Degenerate Frenkel exciton states in the electroabsorption spectroscopy of molecular crystals

A simple model of the coupling between a Frenkel exciton and a charge transfer state is applied to study some consequences of the degeneracy of intramolecular excitations for the electroabsorption (EA) spectrum of a molecular crystal. It is demonstrated that the EA signal of degenerate Frenkel states need not follow the first derivative of the absorption spectrum, as hitherto assumed. This invalidates one of the basic premises underlying the numerical resolution of electroabsorption spectra. The electroabsorption spectrum of the fullerene crystal is discussed in the new context.