End-Group-Dominated Electrochemical Kinetics of Azobenzene Self-Assembled Monolayers on Gold

The self-assembly and electrochemical properties of a new class of thiol-functionalized azobenzene derivatives were studied on gold electrodes by cyclic voltammetry. The compounds (referred to as C n AzoC2, n = 1−4) were synthesized and characterized in our laboratory. They spontaneously adsorb onto a gold surface to form stable and reproducible monolayers. The C n AzoC2 SAMs ( n = 1−3) showed well-behaved voltammetric responses in aqueous solution that corresponded to a two-electron, two-proton reduction/oxidation of the azobenzene redox center. The voltammetric behavior was irreversible, exhibiting very large peak-to-peak splitting and other distortions. The apparent electron-transfer rate decreased with an increase of carbon atoms in the end group. In contrast to C n AzoC2( n = 1−3), the C4AzoC2 SAM did not show a clear-cut electrochemical response. The disparities between the electrochemical behaviors of these azobenzene SAMs were explained by the structural effect arising from different end groups.