Colorimetric determination of metal ions using spiropyran containing copolymer thin film sensors
Fries, Kristen Hollie
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Fabrication of sensors with a switchable surface that can alter between active (sensing) and passive forms provides a unique method for the development of optical sensors. In this context, spiropyran is an excellent candidate to use in designing a switchable surface using light. This dissertation details the design, synthesis, and characterization of a series of spiropyran-containing copolymers used as colorimetric thin film sensors. The copolymer with which spiropyran methacrylate is copolymerized was varied to study the effect of comonomer on the photoinduced conversion of spiropyran (SP) to merocyanine (MC). The composition of SP contained in the polymer backbone was also varied from 10 to 100 mol% to investigate the influence of free volume and sterics on the photochromic response, as well as the merocyanine-metal ion (MC-M2+) interaction. Through UV-vis spectroscopy, we demonstrated that each metal ion gives rise to a unique colorimetric response that is dependent upon the amount of SP comonomer contained in the polymer backbone. Using chemometric methods, UV-vis spectra can be analyzed to selectively and quantitatively identify metal ions in a concentration range from 1 μM to 100 mM and simultaneously identify two metal ions in a binary mixture. We also used UV-vis spectroscopy to investigate the relative binding affinity of merocyanine to each metal ion by displacement studies of a bound metal ion with a second metal ion of higher binding affinity. In addition, we synthesized SP-containing copolymers that were used to investigate the influence of two different spiropyran derivatives, spiropyran methacrylate (SPMA) and the 8’-methoxy substituted derivative (MEO), on the metal ion complexation. FT-IR spectroscopy was used to characterize the photoinduced conversion of SP to MC, as well as the MC-M2+ complex in all of the copolymers. Principal component analysis was used to analyze the FT-IR spectra in order to elucidate the chemical binding environment between MC and the different metal ions.