Electrochemically active organic thin films

The objective of this study is to gain an understanding of the factors which influence and control the formation of self-assembled monolayers (SAMs) chemisorbed on metal surfaces and how these SAMs modulate electron transfer kinetics. To achieve this purpose various alkyl thiol-SAMs with chain lengths from C4SH to C22SH and terminal functional groups such as -CO2H, -OH, -NH2, and -SO3- were prepared on gold surfaces.The electron transfer processes across thiol-SAMs have been extensively studied by electrochemical techniques including cyclic voltammetry and rotating disk electrode (RDE) voltammetry. RDE results indicate that a thiol monolayer greatly reduces the electron-transfer rate at the interface. From the current versus concentration relationships of several redox probes including K 3Fe(CN)6, Ru(NH3)6Cl3, (Bu 4N)3Fe(CN)6, and Co(bpy)Cl2, a partition mechanism is proposed. This mechanism accounts for the observation of saturation in current/concentration plots. Simulations of a pinhole/defects model and the partition model show that saturation in current/concentration curves occurs only in the partition model.Studies show that short-chain thiols adsorbed on gold surfaces can lower the interfacial energy and promote aniline polymerization. Long chain thiol SAMs do not block aniline polymerization. A homogeneous polyaniline film was proposed to be formed in, and on, long-chain thiol SAMs. Such a polyaniline exhibits better conductivity than that of polyaniline formed on bare gold.The voltammetric behavior of dopamine, ascorbic acid, and their mixture has been described at HSC11CO2H-modified Au electrodes. Complex redox processes involving the thiol-Au bond evident only under high sweep rate conditions were found. Depending upon such redox processes, dopamine at levels as low as 1nM can be detected. Such sensitivity is essential for the in vivo application of the o-carboxylic acid thiol SAM/Au electrode.The adsorption process of the thiol monolayer was showed to be electrochemically accessible. Control of electrode potential during the adsorption process apparently assists thiol self-assembly. Potential control allows for the formation of monolayers in a relatively short time and is more likely to be defect free than monolayers prepared under passive adsorption conditions. The potential deposition process allows one to control the ratio of components in a C 16SH/HSC15CO2H mixed monolayer