2-DIRECTIONAL PHOTOINDUCED ELECTRON-TRANSFER IN A TRICHROMOPHORIC SYSTEM

Competition between electron transfer via a through sigma-bond and a t hrough pi-bond mechanism has been studied in 1-(4-cyanophenyl)-4-(cyan omethylene)pipe In this trichromophoric system designed in a configura tion acceptor-donor-acceptor, where the donor chromophore is part of t he 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 t hrough the sigma- or pi-bonds, respectively. Information on the excite d-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 tim e resolution of the experimental setup, and an electron exchange betwe en the two polar states occurs at least in one direction.