Electrochemical properties of mixed self-assembled monolayers on gold electrodes containing mercaptooctylhydroquinone and alkylthiols

Mixed self-assembled monolayers of 2-(mercaptooctyl)hydroquinone (QH(2)) and alkylthiols were formed on gold electrodes in EtOH and the redox process of the hydroquinone moiety of QH(2) was characterized by cyclic voltammetry (CV) in 0.1 M H2SO4. The monolayers were formed at a series of QH(2):alkylthiol ratios and the QH(2):alkylthiol ratio in solution was compared to the electrochemical response from QH(2) in the obtained monolayer. Mixed monolayers of QH(2) with hexylthiol, dodecylthiol, and octadecylthiol were studied. The length of the alkylthiol is crucial for the electrochemical response from QH(2) in the monolayer. The total concentration of thiols during monolayer formation and incubation times were also studied and low concentrations of < 2.5 mM and long incubation times gave rise to lower peak separation, lower peak half widths in the CVs of the mixed monolayers, and lower background current. The stability of a pure QH(2) monolayer and a 1:4 QH(2):hexylthiol monolayer toward high potentials of up to 1.5 V versus Ag/AgCl was also studied and it was observed that the mixed monolayer is significantly more stable than the pure QH(2) monolayer.