Photo-, Thermo-, and Piezochromic Nafion Film Incorporating Cationic Spiropyran

Multistimuli-responsive polymer films incorporating cationic spiropyran are demonstrated based on a Nafion membrane. The films exhibit color changes between yellow and red under photoirradiation, temperature changes, and application of pressure. These characteristic behaviors are based on the stabilization of the zwitterionic merocyanine cation in the polar environment of Nafion.