EVIDENCE FOR THE EXISTENCE OF SULFUR-DOPED FULLERENES FROM ELUCIDATION OF THEIR PHOTOPHYSICAL PROPERTIES

Evidence is presented that carbon atoms of the hollow fullerene cage c an be replaced by sulfur atoms, as has been suggested theoretically. S -doped fullerenes are obtained by arc-vaporization of graphite in the presence of thiophene or 3-methylthiophene, Mass spectra indicate the dominant processes are the substitutions of pairs of carbon atoms by s ulfur atoms with the predominant ratios of sulfur to replaced carbon p airs being 1, 1/3, Or 1/4. Fractions that contain a large group of suc h compounds with a substantial S enrichment can be collected by column chromatography, but no single pure compound can be isolated. Since th e mass spectra can be interpreted in alternate ways involving S incorp oration as an adduct, evidence was sought for their existence from a d etailed study of the fluorescence of these species. The fluorescence e mission spectra are red-shifted from and consistent with absorption sp ectra and can be attributed to the emission from symmetry-broken disto rted S-doped derivatives of fullerenes. An optical bandgap of 2.5 eV i s derived for the S-doped fullerenes resulting from the splitting of t he h(u) degenerate state. The fluorescence lifetimes of these molecule s are 2-7 ns, considerably larger than those of the undoped fullerenes .