Vibronic coupling in energy transfer dynamics and two-dimensional electronic-vibrational spectra

TL;DR

This paper models vibronic coupling mechanisms in a heterodimer to analyze their effects on energy transfer and 2D spectra, revealing signatures of different vibronic effects and proposing spectral analysis for mechanism identification.

Contribution

It introduces a heterodimer model with explicit vibronic coupling mechanisms and demonstrates how 2DEV spectra can distinguish between Franck-Condon and Herzberg-Teller effects.

Findings

2DEV spectra show static and dynamic signatures of vibronic coupling

Franck-Condon activity alters excitonic structure

Herzberg-Teller activity produces side-band transitions

Abstract

We introduce a heterodimer model in which multiple mechanisms of vibronic coupling and their impact on energy transfer can be explicitly studied. We consider vibronic coupling that arises through either Franck-Condon activity in which each site in the heterodimer has a local electron-phonon coupling and as Herzberg-Teller activity in which the transition dipole moment coupling the sites has an explicit vibrational mode-dependence. We have computed two-dimensional electronic-vibrational (2DEV) spectra for this model while varying the magnitude of these two effects and find that 2DEV spectra contain static and dynamic signatures of both types of vibronic coupling. Franck-Condon activity emerges through a change in the observed excitonic structure while Herzberg-Teller activity is evident in the appearance of significant side-band transitions that mimic the lower-energy excitonic structure. A comparison of quantum beating patterns obtained from analysis of the simulated 2DEV spectra shows that this technique can report on the mechanism of energy transfer, elucidating a means of experimentally determining the role of specific vibronic coupling mechanisms in such processes.