Energy transfer quenching of a fluorescent excited radical cation by counter radical anion: dissipation of radical ions generated by photoinduced electron transfer

Fluorescence from the excited 1,3,5-trimethoxybenzene radical cation (TMB⋅+*) coexsisting with 1,4-dicyanonaphthalene radical anion (DCN⋅−) in acetonitrile was studied by the two-step two-laser excitation technique. The fluorescence intensity observed as a function of the delay time of the excitation pulse relative to generation pulse for TMB⋅+ indicated the quenching by DCN⋅− at ⩽220 ns. From the analysis of the fluorescence behavior by the Förster-type energy transfer theory, the distance between TMB⋅+* and DCN⋅− during their dissipation after the initial photoinduced electron transfer was estimated as a function of time.