Solvent free mechanochemical oxygenation of fullerene under oxygen atmosphere

Oxygenation of fullerene took place under mechanical stressing by a simple vibration mill in an oxygen atmosphere at 1 atm. Milled products were mixtures of poly-oxidized fullerene, C60On, containing C-O-C and CO bonds. We observed a concurrent reaction as well, that is, polymerization of C60 and C60O. The average number of oxygen, n, of the overall products obtained by milling for 5 h was 8.6 per molecule of C60. We confirmed generation of singlet oxygen during the present mechanochemical reaction by an ESR spin trapping method. Trapping of 1O2 was completely inhibited the oxygenation of fullerene. Formation of 1O2 is attributed to the energy transfer from mechanically excited state of fullerene and plays a decisive role on the present oxygenation of fullerene under mechanical stressing in O2. In contrast, no 1O2 was observed by mechanically stressing the conventional photo-sensitizer, rosebengal. The difference in the behavior of C60 and rosebengal is interpreted in terms of molecular deformation, being much easier for a 3D molecule, C60, than a planar molecule, in line with the concept of inverse Jahn-Teller effects.