Theoretical calculation of the electroabsorption spectra of polyacene crystals

A two-dimensional analog of the Merrifield model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal is applied for the calculation of the electroabsorption (EA) spectra of polyacene crystals. The approach is essentially nonempirical, with most of the necessary input data estimated either from theoretical calculations or from independent experiments. Good quantitative reproduction of the experimental EA spectra is achieved, both in their absolute amplitude and intensity pattern. The large amplitude of the Frenkel exciton part of the spectra is successfully accounted for without the necessity to invoke anomalously large molecular polarizabilities. Some basic assumptions of previous analyses are shown to be invalid and future prospects of the new approach are discussed.