Controlling the photochromic properties of tungsten oxide based photochromic composite films using boron-, carbon-, and sulfur- tungstic heteropoly acids

Boron, carbon and sulfur conjugated heteropoly tungsic-acid (BW-HPA, CW-HPA and SW-HPA) was synthesized using peroxo-iso-poly tungstic acid (W-IPA) and B2O3, CO2 and H2SO4 solutions, and the photochromic composite films were fabricated using these W-IPA, BW-HPA, CW-HPA and SW-HPA as filler and transparent urethane resin as matrix. All the composite films showed reversible photochromic properties (coloring and bleaching), and the spectra of all the composite films showed two broad absorptions with the peaks at 650 and 900 nm. The composite film using SW-HPA showed a high coloring speed and a low bleaching speed, and the composite films using BW-HPA and CW-HPA showed a slight high coloring speed and a high bleaching speed.