Synthesis and photochroism of a novel organic-inorganic nanocomposite film entrapping tungstosilicate acid

A novel photochromic organic-inorganic nanocomposite film was prepared through entrapping Keggin structure H4SiW12O40 into MAAM/VTEOS/TEOS matrix by combining supramolecular self-assembly technology with sol-gel process. The composite film was characterized by IR, XRD and TG-DSC, and its photochromic behavior and mechanism were also studied and discussed. The transparent film changed from colorless to dark-blue under UV irradiation and was measured by UV-Vis and ESR spectra. The results indicate that [SiW12O40](4-) anions maintain Keggin structure in the composite film and interacted strongly with -NH2 group of the matrix via hydrogen bond. After irradiation under UV fight, a hydrogen atom is transferred to a [SiW12O40](4-) anion, and a free radical is formed at the same time. The bleaching process is closely related to the presence of O-2, and the experiments show that the composite film has excellent photochromic properties, with a short response and bleaching time and good reversibility.