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A novel photochromic nanocomposite film containing polyoxotungstoeuropate K12[EuP5W30O110] entrapped in polyvinylpyrrolidone has been prepared through a spin-on coating technique. Thus-obtained amorphous nanocomposite film was characterized by IR spectra, UV–vis absorption spectra, XRD, SEM, TG-DTA, and ESR. Results show that polyoxotungstoeuropate interacts with polyvinylpyrrolidone strongly and disperses homogeneously in the matrix. The composite film exhibits good photochromic properties. When irradiated with UV light, the transparent film changes from colorless to blue. Then, bleaching occurs when the film is in contact with ambient air or O2 in the dark. The photochromism of the composite film is due to charge transfer by reduction of polyoxotungstoeuropate and oxidation of polyvinylpyrrolidone. [Copyright &y& Elsevier]

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 self-assembled layered superlattice composite film was fabricated by casting the chloroform solutions of ionic complex between dioctadecyldimethylammonium (DODA) and 18-molybdophosphate anion (P2Mo186−) onto CaF2, borosilicate glass, and quartz substrates. Infrared and UV spectra revealed that the Dawson structure characteristic of P2Mo186− was preserved in the composite film. A well-ordered superlattice structure was identified by X-ray diffraction (XRD). From XRD results and the cross-sectional area of DODA cation and P2Mo18 polyanion, a possible structural model was proposed. The P2Mo18/DODA film showed good photochromic properties. Irradiated with UV light, the transparent film changed from light yellow to blue. Then, bleaching occurred when the film was in contact with ambient air or O2 in the dark. A possible photochromic mechanism was proposed according to electron spin resonance (ESR), Fourier transform infrared (FTIR) spectra, and UV–Vis spectra. [Copyright &y& Elsevier]

Novel photochromic nanocomposite thin film containing phosphotungstic acid entrapped in polyacrylamide was prepared using ultrasound technique. TEM image revealed that the polyoxometalates nanoparticles with narrow size distribution were finely dispersed in polymer matrix. IR spectra showed that the Keggin geometry of polyoxometalates was still preserved inside the composite film and strong Coulombic interaction was built between heteropolyoxometalates and polyacrylamide via hydrogen bond. It was found that the thermal stability of the hybrid film was lower than that of pure polymer but the film was stable enough for photochromic application from the TG–DTA curves. The transparent film changed from colorless to blue under UV irradiation and showed reversible photochromism. The bleaching process occurred when the film was in contact with air or O2 in the dark. The photoreduced process was in accordance with radical mechanism. [Copyright &y& Elsevier]

A new photochromic film was prepared based on the Keggin type H3PW12O40 (PW12) with polyacrylamide (PAM) matrix. The microstructure, photochromic behavior and mechanism were investigated with FT-Infrared spectroscopy (FT-IR), atomic force microscopy (AFM), transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV–VIS), and electron resonance spectroscopy (ESR). FT-IR results showed that the Keggin geometry of PW12 was still preserved inside the matrix, and a charge-transfer bridge was built between PW12 and PAM via hydrogen bond. AFM images indicated that the surface topography of the polymer matrix changed after adding PW12. In the hybrid films, the PW12 particles had regular microstucture in nanoscale shown in TEM image. Under UV irradiation, the film was reduced photochemically to yield a blue species. With the increase of irradiation time, the photoreduction proceeded from one-electron to two-electron blue stage. The characteristic signals of W (V) and radical in ESR spectra indicated that the photoreduced process was in accordance with the radical mechanism. [Copyright &y& Elsevier]