A two-dimensional model for energy transfer in pure and mixed J-aggregates

A model, based on numerical simulations, is provided to study the energy transfer and the fluorescence of a two-dimensional mixed J-aggregate featuring the mixing of oxacyanine and thiacyanine molecules. The J-aggregate is modeled as a square arrangement of parallel donor molecules in which a given concentration of acceptors, with a similar structure, is randomly substituted. The Frenkel exciton states of the mixed quantum system are calculated by numerical diagonalization of the aggregate Hamiltonian with inclusion of the static disorder. The concentration dependences of the density of states, the absorption lineshapes and the localization behavior of the mixed exciton states are simulated. The intraband and interband scattering rates are calculated using a model of exciton-phonon coupling. The time evolution of the exciton populations after initial excitation is calculated. The time-resolved and the fluorescence lineshapes are simulated as a function of the concentration ranging from 0 to 1.