Photochromic mesostructured silica pigments dispersed in latex films

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Abstract
We have incorporated the photochromic dyes spiropyran and spirooxazine in surfactant templated mesostructured silica particles. Spherical inorganic–organic hybrid pigments with varying dye content were produced by a one-pot synthesis in an aerosol reactor where the internal mesostructure could be controlled. The mesostructured inorganic–organic hybrid pigments provide a mechanically and chemically rigid framework that protects the dyes and facilitate handling. We show that an organic latex binder can be used to prepare transparent photochromic films of varying thickness. Changing the dye loading in the pigments and the pigment content in the films provides a versatile route for tuning the photochromic response. The pigmented films show both fast and direct photochromism, where the decay time for thermal bleaching is very fast in the case of spirooxazine doped pigments (kSO = 0.094 s−1), being in the range of the best reported values for solid state composites.