Functionalization of fullerene through fullerene cation intermediates
Fullerene cations, namely fullerene radical cation (C60˙+) and organofullerenyl cation (RC60+), are less investigated as intermediates in synthetic fullerene chemistry because of the intrinsic electronegativity of C60. Remarkably, these two intermediates can mediate reactions that afford versatile, unique and unexpected fullerene derivatives. This review article mainly describes these C60˙+ and RC60+ intermediates and includes a variety of topics, from the generation of C60˙+ and RC60+ species to their applications in fullerene modification reactions, such as Friedel–Crafts hydroarylation, nucleophilic addition, dimerization, intramolecular rearrangement reactions, and intramolecular cyclization reactions. Additionally, this review deeply discusses the mechanism of the formation of unique fullerene derivatives involving fullerene radical cation and organofullerenyl cation intermediates. In addition, the electrochemical properties and photovoltaic performance of these fullerene derivatives produced through C60˙+ or RC60+-mediated reactions are discussed in this review.