Abstract
Studies are described whose goal is a quantitative kinetic description of fullerene triplet relaxation. The room-temperature intrinsic lifetimes of solution phase T1 C60 and C70 differ substantially, with values in toluene of 143 μs and 12 ms, respectively. These decay rates exhibit only weak temperature dependence near room temperature. The intrinsic lifetime of T1 C60 has a simple dependence on vibrational energy content up to 1000 K. Efficient triplet-triplet annihilation occurs in C60 and C70 solutions at ca. 50% of the diffusion-limited rate. In mixed solutions, rapid reversible triplet energy exchange was observed between C60 and C70, and between C60 and (CH3)2 C60. A new method for measuring relative triplet enthalpies and entropies in such mixtures has also been applied. Complex kinetics has been uncovered in C70 solutions and modeled by reversible formation of shortlived triplet excimers, accounting for the efficient self-quenching. C60 self-quenching has been found to be highly temperature dependent, but the mechanism remains unresolved.
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