Photophysical properties of heteroatom substituted fullerenes

Summary form only given. By arc vaporization of graphite in the presence of such sources of nitrogen or sulfur as pyrrole or thiophene, fractions can be isolated which have heteroatoms substituted in the cage. As of this writing, no single pure compound has been isolated, but the fluorescence emission spectra of the fractions give strong evidence for the existence and interesting properties of cage doped fullerenes. Whereas C/sub 60/ and C/sub 70/ show very weak fluorescence, heteroatom substitution distorts the symmetry of the molecule and gives strong fluorescence. In the case of N substitution, the fluorescence from the excited states shows a broad band containing vibrational fine structures that are attributed to photo-separated charges in fragmented fullerenes and a shoulder on the low energy side that is related to intrinsic excitation in nitrogen doped species. Fluorescence results also suggest a band gap of 2.36 eV for the N doped fullerenes and the existence of intermediate excitonic transitions localized below the optical band gap. In the case of S substitution, an optical band gap of 2.5 eV results from the splitting of the hu degenerate state and a fluorescence lifetime of 2-7 ns is obtained.