Electron transfer (ET), hole transfer (HT), and proton transfer (PT) are critical processes in photosynthesis. Many essential photochemical redox processes among native photosynthetic proteins undergo proton-coupled electron transfer (PCET) to drive high-energetic reactions. In Photosystem II, PCET is facilitated via the TyrZ-His190 couple, a critical redox intermediate in delivering oxidative equivalents to the Oxygen Evolution Complex (OEC). The integral nature of the TyrZ-His190 couple has inspired much investigation over the past two decades since its crystal structure was first resolved. Thus far most of the work surrounding PCET utilizes ground-state oxidants via the flash-quench method. Until recently, excited-state PCET reactions have been relatively unexplored. The Therien lab utilizes the highly tunable singlet excited-state reduction potentials of organic chromophores to study ultrafast photoinduced proton-coupled electron transfer and hole transfer reactions to oxidize Tyr and Trp analogues in molecular systems.

Migliore, A.; Polizzi, N. F.; Therien, M. J.; Beratan, D. N., Biochemistry and theory of proton-coupled electron transfer. Chemical reviews 2014, 114, 3381-3465.

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