Nocera, DanielJohnston, Brandon2026-07-0720262026-06-052026Johnston, Brandon. 2026. Emerging Methods and Mechanisms in Electrochemical and Photoredox Transformations. Doctoral Dissertation, Harvard University Graduate School of Arts and Sciences.32669294https://dash.harvard.edu/handle/1/42744072Redox reactions are central to biological processes, energy storage transformations, and chemical synthesis. Conventional redox methods, which make use of molecular oxidants and metallic reductants, possess fixed redox strength, generate stoichiometric waste, and lead to substrate overreduction and overoxidation. To address these challenges, electrochemical and photochemical redox catalysis have emerged as complementary techniques to drive selective and sustainable redox reactions for small molecule synthesis and chemical fuels production. Notably, many electrochemical and photoredox reactions proceed through radical intermediates, allowing the formation of chemical bonds via intuitive one-electron bond connection and disconnection pathways. Noteworthy opportunities exist for expanding the scope of existing redox reaction manifolds, including the development of metal-free electrochemical cross-coupling methods, highly reducing and oxidizing photoredox reactions, and stereoselective electrochemical transformations catalyzed by heterogeneous surfaces. Successful implementation of electrochemistry and photochemistry towards these goals requires careful analysis of reaction mechanisms and catalyst speciation pathways using spectroscopic and analytical tools. Chapter 1 begins by introducing legacy strategies for redox transformations, focusing on the limitations of these methods to motivate alternative electrochemical and photochemical approaches. Basic strategies and design considerations for practical and complementary implementation of electrochemical and molecular photoredox methods are discussed, as well as their limitations and opportunities for new reaction development. The chapter also introduces common electroanalytical and spectroscopic methods used to elucidate mechanisms of electrochemical and photochemical redox transformations. Chapter 2 describes the development of a metal-free electrochemical C(sp2)−C(sp3) cross-coupling reaction that links dicyanoarenes, useful precursors to aromatic nitriles, and alkyl bromides. Electrochemical analysis uncovers that dicyanoarene radical anions act as both substrates and mediators in the transformation, obviating the need for nickel catalysts and suppressing C(sp3) radical homocoupling and hydrogenolysis. The transformation is compatible with both oxidatively sensitive and acidic substrates that are difficult to incorporate in alternative approaches that use carboxylic acids as C(sp3) precursors. Chapter 3 explores the mechanisms of photoredox reactions promoted by radical photoreagents. Transient absorption spectroscopy measurements reveal that isolated radical anions of 9,10-dicyanoanthracene (DCA•–), a naphthalene monoimide derivative (NMI•–), and 9-mesityl-3,6-di-tert-butyl-10-phenylacridinium (Mes-Acr•) have short-lived excited-states that cannot support diffusion-limited electron transfer. Instead, a novel super-reducing photoreagent, 10-cyanoanthrolate (10-CA), that forms via reaction of DCA•– with oxygen, is uncovered. Photophysical characterization and chemical reactivity studies confirm that 10-CA is a competent photoreagent for select aryl chloride reductions. Furthermore, DCA•–, NMI•–, and Mes-Acr• are found to be sufficiently reduced to photodetach solvated electrons by a charge-transfer-to-solvent mechanism. Chemical reactivity and quenching studies demonstrate that the resultant solvated electrons are long-lived in acetonitrile and sufficiently reducing to dehalogenate electron-rich aryl chlorides and aryl fluorides. The combination of these two observations leads to the proposal of a unified picture of radical anion photoredox chemistry, which is described. The chapter concludes by describing efforts to explore the excited-state dynamics and photoreactivity of a trisaminocyclopropenium radical dication (TAC•++) photocatalyst. Finally, opportunities for future work to elucidate the mechanisms of photoredox transformations catalyzed by TAC•++ and other radical cations are discussed. Chapter 4 explores the electrochemical stability of PtGa, a topological semimetal that has been previously reported as a high activity, spin-selective electrocatalyst. A combination of electrochemical, mass spectrometry, and electron imaging techniques reveal that PtGa rapidly corrodes during electrochemical operation. This corrosion leads to the formation of a Pt-enriched nanoporous structure at the electrode surface, leading to apparent increases in electrochemical activity that can be attributed to simple changes in active catalytic surface area. These results suggest that the topological surface states of PtGa are quickly ablated by the corrosion process, emphasizing the importance of verifying surface composition when assigning electrochemical activity to topological band structures.application/pdfencross-couplingelectrochemistryphotochemistrytopological semimetalsChemistryThesis or Dissertation2026-07-07000-0001-5308-9537