Disorder-induced exciton scattering in molecular aggregates

Static and dynamic disorders are investigated to analyze the exciton scatte ring in molecular aggregates of finite size like columnar aggregates or J-a ggregates which exhibit strong intermolecular dipolar interactions (V). The static disorder (sigma). of Anderson type, stems from the inhomogeneities in the site energies while the dynamic disorder originates from the exciton -phonon stochastic coupling induced by the thermal bath. The dynamic coupli ng induces the exciton diffusion at rates depending on the amplitude (Delta ) and on the correlation time (tau) of the fluctuations. A theoretical mode l, based on the numerical calculation of the exciton eigenstates and their participation ratios is used to simulate the role of both disorders on the optical responses. It is shown that an increase of the static disorder dimi nishes the coherence length, i.e. the number of coherently coupled molecule s and that the dynamic disorder induces a temperature-dependent scattering among the quasi-exciton band states. Simulation of the effects of static an d dynamic disorders are presented and discussed as a function of the fundam ental parameters. (C) 1999 Elsevier Science B.V. Ail rights reserved.