Distinctive character of electronic and vibrational coherences in disordered molecular aggregates

TL;DR

This paper investigates how electronic and vibrational coherences manifest differently in disordered molecular aggregates using 2D spectroscopy, revealing their distinct sensitivities to disorder and providing insights into their origins.

Contribution

It demonstrates that detailed modeling of 2D spectroscopy signals can distinguish between electronic and vibrational coherences in disordered systems.

Findings

Electronic coherences are quickly dephased by energetic disorder.

Vibrational coherences are less affected by disorder and persist longer.

Modeling 2D spectra helps identify the origin of observed coherences.

Abstract

Coherent dynamics of coupled molecules are effectively characterized by the two-dimensional (2D) electronic coherent spectroscopy. Depending on the coupling between electronic and vibrational states, oscillating signals of purely electronic, purely vibrational or mixed origin can be observed. Even in the "mixed" molecular systems two types of coherent beats having either electronic or vibrational character can be distinguished by analyzing oscillation Fourier maps, constructed from time-resolved 2D spectra. The amplitude of the beatings with the electronic character is heavily affected by the energetic disorder and consequently electronic coherences are quickly dephased. Beatings with the vibrational character depend weakly on the disorder, assuring their long-time survival. We show that detailed modeling of 2D spectroscopy signals of molecular aggregates providesdirect information on the origin of the coherent beatings.