Thermally enhanced visible-light photochromism of phosphomolybdic acid-polyvinylpyrrolidone hybrid films

Phosphomolybdic acid/polyvinylpyrrolidone hybrid films were found to show visible light photochromism. It is identified that the intra-supramolecular charge transfer between the inorganic and organic molecules is responsible for the visible-light coloration. Interestingly, the films show photo-memory and thermal activation. The films show a small change in absorbance after being irradiated with visible light for a short time, and the coloration can be enhanced greatly by subsequent thermal treatment. Electrical measurements indicate that the conductivity of the film increases after the brief irradiation, which promotes transfer of the electrons induced by the thermal treatment.