Photochromic naphthopyrans in sol–gel ormosil coatings

The sol–gel method has been used to entrap photochromic naphthopyran molecules in ormosil coatings. The resulting films exhibited a rapid and reversible color change upon irradiation with UV light, leading to deeply colored coatings. The bleaching of the samples can be attained by both thermal and photo-induced processes. The photochromic properties of different naphthopyran derivatives in the sol–gel matrix were measured, such as the absorption spectra of bleached and colored states as well as the thermal and photoinduced decay kinetics.