Impacts of negatively charged colloidal clay particles on photoisomerization of both anionic and cationic azobenzene molecules.

Although smectite-type clays are used as heterogeneous media for photofunctional guest molecules, the guest species are limited to cationic or polar molecules because of the intrinsic negative electric charges of clay particles. Nevertheless, in this study, aqueous clay colloids are reported to affect the photoisomerization kinetics of anionic and cationic azobenzene molecules dissolved in the colloids. Under UV-light irradiation, the clay colloids decelerate trans-to-cis isomerization, while under visible-light irradiation, the clay colloids accelerate cis-to-trans isomerization. In addition, the sol-gel transition of clay colloids affects the kinetics. The results considerably expand the applicability of clay colloids as matrixes for functional organic species.