Optically detected magnetic-resonance study of triplet-state dynamics inC70

We present studies of fluorescence, phosphorescence, photoinduced absorption, and their respective optically detected magnetic resonance of ${\mathrm{C}}_{70}$ molecules dispersed in polystyrene glasses. Two distinct triplet excitons are identified with principle zero-field splitting parameters ($D\approx 0.0089 \mathrm{and} 0.0098$ ${\mathrm{cm}}^{-1\mathrm{}}$, respectively) almost twice those reported in the literature ($D\approx 0.0052$ ${\mathrm{cm}}^{-1\mathrm{}}$). The first triplet is axially symmetric ($E\approx 0$) and phosphorescent. Dramatic changes in the line shape and intensity of this triplet are observed as the temperature increases due to a dynamic Jahn-Teller effect. The second triplet, which is believed to arise from strained ${\mathrm{C}}_{70}$ molecules, has no axial symmetry ($E\approx \frac{D}{3}$) and is not phosphorescent.