TRIPLET-STATES OF C-60 AND C-70 IN SOLUTION - LONG INTRINSIC LIFETIMES AND ENERGY POOLING

Lifetimes of the lowest triplet electronic states Of C60 and C70 have been measured in room temperature benzene solution. With bimolecular quenching suppressed, the exponential lifetimes are found to be 133 mus for C60 and >2.2 ms for C70. Triplet C60 and C70 are self-quenched with rate constants of 1.5 x 10(7) and 8.5 x 10(7) M-1 s-1, respectively. In mixed solutions Of C60 and C70, triplet electronic excitation is efficiently and reversibly transferred at approximately 20% of the diffusion-limited rate. From the ratio of forward and reverse energy transfer rate constants, the T1-S0 gap Of C60 is deduced to be 102 +/- 30 cm-1 greater than that Of C70. The long intrinsic lifetimes and rapid energy pooling suggest that improved efficiencies may be possible for many applications of fullerene photochemistry and photophysics.