Multi-responsive poly(N-isopropylacrylamide) hydrogel with D-π-A type dye

To get a multi-responsive polymer hydrogel, metal sensible and acid/base-switchable D-π-A type dye monomer was synthesized first. The synthesized electron donor-π-conjugated-electron acceptor (D-π-A) type dye monomer 3 was investigated with not only the selective Ni2+ and Cu2+ metal ion sensing effects, but also an acid/base unit sensing effects in optical properties with UV–vis absorption and fluorescence emission. A thermo-responsive poly(NIPAM-co-dye) copolymer with D-π-A type dye was prepared by typical radical copolymerization. The LCST behavior was investigated by UV–vis spectroscopy, which allows the measurement of the phase transition from 20 to 50 °C in an aqueous solution. The poly(NIPAM-co-dye) copolymer also exhibited color change when not only Ni2+ or Cu2+ cations were used but also when an acid/base unit was used. The morphology of the internal matrix structure of the poly(NIPAM-co-dye) hydrogel was observed by SEM.