Electrochemical Behavior of Azobenzene Self-Assembled Monolayers on Gold

The self-assembly and electrochemical properties of a novel thiol-functionalized azobenzene derivative were studied on gold electrodes by cyclic voltammetry. The compound was 4-ethoxy-4'-((N-(2''-mercaptoethyl)amino)carbonyl)azobenzene (C2AzoC2SH), which was synthesized using a simple and general technique by our laboratory. The C2AzoC2SH formed uniform and reproducible self-assembled monolayers (SAMs) on gold with a surface coverage of 4.21 × 10-10 mol/cm2. The SAMs showed voltammetric responses in a B-R buffer at a pH range of 3.2−8.6 that corresponded to the two-electron, two-proton reduction−oxidation of azobenzene. The voltammetric behavior was totally irreversible, exhibiting very large peak-to-peak splitting and other distortions. The dependence of apparent surface electrochemical rate constant on pH value has a V-shape, owing to the influence of protonation reactions on the multistepped reduction−oxidation of azobenzene functionality.