# Delocalization versus Coherence under Vibrational and Environmental Disorder in Photoexcited Supramolecular Aggregates

## TL;DR

This study explores how disorder in molecular materials affects the spread of energy after light exposure, revealing that vibrations limit coherent energy transfer.

## Contribution

The paper introduces a combined classical and quantum simulation approach to study exciton dynamics in supramolecular aggregates.

## Key findings

- Electronic populations spread rapidly across molecules after photoexcitation.
- High-frequency vibrations limit coherent electronic delocalization.
- Design principles for organic materials should focus on equi-distribution of excited states.

## Abstract

Exciton and charge dynamics in photoexcited molecular
materials
depend critically on how delocalization competes with structural,
vibrational, and environmental disorder. Yet, the origin and extent
of coherent versus incoherent distribution of excitons and charges
in such “noisy” supramolecular systems remain poorly
understood. Here, we integrate all-atom classical dynamics with fully
quantum vibronic dynamics to dissect these competing effects in aqueous
self-assembled perylenediimide stacks. Our simulations quantitatively
reproduce experimental absorption spectra and reveal that strong excitonic
coupling and hybridization with charge-transfer states dictate the
optical response. Following photoexcitation, the electronic populations
rapidly spread across multiple molecules within tens of femtoseconds,
yielding delocalized but largely incoherent exciton, hole, and electron
wave function distributions. We find that high-frequency vibrational
modes, and, to a lesser extent, the slow environmental and vibrational
dynamics, intrinsic to the nature of such solvated supramolecular
systems, set a fundamental limit to achieving fully coherent electronic
delocalization. These results identify vibrational disorder as a universal
constraint on coherent exciton dynamics and indicate that practical
design principles for efficient organic optoelectronic and photocatalytic
materials should focus on robust equi-distribution of the excited-state
population.