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The development of durable photosensitizers is pivotal for advancing phototherapeutic applications in biomedicine. Here, we introduce a core‐shell azobenzene‐spiropyran structure on gold nanoparticles, engineered to enhance singlet oxygen generation. These nano‐photosensitizers exhibit increased structural stability and thermal resistance, as demonstrated by slowed O−N−C bond recombination dynamics via in‐situ Raman spectroscopy. Notably, the in‐situ formation of merocyanine and a light‐induced compact shell arrangement extend its half‐life from 47 minutes to over 154 hours, significantly boosting singlet oxygen output. The nano‐photosensitizer also shows high biocompatibility and notably inhibits tau protein aggregation in neural cells, even with phosphatase inhibitors. Further, it promotes dendritic growth in neuro cells, doubling typical lengths. This work not only advances chemical nanotechnology but also sets a foundation for developing long‐lasting phototherapy agents for treating neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Mechanochromic functionality realized via the force‐responsive mechanophores in polymers has great potential for damage sensing and information storage. Mechanophores with the ability to recognize multiple stimuli for tunable chromic characteristics are highly sought after for versatile sensing ability and color programmability. Nevertheless, the majority of mechanophores are based on single‐component chromophores with limited sensitivity, or require additional fabrication technology for multi‐modal chromism. Here, we report a novel multifunctional mechanophore capable of vividly detectable and tunable mechanochromism in polymers. This synergistic optical coupling relies on strategically fusing rhodamine and spiropyran (Rh−SP), and tethering polymer chains on both subunits. The mechanochromic behaviors of the Rh−SP‐linked polymers under sonication and compression are thoroughly evaluated in response to changes in force and the light‐controlled relaxation process. Non‐sequential ring‐opening of the two subunits under force is identified, endowing high‐contrast mechanochromism. Light‐induced differential ring‐closing reactions of the two subunits, together with the acidichromism of the SP moiety, are employed to engineer elastomers with programmable and wide‐spectrum colors. Our work presents an effective strategy for highly appreciable and regulable mechanochromic functionality, and also provides new insights into the rupture mechanisms of π‐fused mechanophores, as well as how the stimuli history controls stress accumulation in polymers. [ABSTRACT FROM AUTHOR]

With the rapid development of the economy, new imitation methods are keeping emerging and posing a huge challenge to anti-counterfeiting technology. Due to the advantages such as good concealment, high recognizability, water repellency, and dirt resistance, fluorescent fiber has attracted great attention from researchers. To impart good fluorescence to chitosan (CS) for the preparation of anti-counterfeiting fiber, various amounts of fluorescent molecules — carboxyl-containing spiropyran (SP)—were used to label CS to prepare a series of CS–SP with different degrees of labeling (DL). Then, nanofiber membranes were produced by electrospinning using the CS–SP/PVA blend spinning solutions. Effects of the DL on application performance of the CS–SP were studied. It was found that, labeling appropriate amounts of SP units onto CS was an effective way to endow the CS with good fluorescence property. With the increase in the DL of the CS–SP, its fluorescence intensity increased initially, reached the maximum when the DL was 0.499 mol%, and then decreased. At the DL of 0.499 mol%, the CS–SP/PVA nanofiber membrane could emit bright fluorescence, of which the color was able to change dynamically along with the irradiation time of UV light. Meanwhile, the labeling of SP unit would not bring about adverse effects on surface morphology of the electrospun CS–SP/PVA nanofiber membrane. The fluorescent CS–SP nanofibers have overcome many shortcomings of the commonly used fluorescent fibers and shown great application potential in the anti-counterfeiting field. [ABSTRACT FROM AUTHOR]

It is challenging but of practical meaning to provide adsorbents with multiple responsive properties. Here, we report an intelligent microporous polymeric adsorbent constructed by block copolymer‐grafted microporous polymer nanospheres. With its multi‐stimuli‐responsive functions, the adsorbent shows rapid fluorescent response to temperature, pH, and organic reagents. Moreover, it also demonstrates super‐fast adsorption of pollutants in water, enabling efficient treatment of wastewater. [ABSTRACT FROM AUTHOR]

With exceptional photochromic and photoluminescent properties, spiropyrans have demonstrated significant potential for advanced information encryption and anti‐counterfeiting applications. However, its inherent water insolubility leads to incompatibility with aqueous polymers, and even more, its ease of leaching from the matrix hinders the formation of stable stimuli‐responsive platforms through direct blending with all polymers. Here, the fabrication of amphiphilic spiropyran‐octapeptide molecules is reported that can spontaneously self‐assemble into highly water‐dispersible supramolecular nanofibers in water. These assemblies exhibit universal polymer matrix compatibility while retaining the rapid photo‐responsiveness of spiropyrans. The formation of strong interactions between the supramolecular assembly and polymer chains ensures the long‐term stability of the resultant stimuli‐responsive materials in aqueous environments. These platforms fully preserve the base polymers’ processing properties, with silk fibroin as the matrix offering exceptional opportunities for constructing photo‐responsive platforms in various forms (e.g., films, gels, fibers, and coatings) with multiple functionalities using diverse solution processing techniques. Integrating distinct photochromic and photoluminescent responses within a single format without interference, combined with environmental stability and processing flexibility, enables the creation of dual‐mode, high‐security encryption devices for diverse application scenarios. The outlined strategy provides innovative concepts for developing high‐performance, versatile intelligent systems utilizing stimulus‐responsive molecules. [ABSTRACT FROM AUTHOR]

The powerful capability of multi‐stimulus‐responsive fluorescent hydrogen‐bonded organic frameworks (HOFs) to respond to external chemical or physical stimuli in various manners makes them appealing in advanced information encryption. However, it is still a global challenge to manipulate the fluorescence properties finely to achieve dynamic fluorescence properties in the time dimension. Here, a feasible strategy is shown to control the emission of materials by introducing a common SP photochromic compound (1′, 3′, 3′‐trimethyl‐6‐nitro‐spiro‐ [chromene‐2, 2′‐indoline]) into functionalized HOFs, to finely manipulate the fluorescence properties. Two kinds of HOFs are successfully synthesized by modifying the unbonded carboxylic group of HOFs with Tb3+ or 5‐hexene‐1‐ol termed Tb‐HOFs and HOF‐olefin, respectively. Then, spiropyran is loaded into the Tb‐HOFs or HOFs‐olefin and dynamic fluorescence emission can be well controlled by changing the lanthanide dopants and light stimulation time. Relying on the dynamic fluorescence emission, the multilevel information encryption including anti‐counterfeiting ink, QR code, base code, and time‐resolved information storage has been successfully demonstrated, and the security level has been greatly improved. This work opens an avenue for achieving time‐resolved information storage technology, where the “time factor” is equivalent to a dynamic key, which introduces countless unpredictable possibilities and makes imitation more challenging. [ABSTRACT FROM AUTHOR]

The synthesis of a new symmetric bis(spiropyran) of the indoline series existing as an equilibrium mixture of isomeric forms in various organic solvents is described. This equilibrium was in detail studied by dynamic NMR spectroscopy. In particular, the equilibrium constants were found at various temperatures, and the thermal effects of isomerization processes were calculated. The thermal transformations were studied by quantum chemical modeling. As a result, possible isomerization pathways were proposed and the observed ratio of the forms in the NMR spectra was explained. Photo- and thermochromic transformations were studied by UV spectroscopy, which revealed positive photochromic properties of the target compound. The observed changes in the absorption spectra with increasing temperature are completely consistent with the results of NMR studies. The nature of the absorption bands observed in the spectra was explained using time-dependent density functional theory (TD-DFT) calculations. The surface-enhanced Raman scattering (SERS) spectra of the synthesized compound on the surface of silver nanoparticles were detected and analyzed before and after UV irradiation to determine prospects for using similar bis(spiropyrans) as SERS markers and probes. [ABSTRACT FROM AUTHOR]

Visible light is an important energy source for all living organisms on Earth. Given the importance of visible light, visible light sensors have attracted widespread interest from scientists. With the rapid development of wearable devices, the sensors used in them need to be flexible, stretchable, and lightweight. Herein, an intelligent electrolyte based on spiropyran (SP) that responds to visible light is developed. The reversible change rate in the electrical resistance of an SP/FeCl3·6H2O methyl cyanide (MeCN) aqueous solution under visible light irradiation is as high as 19.26%. Additionally, flexible and conductive fibrous visible light sensors with a core‐sheath structure are prepared using an SP/FeCl3·6H2O MeCN aqueous solution and silicon rubber hollow fibers as the core and outer layers, respectively. These fibrous visible light sensors are then woven into fabrics with multiple functions, such as sensing and locating visible light, reversible photochromism, and thermal management. The fibrous visible light sensors and fabrics prepared in this study have broad development prospects and application potential in the fields of fashion, smart textiles, flexible conductive fibers, flexible fibrous sensors, electronic skins, and wearable devices. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) are widely used in antimicrobial applications. However, its easy aggregation and rapid loss hinder the effective antifouling. To address this issue, a novel stimuli-responsive antibacterial nanocomposite (Ag@SP-MSN) was developed based on spiropyran covalently conjugated mesoporous silica nanoparticles (284.6 nm) and AgNPs (27.1 nm) via strong electrostatic attraction. Both transmission electron microscopy (TEM) and atomic force microscopy (AFM) images proved the successful modification of AgNPs onto SP-MSN. The light-induced maximum loading amount towards AgNPs was calculated to be 95.0 wt.% after ultraviolet irradiation, while the amount of AgNPs released from Ag@SP-MSN was 94.4 wt.% under visible light in the aid of ammonia (0.1%, v/v). Upon cycled light irradiation, Ag@SP-MSN could recover 84.5 wt.% of AgNPs even after four cycles. The proposed Ag@SP-MSN exhibited better antibacterial activity against both E. coli and S. aureus than Ag@MSN under visible light illumination, indicating the efficient photo-responsive isomerization of spiropyran. Furthermore, the Ag@SP-MSN embedded gel demonstrated outstanding antifouling ability even after 21 days when compared to AgNPs gel. The long-term photo-controllable antifouling property proved the excellent reversible absorption and release of Ag@SP-MSN towards AgNPs. This work provides new insights into the safe utilization of nanomaterials, offering promising advancements to meet clinical antibacterial requirements. [ABSTRACT FROM AUTHOR]

Abstract The strategy of designing heterogeneous porous catalysts by a post-modification method is a smart strategy to increase the catalytic power of desired catalysts. Accordingly, in this report, metal-organic frameworks based on titanium with acetic acid pending were designed and synthesized via post-modification method. The structure of the target catalyst has been investigated using different techniques such as FT-IR, XRD, SEM, EDX, Mapping, and N2 adsorption/desorption (BET/the BJH) the correctness of its formation has been proven. The catalytic application of Ti-based MOFs functionalized with acetic acid was evaluated in the preparation of new spiropyrans, and the obtained results show that the catalytic performance is improved by this modification. The strategy of designing heterogeneous porous catalysts through post-modification methods presents a sophisticated approach to enhancing the catalytic efficacy of desired catalysts. In this context, our study focuses on the synthesis and characterization of metal-organic frameworks (MOFs) based on titanium, functionalized with acetic acid pendants, using a post-modification method. Various characterization techniques, including Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), mapping, and N2 adsorption/desorption (BET/BJH), were employed to investigate the structure and composition of the synthesized catalyst. These techniques collectively confirmed the successful formation and structural integrity of the target catalyst. The structure of the synthesized products was confirmed by melting point, 1H-NMR and 13C-NMR and FT-IR techniques. Examining the general process of catalyst synthesis and its catalytic application shows that the mentioned modification is very useful for catalytic purposes. The presented catalyst was used in synthesis of a wide range of biologically active spiropyrans with good yields. The simultaneous presence of several biologically active cores in the synthesized products will highlight the biological properties of these compounds. The present study offers a promising insight into the rational design, synthesis, and application of task-specific porous catalysts, particularly in the context of synthesizing biologically active candidate molecules.

Spiropyran containing a propylammonium moiety at the nitrogen atom in the indoline part of molecule was synthesized. Its photochromic behavior, spectral and photoluminescent properties in water, as well as cytotoxicity towards epidermoid carcinoma A431 cells were estimated. The synthesized compound exhibited positive photochromism and high stability towards photodegradation, and is capable of photoluminescence. [ABSTRACT FROM AUTHOR]

Controllable friction regulation has drawn much interest in both scientific and industrial fields. And there have been many researches on friction regulation by many physical fields and chemical factors. Photo-sensitive materials are promising because it is relatively easy to change their properties compared with others. Here, a new kind of photo-induced grease/oil switched lubricant is designed and shows great reversibility under ultraviolet (UV) and visible (Vis) irradiation. Its viscosity can change more than 50 times under different irradiation, and the coefficients of friction (COFs) obviously increase under Vis irradiation and decrease under UV irradiation, which performs better than those of the common grease. According to the experimental results, the phenomena are contributed to the break and reconstruction of the three-dimensional network inside the lubricant. With a switchable grease/oil state under different irradiation, this work provides a new principle for designing a smart lubricant with controllable friction regulation. [ABSTRACT FROM AUTHOR]

The development of photoresponsive systems with non‐invasive orthogonal control by distinct wavelengths of light is still in its infancy. In particular, the design of photochemically triggered‐orthogonal systems integrated into solid materials that enable multiple dynamic control over their properties remains a longstanding challenge. Here, we report the orthogonal and reversible control of two types of photoswitches in an integrated solid porous framework, that is, visible‐light responsive o‐fluoroazobenzene and nitro‐spiropyran motifs. The properties of the constructed material can be selectively controlled by different wavelengths of light thus generating four distinct states providing a basis for dynamic multifunctional materials. Solid‐state NMR spectroscopy demonstrated the selective transformation of the azobenzene switch in the bulk, which in turn modulates N2 and CO2 adsorption. [ABSTRACT FROM AUTHOR]

Visible light is an important energy source for all living organisms on Earth. Given the importance of visible light, visible light sensors have attracted widespread interest from scientists. With the rapid development of wearable devices, the sensors used in them need to be flexible, stretchable, and lightweight. Herein, an intelligent electrolyte based on spiropyran (SP) that responds to visible light is developed. The reversible change rate in the electrical resistance of an SP/FeCl3·6H2O methyl cyanide (MeCN) aqueous solution under visible light irradiation is as high as 19.26%. Additionally, flexible and conductive fibrous visible light sensors with a core‐sheath structure are prepared using an SP/FeCl3·6H2O MeCN aqueous solution and silicon rubber hollow fibers as the core and outer layers, respectively. These fibrous visible light sensors are then woven into fabrics with multiple functions, such as sensing and locating visible light, reversible photochromism, and thermal management. The fibrous visible light sensors and fabrics prepared in this study have broad development prospects and application potential in the fields of fashion, smart textiles, flexible conductive fibers, flexible fibrous sensors, electronic skins, and wearable devices.

Photoswitching of photoluminescence has sparked tremendous research interests for super‐resolution imaging, high‐security‐level anti‐counterfeiting, and other high‐tech applications. However, the excitation of photoluminescence is usually ready to trigger the photoswitching process, making the photoluminescence readout unreliable. Herein, we report a new photoswitch by the marriage of spiropyran with platinum(II) coordination complex. Viable photoluminescence can be achieved upon excitation by 480 nm visible light while the photoswitching can be easily triggered by 365 nm UV light. The feasible photoswitching may be benefited from the formed liquid crystalline (LC) phase of the designed photoswitch as a crystalline spiropyran is normally unable to implement photoswitching. Compared to the counterparts, this LC photoswitch can show distinct and reliable apparent colors and emission colors before and after photoswitching, which may promise the utility in high‐security‐level anti‐counterfeiting and other advanced information technologies. [ABSTRACT FROM AUTHOR]

Recently the need for smart materials has been extremely growing, and the development of materials with appropriate characteristics has become one of the main challenges. Heptamethine cyanine dyes are widely used in theranostics and photovoltaics due to their remarkable optical properties. However, they are characterized by "rigid" non–changable properties. The main aim of the current study is to unveil correlation between structure and optical properties in the range of vinyl‐3H‐indolium substituted spiropyrans, which can be considered as the closest analogs of heptamethine cyanines with the photocontrolable optical and fluorescent properties. The effects of substitution in indoline and 2H‐chromene cycles, as well as anion change are under the study. To achieve this goal, a series of spiropyran iodides and perchlorates with methyl, methoxy substituents or fluorine atom in position 6′, as well as a conjugated vinyl‐3H‐indolium fragment in position 8′, were synthesized. The structure of the compounds was carefully studied using SC XRD, NMR, IR and mass spectroscopy. Then, studies on absorption and photoluminescence characteristics, as well as photochromic behavior were carried out. [ABSTRACT FROM AUTHOR]

Spiropyran photochromic materials have been widely studied in military camouflage, optical data storage, information encryption, and fashion ornaments. The non‐photochromism and low endurance of solid spiropyran make the challenges of their application. Photochromic microcapsules with a butyl acetate solution of spiropyran as core and polyurethane as shell are synthesized via interfacial polymerization. The optimized polyurethane photochromic microcapsules are prepared with a Tween 20 concentration of 4 wt%, core–shell ratio of 16:5, and spiropyran concentration of 0.40 wt%. Polyurethane photochromic microcapsules with a mean particle diameter of 0.33 μm are obtained. The morphology shows smooth spheres, and the core–shell structure is observed. Butyl acetate in the microcapsule core does not evaporate at a temperature lower than 218.01°C as the microcapsule shell insulates heat. The polyurethane photochromic microcapsules are mixed with adhesive, thickener, and water into a paste and screen‐printed on cotton fabric. The printed fabric shows the ΔE of 17.56, 11.93, and 6.96 after 80s irradiation with the xenon lamp intensity of 102, 68, and 34 mW cm−2. The light stability of the photochromic fabric is excellent as ΔE decreases about 8.28% after 20 cycles of UV‐Vis irradiation. [ABSTRACT FROM AUTHOR]

Over the past decade, great efforts have been devoted to both intellectual property protection and information security protection. As a promising electroactive material, MXene is covalently or non‐covalently functionalized with organic species/polymers to produce a large amount of novel functional materials for biomedicine, optoelectronics, and energy storage. By using spiropyran covalently functionalized MXene (MXene‐SP) as an active material, an optoelectronic dual‐response resistive random access memory (RRAM) device is successfully fabricated. Upon UV illumination, the active layer is changed from MXene‐SP (SP: ring‐closed spiropyran form) observed under the illumination of blue light to MXene‐MC (MC: ring‐opened merocyanine form) due to photo‐induced "close‐to‐open" isomerization. The as‐fabricated ITO/MXene‐SP/ITO device exhibits typical nonvolatile optoelectronic dual‐response RRAM performance, with a production yield exceeding 90%. The achieved switch‐on/off voltages are −1.25/2.07 V under the illumination of blue light and −0.58/0.91 V under UV illumination. The switching bias window (Δ|VON − VOFF|) and the ON/OFF current ratio of MXene‐MC are 44.9% and 14.7% of these of MXene‐SP, respectively. By utilizing the window difference between the RRAM performance achieved under the illumination of different lights, one can easily encrypt the quick response code. [ABSTRACT FROM AUTHOR]

Supramolecular multifunctional metal–organic networks offer immense potential in drug delivery, bioimaging, catalysis, and therapeutics. However, the creation of multiple stimuli‐responsive fluorescent hollow nano/microparticles is a formidable challenge in this field. In this study, a novel strategy is reported for synthesizing photochromic hollow microparticles that exhibit responsiveness to light, pH, and glutathione (GSH). With the assistance of templating coordination from zeolitic imidazolate framework‐8 microparticles, bisphosphonate‐merocyanine ligands are successfully assembled to create hollow bisphosphonate‐spiropyran (BPSP)‐Zn2+ microparticles. The photochromic and pH responses stem from the reversible conversion between spiropyran and zwitterionic merocyanine components and between merocyanine and protonated merocyanine, respectively. The GSH response is attributed to the stronger affinity of Zn2+ to thiol groups than to phosphonate groups. These remarkable features render the hollow BPSP‐Zn2+ microparticles highly suitable for applications in stimulus‐triggered drug delivery, and these findings provide a platform for developing innovative materials that have the potential to transform the biomedical field. [ABSTRACT FROM AUTHOR]

The most important area of modern pharmacology is the targeted delivery of drugs, and one of the most promising classes of chemical compounds for creating drugs of this kind are the photochromic spiropyrans, capable of light-controlled biological activity. This work is devoted to the synthesis and study of the photochromic properties of new triphenylphosphonium salts of spiropyrans. It was found that all the synthesized cationic spiropyrans have high photosensitivity, increased resistance to photodegradation and the ability for photoluminescence. [ABSTRACT FROM AUTHOR]

In order to avoid structural instability caused by the hydrolysis of spiropyran unit during responsive process, a new spiropyran monomer named as SPA was prepared by grafting carbamate functional groups to side chain of spiropyran frame. With SPA, 2‐(2‐(2‐methoxyethoxy) ethoxy) ethyl methacrylate (MEO3MA) and 2‐(diethylamino) ethyl methacrylate (DEAEMA) as the organic monomers, a triple responsive copolymer, P(SPA‐co‐MEO3MA‐co‐DEAEMA) abbreviated as PSOD, was obtained by one‐pot random copolymerization. The chemical structure, responsive behaviors and self‐assembly of the resulting copolymer were studied by a series of technical methods. With 5‐Fluoro‐2′‐deoxyuridin (FUDR) as the model anti‐cancer drug, the loading and controlled releasing behaviors of the copolymer micelles were systematically explored. Also, the cytotoxicity test and fluorescence imaging of PSOD copolymer were performed with human breast cancer cell line (MCF‐7) as the experimental subject. The results showed that the copolymer micelles had controllable drug releasing performance in complex combined stimuli conditions, and the releasing process could be well described by Korsmeyer‐Peppas model. The cytotoxicity of PSOD was proved to be relatively low, which laid a foundation for the subsequent in‐vivo drug releasing. Triple responsive performance of the copolymer micelles might provide a new inspiration for the future study of drug‐controlled releasing system. [ABSTRACT FROM AUTHOR]

To further enhance the fatigue resistance of spiropyran‐based photochromic materials and to explore the functionality of organic–inorganic metal oxide microcapsule shell materials, cross‐linked (P(MMA‐PETA)) and homopolymer (PMMA) shells have been developed by cross‐linking TiO2 and hybridizing ZnO on a PMMA matrix. PMMA/TiO2 photochromic microcapsules and PMMA/ZnO photochromic microcapsules with ultraviolet (UV)‐absorbing function are prepared by successfully encapsulating spiropyran photochromic compounds using these two composite shells. The results show that both microcapsules exhibit a complete spherical core–shell structure with good UV resistance and thermal stability. The TG test underlines a 50% coating rate of PMMA/ZnO microcapsules on spiropyran photochromic material, with an optimal ZnO addition of 10% and particle size range from 2 to 8 µm, effectively blocking UV‐A and part UV‐B radiation. Further, a 75% maximal coating rate is observed for PMMA/TiO2 microcapsules on spiropyran with optimal TiO2 addition at 2–4%, a particle size of around 5 µm, diffusely reflecting 48% of UV rays. The photochromic fabrics prepared with PMMA/TiO2 microcapsules have better UV resistance, with a UV protection factor value of 59.48, and excellent fatigue resistance after at least 30 cycles of UV–visible light irradiation. [ABSTRACT FROM AUTHOR]

In this paper, the relaxation isomerization properties of a spiropyran-doped poly(methyl methacrylate) (PMMA) UV light-responsive dynamic material are presented. The polar liquid (acetonitrile) and solid (PMMA matrix) medium may contain two merocyanine isoforms of the selected spiropyran. A complex equilibrium of the colored and colorless spiropyran isoforms resulted in specific transformations of the absorption spectra during the relaxation process. Bands at 522 nm and 580 nm characterized the absorption of the fabricated dynamic material in the ground (non-activated) state in the visible range. The presence of colored and colorless isoforms of spiropyran incorporated into the PMMA matrix using Raman spectroscopy was revealed. The photosensitive polymer samples were irradiated with a UV LED (365 nm and 390 nm) under various temperatures (0–30 °C). Spectral changes within the relaxation process demonstrated their complex dynamics. Surprisingly, the photodegradation of the dynamic material was estimated at about 25% (using 390 nm) and 7% (using 365 nm) after eight photoswitch cycles for one isoform, and no fatigue after an additional one (using 390 nm) was discovered. The presented light-responsive material is of interest for UV sensors and new hybrid material design. [ABSTRACT FROM AUTHOR]

Low-molecular-weight peptide gelators are a versatile class of compounds able to form gels under a variety of conditions, even via simple ultrasound sonication. In this paper, the ability of Boc-L-Phe-D-Oxd-L-Phe-OBn to gelate three organic solvents (toluene, tert-butyl methyl ether, and ethanol) was evaluated. The rheological behaviour of the materials was assessed via strain sweep analysis, while the fibrous network was analysed via optical microscopy on the wet gels. The gel obtained from toluene is a highly transparent material, and the one from ethanol appears translucent, while the one from tert-butyl methyl ether is opaque. These gels were used to study the reversible light-induced transformation from spyropiran (SP) to merocyanine (MC) and back, as a model system to check the effect of the gel medium onto the rection kinetic. We observed that the solvent used to form the organogels has a crucial effect on the reaction, as gels from aprotic solvents stabilize the SP form, while the ones from protic solvents stabilize the MC form. We thus obtained a solid support to stabilize the two photochromic species just by changing the solvent polarity. Moreover, we could demonstrate that the self-assembled gels do not interfere with the light-driven conversion process, either starting from SP or MC, thus representing a valid and economical photochromic material. [ABSTRACT FROM AUTHOR]

The potential of E–Z photoisomerization in molecular organic light-to-thermal conversion and storage in an E–styryl merocyanine system was studied in a polar acidic medium. A photoswitchable styryl merocyanine dye (E)-2-(2-(2-hydroxynaphthalen-1-yl)vinyl)-3,5-dimethylbenzo[d]thiazol-3-ium iodide was synthesized for the first time. The reversible E–Z photoisomerisation of the dye was investigated using UV-Vis spectroscopy and DFT calculations. E–Z isomerization was induced through the use of visible light irradiation (λ = 450 nm). The obtained experimental and theoretical results confirm the applicability of the Z and E isomers for proton-triggered light harvesting.

The title pyrene-fused spiropyran derivative, C30H25NO, crystallizes with two molecules in the asymmetric unit with dihedral angles between their fused-ring sub units of 76.20 (8) and 89.38 (9)°. In the crystal, weak C—H...π interactions link the molecules into a three-dimensional network.

A promising spiro[pyridobenzopyran–indoline] molecular platform for the development of ionochromic systems with a high potential for metal cation chemosensor applications is developed. Evidence for this conclusion is provided the established characteristics and properties of 6-bromo-substituted spiro[pyridobenzopyran–indoline], including ionochromism accompanied by a chromogenic effect in the form of a red shift that reaches 200 nm. The obtained Zn(II), Ni(II), Cu(II), Co(II), and Cd(II) complexes are characterized by a high stability with constants of 105.6–108.6 and 105.0–106.9 for the first and second steps, respectively. The possibilities to obtain selective sensors are associated with the fluorescence detected in the Zn(II) and Cd(II) complexes only. The photostability of the studied complexes, on the one hand, and the high spectral contrast of complex formation of the dynamic 6-bromo-substituted spiro[pyridobenzopyran–indoline] systems on the other, open up the possibility of using chemosensors based on these molecular platforms in the naked-eye colorimetric mode. [ABSTRACT FROM AUTHOR]

The construction of tunable morphological systems has important implications for understanding the mechanism of molecular self‐assembly. In this study, a spiropyran derivative M1 is reported with light‐responsive assembly morphology, which can be tuned from nanosphere to nanorod by ultraviolet light irradiation. The absorption spectra show that M1 molecules are transformed from closed‐ring (SP) isomers into open‐ring (MC) isomers and start to form H‐aggregates with increasing irradiation time. Density functional theory calculations indicate that MC‐MC isomers possess stronger binding energy than SP‐SP isomers. The MC isomers may thus facilitate the dissociation of the SP‐SP aggregates and promote the change of self‐assembled morphology with the aid of stronger π‐π stackings and dipole‐dipole interactions. The research gives an effective method for modulating the morphology of assemblies, with great potential for applications in smart materials. [ABSTRACT FROM AUTHOR]

Spiropyran (SP)‐based dynamic materials undergo structural changes in response to external stimuli. In this paper, we show that digital holographic microscopy (DHM) is an effective candidate for characterisation of SPs (embedded in polymer matrices) and for monitoring of their dynamical changes. The polymer matrices are polylactic acid (PLA) and poly(methyl methacrylate) (PMMA) films, which are decorated with SPs and immobilised on graphene quantum dots (GQDs). GQDs are modified by benzylamines prior to the loading of SP species because of the enhancement of hydrophobic characteristics. UV irradiation is used as the external stimulus and the dynamical changes of the samples before and after UV irradiation are measured. DHM is arranged on a novel self‐referencing setup, which substantially reduces the sensitivity of DHM to environmental vibrations. Morphometric information for characterisation of the samples is obtained by analysis of the recorded digital holograms. The experimental results demonstrate the potential of the presented technique to serve as an alternative technique for surface measurement methodologies such as atomic force microscope and stylus profiler for surface characterisation of similar materials. [ABSTRACT FROM AUTHOR]

This study focuses on the molecular design and synthesis of salt spiropyrans with near-IR fluorescence. The structure of the obtained compounds was confirmed by NMR, IR and mass spectroscopy. In the course of studying the spectral and photoluminescent characteristics, it was possible to reveal the effect of some substituents in various positions on the properties of spiropyran dyes. Due to the structural similarity of one of the isomers to cyanine dyes, the obtained compounds are of interest as potential fluorescent probes for bioimagimg, in particular, for DNA studies. To reveal their ability of binding to DNA molecules molecular docking was carried out. Toxic effects of compounds demonstrating NIR fluorescence were studied on biofilms, as well as using bacterial lux-biosensors. [ABSTRACT FROM AUTHOR]

New indoline spiropyrans containing chlorine and bromine atoms in position 5 of the indoline moiety of the molecule as a substituent were synthesized and studied. The structures of the synthesized compounds were confirmed by NMR and IR spectroscopy. The molecular structure of the chlorine-substituted derivative was determined by X-ray diffraction analysis, and intermolecular interactions in the crystal were studied using the CrystalExplorer21.5 software package. The spectral kinetic studies revealed photochromic properties of novel spiropyrans in an acetonitrile solution. The photoelectrochemical characteristics of dye-sensitized solar cells (DSSC) made from the synthesized compounds before and after UV irradiation were studied in comparison. [ABSTRACT FROM AUTHOR]

One of the popular, low‐cost, efficient, and environmentally friendly methods for separating pollutants and water purification are membrane‐based processes. In this study, nanofiltration membranes were modified using the photo‐responsive graphene oxide‐spiropyran (GO‐SP) nanosheets as novel additive. Graphene oxide was employed to improve permeability, antifouling, and mechanical properties of the membranes. Spiropyran was added due to the increase in the self‐cleaning properties of the PES membranes. First, spiropyran (SP) as a photochromic compound was chemically immobilized onto the graphene oxide (GO) surface. Different examinations such as ultraviolet–visible (UV–Vis) spectroscopy, energy‐dispersive X‐ray spectroscopy (EDS), field emission scanning electron microscopy (FE‐SEM), and atomic force microscopy (AFM) were used to check the effective grafting of spiropyran. Then, nanofiltration membranes containing polyethersulfone (PES) and GO‐SP additive with different weight percentages (0.15, 0.25, 0.5, and 0.75 wt.%) were prepared. Membranes comprising 0.5 wt.% GO‐SP exhibited the best surface properties, and at concentrations above 0.5 wt.%, aggregation of GO‐SP additive occurred on the surface of the membrane. The Young modulus increased from 45.11 MPa for pure PES membrane to 82.63 MPa for PES/GO‐SP‐0.75. The flux of pure water, rejection of bovine serum albumin (BSA) protein, and separation of anionic dyes including Congo Red (CR) and Coomassie Brilliant Blue (CBB) were measured to show the filtration performance of the fabricated membranes. It was observed that the addition of 0.5 wt.% GO‐SP increased the flux of pure water of the PES‐based membrane from 2.97 to 14.6 L/m2 h. All prepared membranes rejected more than 94% of CBB and CR dyes. The addition of GO‐SP also developed the performance of the membranes against fouling. In addition, the effects of UV light on membrane fouling, dye rejection, and contact angle were investigated. According to the results, irradiation of GO‐SP with UV light decreased the contact angle and increased the flux of pure water. In the presence of UV light, the membrane containing 0.5 wt.% GO‐SP exhibited 58.74% reversible fouling, 8.30% irreversible fouling, and 93% flux recovery ratio, indicating its better performance than the pure membrane. [ABSTRACT FROM AUTHOR]

Photoswitchable fluorescent polymers (PFPs) are emerging as a class of promising systems for photowritable pattern, optical anti‐counterfeiting, and information encryption. They typically use harmful UV light as the stimulus, which often leads to inevitable photobleaching and poor reversibility. To address this issue, visible‐light‐driven PFPs by copolymerization of novel negative photochromic spiropyran monomer and methyl acrylate are developed. The obtained copolymers display bright red fluorescence, which can be reversibly turned off by visible light irradiation. Many appealing features are observed in this system, including fast photo‐responsibility, prominent photo‐reversibility and photostability, simple preparation process, and processability. Their applications in photorewritable patterns, optical anti‐counterfeiting, and information encryption are also demonstrated. [ABSTRACT FROM AUTHOR]

Herein, we report a kind of light-responsive metal–organic framework (MOF) adsorption material which was fabricated by covalently immobilizing photoactive spiropyran (SP) molecules onto a chromium-(III)-based amino-tagged MIL-101 framework through amide linkages. The photoisomerization of SP moieties endows these materials with the unique feature of reversible binding to metal ions. In the dark, the SP-modified MOFs were capable of adsorbing multiple monovalent and divalent salts from saline water and effectively released the adsorbed ions into water upon exposure to simulated sunlight. The SP-modified MOFs showed excellent salt adsorption capacity, of which the MOF with an SP modification ratio of 39% had an ion uptake of 2.27, 1.72, 1.0, 0.8, and 0.39 mmol g–1 for the monocomponent solutions of LiCl, NaCl, KCl, CaCl2, and MgCl2, respectively. After 10 adsorption–desorption cycles, the regenerated adsorbent still exhibited a higher ion adsorption of 1.27 mmol g–1 for the NaCl solution. This work provides a synthetic strategy for salt adsorption materials with nonchemical regeneration ability, which are promising for water desalination and purification. [ABSTRACT FROM AUTHOR]

Herein, novel photoresponsive spiropyran (SP)‐based P(DEGMA‐co‐SpMA) copolymers with variable percentages of SP fractions are synthesized. The SP group present in these polymers exhibited the abilities of reversible photoisomerism. Their photoresponsive, structural, and thermal properties have been investigated and compared using various characterization techniques. These light‐responsive copolymers are found to exhibit photoswitchable glass transition temperature (Tg), high thermal stability (Td > 250°C), instant photochromism as well as fluorescence upon exposure to UV light. It is demonstrated that the Tg of these synthesized polymers increased when irradiated with UV light (λ = 365 nm), as a consequence of the photoisomerization of incorporated SP groups into their merocyanine form. This increase in Tg is attributed to an increase in polarity and a decrease in the overall entropy of the polymeric system when it switches from the ring‐closed SP form (less‐ordered state) to the ring‐opened merocyanine form (more‐ordered state). Therefore, such polymers with a unique feature of phototunable glass transition temperatures provide the possibility to be integrated into functional materials for various photoresponsive applications. [ABSTRACT FROM AUTHOR]

An efficient one-pot multicomponent reaction is reported for synthesizing a novel series 4-hydroxy-2-pyridone-fused spiropyran through the reaction of 4-hydroxy-6-methylpyridine-2-ones alkaloids, malononitrile or ethyl cyanoacetate, and ninhydrin or isatin derivatives. The optimized conditions for this reaction were obtained in ethanol solvent, acetic acid as catalyst, ambient temperature (for ninhydrin) or 70 °C (for isatin), and 8 hr reaction time. Mild and safe conditions, easy work-up and separation, high to excellent yields, and eco-compatibility are the main advantages of this synthesis for affording potentially bio-effective novel products. [ABSTRACT FROM AUTHOR]

Phototransformations of 6-nitro-8-methoxy-substituted indoline spiropyran in acetonitrile have been studied by laser kinetic spectroscopy (laser photolysis) with single- and double-pulse excitation. The role of the triplet state in the kinetics of photocoloration of spiropyran has been revealed. It has been shown that photochromic transformations of spiropyran involve unstable trans-isomers (conformers) of the open merocyanine form of spiropyran. Data on the transformation kinetics of the trans-isomers are presented. [ABSTRACT FROM AUTHOR]

The development of smart color-changing wood could facilitate its functional application. Herein, photochromic wood films (PWFs) were synthesized by grafting 1-(2-hydroxyethyl)-3,3-dimethylindolino-6'-nitrobenzopyrylospiran onto the cellulosic skeleton structure of delignified wood using hexamethylene diisocyanate as a bridging linker, followed by the densification process. The microstructural morphology, chemical composition, photochromic properties, and mechanical properties of the prepared PWFs were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, colorimeter, and universal mechanical testing machine. The photochromic capability of the wood film was positively correlated with the grafting amount of spiropyran; the color change is evident when the grafting amount is high. Furthermore, the photochromic and recovery capability of the wood film weakened after sequentially irradiating 40 times using a UV lamp and daylight lamp, which could be partially recovered after a period of rest. However, the wood film strength was negatively correlated with the grafting amount of spiropyran. The grafted spiropyran affected the hydrogen bonding between cellulose nanofibers of the wood film during densification, which caused a reduction in the film strength. However, the strength was still >120 MPa. Meanwhile, temperature and humidity affected the photochromic capability of the wood film. Thus, the developed high-strength PWF has potential applications in various fields, such as intelligent sensing, personalized design, indoor and outdoor architecture, and optoelectronics. [ABSTRACT FROM AUTHOR]

Spiropyran (SP) based mechanochromic systems are intensively interesting in the research area of mechanochromic materials. Herein, an SP mechanophore is chemically incorporated into a liquid crystalline elastomer (LCE) network through Michael addition. The rigidity of mesogens and the orientation of polymer main chains, in which the aligned mesogens and SP moieties are covalently attached, facilitate the transduction of applied force to SP mechanophore to trigger mechanochromic reaction. The LCE network provides enough elasticity for mechanochromic activation. The obtained SP‐LCEs demonstrate strong and reversible mechanochromic response upon mechanical compression. The mechanochromic efficiency and sensitivity are substantially enhanced by doping the SP‐LCE matrix with nano zinc oxide such that it is easy to write on the material surface by using a thin iron wire. The authors hope such SP‐LCE materials will be further developed for real‐time stress detection applications. [ABSTRACT FROM AUTHOR]

Switchable nonlinear optical (NLO) materials have widespread applications in electronics and optoelectronics. Thermo-switches generate many times higher NLO responses as compared to photo-switches. Herein, we have investigated the geometric, electronic, and nonlinear optical properties of spiropyranes thermochromes via DFT methods. The stabilities of close and open isomers of selected spiropyranes are investigated through relative energies. Electronic properties are studied through frontier molecular orbitals (FMOs) analysis. The lower HOMO-LUMO energy gap and lower excitation energy are observed for open isomers of spiropyranes, which imparts the large first hyperpolarizability value. The delocalization of π-electrons, asymmetric distribution and elongated conjugation system are dominant factors for high hyperpolarizability values of open isomers. For deep understanding, we also analyzed the frequency-dependent hyperpolarizability and refractive index of considered thermochromes. The NLO response increased significantly with increasing frequency. Among all those compounds, the highest refractive index value is observed for the open isomer of the spiropyran 1 (1.99 × 10−17 cm2/W). Molecular absorption analysis confirmed the electronic excitation in the open isomers compared to closed isomers. The results show that reversible thermochromic compounds act as excellent NLO molecular switches and can be used to design advanced electronics. [ABSTRACT FROM AUTHOR]

Polymers are ideal materials for information printing and storage and encryption through multiple channels. In this study, the visible color, fluorescent, and stress‐color are combined to print information. Stress‐color is achieved using an acid‐tunable dynamic reaction between a β‐diketone and an amine group via the light‐induced transformation of spiropyran (SP), which also directly prints the visible color information. The color and fluorescent patterns are stable via the reaction between SP and amine released from a dynamic enaminone structure. By achieving the stress‐color information coding, the data is further encrypted in an "acrostic" form by programmatically coding the information at several stages. The pattern or information in stress‐color is closely related to the decoding strain, whereas the fluorescent and color patterns display all the information written in various strains. As a result, the secret information is hidden among public data, resulting in acrostic encryption. [ABSTRACT FROM AUTHOR]

Hydrogels are a type of high-water content and crosslinked polymer networks, which can produce a volumetric expansion or contraction through a water absorption or loss process under external environmental stimulation. Due to their good biocompatibility and adjustable mechanical properties, hydrogels have attracted wide attentions and have been extensively applied in the fields of tissue engineering, biomimetic deformation and intelligent actuation. Light is a noncontact, fast switching and high spatiotemporal resolution stimulus, and therefore is used to regulate the macroscopic structure and properties of hydrogels through photothermal effects, photochemical reactions or photoisomerization. Among them, photoisomerization of molecular switches has a broader application potential because of its advantages of mild irradiation conditions and high reversibility. In this review, we summarize the state-of-the-art of photoresponsive hydrogels based on molecular photoisomerization, emphasizing the principle of molecular design as well as applications in biomimetic actuation, and eventually address their perspectives and challenges in the future development. [ABSTRACT FROM AUTHOR]

Regulation of the discoloration efficiency of mechanochromism materials is a big challenge to date. In this study, a series of polyurethane elastomers (PUEs) using dihydroxyspiropyran (SP2) as functional molecule with varied microstructure were synthesized. The mechanochromic behavior of PUEs and the relationship between it and the microstructure of PUEs was investigated. As a result, when SP2 was covalently bonded to PUE backbones, discoloration phenomenon was clearly detected and appears earlier in PUEs with higher microphase separation degree under stretching. On the other hand, the PUEs with ultralow microphase separation degree could hardly change color until the fracture of the materials. Therefore, the characteristic indigo blue appearance efficiency could be easily controlled (from 300 to 600% strain) by adjusting the microphase separation degree in these PUEs. The results will allow these materials to deal with broader stress range. [ABSTRACT FROM AUTHOR]

The potential of E–Z photoisomerization in molecular organic light-to-thermal conversion and storage in an E–styryl merocyanine system was studied in a polar acidic medium. A photoswitchable styryl merocyanine dye (E)-2-(2-(2-hydroxynaphthalen-1-yl)vinyl)-3,5-dimethylbenzo[d]thiazol-3-ium iodide was synthesized for the first time. The reversible E–Z photoisomerisation of the dye was investigated using UV-Vis spectroscopy and DFT calculations. E–Z isomerization was induced through the use of visible light irradiation (λ = 450 nm). The obtained experimental and theoretical results confirm the applicability of the Z and E isomers for proton-triggered light harvesting. [ABSTRACT FROM AUTHOR]

Here, we report the ability of spiropyrans to initiate two-photon polymerization (TPP) for the first time in the literature. The comparison and synergies between the spiropyran photochromic molecule of interest, namely 6-nitro-BIPS, and well-known photoinitiators of radical photopolymerization have been studied. The spiropyran (SPy) molecule can initiate TPP in the presence of trifunctional acrylic monomers and create true 3D structures. The comparison with Irgacure 819, a well-known Type-I photoinitiator, shows that SPy has a comparable capability for TPP. In addition, the combination of SPy with methyl diethanolamine increased the reactivity of both one- and two-photon polymerizations. In the last section, we discuss which SPy isomer is the active photochromic species capable of generating radicals for initiating two-photon polymerization.

Hypomethylating agents (HMAs), such as azacitidine and decitabine, induce cancer cell death by demethylating DNAs to promote the expression of tumor-suppressor genes. HMAs also reactivate the transcription of endogenous double-stranded RNAs (dsRNAs) that trigger the innate immune response and subsequent apoptosis via viral mimicry. However, the expression patterns of endogenous dsRNAs and their relevance in the efficacy of HMAs remain largely uninvestigated. Here, we employ amidine-conjugated spiropyran (Am-SP) to examine the dynamic expression pattern of total dsRNAs regulated by HMAs. By analyzing the bone-marrow aspirates of myelodysplastic syndrome or acute myeloid leukemia patients who received the HMAs, we find a dramatic increase in total dsRNA levels upon treatment only in patients who later benefited from the therapy. We further apply our approach in solid tumor cell lines and show that the degree of dsRNA induction correlates with the effectiveness of decitabine in most cases. Notably, when dsRNA induction is accompanied by increased expression of nc886 RNA, decitabine becomes ineffective. Collectively, our study establishes the potential application of monitoring the total dsRNA levels by a small molecule as an analytical method and a dynamic marker to predict the clinical outcome of the HMA therapy.