Preparation and photochromic properties of Keggin type tungstophosphate acids based on polyvinyl pyrrolidone

A new photochromic complex of Keggin type tungstophosphate acid/polyvinyl p yrrolidone system was prepared, and its thin films was made by the dipping method. Their photochromic properties were investigated by FTIR, UV-Vis spe ctra. The salts were formed by the combination of the ion based on the N at oms in the polymeric molecules and Hf of the acids. The UV-Vis spectra show ed that this type of system had an excellent photochromic behavior. The g v alues of ESR spectra for the one-electron blues were the characteristic of tetragonal W(V) complex in colored thin film. It was indicated that the cha rge could be transferred between the anion and cation under irradiation of UV light and the result in the oxidation of the cation and the reduction of the anion.