Spiropyran Molecules Research Articles

Preparation of light-responsive polyacrylamide/carboxymethyl chitosan composite aerogel and its adsorption performance for Li.

As an essential material for manufacturing lithium batteries, the demand of lithium is increasing, which means novel extracting method from various lithium-containing solutions is necessary. Spiropyran molecules undergo a photoisomerization reaction under light, transitioning from a closed-ring form (colorless) to an open-ring form (colored), generating multiple coordination sites to form coordination bonds with metal ions. In this paper, a polyacrylamide/carboxymethyl chitosan composite aerogel grafted with photoresponsive spiropyragroups (Fe3O4/CNTs@PAM/CS-SP), used for extracting lithium from solutions, was prepared by dual cross-linking and vacuum freeze-drying. Batch adsorption experimental results showed that the incorporation of Fe3O4 nanoparticles further enhances its adsorption capability, as it enables rapid separation of the aerogel from water using an external magnetic field and also improves the adsorption efficiency due to its magnetic properties. The aerogel exhibits good adsorption capacity in the pH range of 9-12 and shows selectivity for Li in simulated brine, achieving a maximum adsorption capacity of 176.5 mg/g at 35 °C and a Li concentration of 1 g/L. The preparation of this aerogel offers a novel and effective approach to creating environmentally friendly adsorbents, providing a new method for extracting lithium from lithium-containing solutions.

Anion and Substituents Effect on Spectral-Kinetic and Biological Characteristics of Spiropyran Salts.

Spiropyran salts containing a cationic vinyl-3H-indolium moiety are characterized by NIR absorption and fluorescence of their merocyanine forms. This feature makes them promising fluorescent probes and markers for bioimaging. The article focuses on the synthesis and study of the spectral, kinetic and toxic characteristics of such compounds with respect to various substituents in different moieties and the type of anion. A detailed analysis of the acquired data made it possible to draw some important conclusions regarding the influence of structural factors, which will be very useful for the further rational design of such derivatives. In particular, it was shown that the counterion has minimal effect on the spectral and kinetic characteristics of the dyes but dramatically affects the toxicity of the compounds. Following selection of the most appropriate compounds, bioimaging experiments were carried out to visualize planktonic bacteria and bacterial biofilms of E. coli and A. calcoaceticus. The ability to visualize biofilms is critical for the diagnosis of chronic diseases. By the results of molecular docking a theoretical interaction pattern between spiropyran molecules and DNA was proposed.

Switchable near-infrared photoluminescence of PbS quantum dots through light and heat modulated hole transfer to spiropyran molecules

Switchable near-infrared photoluminescence of PbS quantum dots through light and heat modulated hole transfer to spiropyran molecules

Novel core–shell materials SiO2@Tb-MOF for the incorporation of spiropyran molecules and its application in dynamic advanced information encryption

Dynamic fluorescent switches with multiple light outputs offer promising opportunities for advanced security encryption. However, the achievement of dynamic emission, particularly when based on the timing of external stimuli, continues to present a significant challenge. Herein, a unique dynamic fluorescent switch was developed by integrating spiropyran molecules (SP) into a core–shell structure (SiO2@Tb-MOF). The core–shell structure, derived from lanthanide complexes and silica microspheres, was synthesized under solvothermal conditions. This structure not only preserves the green fluorescence emission of Tb-MOF, but also results in a substantial specific surface area and mesoporous pore size from SiO2, which is advantageous for incorporating SP molecules to create a dynamic fluorescent switch, SP ⊂ SiO2@Tb-MOF. Upon exposure to ultraviolet light, SP gradually transitions into the merocyanine form (MC), displaying a pronounced absorption band at approximately 550 nm. Concurrently, a fluorescence resonance energy transfer (FRET) process is initiated between Tb3+ and the merocyanine isomers. With prolonged exposure to UV light, the fluorescence color shifts progressively from green to red, facilitated by the ongoing FRET process. Moreover, SP ⊂ SiO2@Tb-MOF is doped with polydimethylsiloxane to fabricate a film. Utilizing time-dependent fluorescence, dynamic encryption patterns and advanced information encryption were investigated. This work provides a design basis for how to better construct core–shell structures and combine them with SP molecules to prepare dynamic fluorescent materials, and paves a way for constructing advanced encryption materials with higher safety requirements.

Substrate Channeling in Compartmentalized Nanoreactors.

Thermo- and photoresponsive nanoreactors based on shell cross-linked micelles (SCMs) for the rhodium-catalyzed asymmetric transfer hydrogenation (ATH) of ketones have been developed from poly(2-oxazoline) triblock terpolymers. The nanoreactors incorporate thermoresponsive poly(2-isopropyl-2-oxazoline) as the hydrophilic corona and are covalently cross-linked with a photoswitchable spiropyran molecule. UV irradiation or changes in temperature trigger morphology switching of the polymer-based nanoreactors that alters the hydrophobicity in separate layers of the SCMs, resulting in dynamic substrate selectivity of the ATH in water. Control experiments and kinetic studies show that the thermoresponsive outer layer induces the gated behavior for more hydrophobic substrates, whereas the photoresponsive cross-linking layer induces the gated behavior for less hydrophobic substrates. The nanoreactors mimic the multichannels in Nature, transporting substrates and reagents into the catalytic core which can be controlled through external triggers such as temperature and light wavelengths. Additionally, the nanoreactors can be easily recovered and reused with continued high activity and selectivities.

Introduction of photochromic properties to UiO-66-NH2 via “click”-modification by spiropyran molecule

We present a study on incorporating spiropyran photoactive molecules into the UiO-66-NH2 scaffold. Initially, we modified spiropyran molecules by introducing functional groups to facilitate covalent bonding with the MOF structure. Spiropyran molecules with carboxylic groups demonstrated the ability to coordinate zirconium in defect pores of the MOF. Alternatively, the aldehyde group showed potential for forming C–N bonds with amino groups of BDC-NH2 linkers. To validate the formation of C–N bonds within the MOF scaffold, we synthesized a complex salt of spiropyran and individual BDC-NH2 linkers. DFT calculations support our conclusions. We observed that upon introducing the photoactive moiety, the UiO-66-NH2 framework exhibited photoresponse, as demonstrated by FTIR experiments. Based on experimental data and computational results, we hypothesize that both incorporation mechanisms are viable in the functionalization process. However, steric hindrances may impede the incorporation of spiropyran into the pores, leading to surface modification instead. The elucidated mechanisms hold promise for the development of photoresponsive MOF-based smart materials.

Spiropyran molecular aggregates implanted photo-responsive graphene oxide membrane with self-cleaning ability for enhanced water purification

Stimuli-responsive separation membranes with adjustable interfacial properties are highly desired for energy-efficient and sustainable water purification, owing to their exceptional antifouling capability and separation selectivity. However, the construction of highly efficient responsive membranes continues to present a substantial challenge. Herein, photo-responsive spiropyran (SP) molecular aggregates obtained via a "good-poor" solvent self-assembly strategy were implanted into lamellar graphene oxide (GO) membrane. The obtained GO/SP membrane with enriched water transport channels and enhanced hydrophilicity demonstrated superior water permeability (95.0 L h−1 m−2 bar−1). Benefiting from the reversible photoisomerization of SP molecules between the hydrophobic SP upon light irradiation and the hydrophilic zwitterionic merocyanine (MC) in dark conditions, the GO/SP membrane possessed captivating photo-response property verified by tunable water permeability and molecular rejection. Theoretical calculation revealed that the thermodynamic interface energy between bovine serum albumin (BSA) and membrane surface changed from attraction in dark conditions to repulsion under light conditions. Consequently, the water permeability of BSA-fouled membranes could recover to 96.2 % of its initial level after light irradiation, exhibiting fascinating photo-driven self-cleaning capability. The designed photo-responsive membrane with feasible membrane fouling control holds great promise for efficient water purification.

Optical, thermal and mechanical activation of spiropyrans enhanced by hydrogen bonding interactions and its application in time–resolved encryption

Here, a multi–stimuli–responsive spiropyran molecule with enhanced photochromic, thermochromic and mechanochromic properties was constructed by introducing hydrogen bonding interactions, which is highly sensitive to external stimuli, and its solution and powder change color after two seconds of ultraviolet irradiation. After short–term grinding (10 min) or heating (90 ℃ for 3 min), the powder can also show rapid and reversible fluorescence emission change. The molecule can withstand at least 5 reversible grinding–recrystallization cycles, 5 heating–white light cycles or 20 reversible UV– white light cycles. To our best knowledge, it is seldom reported that spiropyran compounds achieve multi–stimuli response by introducing hydrogen bonds, and there are also rare reports on the influence of hydrogen bonds on multi–stimuli performance. Hydrogen bond interaction makes the spiropyran molecule more sensitive to external stimuli to achieve the multi–stimulus response. Combined with this good photochromism, mechanochromism and thermochromism, a time–resolved multilevel information encryption was explored, which has the following advantages: (1) According to the actual demand, designing and adding the combination of numbers or letters can encrypt a lot of information. (2) The process involves three kinds of stimuli responses (photochromism, mechanochromism and thermochromism), and the complex information switching ensures that the real information is not easy to leak. (3) The encryption and decryption steps are easy to operate and can lower the application threshold. This work is a rare example of improving the photochromism, mechanism and thermochromism of spiropyrans by hydrogen bonding, which can also provide guidance for designing functional spiropyrans for multi–level information encryption.

On–off conduction photoswitching in modelled spiropyran-based metal-organic frameworks

Materials with photoswitchable electronic properties and conductance values that can be reversibly changed over many orders of magnitude are highly desirable. Metal-organic framework (MOF) films functionalized with photoresponsive spiropyran molecules demonstrated the general possibility to switch the conduction by light with potentially large on-off-ratios. However, the fabrication of MOF materials in a trial-and-error approach is cumbersome and would benefit significantly from in silico molecular design. Based on the previous proof-of-principle investigation, here, we design photoswitchable MOFs which incorporate spiropyran photoswitches at controlled positions with defined intermolecular distances and orientations. Using multiscale modelling and automated workflow protocols, four MOF candidates are characterized and their potential for photoswitching the conductivity is explored. Using ab initio calculations of the electronic coupling between the molecules in the MOF, we show that lattice distances and vibrational flexibility tremendously modulate the possible conduction photoswitching between spiropyran- and merocyanine-based MOFs upon light absorption, resulting in average on-off ratios higher than 530 and 4200 for p- and n-conduction switching, respectively. Further functionalization of the photoswitches with electron-donating/-withdrawing groups is demonstrated to shift the energy levels of the frontier orbitals, permitting a guided design of new spiropyran-based photoswitches towards controlled modification between electron and hole conduction in a MOF.

Dynamic anticounterfeiting polymeric inks for multipurpose time-dependent encryption with a high level of security

Development of dynamic anticounterfeiting inks with time-dependent photochromism and photoluminescence characteristics has become highly interesting in advanced encryption systems. These inks are applicable in different fields, such as tracking UV rays and gas leakage and also quality monitoring. In this study, semi-continuous copolymerization of butyl acrylate and methyl methacrylate in the heterogeneous miniemulsion medium was used to synthesize colloidal nanoparticles with different flexibilities and polarities. Then, hydroxyl-functional spiropyran (SPOH) was physically incorporated into the nanoparticles to prepare photochromic and photoluminescent inks. The nanoparticles showed low light reflectance due to their small size, which makes them applicable in photoresponsive and sensing applications. In addition, the nanoparticles exhibited different glass transition temperature (Tg) that affects their photoresponsivity. Microscopic analysis revealed that all the latex samples have spherical nanoparticles with a mean size of about 70 nm and a low polydispersity index. UV–vis absorption and fluorescence emission spectra, isomerization kinetics, and photofatigue resistance of the photochromic latex nanoparticles were studied, which depend on chain polarity and flexibility of the latex nanoparticles. The optical properties of the photochromic materials are closely related to the structure and composition of the latex samples. Time-dependent features of the inks originate from their spiropyran molecules which gradually turns into the merocyanine form upon visible light induction. Photochromic inks with advanced encryption and dynamic characteristics were developed from the SPOH-doped colloidal latex nanoparticles. Different polarities and Tg of the inks result in their different dynamic chromism, which show their high level of information encryption technology. By virtue of these unique time-dependent properties, the encryption capabilities of these inks are significantly improved. These inks achieved unprecedented advances in the field of information security and encryption because of their innovative features.

Time-resolved encryption from a spiropyran derivative: High-contrasted and multi-state mechanochromism, photochromism and thermochromism

Developing organic multi-stimuli responsive luminescent (OMSRL) materials in solid state has always been an arduous task. In this work, a simple spiropyran derivative (XG) is constructed, which exhibits excellent photochromism, thermochromism with exceptional reversible absorption/luminescence modulation ability after grinding. This new compound shows different photochromic and thermochromic characteristics under different grinding conditions. Furthermore, this new compound shows tunable dynamic photochromic and thermochromic characteristics due to the reversible isomerization of spiropyran molecule with excellent reversible absorption/luminescence modulation ability. More importantly, the color or emission can be modulated just by changing the time of external stimulation (ultraviolet stimulation, heating or grinding). This can be used not only to encrypt more rich information, but also to develop time-resolved multi-dimensional encryption or dynamic anti-counterfeiting advanced materials. This paper presents a new time-resolved encryption strategy based on this new compound, which provides important guidance for developing advanced information security materials.

Developing Stretchable and Photo-Responsive Conductive Films by Incorporation of Spiropyran into Poly(ionic liquid)s

Poly(ionic liquid)s (PILs) have been widely applied in various disciplines because of their unique physical, chemical, and electrical characteristics. To broaden the applications of PILs, stimuli-responsive PILs based on different stimuli have been investigated. Special stimuli-dependent properties of PILs, especially photo-regulated electrical conductivities, however, have not yet been fully accomplished. In this work, we study the photo-regulated electrical conductivities of PIL films by using [C3mim-MA][TFSI], azobisisobutyronitrile, and poly(ethylene glycol) dimethacrylate as an ionic liquid monomer, an initiator, and a crosslinker, respectively. Spiropyran (SP) molecules, which can convert to merocyanine molecules under UV light irradiation, are used as photo-responsive agents. As a result, stretchable and photo-responsive conductive PIL-SP films can be fabricated, which can be reversibly converted to PIL-merocyanine films under UV and visible light illuminations. The photoluminescence properties are confirmed by fluorescence and UV–vis spectra. Furthermore, the reversible photo-regulated electrical properties are investigated by shining UV and visible lights, presented by the Bode plots and Nyquist plots. The PIL-SP films with different crosslinker ratios (1, 5, and 10×) all exhibit similar photo-regulating electrical properties. At higher crosslinker ratios, the DC resistances are higher, resulting in lower conductivities. The study of stretchable and photo-responsive conductive PIL-SP films expands the applications of PIL materials.

Controllable Wetting Transitions on Photoswitchable Physical Gels.

Softness plays a key role in the deformation of soft elastic substrates at the three-phase contact line, and the acting forces lead to the formation of a wetting ridge due to elastocapillarity. The change in wetting ridge and surface profiles at different softness has a great impact on the droplet behavior in different phenomena. Commonly used materials to study soft wetting are swollen polymeric gels or polymer brushes. These materials offer no possibility to change the softness on demand. Therefore, adjustable surfaces with tunable softness are highly sought-after to achieve on-demand transition between wetting states on soft surfaces. Here, we present a photorheological physical soft gel with adjustable stiffness based on the spiropyran photoswitch that shows the formation of wetting ridges upon droplet deposition. The presented photoswitchable gels allow the creation of reversibly switchable softness patterns with microscale resolution using UV light-switching of the spiropyran molecule. Gels with varying softness are analyzed, showing a decrease in the wetting ridge height at higher gel stiffness. Furthermore, wetting ridges before and after photoswitching are visualized using confocal microscopy, showing the transition in the wetting properties from soft wetting to liquid/liquid wetting.

Photo-Stimuli-Responsive Dual-Emitting Luminescence of Spiropyran-Encapsulated Metal-Organic Framework for Dynamic Information Encryption.

The development of photo-stimuli-responsive luminescent materials is essential to address emerging demands in encryption security. Here, we report a novel photo-stimuli-responsive dual-emitting luminescent material ZJU-128⊃SP (SP = spiropyran), which was obtained by encapsulating spiropyran molecule into a cadmium-based metal-organic framework (MOF), [Cd3 (TCPP)2 ]·4DMF·4H2 O (ZJU-128, H4 TCPP = 2,3,5,6-tetrakis (4-carboxyphenyl)pyrazine). This MOF/dye composite ZJU-128⊃SP exhibits a blue emission from ligand of ZJU-128 at 447nm and a red emitting around 650nm of spiropyran. Utilizing the photoisomerization of spiropyran from ring-closed to ring-open form under UV light irradiation, significant fluorescence resonance energy transfer process between ZJU-128 and spiropyran is achieved. As a result, the blue emission of ZJU-128 is gradually decreased while the red emission of spiropyran increased. This dynamic fluorescent behavior can fully recover to original state when exposed to visible light (> 405nm). By taking advantage of the time-dependent fluorescence, dynamical anti-counterfeiting pattern and multiplexed coding are successfully developed based on ZJU-128⊃SP film. This work provides an inspiring point for the design of information encryption materials with higher security requirements. This article is protected by copyright. All rights reserved.

Tuning the Photochromism of Spiropyran in Functionalized Nanoporous Silica Nanoparticles for Dynamic Anticounterfeiting Applications.

Here, we report a novel invisible ink with different decay times based on thin films with different molar ratios of spiropyran (SP)/Si, which allows the encryption of messages over time. Nanoporous silica has been found to be an excellent substrate to improve the solid photochromism of spiropyran, but the hydroxyl groups of silica have a serious effect on fade speeds. The density of silanol groups in silica has an influence on the switching behavior of spiropyran molecules, as they stabilize the amphiphilic merocyanine isomers and thus slow down the fading process from the open to the closed form. Here, we investigate the solid photochromic behavior of spiropyran by sol-gel modification of the silanol groups and explore its potential application in UV printing and dynamic anticounterfeiting. To extend its applications, spiropyran is embedded in organically modified thin films prepared by the sol-gel method. Notably, by using the different decay times of thin films with different SP/Si molar ratios, time-dependent information encryption can be realized. It provides an initial "false" code, which does not display the required information, and only after a given time will the encrypted data appear.

LIGHT-STIMULATED LOWERING OF GLUCOSE CONCENTRATION IN A DEXTROSE SOLUTION MEDIATED BY MEROCYANINE MOLECULES

Diabetes mellitus is a chronic metabolic disease characterized by elevated blood glucose levels and has become a global challenge. Currently, the widespread and regular treatment of diabetes mellitus involves the administration of insulin. However, insulin is no longer considered the first choice for type 2 diabetes, and an expanding range of new treatment modalities are emerging as noninsulin-based medications that are promising alternatives to regulate blood glucose levels. In this regard, controlling the glucose level in blood by external stimuli, such as light, offers a new route to governing the blood glucose concentration with the required dose and at the appropriate time. Here, we report on a light-stimulated glucose-lowering method based on spiropyran-merocyanine photoisomerization. We show that upon exposure to violet light (405 nm), the closed isoform of spiropyran molecules inside liquid crystal microspheres transforms into the open merocyanine isoform, which in turn stimulates merocyanine to translocate through the interface of the liquid crystal/dextrose emulsion. Merocyanine readily interacts with glucose molecules and causes a lowering of the emulsion’s total glucose concentration by 20 %.

Electrospinning and multilayer modification to construct NH2/EPSP-modified polyacrylonitrile nanofiber films for humidity regulation

Photoresponsive materials may be used to improve the humidity of a microenvironment, thus improving the comfort of people occupying that space. In this work, by constructing a synergistic layer (amino groups) and a regulating layer (spiropyran compounds) on the surface of polyacrylonitrile (PAN) electrospun membranes, we successfully developed fiber materials with excellent mechanical stability that can reversibly regulate the humidity of the microenvironment. Spiropyran molecules can undergo photoisomerization (reversible polar-nonpolar structure interconversion) by conversion of ultraviolet/visible light. The wettability and microenvironment humidity can be controlled bidirectionally under different light sources. More importantly, the amino groups on the fiber surface can assist the ring-opened merocyanine in absorbing water molecule, thus playing a synergistic role. Moreover, changing the electrospinning voltages can help regulate the porosity of the fiber materials, which can change wettability and the humidity range regulation. The energy change of spiropyran before and after water absorption was obtained by density functional theory calculations, and it is further proven that the synergistic layer can promote the ability of humidity regulation.

Photoswitchable spiropyran molecules for specific sensing of thiols and fluorescent inks

This work presents promising photoswitching-based spiropyran molecules as fluorescent probes, which can be used not only for sensitive and selective detection of biological thiols but also as fluorescent inks for information encryption.

Reversible Chiral Optical Switching Based on Co-Assembled Spiropyran Gels.

In recent years, it has been very interesting to dynamically adjust the emission of circularly polarized luminescence (CPL) materials through external stimulation due to their applications and the fundamental interest in them. In this work, luminescence-tunable and light-responsive supramolecular co-assembly CPL-active materials are fabricated by mixing an achiral functional spiropyran (SP-COOH) molecule with a chiral gelator. The spiropyran achieves a reversible change between a white closed ring state spiropyran and a purple zwitterionic merocyanine state in supramolecular co-assembly gels under alternate visible (vis) and ultraviolet (UV) light irradiation. The gel shows strong CPL signals due to the chirality transfer in co-assembly systems. These signals could change reversibly under alternate exposure to UV and vis light. Therefore, utilizing the multistimulus-responsive CPL signals in different states, a CPL switch of the supramolecular system signal according to the combinatorial control of UV-vis light irradiation is constructed.

Molecular platform based on a spiroindolinonaphthopyran of the diphenyloxazole series for the creation of polychromogenic molecular systems

A spiroindolinonaphthopyran of the diphenyloxazole series along with photochromism possesses a number of chromogenic properties such as solvatochromism, ionochromism, solid state phasochromism and fluorescence. The nature of these effects is associated both with the possibility of the spiropyran existence under its two forms (cyclic and merocyanine) and with the peculiarities of the molecular structure, in particular, with the presence of a diphenyloxazole fragment. Photochromic properties of the spiroindolinonaphthopyran do not exhibit a drastic dependence on the nature of solvents, including those that are capable of specific intermolecular hydrogen bond interactions. In addition, good resistance to photodegradation in the mode of photochromic balance opens up possibilities for designing polychromogenic molecular systems based on them. The positive solvatochromism of the first type, which is noticeably manifested in the case of merocyanine isomers, allowed establishing the weak polarity of their ground state. Solvatochromism of the second type demonstrates a significant spectral contrast (up to 227 nm) due to the existence of an equilibrium of cyclic and merocyanine isomers. The intensity of the effect increases upon passing from toluene to DMSO due to the shift of the equilibrium towards the merocyanine isomers. The presence of a chelate center formed by the merocyanine oxygen atom and the nitrogen atom of the diphenyloxazole fragment allows observing ionochromic transformations of the spiropyran molecule associated with the formation of coloured complex compounds upon its interaction with Co, Cu, Ni, Zn, Cd, Mn ions. It has been established that solutions of Zn, Cd, and Mn complexes exhibit the negative photochromism properties. The change in the solid state of spirpyran is accompanied by a change in the ability to undergo photochromic transformations. Under standard conditions the spiropyran exhibits photochromic properties in the crystalline state, but not in the amorphous one. The combination of chromogenic properties makes it possible to implement fluorescent molecular switches, bipolar absorption switches, photodynamic chemosensors, and solid-state phase transitions control the chromogenic properties based on spiropyrans of diphenyloxazole series. The possibility of structural modification leading to an enhancement of some properties and/or a weakening of other ones makes it possible to consider a spiroindolinonaphthopyran of a diphenyloxazole series as a molecular platform for creating polychromogenic molecular systems with desired properties.