Dynamics of Frenkel excitons in disordered molecular aggregates

This article reports on the optical dynamics in aggregates of pseudoisocyanine‐bromide and iodide. For PIC‐Br in an ethylene glycol/water glass, the results of resonance light scattering (RLS), time‐resolved emission, and photon echo decay measurements are discussed. Band structure calculations based on a linear‐chain model for the J aggregate have also been performed. The results show that the J band can be described as a disordered Frenkel exciton band in which superradiant states exist that extend over about 100 molecules. Numerical simulation studies of the J band, based on Anderson’s Hamiltonian with uncorrelated diagonal site energies, show that the ratio κ of the disorder parameter D over the nearest‐neighbor coupling parameter J12 is about 0.11. Using the frequency dependence of the ratio between the yields of vibrational fluorescence and Raman scattering as a probe, the dephasing process and derived parameters for the bath correlation function at three different temperatures have also been examin...