Photoreactivity in Self-Assembled Monolayers Formed from Asymmetric Disulfides Having para-Substituted Azobenzenes

Asymmetric dialkyl disulfides with a para-substituted azobenzene (i.e., 4-substituted 4‘-(12-(dodecyldithio)dodecyloxy)azobenzenes) produced photoresponsive self-assembled monolayers (SAMs) on gold (111) surfaces. Infrared reflection absorption (IR-RA) spectroscopy and reflection ultraviolet (UV) and visible (vis) light absorption spectroscopy gave information on the molecular orientational order of the adsorbates in the SAMs. The photoreactivity was investigated using dynamic contact-angle measurements with a Wilhelmy-type surface balance. The structure and photoreactivity of the SAMs were dependent on the substituent at the para position of an azobenzene moiety. Relatively ordered structures in the methylene parts and the photoisomerization of azobenzene moieties were observed for the SAMs formed from the hexyl- and the nonsubstituted azobenzene disulfides. However, a less-ordered SAM structure was seen for the cyanoazobenzene disulfide SAM, and the photoresponse is rather unstable.