Fluctuation-induced acceleration of inter-ligand exciton transfer in bis(dipyrrinato)Zn(II) complex

TL;DR

This study reveals how structural fluctuations in a zinc complex can dynamically enhance excitonic coupling, leading to accelerated inter-ligand exciton transfer, using simulations and a simple model.

Contribution

It demonstrates the impact of dynamical angular fluctuations on excitonic coupling and transfer rates in a specific zinc complex, combining simulations with analytical modeling.

Findings

Angular fluctuations break symmetry and increase excitonic coupling.

Dynamical coupling accelerates exciton transfer.

Simulations and models agree on fluctuation effects.

Abstract

Exciton transfer dynamics between chromophores depends on excitonic coupling, which is governed by relative orientation between the chromophores. While the excitonic coupling is treated as a static parameter in many cases, structural dynamics can introduce time-dependence on the excitonic coupling. However, influence of the dynamics of excitonic coupling on the exciton transfer has been scarcely understood. In the present study, exciton transfer under dynamical fluctuation in excitonic coupling was investigated via combined use of non-adiabatic molecular dynamics simulations, exciton density analysis, and a simple two-state model, for inter-ligand exciton transfer in bis(dipyrrinato)Zn(II) as the example case. The reaction coordinate for the exciton transfer was obtained a posteriori via regression analysis where the target and explanatory variables are diabatic energy gaps and atomic displacements, respectively. The results suggest that dynamical angular fluctuation between the two dipyrrinato ligands breaks the symmetry to incidentally increase the excitonic coupling, accelerating the exciton transfer between the ligands.