Redox-induced orientation change of a self-assembled monolayer of 11-ferrocenyl-1-undecanethiol on a gold electrode studied by in situ FT-IRRAS

The potential dependent structure change of a self-assembled monolayer of 11-ferrocenyl- 1-undecanethiol (FcC₁₁SH) on a gold electrode surface during the redox reaction of the terminal ferrocene group was investigated in 0.1 M HClO₄ solution by electrochemical in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). A number of bands were observed in the 3200-1200 cm^-1 region with p-polarization measurement, but no band was observed by s-polarization measurement when the potential was kept more negative than +1.2 V. The intensity of these bands corresponded well to the degree of oxidation of the terminal ferrocene group in the monolayer. The potential dependent IRRAS behavior can be explained by considering an orientation change of the monolayer induced by the redox reaction of the terminal ferrocene moiety in the monolayer.