Temperature and Solvent Effects on the Luminescence Spectrum of C₇₀: Assignment of the Lowest Singlet and Triplet States

The temperature, solvent, and concentration dependence of the fluorescence and phosphorescence spectra of C70 in glassy solutions have been examined. Spectra have been recorded over the temperature range 4–200 K. In addition, the AC Stark field modulated phosphorescence and the phosphorescence of ¹³C₇₀ have been recorded and analyzed. The lowest triplet state is identified as a ³E₁′ state and the vibronic structure consists primarily of Herzberg–Teller active e₂′ modes. The intensity of the electronic origin is comparable to the vibronically induced intensity and is extraordinarily solvent sensitive. The solvent sensitivity exhibited by the spectra is shown to have the same origins as that observed in benzene and pyrene, but is several times greater in magnitude. Analysis of the spectra suggests that two electronic excited states contribute to the observed phosphorescence spectrum.