ON THE SINGLET EXCITED-STATES OF C-70 AND C-60

The fullerenes C-70 and C-60 have been studied by excitation and lumin escence spectroscopy. Highly resolved phosphorescence-excitation spect ra of C-70 in n-pentane at 1.5 K are reported. Besides the Origin and e(1)' vibronic bands of the lowest-energy A(2)' <-- S-0 excitation, th e origin, and an a(1)' vibronic band of the E-1' <-- S-0 excitation ar e assigned. For both C-70 and C-60 the fluorescence spectrum changes w ith temperature, which is explained in terms of thermally induced popu lation of excited states above S-1. For C-70, this concerns the E-1' s tate and the corresponding fluorescent state is found to be 130 cm(-1) above the A(2)' state in decalin/cyclohexane. For C-60 in the same ma trix, it concerns the state of predominant G(g) character at 85 cm(-1) above the T-1g state. (C) 1998 American Institute of Physics. [S0021- 9605(98)00845-9].