Photo-, Thermally, and pH-Responsive Microgels†

Microgels with photo-, thermally, and pH-responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV−visible spectroscopy. The new route involved first preparing poly(N-isopropylacrylamide) (PNIPAM)−allylamine copolymer microgels and a spiropyran photochrome (SP) bearing a carboxylic acid group. Then the functionalized spiropyran was coupled to the microgel via an amide bond. The dark-equilibrated gel particles feature spiropyran molecules in the polar, merocyanine form. After irradiation of visible light, the particle size becomes smaller because spiropyran changes to the relatively nonpolar, closed spiro form. The PNIPAM-SP microgels undergo a volume phase transition in water from a swollen state to a collapsed state with increasing temperature under all light conditions. However, the transition temperature range of the PNIPAM-SP is much broader than that for the PNIPAM without SP. The PNIPAM-SP microgels are monodisperse and self-assemble in...