Exciton transport in thin-film cyanine dye J-aggregates

摘要

We present a theoretical model for the study of exciton dynamics inJ-aggregated monolayers of fluorescent dyes. The excitonic evolution isdescribed by a Monte-Carlo wave function approach which allows for a unifieddescription of the quantum (ballistic) and classical (diffusive) propagation ofan exciton on a lattice in different parameter regimes. The transition betweenthe ballistic and diffusive regime is controlled by static and dynamicdisorder. As an example, the model is applied to three cyanine dyeJ-aggregates: TC, TDBC, and U3. Each of the molecule-specific structure andexcitation parameters are estimated using time-dependent density functionaltheory. The exciton diffusion coefficients are calculated and analyzed fordifferent degrees of film disorder and are correlated to the physicalproperties and the structural arrangement of molecules in the aggregates.Further, exciton transport is anisotropic and dependent on the initial excitonenergy. The upper-bound estimation of the exciton diffusion length in the TDBCthin-film J-aggregate is of the order of hundreds of nanometers, which is ingood qualitative agreement with the diffusion length estimated fromexperiments.