Electrochemistry of an open-cage fullerene embedded in a film of hydrophobic ammonium ion on an electrode

Functional electrode devices modified with only the cast films of an open-cage fullerene (compound 1) and of 1/long-chain tetraalkylammonium ion were constructed and the aqueous electrochemistry of the electrodes was investigated. Tetraoctylammonium bromide (TOAB) was used as a long-chain ammonium ion. Almost no electrochemistry was observed for the 1 film-coated electrode. In sharp contrast, the 1/TOAB-coated electrode was found to exhibit well-defined cyclic voltammograms (CVs), leading to the generation of the radical monoanion and dianion of 1 at E₁^0′ = -0.120 and E₂^0′ = -0.594 V (E vs SCE), respectively. The generation of the trianion of 1 at the electrode was not evident. The radical monoanion of 1 was unstable for potential cycling at scan rates of 0.1-1 V/s, whereas the dianion was stable at the scan rate of 1.0 V/s. We also examined the electrolyte dependence. Almost no electrolyte cation dependence was observed on the CVs of the 1/TOAB-coated electrode. On the contrary, electrolyte anions were found to influence the CVs of the electrodes. On the basis of these results, a possible electron-transfer mechanism for the first and second reduction processes of the open-cage fullerene embedded in films on the electrodes is proposed.