Electron Transfer Reactions Induced by Excited State Quenching

Abstract

AbstractElectron transfer quenching of excited states can lead to separated redox products for which back electron transfer can be highly favored. Application of flash photolysis leads to a relaxation technique in which a system at equilibrium is perturbed by separate excitation‐quenching steps. The rates of several electron transfer reactions have been studied using the technique based on redox quenching of the CT excited state Ru(bpy)2+−3. Quenching and back electron transfer has also been observed for a series of excited states including examples of CT(Ru(phen)2+3, etc), π ‐ π * (Pd(OEP)), and f‐f(Eu(phen)3+3) states. In recent work, even non‐emitting excited states have been shown to be quenched by electron transfer which suggests that the technique may have broad applicability. In properly designed systems containing more than one redox reagent, the quenching and back electron transfer steps can be separated and reactions have been studied which are driven photocatalytically by excited states like Ru(bpy)2+−3. A modification of the technique has been used to estimate the self‐exchange rate for the Ru(bpy)3+/2+3 couple and to measure rates of electron transfer for a series of systems where the rates measured do not involve a Ru‐couple.