Resonant energy transfer enhanced by off-diagonal exciton-phonon coupling

TL;DR

This paper investigates how off-diagonal exciton-phonon coupling influences resonant energy transfer in molecular dimers, revealing its critical role in maintaining coherent transfer and identifying temperature-dependent transfer efficiency thresholds.

Contribution

It demonstrates the significant impact of off-diagonal coupling on energy transfer dynamics and uncovers temperature effects and thresholds relevant for optimizing transfer efficiency.

Findings

Off-diagonal coupling enables coherent transfer at any temperature.

An optimal temperature exists for maximum transfer efficiency below a coupling threshold.

Increasing off-diagonal coupling beyond the threshold reduces the optimal temperature to zero.

Abstract

Dynamics of resonant energy transfer of a single excitation in a molecular dimer system is studied in the simultaneous presence of diagonal and off-diagonal exciton-phonon coupling. It is found that the off-diagonal coupling plays an important role in the excitation energy transfer process. Coherent transfer can be found at arbitrary temperature for a non-vanishing off-diagonal coupling strength with an oscillation frequency of site populations that increases with the off-diagonal coupling strength. Furthermore, we identify a threshold of the off-diagonal coupling strength below which there exists an optimal temperature that maximizes the total population transfer from the initially excited monomer to the acceptor monomer at long times. As the off-diagonal coupling strength is increased beyond the threshold, however, the optimal temperature is found to abruptly drop to zero.