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

烷基紫精吸附在汞电极表面，形成自组装单分子薄膜。单分子薄膜在循环伏安曲线上出现一对尖峰，其电位比紫精在溶液中的还原电位高0.2-0.3V。由紫精在镀汞铂电极上自组装分子层的原位光谱电化学测量(紫外可见光谱和红外反射吸收光谱)证实，它们对应于吸附紫精与阳离子自由基之间的氧化还原电极反应。当电极电位沿轮辐状波对应的电位改变约30mV时，吸附的分子集合层的氧化态发生变化。LayR的作用就像一个开关，控制溶液中物种的电极反应进行或停止。红外光谱分析表明，阳离子自由基之间存在吸引人的分子间相互作用，阳离子自由基的分子长轴几乎垂直于电极表面。紫精LayR分子结构的这种变化是导致电极过程受阻的原因之一。研究表明，自组装的分子薄层对电极反应具有开关作用，对于4-hydroxy-2，2，6，6-tetramethylpiperidinyl-1-oxy.的电子转移反应，Ph(II)+2e=Ph(Hg)和Tl(I)+e=Tl(Hg)As这是由上述机制解释的。此外，还发现分子LayR对Pb2+还原的阻碍作用随LayR形成的时间而变化，提示LayR的结构在较短的时间内发生了变化。

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.