Abstract
The photoisomerization characteristics of sterically hindered azobenzenes in self-assembled monolayers (SAMs) on flat gold surfaces have been investigated by ultraviolet–visible (UV–vis) absorption spectroscopy and contact angle measurements. Upon UV light irradiation, 2Et-2S substituted with two ethyl groups at the ortho positions and Me-2S with a methyl group at the meta position showed significant changes in π–π* absorption bands, together with reductions in contact angles for water, as a consequence of trans-to-cis photoisomerization. The reversible trans ↔ cis photoisomerization of azobenzenes in SAMs was clearly observed upon alternating UV and visible light irradiation. Furthermore, 2Et-2S underwent very slow thermal cis-to-trans isomerization over 24 h at ambient temperature, which is likely to be due to the steric hindrance of diethyl groups near the azo linkage.
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