Photoresponsive interpenetrating network photonic crystal

We have developed a photonic crystal-based hydrogel which changes volume upon exposure to light and possesses unique optical properties. The photoswitchable material was created by embedding a crystalline colloidal array into a polyacrylamide network, and then infusing a second network, consisting of an azobenzene derivative, disperse red 1 methacrylate monomer, into the first network. We observed a 55 nm diffraction peak shift under ultraviolet light irradiation, due to the trans-cis isomerization of the azobenzene monomers in the second polymer network. This response is more than three times greater than previously seen for this type of material, and is easily detectable by the human eye. In dark, the cis- isomer is recovered, enabling the material to be reused. This hydrogel may have several applications, such as use as a display or memory storage device or an optical sensor.