PHOTOPHYSICAL PROPERTIES OF FULLERENES PREPARED IN AN ATMOSPHERE OF PYRROLE

Samples of C-60 and C-7O containing a variety of nitrogen-doped specie s were prepared by are vaporization of graphite in the presence of pyr role. Cage-doped fractions were isolated by column chromatography and characterized by mass spectroscopy, optical absorption, and fluorescen ce measurements. Mass spectra were consistent with the substitution of all even number of carbon atoms of the C-60 and C-7O cages by nitroge n atoms. Carbonaceous clusters including fragmented fullerenes contain ing hydrogen atoms were also formed. UV-visible spectral analysis indi cated that there is an influence of the molecular weight on the fundam ental pi-pi electronic transition. Fluorescence spectra showed a broa d band containing vibrational fine structure that is attributed to pho toseparated charges in the fragmented fullerenes and a shoulder on the low-energy side that is related to intrinsic excitation in the nitrog en-doped species. Fluorescence results imply a bandgap of 2.36 eV for the N doped fullerenes and the existence of intermediate excitonic tra nsitions below the optical bandgap. Although it has not yet been possi ble to isolate a pure cage-doped material, the photophysical studies a dd credence to their existence and the importance of further attempts at their isolation.