloxy-2-(2-{2-[2-(2methoxy-ethoxy)-ethoxy]-ethoxy}-1-{2[2-(2-methoxy-ethoxy)-ethoxy]ethoxymethyl}-ethoxy)-4,40dimethyl-biphenyl].26 Most approaches use flexible alkyl side -chains to induce disorder and prevent -stacking. Ionic groups have provided water solubility.25 Oxyethylene and crown ether derivatives can be used to induce conformational changes in the polymer backbone. These ionochromic polymers have their effective conj ugation lengths decreased.26 Soluble analogues of both poly(phenylene vinylene) and polythiophene have led to the deve lopment of all polymer devices, especially in the fields of electroluminescence,27 electrochromism,28-30 and photovoltaic7 devices. Soluble polymer devices have enabled significant understa nding of hole and electron transport properties through the development of orga nic field effect transistors.31,32 Thus, the synthetic organic chemistry is nearly as significant as the phys ical organic chemistry in conjugated polymers.

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21 Soluble conjugated polymers allow for more complete characterization via traditional methods. Structural repeat uni ts can be unambiguously defined, and polymer properties can be studied via gel permeation-size exclusion chroma tography, differential scanning calorimetry, and thermogravimetric analysis.33 Aspects such as morphology and its effect on conductivity, luminescence, and transport can also be studied.34,35 At the core of the soluble polymer approach are two distinct polymerization methods: the simp le, effective oxidation approach and the more chemically elegant transition metal-mediated approach. These two methods have allowed increased levels of structural control through organic chemistry. Chemical and Electrochemical Oxidative Polymerization The fundamental chemical process in oxida tive polymerization is the generation of a radical cation.36 As opposed to the doping process, th e radical produced dur ing polymerization is reactive and undergoes sequentia l radical-radical coupling (Figure 1-3). A stable free radical is generated on the monomer molecule; however, the aromaticity of the monomer is compromised. The restoration of aromaticity becomes the driv ing force for coupling between nearby radical molecules. The result of multip le coupling reactions is the desired conjugated polymer. S S S S S S H H S S [Ox] [Ox] S S S S S S H H S S S Figure 1-3. Mechanism of radical-ra dical coupling in polythiophene. This process is effected by the application of sufficient potential via electrochemistry, or the use of a chemical oxidant such as iron trichloride (FeCl3)37 or antimony pentafluoride (SbF5).38 In either case, the resulting polymer is more easily oxidized than the initial monomer

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22 heterocycle, resulting in the doped polymer form . In the case of thiophene a phenomenon known as the “thiophene paradox,” must also be considered.36,39 During electrodeposition, care must be taken to avoid performing the monomer oxidatio n at a potential which significantly overoxidizes the produced polymer. Chemical oxida tive polymerizations follow a similar path mechanistically in addition to side reactions that satisfy the catalytic or stoichiometry requirements of the chosen oxidant. Oxidative methods are useful to obtain polymer quickly. However, the lack of tolerance to functional gro ups and high reactivity pr ohibits study of more complex conjugated systems. Therefore, more ch emically tolerant polymerizations have been developed. Transition Metal-Mediated Polymerization Concomitant with the growth of conjugated polymer research has been the development of organometallic cross-coupling reactions. This is especially true for aryl carbon-carbon bond formation.40 The generation of sp2 C-C bonds directly from arom atic starting materials has provided a route to new chemical structures. That the method is useful for aromatic molecules has been especially beneficial for conjugated polymer research. Transition metal-mediated cross-coupling methods react aromatic halides wi th certain non-metals under the influence of a transition metal complex. These reactions allow th e use of easily available starting materials to produce molecules with significantly higher complexity. The reactions can tolerate multiple functional groups, and the products are often easily isolated and purified. The overall reaction is the sum of several specific component reactions (Figure 1-4). In polymerization reactions, these individual component reactions repeat multip le times to achieve high molecular weight macromolecules. The most important reactant is the transition metal catalyst chosen to perform the metal-mediated cross-coupling reaction.

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23 M(II) M(0) RMII X RX R MII R' R' R R'M' OxidativeAddition Transmetallation ReductiveElimination Figure 1-4. Generalized catalytic cycle for transition metal mediated cross coupling. M is the catalytic metal complex, and RX is the aryl halide component, RÂ’MÂ’ is the organometallic reagent. The catalyst transition metal operates from its 16 or 14 electron configuration, using the highest energy d and s orbitals. As a 16 electr on species, most transition metal complexes are unstable, or highly reactive, so they are stored as 18 electron compounds.41 The metal undergoes a preliminary reaction in which some of the starting material is consumed to produce the activated metal species. In the next step, the me tal inserts itself into the aryl halide bond, known as oxidative addition. The new organometallic reagent then undergoe s a ligand exchange between the metal center and the non-metal ar omatic molecule. This step is known as transmetallation, and may be extremely sensitive to additives in the reacti on medium, as seen in the Suzuki cross-coupling. Reduc tive elimination, the essential ke y of bond making, follows. It involves a return of the catalyst metal to a zerovalent oxidation state, and the disassociation of the two aromatic ligands to form a new C-C bond. The metal catalyst is now ready to re-enter the reaction process, completing the catalytic cycle. Ideally, the process continues until all starting material is consumed. However, most metal catalysts have a finite limit of reaction capability, often expressed as a turnover number. This is the number of moles of reactant substrate that a mole of cata lyst converts before dying.42

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24 The transition metal cross-coupling mech anism translates well to polymerization chemistry. The polymerization reaction maintains the chemical specificity seen in the small molecule analogues.43 Conveniently, this has meant the prevention of undesirable reactions, such Â’-coupling in polythiophene.44 Such chemical defects often lead to significant losses in the desired electronic an d optical properties.45 Conjugated polymer applications require that purification of the final polymer be high. Un-re moved catalyst can have deleterious effects to electronic properties and conjugate d polymer device performance. While any transition metal method can be appl ied, great success has been achieved using the approaches developed by Stille, Suzuki , Rieke, Kumada, Yamamoto, and McCullough. Mechanistically, these methods closely follow the general cycle (Figure 1-4), however the identity of the organometallic r eagent, or the active transition me tal complex changes. Various palladium and nickel catalysts have been developed, such as Pd(PPh3)4, PdCl2(PPh3)2, Pd(otolyl)3, NiCl2, NiCl2(dppp), and NiCl2(PPh3)2. Also, the nonmetal species undergoing transmetallation can be zinc, tin, boronic este rs, and especially, Grignard reagents. These individual methods will be discussed in greater detail. A significant advantage of employing known s ynthetic organic chemistry is functional group specificity. Reactions occur only between compatible functional groups. In the case of aromatic and heteroaromatic systems, all functi onal groups are not created equal. Due to either steric or electronic constraints within the monomer, the result ing repeat unit, and its local stereochemistry, may greatly affect the electronic or optical performance. In traditional polymer science, the organization of side chains due to steric effects is calle d tacticity. Even though polymer repeat units are struct urally equivalent, the relative stereochemistry between adjacent repeat units and substituen ts can vary greatly.

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25 Sighting down the main chain backbone, substitu ents may be arranged such that they lie all to one side of the backbone, or alternate sides of the backbone, or have some indeterminable position along the backbone. Thes e stereoisomers (Figure 1-5) ar e called isotactic, syndiotactic, and atactic, respectively. Adjacent repeat units may also show a preference for configuration, called regioregularity. Regioregul ar polymers are often described as having head-to-tail, head-tohead, and tail-to-tail configuration (Figure 1-6). R R R R R R RR R R R R isotactic syndiotactic atactic Figure 1-5. Tacticity in generalized pentads. S R X X head tail S R X S R X S R X S R X S R X S R X head-to-head head-to-tail tail-to-tail Figure 1-6. Regioisomers in 3-akylthiophene diads. Conjugated polymers with primarily H-T configurations thro ughout the polymer backbone have demonstrated improved conductivit y, hole mobility, and de vice performance over regiorandom and regi oirregular analogues.27,32,45 These configurations allow for greater orbital overlap by eliminating steric congestion due to substituents.46 Transition metal synthetic methods control the polymer regiochemistry becaus e of the functional gro up specificity of crosscoupling reactions. Transition metal methods also allow the polymer morphology to be

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26 controlled via incorporation of differing repeat unit precursors.47 The synthesis of regioregular conjugated polymers is a significant asp ect of soluble conjugated polymers. Polymerization Mechanisms Stille Cross-Coupling The Stille reaction (Figure 1-7) has developed into an invaluable synthetic technique for the conjugated polymer organic chemist.48 Its utility goes beyond polym erization, as it is often used to construct multi-ring monomers for electrochemical polymerization studies.49 In polymerization, its advantage is that starti ng materials can be synthesized and purified separately. The stannyl reagent is also stable to air and moisture, simplifying the handling of monomer compounds. The Stille reaction allows synthetic chemists to design polymers with multiple aromatic rings in the repeat unit.50 Pd0 R1X PdIIR1 X PdIIR1 R2 R2SnMe3 R1R2 PdX22 R2SnMe3 R2PdR2 XSnMe3R2R2 Figure 1-7. Mechanism of the Stille coupling.51 Classically, one reactant is synt hesized as an aryl halide or triflate. This is the reaction electrophile and undergoes the initial oxidative addition step. In most systems, the halide will be placed on the more electron poor monomer. Low electron density is thought to encourage the oxidative addition step in conjugated polymer synthesis.50 Conversely, the more electron rich co-monomer is usually converted to the trialkls tannane reageant. The reagent acts as the nucleophile in the organometall ic reaction and undergoes hete rolytic cleavage to lose R3Sn+.51

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27 The stannane is significant to the transmetallation step. While several exceptions have been reported, it is accepted that the transmetallation pro cess is the rate determining step of the Stille catalytic cycle. The reaction is complete wh en the newly formed A r-Ar bond is produced by reductive elimination. The catalyst, a pallad ium[0] complex, re-enters the cycle to add subsequent monomer molecules. This suggests to the organic polymer chemist that the reaction should follow traditional step-growth kinetics, resulting in very low molecular weight until monomer conversion to polymer has passed 99%.52 Stille polymerizatio ns have recently been used to produce very low gap polymers having an estimated band gap of 0.7 eV.53 Suzuki Cross-Coupling A close cousin of the Stille coupling, the Suz uki reaction is also a palladium catalyzed reaction.54 (Figure 1-8) Boronic acids and esters serve as the organometallic reagent that undergoes transmetallation to the pallado-aryl-h alide. Similarly, thes e boronic esters are relatively easy to handle and purify. Pd0(PPh3)2 R1X PdII(PPh3)2R1 X PdII(PPh3)2R1 R2 R2B(OR2) R1R2 Pd(PPh3)42 x PPh3 Figure 1-8. Mechanism of the Suzuki cross-coupling. The selections of halide and organoboron species involve elec tronic considerations, vis-àvis electrophile-nucleophile inte ractions. More importantly, Suz uki-type polymerizations allow the polymerization of single monomers whic h have both the halide and organoboron functional groups.55 In the languag e of polymer chemistry, these difunc tional molecules are referred to as AB-type monomers. AB monomers obviate the concerns for perfect stoichiometric balance due

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28 to the inherent balance provided by having bot h functionalities on a single monomer compound. Perfect stoichiometry can be achieved by converting aryl halides into the de sired boronic acid or ester (Figure 1-9). Ar X X Conversion to Boronate Ar X (RO)2B Suzuki Polycondensation Ar * * n Figure 1-9. Generation of AB-type m onomer for Suzuki polymerization. The aryl halide is singly lithiated and converted via reaction with trimethylborate.56 The boronic acid is produced upon work up, and subseque ntly esterified usin g any desired alcohol derivative. Unlike the Stille reaction, several drawbacks limit the application of Suzuki polycondensation in conjugated polym er synthesis. The Suzuki re action is heavily influenced by the nature of the base added to encourag e the transmetallation of the boronic esters.54 As the reaction progresses, the esters may hydrolyze completely away from the aromatic molecule, preventing continued polymerization.57 Another phenomenon was obs erved during the synthesis of poly(p-phenylene). A side reaction occurs between the aromatic rings of the phosphorus ligand of the palladium catalyst. In this case, the aromatic ring on th e growing polymer chain exchanges with the aromatic ring of the tripheny lphosphine ligand when both species are part of the palladium intermediate. This leads to conjugation-breaking def ects or growth-killing diphenylphosphine endgroups.58 Both defects reduce the polymersÂ’ -conjugation, and phosphorus may destroy the photophysic al processes. This defect can be avoided by use of (tri-otoluyl)phospine rather than triphenylphosphine as a ligand on the palladium[0] catalyst.59 Currently, Suzuki polymerizations are the met hod of choice to produce water soluble polymers,60 as well as polyelectrolyte synthesis.25

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29 Yamamoto Cross-Coupling Palladium catalyzed methods described above re present the current interest in more robust syntheses. However, the history of metal me diated coupling lies with nickel catalysis. Described as a dehalogenation condensation re action, the Yamamoto coupling has developed from the initial success of the Kuma da coupling reaction (Figure 1-10).61, 62 The Yamamoto coupling distinguishes itself due to its use of a zerova lent nickel complex as the catalyst species. Ni0LnAr X X Ni0LnX Ar X Ni0LnX Ar X Ni0LnX Ar X Ni0LnAr Ar X X Ni0LnX2Ni0LnAr Ar X X Ar2X X Ni0Ln Figure 1-10. Yamamoto coupling vi a zerovalent nickel catalyst. The reaction is improved by cis-bidentate ligan ds on the nickel cente r, as those ligands allow the reductive elimination step to proceed much more easily. Mechanistically, there is some divergence between the nickel zero cataly sis and other cross-c oupling reactions. The Yamamoto coupling does not involve a transmetallation step because the coupling occurs between two aromatic dihalides. After the ox idative addition step, two arylnickel halides undergo a disproportionation reaction.63 The result of this step is th e transfer of one of the aryl groups to give a bisarylnickel ha lide. Reductive elimination then occurs to give the coupled aromatic halide and zerovalent ni ckel. The other nickel center is converted to its dihalide. The reaction has been applied in polyphenylenes,64 polythiophenes,65 polypyridines,62 and electron poor aromatic polymers such as 2,3-diarylquinoxaline,66 phenanthroline,67 and bithiazole.68 In its initial reports, an increase in head to head coupling over oxidat ive polymerization in

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30 polythiophene was observed. The 5-position of 3-alkylthiophene is less sterically hindered, which is thought to ease the oxidative addition step. The met hod has been extended to chiral substituted arylenes,64 post-polymerization r eactive materials such as a poly(benzotriazole) substitituted with carbazole,69 and polypyrroles.70 Kumada Cross-Coupling Before the Yamamoto, Suzuki, and Stille couplings, transition metal cross-coupling reactions tended to be very sp ecific and lacked broad applicabili ty to many chemical compounds. The development of the Kumada cross-coupli ng paved the road to the coupling methods previously discussed.71 Two reports in 1972 demonstrated th e coupling of an aryl halide with Grignard reagents.72 Catalyzed by a nickel-phospine complex, the synthesis of trans-stilbenes, ethylbenzene, and dibutylbenzene was shown. These results spurred the development of transition metal mediated reactions. KumadaÂ’s extensive review in 1980 outlined the catalytic cycle view of organometallic mechanisms (Figure 1-11).73 NiIIL2NiL2X2R2MgX NiL2R2 R2 R2MgX NiIIL2R1 R2 NiIIL2R1 R2 R1R2 22MgX2R1X R2R2R1 X R1X R1X Figure 1-11. Mechanism of th e Kumada coupling circa 1980.73 An induction period where the Ni( II) starting material is converted to an organohalo Ni(0) complex was suggested. During the induction peri od, two equivalents of aryl Grignard reagent exchange with the halogens on the Ni(II) complex. The resulting bisorga no nickel complex then adds the organiohalide to obtain an organohalo nickel(II) complex. The final complex then

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31 enters a catalytic cy cle involving transmetallation, associ ation of another molecule of organohalide, and reductive elimination of the cr oss-coupled product. By 1986, the reaction was represented as a radical chain process involving an equilibrium between Ni(I) and Ni(III) (Figure 1-12).74 NiIX e Ar'X NiIIIX2Ar' ArMgX NiIIIX Ar' Ar MgX2 Figure 1-12. Mechanism of th e Kumada coupling circa 1987.74 The cycle was initiated by an electron transfer to the aryl halide, or electrochemically, to give an organohalo Ni(III) complex. This Ni(I II) undergoes transmetallation with the Grignard or organozinc regeant. Reductive elimination from the bisorganohalo Ni(III) gives the crosscoupled product. This secondary mechanism appears to be operable on -allyl or aryl complexes, with the 1980 mech anism more applicable to 1 or 2 alkyl Grignard reagents. The effect of phosphine ligands on the catalyt ic activity of nickel has been studied thoroughly.73,74 Diphenylphosphino propane (dppp) is th e ligand of choice for unhindered alkyl and aryl Grignard reagents. Allylic and vinylic Grignard reagents proceed more smoothly with dimethylphosphino ethane (dmpe), which is an electron donating ligand. Sterically hindered Grignard reagents proceed with two simple tr iphenylphosphine ligands. Phospine-free Ni salts have also been shown to give cross-coupled prod ucts with aryl Grignard regeants. The reaction has also been applied to asymmetric cross-coupling.75

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32 As time passed, the Kumada coupling was modi fied to replace the Gr ignard reagent with zinc, boron, and tin organometallic species, and palladium replacing nick el as the catalytic metal. The application of palladium was noted due to its greater tolerance fo r functional groups, and fewer side reactions which were plentiful with nickel catalysis.71 Those improvements have resulted in the wealth of cross-coupling met hods available for the synthesis of conjugated polymers. However, nickel-mediated methods have found renewed interest through the development of regioregular conjugated polymers. Rieke Cross-Coupling The use of activated zinc to produce regi ogregular polymers has been developed by Reuben Rieke.76,77 The production of “highly reactive” zinc from the reduction of ZnCl2 by lithium naphthalide produces a metal which unde rgoes oxidative addition to halides easily.78 In the case of polythiophenes, this ox idative addition occurs predomin ately at the 5 position, with 2bromozinc-5-bromothiophene occurring (Figure 1-13). The regioselectivity is approximately 97-98%.79 S R Br Br Zn*/THF S R Br BrZn S R ZnBr Br Figure 1-13. Regiospecific oxidative addition of activated Zinc in the Rieke coupling.77 Both the choice of metal and the ligand involve d affect the regiosel ectivity observed. The reaction is catalyzed by both ni ckel and palladium, with the latter leading to decreased regioregularity. The transmetallation/disproport ionation steps are rate-d etermining. The larger metal ion and smaller ligand produced regiora ndom polythiophenes in any combination. The Rieke method is sensitive to the steric c ongestion in the catalyst-thiophene complex.

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33 McCullough Cross-Coupling and Grignard Metathesis The development of polymerization met hods that produce regioregular polymer structures is a significant aspect of conjugated polymer research.80 Some of the initial approaches to regioregular polyt hiophenes involved the polymeriza tion of dimer molecules. In these cases, the head-to-head or tail-to-tail dimer was synthesized separately. A head-to-head bithiophene was produced by self-coupling a 2iodo-3-alkylthiophene us ing a Ni(0) catalyst.46 When compared to oxidatively produced polythi ophene, the regioregular head-to-head polymer showed an increased band gap, likely due to steric repulsion. Tail-to-t ail analogues were also synthesized, showing strong regior egularity and increased band gap.81 Recently, these types of regioregular systems have been st udied for use in photovoltaic devices.82 The remaining regioregular system, head-to-tail , has provided the bulk of resear ch interest. This was first delineated by the McCullough group (Figure 1-14). S R Br S R Br Li LDA MgBr2 Et2O S R Br BrMg NiCl2(dppp) S R Br S R S R H n Figure 1-14. Regioregular poly(3-alky lthiophene) via the McCullough method.80 A polythiophene of near 100% head-to-tail couplings was produced by Kumada coupling of 2-bromo-3-alkyl-5magnesiobromo-thiophene.45 The Grignard reagent is introduced regiospecifically through the l ithiation of 2-bromo-3-alkylthiophene. Lithium diisopropylamide is used because it does not perform metal-halogen exchange.83 Subsequent reaction with magnesium dibromide etherate gave the desired Gri gnard reagent. This me thod is currently used in the synthesis of non-alkyl substituted thi ophenes. Iraqi has synthesized both ferrocene84 and anthraquinone85 derivatives via the Mc Cullough regioregular polymerization. The Rieke method, described above, also pr oduces head-to-tail polythiophenes.79 However, the

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34 McCullough method avoids the regi oregularity controlli ng isomers present in the Rieke method. McCullough has expanded the chemical sy nthesis of polythio phenes via Grignard Metathesis.86,87 Grignard Metathesis (GRiM) involves the magnesium-halogen exchange between a thienyl halide and an alkyl Grignard reagent (Figure 1-15). The exchange occurs with a regiospecificity of approximately 80:20 in favor of the 5-position of 3-alkylthiophene. S R Br BrMg S R MgBr Br NiCl2(dppp) S R BrMg S R Br A B S R MgBr Br S R MgBr Br S R Br S R MgBr NiCl2(dppp) S R Br BrMg C S R Br BrMg S R BrMg S R Br NiCl2(dppp) HT-PT Regioregular Polymer with a single defect Figure 1-15. Dyads produced by regioisomers duri ng Grignard Metathesis. A) Coupling of both regioisomers gives mostly head-to-tail polym er with a single defect. B) Self-coupling of minor regioisomer gives head-to-ta il polymer. C) Self-coupling of major regioisomer give head-to-tail polymer. The 20% 2-substitution results in a polymer chai n with a single defect, but otherwise gives the desired head-to tail polythi ophene. GRiM has been applied in the synthesis of various functional polythiophenes, including chiral,88 solvatochromic,89 and photovoltaic90 polymers. The key advantage of GRiM is that it allows fo r the production of larger amounts of regioregular polymer. That the reaction can be performed at ambient or reflux temperature is an additional improvement above other polymerization methods. There has been vigorous debate into the polymerization mechanism of the GRiM reac tion. Since the catalyst is often NiCl2(dppp), it was presumed to follow a catalytic cycle similar to the Kumada coupling, which was presumed to be

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35 a step growth-type mechanism.87 This is due to the observe d broad polydispersities, and uncontrolled molecular weights. However, Yokozaw a suggested that GRiM actually proceeds by a chain growth process.91 In the reaction of 2-bromo-3-he xyl-5-iodothiophene with isopropyl magnesium chloride and 0.4 mol % NiCl2(dppp) head-to-tail poly( 3-hexylthiophene) was produced with a conversion profile of 50% af ter 15 minutes, 75% afte r 1 hour, and 93% in 1 day. From gel permeation chromatography of the cr ude polymer, it was determined that a PDI of ~1.3-1.4 persisted throughout the polymerization. The addition of “new” monomer was also added to a pre-polymer sample of poly(3hexylthiophene). This “monomer-addition” experiment resulted in the doubling of the molecular weight from 8900 to 17200 and no change in the PDI of 1.34.92 Yokozawa proposed two possible mechanisms: 1. the carbon-metal bond in the monomer suppresses oxidative addition of the nickel catalyst93 or 2. the nickel catalyst fails to diffuse away from the growing polymer chain end via coordination to the bond or sulfur lone pair. McCullough confirmed that the older magnesium dibromide etherate method proceeded via a chain growth mechanism by produc ing block copolymers from the ends of headto-tail polythiophenes.94 Later, it was suggested that the po lymer chain exists as an associated pair with the nickel comple x after reductive elimination.95 Yokozawa further proposed the “catalyst transfer polycondensation” model (Figur e 1-16) with the nickel catalyst moving to the end of polymer chain, but never disassociating from the polymer.96,97 S ClMg Br R NiCl2(dppp) S ClMg NiL2 R S Br R S ClMg R S NiL2Br R S ClMg R S NiL2 R S Br R S ClMg R S R S NiL2Br R Figure 1-16. Yokozawa’s proposed Catalyst Transfer Polycondensation mechanism.97

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36 McCullough has continued to demonstrate the living or near living nature of GRiM by performing various end functi onalization of the monomers, 98 and sequential monomer addition.99 These nickel catalyzed met hods will be essential in the development of soluble conjugated polymers, especially as these materials incorporate gr eater chemical functionality. The tolerance to functional groups, regiospecificity, control of mo lecular weight, and scalability will provide conjugated polymer chemists with very impressive to tools to generate polymers for increasingly complex applications. Electronic Effects in Conjugated Polymers Conjugated polymers are interesting due to the electronic and optical properties that result from the extended system in conjugated aromatic systems. These properties are intimately associated with the polymerÂ’s molecular weight.100 Conjugated polymers can be represented as a series of concatenated p orbita ls. As two p orbitals form a bond in small molecules, multiple p orbitals produce extended electron density in conjugated polymers.101 This is illustrated in polyacetylene. As the p orbitals combine in to conjugated systems, polyacetylene undergoes a geometric distortion rather than producing a macromolecule of single bond length. The distortion is similar to a PierlÂ’ s distortion and produces two types of electron density within the conjugated macromolecule.102 The system splits into an unfilled, higher energy orbital and a filled, lower energy orbital. While more closel y related to the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of frontier molecular orbital theory, these orbitals can be interpreted in th e solid state physics cons tructs of valence and conduction bands. The separation between the two orbitals is called the band gap, and determines the ease of access to th e polymersÂ’ electronic properties.103 The size of the band gap relates to electronic performance, with no band gap being a conducting species, band gap less

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37 than 3 – 4 eV being a semiconductor, and band gap greater than 3 – 4 eV be ing an insulator. The band gap also controls a conjugated polyme r’s optical properties, as it serves as the * transition. The control and modi fication of band gap is a significant portion of conjugated polymer research.104-107 Doping and Optical Properties Access to the electronic and optical properties in conjuga ted polymers is granted via doping. Doping is the creation of charge within the extended system. This may occur by removing or adding a single electron along the polymer chain. These oxidation and reduction events may occur on multiple regions along the chain. Doping may be performed by several methods with specific applications (Table 1-1). Table 1-1. Applications and met hod of doped conjugated polymers Method Counter-ion Application Chemical Supplied by dopant compound Antistatic coatings, transparent electrodes Electrochemical Supplied by supporting electrolyte Batteries, light emitting electrochemical cells Metal-Polymer junction None FETs, LEDs Photochemical None; donor-acceptor charge transfer Photovoltaic devices Chemical and electrochemical doping usually in volves the transport of a counter-ion throughout the bulk polymer. Methods that do not involve counter-ions have received significant attention. Field effect transistors, photovoltaic devices , and light emitting diode s all involve charge creation in neutral polymers. The ultimate resu lt of doping is the generati on of electronic states within the band gap region.108 The singly doped state is called a polaron, and can be construed as a radical cation which rearra nges the neutral aromatic struct ure to a quinoidal system. A second oxidation produces a bipolaro n, or di-cation. These intra-gap states are responsible for the optical and electronic properties of conjugated polymers. The band gap can be viewed as a *

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38 absorption in the electromagnetic spectrum. Upon doping, this absorption shif ts to lower energy. The effects of these change s are the basis for the polym er devices developed today. Electrochromism Chromism is the reversible change in the colo r of a material due to some stimulus. Most chromic phenomena are the result of conjuga tion breaking conformational changes in the polymer, which can be induced by solvent, temperature, and absorption of light.109 More useful is electrochromism.110 This is the reversible change in the absorption or transmission properties due to an external voltage. In addition to c onjugated polymers, electrochromism has been shown in inorganic oxides,28 viologens,34 and nanoparticle-metal oxide composites.111 Electrochromic materials can be classed according to their color states (Figure 1-17). Materials may transition between a colored and bleached state, between two color states, or between multiple color states. N S S S S S OC12H25 C12H25O * * O O O O O O O O O O * * * * Me n n n PBEDOT-NMeCz PBEDOT-BP LPEB Figure 1-17. Polythiophenes having multiple color states. PBEDOT-NMeCz = Poly(bisEDOTn-methyl carbazole) has three color states : sky blue, green, and yellow. PBEDOT-BP = Poly(bisEDOT-biphenyl) has two color st ates: navy blue, and light brown. LPEB = Linear poly(EDOT-benzene) has three color states: blue, green, orange.112 Color control can be achieved synthetically by substitution of the polymer repeat unit.112 Adding electron withdrawing or donating subst ituents affects the HOMO and LUMO energy levels and the polymer band gap. Substituents can also be used to affect the conformational

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39 properties of the polymer. Similar to ionochrom ic polymers discussed earlier, the effective conjugation length is modified due to the steric requirements of substitution. Copolymerization is another means to control color states. The incorporation of differing aromatic groups, some heterocycl ic, typically results in a hybri d electronic system. This is especially seen in systems whic h use the donor-acceptor approach.106,113 The perception of color is inhe rently subjective. Therefore, effort has been made to standardize the measurement and representation of color in science. The result has been the definition of three components,114 which have been used to quantify electrochromic materials. Hue, also called dominant wavelength or chroma tic color, is the speci fic wavelength of light associated with an observed color. Saturati on, also called chroma, t one, intensity, or purity, describes the level of white or black observed. Finally, brightness is also referred to as value, lightness, or luminance. These attributes are most often reported against the The Commission Internationale de lÂ’Eclairage (International Commi ssion on Illumination) scal e, in particular the CIE 1931 Yxy . In this system, luminance is repr esented by Y, while hue and saturation correspond to x and y. Yxy values can be converted to a 2-D pl ot with predictive function for the colors observed in a material. The quality of electrochromic polymers is measured with several methods. The most significant feature of electrochromic materials is the contrast between the colored and bleached states, usually corresponding to neutral and oxidized polymer. This contrast is usually given as the change in percent transmittance at the wavelength of highest optical contrast. However, it is also instructive to follow the change in color with applied potential. In those cases, the ratio of polymer luminance to purely transmissive luminan ce versus voltage can be recorded in a process

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40 known as in situ colorimetry.112 Relative luminance measures th e perception of brightness with respect to the human eye.115 A second measure is the switching speed of th e material. The time that passes between colored and bleached states is significant for dynam ic applications which may use the material as an on/off marking system. The electrolyte ioni c conductivity, diffusion ability of ions to the polymer chain, and applied potenti al magnitude all affect the sw itching speed. The thickness and morphology of thin films also strongly influences the switching time. The third measure of electrochromic quality is the coloration efficiency, sometimes called electrochromic efficiency. CE can be used to determine the change in optical density due to amount of charge transport th rough an electrochromic polymer . Typically reported as in cm2/C, the measurement is performed at a spec ific wavelength, record ing the bleached and colored transmittance. In this document we w ill use composite coloration efficiency, which captures the overall optical density change for a near complete optical switch.116 Reviews of devices which use electrochromism can be found in the primary literature.117 Thesis of this work This work presents the synthesis and ch aracterization of a series of poly(3,4akylenedioxythiophene)s. In Chapter 3, two pol ymers with medium length alkoxy chains will be studied. These compounds will be compared to prior alkoxy ProDOTs to complete the family of linear, soluble, alkoxy ProDOT polymers. Ch apter 4 begins the incorporation of aryl substituents into dioxythiophene polymers. The compounds are e xpected to demonstrate that aryl groups can control the orde ring of dioxythiophene polymers while maintaining the desirable optoelectronic properties. Electrochemical deposi tion will be used to prepare these polymers, and the effect of aryl substitution on the electrochromic properties will be characterized. Chapter

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41 5 will attempt to produce materials with an electroactive process separate from the main dioxythiophene chain. The emphasis will be placed on the synthesis and characterization of these materials as foundation to extend the family of poly(3,4-aklyenedioxythiophene) polymers.

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42 CHAPTER 2 OVERVIEW OF EXPERIMENTAL METHODS Monomer Characterization All compounds were characterized by 1H and 13C NMR and high resolution mass spectrometry. Spectra were recorded on a Gemini 300 FT-NMR, a VXR 300 FT-NMR, or a Mercury 300 FT-NMR. Elemental analyses were performed by Spectroscopic Services at the University of Florida, Department of Ch emistry. High resolution mass spectrometry was obtained by Spectroscopic Services at the Univers ity of Florida, Department of Chemistry using either a Finnigan MAT95 Q Hybrid Sector, an Agilent 6210 time-of-flight LC/MS, or a 4.7T Bruker Bioapex II Fourier Transform Ion Cyclot ron Resonance mass spectrometer equipped with a Bruker Apollo API 100 source. Typically, th e method of introduction to the spectrometer was electrospray ionization or direct infusion with Harvar d Apparatus PHD 2000 Injector. General Synthesis All chemicals were used as purchased, or purified according to standard procedures.118 Specific experimental details are pres ented at the end of each chapter. X-ray Spectroscopy X-ray information was obtained by the Center fo r X-ray Crystallography at the University of Florida, Department of Chemistry. 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 Ã…). Cell parameters were re fined using up to 8192 reflections. A full sphere of data (1850 fram es) was collected using the -scan method (0.3 frame width). The first 50 frames were re-measured at the end of da ta collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces.

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43 The structure was solved by the Direct Methods in SHELXTL6 , from Bruker-AXS, Madison, Wisconsin, USA, and refined using full -matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. For ProDOT-(OPh)2, The asymmetric unit consists of four half molecules; all molecules are located on 2-fold rotation axes. A total of 473 parameters were refined in the final cycle of refinement using 5525 reflections with I > 2 (I) to yield R1 and wR2 of 3.92% and 8.58%, respectively. Refinement was done using F2. For ProDOT-(OPhMe)2, The asymmetric unit co nsists of a 1.5 molecu le and a molecule of dioxane. The latter was severely disordered and could not be modeled properly, thus program SQUEEZE,119 a part of the PLATON120 package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. A total of 380 parameters were refined in the final cycle of refinement using 5632 reflections with I > 2 (I) to yield R1 and wR2 of 4.14% and 10.71%, respectively. Refinement was done using F2. For ProDOT-EB, The methyl group on C26 is diso rdered and is refine d in two parts with their site occupation factors depende ntly refined. A total of 328 parameters were refined in the final cycle of refinement usi ng 15901 reflections with I > 2 (I) to yield R1 and wR2 of 4.71% and 12.17%, respectively. Re finement was done using F2. For ProDOT-(OC6F5)2, a total of 325 parameters were refined in the final cycle of refinement using 6414 reflections with I > 2 (I) to yield R1 and wR2 of 3.61% and 10.25%, respectively. Refinement was done using F2.

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44 The toluene molecule were disordered and could not be modeled properly, thus program SQUEEZE,119 a part of the PLATON120 package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. Polymer Characterization All polymers were characterized by 1H and 13C NMR on a Gemini 300 FT-NMR, a VXR 300 FT-NMR, or a Mercury 300 FT-NMR Gel Permeation Chromatography-UV/VIS GPC was performed on two 300 x 7.5 mm Poly mer Laboratories PL Gel 5 µM mixed-C columns with a Waters 2996 phot odiode array detector at the max of the polymer solution. Polymer solutions (0.5 mg/ml) were prepared in THF, and the retention times were calibrated to known polystyrene standards. Differential Scanning Calorimetr y/Thermogravimetric Analysis Thermogravimetric analysis was obtained with a Perkin-Elmer TGA 7 thermogravimetric analyzer at a heating rate of 20 C/min from 55 C to 850 C under nitrogen. Differential Scanning Calorimetry (DSC) wa s performed on a TA Instruments DSC Q1000 equipped with liquid nitrogen cooling accessory ca librated with sapphire and indium standards. All samples were prepared in hermetically sealed pans (4-7 mg/sample) and were referenced to an empty pan; samples were scanned from -150 °C to 250 °C at 10 °C per min. Fluorescence Spectroscopy Fluorescence data was collected with a Sp ex F-112 photon counting fl uorimeter at room temperature. Emission quantum yields of the polymer solutions were measured relative to Rhodamine 6G in methanol using known procedures.121 The standard spectrum was obtained from the Alphabetical Index of Photochem CAD Spectra122 on the Oregon Medical Laser Center website. Rhodamine 6G shows a fluorescence qu antum efficiency of 0.95 when excited at 480

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45 nm. At this excitation wavelength, the polymer solution still exhibits a significant absorbance that facilitates photoluminescence. The concentrations of the solutio ns were chosen such that the absorbance at 480 nm was close to 0.1. Polymer Electrochemistry Electrochemical studies were carried out using an EG&G PAR model 273A potentiostat/ galvanostat in a three electrode cell configuration consisting of a Ag° wire pseudo reference electrode, platinum button (0.02 cm2), or indium-tin oxide (ITO )-covered glass slide (7 x 50 x 0.6 mm, 20 /cm) as the working electrode, and a Pt flag or wire as the c ounter electrode in a 0.1 M tetrabutylammonium hexafl uorophospate-acetonitrile solution. The use of button electrodes allowed the study of the electrochemical properties of the monomer and electrochemically de posited polymers. The ITO-covered glass slides were used as transparent electrodes for electrochromic and spect roelectrochemical study of the polymer films. For electrochemical experiments th at did not involve optical meas urements, a platinum flag was used to increase surface area of the counter elec trode and improve current flow. For use as a pseudo reference, silver wire was sanded to rem ove any residual oxides. The silver wire was calibrated after each experiment by the additi on of ferrocene to the electrolyte solution. All potentials are reco rded versus Fc/Fc+ by subtracting the E1/2 of ferrocene from the potential of the silver wire. The Fc/Fc+ redox couple is a reversib le redox process where the concentrations of oxidized and reduced sp ecies are predicted by the Nernst equation. Additionally, the peak to peak separation ( Ep) at 25 °C is 58 mV although some processes having Ep of 6065 mV are considered reversible. The ratio of the anodi c and cathodic peak currents is 1, and the peak currents typically scale linearly with the square root of the scan rate.

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46 It should be noted that all films, prior to el ectrochemical study, are switched between their oxidized and reduced states several times to condition the polymer a nd promote electrolyte transport through the films. This “break-in” behavior is stabilized after several cycles resulting in more reproducible expe rimental observations. Repeated Scan Cyclic Voltammetry Much of the analysis in this work is obtai ned from repeated scan cyclic voltammetry experiments. In this experiment, the applied po tential is varied over ti me at a constant rate, called the scan rate, while the current is meas ured. The current response is proportional to the rate of electrolysis of the elec troactive species at the electr ode, and higher rates of current response imply higher el ectrolysis rates. With respect to conjugated polymers, cyclic voltammetry results in the generation of radical species which couple to form oligomers and polymers. These polymers then deposit onto the electrode surface. Subsequent cyclic voltammetric scanning leads to the accumulation of electroactive material on the electrode, and it is this material whose electronic systems are studi ed. In the initial scan, very little current response is observed until the monomer oxidation potential, Ep,m, is reached. The resulting deposition shows a nucleation loop, due to the increased surface ar ea of the electrode. As the applied potential switches to a more reducing value, the curre nt response falls until the reduction of the adsorbed polymer is observed at the polymer reduction potential, Ep,c. Subsequent scans show the polymer oxidation potential, Ep,a, in addition to the other re sponses. Each scan also occurs at a larger current valu e than the prior one due to th e increased surface area of the electrode. The electrochemical potential values can be converted to HOMO-LUMO values by adding the energy distance of the reference elec trode from absolute vacuum. A more thorough consideration can be found in the dissertation of Barry C. Thompson.21

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47 Potentiostatic Deposition Conjugated polymers can also be prepared by pot entiostatic deposition. In this experiment, a constant potential is applied until a specified amount of charge is passed. Potentiostatic methods deposit polymer more efficiently than re peated scan cyclic voltammetry. This process produces smooth conjugated polymer films on IT O-covered glass electrodes especially for electrochromic and spectroelectrochemical experi ments. The amount of charge passed can also be correlated to the thickness of the deposited polymer film. Differential Pulse Voltammetry Differential pulse voltammetry (DPV) has severa l advantages over CV while obtaining the same basic values for polymer films. DPV is fa ster than CV over the same potential range. DPV allows easier determination of polymer E1/2 values since the peak poten tial is more accurate due to the removal of capacitive charging effects. Conjugated polymers have more complex doping processes, and the peaks for the anodic and ca thodic scans are often not symmetrical. In CV, these peaks rarely occur at th e same potential, but in DPV th e resulting waveform is more symmetrical. DPV removes charging currents by sa mpling the current twice at each potential. The current is sampled first at time Â’, immediately before the pulse and then again at , immediately after the pulse. The current reported is the differential current i = i( ) i( Â’) at each base potential. The pulse height (step size + step amplitude) is maintained at 100 mV at each potential in the experiment and the timing is c hosen to minimize noise and maximize experiment speed. The result of these gains is that the on set potential values obt ained by DPV are more reflective of the polymer materi als HOMO-LUMO electronic states.

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48 Electrochromic Characterization All absorption spectra were carried out on a Varian Cary 500 UV-VIS-NIR spectrophotometer in scan mode, using quartz cr ystal cells (1cm x 1cm x 5.5cm, Starna Cells, Inc.). Spectroelectrochemistry A key measure of both the polymerÂ’s electronic state and the potential for electrochromic application is spectroelectrochemistry. Multiple UV-VIS-NIR spectra of the polymer film are obtained as the applied potential on the film is varied in small increments. In a typical experiment, electrolyte solution and blank ITO slides are first used to obtain a blank spectrum over the desired spectral range. An upper lim it of 1600nm is chosen because significant absorptions due to water are eliminated. The spectra may be displayed in energy units of electron-volts (eV), where 1240/ (nm) = eV, or in waveleng th. In the energy domain, the lower wavelength region (above 1600nm) is hi ghly compressed, while the visible region is expanded, allowing easier consideration of the pol ymerÂ’s colored features . Next, the polymer film electrode assembly is pla ced in the spectrophotometer. Usi ng the CV results as a guide the film is incrementally oxidized or reduced potentiostatically to access the polymer redox electrochemistry. The observed electronic transitions occurring upon doping can be explained through the Su-Schrieffer-Heeger (SSH) model123 or the electron-phonon theory of Fesser, FBC theory.124 Spectroelectrochemistry provides info rmation regarding the polymerÂ’s band gap, * transition, polaron, and bipolaron absorptions. In situ Colorimetry Colorimetry is a quantitative an alytical tool that provides an objective method to compare and evaluate the optical respons es of electrochromic polymers and devices. The standardization of color measurement was described (Chapter 1). In situ colorimetry of the film was measured

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49 by a Minolta CS-100 Chroma Meter. The Chroma Me ter gives three values, Y, x, and y. A cuvet containing electrolyte solution and a blank ITO-covered glass slide was backlit from a D50 (5000 K) light source and measured to obtain the initial luminance value, Yo. The luminance value, Y, is then recorded as the potential is applied incrementally. The potential is increased similar to spectroelectrochemistry. The hue and saturation values, x and y, can be used to quantify the color of th e film graphically via a two-dime nsional color space, known as a chromaticity diagram, illustrated with PProDOT -EB (Figure 2-1). Neutral polymer is very absorptive and does not permit much light to pass. Upon oxidation, the polymer becomes highly transmissive allowing light to reach the colori meter. The difference between the absorptive and transmissive states, allows the determination of the total change in luminance, %Y. Figure 2-1.CIE 1931 Chromaticity diagram for PProDOT-EB Coloration Efficiency With a potentiostat and UV-VIS-NIR spect rophotometer, tandem chronocoulometry/ chronoabsorptometry experiments were performed. The data was then used to determine the composite coloration efficiency for the polymer films studied in this work. After the films were S OO O O O O O O n

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50 deposited and broken-in, the percent transmitta nce was recorded as the polymer underwent a series of double potential steps. The experi ment was performed nearest the polymerÂ’s max as possible. A background experiment is also performed on a nake d electrode; this data is subtracted from the polymer electrochemical data to obtain corrected information. Composite coloration efficiency116 is a value calculated from the results of the tandem chronocoulometry/chronoabsorptometry experiment. First, the percent transmittance of the fully oxidized and fully neutral specie s is recorded during the electr ochemical switch. These values give the change in percent transmittance, %T or optical contrast, starting from the %T of the fully reduced film, Tred, up to the fully oxidized film. The %T at 95% of the full optical switch, Tox, is then determined because the majority of the color change w ith respect to ocular perception occurs prior to this point. Th e logarithm of the ratio of Tox to Tred is the change in optical density, OD, as shown below. red oxT T OD log (2-1) The switching time, tswitch, from colored to transmissive is al so obtained at 95% of the full optical switch. This value is used to determine the amount of charge passing through the polymer film as a function of electrode area from the chronocou lometry experiment. The initial charge value and the charge passed at 95% of the full optical switch are used to obtain Qd. Finally, the coloration efficiency, CE or , is obtained by dividing the cha nge in optical density by the charge density (Equation 2-2). electrode d A Q OD (2-2)

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51 CHAPTER 3 ALKOXY SUBSTITUTED POLY(3,4PROPYLENEDIOXYTHIOPHENE) Dioxythiophene History One of the more successful conjugated polymers has been the derivative poly(3,4-ethylenedioxythiophene) (PEDOT). PE DOT was intended as a soluble conducting material that avoided the undesirable , Â’ coupling of polythiophenes.104 Oxygen substitution at the 3 and 4 positions prevented that undesired co upling and stabilized the polymerÂ’s oxidized form. The addition of a cyclic substituent prevents torsional distortion betw een repeat units as is seen in regioirregular polythi ophenes. In comparison to polythiophene, PEDOT has higher hydrophilicity and a smaller band gap.49 The effects of these structur al modifications are seen in the increased conductivity at almost 300 S/cm, in a ddition to transparency and enhanced stability of the oxidized state.105,125 PEDOT has been used effectively in coatings, but still suffered from the insolubility inherent to conjugated polymers. Significant attention has been directed to the synthesis and functionalization of PEDOT to overcome its inherent insolubility. Jonas re ported the first widely used synthetic route in 1992 converting thiodiglycolic acid to a 2, 5diester-3, 4-dihydroxyt hiophene via a double Williamson etherification with dihaloalkanes.126 Decarboxylation mediated by copper salt gave the parent EDOT monomer. Methyl, hexyl, and decyl substituted EDOTs were reported; Reynolds reported octyl,127 tetradecyl,128 and phenyl129 derivatives. However, this methodology was ineffective for sterically demanding dihaloalkanes. The steric effect of the substituent is one of the drawbacks of functionalized EDOT monomers. The substituen t, attached through an sp3 carbon, encourages twisting of the polymer backbone due to steric repulsion from the substitu ent of an adjacent repeat unit. Desire for a molecule without this steric repulsion led to the synthesis of substituted

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52 3,4-propylenedioxythiophene (ProDOT), a symmet rical molecule. Di-substituted alkylene bridges were installed through transetherification between the functionalized diol and 3,4-dimethoxythiophene to obtain dimethyl,130 diethyl,131 dibutyl,132 octadecyl,133 and bis-ethylhexyloxy29 ProDOTs. These alkyl and alkoxy substituted poly(propylenedioxythiophene)s (P ProDOTs) have demonstrated high solubility in common organic solvents. Electroactiv e films can be produced by dr op-casting, spin-coating, and spraycasting from polymer solutions. Halogenation of the monomers allows polymerization by the transition metal-mediated methods (Chapter 1). Pendant functionality rare ly affects the polymerÂ’s ba nd gap significantly. Band gap manipulation is more easily achieved by substitu ting the monomer repeat unit with an additional aromatic or unsaturated system. Arylene s ubstituted EDOT systems produced by Negishi or Kumada coupling134 have been reported. Stille coup ling has been used to produce bis-EDOT (BEDOT) systems, incorporating bipyridine,135 thienyl-benzothiophene-dicarboximide,136 and naphthalene137 as well as donor-acceptor material such as BEDOT diphenylpyridopyrazine,138 BEDOT-benzothiadiazole,139 and BEDOT-thienothiadiazole.140 BEDOT functionalized alkylated carbazoles were also reported.60,112,141 An advantage of bis-substituted dioxythiophene systems is that the materials can be studied by electrochemical deposition and chemical polymerization. Two additional synthetic methods have pr oduced dioxythiophene monomers. Knoevenagel condensation between an EDOT cyano me thylene and an EDOT aldehyde gave BEDOT-vinylene and other ar yl cyanovinylene monomers.142,143 These monomers gave donoracceptor polymers with low band gap energies and were applied in photovoltaic devices.142 The second method employed the Mitsonobu reaction of the thiophene di-ester diol with

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53 functionalized diols.144,145 It is an improvement over previous syntheses because dihaloalkanes are no longer necessary. Chemically Polymerized Alk oxy Propylenedioxythiophenes Current conducting polymer research is focuse d on the generation of processable materials, where the alkoxy substituted PProDOTs are a good example.29,133 Using 3, 4dimethoxythiophene, or 2,2-bis( bromomethyl)propylenedioxythi ophene, as the keystone synthon, a series of alkoxy substituted polymers were produced. Initially, the 2,2-dihexyl and 2,2-(2-ethylhexyl) propanediols were produced from the alkylation of diethyl malonate.133 Following reduction of the esters, the new propanedi ols underwent transetherification to give the desired propylenedioxythiophene. An alternative method reacts 2,2-bis(bromomethyl)-1,3-propanediol w ith 3,4-dimethoxythiophene to give 2,2-bis(bromomethyl)-propylenedi oxythiophene. This molecule was then reacted under Williamson etherification conditions using the al cohols, 2-ethylhexanol and 1-octadecanol, to give bis(octadecyloxy)-, and bis(ethylhe xyloxy)-propylenedioxythi ophenes. All of the propylenedioxythiophenes were then halogenated using NBS to produce the final monomer. Grignard Metathesis86 polymerization was used to produce soluble, conjugated polymer. After precipitation, filtration, and extraction using a soxhlet appa ratus, polymer samples with number-average molecular weights between 38 kDa and 48 kDa by gel permeation chromatography (GPC) were obtained. The technique tends to overestimate molecular weight in conjugated polymers.146 At low molecular weights, this fact or is 1.2-1.5 times that seen in other molecular weight methods, while the factor is 1.5-2.3 times greater for high molecular weight samples. Conjugated polymers are rigid-rod systems that tend to aggregate at all temperatures,147,148 but may act as conformationally-limited flexible coils in dilute solutions preventing good correlation with polystyrene stan dards. However, poly(3-hexylthiophene) has

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54 shown good agreement with GPC molecular we ights due to THF being a moderately good solvent with a Mark-Houwink exponent of 0.58.149 The resulting PProDOTs showed good film forming ability, as evidenced by th e ability to deposit films using a small airbrush. As films, the polymers have fluorescence quantum efficiencies between 2-3%, much lower than the maximum 45% seen in solution measurements. Via superimposed in situ colorimetry and cyclic voltammetry, the electrochromic switching of the polymer was observed to occur at potentials nearly identical to the poly mer oxidation and reduction. In this chapter, ProDOT-(CH2OC8H17)2 and ProDOT-(CH2OC10H21)2 polymers were synthesized and characterized. These polymers s hould have similar properties to other alkyl and alkoxy PProDOTs discussed earlier in this chapte r. These medium length alkoxy chains should not differ greatly from the hexyl and ethylhexy l derivatives developed earlier. Following synthesis, the electropolymerized and chemical ly polymerized results were compared. The polymers behave as electrochromic materials with large contrasts, high coloration efficiencies, and fast switching times. Monomer and Polymer Synthesis Alcohol based substituents present a facile method to derivatize conjugated polymers. The ability to start from commerci al and easily synthesized precurs ors provides an important means to increase the structural complexity of 3,4-propyl enedioxythiophene polymers. The key to this method is the use of a keystone molecule that can be produced in large amounts. For this work, that molecule is 2, 2-bis(bromomethyl )-3,4-propylenedioxyth iophene (ProDOT-(CH2Br)2). ProDOT-(CH2Br)2 has been reported in the synthesis of processable polymers with straight chain and branched alkyl substituents.133,145,150 This molecule allows us to focus on the functionality being introd uced. As a ProDOT molecule, it is more tolerant to harsh reaction conditions, and more stable to ambient oxida tion than the parent EDOT molecule. The

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55 compound results from a multi-step synthesis (Figure 3-1), beginning with the exhaustive bromination of thiophene. Selective debr omination is performe d using butyllithium.151 Metalhalogen exchange occurs primarily at the 2 and 5 positions of the thiophene ring. The lithiated thiophene is subsequently protona ted to give 3, 4-dibromothiophene , which is then converted to 3, 4-dimethoxythiophene.152 S S Br Br Br Br S Br Br Br2CHCl366% nBuLi Et2O,0°C 51% KI,CuO NaOMe,MeOH 51% S OMe MeO Figure 3-1. Synthesis of 3,4-dime thoxythiophene from thiophene. Figure 3-2 presents a method which slightly modified the ether synthesis to obtain the 3,4-dimethoxythiophene in shorter reaction time by using a Cu(I) salt, rath er than the Cu(II) salt used initially.153 During the last 5 years, 3, 4-dimethoxyt hiophene has become available in small amounts, less than 5g, from large chemical manufact urers such as Aldrich, and kilogram scale from smaller manufacturers like Small Molecules, Incorporated. 3, 4-Dibromothiophene is also commercially available from Waterst one Technology and Frontier Scientific. S Br Br NaOMe,DMF CuI,110°C,48hrs 74% S O O PTSA Toluene 71% OHOH BrBr S O O B r B r S O O Figure 3-2. Synthesis of ProDOT-(CH2Br)2 using modified synthesi s of 3,4-dimethoxythiophene. The subsequent transetherification in stalls the propylenedioxy ring using 2,2-bis(bromomethyl)-1,3-propanedi ol. Once obtained, ProDOT-(CH2Br)2 was reacted with the appropriate alcohol under Williamson conditions (Fi gure 3-3). The reaction is performed in two parts. First, the sodium alkoxide is generated by heati ng a solution of the al cohol in DMF in the presence of 6 equivalents of NaH. After 4 hours at 110 C, ProDOT-(CH2Br)2 is added. The reaction is allowed to continue at temperature for one full day.

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56 S OO OR OR NBS,CHCl3S OO OR O R Br Br 1.MeMgBr,THF 2.NiCl2(dppp) S OO OR O R * * R=C8H17,94% C10H21,99% S OO BrBr NaH,ROH DMF R=C8H17,45% C10H21,49% Figure 3-3. Williamson etherification of ProDOT-(CH2Br)2 followed by bromination and Grignard Metathesis polyme rization to give PProDOT-(CH2OC8H17)2 and PProDOT-(CH2OC10H21)2. The Williamson etherification reactions are wo rked up using a large excess of water to solubilize the DMF. Diethyl et her is then added, and a sequen ce of extractions involving water and brine were found to remove the majority of DMF. Column chromatography with hexanes and dichloromethane produced pale yellow oils. Electropolymerization provides a unique m eans to study the electronic and optical properties of the polymer films produced from the di-hydro ProDOT-(CH2OC8H17)2 and ProDOT-(CH2OC10H21)2. Easily obtained, electrochemical polymer films allow complete characterization of the polymerÂ’s electronic properties. Electroc hemical methods directly probe the polymerÂ’s electronic system via the injection or removal of charge carriers into the frontier molecular orbitals. However, the difficulty of using electropolymerized polymers in device applications requires the synthesis of solution processable polymers. Halogenation of the di-hydro molecules gives dihalo monomers that can undergo transition metal-mediated polymerization. Bromination was achieved using N-bromosuccinimide in chloroform (Figure 3-3). This method is mild,154 and the reaction occurs at room temperature. Chromatography gives a clear oil th at solidifies overnight. The alkoxy-substituted dibromo-ProDOTs we re then polymerized using Grignard Metathesis,86 proceeding smoothly to give a deep purple polymer. Methyl magnesium bromide was titrated immediately prior to use, and then added to a THF solution of the monomer. After 1

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57 hour at reflux, the solutions often take on a slight pink color. Addition of the NiCl2(dppp) catalyst leads to a red coloring, followed quickly by the bright pur ple color of the polymer in solution. The polymer reaches high molecular wei ght within 1 hour of the catalyst addition, but the reaction was allowed to cont inue at reflux for 48 hours. To quench the polymerization, the material is precipitated into methanol, a nd extracted via Soxhlet apparatus. The appearance of high molecular weight materi al during Grignard metathesis was studied via a series of test polymer izations using ProDOT-Hexyl2. Both large scale and small scale polymerization reactions were prepared; sample s were removed, quenched, and then analyzed by GPC. At the 0.5 g scale, polymer with mol ecular weight of 3.3 kDa was observed after 15 minutes of catalyst addition; samples obtai ned at 15 minutes, 30 mi nutes, 1 hour and 3 hours were used to compare Mn against time, and showed a linear increase in molecular weight. The large scale reaction showed a change in Mn from 13 kDa to 21 kDa between 20 minutes and 75 minutes of catalyst addition with a final Mn of 20 kDa after 4 hours of reaction. Soxhlet extraction was used to purify th e polymer, removing low molecular weight oligomers and metal catalyst. The product was placed in a cellulose thimbl e, and the solvent is refluxed over several days. Sequential extractions using methanol and hexanes were used to remove monomer, catalyst, and low molecular weight compounds. An extraction with chloroform was used to recover the high molecula r weight polymer from the cellulose thimble. Any remaining insoluble material was discarded. As discussed (Chapter 1), Soxhlet extraction can disguise the actual quality of the polymeri zation due to obscuring th e polydispersity of the reaction. PProDOT-(CH2OC8H17)2 gave a Mn of 38 kDa by GPC, while PProDOT(CH2OC10H21)2 gave a Mn of 57 kDa both in THF.

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58 100200300400500600700800 20 40 60 80 100 120 PProDOT-(CH2OC10H21)2PProDOT-(CH2OC8H17)2Weight %Temperature (°C) Figure 3-4. Thermogravimetric analysis of PProDOT-(CH2OC8H17)2 and PProDOT-(CH2OC10H21)2. The samples were heated from 55 C to 850 C at 20 C/min under nitrogen purge. During thermogravimetric analysis (TGA) (Fi gure 3-4), the polymers were equilibrated at 55 C for 5 minutes under N2 flow to remove any residual solvent. The bisdecyloxy polymer shows a small degradation (< 3%) between 100 and 300 C, while the bisoctyloxy polymer shows no change over the same temperature rang e. Both polymers show a sharp weight loss centered at 390 C for PProDOT-(CH2OC8H17)2 and 380 C for PProDOT-(CH2OC10H21)2 with onsets at 338 C and 351 C, respectively. The PProDOT b ackbone results in an amorphous polymer, rather than semi-crystal line as in poly(3-octylthiophene).155 Electrochemistry The electropolymerization of alkoxy substi tuted ProDOTs and redox switching of the resulting polymers was studied via button electro chemistry. Repeated scan cyclic voltammetry (CV) was used to deposit polymer on a Pt button electrode. The experiments were performed in acetonitrile with tetr abutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte. For ProDOT-(CH2OC10H21)2 (Figure 3-5), oxidation of the monomer begins at 0.84 V versus Fc/Fc+, with a peak oxidation potential of 0.91 V. Subsequent scans show a redox process attributed to the dioxyt hiophene backbone. A half-wave potential of -0.19 V resulting from an oxidation peak at -0.17 V and a reduction peak at -0.21 V is observed.

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59 -1.0-0.50.00.51.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Ep,m = 0.91 V Onset = 0.84 V Current (mA/cm2)Potential vs. Fc/Fc+ (V)-1.0-0.50.00.51.01.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 S O O OC10H21 OC10H21 * * nEp,a =-0.17 V Ep,c = -0.21 V Current (mA/cm2)Potential vs. Fc/Fc+ (V)B A Figure 3-5. Electrochem istry of ProDOT-(CH2OC10H21)2. A) Monomer oxidation showing an onset potential of 0.84 V and a peak oxidation potential of 0.91 V. B) Electrochemical deposition performe d in acetonitrile with 0.1 M TBAPF6 electrolyte. The shorter alkoxy chain, PProDOT-(CH2OC8H17)2 (Figure 3-6), shows lower potential values for polymerization and redox switching than in the ProDOT-(CH2OC10H21)2 polymer. Onset of monomer oxidation occurs at 0.83 V, with peak oxidation observed at 0.97 V. The polymer redox process has an E1/2 of -0.14 V. This suggests that the longer chain prevents ion transport within the electrochemically deposited film, and will be discussed with the scan rate dependence data of Figure 3-7. -1.0-0.50.00.51.01.5 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Ep,m = 0.97 V Onset = 0.83 V Current (mA/cm2)Potential vs. Fc/Fc+ (V)-1.0-0.50.00.51.01.5 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 S O O OC8H17 OC8H17 * * n Ep,c =-0.15 V Ep,a = -0.12 VCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)A B Figure 3-6. Electrochem istry of ProDOT-(CH2OC8H17)2. A) Monomer Oxidation showing onset potential of 0.83 V and a peak oxidation potential of 0.97 V. B) Electrochemical depositions performed in acetonitrile with TBAPF6 electrolyte. Polymer anodic and cathodic potentials are shown. Reeves studied the electrochemistry of alkoxy substituted PProDOTs using a mixed solvent system of 4:1 propyl ene carbonate (PC)/toluene.20 This solvent system was chosen due

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60 to the low monomer solubility seen with li near alkoxy ProDOT mono mers, C12, C14, C16, and C18, in acetonitrile. Short chain monomer, ProDOT-(CH2OEtHx)2, was freely soluble in PC and gave Ep,m of 1.1 V vs. Fc/Fc+. The Ep,m values of longer chain compounds were observed to decrease to 0.95 V vs. Fc/Fc+ in the mixed solvent system. In the present work, polymer was successfully deposited in acetonitr ile electrolyte solution, and oxida tion potentials were seen to decrease when toluene was added. Repetition of the electrochemical deposition in PC with TBAPF6 was consistent with a decrease in Ep,m with increased chain length. The effects of mixed ion-solvent transport in poly mer redox process have been studied.156 The polymer electrochemical processes of ProDOT-(CH2OC10H21)2 (Figure 3-7) were then studied after transferring the f ilm covered electrode to a monome r-free electrolyte solution. The film, switched between -0.3 V and 0.85 V, shows a sharp oxidation and a broad reduction. The scan rate dependence of the film is also shown. -1.0-0.8-0.6-0.4-0.20.00.20.4 -0.4 -0.2 0.0 0.2 0.4 0.6 S O O OC10H21 OC10H21 * * nCurrent (mA/cm2)Potential vs Fc/Fc+ (V)-1.0-0.50.00.51.01.5 -4 -2 0 2 4 ip,cip,a Current (mA/cm2)Potential vs. Fc/Fc+ (V)C B0100200300400500 -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 ip,a ip,cCurrent (mA/cm2)Scan Rate (mV/s)A Figure 3-7. Button electroc hemistry of PProDOT-(CH2OC10H21)2 in 0.1 M TBAPF6 and acetonitrile. A) Voltammetric break-in. B) Scan Rate Dependence. C) Peak Currents versus Scan Rate. Using the peak current values of both the anodi c and cathodic processes, the quality of the electrochemical system can be determined. Wh en compared versus the scan rate, the peak current values show a linear dependence. This suggests that electron tran sport process is surface bound, and not due to some freely di ffusing species from the solution.157 This demonstrates that the electroactivity of these syst ems is not hindered by the incorporation of alkoxy substituents.

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61 But, the higher potential values observed between the two chain lengths, oc tyl and decyl, suggest that there is some opposition to counter-ion transp ort, i.e. the additional methylene atoms require more energy to force the hexafl uorophosphate counter ion into the polymer film. This trend is supported by Grenier,158 where electrochemically deposit ed films of alkoxy substituted PProDOT had increasing E1/2 values with increasing number of carbons in acetonitrile. Electrochromism Interest in these polymers is a result of th eir electrochromic properties. Changes in the visible spectrum are observed using spectroelectr ochemistry where polymer is deposited onto an ITO-covered glass slide by main taining a constant potential above the monomer oxidation. The resulting polymer film is then cycled 25 times at 25 mV/s in monomer-free electrolyte to prepare the film for repeated switching and incorpor ate supporting electrolyte throughout the deposited film. The UV-VIS-NIR spectra ar e recorded as the polymer is oxidized stepwise from its neutral state to its oxidized stat e (Figure 3-8). For dioxythiophene polymers, a strong * absorption in the visible range is seen in the spectrum of the neutral polymer. This absorption is similar to the * in small organic molecules, but is more accurately seen as an absorption between the HOMO and LUMO frontier molecular orbi tals of the polymer. PProDOT-(CH2OC8H17)2 shows a maximum absorption of 574 nm, or approximately 2.2 eV. As the polymer film is oxidized from -0.1 V to 0.9 V, the visible range absorpti on disappears, and a new absorption occurs at approximately 900 nm. This absorption is attribut ed to the radical cati on, or polaron, produced by the oxidation of the film. As the oxidation continues, this polaron absorption disappears producing an optically transmissive film. Finally, a broad absorpti on in the NIR is attributed to bipolaron, or di-cation formation.

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62 4006008001000120014001600 0.5 1.0 1.5 2.0 Absorbance (a.u.)Wavelength (nm)max = 584 nm; ~2.1 eV 0.0 V 0.1 V 0.2 V 0.3 V 0.4 V 0.45 0.5 V 0.55V 0.6 V 0.65 V 0.7 V 0.75 V 0.8 VS O O OC10H21 OC10H21 * * nS O O OC8H17 OC8H17 * * nB4006008001000120014001600 0.5 1.0 1.5 2.0 Wavelength (nm)Absorbance (a.u.)max = 574nm; ~2.2 eV -0.1 V 0.0 V 0.1 V 0.2 V 0.3 V 0.3 V 0.5 V 0.6 V 0.7 V 0.8 V 0.9 V 0.75 VA Figure 3-8. Spectroelectrochemistry of electrochemically deposited films. A) PProDOT-(CH2OC8H17)2 oxidized in 100 mV increments. B) PProDOT(CH2OC10H21)2 oxidized in 100 mV increments until 0.4 V, then oxidized in 50 mV increments. Electrochemically deposited PProDOT-(CH2OC10H21)2 has a higher max value at 584 nm. The polaron absorption occurs at near 970 nm. Th e longer wavelength of the decyloxy polymer may be due to higher molecular weight, or more extended conformation due to the longer alkoxy chain. Spectroelectrochemistry was also perf ormed on the chemically polymerized polymer samples sprayed onto ITO-covered glass from solu tions of toluene (Figure 3-9). The polymers were dried overnight in a vacuum desi ccator prior to electrochemical study. 4006008001000120014001600 0.0 0.5 1.0 1.5 2.0 2.5 max = 596 nm; ~2.1 eVS O O OC8H17 OC8H17 * * n0.65 V 0.65 V 0 V 0 VAbsorbance (a.u.)Wavelength (nm)4006008001000120014001600 0.0 0.5 1.0 1.5 2.0 2.5 3.0 max = 598 nm; ~2.1 eV 0.85 V 0.85 V 0.1 V 0.1 VS O O OC10H21 OC10H21 * * nAbsorbance (a.u.)Wavelength (nm)B A Figure 3-9. Spectroelectroche mistry of chemically polymerized films. A) PProDOT(CH2OC8H17)2 oxidized in increments of 100 mV until 0.4 V, then oxidized in increments of 50 mV un til 0.65 V. B) PProDOT-(CH2OC10H21)2 oxidized in increments of 50 mV until 0.7 V, then oxidi zed in increments of 25 mV until 0.85 V.

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63 While electrodeposition gives a more comple te picture of the polymerÂ’s electronic processes, the information obtained from the chem ically polymerized samples shows the effect of molecular weight control.159 The electrochemically deposited films show broader absorptions and have lower max values. This is likely due to the di sordered nature of electrochemically deposited films. The more homogenous chemi cally polymerized polymers result in much sharper onsets of absorption. The homogene ity of the chemical polymers helps when determining the best polymer for electrochromic devices. In situ colorimetry was performed to measure the perception of brightness through the polymer as it changes during oxidation. Most di oxythiophene polymers oxidi ze to a transmissive sky blue. The transmissivity is seen in th e change in relative luminance of PProDOT(CH2OC10H21)2 (Figure 3-10). This m easurement provides a valuab le quantification of the differences between the colored and transmissive states of optoelectronic polymers. In situ colorimetry results allow for easier comparison between electrochromic polymers, leading to better material selection in devices. -0.6-0.4-0.20.00.20.4 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 S O O OC10H21 OC10H21 * * nRelative Luminance (Y/Y0)Potential vs. Fc/Fc+ (V) Figure 3-10. In situ colorimetry of spraycast polymer PProDOT-(CH2OC10H21)2. Both polymers show gradual ch anges in the relative lumina nce, rather than the sharp change seen in branched alkoxy substituents.158 This gradual shift is most likely due to the multiple effective conjugation lengths as result of the conformation controlled by the substituent.

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64 Different conformations and diffe rent conjugation lengths possibly oxidize at slightly different potentials leading to the gradual change in transmissivity of the polymer. The amount of light transmitted as the polymer oxidizes favor ably follows the CV for PProDOT-(CH2OC8H17)2 (Figure 3-11). -1.0-0.8-0.6-0.4-0.20.00.20.40.6 -5 0 5 10 15 Current (mA/cm2)Potential vs. Fc/Fc+-0.6-0.4-0.20.00.20.4 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Relative Luminance (Y/Y0) Figure 3-11. In situ colorimetry overlaid onto volta mmetric break-in of spray-cast PProDOT-(CH2OC8H17)2. CV is performed between -0.3 V and 1.2 V at 50 mV/s. Here, the in situ colorimetry is super-imposed on the cyclic voltammagram of PProDOT-(CH2OC8H17)2 illustrating that the change in lumi nance, or the transmissivity, of the polymer film occurs at a potential similar to oxi dation of the film. In this case, both processes occur around 0.1 V. A tandem chronoabsorptometry/ chronocoulomet ry experiment, measuring the amount of charge passed as the polymer sw itches between its neutral, colo red and oxidized, transmissive state was used to determine the coloration effi ciency (Table 3-1). The chronoabsorptometry measurement was recorded at the max of the spray-cast polymer; a pristine ITO-covered glass electrode was used as a blank for the chronocoulom etry experiment. Coloration efficiency is a calculation that relates the color change of the polymer to the am ount of charge passed (Chapter 2). Since the majority of color change occurs prior to completion of the electrochromic switch, the Tox and Tred values at 95% of the full optical switch ar e used to calculate the change in optical

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65 density of the films. The ch arge passed is recorded by th e simultaneous chronocoulometry experiment. At 598 nm, the change in transmittance of PProDOT-(CH2OC10H21)2 between the fully reduced and fully oxidized state is 61.9%. The ti me to complete this switch was 10s, while 95% of the optical switch was reached after 4.6s. At 95% of the full switch, the change in optical density is 1.35. Using those values, along with the 1.57 mC/cm2 of charge needed to complete the full optical sw itch and 1.32 mC/cm2 to attain 95% of the optic al switch, led to coloration efficiencies of 860 at 100% or 1020 at 95%. Table 3-1. Coloration Efficiency data for chemi cally polymerized ProDOTs. Electrode area was 1.4 cm2 for all experiments. All values except %T taken at 95% of full switch. PProDOT-(CH2OC8H17)2 PProDOT-(CH2OC10H21)2 Y 0.59 0.58 %T 62.8 61.9 Tox 61.1 61.4 Tred 0.7 2.77 tswitch (s) 2.2 4.6 (OD) 1.94 1.35 Qd95% (mC/cm2) 2.87 1.32 CE (cm2/C) 676 1020 The same experiment was performed on PProDOT-(CH2OC8H17)2 at 595 nm. The change in transmittance between the fully reduced and fully oxidized state is 62.8%. The time to complete 95% of the switch was reached after 2.2s. At 95% of the full switch, th e change in optical density is 1.94. Based on those values, 2.87 mC charge was passed to reach 95% of the optical switch. This value gives a co loration efficiency of 676 cm2/C. Photophysics The band gap of conjugated polymers can be de termined from the optical spectra of the polymers or their films. The polymer HOMO a nd LUMO orbitals are analogous to bonding and anti-bonding orbitals in simple organic molecule s. Therefore, the difference in energy between

PAGE 66

66 these two orbitals is considered the band gap, and approximated by the * transition seen in spectroscopy. The optical band gap is taken from the onset of the * absorption. For PProDOT-(CH2OC8H17)2 the optical band gap is 1.95 eV, while PProDOT-(CH2OC10H21)2 has an optical band gap of 1.93 eV. 350400450500550600650700750 0.00 0.05 0.10 0.15 0.20 0.25 0 2000000 4000000 6000000 8000000 10000000 12000000 14000000 AbsorbanceWavelength(nm) PL Intensity350400450500550600650700750 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 AbsorbanceWavelength0 2000000 4000000 6000000 8000000 10000000 PL IntensityA B Figure 3-12. Photophysical Spectra for chemically polymerized A) PProDOT-(CH2OC8H17)2 and B) PProDOT-(CH2OC10H21)2. Since many of the applications for dioxyt hiophene polymers invol ve light emission, fluorescence spectroscopy was also performed (F igure 3-12) and the sp acing between vibronic bands was calculated (Table 3-2). Both polymer s demonstrate very small Stokes shifts between the absorbance and fluorescence maxima. This is because the excited state of the polymer has very little geometrical differe nce from the neutral ground state. Similar to PProDOT-(Butyl)2, the polymers have a broad emission profile.132 The 0-0 transition, which corresponds to excitation from the lowest ground stat e vibrational level to the lowest vibrational level of the first excited state, occurs at 606 nm for PProDOT-(CH2OC8H17)2 and at 604 nm for PProDOT-(CH2OC10H21)2. Table 3-2. Calculated vibronic spacing (cm-1) for chemically polymerized polymers. PProDOT-(CH2OC8H17)2 PProDOT-(CH2OC10H21)2 0-1 1359 1388 1-2 1363 1445

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67 The quantum efficiency of the polymersÂ’ so lution fluorescence was also obtained using toluene solutions whose concentr ation was chosen so that the absorbance was nearest 0.1. For the PProDOT-(CH2OC10H21)2 the quantum efficiency was 39.3%, while the PProDOT(CH2OC8H17)2 was 61.5%. Conclusion This chapter has demonstrated the synthesi s and characterization of soluble conjugated polymers. From simple alcohols, soluble polyp ropylenedioxythiophenes have been developed. Synthetically, we have shown an improve d methodology to produce 3,4-dimethoxythiophene using CuI, rather than CuO. This methodol ogy allows for a shorter reaction times producing somewhat equivalent yields. The resulting mono mer molecules were then used to demonstrate the utility of electrochemical and chemical polymerization met hods. The electronic processes can be studied thoroughly and eas ily via electrochemistry. The electrochemistry shows higher absolute values likely due to solubility and transp ort differences from prev ious work. These data were obtained in acetonitrile rather than pr opylene carbonate, and use hexafluorophophate rather than perchlorate as the dopant ion. This presents interactions which inhi bit the charge transport processes, and leads to higher values for the electrochemical processes. Even with these differences, the polymers still show good electroactivity. Both polymers have E1/2 values near 0.1 V. Scan rate dependence studies show that the polymers retain the ex pected electroactivity. The spectroelectrochemistry of the electrochemi cally deposited films shows lower intensities, and more diffuse absorptions. This is likely due to the lack of molecular weight control in the electrochemical deposition. The chemically pol ymerized polymers show very sharp absorption onsets and high absorption intensities. In these materials the change s in color and transmissivity with potential has been studied. PProDOT-(CH2OC8H17)2 shows a 55% change in luminance, while PProDOT-(CH2OC10H21)2 has a 57% change. Both of these transitions are gradual,

PAGE 68

68 supporting that branching rather th an substitution can have large effects on the transmissivity of the dioxythiophene polymers. The coloration e fficiency of both polymers was also obtained, with values of 0.67 and 1.02 cm2/mC, respectively. The polymers studied here support the idea that increas ing chain length does not drastically affect the electronic properties of polypropylen edioxythiophenes. These polymers fit into the continuum of alkoxy-substituted PProDOTs developed by the Reynolds group. Experimental Section Materials 2,2-bis(bromomethyl)-1,3-propanediol, octyl al cohol, decyl alcohol, 1.0 M MeMgBr in butyl ether, p-tolu enesulfonic acid, NiCl2(dppp), and other inorganic re agents and solvents were purchased from Aldrich or Fisher and used without further pu rification. N-bromosuccinimide was recrystallized from water be fore use. THF was obtained eith er from a pure pack anhydrous keg connected to aluminum oxide packed column, or distilled from sodium-benzophenone ketyl. Anhydrous DMF and methanol were purchas ed from Acros in Sure-Seal bottles. 2,2-Bis(bromomethyl)-propylenedioxythiophene wa s adapted from a literature procedure.133 Synthesis [3, 4-dimethoxythiophene]. Sodium metal (2.85 g, 0.124 M) wa s dissolved in methanol (20 mL, 10 M solution) in a 250 mL round-bottomed fl ask. The solution was heated to reflux to ensure complete dissolution, and then cooled back to room temperature. 3, 4-dibromthiophene (10 g, 0.04 moles) was then dissolved into the alkaline solution. Purified CuI (1.57 g, 8.2 mmol) was then added quickly, and the solution heated to reflux. The reaction was observed to turn deep red over the course of 6 hours. After 648 hours at reflux, the so lution was cooled and poured into water (200 mL). Ex traction with diethyl ether (3 x 150 mL), brine (100 mL), and drying with MgSO4 gave a pale yellow residue. This oil was distilled at 55 C at 0.1 mm Hg to

PAGE 69

69 give a clear oil (4.46 g, 74%). 1H NMR (300 MHz, CDCl3): s, 2H), 3.86 (s, 6H). 13C NMR (75 MHz, CDCl3): 147.96, 96.41, 57.78. [ProDOT-(CH2Br)2] . In a 250 mL round bottomed flask, toluene (50 mL) was added to 2,2-bis (bromomethyl)-1,3-propa nediol (7.2 g, 27.7 mmol), 3,4dimethoxythiophene (2 g, 13.9 mmol) in toluene (20 mL), and p-toluene sulf onic acid (0.26 g, 1.4 mmol). A reflux condenser and soxhlet extraction apparatus containing 4Ã… molecular sieves in the thimble was connected. After heating under argon at refl ux overnight, the reaction was cooled to room temperature, diluted with ether, and washed with brine (3x150 mL). The organic layers were then combined, dried with MgSO4, and reduced to give yellow oil. Th e oil was purified by silica gel column chromatography (3:2 Hexanes: Dichlorometh ane) to give a clear oil (3.35 g, 71%). 1H NMR (300 MHz, CDCl3) 6.476 (s, 2H), 4.082 (s, 4H), 3.594 (s, 4H) 13C NMR (75 MHz, CDCl3) 141.07, 106.19, 74.58, 46.63, 37.27. [ProDOT(CH2OC10H21)2]. Decyl alcohol (4.16 g, 0.0263 mo l) and sodium hydride (2.017 g, 60%, 0.05262 mol) were dissolved in dimethyl formamide (50 mL, anhydrous) in a 250 mL round-bottomed flask. The mixture was then heated to 110 C for 4 hours. Bis(bromomethyl) ProDOT (3 g, 0.00877 mol) was then added to the reaction flask, and return ed to temperature. The reaction was heated 26 hours and cooled to ro om temperature. The solution was poured into 200 mL of water, extracted with diethyl ether (3 x 150 mL), and retained. The organic layers were the extracted with water (3 x 100 mL) and brine (150 mL). Magnesium sulfate was used to dry the organic layer, and the volume reduced via ro tary evaporation giving a deep red oil. This was chromatographed on silica gel with 3:2 hexane s:dicholoromethane to give a pale yellow oil (2.1 g, 48.5%). 1H NMR (300 MHz, CDCl3): 6.44 (s,2H), 4.01 (s, 4H), 3.48 (s, 4H), 3.39 (t, 4H), 1.50 (m, 4H,), 1.26 (br s, 28H), 0.88 (t, 6H). 13C NMR (75 MHz, CDCl3): 149.9, 105.3,

PAGE 70

70 73.9, 71.9, 69.8, 47.9, 32.1, 29.9, 29.8, 29.7, 29.7, 29.6, 26.4, 22.9, 14.3. ESI-FT-ICRMS [M+Na]+: calcd. for C29H52O4SNa, 519.3484; found, 519.3481. [ProDOT(CH2OC8H17)2]. Octyl alcohol (3.43 g, 0.02634 mol) and sodium hydride (2.01 g, 60%, 0.05262 mol) were dissolved in dimethyl formamide (50 mL, anhydrous) in a 250 mL round-bottomed flask. The mixture was then heated to 110 C for 4 hours. Bis(bromomethyl) ProDOT (3 g, 0.00877 mol) was then added to the reaction flask, and return ed to temperature. The reaction was heated 26 hours and cooled to ro om temperature. The solution was poured into 200mL of water, extracted with diethyl ether (3 x 150 mL), and retained. The organic layers were the extracted with water (3 x 100 mL) and brine (150mL). Magnesium sulfate was used to dry the organic layer, and the volume reduced via ro tary evaporation giving a deep red oil. This was chromatographed on silica gel with 3:2 hexane s:dicholoromethane to give a pale yellow oil (1.72 g, 44.5%). 1H NMR (300 MHz, CDCl3): 6.44 (s, 2H), 4.01 (s, 4H), 3.48 (s, 4H), 3.39 (t, 4H), 1.54 (m, 4H,), 1.27 (br s, 21H), 0.88 (t, 6H). 13C NMR (75 MHz, CDCl3): 149.9, 105.3, 74.0, 71.9, 69.8, 47.9, 32.1, 29.8, 29.7, 29.5, 26.4, 22.9, 14.3. ESI-FT-ICRMS [M+H]+: calcd. for C25H44O4SH, 441.3039; found, 441.3039. [Br2-ProDOT(CH2OC10H21)2]. ProDOT(CH2OC10H21)2 (1.87 g, 0.00376 mol) was dissolved in chloroform (20 mL). The so lution was purged with argon for 10 minutes, and N-bromosuccinimide (1.4 g, 0.0079 mol) was added. The solution was stirred for 20 hours, then two additional hours until a sing le spot was observed on TLC. The solution was then reduced via rotary evaporation and chromatography was performed using 3:2 hexanes:dicholoromethane as eluent to give a clear oil, which b ecame a white solid overnight (2.32 g, 94.3%). 1H NMR (300 MHz, CDCl3): 4.09 (s, 4H), 3.49 (s, 4H), 3.39 (t, 4H), 1.53 (m, 4H,), 1.27 (br s, 28H),

PAGE 71

71 0.89 (t, 6H). 13C NMR (75 MHz, CDCl3): 74.3, 71.6, 69.3, 47.8, 31.9, 29.6, 29.5, 29.3, 26.1, 22.7, 14.1. ESI-FT-ICRMS [M+Na]+: calcd. for C29H50O4SBr2Na, 675.1697; found, 675.1685. [Br2-ProDOT(CH2OC8H17)2]. ProDOT(CH2OC8H17)2 (1.41 g, 0.00319 mol) was dissolved in chloroform (20 mL). The solution was purged with argon for 10 minutes, and N-bromosuccinimide (1.19 g, 0.006719 mol) was a dded. The solution was stirred for 20 hours, then two additional hours until a single spot was observed on TLC. The solution was then reduced via rotary evaporation and ch romatography was performed using 3:2 hexanes:dicholoromethane as eluent to give a clear oil, which became a white solid overnight (1.91 g, 99.9%). 1H NMR (300 MHz, CDCl3): 4.01 (s, 4H), 3.49 (s, 4H), 3.39 (t, 4H), 1.53 (m, 4H,), 1.28 (br s, 21H), 0.89 (t, 6H). 13C NMR (75 MHz, CDCl3): 147.2, 91.2, 74.5, 71.9, 69.6, 48.0, 32.1, 29.7, 29.6, 29.5, 26.4, 22.9, 14.3. ESI-FT-ICRMS [M+Na]+: calcd. for C25H42O4SBr2Na, 619.1071; found, 619.1064. Poly[ProDOT(CH2OC10H21)2]. Br2-ProDOT-(CH2OC10H21)2 (2.3 g, 0.0035 mol) and MeMgBr( 5 mL, 0.63M by titration) were dissolved in tetrahydro furan (100 mL, anhydrous). This solution was refluxed for 1 hour. NiCl2(dppp) (0.0189 g, 0.035 mmol) was then added to the solution producing a deep purpl e color. The mixture was then refluxed 48 hours and cooled to RT. The reaction was poured into methanol, f iltered, and placed in the thimble of a soxhlet extraction setup. The solid was se quentially extracted with metha nol (24 hrs), he xanes (48 hrs), and dichloromethane (24 hrs). The final fraction was reduced via rotary evaporation to give a metallic purple solid (0.94 g). 1H NMR (300 MHz, CDCl3): 4.16 (s, 3H), 3.62 (s, 3H), 3.45 (t, 4H), 1.58 (m, 5H,), 1.26 (br s, 30H), 0.88 (t, 6H). 13C NMR (75 MHz, CDCl3): 72.1, 32.2, 29.9, 29.8, 29.7, 29.6, 26.4, 22.9, 14.3, 1.2.

PAGE 72

72 Poly[ProDOT(CH2OC8H17)2]. Br2-ProDOT(CH2OC8H17)2 (1.8 g, 0.003 mol) and MeMgBr ( 5 mL, 0.63 M by titration) were dissolv ed in tetrahydrofuran (100 mL, anhydrous). This solution was refluxed for 1 hour. NiCl2(dppp) (0.016g, 0.029 mmol) was then added to the solution producing a deep purple color. The mi xture was then refluxed 48 hours and cooled to RT. The reaction was poured into methanol, filt ered, and placed in the thimble of a soxhlet extraction setup. The solid was se quentially extracted with metha nol (24 hrs), he xanes (48 hrs), and dichloromethane (24 hrs). The final fraction was reduced via rotary evaporation to give a metallic purple solid (0.94 g). 1H NMR (300 MHz, CDCl3): 4.15 (s, 3H), 3.61 (s, 3H), 3.45 (t, 4H), 1.55 (m, 6H,), 1.27 (br s, 19H), 0.87 (t, 6H). 13C NMR (75 MHz, CDCl3): 72.1, 32.1, 29.8, 29.7, 29.6, 26.4, 22.9, 14.3, 1.2.

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73 CHAPTER 4 ARYLOXY SUBSTITUTED POLY(3,4PROPYLENEDIOXYTHIOPHENE)S Aryl Substituted Polythiophenes While a major success of conjugated polymer research was the development of regioregular poly(3-substituted-thiophene)s, the in corporation of aryl groups into polythiophenes has also received significant attention.160 Aryl substituted polythiophenes are especially interesting for their p-doping and n-doping possi bilities where substituti on of the phenyl ring allows access to both electrochemical processes.161 Subsequent research has targeted this class of materials for application as supercapacitors.162, 163 S S C8H17 S O C8H17 S O O C6H13 C6H13 Figure 4-1. Monomer structures for 3-octylth iophene, 3-(4-octylphe nyl)thiophene, 3-(4octyloxyphenyl)thiophene, and 3 -(1,3-hexyloxyphenyl)thiophene. The simplest aryl polythiophene is th e highly p-dopable poly(3-phenylthiophene).164 (Figure 4-1). Its phenyl ring is conjugated with the thiophene bac kbone providing a facile method to alter the electronic prope rties of the molecule. However, substitution at the 3-position also induces torsional strain between adjacent repeat units, thereby raising the polymerÂ’s band gap. Because the band gap for poly(3-phenylthiophene) was lower than in unsubstituted polythiophene, Onoda suggested that the phe nyl ring was orthogonal to the polythiophene backbone rather than coplanar.165 Recently, the conjugative effect of the aryl substituent on the electrochemical properties was studied.166 The electrochemistry of substituted poly(3-phenylthiophene)s was found to correlat e well with Hammett substituent constants.

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74 Thus, the redox properties shift to lower potenti als with electron donating groups, and shift to higher potentials with el ectron withdrawing groups.167 These monomers were produced by Suzuki coupling of substituted aryl halides with the 3-boronato thiophene,168 then electrochemically deposited. A series of phenyl and naphthyl substitu ted polythiophenes have also been studied.169 Monomers based on thiophene, bithiophene, and terthiophene backbones were synthesized. Increasing the thiophene substitution with aryl rings led to lower mono mer oxidation potentials, but the polymer redox potentials were raised for compounds with multiply substituted backbones. This was presumed to be due to st eric congestion from the substituent groups. The amount of charge passed was also determined fr om the polymersÂ’ electrochemistry. For both the pand n-doping processes, the el ectrochemically deposited polymers showed a charge imbalance between the anodic and cathodic portions of the vo ltammetry. This was presumed to be due to an irreversible degradation pro cess. Additionally, some of the da ta suggests that for the more stable polymers, the p-/ncharge ratio is 2-3. The relationship to the po lymerÂ’s electrochemical stability was unclear. Substituted poly(3-phenylthiophene)s have also been used as color tunable materials for LEDs.170 Ideally, the steric bulk of the substituted phenyl substituent affects the polymerÂ’s conjugation length by changing the dihedral angl e between adjacent repeat units. The differing conjugation lengths then give ri se to variable photoluminescence across the visible spectrum. These substituted, regioregul ar poly(3-phenylthiophene)s were obtained from oxidative polymerization with FeCl3, 171 where the phenyl substitution is thought to encourage a radical cation propagation during the polymerization. The conformations of these regioregular polymers

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75 are controlled by the size of the substituted phenyl substituent. A ll colors have been demonstrated using simple substitutions. One of the benefits of sterically demanding phe nyl rings is that mol ecular ordering can be studied more effectively. Poly(3-octylphenyl thiophene) was characterized by X-ray diffraction to compare solution-cast and spin-cast films.172 The solution-cast films were regarded similar to poly(3-octylthiophene), with thiophene b ackbone stacking distances of 5.1 Ã… for poly(3-octylphenylthiophene) vers us 3.8 Ã… for poly(3-octylthiophene). The octylphenyl chains were aligned normal to the substrate with the th iophene backbone lying parallel. The spin-cast films were initially amorphous, but after exposure to chloroform vapor or heat, the crystallinity increased. The solid state structure of substituted 3phenyl thiophenes has also been studied.173 Two families of poly(3-phenylthiophene)s were synt hesized. The first family, having long alkyl chains at the ortho position of the phenyl subs tituent, and the second having a shorter methoxy group, or no ortho substituent at al l. The resulting crystal structur es showed that the phenyl rings in the first family were orthogonal to the plane of the thiophene backbone with the alkyl chains extending above and below the main chain. Th ese compounds also gave more crystalline materials. The second family, without sterica lly demanding alkyl chains at the ortho position, appears to orient similar to pol y(3-akylthiophene)s with the alkyl chains remaining in the plane of the backbone. Aryl Substituted Propylenedioxythiophenes The incorporation of aryl groups into propyl enedioxythiophene materials has also been studied (Figure 4-2). Using th e diethyl malonate alkylation de scribed in Chapter 3, a benzyl substituted 3, 4propylened ioxythiophene was obtained.174

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76 S O O H S O O H S O O H S O O Figure 4-2. Aryl substituted propylenedioxythiophene (Pro DOT) monomer structures: ProDOT-Benzyl, ProDOT-Hexyl, ProDOT-Dodecyl, ProDOT-Benzyl2. The goal was to improve the electrochromi c contrast by maximizing the inter-chain separation.129 The monomer crystal structure shows th at the benzyl groups sit above and below the plane of the thiophene ring. A film of PProDOT-Benzyl2 on ITO-covered glass was obtained, and a contrast ( %T) of 89% at max = 632 nm was observed. The polymerÂ’s coloration efficiency was measured between 550 and 600 cm2 C-1over several thicknesses, and the electrochromic contrast was st able after 5000 cycles. Since the polymer was insoluble in common organic solvents, differentially substitu ted ProDOTs were synthesized using the same method.175 Benzyl-, hexyl-, dodecylProDOT, and their di-substituted analogues were synthesized and electrochemically polymerized. The electropolymerized polymers performed as expected, with PProDOT-Benzyl giving a contra st of 63% at 572 nm. Each monomer was chemically polymerized by FeCl3 in chloroform. After reduction w ith hydrazine, and purification by Soxhlet extraction, only two soluble polymers, PProDOT-Hexyl2 and PProDOT-Dodecyl2 were recovered. No reasoning was given for the insolubility of the PProDOT-Benzyl2 and mono-substituted polymers. Solution cast film s for these polymers were used to perform electrochromic characterization. The contrast ratios for these two polymers were significantly less than their electropolymerized counterparts. For example, th e contrast for electrochemical

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77 PProDOT-Hexyl2 fell from 74% at max = 627 nm to 40% at max = 601 nm for the chemically polymerized polymer. Based upon these examples, aryl substituted dioxythiophenes are a ttractive targets for electrochromic polymers. Additionally, the ability of the aryl group to affect the solid state ordering of the polymer presents another method to affect the processa bility of dioxythiophene polymers. In this chapter, we introduce phenyl and cresyl substituted propylenedioxythiophenes, developed from commercially ava ilable phenols. The synthesis avoi ds the complexity of prior approaches, and these polymers will provi de a foundation to explore more complex propylenedioxythiophenes. Monomer Synthesis It was intended that aryl subs tituents could be installed on 2,2-bis(bromomethyl)-propylen edioxythiophene (ProDOT-(CH2Br)2) similar to the alkoxy groups of Chapter 3. We initially sought alkyl substituted phenols to influence the ordering via -stacking while maintaining solubility to produce chemically polymerized PProDOTs. Therefore a synthetic route involv ing the Friedel-Crafts acylation of phenol with the appropriate acyl chloride was pursued. This reaction produced a difficult-to-purify resi due in low yields. An alternative approach attempted the Fries rearrangement of th e corresponding alkyl benzoate ester. Again, the synthesis fa iled to provide the alkyl phenol in significant yields. Therefore, reconsideration led to the use of commercial phenols as a basis for aryl substituted propylenedioxythiophenes (Figure 4-3). To that end, freshly distilled phe nol and cresol were reacted with ProDOT-(CH2Br)2. Potassium carbonate, a poorer base, was used rather than sodium hydride to prevent oxidative side re actions from the sodium phenoxide.

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78 S OO BrBr K2CO3,DMF S OO OO ArOH A r A r Ar=Phenyl,65% Cresyl,35% Figure 4-3. Synthesis of aryloxy propylened ioxythiophenes by Williamson etherification. The base and phenol were heated in DMF for 18 hours, followed by the addition of the ProDOT-(CH2Br)2. The reaction was allowed to proceed for 96 hours, and then worked up as in Chapter 3. The reaction was cooled, poured into water, and recovered in dichloromethane. Subsequent extractions with wate r and brine gave a yellow oil. In the initial ProDOT-(CH2OC6H5)2 purification, unreacted starting material was observed to persist with the product during column ch romatography. A solution of the incompletely purified molecule in petroleum ether was extrac ted with saturated aque ous potassium hydroxide to remove the remaining phenolic impurities. Later syntheses were pur ified by stirring the product in diethyl ether. ProDOT-(CH2OPhMe)2, however, undergoes purification by column chromatography using 4:1 hexanes: diethyl ethe r as the eluent. Following char acterization by NMR, HRMS, and elemental analysis, the monomers were then used for electrochemical polymerization and characterization. Single crystal X-ray crysta llography was obtained for both monomer compounds. The monomers were grown by slow evaporation from either acetone or dioxane. Both molecules have an interesting packing st ructure (Figure 4-4 a nd Figure 4-6), involving the aryl groups.

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79 Figure 4-4. Unit cell of ProDOT-(CH2OC6H5)2. Viewed along the C* axis. For ProDOT-(CH2OC6H5)2 the unit cell consists of four molecules. The sulfur atom of the thiophene ring sits 3.7 Ã… away from the oxygen at om of the phenoxy substituents and 4.3 Ã… from the para carbon of both phenoxy groups. The central quate rnary carbon of ProDOT-(CH2OC6H5)2 has two angles of interest. The a ngle between the two substituent groups is ~111 . The angle of propylenedioxy ring, cent ered at the quarter nary carbon, is 110 . Both ProDOT-(CH2OC6H5)2 and ProDOT-(CH2OPhMe)2 crystals align such that the thiophene of one monomer lies between the subs tituent aryl rings of another molecule. ProDOT-(CH2OPhMe)2 has two molecules comprising its unit cell (Figure 4-5). Figure 4-5. Unit cell of ProDOT-(CH2OPhMe)2.

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80 . In ProDOT-(CH2OPhMe)2, the sulfur atom sits 4.9 Ã… a bove the quaternary carbon of the second molecule. The distance between the pendant groupsÂ’ oxygen atoms is 5.4 Ã…. The distance between adjacent ProDOT-(CH2OPhMe)2 molecules is variable (Figure 4-6), but the sulfur atom lies ~3.5 Ã… between both pendant aryl rings. Figure 4-6. Crystal packing in ProDOT-(CH2OPhMe)2. A) Viewed along the a axis. B) Stacked view along the b axis. The methyl groups in maroon outline the void between the stacks. The monomer molecules alternate direction as you move laterally through the crystal. Figure 4-6b shows a stacked view that demonstr ates the regularity of the crystal. When vertically spaced the sulfur di stances alternate between 7.2 Ã… a nd 6.1 Ã…, this continues until a defect is reached. This defect is identified by the methyl distan ces between the two stacks. The methyl-methyl distances decrease from 14.1 Ã… to 13.3 Ã… to 4.1 Ã… until the void is reached, at which point the distances begin to increase following the same values . This is different from ProDOT-(CH2OC6H5)2, which has a screw sense between the molecules (Figure 4-7). The crystal structure of ProDOT-(CH2OPhMe)2 suggests a much more open spacing, due to the accommodation of the methyl substituents. This more open spacing should allow for easier dopant ion transport throughout the polymer fi lm, thereby improving the optoelectronic properties of the resulting pol ymer. The monomer ProDOT-(CH2OC6H5)2 takes on the typical herringbone order with the sulfur atoms between the aryl rings (Figure 4-8). A B

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81 Figure 4-7. Unit cell of ProDOT-(CH2OC6H5)2 viewed along the b axis . Two molecules located behind the nearer molecules. The upper molecules have the substituents aligned counter clockwise, while the lower substituents are aligned clockwise. Figure 4-8. Crystal packing in ProDOT-(CH2OC6H5)2.

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82 It was expected that ProDOT-(CH2OC6H5)2 and ProDOT-(CH2OPhMe)2 would become insoluble during a chemical polymerization. Ther efore, these molecules where electrochemically polymerized to obtain a thorough characterizat ion of the familyÂ’s electrochemical and optoelectronic properties. Electrochemistry ProDOT-(CH2OC6H5)2 was electrochemically deposited from acetonitrile with tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte. The monomer oxidation (Figure 4-9) shows an onset at 1.0 V versus Fc/Fc+, and a peak oxidation at 1.11 V. These values increase for the cresol derivative, ProDOT-(CH2OPhMe)2 (Figure 4-10). The onset of oxidation occurs at 0.99 V with the peak oxidation at 1.16 V. Repeated scan cyclic voltammetry (CV) shows a very different grow th response from the alkoxy derivatives of Chapter 3. Rather than the usua l peaks associated with polymer redox, the phenyl polymer shows an additional redox processes. The first pro cess has a half-wave poten tial of 0.03 V, and the second process has a potential of 0.39 V. For ProDOT-(CH2OPhMe)2, two processes are shown, but the second lacks an obvious reducti on peak. The first peak has an E1/2 of -0.01 V, with the second process having a more pos itive potential of 0.3 V. -0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -2 -1 0 1 2 3 4 5 6 7 Ep,c2 = 0.33 V Ep,c1 = -0.04 V Ep,a2 = 0.40 V Ep,a1 = 0.10 VS OO * * OO nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -1 0 1 2 3 4 5 6 7 Ep,m = 1.11 V Onset 1.0 V Current (mA/cm2)Potential vs. Fc/Fc+ (V)A B Figure 4-9. Electrochem istry of ProDOT-(CH2OC6H5)2. A) Monomer oxidation showing onset potential of 1.0 V and a peak oxidation pot ential of 1.11 V. B) Electrochemical deposition. Experiments performe d in acetonitrile with 0.1 M TBAPF6 electrolyte

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83 Independent CV suggests the two processes are not linked to each other. A potential window involving only the first process was scanned and the oxidation observed. The peaks were then compared to the oxidations of small molecule analogues of the substituent groups. There are few reports on the electrochemical oxi dation of phenol that do not deal with its conversion to other organic produc ts. Iotov and Kalcheva focused on the voltammetry of phenol at Pt and Au alloy electrodes.176 Phenol is known to “foul electrodes,” more correctly described as coupling of phenoxy radicals. After the initial oxidation sc an, two small anodic peaks are observed at 0.7 and 0.9 V vs. Ag/Ag+ with both electrodes. The or igin of these peaks was not discussed, but they remain unchanged as the curr ent response of other processes falls with increasing passivation of the electrode. By analog y, the first processes in Figure 4-9 and Figure 4-10 are likely due to the phenolic oxidation. A comparison of the voltammetry of thes e polypropylenedioxythi ophenes does not support that the substituents are mimicking anisole electr ochemistry. The Pt oxidation of anisole occurs at 1.49 V vs. Ag/Ag+, while p-methylanisole oxidizes at 1.2 V,177 which was confirmed at 1.23 V vs. Fc/Fc+ in TBAPF6 and acetonitrile. Neither PProDOT demonstrates a similar response. -0.8-0.6-0.4-0.20.00.20.40.60.81.01.21.4 -2 0 2 4 6 8 10 12 S O O OO Me Me * * n Ep,c = -0.05 V Ep,a2 = 0.30 V Ep,a1 = 0.04 VCurrent (mA/cm2)Potential vs Fc/Fc+ (V)-0.8-0.6-0.4-0.20.00.20.40.60.81.01.21.4 -2 0 2 4 6 8 10 Ep,m = 1.16 V Onset 0.99 V Current (mA/cm2)Potential vs Fc/Fc+ (V)B A Figure 4-10. Electrochemistry of ProDOT-(CH2OPhMe)2. A) Monomer oxidation showing an onset potential of 0.99 V and a peak oxidation potential of 1.16 V. B) Electrochemical deposition performe d in acetonitrile with 0.1 M TBAPF6 as electrolyte.

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84 The redox current increases as the polymers ar e deposited, and the first process remains at approximately the same potential. This suggests th at the second redox proce ss is the result of the actual dioxythiophene polymer backbone. The di fference between the anodi c potentials of this second redox process in ProDOT-(CH2OPhMe)2 versus ProDOT-(CH2OC6H5)2 is likely due to the methyl substituent. The methyl group is st erically demanding, which should lead to a more open morphology than in ProDOT-(CH2OC6H5)2. Considering the voltammetric break-in (Figure 4-11a and Figure 4-12a), PProDOT-(CH2OC6H5)2 shows a sharp oxidation associated with the pendant groups, a small oxidation that decr eases as the CV progresses, and a deep broad reduction. This broad reduction is not seen in the PProDOT-(CH2OPhMe)2 cyclic voltammetry. In Figure 4-12a, the PProDOT-(CH2OPhMe)2 reduction changes from a very broad peak to a small peak near 0.4 V. The scan rate dependence provides some information on the redox processes. For PProDOT-(CH2OC6H5)2 (Figure 4-9b), the two oxidation peak s merge at high scan rates leading Figure 4-11c presents the results when the currents are plotted versus scan rate. The plot is linear confirming a surface bound redox process.157 Perhaps the species responsible for the initial process at E1/2 = 0.03 V must be overcome, with regular transport occurring thereafter. -0.6-0.4-0.20.00.20.40.6 -0.5 0.0 0.5 1.0 S OO * * OO nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)-0.8-0.40.00.40.81.2 -10 -5 0 5 10 ip,c ip,aCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)0100200300400500 -6 -4 -2 0 2 4 6 8 10 Current (mA/cm2)Scan Rate (mV/s) ip,a ip,cA B C Figure 4-11. Button electroc hemistry of PProDOT-(CH2OC6H5)2 in 0.1 M TBAPF6 and acetonitrile A) Voltammetric break-in. B) Scan rate dependence C) Peak current versus scan rate.

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85 In Figure 4-12c, the peak currents can be sepa rated, and the anodic current of the initial redox process is plotted alongside the anodic current due to the pol ymer. The resulting plots do not show complete linearity. The divergence from linearity is most pronounced above 225 mV/s. Both cyclic voltammetry plots show small decrease s in the potential as the polymer adjusts to the dopant ion transport during electrochemical switching. -0.8-0.40.00.40.81.2 -12 -8 -4 0 4 8 12 16 ip,cip,aPotential vs Fc/Fc+ (V)Current (mA/cm2)-0.8-0.6-0.4-0.20.00.20.40.60.8 -1.0 -0.5 0.0 0.5 1.0 S O O OO Me Me * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)0100200300400500 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 Current (mA/cm2)Scan Rate (mV/s) ip,a1 ip,a2 ip,cA B C Figure 4-12. Button electrochemistry of PProDOT-(CH2OPhMe)2 in 0.1 M TBAPF6 and acetonitrile. A) Voltammetric break-in. B) Scan rate dependence. C) Peak current versus scan rate. Whereas the scan rate dependence experiments in Chapter 3 confirmed that those polymers acted indistinguishably from the elec trode, here the unusual behavior for ip,a1 suggests that an additional electrochemical process is occurring. It is lik ely the result of a redox site within the deposited film no longer meeting the rate of electr on transfer required at very high scan rate. The redox process associated with ip,a2, however, performs as expected with the scan rate; this process is most likely the actual polymer redox. Electrochromism Polymer films were produced and characterized as electrochromic films on ITO-covered glass by potentiostatic deposition. The spectroelectrochemistry for PProDOT-(CH2OC6H5)2 is shown (Figure 4-13). The polymer was switche d from a purple color at 0 V to obtain a transmissive grey film at 0.65 V. At 0 V, th e spectrum of the polymer films shows a single absorption with max = 580 nm. This is attributed to the * transition between the HOMO and

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86 LUMO orbitals of the polymer. In its neutral state, the polymer has no absorbance at low energy values. As the potential is ra ised, the polaron absorption appears at 900 nm, in addition to the decrease in the * absorption. The film is observed to lose its color as the oxidation progresses. Near 0.65 V, the pol ymer no longer has an absorbance in the visible, and the polaron absorption has also disappeared. Only the NIR region shows absorption due to the formation of bipolarons, or radical di-cations. Degradation was observed beyond 0.65 V. 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 580nm; ~2.1 eV 0.65 V 0.65 V 0 V 0 V S OO * * OO nAbsorbance (a.u.)Wavelength (nm) Figure 4-13. Spectroelectrochemistry of electrochemically deposited PProDOT-(CH2OC6H5)2 from TBAPF6 in ACN. Oxidized in increments from 0.0 V to 0.2 V in 100 mV increments; 0.25 V to 0.4V in 25mV increments; from 0.4 V to 0.65 V in 50 mV increments. In the PProDOT-(CH2OPhMe)2 spectroelectrochemistry (Figure 4-14), the * transition shows a split absorption at 557 and 601 nm, due to vibronic coupling,178 Davydov splitting,147,179 or discrete conjugation lengths83 within the polymer. The polar on peak occurs at 855 nm with sharper absorption changes in the NIR region, li kely due to the more open morphology caused by incorporating the methyl substituents.129 A sharp change in the ne ar infrared region of the polymer filmÂ’s absorption can be seen. These has been noticed in other sterically demanding poly(propylenedioxythiophene)s. Still, the el ectrochromic response of both polymers is consistent with prior observations.

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87 4006008001000120014001600 0.0 0.5 1.0 1.5 2.0 max = 557, 601 nm; ~2.2, 2.1 eVS O O OO Me Me * * n0.95 V -0.4 V 0.95 V -0.4 V Absorbance A.U.Wavelength (nm) Figure 4-14. Spectroelectrochemistry of electrochemically deposited PProDOT-(CH2OPhMe)2 from TBAPF6 in ACN. Oxidized from -0.4 V to 0.3 V in 100 mV increments; from 0.3 V to 0.4 V in 50 mV increments; from 0.4 V to 0.8 V in 25 mV increments; from 0.8 V to 0.95 V in 50 mV increments. The in situ colorimetry of both polymer films is shown (Figure 4-15). With the Y of 36%, PProDOT-(CH2OC6H5)2 shows a single divergence from t ypical colorimetry results. In most cases after oxidation, the luminance asymptotes to a value of high tran smissivity. After the maximum transmissivity is attained in PProDOT-(CH2OC6H5)2, the relative luminance quickly falls, and the film is observed to color sligh tly. This occurs above 0.2 V and mirrors the oxidation limit in the spectroelectrochemi stry experiment. The colorimetry of PProDOT-(CH2OPhMe)2 is typical. The film follows an asymptote to 43% relative luminance -0.8-0.6-0.4-0.20.00.20.40.6 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 S O O OO Me Me * * nRelative Luminance (Y/Y0)Potential vs Fc/Fc+ (V)-0.8-0.6-0.4-0.20.00.20.40.6 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 S OO * * OO nRelative Luminance (Y/Y0)Potential vs. Fc/Fc+ (V) Figure 4-15. In situ colorimetry of PProDOT-(CH2OC6H5)2 and PProDOT-(CH2OPhMe)2

PAGE 88

88 Finally, the composite coloration efficiency (C E) was obtained from several. CE can be used to determine the change in optical density due to amount of charge transport through an electrochromic polymer. Composite coloration ef ficiency captures the overall optical density change for a near complete optical switch. In itially, the polymers were potentiostatically deposited at 1.85 V from a solution of TBAPF6 and acetonitrile to a limit of 0.06 C. The deposition was later repeated us ing a limit of 0.08 C to produce films of differing thicknesses. Following cyclic voltammetric break-in, a ta ndem chronocoulometry/ chronoabsorptometry experiment (Figure 4-16), was performed to reco rd the charge passed as the polymer films were switched between oxidized and reduced states. 051015202530354045 -5 0 5 10 15 20 25 30 35 40 100%T = 38.8 Qi = -0.0176 C Tox = 36.2 Tred = 0.58Percent Transmittance (a.u.)Time (s)-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Charge (C/cm2)Qf = 0.354 C Figure 4-16. Tandem chronoabsorptometry / chronocoulometry for a PProDOT-(CH2OPhMe)2 film. The difference between the transmissive and colored state at max = 557nm is compared to the charge passed during the el ectrochemical switch. The labeled values were used to calculate the composite coloration efficiency. Since the majority of color change occurs pr ior to completion of the electrochromic switch, the Tox and Tred values at 95% of the full optical switch were used to calcul ate the change in optical density for the films. The results were ob tained for two different thicknesses (Table 4-1).

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89 Table 4-1. Coloration Efficiency Data for Aryloxy Substituted ProDOTs. ~300 Ã… film ~600 Ã… film Phenoxy Cresoloxy Phenoxy Cresoloxy %T 26.3 38.2 21.4 49.1 Tox 80.6 36.2 38.8 64.9 Tred 58.6 0.58 19.9 18.9 tswitch (s) 0.4 2.3 3.3 2.7 (OD) 0.14 1.8 0.29 0.54 Qd95% (C/cm2) 1.41 x10-4 2.7 x 10-1 5.0 x10-4 1.43 x10-3 CE (cm2/C) 983 678 581 377 In the initial experiment, films were cycled to alleviate trapped charges, and then multiply switched multiply according to the following profile. The films were held at 0 V for 10s, then reduced to -0.3 V. After another 10 seconds, th e film was oxidized to 1 V, and then reduced back to 0 V. The electrochemical responses were then converted to charge passed, and the change in percent transmittance was recorded. Both polymer films show the expected slow oxidation, followed by a much faster reduction (Figure 4-16). While electroactive, the polymer films did not appear to pass large amounts of charge as seen in Table 4-1. The result is that capacitive charging and discharging effects due to the ITOglass electrode are seen. In Figure 4-16, the c oulometric decay of the film is not observed to return to zero, but rath er a 100 mC jump is observed between successive potential switches. This capacitive charging is not seen when a control e xperiment using the same electrolyte and Pt button electrode is used. The second set of CCE experiments were performed using longer times to allow the thicker material to equilibrate. For PProDOT-(CH2OC6H5)2, the potential was held at 0 V for 15s. The film was then oxidized to 1 V, and held at that potential for 20 seconds before returning to 0 V for 15s. This resulted in a broader oxidative char ge profile, but retained the fast reductive phenomenon discu ssed. The corresponding experiment for PProDOT-(CH2OPhMe)2 was held at 0 V for 15s, oxidized to 1 V for 30s, then reduced to 0 V for 30s.

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90 When comparing the two sets of experiment s, it is apparent that aryloxy substituted PProDOTs pass smaller amounts of charge than the alkoxy substituted PProDOTs of Chapter 3. The contrast ratio is also far be low that seen in other substitute d PProDOTs. This may be due to the polymerÂ’s ordering, or the aryl groups ma y be involved in the oxidative process. In the crystal structure, the thiophene ring lies between two aryl groups. It is possible that the aryloxy groups participate in radical coupling during electrochemical deposition. However, the marked increase in the contrast of PProDOT-(CH2OPhMe)2 over PProDOT-(CH2OC6H5)2 supports previous observation that substituent bulk gives greater electrochromic contrast, presumed to be a result of the incorporation of the methyl substituent. An additional observation is that coloration efficiency decreases and switching time increases with increased film thickness due to po or dopant ion transport through the film, and not the result of a chemical process. The increased film thickness was observed to decrease both the switching time and the colorati on efficiency as expected. Conclusion In this chapter, monomer derivatives of the 3, 4-propylenedioxythiophene backbone have been produced using commercial starting material s. The materials are produced in reasonable yields, and are easily purified. The monomers were then electro chemically deposited to produce electroactive polymer films. These films were used to establish a baseline performance for aryloxy substituted PProDOTs as electrochromic materials. The films have the typical dioxythiophene characteristics with a maximu m absorption in the vi sible region between 500-600 nm. Both materials show a reversible el ectrochemical process around 0.3 V, in addition to an earlier process near 0.01 V. The former is more likely due to the dioxythiophene backbone, as the latter process compares favorably with electrochemical oxidations of phenol seen in the literature. No color change is observed during the latter process. However, the process does

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91 appear to affect the material, as the scan ra te dependence of both compounds shows deviation from linearity at scan rates between 75 and 225 mV/s. X-ray crystallography shows that ProDOT-(CH2OC6H5)2 has a unit cell consisting of four monomer molecules, and that ProDOT-(CH2OPhMe)2 has a unit ce ll composed of two monomer molecules. If this arrangement is maintained in solution, where the monomer has low solubility, the aryloxy substituent groups may be involved in the radical coupling process that occurs during electrochemical deposition. There may be defect s in the polymer films that oppose the transport of dopant ions throughout the film. This, in turn, may explain the lo w amounts of current and charge passed through the films dur ing coloration efficiency meas urements. The films produced to be somewhat transmissive, even in the highe r thickness examples, giving contrast ratios of ~24% for the phenyl derivative and ~45% for cr esol derivative. The higher contrasts for PProDOT-(CH2OPhMe)2 are thought to be due to the increased bulk of the methyl group, suggesting that functional aryl groups which do not inhibit the dopant ion tr ansport could be used to improve the electrochromic contrast of 3,4propylenedioxythiophene polymers. However, care must taken to ensure that the electroactivity of the polymers is not affected, and that the polymerÂ’s electrochemistry should be thoroughly co mpatible with the electrolyte of choice. Experimental Section Materials 2,2-Bis(bromomethyl)-propylenedioxythiophene s ynthesis was adapted from a literature procedure.133 All reagents and solvents were purchased from Aldrich or Fisher and used without further purification. Anhydrous DMF was purch ased from Acros in Sure-Seal bottles. Synthesis [ProDOT-(CH2OC6H5)2]. Phenol (0.83 g, 0.00877 mol) and potassium carbonate (2.43 g, 0.0175 mol) were dissolved in dimethylformamide (50 mL, anhydrous) in a 250 mL

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92 round-bottomed flask. The mixture was then heated to 110 C for 18 hours. Bis(bromomethyl) ProDOT (1 g, 0.002924 mol) was then added to the re action flask, and returned to temperature. The reaction was heated 96 hours and cooled to ro om temperature. The solution was poured into 300 mL of water, extracted with dichloromethane (3 x 100 mL). The organic layers were the extracted with water (3 x 100 mL) and brine (150 mL). The organic extracted were collected and washed with brine (100 mL). Magnesium sulfat e was used to dry the organic layer, and the volume reduced via rotary evaporation giving a br own oil. This was chromatographed on silica gel with 1:1 petroleum ether: dichloromethane to give brown oil. The re sulting light brown solid was dissolved in petroleum ether and washed w ith potassium carbonate (satÂ’d., aqueous). This oil was then recrystalli zed from 4:1 hexanes:diethyl ethe r as a white solid (0.73 g, 65%). 1H NMR (300 MHz, CDCl3): 7.25 (d, 4H), 6.93 (d, 6H), 6.5 (s, 2H), 4.28 (s, 4H), 4.22 (s, 4H).13C NMR (75 MHz, CDCl3): 158.85, 149.58, 129.66, 121.40, 114.82, 105.69, 73.41, 67.02, 47.58. ESI-FT-ICRMS [M+Na]+: calcd. for 391.0975; found, 391.0975. [ProDOT-(CH2OPhMe)2]. p-Cresol (1.42 g, 0.0132 mol) and potassium carbonate (3.63 g, 0.0263 mol) were dissolved in dimethylformamide (50 mL, anhydrous) in a 250 mL round-bottomed flask. The mixture was then heated to 110 C for 18 hours. Bis(bromomethyl) ProDOT (1.5 g, 0.004385 mol) was then added to the re action flask, and returned to temperature. The reaction was heated 96 hours and cooled to ro om temperature. The solution was poured into 300 mL of water, extracted with dichloromethane (3 x 100 mL). The organic layers were the extracted with water (3 x 100mL) and brine (150 mL). The organic extracts were collected and washed with brine (100 mL) and potassium carbonate (satÂ’d., aqueous). Magnesium sulfate was used to dry the organic layer, and the volume redu ced via rotary evaporati on giving a yellow oil. This was chromatographed on sili ca gel with 4:1 hexanes:diethyl ether as a white solid (0.61 g,

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93 35%). 1H NMR (300 MHz, CDCl3): 7.05 (d, 4H), 6.78 (d, 4H), 6.48 (s, 2H), 4.26 (d, 4H), 4.17 (d, 4H), 2.27 (s, 6H). 13C NMR (75 MHz, CDCl3): 156.82, 130.58, 130.06, 114.67, 105.62, 73.45, 67.27, 20.70. ESI-FT-ICRMS [M+Na]+: calcd. for 419.1288; found, 419.1303.

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94 CHAPTER 5 REDUCIBLE SIDE GROUP POLY( 3,4-PROPYLENEDIOXYTHIOPHENE)S Literature Review One of the many applications receiving attention is the development of polymer-based batteries8,15,16 and supercapacitors.17 Conjugated polymers can act as either anode or cathode in these devices, and offer some electrochemi cal control via manipulation of the monomer structure, or the degree of doping.16 Conjugated polymers that unde rgo p-doping easily, such as polythiophenes, polypyrroles, and polyanilin es have been the preferred materials180 for devices which employ these polymers as the cathode, usua lly combined with an anionic electrolyte. Current focus has shifted to the development of all polymer devices, where both electrodes are appropriately charged polymers, or the inco rporation of reducible pendant groups onto nonconjugated polymer backbones.15,69 It would be therefore be advantageous to develop a conjugated polymer which can unde rgo both n-doping and p-doping.162,181 The major inhibition to nand pdopable polym ers has been the stabil ity of the reduced, or n-doped, state.182 To circumvent these inhibitions, polymers have been developed using the donor-acceptor approach to attain an electrochemical window which does not allow the negative interactions of water and/or oxygen with the reductive state.113 In these systems the position of the HOMO and LUMO orbitals relati ve to the vacuum energy level is controlled by the strengths of electron donation and withdraw al via monomer substitution. This has led to questions regarding the nature of true n-doping in conjugated polymer systems.138 In the case of bis(EDOT)-pyridine and bis(EDOT)-diphenyl-pyr idopyrazine, n-doping is believed to require the generation of negative char ge carriers in the polymer bac kbone. While these polymers show typical oxidative behavior, accessing multiple color states with organic and alkaline electrolyte salts, the reductive behavior shows no electrochromism, likely due to pinning.183 The polymers

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95 were also explored using differential pulse voltammetry.184 DPV provides more accurate current response than cyclic voltammetry. These BE DOT systems show no current response upon application of reductive potentials w ith alkaline elec trolyte salts, and bis(EDOT)-diphenyl-pyridopyrazin e shows a single color change upon the first reduction. Subsequent conductivity and spectro electrochemistry measurements gave similar results with small, or no, changes in the response using alkaline electrolyte salts. The second approach mentioned incorporates redox active molecules as pendant groups.185 One method synthesized poly(3-bromohexyl )thiophene, followed by reaction with 2-carboxyanthraquinone.85 This post-polymerization process led to 87% incorporation of the anthraquinone substituent. Two reduction waves were attributed to th e anthraquinone group, and third reduction was attributed to n-doping of the polythiophen e backbone. The polymer also demonstrated thermochromic properties between 10 C and 90 C. p-Nitrophenyl groups have also be en covalently attached to polythiophenes. These groups are interesting because of their electroactivity, and the nitro substi tuents can be electrochemically converted to amine functionaliti es. The p-nitrophenyl functiona l groups have also shown some non-linear optical characteristics.186 Using a monomer synthesis involving 2-(thiophen-3-yl)-acetic acid, th e p-nitrophenyl unit was inco rporate via oxo, amino, and oxymethyl linkages.187 The polymers were then el ectrochemically deposited from tetrabutylammonium perchlorate (TBAP) and acetonitrile. The oxy and amine linked polymers were observed to lose the reversibility of the p-nitrophenyl el ectrochemistry after polymerization. The loss of elect rochemical reversibility was re lated to the pr esence of TBAP absorptions in the polymerÂ’s IR spectrum. This suggests that the elect rolyte was not expelled

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96 from the films following the reduct ion. The reduction of the nitro groups also seems to affect the polymer backbone electrochemistry. More recently, electron accepto r functionalized poly(3,4-ethy lenedioxythiophene)s were reported.188 Via acid-catalyzed transetherificat ion, chloromethyl-substituted EDOT was produced as the keystone synthon for these m onomers. Hydroxyl func tionalized anthraquinone, perylene tetracarboxylic diimide, and tetracyan o-9, 10-anthraquinodimethane were then reacted with chloromethyl EDOT to produce the desi red monomers. All three monomers showed reversible reduction waves due to the electron acceptor units. Afte r polymerization, these reduction waves were observed at more posi tive potentials due to the influence of the electroactive PEDOT backbone. The polymers were then characterized optically, and suggested as light-harvesting or ch arge storage candidates. One concern with performing reductive electroche mistry is the occurrence of irreversible phenomena during reduction. This is seen in polythiophenes. Po lythiophenes are observed to ndope with tetra-alkylammoni um electrolyte salts, however, use of alkaline cations leads to the failure of the polythiophene films.189 The tetra-alkylammonium reductions show “pre-peaks” which are determined to be due to “charge tra pping,” i.e. un-resolved co nductive charge carriers along the polymer backbone. These pre-peaks were seen in other systems such as polyfluorene, and pyridine-thiophene copolymers. CV, EQCM, a nd IR suggest the “pre-peaks” seen in the ndoping of polythiophenes are due to changes in the polymer chain via reaction with hydroxide to produce thieno-quinone moieties along the polymer chain.190 With that consideration, we sought to produce n-dopable, or reducible, polypropylenedioxythiophenes (PProDOTs) base d upon the synthetic methodology developed in Chapter 4. Aryl substituents with elect ron-withdrawing groups were grafted onto

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97 2,2-bis(bromomethyl)-ProDOT (ProDOT-(CH2Br)2). Using the Williamson etherification of substituted phenols, electrochemically pol ymerizable monomers were produced and characterized as p-dopable materials, and then the reductive capability of the monomers was determined. Ideally, this should produce a pol ymer which can be oxidized and reduced at sufficiently different potentials to provide a single active material for charge storage devices. Monomer Synthesis Following methodology similar to Chapter 4, substituted phenols with electron withdrawing groups were reacted under basic conditions with ProDOT-(CH2Br)2. Initially, substituted nitrophenols were t hought to provide an ideal subs trate for reduction. Recent literature has demonstrated the reduction191 of 4-nitrophenol, 4-cy anophenol, and 2-cyanophenol, in addition to study of the radical anions192 produced electrochemically. Concerns about the stability of the electron poor phenols led to the use of less reactive base , cesium carbonate, rather than the standard sodium hydride. Monomers , from cyanophenol and pentafluorophenol, were synthesized (Figure 5-1). The r eagents were combined in a dry round-bottomed flask and heated for a minimum of 48 hours. S OO BrBr S OO OO 4-cyanophenol,Cs2CO3DMF 39% NC CN S OO BrBr S OO OO Pentafluorophenol,Cs2CO3DMF 44% F F F F F F F F F F Figure 5-1. Synthesis of electron poor aryloxy ProDOT monomers. In the case of ProDOT-(OPhCN)2, the compound was obtained via a work-up of sequential extractions with diethyl ether, water, and brine. After remova l of the organic solvent, an off-white, mauve solid was obtained, and then recrystallized from an acetone/water mixture. This method involved the dropwise addition of water un til the first precipitatio n of the organic solid

PAGE 98

98 was observed. A minimal amount of acetone was readded to solubilize the newly formed precipitate. The solution was then chilled overnight to allow for complete precipitation. The ProDOT-(OC6F5)2 synthesis, adapted from a literature synthesis of substituted tetrathiafulvalenes,193 differed in that hydrolysis gave a wh ite solid which was filtered away from the desired product. The filtrate was then acidi fied, and extracted with dichloromethane. Washing with water, and removal of the organic solvent gave an off-white solid, which was also recrystallized from acetone and water. The final monomer was a white solid. Commercial 4-hydroxy benzoate was reacted with ProDOT-(CH2Br)2 using sodium hydride and DMF to obtain ProDOT-EB. Whereas previous syntheses used carbonate bases, the presence of the ester group dissuaded the use of an equilibrium controlled deprotonation. As in Chapter 3, sodium hydride was used to produce th e desired phenoxide (Figure 5-2). The reaction was heated overnight, then cooled and diluted wi th water. Subsequent extraction with diethyl ether, washing with brine a nd water gave the crude product as a white, yellow solid. After washing with hexanes, the colored impurity wa s removed, giving the final monomer as a pure, white solid. S O O Br Br S O O O O O O O O NaH, DMF 81% OH O O Figure 5-2. Synthesis of ProDOT-EB. All monomers were then ch aracterized by standard methods as recorded in the experimental methods at the end of this chapter.

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99 Single crystals were prepared by slow evaporation from dioxane for ProDOT-(OC6F5)2 and acetone for ProDOT-EB. ProDOT-(OPhCN)2 was not submitted for X-ray analysis due to the timing of purification. The crystal of ProDOT-(OC6F5)2 appears to be composed of two monomer molecules, with sulfur atoms directed in oppos ite directions (Figure 5-3). Figure 5-3. Unit Cell for ProDOT-(OC6F5)2 viewed along the a axis. However, when nearest neighbor molecules ar e considered, a differe nt picture emerges. There appears to be two modes of ordering betw een neighboring molecules. The molecules are associated vertically and translationally within th e crystal structure. The primary interaction is governed by the fluorine atoms of the aryl ring. The pentafluorophe noxy rings lie above one another, but it can also be seen that the pent afluorophenoxy rings are offset creating a stair-step effect within the crystal structure (Figure 5-4). Closer inspection shows that a single pentafluorophenoxy ring is involved in a F-F interaction, while the second ring adjusts to allow the initial overlap to occur. The second pentafluorophenyl ring does not have any ordering interaction associated (Figure 5-5) . The overlap is regular and lead s to standard distances within the crystal.

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100 Figure 5-4. Stacked views of ProDOT-(OC6F5)2. Figure 5-5. Expanded View of Packing of ProDOT-(OC6F5)2 with intermolecular distances shown. F-F interaction (light blue) has a dist ance of 2.9 Ã…. The translational distance (green) is 4.3 Ã…. The vertical dist ance between interac ting sets is 3.3 Ã….

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101 The F-F interaction has a distance of 2.9 Ã…. The translational distance between the two pentafluorophenoxy rings involved th e F-F interaction is 4.3 Ã…. These two molecules are then related to a second set of m onomer molecules that also ha ve the pentafluorophenoxy rings separated by 2.9 Ã…. The distance be tween sets of molecules is 3.3 Ã… The ProDOT-EB crystal shows a regular or dering of the monomer molecules with a recurring sulfur-sulfur distance of 6.0 Ã… between adjacent molecules (Figure 5-6). This crystal is nearest to the intended solid-state structure th at was desired. The st ructure appears to be influenced by the aryl groups as expected, with very close associations between the pendant aromatic groups. The distance between faces of th e aryl substituents is 4.0 Ã…, while the edge-toedge distance is 3.8 Ã… (Figure 5-7). Figure 5-6. Crystal packing for ProDOT-EB. This molecule clearly demonstrates that ordering in dioxythiophe nes can be governed by the substituent rather than the polymer backbone . If these interactions persist in soluble analogues of the molecule, substituent choice ma y be a convenient method to affect the ordering of dioxythiophene polymers.

PAGE 102

102 Figure 5-7. Crystal packing for ProDOT-EB showing aryl-aryl distance measurements. Ambient Atmosphere Electrochemistry To obtain a complete understanding of the pol ymerÂ’s electrochemical properties, button electrochemistry was performed on the bench top in ambient conditions. Initially, the monomers were characterized using the same methods as ot her dioxythiophene materials. The polymers, were electrochemically deposited from monomer electrolyte solutions of tetrabutylammonium hexafluorophosphate (TBAPF6) and acetonitrile by repeated s can cyclic voltammetry (CV). -0.50.00.51.01.5 -0.08 -0.04 0.00 0.04 0.08 0.12 0.16 S OO OO F F F F F F F F F F * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V) Ep,a = 0.31 V Ep,c = 0.13 V -0.50.00.51.01.5 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Potential vs. Fc/Fc+ (V) Current (mA/cm2) Onset 1.18 V Ep,m 1.31 V AB Figure 5-8. Ambient atmosphere electrochemistry of ProDOT-(OC6F5)2. A) Monomer oxidation showing an onset potential of 1.18 V a nd a peak oxidation of 1.31 V vs. Fc/Fc+. B) Electrochemical deposition. Polymer a nodic and cathodic pote ntials are shown. Experiments performed in acetonitrile with 0.1 M TBAPF6 electrolyte.

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103 The initial CV scan of ProDOT-(OC6F5)2 shows an onset of oxidation occurring at 1.18 V followed by the monomerÂ’s peak oxidation at 1.31 V vs. Fc/Fc+ (Figure 5-8). The redox process is demonstrated by repeated cycling. Well-de fined oxidative and reduc tive current responses nearest 0.31 V and 0.13 V delineate the polymer film Â’s electroactive process. The resulting halfwave potential is 0.22 V. Similar results are seen in the CV of ProDOT-(OPhCN)2 (Figure 5-9). -0.90.00.91.8 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Ep,m 1.26 V Onset 1.07 V Current (mA/cm2)Potential vs. Fc/Fc+ (V)-0.50.00.51.01.5 -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 S O O O O NC CN * * n Ep,c = -0.07 V Ep,a = 0.19 VCurrent (mA/cm2)Potential vs Fc/Fc+ (V)B A Figure 5-9. Ambient atmosphere el ectrochemistry of ProDOT-(OPhCN)2. A) Monomer oxidation showing onset potenti al of 1.07 V and a peak potential of 1.26 V vs. Fc/Fc+. B) Electrochemical depos ition of ProDOT-(OPhCN)2. Polymer anodic and cathodic potentials are shown. Experiments perf ormed in acetonitrile with 0.1 M TBAPF6 electrolyte. The peak oxidation of the monomer is observe d at 1.26 V with an onset of 1.07 V vs. Fc/Fc+. The electroactive process has a half-wave potential of 0.06 V. The unsymmetrical electrochemical cycle is likely due to differential transport rate s of the supporting electrolyte through the ProDOT-(OPhCN)2 polymer film. The peak potentia ls are consistent with those obtained in Chapter 4 for aryl substituted dioxythiophenes. When compared to the series of substituted phenyl thioph enes in the literature,167 the values obtained for ProDOT-(OC6F5)2 and ProDOT-(OPhCN)2 are 0.1 mV lower. In the literature , tetraethylammonium tetrafluoroborate (TEABF4) is used rather than TBAPF6. The major contributor is likely the increased electron

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104 donation due to the propylenedioxy ring, and th e absence of torsiona l strain seen in 3-phenylthiophenes. -1.0-0.50.00.51.01.5 -1 0 1 2 3 4 5 6 Current (mA/cm2)Potential vs. Fc/Fc+ (V) Onset 1.06 V Ep,m = 1.13 V -1.0-0.50.00.51.01.5 -2 -1 0 1 2 3 4 5 6 S OO OO O O O O * * nCurrent (mA/cm2)Potential vs Fc/Fc+ (V) Ep,a2 = 0.06 V Ep,c2 = -0.03 V Ep,a1 = -0.16 V Ep,c1 = -0.20 V A B Figure 5-10. Ambient atmosphere electrochemis try of ProDOT-EB. A) Monomer Oxidation showing on onset potential of 1.06 V and a peak oxidation potential of 1.13 V. B) Electrochemical deposition. Polymer a nodic and cathodic poten tials are shown. Experiments performed in acetonitrile with 0.1 M TBAPF6 electrolyte. ProDOT-EB (Figure 5-10) has a monomer oxi dation with a peak potential of 1.13 V vs. Fc/Fc+. As in the simple phenols of Chapter 4, the polymer shows two redox processes. The first process has a peak anodic potential of -0.06 V, a peak cathodic potential of -0.2 V, and a halfwave potential of -0.18 V. This is close to the peak-to-peak sepa ration for the corresponding peaks in PProDOT-(OC6H5)2, which was 0.04 V. The second redox process is considered the polymer process, and has peak potentials of 0.06 V and -0.03 V versus Fc/Fc+, and a half-wave potential of 0.02 V. All films were transferred to a fr esh, monomer-free solution of TBAPF6 in acetonitrile. After repeated CV cycling to “bre ak-in” the films, the scan rate dependence of all polymers was obtained. PProDOT-(OC6F5)2 shows good current response between 25 mV/s and 600 mV/s. The peak current values were plotted against the scan rate (Figure 5-11c). Both processes are reasonably linear, though some curvat ure is seen in the plot of anodi c current versus scan rate for PProDOT-(OC6F5)2. The voltammetric break-in (Figure 5-11a) shows the symmetrical current

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105 response of the electroactive polymer redox pro cess. The anodic and cathodic poten tials are constant because the electronic properties are saturated at the optimum conjugation length. The same experiment was performed from 50 mV/s to 750 mV/s for PProDOT-(OPhCN)2 (Figure 5-12). The scan rate dependence experiments fo r PProDOT-EB are shown (Figure 5-13). The polymer film showed good linear response between 0 and 500 mV/s. -0.6-0.4-0.20.00.20.40.60.81.0 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 S OO OO F F F F F F F F F F * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)-0.50.00.51.0 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Current (mA/cm2)Potential vs. Fc/Fc+ (V) ip,a ip,c C B0100200300400500600 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Current (mA/cm2)Scan Rate (mV/s) ip,a ip,cA Figure 5-11. Button electrochemistry of PProDOT-(OC6F5)2 in 0.1 M TBAPF6 and acetonitrile. A) Voltammetric Break-in. B) Scan rate depe ndence C) Plot of peak currents versus scan rate. All polymers show reasonably linear scan rate dependence sugges ting the electroactive species is surface bound and not diffusion dependent, i.e. the deposited polymer performs similarly to the pristine electrode surface.157 The films appear to have several trapped charges at low scan rates that are easily overcome. Pr eliminary reduction electrochemistry was also performed under ambient conditions, a nd good current response was obtained. -0.6-0.4-0.20.00.20.40.6 -0.0010 -0.0005 0.0000 0.0005 0.0010 0.0015 S O O O O NC CN * * nCurrent (A/cm2)Potential vs. Fc/Fc+ (V)-1.2-0.8-0.40.00.40.81.21.6 -15 -10 -5 0 5 10 15 ip,cip,aCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)C B0100200300400500600700800 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 Current (mA/cm2)Scan Rate (mV/s)A Figure 5-12. Button electrochemistry of PProDOT-(OPhCN)2 in 0.1 M TBAPF6 and acetonitrile. A) Voltammetric break-in. B) Scan rate depe ndence. C) Plot of peak currents versus scan rate.

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106 -0.50.00.5 -1.2 -0.8 -0.4 0.0 0.4 0.8 1.2 S OO OO O O O O * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)-0.8-0.6-0.4-0.20.00.20.40.60.8 -15 -10 -5 0 5 10 15 Current (mA/cm2)Potential vs Fc/Fc+ (V)ip,a ip,c C B0100200300400500 -15 -10 -5 0 5 10 15 ip,a1 ip,a2 ip,c1 ip,c2Current (mA/cm2)Scan Rate (mV/s)A Figure 5-13. Button electrochemist ry of ProDOT-EB in 0.1 M TBAPF6 and acetonitrile. A) Cyclic voltammetric break-in of polymer film . B) Scan rate dependence. C) Plot of peak current versus scan rate. Electrochromism Electrochromism is the reversible change in the absorption or tran smission properties due to an applied external voltage. PProDOT materials can switch between a colored, neutral state and a transmissive, oxidized state. Th ese polymer films were characterized by spectroelectrochemistry to follow the loss of the * transition in the neutral state, and the growth of an absorption attributed to polaronic charge ca rriers in the oxidized state. A film of PProDOT-(OC6F5)2 was deposited onto glass slides c overed with indium tin oxide (ITO), switched repeatedly in monomer free electrolyt e solution to “break-in” the film, then the UV-VIS-NIR spectrum was recorded as the poten tial was increased stepwise from neutral to oxidized state (Figure 5-14). Similar to the polymers in previous chapters, the * absorption is split into two peaks at 574 nm and 624 nm. Typical absorptions due to polaron generation were observed at 990 nm. If the alignment seen in the monomer X-ray crys tal structure persists in the polymer films, then the * splitting may be due to conformationa lly limited conjugation lengths in the polymer film. The polym er film of PProDOT-(OC6F5)2 is electrochromic, switching from a typical PProDOT blue-purple in the ne utral state to a tr ansmissive grey film in the oxidized state.

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107 4006008001000120014001600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 max = 574nm, 624nm; ~ 2.2eV, 2.0evS OO OO F F F F F F F F F F * * n 0 V 0.75 V 0.75 V 0 VAbsorbance (a.u.)Wavelength (nm) Figure 5-14. Spectroelectroc hemistry of PProDOT-(OC6F5)2. Film was oxidized in increments of 100 mV from 0 V to 0.4 V, then increm ents of 50 mV from 0.4 V until 0.65 V The in situ colorimetry (Figure 5-15) shows the cha nge in luminance for the polymer. The polymer film has a change in luminance of about 30% which is low when compared the alkoxy PProDOTs in Chapter 3; those polymers with lumi nance changes of 60% are much more typical of dioxythiophene polymers. The lack of contrast may be due to the regular orientation of the aryl rings, rather than the random orie ntation expected in the alkoxy PProDOTs. -0.8-0.6-0.4-0.20.00.20.40.6 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 S OO OO F F F F F F F F F F * * nRelative Luminance (Y/Y0)Potential vs. Fc/Fc+ (V) Figure 5-15. In situ colorimetry of PProDOT-(OC6F5)2. The spectroelectrochemistry of PProDOT -EB (Figure 5-16) and PProDOT-(OPhCN)2 (Figure 5-18) was obtained. A polymer film was deposited potentiostatically onto an ITO-covered glass slide, and repeatedly switche d in monomer-free elect rolyte to condition the films. The conditioning process, or break-in, serv es to swell the polymer film with supporting electrolyte and to improve the material transp ort properties of the electroactive film. The

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108 UV-VIS-NIR spectrum was then recorded as the polymer film was oxidized stepwise from the neutral, colored state to the oxidized, transmissive state. 4006008001000120014001600 0.0 0.1 0.2 0.3 0.4 0.5 S OO OO O O O O * * n Absorbance (a.u.)Wavelength (nm) Neutral 0.8 V Neutral 0.8 V Figure 5-16. Spectroelectrochemist ry of PProDOT-EB. Film was oxidized from Neutral to 0.4 V in 100 mV increments; from 0.4 V to 0.7 V in 50 mV increments; from 0.7 to 0.8 V in 100 mV increments. PProDOT-EB shows a maximum absorption at 586 nm or 2.1 eV, with the low energy edge of the absorption occurring at 686 nm, or 1.8 eV. This is the * absorption of the polymer. A polaron absorption near 924 nm is also observed as the polymer is oxidized. Unlike some of the previous films, large changes in the NIR region of the spectrum are not seen. -1.0-0.8-0.6-0.4-0.20.00.20.40.60.8 0.0 0.1 0.2 0.3 0.4 0.5 S OO OO O O O O * * nRelative Luminance (Y/Y0)Potential vs Fc/Fc+ (V) Figure 5-17. In situ Colorimetry of PProDOT-EB. The transmissivity of the f ilm was also characterized by in situ colorimetry (Figure 5-17). Similar to the other aryloxy polymers, PProDOT -EB shows a change in luminance of ~48%. The transition is also smooth and gradual with no sharp changes as observed in branched

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109 PProDOTs.158 There were no obvious effects from in corporation of the ester group into the electroactive polymer film. It is presumed that the es ters have not been converted to acid groups, and are not forming cross-links within the polymer film. B4006008001000120014001600 0.0 0.4 0.8 1.2 1.6 2.0 S O O O O NC CN * * n0 V 0.7 V 0.7 V 0 VAbsorbance (a.u.)Wavelength (nm) 0 V 0.7 V * max= 557nm;607nmmax2 = 300nm4006008001000120014001600 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 S O O O O CN NC H H OH CN Absorbance (a.u.)Wavelength (nm)A Figure 5-18. UV-VIS spectro scopy of PProDOT-(OPhCN)2. A) Spectroelectrochemistry The spectrum shows absorptions due to the polymer backbone at 557 nm and 607 nm, while a stronger absorption tails into the visible region with a maximum absorbance of 300nm. Film oxidized from 0 V to 4 V in 100 mV increments, from 0.425 V to 0.475 V to 0.5 V, then from 0.5 V to 0.7 V in 50 mV increments. B) Solution spectroscopy of phenol and ProDOT-(OCPhCN)2. For PProDOT-(OPhCN)2, the results are quite different from the other polymers studied (Figure 5-18). The film had the expected purpl e color in its neutral st ate. However as the polymer was oxidized, the UV-VI S-NIR spectrum did not show complete bleaching of the * transition, or the appearance of polaronic or bi polaronic transitions in the NIR region of the spectrum. Instead, a high energy absorption at 30 0 nm appears. Further experiments determined that this absorption is constant , and the decrease in the poly mer absorbance at 557 nm and 607 nm leads to the increase in the intens ity of the 300 nm absorption. This max2 tails far into the visible region obscuring the polar on absorption which occurs as th e polymer oxidizes. The tail of max2 in the visible region between 420 nm and 700 nm is not seen in the neutral polymer film. Comparison with reference spectra suggests that the high energy absorption is due to the cyanophenoxy groups.194 The UV-VIS spectrum of phydroxybenzonitrile shows a broad

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110 absorption at 247 nm, and several smaller ab sorptions which extend up to 300 nm. The comparison suggests that the absorption of th e cyanophenoxy group is stronger than the polymer backbone, but is outside the visible range. To complete the characterization, the in situ colorimetry (Figure 519) was also obtained. The luminance transmitted was recorded as the fi lm was oxidized from neutral to 0.8 V. The change in luminance was approximately 45%. Like previous aryloxy substituted PProDOTs, the change occurs gradually with step wise potential increases. -0.6-0.4-0.20.00.20.40.6 0.0 0.1 0.2 0.3 0.4 0.5 S O O O O NC CN * * nPercent Luminance (%Y)Potential vs. Fc/Fc+ (V) Figure 5-19. In situ colorimetry of PProDOT-(OPhCN)2. Inert Atmosphere and Reduction Electrochemistry The key motivation for designing these type s of molecules is to perform reductive electrochemistry not involving the dioxythiophene backbone. Ideally, the pendant group should have a complete reductive electr ochemical process. Most re ductive electrochemistry is susceptible to attack by water and o xygen found in the ambient atmosphere,195 so the button electrochemistry was repeated in a controlled oxygen-free, wa ter-free environment of an argon atmosphere glove box. The electroche mical deposition results for ProDOT-(OC6F5)2 (Figure 5-20), for ProDOT-(OPhCN)2 (Figure 5-22), and for ProDOT-EB (Figure 5-24). The experiments were performed with acetonitrile that was degassed via multiple freezepump-thaw cycles over 3 hours. The monomer solids and acetonitr ile were then cycled between

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111 full vacuum and argon atmosphere twice in the gl ove box antechamber. After storing overnight at full vacuum, the materials were brought into the glove box whilst maintaining an oxygen and water free atmosphere. Repetitive CV and SRD we re performed using sim ilar conditions to the ambient experiments. -1.0-0.50.00.51.01.5 -1 0 1 2 3 4 5 Current (mA/cm2)Potential vs. Fc/Fc+ (V)Ep,m = 1.14 V -0.80.00.81.6 -3 -2 -1 0 1 2 3 4 5 6 7 8 S OO OO F F F F F F F F F F * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)Ep,a = 0.18 V Ep,c = 0.04 VBA Figure 5-20. Inert atmosphere electrochemistry of ProDOT-(OC6F5)2. A) Monomer oxidation showing a peak oxidation at of 1.14 V vs Fc/Fc+. B) Electrochemical deposition. Polymer anodic and cathodic potentials are shown. Experiments performed in acetonitrile with 0.1 M TBAPF6 electrolyte. PProDOT-(OC6F5)2 showed a half-wave potential of 0.11 V, and the monomer oxidation occurred at 1.14 versus Fc/Fc+. The values were lower than the bench top, likely due to the lack of dissolved water in the aceton itrile affecting the el ectrochemical process. Figure 5-21 shows the PProDOT-(OC6F5)2 peak current plots are consistent with ambient results, while Figure 5-22 shows the electrochemical deposition of ProDOT-(OPhCN)2. B51015202530 -25 -20 -15 -10 -5 0 5 10 15 20 25 Current (mA/cm2)Sq Root of Scan Rate (mV/s)1/2 ip,a ip,c02004006008001000 -25 -20 -15 -10 -5 0 5 10 15 20 25 Current (mA/cm2)Scan Rate (mV/s) ip,a ip,cA Figure 5-21. Cottrell-type analysis for PProDOT-(OC6F5)2 A) Plot of peak currents versus scan rate. B) Plot of peak currents ve rsus square root of scan rate.

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112 -0.50.00.51.01.5 -2 0 2 4 6 8 Onset 1.02 V Ep,m = 1.18 VCurrent (mA/cm2)Potential vs Fc/Fc+ (V)-0.50.00.51.01.5 -8 -6 -4 -2 0 2 4 6 8 10 12 S O O O O NC CN * * n Ep,c = 0.03 V Ep,a = 0.39 VCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)B A Figure 5-22. Inert atmosphere el ectrochemistry of ProDOT-(OPhCN)2. A) Monomer oxidation showing onset potential of 1.02 V and a peak oxidation of 1.18 V vs Fc/Fc+. B) Electrochemical deposition. Polymer a nodic and cathodic poten tials are shown. Experiments performed in acetonitrile with 0.1 M TBAPF6 electrolyte. The monomer oxidation occurred at 1.18 V, whic h was much lower than the potential seen in the ambient experiments. The polymer had a half-wave potential of 0.35 V. Figure 5-23 shows the results of the scan rate dependence experiment. Again, no significant change was observed from the bench-top experiments. Thus, the nature of the polymer is not substantively affected by deposition under inert atmosphere. However, the smaller potential values observed during the electrochemical depositions suggested th at the solvent conditions greatly affect the observed results. B4681012141618 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 Current (mA/cm2)Square Root of Scan Rate (mV/s)-1/2 ip,a ip,a050100150200250300 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 Current (mA/cm2)Scan rate (mV/s) ip,a ip,aA Figure 5-23. Cottrell-type an alysis for PProDOT-(OPhCN)2 A) Plot of peak currents versus scan rate. B) Plot of peak currents ve rsus square root of scan rate

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113 Figure 5-24 shows the electrochemical depos ition of ProDOT-EB. As expected, two electrochemical processes are observed. The firs t is likely associated with the aryl pendant groups, and the second is the expected polymer electrochemical process. -0.8-0.6-0.4-0.20.00.20.40.60.81.01.2 -2 -1 0 1 2 3 4 Current (mA/cm2)Potential vs. Fc/Fc+ (V)E p,a = -0.18, 0.08 VEp,c = -0.2, -0.01 V-0.6-0.4-0.20.00.20.40.60.81.01.2 -0.4 0.0 0.4 0.8 1.2 1.6 2.0 2.4 Current (mA/cm2)Potential vs Fc/Fc+ (V)Ep,m = 1.12 V Onset 1.01 VB A Figure 5-24. Inert atmosphere electrochemistry of ProDOT-EB. A) Monomer oxidation showing onset potential of 1.01 V and peak potential of 1.12 V vs. Fc/Fc+. B) Electrochemical deposition. Polymer anodic and cathodi c potentials are shown. Experiments performed in acetonitrile with 0.1 M TBAPF6 electrolyte. The half-wave potentials are -0.19 V and 0.04 V, respectively. These values are significantly lower than those observed in am bient atmosphere, which is analogous to the decrease in observed po tentials of PProDOT-(OC6F2)2 and ProDOT-(OPhCN)2. It was also advantageous to use differen tial pulse voltammetry (DPV) to study these systems. DPV allows for more accurate dete rmination of electrochemical response than traditional cyclic voltammetric methods. The experiment was performed for PProDOT-(OC6F5)2 (Figure 5-25) and PProDOT-(OPhCN)2 (Figure 5-26) using the Pt button electrochemical cell. The films were held at the st arting potentials for at least 30 seconds before each individual experiment began. The scans were performed in segments beginning with the oxidative process. The potential was scanned from -0.1 V to 0.85 V, then back to -0.1 V. The reductive segment was started at -1 V and lowered to -3 V, then back to -1 V. Only the oxidative process was reversible having an anodic onset potential at -0.26 V vs. Fc/Fc+ and a peak plateau at 0.21 V.

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114 This value is nearly identical to that seen in the inert cyclic voltammetry. The cathodic portion of the oxidative process had an onset at -0.19 V a nd peak plateau at 0.04 V. Both peak potentials were only 20 mV different from earlier meas urements. The reduction of the pentafluorophenoxy pendant groups was irreversible giving no anodic cu rrent response, even af ter repeated reductive cycling. The cathodic process has an onset of -1.88 V and a peak plateau of -2.43 V. -3.0-2.5-2.0-1.5-1.0-0.50.00.5 -10 -8 -6 -4 -2 0 2 4 6 8 S OO OO F F F F F F F F F F * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)Onset -0.26 V Ep,a = 0.21 V Onset -0.19 V Ep,c = 0.04 V Onset -1.88 V Ep,c = -2.43 V Figure 5-25. Differential pulse voltammetry of PProDOT-(OC6F5)2. The potential was scanned from -0.1 V to 0.85 V, then 0.85 V to -0.1 V for the oxidative process (Figure 5-26) with onset s of -0.23 V and -0.22 V for the anodic and cathodic processes. The anodic peak plateau was 0.25 V, and the ca thodic peak plateau was 0.26 V. The reductive process was scanned from -0.5 V to -1.8 V. The reduction began at -1.88 V, and does not asymptote within the potential window. No reciprocal anodic process was observed. -2.0-1.5-1.0-0.50.00.5 -9 -6 -3 0 3 6 9 S O O OO NC CN * * nCurrent (mA/cm2)Potential vs. Fc/Fc+ (V)Onset -0.23 V Onset -0.22 VEp,a = 0.25 VEp,c = 0.26 V Onset -1.88 V Figure 5-26. Differential pulse voltammetry for PProDOT-(OPhCN)2.

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115 The reduction of 4-cyanophenol has been observed at -1.6 V versus Ag[sic]192 using a gold macroelectrode in tetrabutylammonim perchl orate and DMF. The resulting calculations suggested that the reduction of 4-cyanophenol phenol is followed quickly by the protonation of the radical anion. Repetition of the experiments using a gold micr odisk electrode also revealed an irreversible reduc tion peak at -1.6 V. The PProDOT-EB films were also characteri zed by DPV (Figure 5-27). The electron withdrawing ability of the este r should improve the electrochemi cal reduction processes within this molecule. -3.0-2.5-2.0-1.5-1.0-0.50.00.5 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 S OO OO O O O O * * nEp,c = -2.26V Ep,a = -2.24 VCurrent (mA/cm2)Potential vs.Fc/Fc+ Onset -0.37 V Onset -0.27 VEp,a = 0.07 V Ep,c = 0.03 VOnset -1.96 V Onset -1.82 V Figure 5-27. Differential pulse voltammetry for PProDOT-EB. For the oxidative process, the potential was scan ned from 0 V to 1 V, then from 1 V back to 0 V. This produced an anodic onset at -0.37 V, a peak plateau of 0.07 V, a cathodic peak plateau of 0.03 V, and an anodic onset at -0.27 V. The reductive process was studied similarly. The potential was scanned from -0.4 V to -3 V, then from -3 V back to -0.4 V. The reductive electrochemistry gave a cathodi c onset at -1.82 V, a cathodic plateau at -2.26 V, an anodic plateau at -2.24 V, and an anodic onset at -1.96 V. For comparison, a film of PProDOT-(CH2OC6H5)2 was also studied under reductive conditions (Figure 5-28). The oxidative plot was obtained by s canning the potential between 0 V and 1 V, then from 1 V to 0 V.

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116 -3.5-3.0-2.5-2.0-1.5-1.0-0.50.00.5 -3 -2 -1 0 1 2 3 S OO * * OO nEp,c = -3.64 V Ep,a = -3.61 VCurrent (mA/cm2)Potential vs. Fc/Fc+Ep,a = 0.36 V Ep,c = 0.35 V Onset -0.19 V Onset -0.22 V Figure 5-28. Differential pul se voltammetry for PProDOT-(CH2OC6H5)2. The reductive segment was obtained by beginning at -3 V and scanning back to 0 V. Attempts to scan forwards from 0 V to -3 V in itially gave no response. When the experiment was repeated beginning at -1.5 V towards -3 V, the current response was finally observed. This phenomena suggests that there is a charging capacity that must be reached before reduction can be observed with PProDOT-(CH2OC6H5)2. This was not seen in the substituted aryl PProDOTs. PProDOT-(OC6F5)2 and PProDOT-(OPhCN)2 showed much smaller potential windows where reduction could occur. This confirms that electr on withdrawing substituents enhance the ability of aryl substituted dioxythiophenes to undergo re ductive electrochemical processes. Also significant is that the curre nt responses of PProDOT-(CH2OC6H5)2 were lower than the other polymer films. This is consistent with prior observations which suggested that simple aromatic groups do not pass charge as well as other dioxythiophenes. Conclusion In this chapter, we have used the phenol based Williamson etherification methodology to produce functional aryloxy substi tuted 3,4-propylenedioxythiophenes. Commercially available, 4-cyanophenol, pentafluorophenol, a nd ethyl 4-hydroxybenzoate were used to generate ProDOT monomers which are able to be electrochemical ly reduced. The polymers are electrochemically deposited at potentials similar to those seen in simple arylox y substituted monomers. Both

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117 compounds have monomer oxidation pot entials near 1.1 V versus Fc/Fc+. The polymer electrochemistry was unchanged when the expe riments were repeated in the argon-filled atmosphere of a glove box. The difference in monomer oxidation potential between the glove box and bench top is likely the re sult of greater purity in the supporting electrolyte solution. The incorporation of an aryl este r into PProDOT has also been shown. This monomer can be produced in good yields, and shows good contro l of ordering as seen in the x-ray crystallography. The electrochemistry is similar to that of ProDOT-(OPh)2 and ProDOT(OPhMe)2. Two redox processes are observed with the second likely being due to the polymerÂ’s -conjugation system. The deposited polymer performs as a surface bound electroactive species as expected, with linear responses to s can rate and scan rate dependence. The X-ray crystal structure of the ProDOT-(OC6F5)2 monomer presents some future opportunities. The interaction between F atoms in the monomer structure suggests the possibility to control polymer ordering and morphology. The pentafluorophenoxy rings participating in a FF interaction may allow for new multidimensional structures to be created. The spectroelectrochemistry shows that all polymers are el ectrochromic as is typical of PProDOTs, and gave films with contrasts of 30-45%. The observation of a high energy absorption due to the cyanophenoxy group in PProDOT-(OPhCN)2 was also made. The absorption likely affects the transmissive state of the polymer, and appears to reach into the visible region when the polymer is oxidized. Fi nally, the reduction capa bilities of the polymer films were studied. PProDOT-(OPhCN)2 and PProDOT-(OC6F5)2 show irreversible reduction phenomena, while PProDOT-EB gives a complete electrochemical cycle. In the case of PProDOT-(OPhCN)2, this is supported by similar work in the literature. Th e incorporation of

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118 phenols that have known reduction capabi lities is next step to produce poly(3,4-propylenedioxythiophene)s capable of oxidative and reductive electrochemistry. Experimental Section Materials 2,2-Bis(bromomethyl)-propylenedioxythiophene s ynthesis was adapted from a literature procedure.133 All reagents and solvents were purchased from Aldrich or Fisher and used without further purification. Anhydrous DMF was purch ased from Acros in Sure-Seal bottles. Synthesis [ProDOT-(OPhCN)2] . Cyanophenol (1.88 g, 0.0158 mol) an d Cesium carbonate (5.14 g, 0.0158 mol) were dissolved in dimethylformamide (25 mL, anhydrous) in a 250 mL round-bottomed flask. Bis(bromomethyl)-ProDO T (1.8 g, 0.0053 mol) was then added to the reaction flask, and The mixture was then heated to 110 C for 58 hours. The reaction was cooled to room temperature. The solution was poured into 300 mL of water, extracted with diethyl ether (3 x 100 mL). The organic layers were collected and washed with water (3 x 100 mL) and brine (150 mL). Magnesium sulfate was used to dry the organic layer, and the volume reduced via rotary evaporation giving a mauve solid. This wa s recrystallized from acetone and water to give a white solid (0.86 g, 39 %). 1H NMR (300MHz, CDCl3 ) 7.59 (d, 4H), 6.98 (d, 4H), 6.53 (s, 2H), 4.25 (s, 8H). 13C NMR (75 MHz, CDCl): 149.16, 134.28, 115.45, 106.17, 105.12, 72.75, 66.91, 47.48. HRMS [M+H]+: calcd. for 419.1098; found, 419.1086. Anal. CalcÂ’d: C, 66.01; H, 4.34; N, 6.69; Found: C, 65.517; H, 4.378; N, 6.398. [ProDOT-(OC6F5)2]. Pentafluorophenol (3.2 g, 0.0174 mo l) and cesium carbonate (11.34 g, 0.0348 mol) were dissolved in dimethylformamide (30 mL, anhydrous) in a 250 mL roundbottomed flask. Bis(bromomethyl) ProDOT (2 g, 0.0058 mol) was then added to the reaction

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119 flask, and the mixture was then heated to 110 C for 48 hours. The reaction was cooled to room temperature. The solution was poured into 300 mL of water and filtered to collect a white solid. The filtrate was acidified to pH 4 and extracted with dichloromethane (2 x 150 mL). The organic layers were washed with wate r (3 x 100 mL) Magnesium sulfat e was used to dry the organic layer, and the volume reduced via rotary evaporation givi ng a mauve solid. This was recrystallized from acetone and water to give a white solid (1.4 g, 44%). 1H NMR (300 MHz, CDCl3 ) 6.52 (s, 2H), 4.42 (s , 4H), 4.24 (s, 4H). 13C NMR (75 MHz, CDCl3): 141.94, 105.98, 73.44, 72.02, 66.67. HRMS[M]+: calcd. for 548.0140; found, 548.0134. [ProDOT-EB]. Ethyl 4-hydroxy benzoate (3 g, 0.0175 mo l) and sodium hydride (1.33 g, 60%, 0.0348 mol) were dissolved in dimethylfo rmamide (30 mL, anhydrous) in a 250 mL roundbottomed flask. The mixture was then heated to 110 C for 4 hours. Bis(bromomethyl) ProDOT (2 g, 0.0058 mol) was then added to the reacti on flask, and returned to temperature. The reaction was heated overnight and cooled to r oom temperature. The solution was poured into 200 mL of water, extracted with diethyl ether (3 x 100 mL), and retained. The organic layers were the washed with brine (150 mL). Magnesium sulfate was used to dry the organic layer, and the volume reduced via rotary evaporation to a yellow-white solid. This was washed with hexanes to give a white solid.(2.4 g, 81%) 1H NMR (300 MHz, CDCl3): d, 4H), 6.9 (d, 4H), 6.5 (s, 2H), 4.33 (q, 4H), 4.26 (d, 8H), 1.37 (t, 6H) 13C NMR (75 MHz, CDCl3): 166.7, 163.4, 131.8, 123.8, 114.3, 105.9, 73.0, 66.9, 60.9, 47.5, 14.6. HRMS [M+]: CalcÂ’d. for C27H28O8S, 512.1505; found, 512.1495. Anal. CalcÂ’d: C, 63.27; H, 5.51; O, 24.97; S, 6.26; Found: C, 63.905; H, 6.22.

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120 APPENDIX A CRYSTALLOGRAPHIC DATA Figure A-1. Crystal Structur e Numbering for ProDOT-EB. Figure A-2. Unit Cell for ProDOT-EB.

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121 Table A-1. Crystal data and stru cture refinement for ProDOT-EB. Identification code gj03 Empirical formula C27 H28 O8 S Formula weight 512.55 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P2(1)/c Unit cell dimensions a = 6.0058(4) Å = 90°. b = 19.014(2) Å = 91.931(2)°. c = 21.8257(13) Å = 90°. Volume 2491.0(3) Å 3 Z 4 Density (calculated) 1.367 Mg/m 3 Absorption coefficient 0.180 mm -1 F(000) 1080 Crystal size 0.26 x 0.07 x 0.06 mm 3 Theta range for data collection 1.42 to 27.49°. Index ranges -7 h 6, -22 k 24, -25 l 27 Reflections collected 15901 Independent reflections 5610 [R(int) = 0.0466] Completeness to theta = 27.49° 98.1 % Absorption correction Integration Max. and min. transmission 0.9896 and 0.9685 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 5610 / 0 / 328 Goodness-of-fit on F 2 1.032 Final R indices [I>2sigma(I)] R1 = 0.0471, wR2 = 0.1217 [4086] R indices (all data) R1 = 0.0718, wR2 = 0.1336 Largest diff. peak and hole 0.493 and -0.349 e.Å -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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122 Figure A-3. Crystal Structur e Numbering for ProDOT-(CH2OC6H5)2.

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123 Table A-2. Crystal data and stru cture refinement for ProDOT-(CH2OC6H5)2. Identification code gj05 Empirical formula C21 H20 O4 S Formula weight 368.43 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Unit cell dimensions a = 11.6376(8) Å = 90°. b = 41.650(3) Å = 110.882(1)°. c = 15.7981(10) Å = 90°. Volume 7154.5(8) Å 3 Z 16 Density (calculated) 1.368 Mg/m 3 Absorption coefficient 0.205 mm -1 F(000) 3104 Crystal size 0.15 x 0.15 x 0.15 mm 3 Theta range for data collection 0.98 to 27.50°. Index ranges -14 h 14, -54 k 45, -19 l 20 Reflections collected 23285 Independent reflections 8094 [R(int) = 0.0502] Completeness to theta = 27.50° 98.3 % Absorption correction Integration Max. and min. transmission 0.9759 and 0.9632 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 8094 / 0 / 473 Goodness-of-fit on F 2 0.993 Final R indices [I>2sigma(I)] R1 = 0.0392, wR2 = 0.0858 [5525] R indices (all data) R1 = 0.0697, wR2 = 0.0974 Largest diff. peak and hole 0.268 and -0.378 e.Å -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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124 Figure A-4. Crystal Structur e Numbering for ProDOT-(CH2OPhMe)2.

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125 Table A-3. Crystal data and stru cture refinement for ProDOT-(CH2OPhMe)2. Identification code gj07 Empirical formula C77 H88 O16 S3 Formula weight 1365.65 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Unit cell dimensions a = 27.1473(13) Å = 90°. b = 10.2516(5) Å = 113.882(1)°. c = 27.5514(13) Å = 90°. Volume 7011.1(6) Å 3 Z 4 Density (calculated) 1.294 Mg/m 3 Absorption coefficient 0.174 mm -1 F(000) 2904 Crystal size 0.21 x 0.18 x 0.08 mm 3 Theta range for data collection 1.62 to 27.49°. Index ranges -19 h 35, -13 k 13, -35 l 35 Reflections collected 22456 Independent reflections 7931 [R(int) = 0.0504] Completeness to theta = 27.49° 98.4 % Absorption correction Integration Max. and min. transmission 0.9879 and 0.9648 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 7931 / 0 / 380 Final R indices [I>2sigma(I)] R1 = 0.0414, wR2 = 0.1071 [5632] R indices (all data) R1 = 0.0607, wR2 = 0.1133 Largest diff. peak and hole 0.303 and -0.334 e.Å -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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126 Figure A-5. Crystal Structur e Numbering for ProDOT-(CH2OC6F5)2

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127 Table A-4. Crystal data and stru cture refinement for ProDOT-(CH2OC6F5)2. Identification code gj08 Empirical formula C21 H10 F10 O4 S Formula weight 548.35 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P 1 Unit cell dimensions a = 8.3361(7) Å = 104.702(2)°. b = 9.9200(8) Å = 100.207(2)°. c = 13.6855(11) Å = 107.346(2)°. Volume 1004.92(14) Å 3 Z 2 Density (calculated) 1.812 Mg/m 3 Absorption coefficient 0.284 mm -1 F(000) 548 Crystal size 0.20 x 0.17 x 0.15 mm 3 Theta range for data collection 1.60 to 27.49°. Index ranges -9 h 10, -12 k 12, -17 l 17 Reflections collected 6414 Independent reflections 4296 [R(int) = 0.0303] Completeness to theta = 27.49° 93.2 % Absorption correction Integration Max. and min. transmission 0.9673 and 0.9228 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4296 / 0 / 325 Goodness-of-fit on F 2 1.049 Final R indices [I>2sigma(I)] R1 = 0.0361, wR2 = 0.1025 [3629] R indices (all data) R1 = 0.0426, wR2 = 0.1065 Largest diff. peak and hole 0.365 and -0.232 e.Å -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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128 APPENDIX B GEL PERMEATION CHROMATOGRAPHY WI TH PHOTODIODE ARRAY DETECTION Chromatographic Theory Molecular weight is a key piece of information that must be determined in polymer chemistry. Many methods have been developed fo r molecular weight determination; most rely on some physical property of the material to ascer tain if a high molecula r weight, or polymer, regime has been reached. Viscosity, light sc attering, and end group reactivity methods can be used to determine the molecular weight of a polymer sample. However, the most commonly used method is size exclusion chromatography (SEC ). For most synthetic polymers, it is often referred to as gel permeation chromatography (GPC). This method is relatively fast, consistently reproducible, and reasonably gene ral for many high molecular weight materials. This chapter provides a brief introduc tion to the technique,196 and a tutorial of its application to conjugated polymers. Column Choice GPC/SEC is a chromatographic separation me thod which characterizes molecules by their size. The method is derived from column chro matography and liquid chromatography. In those methods, species are separated by chemical interaction with a st ationary substrate, typically molecular polarity. The stationary phase perf orms the separation. This phase may be porous silica, a cross-linked organic gel, or a styren e-divinylbenzene copolymer. The latter is the preferred stationary phase mate rial. Columns can be chosen based on the following conditions. The separation range is adequate for the materi al being studied. This means that separation must occur between the initial and fina l elution times for the chosen column Resolution is controlled by th e particle size. At 5 m, effective resolution of the polymer molecules occurs with short column lengths, th ereby using less solvent. However, impurities are not tolerated with smaller particle sizes

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129 Columns which combine multiple pore sizes can be used to increase the separation range while also providing a linear ca libration curve. This type is useful for general molecular weight determination. Two column systems are preferred to mi nimize band spreading and peak broadening. The process of separation is well underst ood. Though one speaks of the separation being due to size, it is actually th e result of differences in the hydr odynamic volume of molecules of differing molar mass. The hydrodynamic volume is the space occupied by both the polymer and its cage of solvent molecules as it moves through the chromatography column. GPC/SEC provides a simple means to determine the distribut ion of molecular masses within in a sample, in addition to the average molecular masses of that sample. Within the stationary phase are pores into which the solvated polymer chains can flow . The pore sizes are such that larger chains spend very little time within the pores of the column, and sma ller chains have a high residency within the pores. The result is that larger molecular weight fractions of the polymer will elute off the column well before smaller molecular weight fractions. This provides information as to the distribution of molecular weight s within the polymer sample. Separation The separation itself is governed by the ra ndom distribution of molecules within and without the pores of the stationary phase. The volume of solvent outside the pores of the stationary phase is called the in terstitial, or exclusion, volume (Vi). It is this limit that defines the high molecular weight end of the separation range; this value is used to determine if a particular column can adequately separate the desired polymer molecular weight fractions. The total volume of the pores within the stationa ry phase is represen ted by the pore volume (Vp). Smaller molecules are presumed to have complete access to this volume, and will have the longest elution times. The sum of the intersti tial volume and the pore volume is called the void

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130 volume, and defines the total permeation of the st ationary phase. The eluti on time of a particular fraction is the sum of the interstitial volume a nd the equilibrium residen ce of the fraction within the pore volume (Equation B-1). Vp K V VSEC i e (B-1) The separation can also be explained in terms of thermodynamic properties. The equilibrium distribution of mol ecules depends on the Gibbs free energy. Ideally, there is no contribution from the enthalpy component, i.e. no interaction between the solvent or stationary phase with the molecular distri bution. Thus, the equilibrium di stribution simplifies to Equation B-2. R S SECe K/ (B-2) This equilibrium distribution expression gives KSEC as zero for large molecules and 1 for molecules which access the entire pore volume. Calibration Once separation is achieved, the mo lecular weight values must be assigned to the detected fractions of the polymer. This is achieved by calibrating the separation column to polymer standards of known molecular we ight. Most researchers use polymer of narrow molecular weight to calibrate GPC/SEC columns. The eluti on volume or time of the sample is correlated to the known molecular weight resulting in a linear relationship (Equation B-3). log M = A + BVe (B-3) The constants, A and B are obtained by linear regression of the plot of log M versus Ve. Most columns, however, do not give a simple linear relationship, and the calibration equation above is typically a polynomial expression. The number of terms in the expression is kept minimal and methods to determine the quali ty of the linear fit have been studied.197 It also

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131 instructive to calibrate the column using a br oad standard. This is often required by GPC software to obtain a proper mol ecular weight distribution informa tion. The sample may be from a commercial source, or merely a typical exam ple of the regularly characterized polymer. The second method of calibration is called unive rsal calibration. This method accounts for the hydrodynamic volume of the sample to prod uce a calibration curve that is somewhat independent of the polymer sample being characterized. Based upon the Mark-Houwink equation (Equation B-4), universal calibra tion relies upon the hydrodynamic volume being reasonably proportional to the intrin sic viscosity and molar mass of the polymer. In essence, two different polymers have calibration points which lie on the same curve, because their molecular weight fractions have similar hydrodynamic volumes. a vKM ] [ (B-4) This relationship was determined by plotting l og [n]M versus the elution volume for both a standard polymer and an unknown polymer.198 In this equation Mv is a viscosity average molecular we ight, a and K are constants specific to the polymer-solvent conditions. The constant, a, relates to the conformation of the polymer chain. For a = 0, the chain appr oximates a tight sphere, a = 1, a slightly extended coil, a = 0.5, polymer in its theta solvent, and for a = 0.8, a polymer in its extended ra ndom coil conformation. When a = 2, the polymer is presumed to be a ri gid rod material; it is this condition which might be expected for most conjugated polymers. Substitution of the Mark-Houwink equation for the intrinsic viscosity term for the two polymers gi ves Equation B-5. This equation allows the generation of an additional calibration curve for a column that has been previously calibrated. The analysis assumes that the a and K values for both polymers are accurate. 1 2 2 1 1 12 1 a aM K M K (B-5)

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132 Sample Detection The final consideration is the method of detec ting the eluted fractions , and quantitation of those amounts. Detectors can be placed into two categories: those that sense the concentration of eluted material, and those that respond to some physical proper ty, especially molar mass. The concentration sensitive detectors respond to either changes in the mobile phase, or changes in the eluting sample. The most common detection method in GPC/SEC is the refractive index detector (RI). RI detectors are useful because in addition to providing sample detection, they can be used to monitor the state of the chromatogra phic system. They provide information regarding the purity of the solvent, the efficiency of the solvent delivery system, and sample stationary phase interaction. The RI detect or recognizes the change in the re fractive index of the solvent as the molecular weight fractions elute from the colu mn. Almost every instrument will have an RI detector as part of the chromatography system. Other concentration sensitive detectors such as ultraviolet, infrared, and fluorescence spectroscopy, or an electrochemical detector may be used. The alternative to concentration detectors are molar mass sensitive methods. There are two main types, viscosity-based detection and light scattering based detecti on. Typically, the instrument set-up uses both types of mass-se nsitive detection. Viscosity detectors typically measure the pressure drop across a capillary of the flowing solvent. Since the viscosity of the solvent, o, is known, the pressure drop is proportional to the specific viscosity, sp, and the sample concentration is low, the definition of intrinsi c viscosity is easily determined (Equation B-6). csp c lim0] [ (B-6) Information such as the radius of gyration and hydrodynamic volume can be determined in addition to the molecular weight from light sc attering the detection. The weight average

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133 molecular weight is given by Equation B-7, where R( ) is the intensity of scattered light, P( ) is angular dependence of scattered light, and A2 is second virial coefficient. c A P M R c Kw 22 ) ( 1 ) ( * (B-7) The value, K*, is the optical constant and is defined by Equation B-8. The value dn/dc is the incremental refractive index, and is the key value in calculating the constant. The incremental refractive index relates how much the index of refraction of a solution changes with small variance in the concentration. AN dc dn K4 2 2/ 4 * (B-8) Finally, consideration of the variables th at affect the reproducibility of GPC/SEC measurements must be discussed. To convert elution time to elution volume, the flow rate generated by the solvent delivery system must be constant. Vibrations fr om the pump should also be minimal, as the detector will give a poor ba seline and stray peaks due to a faulty solvent delivery system. Solvent lines should be checked for leaks, air bubbles, and blockages due to impurities. Occasionally, a guard column may be installed to prevent fouling of the column. The detector response should be linear over a wi de range. The range should be nearest that of the separation region. The choice of the detect or also should involve a reproducible material property. This will increase the confidence in th e observed results with synthetic polymers. Columns should only be operated in the designa ted direction, unless attempting to remove a large blockage. Solvent changes must be pe rformed slowly, allowing the column to condition to new solvent. Typically, solvent changes take 1-2 hours, and are performed at very low flow rates. Several mixtures of the two solvents ar e prepared, and introduced to the column over the

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134 course of 4-6 hours. After each solvent change , a new calibration curve should be produced and checked against previous calibrations. GPC-UV-VIS One of our most powerful analytical tools comb ines electrochemistry with spectroscopy to obtain information on the polymersÂ’ optical properties as the electr ochemical potential is varied. Spectroelectrochemistry, shown th roughout this work allows us to follow the conversion of the neutral * absorption into both polaron and bipol aron states. Spectroelectrochemistry is performed on a conjugated polymer film immers ed in some electrolyte solution. While providing significant information about the electronic properties of our polymers, it does not comment on the polymerization process. The onset of the neutral * absorption approximates the energy difference between HOMO and LUMO orbitals. During conversi on from monomer, the coalescence of the monomer p orbitals leads to an increase in the extent of conjugation for the molecular orbitals. This narrows the HOMO-LUMO difference leading to changes in the * absorption. These optical changes with molecular weight cannot be followed easily via sp ectroelectrochemical methods. Incorporation of monome r necessarily leads to changes in polymer size. Therefore, it should be possible to correlate conjugated polymer molecular weights with UV-VIS absorption spectroscopy. We have coupled size exclusi on chromatography with ultrav iolet-visible sp ectroscopy to determine molecular weight and observe those ch anges in optical properties that relate to molecular weights. Our analytical system is an isocra tic HPLC pump feed ing a mixed-bed 5 m GPC column with refractive index and photo diode array detect ors. Good chromatographic separation is the

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135 backbone of this analysis. An is ocratic dual headed pump is used to provide smooth, stable flow rates of the eluent. This system prevents the r ecognition of pulses at th e detector, thus providing a smooth baseline. In the dual-headed system , two pump pistons operate approximately 180 out of phase. As solvent is delivered to the column from one piston, the other is filling with eluent from the reservoir. This system leads to a stab le, reproducible baseline and is monitored via the RI detector. We use a Waters 2996 photodiode array UV-VIS dete ctor as the primary method of detection of our soluble conjugate d polymers. All source radiation is focused on the sample flow cell. A prism/dispersive element separates the light into its various wavelengths. After passing through the sample, the light impinges upon photodiodes corresponding to the particular wavelengths within the spectrum. The PDA is most useful in that a sample chemical identity can also be confirmed via comparison to traditional polymer UV-VIS spectroscopy. Operation of the GPC-UV/VIS Instrument Pre-Analysis Items The following paragraphs comprise actions that may be taken prior to use of the instrument. If the instrument is already availa ble, please continue to Sample Analysis. Computer, Pump Assembly, Column Heater, P DA, and RI Detector should be powered. 1. The computer is typically run from the Wi ndows Administrator login. A small “E” icon is used to start the Empower Chromatogr aphy Software. The switches for the pump and column heater are on opposite sides of the inst rument. The PDA switch is at the front of the detector. Two small green lights should be visible when the de tector is powered. Initially, the “Lamp” light blinks. This st ops when the lamp is ready. The RI detector will provide a screen showing the sensitivity and the current detector temperature. 2. The chromatographic system should have spent at least 24 hours at temperature before a sample is performed. This involves deliveri ng eluent at the desire d flow rate with all components powered. The equilibration time is necessary for a stable baseline. 3. The Empower Software is used to set flow ra tes, system temperature, and RI detector sensitivity.

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136 Sample Analysis 1. If the flow rate must be changed, click th e “running faucet” icon. Set the desired flow rate in addition to a ramp time of 5 minutes. 2. After the flow is achieved, click the “cylinder’ icon to begin an equilibration procedure. On the popup window, click equilibrate monitor. The correct instrument method should already be selected from previous use. 3. Click the “Stop” icon, which is above the Equi librate “cylinder”. This icon contains a red square. 4. The topmost button shows needle entering the in jection port. This is the “Single Sample” button. 5. Click the Single Sample button, Enter a sample name. 6. All Sample Names should begin with YOUR in itials and contain an abbreviation for your polymer. 7. Ensure that the vial number is correc t for the injection you are performing. 8. Set the injection volume at 10 L. 9. Click “Inject”, you should see a small message window appear. 10. Inject your 10 L of sample into the Injection Port. This port should already be in the load position. 11. Turn the injector to the right. Hold for ~0.2s ec. Return the injector to the load position. Wait for the time of your injection. Data Quantitation This area will most likely be performed with the instrument owner. However a reference procedure will be provided here. For GPC-UV/Vis data, click the Browse Project button to open a column which contains all samples run. You should see channel information for both the RI and PDA detectors. Select the PDA data by right clicking the desired sample. 1. Select Review-Replace in the right-click context menu. 2. You should be taken to the Review Window/Work Area. 3. Extract a chromatogram near the max of your polymer

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137 4. File->Open->Processing Method 5. Select the most recent processing method. 6. Go to Process-> Integrate to select your peak. 7. Go to Process->Quantitate to calculate your MW values If the information is sa tisfactory, select Save Result. If you would like to recalculate your data, you must re-enter the Review Work Area as earlier. UV-Vis spectra are extracted from your chromatogram via the right clicking the ac tual chromatogram. Once your analysis is complete, reset the flow rate to 0.1mL/min via a 5 min ra mp through the faucet icon.

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PAGE 149

149 BIOGRAPHICAL SKETCH Adolphus G. Jones was born at Dekalb Gene ral Hospital in Decatur, Georgia at 6:35pm on July 4th, 1977. His friends simply call him, Genay. His formative years were spent in the Atlanta suburbs with weekend trip s to his grandparents who lived in side the Perimeter. Always a fond reader, his appreciation for the physical world was developed by space and science magazines. He graduated from Stone Mountain Christian School to matr iculate at the Georgia Institute of Technology. As a cooperative student , he worked in the Carolinas for a German polymer company. He graduate d in 2000, having made lifelong friends, and being mesmerized by the exploits of Heisman Trophy runner-up, Jo e Hamilton and the Yellow Jackets. After moving to Gainesville, Florida to begin gr aduate school, he became “that guy” whose fall weekends revolved around returning to the Nort h Avenue Trade School to watch the Ramblin’ Wreck. He also developed quite a taste for outdo or cooking, and looks fo rward to the day that both time and money allow him to show up to tailg ate two days prior to the actual game. He intends to complete a postdoctoral research a ssignment prior to joining the “real world.” Retirement will consist of saving the world by preventing people from attending medical school.