Marcus locally excited state

The effect of the FC term on ICT and MLCT-based chemosensors appears when the electron transfer rate constant is generalized within the context of nonradiative decay theory [191-193], MLCT excited states are produced directly upon excitation whereas ICT states are produced by a surface crossing from an initially prepared localized excited state (see Fig. 9). Return of the system from the charge transfer excited state to ground state has the overall form of an electron transfer recombination problem that is described by the inverted Marcus curve of Fig. 13. As described by the FC term of Eq. (5), the rate constant for... 

In an asymmetric system, the ground state will be mainly localized on one of the centers. If the sites are identical, asymmetry may be created if and y are added or subtracted. The sum + y gives f, which corresponds to an excitation on site A. Polarization will lower the energy of this state, and cause permanent localization of the excitation on A. The EET between A and B is described by the Marcus model. There may be an activation barrier. In that case, we are back to the case with ordinary local excitation. 

---