Isolation and structure of fullerene photodimer, C120

Photopolymerization of C60 was performed on a gram scale via a new monomer transport method. After subsequent extractions of the raw polymer in organic solvents, 100mg dimer and 10mg mixture of soluble oligomers were yielded. The structures of the soluble fractions and the insoluble polymer were studied by optical spectroscopy and x-ray diffraction methods. According to IR and UV-VIS spectroscopic data, the obtained photodimer is identical to the (2+2) cycloadduct C120 prepared previously. In contrast to previous crystallization studies, a fast precipitation of the dimer from toluene gives rise to the formation of a solvent-free microcrystalline solid. The crystal structure of the pure dimer is fcc (a=14.05 A) consisting of closely packed balls with the cycloadduct bonds oriented randomly along the 12 nearest neighbor directions. A linear relationship is found to exist between the fcc lattice parameter (a) and the average number of bonded neighbors (nB) in various photopolymerized structures. For insoluble polymers nB≅2 is estimated, supporting previous photopolymer models of small ring or branched clusters