Pyrazolinofullerenes: a less known type of highly versatile fullerene derivatives.

The cycloaddition of readily available nitrile imines to [60]fullerene affording 2-pyrazolino[60]fullerenes is a versatile procedure for the functionalization of fullerenes. In contrast to other functionalization methods these cycloadducts are obtained generally in good yields as single isomers, thus avoiding the formation of undesired stereoisomers. This tutorial review discusses these less known fullerene compounds that display, however, interesting electrochemical and photophysical properties. Owing to their outstanding electron acceptor character, similar to pristine C(60), and their remarkable thermal stability, these cycloadducts are good candidates for incorporation in photovoltaic devices. However, more work is needed in order to design better pyrazolinofullerenes exhibiting improved performances for PV applications.