Temperature-induced phase transition and intramolecular charge-transfer process based on poly(N-isopropylacrylamide) hydrogel with covalently attached D-π-A type dye

A thermoresponsive poly(NIPAM-co-dye) copolymer with covalently attached D-π-A type dye was prepared by typical radical copolymerization. Software was used to calculate the electron density distribution of the push-pull, intramolecular charge transfer (ICT) operating in donor-π-conjugation-acceptor (D-π-A) configurations of dye monomer 3. It can be constructed an acid/base-induced molecular switch by modulation of intramolecular charge transfer with protonation/deprotonation. The lower critical solution temperature (LCST) behavior was investigated by means of UV-vis spectroscopy that allows the measurement of the phase transition from 25 to 40 °C in aqueous solution. The poly(NIPAM-co-dye) copolymer also exhibited color change when used an acid/base-induced molecular switch via control of intramolecular charge transfer (ICT). The morphology of the internal microstructure of the poly(NIPAM-co-dye) hydrogel was observed by scanning electron microscopy (SEM). The reversible switch could be obtained by thermal and acid/base stimuli.

► A thermoresponsive poly(NIPAM-co-dye) copolymer was prepared by radical polymerization. ► The LCST behavior of the copolymer was investigated by UV-vis spectroscopy that allows the measurement of the phase transition from 25 to 40 °C in aqueous solution. ► The copolymer also exhibited color change when used an acid/base-induced molecular switch via control of intramolecular charge transfer. ► The reversible switch of the copolymer could be obtained by thermal and acid/base stimuli.