Electrochemical and ESR characterization of C-84 and its anions in aprotic solvents

Abstract

Cyclic voltammetry and differential pulse voltammetry studies on the D-2 and D-2d isomers of C-84 are reported in pyridine, benzonitrile, acetonitrile/toluene (15/85), dimethylformamide/toluene (15/85), and 1,2-dichlorobenzene. The nature of the solvent is found to greatly affect the number and half-wave potentials of the observed redox processes. For example, 10 reduction processes are observed in pyridine, while seven are detected in benzonitrile. The multiple redox processes in pyridine, are taken as evidence for the presence of two isomeric forms of C-84 in solution, namely, the D-2 and D-2d isomers, each of which has distinct half-wave reduction potentials. A comparison between the electrochemistry of C-60, C-70, C-76, C-78, C-84, and C-86 is presented. ESR studies were performed on solutions containing one or a mixture of the C-84 anion(s) and confirmed the presence of two isomers, D-2- and D2d-C84. Emphasis in this paper is placed on D-2d-C-84(2-); its ESR spectra at different temperatures are discussed and interpreted in terms of a thermally accessible triplet excited state and rotation of the dianion.