Mediator centres and light-induced electron transfer in donor-acceptor systems

Abstract

Frozen vitreous triethylamine solutions of magnesium etioporphyrin-1 (MgEP) both with and without CCl 4 or CHCl 3 additives have been studied at 77 K. It was shown that light irradiation of the solutions in the Soret band or the long-wave absorption band of the porphyrin molecules results in charge separation by means of electron transfer from a triethylamine molecule to an excited porphyrin molecule and subsequent light-induced tunnel electron transfer from complexes (MgEP −·[N(C 2H 5) 3] 2 +) to remote porphyrin molecules. An addition of CCl 4 or CHCl 3 into a triethylamine solution of MgEP was observed to increase the efficiency of the light-induced tunnel electron transfer from (MgEP −·[N(C 2H 5) 3] 2 +) to MgEP by several orders. A theoretical explanation of this phenomenon, in which molecules CCl 4 or CHCl 3 were treated as mediators, was offered. A comparison of experimental and theoretical data made it possible to estimate the energy structure of additives' molecules.