Exciton transport in thin-film cyanine dye J-aggregates

TL;DR

This paper develops a theoretical model to study exciton dynamics in thin-film cyanine dye J-aggregates, capturing quantum and classical transport regimes and analyzing how disorder affects exciton diffusion and length.

Contribution

It introduces a Monte-Carlo wave function approach to unify quantum and classical exciton transport in J-aggregates, with molecule-specific parameters derived from DFT.

Findings

Exciton diffusion coefficients vary with disorder and molecular structure.

Transport is anisotropic and energy-dependent.

Estimated exciton diffusion length aligns with experimental data.

Abstract

We present a theoretical model for the study of exciton dynamics in J-aggregated monolayers of fluorescent dyes. The excitonic evolution is described by a Monte-Carlo wave function approach which allows for a unified description of the quantum (ballistic) and classical (diffusive) propagation of an exciton on a lattice in different parameter regimes. The transition between the ballistic and diffusive regime is controlled by static and dynamic disorder. As an example, the model is applied to three cyanine dye J-aggregates: TC, TDBC, and U3. Each of the molecule-specific structure and excitation parameters are estimated using time-dependent density functional theory. The exciton diffusion coefficients are calculated and analyzed for different degrees of film disorder and are correlated to the physical properties and the structural arrangement of molecules in the aggregates. Further, exciton transport is anisotropic and dependent on the initial exciton energy. The upper-bound estimation of the exciton diffusion length in the TDBC thin-film J-aggregate is of the order of hundreds of nanometers, which is in good qualitative agreement with the diffusion length estimated from experiments.