Synthesis of spiropyran-containing random copolymer by atom transfer radical polymerization and its complexation with metal ions

An amphiphilic random copolymer containing a monomer 2-(dimethylamino) ethyl methacrylate (DMAEMA) and a light-responsive unit 1′-(2-acryloxyethyl)-3′,3′- dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) (SPMA) was synthesized by atom transfer radical polymerization. The solvatochromic and light responsive behaviors of the resulting P(SPMA-co-DMAEMA) copolymer in solution were investigated by UV–vis absorption spectroscopy. The ‘negative’ solvatochromism upon the increasing solvents polarity was observed. A strong absorption band was recorded at 589 nm in THF, while the lower values were found at 542 and 520 nm in methanol and water, respectively. Moreover, the random copolymer exhibited a good cycling performance by the alternating illumination with ultraviolet (UV) and visible (Vis) lights. Finally, we studied the complexation of zwitterionic merocyanine (MC) with divalent metal ions, and an obvious shift of the location for the maximum absorption peak was found upon addition of Co2+ or Mn2+. A slight color change of the copolymer solution from blue to purple after complexation with Co2+ or Mn2+ was also observed and this phenomenon might provide a potential visual observation for the complexation of P(SPMA-co-DMAEMA) with different metal ions.