Electronic excited-state transport and trapping in solution

A theoretical study of transport and trapping of electronic excitations in a two-component disordered system is carried out. The results are applicable to energy transport in solutions containing randomly distributed donor and trap solute species or lattices with randomly distributed donor and trap impurities. The diagrammatic expansion of the Green function, developed by Gochanour, Andersen, and Fayer to study excited-state energy transport in a one-component system is applied to the trapping problem. The following quantities are calculated from the Green function: the time-dependent probabilities that an excitation is in the donor or in the trap ensembles, the generalized diffusion coefficient, and the mean-squared displacement of an excitation. For Förster transfer, transport properties are shown to depend on the ratio of the Förster interaction lengths RDT0 and RDD0 as well as on the reduced concentrations of donors and traps [CD = 4/3π(RDD0)3ρD, CT = 4/3π (RDT0)3ρT]. The tranport of excitations is found to be nondiffusive. A comparison to other theoretical treatments is presented.