pH-modulated vectorial electron transfer reactions at a self-assembled monolayer on a gold electrode

A self-assembled monolayer of 1-dodecanethiol (C12SH) on a gold electrode was prepared by dipping a polished bare electrode into an ethanolic solution of C12SK (1.0 mmol dm(-3)) for 10 min. The obtained modified electrode blocked the direct electron-transfer reaction of [Fe(CN)(6)](3-) and [Fe(CN)(6)](4-) with the underlying electrode. However, a pH-dependent redox compound, 4,4'-biphenyldiol (Ij in solution, was permeable into the monolayer and save well-defined cyclic voltammograms at both higher and lower pHs. Using this chemical-recognition ability of the modified electrode together with the formal potential shift of 1 according to the Nernst equation, pH-modulated vectorial electron transfer reactions were examined. At pH 3, cyclic voltammograms at the modified electrode in a 1+[Fe(CN)(6)](4-) aqueous solution revealed that one-way electron how from [Fe(CN)](4-) to the electrode via 1 (oxidized form) occurred. On the contrary, at higher pHs (pH 9-11), the vectorial electron flow at the electrode in 1+[Fe(CN)(6)](3-) solution was reversed. A triggered change ('switching') between the anodic and cathodic vectorial electron transfer reactions by changing the pH was also possible at the C12SH-modified electrode in the presence of 1, [Fe(CN)(6)](4-) and Fe(CN)(6)](3-) in solution. This Ending may offer possibilities for the construction of functional molecular devices based on the tuning of rectified electron transfer reactions.