Fig. 3. Categories of electron transfer steps.
a–c Nature of each electron transfer step in OQP (a), RQP (b) and O-RQP (c) catalytic cycles. OQP oxidative quenching pathway, RQP reductive quenching pathway, O-RQP oxygen-mediated reductive quenching pathway, ES–GS SET single electron transfer from an excited state to a ground state, GS–GS SET single electron transfer between two ground states, CT-assisted SET single electron transfer assisted by charge transfer in the donor–acceptor complex.