Kinetics of fullerene triplet states

Studies are described whose goal is a quantitative kinetic description of fullerene triplet relaxation. The room-temperature intrinsic lifetimes of solution phase T-1 C-60 and C-70 differ substantially, with values in toluene of 143 mu s and 12 ms, respectively. These decay rates exhibit only weak temperature dependence near room temperature. The intrinsic lifetime of T-1 C-60 has a simple dependence on vibrational energy content up to 1000 K. Efficient triplet-triplet annihilation occurs in C-60 and C-70 solutions at ca. 50% of the diffusion-limited rate. In mixed solutions, rapid reversible triplet energy exchange was observed between C-60 and C-70, and between C-60 and (CH3)(2)C-60. A new method for measuring relative triplet enthalpies and entropies in such mixtures has also been applied. Complex kinetics has been uncovered in C-70 solutions and modeled by reversible formation of short-lived triplet excimers, accounting for the efficient self-quenching. C-60 self-quenching has been found to be highly temperature dependent, but the mechanism remains unresolved.