Progressive Readout Platform Based on Photoswitchable Polyacrylic Nanofibers Containing Spiropyran in Photopatterning with Instant Responsivity to Acid–Base Vapors

Abstract

Covalent bonding of photochromic molecules to a polymer matrix, flexibility of the polymeric host, and also its nanofibrous state are appropriate conditions to enhance the switching rate, photofatigue resistance, sensitivity, and long-term performance of these photo-active groups. Herein, photoresponsive polymethyl methacrylate and poly(methyl methacrylate-co-butyl acrylate) chemically modified with spiropyran (MSP and MBSP, respectively) were prepared through emulsion polymerization. To improve photosensitivity and reduce response time, the corresponding nanofibers (MSP@NF and MBSP@NF) were prepared by an electrospinning technique. Smooth and beadless morphology, high porosity (above 85%), and uniform diameter size distribution of MSP@NF (169 ± 39 nm) and MBSP@NF (203 ± 47 nm) were identified. Time-dependent UV–vis spectra and photo-isomerization kinetics revealed that flexible MBSP@NF has remarkable enhancement in the SP to merocyanine isomerization rate (19 folds) relative to the corresponding film. Reversible responsivity to HCl and ammonia vapors showed a dramatic color change and maximum absorption peak displacement for nanofiber samples immediately, together with fluorescence switching “on” and “off”, while this took about 10 min for the MBSP@F sample. This was attributed to the high surface area and porous structure of these nanofibers, providing enhanced diffusion and interaction with the photo-active groups. Reversible optical write–erase cycles with improved response time and color intensity approved photopatterning capability of MBSP@NF. Enhanced photochemical, photostability, and photofatigue resistance of MBSP@NF within 10 cycles of alternating exposure to HCl–ammonia vapors and also UV–vis irradiations revealed the potentiality of such nanofibers in visual reversible photopatterning and optochemical acidochromic and ammonia-chromic portable probes.