Modified carbon surfaces as "organic electrodes" that exhibit conductance switching.
Modified carbon surfaces as "organic electrodes" that exhibit conductance switching.
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改性碳表面作为“有机电极”，表现出电导切换。
作者：
A. Solak;Laura R Eichorst;W. J. Clark;R. McCreery
用联苯和硝基联苯分子单层膜修饰玻碳表面，考察了二茂铁、苯醌和四氰基醌二甲烷在乙腈中的伏安电化学行为。改性电极表现出较慢的电子转移比未改性的GC，与单层和氧化还原系统不同的因素。然而，在相对于Ag+/Ag负电位偏移至约-2.0 V后，改性电极表现出快得多的电子转移动力学，接近在未改性GC上观察到的那些。这种效应归因于联苯或硝基联苯单分子层中明显不可逆的结构变化，这增加了电子隧穿速率。到“ON”状态的过渡与电子注入到单层中类似于在先前的光谱调查中观察到的，并导致单层分子的计算HOMO-LUMO间隙显着减少。一旦单层被打开，它支持与外层氧化还原系统的快速电子交换，但不支持与多巴胺的快速电子交换，多巴胺需要吸附到GC表面。随着电子注入的电子转移速率的增加与通过单层的电子隧穿速率的增加一致，这是由隧穿势垒高度的显著降低引起的。ON电极可以还原溶液中的联苯或硝基联苯重氮试剂，以允许形成联苯或硝基联苯分子的第二改性层。这种“双重衍生化”的程序被用来制备四苯基和硝基四苯基修饰电极，表现出显着较慢的电子转移比他们的联苯和硝基联苯对应物。“开关”电极可具有用于电分析应用和可能用于电催化的有用性质。另外，ON状态表示在有机导体和溶液之间的界面而不是在溶液和金属或碳电极之间的界面处发生电子转移的“有机电极”。
Glassy carbon (GC) surfaces modified with monolayers of biphenyl and nitrobiphenyl molecules were examined as voltammetric electrodes for ferrocene, benzoquinone, and tetracyanoquinodimethane electrochemistry in acetonitrile. The modified electrodes exhibited slower electron transfer than unmodified GC, by factors that varied with the monolayer and redox system. However, after a negative potential excursion to approximately -2.0 V versus Ag+/Ag, the modified electrodes exhibited much faster electron-transfer kinetics, approaching those observed on unmodified GC. The effect is attributed to an apparently irreversible structural change in the biphenyl or nitrobiphenyl monolayer, which increases the rate of electron tunneling. The transition to the "ON" state is associated with electron injection into the monolayer similar to that observed in previous spectroscopic investigations and causes a significant decrease in the calculated HOMO-LUMO gap for the monolayer molecule. Once the monolayer is switched ON, it supports rapid electron exchange with outer-sphere redox systems, but not with dopamine, which requires adsorption to the GC surface. The increase in electron-transfer rate with electron injection is consistent with an increase in electron tunneling rate through the monolayer, caused by a significant decrease in tunneling barrier height. The ON electrode can reduce biphenyl- or nitrobiphenyldiazonium reagent in solution to permit formation of a second modification layer of biphenyl or nitrobiphenyl molecules. This "double derivatization" procedure was used to prepare tetraphenyl- and nitrotetraphenyl-modified electrodes, which exhibit significantly slower electron transfer than their biphenyl and nitrobiphenyl counterparts. A "switching" electrode may have useful properties for electroanalytical applications and possibly in electrocatalysis. In addition, the ON state represents an "organic electrode" in which electron transfer occurs at an interface between an organic conductor and a solution rather than an interface between a solution and a metal or carbon electrode.