Figure 6. Temperature dependence of the triplet-triplet energy transfer from C-P-³C₆₀ to yield ³C-P-C₆₀ in triad 1. The point at 300 K was determined from the rise of the carotenoid triplet state in toluene, as C-P-³C₆₀ is not observed in 2-methyltetrahydrofuran at this temperature due to decay of C-P-¹C₆₀ by photoinduced electron transfer. The other points were obtained from transient absorption experiments in 2-mehtyltetrahydrofuran with excitation at 625 nm and detection at 700 nm. The solid line is a fit to eq 1, and yields an Arrhenius activation energy of 0.17 eV for the transfer.