Preparation of a fast photochromic ormosil matrix coating for smart windows

A novel photochromic dye (NPB)-doped ormosil matrix coating with fast spectrokinetics was studied as functional materials for smart windows. First, the NPB was modified into a reactive silylated dye (NPB-Si) by a silane coupling agent. Then, the NPB-Si was hydrolyzed and copolycondensed with methyl triethoxysilane to form the ormosil (NPB-PMS) via the sol–gel method. Finally, the photochromic ormosil matrix coating on the substrate was obtained by the following spin-coating process. Upon the activation by the UV irradiation, the ormosil coating displayed the characteristic dual absorption peaks at 504 and 628 nm, which indicated as a valuable neutral tone. The dual absorption is due to the existence of photoisomers. On the basis of the theoretical calculation, the trans–cis photoisomers displayed the longer wavelengths in visible region than those of trans–trans ones, which was due to the less coplanarity. The kinetics studies of coloration and decoloration of NPB-PMS indicated an accelerated conversion process than that of NPB-doped polystyrene coating. The improved spectrokinetics of NPB-PMS coating is ascribed to the nanoscaled cavities observed in their surfaces, which offered enough space for molecular rotation during the photochromism. Our results also demonstrated that the NPB-PMS coating had much better solvent wash-off resistance than the physically doped coating.