Control of Charge-Transher Reaction at the Electrode-Solution Interface with Self-assembled Molecular Thin Film

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Alky viologens adsorb on mercury electrode surface and form a self-assembly monomolecular thin film. The monomolecular thin film exhibits a pair of spike-like waves on cyclic voltammograms at the potentials about 0.2-0.3 V more positive than the reduction potentials for viologen species in the solution. It has been confirmed that these weves correspond to the redox electrode reaction between the adosorbed viologen dication and the cation radical from in situ spectro-electrochemical measurements (UV-visible and IR reflection absorption spectroscopy) of self-assembled molecular layr of viologens on mercury-plated platinum electrodeswhen the electrode potential is changed by ca. 30 m V across the potential corresponding corresponding to the spoke-like waves, the oxidation state of the adsorbed molecular assembly layr changes. The layr behaves like a switch which controls for the electrode reaction of species in solution to proceed or to stop. Attractive intermolecular interaction among cation radicals and the orientation of cation radicals with their longe molecular axis almost perpendicularly toward the electrode surface have been suggested from the IR spectroscopic measurements. This change in the molecular structure of the viologen layr is responsible for the hindramce of the electrode processes.It has been shown that the self-assembled molecular thin layr exhibits the switching function for the electrode reactions, Pb(II)+2e=Pb (Hg) and Tl(I)+e=Tl(Hg)as for the electron-transfer reaction of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy. This is explained by the mechanism described above. It has been also found that hindrance effect of the molecular layr on the reduction of Pb(II) changes with time elapsed from the formation of the layr and the change in structure of the layr in rather short period is suggested.