Anion exchange-promoted Ru^3+/2+ redox switch in self-assembled monolayers of imidazolium ions on a gold electrode

1,3-Dialkylimidazolium salts, known as one of the ionic liquids, are very attractive molecules because their physicochemical properties can easily be tuned by the variation of the alkyl appendages of the imidazolium cations and counteranions. In this paper we report that the self-assembled monolayers (SAMs) terminating in 1,3-dialkylimidazolium salts with various counteranions [except Fe(CN)₆^3-] on a gold substrate exhibited a selective electron-transfer toward redox-probe molecules: the electron transfer occurred in the presence of Fe(CN)₆^3- (anionic redox-probe molecule) but did not occur in the presence of Ru(NHs)₆³⁺ (cationic redox-probe molecule). The SAM having Fe(CN)₆^3- as an anion showed the electron-transfer toward Ru(NH₃) ₆³⁺, and the Ru^3+/2+ redox-switchable SAM was generated by reversible anion exchange between Fe(CN)₆^3- and SCN^- (or OCN^-).