Anion radicals of [60]-fullerene and its ortho-quinodimethane adducts generated by cathodic reduction and photochemical electron transfer: an EPR and vis-near-IR study

Abstract [60]-Fullerene and its four ortho -quinodimethane adducts, one of them in oligomeric form, were reduced by three different methods, (a) by cathodic reduction, (b) in photoexcited TiO 2 suspension, and (c) quenching photoexcited fullerene by triethylamine donor. The radicals obtained were mainly investigated by EPR and also characterized by vis—near-IR measurements. All three methods of generation gave two identical radical products: the primary radical A , which is a fullerene mono-anion, with EPR spectral parameters g A = 2.0000 and peak-to-peak width pp A = 0.09 mT for [60]-fullerene, pp A = 0.105 for its adducts and pp A = 0.19 mT for the fullerene oligomer. The near-IR band of A at 1077 nm for [60]-fullerene shiftd into the region of 1010 nm for its ortho -quinodimethane adducts. As a consecutive product of A , radical B was found with g B = 2.0006 and pp B = 0.07 mT for all [60]-fullerene adducts. The EPR signal of B converts to A after stopping photogeneration, resulting in a total increase of the spin susceptibility in the form of fullerene mono-anion A . The formation of fullerene di-anion or fullerene associates is considered as an alternative.