EXPERIMENTAL AND THEORETICAL APPROACHES TO INORGANIC SPIN CHEMISTRY Alexander M. Brugh A dissertation submitted to the faculty at the University of North Carolina at Chapel Hill in partial fulfilment of the requirements for a degree of Doctor of Philosophy in the Department of Chemistry. Chapel Hill 2020 Approved by: Malcolm D. E. Forbes Gerald J. Meyer James F. Cahoon Andrew M. Moran Wei You Zhiyue Lu © 2020 Alexander M. Brugh ALL RIGHTS RESERVED ii ABSTRACT Alexander M. Brugh: Experimental and Theoretical Approaches to Inorganic Spin Chemistry (Under the direction of Malcolm D. E. Forbes) Electron paramagnetic resonance (EPR) is employed in investigating inorganic spin chemistry related phenomena. Steady state electron paramagnetic resonance (SSEPR) was used to explore the electron-electron exchange interaction (J) in alkyne-bridged multi[copper(II) porphyrin] species. A simulation routine was developed to calculate the effects of J and the modulation of J on the SSEPR spectra. Spin trapping is used to trap and identify ethyl radicals formed from the photoexcitation of alkyl-cobalamin. These cobalamins are augmented with fluorophores to show efficient photolysis at wavelengths as long as 777 nm when exciting the fluorophore. These cobalamins can serve as photoinitiators for hydrogel polymerization in medical use. The proton coupled electron transfer (PCET) II 2+ reaction of [Ru (bpy)2(bpz)] with hydroquinone is investigated by time resolved EPR (TREPR). The TREPR spectrum confirms the presence of a triplet intermediate and reveals the effect of electron donating and withdrawing groups on polarization mechanism. iii ACKNOWLEDGEMENTS These have been a tough few years and I owe an enormous amount of gratitude to many people for their support and encouragement. Thank you Prof. Malcolm D. E. Forbes for your teaching and guidance in accomplishing this work. Thank you Dr. Lauren E. Jarocha for teaching me how to be a proper graduate student and putting up with me. For the numerous lessons in lab and in life, thank you Dr. Marek Danilczuk. Dr. Valery F. Tarasov, thank you for many interesting talks; I wish we could have had more. Thank you to my collaborators Dr. Zach Rodgers, Dr. Ruobing Wang, Chih-Hung Ko, Dr. Baillie DeHaven. My fellow group members throughout the years; Trey, Soo, Sam, Rufai, Anginelle, Ian, Willy, Larry, Joshua, Sophena, and Chathu, thanks for all the company and some exciting adventures. Dr. Gerard Rowe, Dr. Monty Fetterolf and Dr. Chad Leverette, thank you for your guidance, encouragement and support during my undergraduate career. Thanks to my friends Brandon, Sam, and Trandon. Sepi, Mom and Dad, I am glad you were around to listen to me whine and complain, thank you. I appreciate all the support from my friends and family. And if anyone actually reads this section, thank you, I know it is cheesy. iv TABLE OF CONTENTS LIST OF TABLES ..............................................................................................................................................ix LIST OF FIGURES ............................................................................................................................................ x LIST OF SCHEMES ........................................................................................................................................ xiii LIST OF CHARTS ........................................................................................................................................... xiv LIST OF SYMBOLS AND ABBREVIATIONS ...................................................................................................... xv CHAPTER 1: Introduction .............................................................................................................................. 1 1.1. General Introduction ...................................................................................................................... 1 1.2. Electron Paramagnetic Resonance Spectroscopy .......................................................................... 2 1.2.1. Electron Spin .......................................................................................................................... 2 1.2.2. The Electron-Nuclear Hyperfine Interaction .......................................................................... 4 1.3. Steady-State EPR (SSEPR) ............................................................................................................... 7 1.3.1. Experimental Overview .......................................................................................................... 7 1.3.2. Spin Trapping ....................................................................................................................... 11 1.4. Time Resolved EPR (TREPR) .......................................................................................................... 12 1.4.1. Experimental Overview ........................................................................................................ 12 1.4.2. Chemically Induced Dynamic Spin Polarization (CIDEP) ...................................................... 14 1.5. EPR Line Shapes ............................................................................................................................ 17 1.6. EPR Spectroscopy of Biradicals ..................................................................................................... 18 1.7. Thesis Overview ............................................................................................................................ 20 1.7.1. Exchange Interaction in Copper(II) Porphyrins .................................................................... 21 v 1.7.2. Spin Trapping: Applications in Inorganic Photochemistry ................................................... 22 1.7.3. Anomalous Chemically Induced Electron Spin Polarization in Proton- Coupled Electron Transfer Reactions ................................................................................... 22 References .................................................................................................................................. 24 CHAPTER 2: Copper(II) Porphyrins I: Porphyrins I: Alkyne-Bridged Multi[Copper(II) Porphyrin] Structures: Nuances of Orbital Symmetry in Long-Range, Through- Bond Mediated, Isotropic Spin Exchange Interactions .................................................................. 26 2.1. Introduction .................................................................................................................................. 26 2.2. Methods........................................................................................................................................ 30 2.3. Results and Discussion .................................................................................................................. 32 2.4. Conclusion .................................................................................................................................... 36 References .................................................................................................................................... 36 CHAPTER 3: Copper(II) Porphyrins II: Topology, Distance, and Orbital Symmetry Effects on Electronic Spin–Spin Couplings in Rigid Molecular Systems: Implications for Long Distance Spin-Spin Interactions .................................................................. 39 3.1. Introduction .................................................................................................................................. 39 3.2. Methods........................................................................................................................................ 41 3.3. Results and Discussion .................................................................................................................. 41 3.4. Conclusion .................................................................................................................................... 47 References .................................................................................................................................... 49 CHAPTER 4: Copper(II) Porphyrins III: Spinning Molecules, Spinning Spins: Modulation of the Exchange Interaction in a Highly Anisotropic Hyperfine Field ............................................ 51 4.1 Introduction ................................................................................................................................... 51 4.2 Experimental .................................................................................................................................. 55 4.3 Theory ............................................................................................................................................ 55 4.4 Additional Background on Manifestations of J Modulation in Biradicals ...................................... 61 vi 4.5 Results and Discussions ................................................................................................................. 62 4.6 Conclusion ...................................................................................................................................... 71 References ..................................................................................................................................... 72 CHAPTER 5: Spin Trapping: Applications in Inorganic Photochemistry .....................................................