Photochromic spiropyran was covalently immobilized using alkyldiamine couplers with varying chain length(2,4,6,8 methylene groups)onto an optically transparent polymeric surface.The relatively nonpolar and colourless spiropyran form can be reversibly switched to a charged,highly coloured,zwitterionic merocyanine isomer using UV and visible light,respectively.The merocyanine form complexes with metal ions,and this results in a shift in the absorbance spectrum,and a corresponding colour change is observed.Upon irradiation of the complex with visible light,the cation is released and the merocyanine(active)isomer reverts back to the spiropyran(passive)form.Optical switching and complexation behaviour of the polymer-bound spiropyran-merocyanine system is highly dependent on the tether length of the spiropyran from the polymeric surface.The effect is demonstrated using cobalt(II)chloride in solution.
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