Singlet excited state (S1) of higher fullerenes C76 and C84: correlation between lifetime and HOMO–LUMO energy gap

Photophysical properties of higher fullerenes C76 and C84 were investigated in toluene by steady-state and transient absorption spectroscopy. Lifetimes of 75 and 35 ps were measured for the lowest excited state of C76 and C84, respectively, which are much shorter than the values estimated from previous triplet–triplet absorption studies. It was found that the internal conversion rate constants, kIC, increased as the size of fullerene increased, and that kIC was strongly correlated with the HOMO–LUMO energy gap, ΔEg. From this correlation, an empirical relationship was obtained: log kIC (s−1)=14.59 − 3.39 ΔEg (eV).