Control of the charge-transfer rate at a gold electrode modified with a self-assembled monolayer containing ferrocene and azobenzene by electro- and photochemical structural conversion of cis and trans forms of the azobenzene moiety

Self-assembled monolayers (SAMs) of a novel alkylthiol molecule containing ferrocene and azobenzene moieties have been constructed on gold. A cyclic voltammogram (CV) of the gold electrode modified with the SAM with 100% trans form of the azobenzene group showed only a pair of waves due to the redox of ferrocene in the potential range between 0 and +750 mV (vs Ag/AgCl) and did not change its shape after the potential scan or UV irradiation. The CV of a gold electrode modified with the SAM with 20% cis and 80% trans forms showed a pair of waves due to the redox of the azobenzene moiety in addition to that of ferrocene in the first potential scan between 0 and +750 mV. The wave due to the redox of azobenzene, however, disappeared, and the peak separation of the redox wave due to ferrocene became smaller in the second scan. The peak separation returned to the original value after UV irradiation for 1 week. These changes in the electrochemical characteristics of the latter electrode were reversible. Structural analysis by in situ Fourier transform infrared reflection-absorption spectroscopy showed that these changes were induced by the electrochemical conversion of cis to trans forms and photochemical conversion of the trans to cis forms of azobenzene in the SAM.