Origin of the Puzzling Narrow Line in the EPR Spectrum of Triplet C70

Abstract

X-band light-induced continuous wave EPR (LEPR) spectroscopy was employed to study triplet fullerene C₇₀, ³C₇₀, in glassy decalin and o-terphenyl. The EPR lineshapes observed in the temperature ranges between 50 and 130 K (for decalin) as well as between 77 and 200 K (for OTP) were successfully simulated. The results show that the narrow LEPR line does not originate from a radical S = 1/2, but arises from jumps of the EPR lines within the LEPR spectrum of ³C₇₀ between symmetrical LEPR positions provided by paramagnetic relaxation process of ³C₇₀. This process can be described by a relaxation-induced coherence transfer between two resonance transitions having close transition frequencies.