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. 2019 Jan 7;5(1):192–200. doi: 10.1021/acscentsci.8b00882

Scheme 1. (A) Photoinduced ET Cycle of Re124W122CuI (ref (7)) and (B) Analogous Photoinduced ET Cycle of Re126WWCuI.

Scheme 1

(A) *3CT and 3CT denote hot and relaxed excited states of the Re label, respectively. The photocycle starts with optical excitation to the 1CT state *ReII(CO)3(dmp•–)H124W122AzCuI followed by several relaxation steps, establishing an equilibrium between 3CT and the charge-separated (CS) state ReI(CO)3(dmp•–)H124(W122•+)CuI. The oxidized tryptophan intermediate W122•+ then undergoes ∼30 ns reduction by CuI over a ∼11 Å distance, forming the redox product (RP) ReI(CO)3(dmp•–)H124W122CuII. The cycle is completed by ∼3 μs dmp•– → CuII back electron transfer across 19.4 Å (refs (7 and 9)). (B) The time constants were determined in this work. The Re–Cu charge separation takes place over 23 Å via hopping through two Trp residues. The hot *3CT state and its relaxation were omitted for clarity. 3CT is a mixed Re → dmp MLCT/dmp-intraligand state.