Quasiresonant excitation transfer in molecular aggregates@fa@f)

Abstract

Excitation transfer in finite molecular aggregates is analyzed in the context of the Haken–Strobl model. Explicit solutions are presented for a trimer and a rectangular tetramer. Special emphasis is placed upon population transfer among subunits (monomers, dimers) and its relationship to energy transfer, and upon the problems associated with coherence of this transfer process. These aggregates serve as models for the problem of excitation transfer in disordered media, where partial coherence resulting from short‐range interactions has been largely ignored. Our most intriguing result is the greatly diminished effectiveness of the longer‐ranged transfer in the presence of short‐range clusters. Under some conditions the ensuing energetic mismatches may well dominate the overall energy transport and render invalid the usual description in terms of hopping among individual sites. An application to triplet energy transport in isotopic mixed naphthalene crystals is given; it is seen that the reduced efficiency of non‐nearest‐neighbor transfer processes reinforces the two‐dimensional characteristics of the energy transport.