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Thiazole Vs. Thiophene: Heterocycle Effects on the Properties of Fused-Ring Conjugated Materials

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Thiazole Vs. Thiophene: Heterocycle Effects on the Properties of Fused-Ring Conjugated Materials THIAZOLE VS. THIOPHENE: HETEROCYCLE EFFECTS ON THE PROPERTIES OF FUSED-RING CONJUGATED MATERIALS A Dissertation Submitted to the Graduate Faculty of the North Dakota State University of Agriculture and Applied Science By Eric James Uzelac In Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Department: Chemistry and Biochemistry October 2017 Fargo, North Dakota North Dakota State University Graduate School Title Thiazole vs. Thiophene: Heterocycle Effects on the Properties of Fused-Ring Conjugated Materials By Eric James Uzelac The Supervisory Committee certifies that this disquisition complies with North Dakota State University’s regulations and meets the accepted standards for the degree of DOCTOR OF PHILOSOPHY SUPERVISORY COMMITTEE: Dr. Seth C. Rasmussen Chair Dr. Kenton Rodgers Dr. Gregory Cook Dr. Andrew Croll Approved: 11-13-17 Dr. Gregory Cook Date Department Chair ABSTRACT Conjugated polymers and related molecular materials comprise a field of materials chemistry focused on the development of semiconducting organic plastics that find use in applications such as organic solar cells and organic light-emitting diodes. The optical and electronic properties of these molecules, such as absorption and emission of light, can be tuned through engineering at the molecular level. However, many of the current molecules of choice suffer from high-lying frontier orbitals, which results in a mismatch of energy levels to common components of electronic devices along with potential oxidative instability, constraining device performance in real environments. To rectify these issues, the electron-deficient thiazole heterocycle has been incorporated into fused-ring conjugated motifs of both organic and inorganic nature. The new thiazole materials all exhibited the expected stabilization of their frontier orbitals compared to the thiophene analogues. The absorption profiles of the thiazole materials are similar to the thiophene analogues, but with reduced molar absorptivity as a general trend, potentially limiting the efficiency of thiazole derived materials as components of photovoltaic devices. Through experimentation and development of multiple new classes of organic and inorganic thiazole materials, it was found that a larger proportion of thiazole content correlates to a larger decrease in molar absorptivity, but also a larger relative stabilization of the frontier orbitals. The limitations in molar absorptivity can thus be mitigated to an extent by increasing the molecule’s effective conjugation path through functionalization with additional conjugated units, but with the countereffect of less-stabilized frontier orbitals. iii ACKNOWLEDGEMENTS I would foremost like to thank my advisor, Dr. Seth C. Rasmussen, for his continued support and conversations over the last five years. His door was always open to discuss books, movies, games, and, of course, chemistry. I do not take for granted being able to work for such an approachable and relatable boss, and plenty of good times were had during the course of my schooling. I truly have Seth to thank for teaching me how to think like a scientist. Also, I would like to thank my committee members Dr. Greg Cook, Dr. Andrew Croll, and especially Dr. Kent Rodgers, whose guidance and support was instrumental in my passing of the maxi proposal the second time around. Also, thanks to Amy Kain, for her quick response any time I needed assistance, Greg Oswald for making teaching smooth and enjoyable, and Dr. Angel Ugrinov for obtaining X-ray data. I would like to thank my fiancée, Sammy, who walked through the door of Ladd 105 on a warm summer day and became the greatest source of happiness I have ever known. I could not have done this without her boundless support, and look forward to our wedding as next step in our long and happy voyage through life. I would like to thank my family, who was always there to talk during both the good and rough times, who never stopped encouraging me to preserve through my PhD. Hunting, fishing, holidays, and tea with my grandparents provided much-needed intermissions from graduate life. I am glad to have been able to spend many weekends with my family in Grand Rapids over the course of my graduate studies. I would also like to thank my colleagues past and present: Dr. Michael Mulholland, Casey McCausland, M.S., Dr. Ryan Schwiderski, Kristine Konkol, Trent Anderson, and Evan Culver. Thanks also to the members of the D&D/Savage Worlds group, especially the Dungeon Masters Erik Janssen and Jesse Joyce, whose weekly adventures iv provided an engaging escape for the majority of my time here. Also, many thanks to Eric Serum, who spent many hours discussing organic chemistry with me when I needed it most. It must be said that I would not have gone to graduate school if it were not for two wonderful people. The engaging teaching style and great personality of Melissa Ewen at Grand Rapids High School made chemistry courses interesting and drove me towards a chemistry major at St. John’s. There, Dr. Thomas Nicholas Jones let me into his research group for two years and showed me that chemistry research was a challenging and highly-satisfying endeavor. Although I infamously brominated his laboratory, he never lost faith in me to work hard and get results. As evidenced by this lengthy section, I have a lot of people to thank, and I do not take their support for granted. Thank you all. v TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii ACKNOWLEDGMENTS ............................................................................................................. iv LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ........................................................................................................................ x LIST OF SCHEMES.................................................................................................................... xiii CHAPTER I. INTRODUCTION .................................................................................................... 1 1.1. Conjugated and Conducting Polymers.................................................................... 1 1.2. Bandgap in Conjugated Materials ........................................................................... 6 1.3. Bandgap Control and Tuning ................................................................................ 11 1.4. Thiophene-Based Conjugated Materials ............................................................... 15 1.5. Fused-Ring Thiophene Materials .......................................................................... 17 1.6. Hybrid Thiophene Materials ................................................................................. 20 1.7. Thiazole Modifications to Thiophene Materials ................................................... 22 1.8. Research Goals...................................................................................................... 24 1.9. References ............................................................................................................. 25 CHAPTER II. SYNTHESIS OF BROMINATED THIAZOLES AS PRECURSORS TO THIAZOLE-BASED MATERIALS ............................................................................................ 32 2.1. Introduction ........................................................................................................... 32 2.2. Synthesis of 2-bromothiazole ............................................................................... 34 2.3. Synthesis of 4-bromothiazole ............................................................................... 35 2.4. Synthesis of 2,4-dibromothiazole ......................................................................... 36 2.5. Synthesis of 2,5-dibromothiazole ......................................................................... 38 2.6. Synthesis of 2,4,5-tribromothiazole ...................................................................... 40 2.7. Synthesis of 4,5-dibromothiazole ......................................................................... 41 vi 2.8. Synthesis of 5-bromothiazole ............................................................................... 44 2.9. Conclusions ........................................................................................................... 47 2.10. Experimental ......................................................................................................... 48 2.11. References ............................................................................................................. 52 CHAPTER III. INVESTIGATION OF OPTICAL AND ELECTRONIC TRENDS IN PYRROLO[2,3-d:5,4-d’]BISTHIAZOLE MONOMERS ............................................................ 56 3.1. Introduction ........................................................................................................... 56 3.2. Synthesis of PBTz Monomers .............................................................................. 61 3.3. Electrochemical Characterization of PBTz Monomers ........................................ 67 3.4. Optical Properties of PBTz Monomers ................................................................. 69 3.5. X-Ray Crystallography ......................................................................................... 72
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