Preparation and characterization of a photochromic hydrogel

A new type of photochromic hydrogel, spiropyran (SP)-Polyvinylpyrrolidone (PVP)-poly (N-isopropyl acrylamide) (PNIPAM) hydrogel with functionalized SP chemically incorporated, was synthesized. The molecular structure of synthesized products was given by nuclear magnetic resonance (NMR) spectra and infrared spectrum (IR). The photochromism of the hydrogel was evidenced by photography and characterized by ultraviolet-visible (UV-Vis) spectroscopy. The photochromic reversibility of the hydrogel was tested through observing its responses to the alternating UV irradiation to dark environment. The fluorescence micrographs showed the fluorescent effect as well as confirmed the photochromic properties of the hydrogel, and indicated that the chemical incorporation made the functionalized SP distribute well in the gel.