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

Abstract

Reversible one-electron oxidations and reductions have been observed by Osteryoung square wave voltammetry (OSWV) for the three higher fullerenes C76, C78, and C84 in 1,1,2,2-tetrachloroethane (TCE) containing 0.1 M tetrabutylammonium hexafluorophosphate ((TBA)PF6). Potentials are reported versus the internal ferrocene redox couple. Under these conditions C76 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 C78 show evidence of two species, which is consistent with the proposed isomerism for C78. The predominant C78 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, C84 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, (Eox – Ered), shows that this difference becomes generally smaller as fullerene size increases, with the exact order being C60 > C70 > C78(C2v) > C76 > C84 > C78(D3). The experimental (Eox – Ered) differences correlate well with calculated HOMO-LUMO separations for a series of five fullerenes. © 1995, American Chemical Society. All rights reserved.