Spin Signature of the C60 Fullerene Anion: A Combined X-and D-Band EPR and DFT Study

Fullerenes attract much attention in various scientific fields, but their electronic properties are still not completely understood. Here we report on a combined EPR and DFT study of the fullerene anion C-60(-) in solid glassy environment. DFT calculations were used to characterize its electronic structure through spin density distribution and magnetic resonance parameters. The electron spin density is not uniformly distributed throughout the C-60(-) cage but shows a pattern similar to PC61BM-. EPR spectroscopy reveals a rhombic g-tensor sensitive to the environment in the frozen glassy solutions, which can be rationalized by deformation of the fullerenes along low frequency vibrational modes upon cooling. DFT modeling confirms that these deformations lead to variation in the C-60(-) g values. The decrease in g-tensor anisotropy with sample annealing is related to the lessening of g-tensor strain upon temperature relaxation of the most distorted sites in the glassy state.