Energy level diagram of the states of the PSII RC involved in energy transfer and charge separation. C670, C681, and P680 denote (groups of) pigments or states absorbing at that particular wavelength; arrows denote energy transfer and charge separation. All reactions are reversible, but those that are on the time domain of interest effectively unidirectional are indicated as such. Note that due to inhomogeneous broadening the energy levels are actually broader as depicted here (≈5 nm FWHM) and therefore overlap extensively. C670 represents one or two pigments that transfer slowly [≈15 ps (13, 31, 37)] to the other pigments and can be inferred at T ≥ 240 K to equilibrate with the states absorbing around 680 nm in about 10 ps; C681 or the trap-state is degenerate with P680 and transfers to P680 directly in ≈35 ps or slower at low temperature; P680 is the primary electron donor; and X may represent the higher excitonic multimer levels or a multimer state with charge transfer character that mediates electron transfer from P680*. The 2.4 → 0.4-ps component is essentially ascribed to equilibration between P680 and X and its decay into P+I−, the 120 → 18-ps component to the C681 to P680 transfer which at higher temperature is accelerated through the C681 → C670 → P680 decay channel (see Discussion).