Theoretical interpretation of the electroabsorption spectrum of fullerene films

Abstract

A three-dimensional analogue of the Merrifield model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal is used to calculate the electroabsorption (EA) spectrum of buckminsterfullerene films. The approach is essentially nonempirical, with most of the input parameters estimated from theoretical calculations or from independent experiments, but in doubtful cases a comparison of the calculated and experimental EA spectra guides the choice between alternative sets of parameters. Semiquantitative agreement between the calculated and experimental EA spectra lends credence to the model, which can therefore be used to draw conclusions concerning the underlying physical mechanisms. The EA signal of the CT states is shown to be substantially affected by the off-diagonal CT interactions, and by interactions with the optically inactive Frenkel excitons, whose intramolecular parentage is tentatively assigned. The results confirm the validity of previous calculations of the electrostatic CT state energies.