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膜。该单分子薄膜在循环伏安图上显示出一对尖峰状波，其电位比溶液中紫精物种的还原电位正约0.2-0.3 V。通过紫外-可见和红外反射吸收光谱法对紫精自组装分子层在镀汞铂电极上的原位电化学测量，证实了当电极电位改变约100时，吸附的紫精二价阳离子与阳离子自由基之间的氧化还原电极反应。30 mV的电位时，吸附分子组装层的氧化态发生变化。层的行为就像一个开关，控制溶液中物质的电极反应进行或停止。红外光谱表明，阳离子自由基间存在分子间吸引作用，阳离子自由基的长轴取向几乎垂直于电极表面。紫精分子结构的这种变化是阻碍电极过程的原因，表明紫精分子自组装薄膜对电极反应具有开关功能，Pb（II）+2 e =Pb（Hg），Tl（I）+e=Tl（Hg），对4-羟基-2，2，6，6-四甲基哌啶-1-氧的电子转移反应也具有开关功能。这可以通过上述机制来解释。还发现，分子层对Pb（Ⅱ）还原的阻碍作用随层形成时间的变化而变化，并提出了层结构在相当短的时间内发生变化的观点。

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.