Optical kinetic spectroscopy is used to investigate the triplet state properties of solution phase fullerenes. These triplet states, which are the molecules' lowest-energy and longest-lived electronic excitations, show lifetimes and absorption spectra that vary from fullerene to fullerene. In room temperature toluene solution, the intrinsic triplet lifetime of C70 exceeds that of C60 by a factor at of least 80. The 'self-quenching' deactivation of triplet states through encounters with ground state molecules occurs with rate constants of 1.6 X 1070 M-1s-1 for C60 and 3 X 107 M-1s-1 for C70. In solutions containing mixtures of fullerenes, transfer of triplet excitation between species is efficient and reversible, with rate constants up to 2 X 109 M-1s-1. When C60 is aliphatically derivatized at two adjacent sites to form (6,6)-closed dihydrofullerene structure, intrinsic triplet lifetimes are shortened by more than a factor of 3 to approximately 45 microsecond(s) . The triplet spectra of these compounds, in which the derivitizing groups are not sterically strained, are very similar to each other but significantly different from the C60 spectrum. The (6,6)-closed epoxide, C60O, displays unusual triplet state behavior. Its initial triplet spectrum is distinct from that of the other derivatives studied and decays in approximately 6 microsecond(s) through nonexponential kinetics. Evolution of the induced spectrum suggest the possibility of epoxide ring opening form the triplet state of C60O.
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