Fig. 1.

Optical excitation of Re^I(His124)(Trp122)AzCu^I produces a singlet charge transfer excited state (¹CT) that undergoes ~100 fs conversion to a hot triplet that relaxes on the ps timescale. The relaxed ³CT state is in equilibrium with a charge-separated state ³CS (the hopping intermediate) that undergoes Cu^I →Trp122^•+ ET in 31 ns. Single-step back ET regenerates the ground state (3.1 μs time constant). Shown also are low-yield ultrafast forward ET steps from hot states and charge recombination from the ³CS state.

Adapted from [9].