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Fundamental Insights Into Photo-Induced Charge Transfer in Metal Complexes Through Electroabsorption Spectroscopy

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Fundamental Insights Into Photo-Induced Charge Transfer in Metal Complexes Through Electroabsorption Spectroscopy FUNDAMENTAL INSIGHTS INTO PHOTO-INDUCED CHARGE TRANSFER IN METAL COMPLEXES THROUGH ELECTROABSORPTION SPECTROSCOPY Andrew B. Maurer A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry. Chapel Hill 2020 Approved by: Gerald J. Meyer Jillian L. Dempsey James F. Cahoon Alexander J. M. Miller John M. Papanikolas ©2020 Andrew B. Maurer ALL RIGHTS RESERVED ii ABSTRACT Andrew B. Maurer: Fundamental Insights into Photo-Induced Charge Transfer in Metal Complexes through Electroabsorption Spectroscopy (Under the direction of Gerald J. Meyer) As pervasive as light and electron motion is to our world, it comes as no surprise that a long line of research in chemistry has involved developing methods to understand and harness these useful processes. However, there are limitations to humanity’s knowledge even after the several hundred years of development. In particular there is hardly a true way to track electron motion during or the identity of the excited state after photon absorption. Chapter 1 establishes a background on the development of photochemistry and provides a thorough delve into the theory and use of electroabsorption spectroscopy, or Stark spectroscopy, which allows for a more descriptive picture of the Franck-Condon state. 2+ Chapters 2 and 3 introduce the home-built Stark apparatus and analyzes a series of Metal(diimine)3 compounds. These chapters outlines the basic principles that can be measured through the use of Stark spectroscopy. Chapter 2 continues by providing insight into how significant substituents of the diimines in the 4 and 4’ positions can be to the electron transfer during the metal-to-ligand charge transfer excitation. Chapter 3 instead of altering the ligand alters the metal center, and provides insight into how the metal center can effect the metal-to-ligand charge transfer. Additionally the results of Chapter 3 indicate a possiblity for a change of polarizaiton during the spin flip process that can be uniquely measured by Stark spectroscopy, enhancing transitions normally hidden due to their low transition probability from the spin change. Chapter 4 and 5 take a slight deviation by demonstrating a more common application of Stark spectroscopy. In these chapters, Stark spectroscopy is used to assist in confirming the results of the other iii techniques and theoretical assumptions by providing evidence for the amount of charge transfer, the direction of charge transfer, and the overall efficiency of the excited electron for subsequent electron transfers. Chapter 6 outlines the Stark apparatus and the standard operating procedure for the clarity of the reader and for future reference for lab members. iv To always question and always pursue the truth v ACKNOWLEDGEMENTS There seldom is a true opportunity in a lifetime to sit down and thank all the individuals that have made an achievement possible. With the completion of my dissertation, I have the opportunity for such a moment and I find the task at hand one of the most daunting I’ve had during my graduate work and my life before. I have been lucky enough to have many friends, family, and coworkers that have shaped me both as a person and as a scientist in ways they may have never known. Each person who is willing to share their perspective of life or science helps alter or reinforce my views on the world and turned me into the person I am today. Even those who I meet in passing have had lasting impacts likely beyond their wildest intentions. With all this in mind, I would like to take a moment here to reflect on the efforts of those around me to thank them for what they have done. I’d like to begin this acknowledgement with recognizing my parents, Debra and David, and all of my brothers, Daniel, Michael and Matthew, for their guidance and help through my earlier years and their continued efforts today. For my parents, their willingness to put up with any and all of my after school activities and clubs, their support and help in the early years to learn beyond the classroom, their financial support in all years of schooling, and so much more I can’t recount it all here. Their help allowed me to focus on my studies and pursue whatever dream I had without a worry in the world, an opportunity for which I can never thank them enough. For my brothers, their friendship in the early years to today will always reassure me I have people I can count on, but beyond that their own personal drives and passions helped to drive me to find my own path in life and excel to the same extents that they did. I doubt they will ever know how much just being themselves helped me grow, and I can only hope that I had a similar effect on them. vi While I could go on for pages discussing the multitude of college friends that have molded me into who I am today, I wanted to select a few groups of people to whom I owe the most. The first bunch I’d like to highlight are my fellow chemistry majors. The whole class was relatively small and allowed for a tightly knit group of friends to develop. These people all pushed me to be the best I could at the subject, with them often times looking to me as a source of knowledge and never wanting to let them down. In particular I’d like to mention Lukas Ronner, Ashley Reeder, Leela Chockalingam, and Dan Nelson. They all helped me stay calm in the face of the mountain of stress that college can bring and not unlike my brothers their strong personalities and successes in life made me want to be the best I could be. Another group that made my college journey possible is that of the student life on campus. The camaraderie between us brought a vast collection of lifestyle tips and developed many of my current interests outside of chemistry. Through late night on-duty grub hub dinners together, parties, and events I developed a strong sense of family away from home that I’m not sure I’ll ever be able to recreate. This group reminded me that there was so much more to life than just science and studying. Specifically I’d like to call out Hira Ahmad and Kyle Mueller for their continued friendship (and teasing of me occasionally) that has always been a breath of fresh air and a reminder that there is a lot more out there. The two of them with the rest of student life taught me how important the balance between work and life can be. The last group of college friends that I need to make sure I thank I have managed to stay close with and even grow closer since we have left college. I am of course talking about the group known formally as Team Positivity, consisting of Dan Nelson, Tyler Healy, Ian McIntyre, Shane McGraw and myself. At a simple level we play video games together at least once a week. While some may not understand the bonds that can be built through playing video games online, this group has helped have a consistent dose of teamwork that reminds me how important working with other can be. The group has also helped instill in me the belief that people all can and will try in the right circumstances to be better, and that positive reinforcement, self-reflection, and well delivered criticism can make a world of difference. Beyond all that vii though, keeping close friends with similar interests and having a good laugh every week is something that I doubt I’ll ever fully appreciate. Over my long academic career I have had many great instructors and advisors who I am glad to have met and can consider my friends. They have motivated my scientific drive, shaped my learning abilities, and validated my choice to study Chemistry in life. In high school, Paul Vetscher gave me a mind to pursue beyond that which was taught and gave me my love of math, which has proven useful to this day. Also in high school, Jeff Trinh’s teaching style inspired my own teaching style of never giving answers and only asking questions, it also helped my learning abilities in being able to return to fundamentals and work up from there to fully understand a system instead of memorization of details. At Carnegie Mellon University, David Chickering was my housefellow who instilled me with a sense of responsibility and leadership through his recognition of me as a RA and beyond that as a friend. I still distinctly remember one-on-one meetings with him that involved chatting about life and my dreams, and David, even with his several hundred person large dorm, would remember details about my life from years past. I would be remisce to not mention and thank potentially the most important faculty member to my development as a chemist, Dr. Stefan Bernhard. Starting with recruiting me into his lab after taking an inorganic chemistry course my freshman year, his recognition for my abilities brought a revivified drive to learning beyond what is expected. He always was up for talking, usually about science, but that included almost anything. Frequent visits to his office to share data or ask for help or guidance in how to approach a problem has given me the tools I’ve used substantially through my own graduate work presented in this dissertation. He may deny his usefulness and assure you that I was easy to work with and point in the right direction, but I know his advising is invaluable to my capabilities as a scientist and teacher.
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