Optical and paramagnetic line shapes of excited states in energetically disordered molecular aggregates

Abstract

We investigate numerically ESR and optical line shapes of a quantum particle in a solid with Gaussian and dichotomic energy disorder using continued fraction methods. In the case of a spin hopping in one dimension we find, with increasing hopping rate γ, first a line shape corresponding to the energy distribution on the sites, then a slow motional narrowing of the line. Increasing γ further, cluster effects of the finite chain result in a structured ESR line which finally becomes Lorentzian. In the case of optical absorption the excitonic system is described by a tight-binding one-band Hamiltonian with Gaussian and dichotomic energy fluctuations. Our results indicate that the physical quantities associated with the optical spectra do not depend sensitively on the configuration of site energies (self-averaging). Moreover we have shown that for a dichotomically disordered solid in the band-splitting limit, spectra are dominated by cluster effects.