Reversible Fullerene Electrochemistry: Correlation with the HOMO-LUMO Energy Difference for C60, C70, C76, C78, and C84

Reversible one-electron oxidations and reductions have been observed by Osteryoung square wave voltammetry (OSWV) for the three higher fullerenes C{sub 76}, C{sub 78}, and C{sub 84} in 1,1,2,2-tetrachloroethane (TCE) containing 0.1 M tetrabutylammonium hexafluorophosphate (TBA)PF{sub 6}. Potentials are reported versus the internal ferrocene redox couple. Under these conditions C{sub 76} displays a reversible oxidation at 0.81 V, an irreversible oxidation at 1.30 V, and two reversible reductions at -0.83 and -1.12 V. The oxidations of C{sub 78} show evidence of two species, which is consistent with the proposed isomerism for C{sub 78}. The predominant C{sub 78} species shows a reversible oxidation at 0.95 V, an irreversible oxidation at 1.43 V, and two reversible reductions at -0.77 and -1.08 V. The minor species displays a reversible oxidation at 0.70 V and an irreversible oxidation at 1.17 V, while the reductions seem to coincide with those of the other isomer. Finally, C{sub 84} yielded an oxidation at 0.93 V and three reversible reductions at -0.67, -0.96, and -1.27 V. A comparison of the differences in potential of the first reduction and first oxidation, (E{sub ox} - E{sub red}), shows that this difference becomes generally smaller as fullerene size increases. 43 refs., 4more » figs., 1 tab.« less