Fullerene C70 Triplet Zero-Field Splitting Parameters Revisited by Light-Induced EPR at Thermal Equilibrium

Abstract

Continuous-wave (CW) electron paramagnetic resonance (EPR) and echo-detected (ED) EPR spectra of triplet state of fullerene C70 in molecular glasses of decalin, o-terphenyl and toluene, and in polymethylmethacrylate polymer were obtained under continuous light illumination. Temperature was high enough so that the EPR spectra corresponded to thermal equilibrium between the spin sublevels. The comparison of CW EPR and ED EPR data has shown that pseudorotation in the 3C70 frame does not remarkably affect deriving the zero-field splitting (ZFS) D and E parameters from the EPR spectra. 3C70 EPR spectra were simulated at 77 K fairly well using the distribution of the ZFS D and E parameters. These distributions may be caused by the inhomogeneity of the glassy matrix surrounding, which affects the Jahn–Teller distortions of 3C70 molecules (D-strain and E-strain).