Excitation Dynamics and Relaxation in a Molecular Heterodimer

TL;DR

This paper investigates the excitation and relaxation processes in a molecular heterodimer, comparing different quantum master equations and discussing implications for photosynthesis regulation.

Contribution

It provides a comparative analysis of Redfield and HQME methods for modeling heterodimer excitation dynamics and highlights the dominant role of system-bath interactions in excitation quenching.

Findings

System-bath interaction governs excitation quenching.

Redfield and HQME methods show consistent results.

Heterodimer can act as an excitation quenching center.

Abstract

The exciton dynamics in a molecular heterodimer is studied as a function of differences in excitation and reorganization energies, asymmetry in transition dipole moments and excited state lifetimes. The heterodimer is composed of two molecules modeled as two-level systems coupled by the resonance interaction. The system-bath coupling is taken into account as a modulating factor of the energy gap of the molecular excitation, while the relaxation to the ground state is treated phenomenologically. Comparison of the description of the excitation dynamics modeled using either the Redfield equations (secular and full forms) or the Hierarchical quantum master equation (HQME) is demonstrated and discussed. Possible role of the dimer as an excitation quenching center in photosynthesis self-regulation is discussed. It is concluded that the system-bath interaction rather than the excitonic effect determines the excitation quenching ability of such a dimer.