Optically-detected magnetic-resonance study of triplet state dynamics in C70

We present studies of fluorescence, phosphorescence, photoinduced absorption, and their respective optically detected magnetic resonance of C70 molecules dispersed in polystyrene glasses. Two distinct triplet excitons are identified with principle zero-field splitting parameters (D≈0.0089 and 0.0098 cm-1), respectively! almost twice those reported in the literature (D≈0.0052 cm-1). The first triplet is axially symmetric (E≈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 C70 molecules, has no axial symmetry (E≈D/3) and is not phosphorescent.