Electronic excitation dynamics in multichromophoric systems described via a polaron-representation master equation

TL;DR

This paper develops a multichromophoric polaron master equation to accurately model electronic excitation dynamics, capturing non-Markovian effects, initial bath states, and environment correlations, with applications to light-harvesting complexes.

Contribution

It introduces a generalized non-Markovian polaron master equation for multichromophoric systems, enabling analysis of complex excitation dynamics beyond previous models.

Findings

Oscillations in site populations depend on non-equilibrium bath effects.

The formalism distinguishes electronic from vibrational origins of oscillations.

Markovian and secular approximations may not hold in the original frame.

Abstract

We derive a many-site version of the non-Markovian time-convolutionless polaron master equation [S. Jang et al., J. Chem Phys. 129, 101104 (2008)] to describe electronic excitation dynamics in multichromophoric systems. By treating electronic and vibrational degrees of freedom in a combined frame (polaron frame), this theory is capable of interpolating between weak and strong exciton-phonon coupling and is able to account for initial non-equilibrium bath states and spatially correlated environments. Besides outlining a general expression for the expected value of any electronic system observable in the original frame, we also discuss implications of the Markovian and secular approximations highlighting that they need not hold in the untransformed frame despite being strictly satisfied in the polaron frame. The key features of the theory are illustrated using as an example a four-site subsystem of the Fenna-Mathew-Olson light-harvesting complex. For a spectral density including a localised high-energy mode, we show that oscillations of site populations may only be observed when non-equilibrium bath effects are taken into account. Furthermore, we illustrate how this formalism allows us to identify the electronic or vibrational origin of the oscillatory dynamics.