Tempo-C-61: An unusual example of fulleroid to methanofullerene conversion

An electrochemical and EPR study is reported on two isomeric C-60 derivativ es containing a covalently linked free radical TEMPO: a fulleroid and a met hanofullerene. In line with other C-60-based nitroxide derivatives, the lat ter one gives a stable biradical anion upon one-electron reduction, and a m etastable excited quartet state by visible light photoexcitation. Both spec ies have characteristic EPR spectra. For the fulleroid derivative, the firs t reduction step is not chemically reversible and no excited state EPR sign al is observed after LASER excitation, Electrochemical and spectroelectroch emical techniques indicate that fulleroid to methanofullerene conversion ta kes place by photoexcitation and, more interesting, upon injection of a sin gle electron, contrary to the cases of other fulleroids so far reported.