Photophysical properties of nitrogen substituted fullerenes

By arc vaporization of graphite in the presence of pyrrole vapor, products are formed containing nitrogen atoms substituted in the C60 and C70 cage accompanied by other carbonaceous clusters. Fractions which are rich in nitrogen were isolated by high performance liquid chromatography using a gel permeation column and characterized by optical absorption, fluorescence, transient absorption, and time-resolved fluorescence measurements. Fluorescence spectra are attributed to intrinsic excitation in the nitrogen doped species as well as to separated charges in the fragmented fullerenes. Transient absorption spectra at time delays of 20 ns following excitation of the ground state molecules are attributed to delayed fluorescence. The average fluorescence lifetime of these molecules were determined to be 4 ns. These data, together with earlier studies from this laboratory of the mass spectra, absorption and fluorescence of fractions isolated by column chromatography, add further credence to the existence of stable nitrogen doped fullerenes.