Tuning chelating groups and comonomers in spiropyran-containing copolymer thin films for color-specific metal ion binding

Photochromic molecules can be used to selectively bind divalent metal ions. In order to study the influence of increased chelation in spiropyran-containing copolymers, we synthesized two derivatives: spiropyran methacrylate (SPMA) and spiropyran methacrylate with a methoxy substituent in the 8′ position of the benzopyran ring (MEO). Additionally, the comonomer with which spiropyran was polymerized is also varied between methyl methacrylate (MMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA) to tune the colorimetric response. Fourier transform-infrared (FT-IR) spectroscopy was used to characterize the photoinduced conversion of spiropyran to merocyanine, as well as the merocyanine–metal ion (MC–M2+) interaction. By means of UV-Vis absorption spectroscopy, we demonstrate that each metal ion gives rise to a unique colorimetric response for the various spiropyran-containing copolymers studied.