Effects of Donor–Acceptor Quantum Coherence and Non-Markovian Bath on the Distance Dependence of Resonance Energy Transfer

Abstract

Accurate information on the distance dependence of resonance energy transfer (RET) is crucial for its utilization as a spectroscopic ruler of nanometer scale distances. In this regard, understanding the effects of donor–acceptor quantum coherence and non-Markovian bath, which become significant at short distances, has significant implications. The present work investigates this issue theoretically by comparing results from a theory of coherent RET (CRET) with a nonequilibrium version of Forster’s RET (FRET) theory, both accounting for non-Markovian bath effects. Even for a model where the donor–acceptor electronic coupling is of transition dipole interaction form, it is shown that the RET rate in general deviates from the inverse sixth power distance dependence as opposed to the prediction of the original FRET. On the one hand, it is shown that the donor–acceptor quantum coherence makes the distance dependence steeper than the sixth power, although detailed manner of enhancement is sensitive to specific v...