Anisotropy of alkyl chains of azobenzene molecules at the air/water interface observed by sum-frequency vibrational spectroscopy.

Surface-specific sum-frequency vibrational spectroscopy has been used to study the structure of alkyl chains of azobenzene molecules at the air/water interface. The results show that the alkyl chains are well aligned before UV irradiation and protruding out of the surface with a certain distribution. Although the alkyl chains become less ordered by UV irradiation following dynamical motion due to cis-trans isomerization of the azobenzene core, the alkyl chains show anisotropy in the direction perpendicular to that of the azobenzene core by linearly polarized UV irradiation.