Excitons in molecular J-aggregates of cyanine dyes: Simulation of trapping and energy transfer

A theoretical model is provided to simulate the energy transfer and trapping of excitons in cyanine J-aggregates for various geometrical configurations. Intermolecular interactions are calculated using the extended dipole method. Frenkel exciton states are obtained by a numerical diagonalization of the aggregate Hamiltonian taking into account the static disorder. A model of exciton–phonon coupling is used to describe the trapping and the energy transfer processes among the exciton states. Scattering rates are calculated and used in a Master Equation to obtain the time evolution of the excitonic populations after initial excitation. Configurationally averaged absorption lineshapes and time-resolved fluorescence decays are obtained. Our simulation model is applied to describe the excitation energy transfer between two closely spaced linear chains of pseudoisocyanine (PIC) molecules and to a two-dimensional monolayer composed of a mixing of oxacyanine and thiacyanine molecules.