Mesostructured self-assembled silica films with reversible thermo-photochromic properties

A spiropyran molecule has been introduced via one-pot synthesis into mesostructured silica films, which have been obtained through a micelle templating self-assembling process. The mesostructure has been characterized by transmission electron microscopy and small-angle X-ray scattering performed with synchrotron light. The final material exhibited a p6mm 2d-hexagonal organization and the mesostructure has not been affected by the introduction of spiropyrans in the precursor solution. A comparative characterization of the optical properties of the spiropyrans dissolved in different solvents and after incorporation in the mesostructured films has been done by UV–Vis absorption spectroscopy, fluorescence spectroscopy and ellipsometric spectroscopy. The spiropyran-doped films appeared transparent before external stimuli had applied, a colour change to yellow (thermally induced) or to red (light induced) has been observed. Both the colour changes have been observed to be reversible under room temperature or visible light exposure; the colour transitions have been attributed to different equilibria among the various forms of merocyanine of spiropyrans.