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A novel photochromic gel film was prepared through entrapping 12-phosphotungstic acid (PWA) into a kind of inorganic–organic matrix co-hydrolyzed from tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES). Infrared (IR) spectra revealed that the Keggin structure characteristic of PW12O403− anions was present in the amine-functionalized silica gel skeleton and PWA interacted with R-NH3+ cations strongly. The amorphous state of the gel film was proved by X-ray diffraction (XRD) pattern. The gel film exhibited reversible photochromicity. Irradiated with ultraviolet light, the transparent film changes from colorless to blue. Then, bleaching occurs when the film is in contact with air or O2 in the dark. [Copyright &y& Elsevier]

A series of photochromic hybrid films were prepared through entrapping tungsten heteropolyoxometallate (PW12O403−) and molybdenum heteropolyoxometallate (PMo12O403−) in polyacrylamide (PAM) matrix, the corresponding structure and photochromic behaviors of the films were investigated with Fourier transform infrared (FT-IR), UV–Vis–near-infrared (NIR) absorption spectra (UV–Vis–NIR) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of heteropolyoxometallate was still preserved inside the composites and strong Coulombic interaction was built between heteropolyoxometallate and PAM via hydrogen bonding. Irradiated with ultraviolet light, the transparent films changed from colorless to blue and showed reversible photochromism. The bleaching process occurred when the films were in contact with air or O2 in the dark. The molybdenum heteropolyoxometallate hybrid film had higher photochromic efficiency and slower bleaching reaction than tungsten heteropolyoxometallate hybrid film. The characteristic signals of radical and W(V) or Mo(V) in ESR spectra indicated that PAM is a hydrogen donor and the photoreduced process is in accordance with the radical mechanism. [Copyright &y& Elsevier]