Photomechanical organosiloxane films derived from azobenzene-modified di- and tri-alkoxysilanes

Photoresponsive materials that reversibly change their shape upon light irradiation have a wide range of applications, such as sensors and actuators. Previously, we reported a free-standing film of a lamellar azobenzene–siloxane hybrid exhibiting reversible bending triggered by trans–cis photoisomerization of azobenzene. This material was prepared by an evaporation-induced self-assembly process using azobenzene-modified trialkoxysilanes as precursors. In this study, azobenzene-modified diethoxymethylsilane (AzoDES) was used in combination with conventional azobenzene-modified triethoxysilanes as the precursors to investigate the molecular factors affecting the structures and photoinduced bending behaviors of the lamellar azobenzene–siloxane hybrid materials. A lamellar hybrid film showing a higher degree of bending upon UV irradiation was obtained by adjusting the AzoDES content in the alkoxysilane precursors, although a further increase of the AzoDES content resulted in a disordered structure and lower degree of bending. The enhanced photo-deformation was attributed to the decrease in the degree of cross-linking of the siloxane networks.