Evolution of the reaction mechanism during ultrafast photoinduced electron transfer

Specific features of ultrafast photoinduced electron transfer (ET) in concentrated liquid solutions and in neat electron donating solvents are discussed in terms of continuous distribution of ET rate constants, related to electron tunneling with statistical distribution of electronic coupling matrix element and distances between reactant molecules. Available data on photoinduced electron transfer in solutions for several systems are analyzed. Electron tunneling approach is shown to provide global description of nonexponential kinetics of excited states decay at various concentrations of reactant and in neat solvents.