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-cobutyl 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.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

“…Stimuli-chromic materials are defined as chromophores with the ability of coloration or changing color by induction of external stimuli, such as light, pH, humidity, mechanical force, pressure, and electrical field. , These compounds display coloration and fluorescence emission in response to the induced stimuli by an isomerization reaction between two chemical structures with different properties. Some of the most important photochromic compounds are spiropyran, spirooxazine, diarylethene, oxazine, and oxazolidine, which have extensively been studied in a wide range of advanced applications. − Simultaneous photochromism and fluorescence emission by the photochromic compounds make them very useful in the design and development of anticounterfeiting materials. ,,, All photochromic, fluorescent, and phosphorescent materials could be used in the development of efficient anticounterfeiting technologies (Figure ). The most significant challenge is selection of the state (solution, colloids, solid, or fiber), in which they show higher intensity, brightness, and emission with different colors.…”

Photochromic Polyamide 6 Based on Spiropyran Synthesized via Hydrolyzed Ring-Opening Polymerization

“…To further demonstrate the structure of SP-modified PA6, UV-visible absorbance spectra and fluorescence spectra were measured, which are displayed in Figure 4 . UV-visible absorbance spectrum of spiropyran/HOOCH solution in Figure 4 A reveals that absorbance peaks at 310 nm and 404 nm are assigned to the characteristic peaks of spiropyran and MCH [ 8 , 26 ]. From spectra of SP-modified PA6, it can be seen that absorbance peak of spiropyran occur in all samples and the peak of SP-PA6-3 sample are strongest at the same concentration which proves the high content of spiropyran derivative in PA6 polymer chains.…”

“…Chemical modification and covalent bonding of SP to the polymer matrix via polymerization will enhance the photostability and photofatigue and the spiropyran moiety can be used in most polymerization conditions. Polymer materials with SP could be found in films [ 19 , 20 , 21 ], gels [ 22 , 23 , 24 ] and electrospun nanofibers [ 25 , 26 , 27 ]. For instance, Mahdavian and coworkers [ 26 ] synthesized photoresponsive polymethyl methacrylate and poly(methyl methacrylate- co -butyl acrylate) chemically modified with spiropyran through emulsion polymerization and the corresponding nanofibers had excellent responsivity of acid-base vapors.…”

“…Polymer materials with SP could be found in films [ 19 , 20 , 21 ], gels [ 22 , 23 , 24 ] and electrospun nanofibers [ 25 , 26 , 27 ]. For instance, Mahdavian and coworkers [ 26 ] synthesized photoresponsive polymethyl methacrylate and poly(methyl methacrylate- co -butyl acrylate) chemically modified with spiropyran through emulsion polymerization and the corresponding nanofibers had excellent responsivity of acid-base vapors. Wu and coworkers [ 25 ] developed smart photoresponsive acrylated spiropyran (SPA)-methyl methacrylate (MMA) copolymer films.…”

Stimuli‐responsive mechanical properties in polymer glasses: challenges and opportunities for defense applications

“…Within each of these spaces, common motifs fall under three categories of micelles, 68-90 hydrogels [91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107][108] and thin films. 32,[65][66][67][109][110][111][112][113][114][115][116][117][118][119][120][121][122] Moreover, the field consists of a variety of photoresponsive compounds, which then are added to a range of polymer architectures (e.g. random and block polymers, host-guest polymer networks, chemically crosslinked networks), with the addition of varying monomer chemistries (ring-opening metathesis polymers, acrylates, methacrylates, styrenics, etc.).…”