Abstract
The structure of alkyl chains of azobenzene molecules at the air/water interface was studied using surface-specific sum-frequency vibrational spectroscopy. It was shown that the alkyl chains were well aligned before ultraviolet (UV) irradiation and protruding out of the surface with a certain distribution. The alkyl chains become less ordered by UV irradiation following dynamical motion due to cis-trans isomerization of azobenzene core. The alkyl chains show anisotropy in the direction perpendicular to that of the azobenzene core by linearly polarized UV irradiation.