Modulation of the reduction potentials of fullerene derivatives.

The cyclic voltammetric (CV) study of a series of novel bisfulleropyrrolidines (3) and bisfulleropyrrolidinium ions (4) is reported. The eight possible stereoisomers of each series were systematically investigated under strictly aprotic conditions that allowed the observation of up to four and five subsequent reversible reductions in 3 and 4, respectively. Because of the stabilizing effect of positive charges, a significant enhancement of the electronegative properties was observed in 4. In fact, 4-trans-2 and 4-trans-1 result among the strongest reversible electron-accepting C(60) oligoadducts. Furthermore, the study evidenced that, in both 3 and 4, the CV pattern, and in particular the potential separation between the second and third reductions, changes significantly with the addition pattern. A sequential pi-electron model that simulates the effect of subsequent reductions of C(60) bis-adducts gives a good correlation (r > 0.96) with the cyclic voltammetry data when the molecules are divided in two sets dependent on the location of the addends in the same or in opposite hemispheres.