Optical and Electrical Properties of Fullerenes

We have investigated the properties of intermolecular charge transfer (CT) excited states and demonstrated their contribution to the excitation-relaxation and photocarrier generation mechanisms for both C₆₀ and C₇₀ polycrystalline films: 1) Experimentally, using UV-visible absorption (Abs) and electroabsorption (EA), luminescence and its modulation by external electric field, and steady photoconductivity; 2) Semi-empirically, analyzing the Abs and EA spectra in order to determine the CT state energies and to estimate the variation of the average polarizability tensor and the dipole moment; 3) Theoretically, by performing the calculations of polarization energies and electrostatic stabilization energies. The most significant CT states have been identified at approximately 2.43 and 3.50 eV for C₆₀ films and at 2.26 and 3.60 eV for C₇₀ films (data from the semi-empirical analysis). Their properties have been discussed in terms of crystallographic and electronic structure. We have also discussed the photocarrier generation processes in fullerenes, for which the existence of CT states is of crucial importance. These materials might be of potential applications in xerography and photovoltaic devices.