Coupling of Frenkel excitons, charge transfer excitons and vibrations in linear absorption spectra of polyacene crystals

The linear absorption spectra of the crystals of anthracene, tetracene, and pentacene have been calculated in the case of coupling between Frenkel excitons (FEs), charge transfer excitons (CTEs) and intramolecular vibrations. The model and its parametrization for FEs and CTEs in the (a,b) plane of those crystals, first developed by Petelenz et al. have been used in the numerical simulations of the linear absorption. The calculated excitonic and vibronic spectra allow us to draw two main conclusions. First, CTEs and their vibronics will manifest themselves in the linear absorption of light polarized along the monoclinic axis only (i.e. for tetracene and pentacene along the crystallographic b-axis). Second, the vibronic coupling (FE-phonon and CTE-phonon) emphasizes and increases the number of the maxima due to CTEs manifested in the linear absorption.