Spiropyran Units Research Articles

Quantum ChemicalStudyof a Dihydroazulene‐SpiropyranMulti‐StateMulti‐FunctionalMolecularSwitch

Quantum chemistry methods have been enacted to characterize the second‐order nonlinear optical (NLO) properties of a multi‐state molecular switch combining dihydroazulene and spiropyran units. They have demonstrated that the first hyperpolarizabilities constitute a novel output signal from the viewpoint of molecular logic, owing to the contrasts of NLO responses between the different forms of the dyad. On the one hand, the DFT calculations demonstrate that switching either unit has only a negligible impact on the geometrical parameters of the other one, as well as on the thermodynamics of their transformations. Similarly, as determined by time‐dependent DFT calculations, the UV/vis absorption spectra are in good approximation a superposition of those from the parent units. On the other hand, this additivity trend is not consistently observed for the NLO responses. However, an interpretation of these NLO responses has been proposed by using the unit sphere representation of the first hyperpolarizability tensors to address their orientational aspects as well as by resorting to the few‐state approximation and the missing state analysis to highlight the localized or charge‐transfer nature of the dominant excited states.

Spiropyran-Based Photoisomerizable α-Amino Acid for Membrane-Active Peptide Modification.

Photoisomerizable peptides are promising drug candidates in photopharmacology. While azobenzene- and diarylethene-containing photoisomerizable peptides have already demonstrated their potential in this regard, reports on the use of spiropyrans to photoregulate bioactive peptides are still scarce. This work focuses on the design and synthesis of a spiropyran-derived amino acid, (S)-2-amino-3-(6'-methoxy-1',3',3'-trimethylspiro-[2H-1-benzopyran-2,2'-indolin-6-yl])propanoic acid, which is suitable for the preparation of photoisomerizable peptides. The utility of this amino acid is demonstrated by incorporating it into the backbone of BP100, a known membrane-active peptide, and by examining the photoregulation of the membrane perturbation by the spiropyran-containing peptides. The toxicity of the peptides (against the plant cell line BY-2), their bacteriotoxicity (E. coli), and actin-auxin oscillator modulation ability were shown to be significantly dependent on the photoisomeric state of the spiropyran unit.

Photoinduced Solubility Modulation in the Copolymers of Fluoroalkyl, Spiropyranyl, and Isobornyl Methacrylates

This article reports photoinduced solubility modulation in copolymer thin films derived from spiropyranyl, perfluoroalkyl, and isobornyl methacrylates. A random copolymer of spiropyranyl methacrylate (SPMA) and 1H,1H,2H,2H-perfluorooctyl methacrylate (FOMA) was first prepared in the absence of isobornyl methacrylate (IBMA). The resulting as-prepared thin film could be dissolved in highly fluorinated or fluorous solvents but became insoluble following exposure to UV light (λ = 365 nm) via the photoisomerization transformation of spiropyran units into merocyanine moieties. On the other hand, the incorporation of IBMA into the copolymer structure above a certain threshold resulted in copolymers exhibiting the opposite dissolution behavior. UV–vis spectroscopic measurements on the copolymer films and solutions indicated that dipolar attraction between the photoisomerized merocyanine moieties contributed to the decrease in solubility. The incorporation of IBMA into the copolymer chains diluted the merocyanine moieties and increased their glass-transition temperature, resulting in the disruption of the intermolecular attraction and an increase in the solubility of the UV-exposed polymer chains. These results suggested that stencils could be developed without additives to generate strong acid molecules or free radicals in polymer thin films. The proposed processing technique for fluoroalkylated copolymers was thus tested in the fabrication of orthogonal copolymer stencils and demonstrated to be a useful tool for the pixel patterning of chemically vulnerable organic light-emitting diodes.

Excitation-wavelength-dependent fluorescent organohydrogel for dynamic information anti-counterfeiting

Anti-counterfeiting labels with various fluorescent colors are of great importance in information encryption-decryption, but are still limited to static information display. Therefore, it is urgent to develop new materials and encryption-decryption logic for improving the security level of secret information. In this study, an organohydrogel made up of poly(N,N-dimethylacrylamide) (pDMA) hydrogel network and polyoctadecyl methacrylate (pSMA) organogel network that copolymerized with two fluorophores, 6-acrylamidopicolinic acid moieties (6APA, fluorescent ligand) and spiropyran units (SPMA, photochromic monomer), was prepared by a two-step interpenetrating method. As UV light of 365 nm and 254 nm can both cleave Cspiro-O bonds of SPMA, and the green fluorescence of 6APA-Tb3+ can only be excited by 254 nm light, the organohydrogel displays yellow and red under the irradiation of 254 nm and 365 nm, respectively. In addition to wavelength selectivity, these two fluorophores are thermal-responsive, leading to the fluorescence variation of the organohydrogel during heating process. As a result, secret information loaded on the organohydrogel can be decrypted by the irradiation of UV light, and the authenticity of the information can be further identified by thermal stimulation. Our fluorescent organohydrogel can act as an effective anti-counterfeiting label to improve the information security and protect the information from being cracked.

Effect of Polymer Composition and Morphology on Mechanochemical Activation in Nanostructured Triblock Copolymers.

The effect of composition and morphology on mechanochemical activation in nanostructured block copolymers was investigated in a series of poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA) triblock copolymers containing a force-responsive spiropyran unit in the center of the rubbery PnBA midblock. Triblock copolymers with identical PnBA midblocks and varying lengths of PMMA end-blocks were synthesized from a spiropyran-containing macroinitiatior via atom transfer radical polymerization, yielding polymers with volume fractions of PMMA ranging from 0.21 to 0.50. Characterization by transmission electron microscopy revealed that the polymers self-assembled into spherical and cylindrical nanostructures. Simultaneous tensile tests and optical measurements revealed that mechanochemical activation is strongly correlated to the chemical composition and morphologies of the triblock copolymers. As the glassy (PMMA) block content is increased, the overall activation increases, and the onset of activation occurs at lower strain but higher stress, which agrees with predictions from our previous computational work. These results suggest that the self-assembly of nanostructured morphologies can play an important role in controlling mechanochemical activation in polymeric materials and provide insights into how polymer composition and morphology impact molecular-scale force distributions.

Cast, Dip, Spray, and Print─Covalently Embedded Photochromic Materials from a Versatile Spiropyran Conjugate

Dynamic photochromic dyes are in great demand for various applications. These are used as active materials with tunable optical properties. However, producing photochromic materials in significant quantities is still a challenge. The ability to retain and prolong the interconversion of switching between open and closed forms is affected by undesirable aggregation of dyes in the matrix. The often-employed method of adding photochromic dyes into bulk materials causes issues such as aggregation, leaching of dye, and photoinstability. A versatile light-responsive spiropyran substituted azo-initiator was conveniently synthesized and utilized for incorporating photochromic units at the α-chain end of the vinyl polymers. Accordingly, processes in bulk, solution, and emulsion/dispersion were developed by radical polymerization of common vinyl monomers such as styrene and acrylates. This approach enabled the preparation of light-responsive polymers possessing photochromic spiropyran units covalently incorporated at the polymer chain end. Thus, monodisperse, covalently embedded photochromic colloidal particles with low dye content (<0.1 mmol) were prepared. The fabrication and high-resolution spatiotemporal control of materials such as gels, elastomers, resins, and transparent films of commodity polymers embedded with photochromic units are demonstrated with detailed coloring, fading, and fatigue behavior. The facile and straightforward approach developed to prepare photochromic colloidal particles can be applied to any substrate through cast, dip, spray, or print to make “smart” photochromic materials.

Porous Electrospun Films with Reversible Photoresponsive Microenvironmental Humidity Regulation: A Controllable Hydrogen-Bonding Synergistic Effect Exhibited by Acrylic Acid Segments

Suitable relative humidity is essential for the preservation of cultural relics, food storage, and so on. A special material that can regulate the relative humidity in the microenvironment is particularly important. In this work, several innovative electrospun films with reversible photoresponsive wettability and the ability to regulate microenvironmental relative humidity were prepared. The spiropyran unit of the synthesized copolymer played the most important role in humidity regulation due to its reversible transition between a nonpolar ring-closed state and a polar ring-opened state induced by alternating ultraviolet/visible illumination. More interestingly, the introduction of acrylic acid segments exhibited a controllable hydrogen bond synergistic effect for increasing the range of humidity regulation. The color change and the reversible change ranges of wettability and microenvironmental relative humidity under ultraviolet/visible irradiation are all closely related to the number of acrylic acid segments. Cassie theory, density functional theory (DFT), and interaction region indicator (IRI) analysis were used to characterize this phenomenon. Electrospinning is a promising method to achieve large-scale production that can put such material into practical applications.

Multi-stimuli responsive fluorescence switching behaviours of AIE polymers for acid-base vapour sensing and highly sensitive ferric ion detection

Novel aggregation-induced emission (AIE) polymers, i.e., P1-SP and P2-SP, consisting of AIEgenic tetraphenylethylene (TPE) and photochromic spiropyran (SP) units are reported. Both P1-SP and P2-SP exhibit excellent AIE behaviours of TPE moieties in near-aqueous solutions THF/H2O (95% water) and solid states with strong cyan and blue emissions at 494 and 477 nm, respectively. Upon acidification, the close forms of P1-SP and P2-SP can be opened and switched to open P1-MCH+ and P2-MCH+ structures of protonated merocyanine (MCH+), resulting in fluorescence quenching of TPE units through corresponding intramolecular charge transfer (ICT) and Förster resonance energy transfer (FRET) processes. The fluorescence recovery of TPE can be monitored by the neutralization of P1-MCH+ and P2-MCH+ with base solutions under ambient/visible light attributed to the re-close P1-SP and P2-SP structures, which led to respective turn-off ICT and FRET phenomena. Distinct fluorescence quenching behaviours of P1-SP and P2-SP can be observed under various stimuli, including acid conditions and ferric ion interactions, which are also confirmed by theoretical studies. Moreover, P1-SP and P2-SP can be utilized as fluorescence quenching sensors for nanomolar level detections of ferric ion (LOD = 166 and 110 nM for corresponding P1-SP and P2-SP) with excellent selectivities in near-aqueous solutions and paper test strips. Additionally, the interesting visible and fluorescence colour changes of coated cellulosic papers, blended PMMA films and powder forms based on P1-SP and P2-SP under multi-external stimuli (acid-base vapour and visible light/heating processes) are also explored in this report.

Dynamic Anticounterfeiting Through Novel Photochromic Spiropyran-Based Switch@Ln-MOF Composites.

Fluorescent materials presenting unique color changes in response to external stimuli have wide applications in information storage and anticounterfeiting. However, developing intelligent fluorescent materials with high security levels and dynamically displaying encrypted information is still a challenge. Herein, we report a new method for constructing excellent fluorescent materials by loading the photochromic molecule spiropyran into a lanthanide metal-organic framework. Controlling the isomerization of the spiropyran unit regulates the fluorescence resonance energy transfer (FRET) mechanism between the spiropyran acceptor and the lanthanide donor, leading to an exceptional reversible absorption/luminescence modulation ability. As the irradiation time is extended, the fluorescent color changes continuously from yellow-greenish to orange and then to red through the FRET process within 60 s. This composite system has great potential in anticounterfeiting because of the following advantages: (1) the materials have different fluorescence emissions and optical colors regulated by ultraviolet radiation, which is convenient for designing complex anticounterfeiting patterns; (2) the system can be repeatedly verified quickly and exhibit dynamic fluorescence color within 60 s, having great potential in advanced anticounterfeiting, where time is key in encryption/decryption. These unique advantages will greatly enhance the reliability of anticounterfeiting measures and increase the difficulty of anticounterfeiting.

Multimodal stimuli-responsive behaviors of photochromic spiropyran-bearing telechelic poly(2-isopropyl-2-oxazoline)

Spiropyran-bearing telechelic poly (2-isopropyl-2-oxazoline) (SP-PiPrOx-SP) was designed as a multimodal stimuli-responsive polymer. Formed via living cationic ring-opening polymerization and ester coupling of spiropyran units, the resultant SP-PiPrOx-SP had an average molecular weight of 8.0 kDa with a narrow molecular weight distribution. SP-PiPrOx-SP exhibited a sharp hydrophilic-hydrophobic thermal transition at a specific temperature. Moreover, SP-PiPrOx-SP showed reversible photochromic changes between the colorless SP-PiPrOx-SP and purple MC-PiPrOx-MC states upon UV or visible light irradiation. The addition of DBU to MC-PiPrOx-MC resulted in the formation of a stable yellow complex that did not exhibit photochromic behavior. When CO2 was added to the yellow DBU adduct of MC-PiPrOx-MC, the solution immediately changed to purple due to the dissociation of DBU from MC-PiPrOx-MC. The addition of DBU to MC-PiPrOx-MC induced dramatic changes to the thermal transition temperature. Because SP-PiPrOx-SP simultaneously shows thermal transition, photochromic, and chemoresponsive properties, the introduction of spiropyran units has great potential for the design of functional materials.

A Dual pH- and Light-Responsive Spiropyran-Based Surfactant: Investigations on Its Switching Behavior and Remote Control over Emulsion Stability.

A cationic surfactant containing a spiropyran unit is prepared exhibiting a dual‐responsive adjustability of its surface‐active characteristics. The switching mechanism of the system relies on the reversible conversion of the non‐ionic spiropyran (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH‐dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli‐responsive behavior enables remote‐control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH‐dependent manipulation of oil‐in‐water emulsions.

Dual photochromics-contained photoswitchable multistate fluorescent polymers for advanced optical data storage, encryption, and photowritable pattern

Stimuli-responsive fluorescent materials that can alternate their emission states on-demand are always desired in many applications. In this study, novel photoswitchable multistate fluorescent polymer (PMFP) was prepared via simple free-radical copolymerization of butyl acrylate (BA) and styrene (St) with two photochromic fluorescent monomers, i.e. sulfonyl diarylethylene-linked 4-hydroxybutyl acrylate (SDTE) and spiropyran-linked methacrylate (SP8). The PMFP displays excellent processability, due to its rational feed ratio of BA and St which result in the relative low glass transition temperature. By changing irradiation light, the non-fluorescent ring-closed spiropyran units and ring-opened diarylethylene moieties in PMFP can be selectively converted into their corresponding luminescence states. Furthermore, as a result of the controllable fluorescence resonance energy transfer (FRET) from the excited diarylethylene to the spiropyran moieties, the emission of the polymer in solution or film can be reversibly switched among distinguishable no-emission, red, and green fluorescence states. Moreover, the PMFP exhibits high brightness, high contrast, rapid photoresponse, and excellent photoreversibility. We also demonstrated that PMFP can be directly used for advanced high-density data storage, multilevel information encryption, and multicolor photorewritable pattern, as well as high-level anticounterfeiting.

Hydrogen-Bonded Dimeric Capsules with Appended Spiropyran Units: Towards Controlled Cargo Release.

We report the synthesis of unprecedented tetra‐urea derivatives of calix[4]arene and calix[4]pyrrole containing four spiropyran (SP) units at their upper rim. We investigate the photo‐ and acid‐induced isomerization of the monomeric and homo‐dimeric tetra‐ureas derivatives using UV‐Vis and 1H NMR spectroscopies. At micromolar concentration, irradiation of the samples with 365 nm light induces changes in their absorption spectra that are consistent with SP→merocyanine (MC) isomerization. However, analogous experiments at millimolar concentration do not produce noticeable changes in the 1H NMR spectra. The addition of triflic acid to micromolar and millimolar solutions of the tetra‐ureas produces the quantitative isomerization of the SP units to the protonated merocyanine form (E‐MCH+) and the simultaneous disassembly of the capsular dimers to form ill‐defined aggregates. The neutralization of the acid solutions resets the SP form. Under these acid/base treatment conditions, the controlled release of the included guest and the reassembly of the all‐SP tetra‐urea dimers occurs at different extents depending on its calix[4]arene or calix[4]pyrrole scaffold.

Dynamic Photochromic Polymer Nanoparticles Based on Matrix-Dependent Förster Resonance Energy Transfer and Aggregation-Induced Emission Properties.

Dynamic color-tunable fluorescent materials are sought-after materials in many applications. Here, we report a polymeric matrix-regulated fluorescence strategy via synergistically modulating aggregation-induced emission (AIE) properties and the Förster resonance energy transfer (FRET) process, which leads to tunable dynamic variation of color and photoluminescence (PL) intensity of fluorescent polymeric nanoparticles (FRET-PNPs) driven by photoirradiation. The FRET-PNPs were prepared via a facile one-pot miniemulsion copolymerization with the tetraphenyletheyl (TPE) and spiropyran (SP) units chemically bonded to the polymer matrix. The FRET-PNPs exhibited dynamic variation of fluorescence properties (colors and PL intensity) under photoirradiation on the timescale of minutes. The variation of the polymer matrix composition could deliberately influence the AIE property of TPE units and the isomerization process of SP to merocyanine units, which further affect the FRET efficiency of FRET-PNPs and, eventually, lead to versatile dynamic fluorescence variation. The dynamic fluorescence property as well as the excellent processability and film formation ability of FRET-PNPs allowed for diverse applications, such as warning labels, dynamic decorative painting, and multiple information encryption. Without sophisticated molecular design or tedious preparation processes, a new perspective for the design, fabrication, and performance optimization of fluorescent nanomaterials for innovative applications was proposed.

FRET processes of bi-fluorophoric sensor material containing tetraphenylethylene donor and optical-switchable merocyanine acceptor for lead ion (Pb2+) detection in semi-aqueous media

A novel aggregation-induced emission (AIE) structure containing a tetraphenylethene (TPE) unit covalently linked with a spiropyran (SP) unit was synthesized and investigated in semi-aqueous solutions with 90% water fraction. The open-form structure of red-emissive merocyanine (MC) unit combined with TPE unit was utilized as a bi-fluorophoric sensor to detect lead(II) ion, which could be transformed from the close-form structure of non-emissive SP unit upon UV exposure. Moreover, the TPE unit as an energy donor with the blue-green photoluminescence (PL) emission at 480 nm was combined with the MC unit as an energy acceptor with the red PL emission at 635 nm. Due to the Förster resonance energy transfer (FRET) processes, the bi-fluorophoric sensor produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the mono-fluorophoric MC unit. Hence, the PL sensor responses of the AIE bi-fluorophoric structure toward lead(II) ion could be further amplified via the FRET-OFF processes to turn off red PL emission of the coordinated MC acceptor and to recover blue-green PL emission of the TPE donor. Accordingly, the best LOD value for the AIE sensor detection toward Pb2+ was 0.27 μM. The highest red MC emission with the optimum FRET process of AIE sensor could be utilized in cell viability tests to prove the non-toxic and remarkable bio-marker of AIE sensor to detect lead(II) ion in live cells. The developed FRET-OFF processes with ratiometric PL behavior of the bi-fluorophoric AIE sensor can be utilized for future chemo- and bio-sensor applications.

Highly Efficient Förster Resonance Energy Transfer Modulations of Dual-AIEgens between a Tetraphenylethylene Donor and a Merocyanine Acceptor in Photo-Switchable [2]Rotaxanes and Reversible Photo-Patterning Applications.

A series of novel photo-switchable [2]rotaxanes (i.e., Rot-A-SP and Rot-B-SP before and after shuttling controlled by acid-base, respectively) containing one spiropyran (SP) unit (as a photochromic stopper) on the axle and two tetraphenylethylene (TPE) units on the macrocycle were synthesized via click reaction. Upon UV/visible light exposure, both mono-fluorophoric rotaxanes Rot-A-SP and Rot-B-SP with the closed form (i.e., non-emissive SP unit) could be transformed into the open form (i.e., red-emissive merocyanine (MC) unit) to acquire their respective bi-fluorophoric Rot-A-MC and Rot-B-MC reversibly. The aggregation-induced emission (AIE) properties of bi-fluorophoric TPE combined with MC AIEgens of these designed rotaxanes and mixtures in semi-aqueous solutions induced interesting ratiometric photoluminescence (PL) and Förster resonance energy transfer (FRET) behaviors, which were further investigated and verified by dynamic light scattering (DLS), X-ray diffraction (XRD), and time-resolved photoluminescence (TRPL) measurements along with theoretical studies. Accordingly, in contrast to the model axle (Axle-MC) and the analogous mixture (Mixture-MC, containing the axle and macrocycle components in a 1:1 molar ratio), more efficient FRET behaviors and stronger red PL emissions were obtained from dual-AIEgens between a blue-emissive TPE donor (PL emission at 468 nm) and a red-emissive MC acceptor (PL emission at 668 nm) in both novel photo-switchable [2]rotaxanes Rot-A-MC and Rot-B-MC under various external modulations, including water content, UV/Vis irradiation, pH value, and temperature. Furthermore, the reversible fluorescent photo-patterning applications of Rot-A-SP in a powder form and a solid film with excellent photochromic and fluorescent behaviors are first investigated in this report.

Visible light and temperature dual-responsive microgels by crosslinking of spiropyran modified prepolymers

HypothesisLight-responsive microgels are interesting colloidal systems with potential applications in the biotechnology and medicine. However, synthesis of light-responsive microgels with high loading of photoswitchable molecules is still very challenging. ExperimentsHerein we developed a new method to synthesize light and temperature dual-responsive spiropyran-modified poly(N-vinylcaprolactam) microgels. The novel and straightforward microgels synthesis route involved: a) synthesis of poly(N-vinylcaprolactam-co-vinylformamide) copolymers via RAFT polymerization followed by the hydrolysis to obtain primary amine groups, b) attachment of carboxyl-modified spiropyran molecules to polymer chains via coupling, and c) crosslinking of spiropyran-modified polymer chains in W/O miniemulsion to form microgels. FindingsVia this method, we successfully synthesized poly(N-vinylcaprolactam) microgels containing more than 10 mol% spiropyran. The reversible light responsiveness of the spiropyran-modified copolymers and microgels in aqueous solution, which originates from the spiropyran photoisomerization under irradiation with different wavelengths, was demonstrated by UV–Vis spectroscopy. Spiropyran-modified copolymers demonstrate shift of the lower critical solution temperature (LCST) due to the polarity change of spiropyran molecules under dark, UV and visible light. Surprisingly, dynamic light scattering (DLS) results show that the microgels based on the same copolymers are less affected by UV irradiation. Microgels are swollen in darkness when spiropyran molecules are in the polar, merocyanine form, and collapse after irradiation with visible light, due to the transformation of spiropyran to the relatively nonpolar, closed spirocyclic form. In addition, the spiropyran-modified microgels exhibit reversible temperature responsiveness by presenting a volume phase transition in water from a swollen state to a collapsed state with increasing temperature and the transition temperature decreased compared to the pristine microgels due to the hydrophobicity of spiropyran units.

Noncommutative Switching of Double Spiropyrans.

The spiropyran family of photochromes are key components in molecular-based responsive materials and devices, e.g., as multiphotochromes, covalently coupled dyads, triads, etc. This attention is in no small part due to the change in properties that accompany the switch between spiropyran and merocyanine forms. Although the spiropyran is a single structural isomer, the merocyanine form represents a family of isomers (TTT, TTC, CCT, etc.) and protonation states. Combining two spiropyrans into one compound increases the number of possible structures dramatically and the interaction between the units determines, which are impeded due to intramolecular quenching of excited states. Here, we show that the coupling of two spiropyran photochromes through their phenol units yields favorable interactions (crosstalk) between the components that provides access to species inaccessible with the component monospiropyran alone. Specifically, the ring opening of one spiropyran unit, which is thermally stable at −30 °C, prevents ring opening of the second spiropyran unit. Furthermore, whereas protonated E- and Z-monomerocyanines were previously shown to undergo thermal- and photo-equilibration, the corresponding protonated E- and Z- bimerocyanines are thermally stable and show one-way photoisomerization from the Z,Z- to an emissive E,E-bimerocyanine form. Subsequent deprotonation at room temperature resets the system to the bispiro ring-closed form, but deprotonation at −30 °C yields the otherwise inaccessible bimerocyanine form. This form is photochemically inert but undergoes a two-step thermal relaxation via the merocyanine-spiropyran form, showing that the connection at the phenol units provides sufficient intramolecular interaction to fine-tune the complex isomerization pathways of spiropyrans and demonstrating noncommutability in photo- and pH-regulated multistep isomerization pathways.

Confining Photoacidity

Confining Photoacidity

Preparation of Reversible Photoresponsive Poly(SPA‐co‐MMA) Films by Electrospinning: A Possible Route to Smart Materials for Regulating Wettability and Humidity

AbstractThe control of surrounding humidity by porous films is an interesting aspect for improving human comfort. Especially, light triggered humidity control is of relevance because light stimulus is contactless so that reducing the impact on both materials and surroundings. In this work, reversible light responsive films with tunable wettability and the ability of regulating surrounding humidity are developed from acrylated spiropyran (SPA)–methyl methacrylate (MMA) copolymer by electrospinning. The electrospun films for regulating wettability and surrounding humidity can be reversibly manipulated by the simple switch of UV and visible light irradiation because of the unique transformation between polar ring‐opened status and nonpolar ring‐closed status of spiropyran units. Morphology analyses and Cassie theory are used to explain this phenomenon and it is found that surface microstructure and effective chemical composition of the film surface can both significantly influence the reversible variation range of the value of surrounding humidity and surface wettability. The results show that the ability to regulate humidity of 40 wt% poly(SPA‐co‐MMA) film possessing bead‐on‐string fiber surface structure is the best.