KINETICS OF FULLERENE TRIPLET-STATES

Studies are described whose goal is a quantitative kinetic description of fullerene triplet relaxation. The room-temperature intrinsic lifet imes of solution phase T-1 C-60 and C-70 differ substantially, with va lues in toluene of 143 mu s and 12 ms, respectively. These decay rates exhibit only weak temperature dependence near room temperature. The i ntrinsic lifetime of T-1 C-60 has a simple dependence on vibrational e nergy content up to 1000 K. Efficient triplet-triplet annihilation occ urs in C-60 and C-70 solutions at ca. 50% of the diffusion-limited rat e. In mixed solutions, rapid reversible triplet energy exchange was ob served 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 suc h mixtures has also been applied. Complex kinetics has been uncovered in C-70 solutions and modeled by reversible formation of short-lived t riplet excimers, accounting for the efficient self-quenching. C-60 sel f-quenching has been found to be highly temperature dependent, but the mechanism remains unresolved.