Localization length and intraband scattering of excitons in linear aggregates

A theoretical model to describe the intraband scattering of excitons in lin ear aggregates of finite size which exhibit strong intermolecular interacti ons is presented. From the calculation of the aggregate eigenstates, the lo calization length of excitons is evaluated for various configurations featu ring physical situations like trapping, edge effects, inclusion of diagonal and/or orientational disorders. The intraband scattering is studied by con sidering the exciton-phonon stochastic coupling induced by the thermal bath . This coupling creates local dynamical fluctuations in the site energies w hich are characterized by their amplitude (Delta) and their correlation tim e (tau(c)). Expressions of scattering rates are provided and used in a Paul i master equation to calculate the time dependence of the eigenstates popul ations after initial excitation of the quasi exciton-band. It is shown that the time evolution of the lowest state population as well as the Stokes sh ift strongly depend on tau(c). Comparison of the theoretical results to tim e-resolved experiments performed on triaryl pyrylium salts allows us to int erpret the observed Stokes shift and to derive an average value of the exci ton-phonon correlation time. (C) 1999 Published by Elsevier Science B.V. Al l rights reserved.