Energy quenching kinetics beyond the rate concept

The non-Markovian integro-differential kinetic theory of bimolecular transfer reactions in solutions is considered as well as a number of its applications to the photo-induced multistage reactions of energy and electron transfer. The theory valid in the lowest order approximation with respect to the concentration of reaction partners. It is known as integral encounter theory (IET) which uses integral terms instead of reaction rates and memory functions as their kernels instead of time-dependent rate constants. The reversible inter-molecular energy transfer and quenching by charge separation are considered more in detail as excellent examples of the processes whose conventional rate description is impossible. A number of other applications of IET are listed and briefly refereed. An important modification of the theory extending its validity region for larger concentrations and longer times is also reported.