Spin Dynamics of Photoexcitations in C60 and C60

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Abstract
We have used absorption detected magnetic resonance (ADMR) spectroscopy to study the spin dynamics of spin 1/2 and spin 1 photoexcitations in C60 and C70′ in molecular and solid-state forms. In C60 molecules dispersed in polystyrene matrix (C60:PS), two S = 1 powder patterns were observed at 4 K; they collapse towards the central g ≊ 2 magnetic resonance line with increasing temperature. We fit the results with a model that relates the two observed triplets with two Jahn-Teller distortion levels, respectively, subject to a temperature dependent pseudo rotation dynamics. In C70:PS, we found that a S = 1/2 signal, which is associated with existing radicals in the sample, accompany the S = 1 ADMR signal. In sublimed C60 and C70 films, in addition to the triplet excitations with a quenching ADMR signal, we found an enhancing spin 1/2 ADMR signal. We explain this feature as due to charge separation, which uniquely occurs in sublimed films with excitation above the respective C60 and C70 energy gap.