Highly Efficient Photochromic Tungsten Oxide@PNIPAM Composite Spheres with a Fast Response

Coloration efficiency and a fast response are important in developing materials for optical switching. A novel, highly efficient photochromic tungsten oxide@poly(N-isopropylacrylamide) (PNIPAM) hybrid sphere is reported, whose colors can be rapidly converted between yellow and blue under different lights. The color change can be seen clearly even if the tungsten oxide content in the hybrid sphere is very low, exhibiting outstanding coloration efficiency of tungsten oxide. A photochromic mechanism is proposed in which the amide group in PNIPAM spheres participates in electron injection and the transition of valence states between W⁵⁺ and W⁶⁺ in the photochromic process. The interaction between tungsten oxide and PNIPAM plays a key role in enhancing the coloration efficiency of tungsten oxide and accelerating the switchable speed of color transformation, which is very useful in developing new photochromic materials. These hybrid spheres can be used in rewritable record displays and have wide potential applications in controlling energy transmittance in smart windows or in detecting UV light in optical sensors.