Quantum master equations for systems off-diagonally driven by a time-dependent external field

A useful approach to modeling charge transfer (CT) dynamics in complex molecular systems is based on off-diagonal quantum master equations (OD-QMEs), which treat terms that couple different electronic states as a small perturbation. In this paper, we present OD-QMEs for systems with time-dependent electronic coupling terms, which can be accomplished by driving the system with a time-dependent external field. We also present an asymptotic analysis that shows how the dynamics described by the OD-QMEs for a CT system driven by a CW field turns into rate kinetics governed by field-modified Marcus theory rate constants at long times and high temperatures (when Gaussian statistics is assumed). The ability of off-diagonal driving to open up new CT pathways that can compete with non-radiative pathways is demonstrated in the case of the Garg-Onuchic-Ambegaokar CT model driven by a CW field.