Two-directional photoinduced electron transfer in a trichromophoric system

Competition between electron transfer via a through sigma-bond and a through pi-bond mechanism has been studied in 1-(4-cyanophenyl)-4-(cyanomethylene)pipe In this trichromophoric system designed in a configuration acceptor-donor-acceptor, where the donor chromophore is part of the initially excited state, electron transfer occurs in two directions. The results of the single-photon-timing measurements indicate that, in both diethyl ether and acetonitrile, two charge-transfer states, a sigma CT and a pi CT state, are formed, by transferring the electron through the sigma- or pi-bonds, respectively. Information on the excited-state kinetics is obtained by means of global compartmental analysis of the fluorescence decay surface in acetonitrile. Both the sigma CT and pi CT state are formed immediately upon excitation, within the time resolution of the experimental setup, and an electron exchange between the two polar states occurs at least in one direction.