Spiropyran Form Research Articles

Fabrication and Characterization of Co-Sensitized Dye Solar Cells Using Energy Transfer from Spiropyran Derivatives to SQ2 Dye

We developed dye-sensitized solar cells (DSSCs) using 1,5-carboxy-2-[[3-[(2,3-dihydro-1,1-dimethyl-3-ethyl-1H-benzo[e]indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-dimethyl-1-octyl-3H-indolium and 1,3,3-trimethyl indolino-6′-nitrobenzopyrylospiran. The DSSCs incorporate photochromic molecules to regulate photoelectric conversion properties. We irradiated photoelectrodes adsorbed with SQ2/SPNO2 using both UV and visible light and observed the color changes in these photoelectrodes. Following UV irradiation, the transmittance at 540 nm decreased by 20%, while it increased by 15% after visible light irradiation. This indicates that SPNO2 on the DSSCs is photoisomerized from the spiropyran form (SP) to the photomerocyanine (PMC) form under UV light. The photoelectric conversion efficiency (η) of the DSSCs increased by 0.15% following 5 min of UV irradiation and decreased by 0.07% after 5 min of visible light irradiation. However, direct electron injection from PMC seems challenging, suggesting that the mechanism for improved photoelectric conversion in these DSSCs is likely due to Förster resonance energy transfer (FRET) from PMC to the SQ2 dye. The findings suggest that the co-sensitization of DSSCs by PMC-SQ2 and SQ2 alone, facilitated by their respective photoabsorption, results in externally responsive and co-sensitized solar cells. This study provides valuable insights into the development of advanced DSSCs with externally controllable photoelectric conversion properties via the strategic use of photochromic molecules and energy transfer mechanisms, advancing future solar energy applications.

Black phosphorus quantum dots functionalized with photochromic poly(vinylspiropyran)-grafted polydopamine for transient digital-type memristors

Abstract The covalent functionalization of black phosphorus quantum dots (BPQDs) with organic species or polymers will inevitably change or damage their electronic structure and intrinsic structure. To address this problem and explore the application of BPQDs in transient digital-type memristors, a polydopamine (PDA) thin film is first synthesized in situ onto the surface of BPQDs to produce a donor–acceptor-type BPQDs@PDA composite that is directly used to react with 2-bromoisobutyryl bromide to give BPQDs@PDA-Br. By using BPQDs@PDA-Br as an atom transfer radical polymerization agent, a large number of polyvinylspiropyran (PSP) chains are in situ grown from the PDA surface to yield BPQDs@PDA-PSP. Upon ultraviolet (UV)–visible light illumination, the 2 isomers of the spiropyran (ring-closed spiropyran form and ring-opened merocyanine) in the PSP moieties will interconvert into each other rapidly. As expected, the as-fabricated indium tin oxide (ITO)/BPQDs@PDA-PSP/ITO device exhibits typical nonvolatile digital-type memristive performance under visible irradiation, with a small turn-on voltage of −1.52 V, a turn-off voltage of +1.16 V, and an ON/OFF ratio current ratio of 1.02 × 104. Upon UV illumination, the information stored in the device is quickly and completely erased within 6 s. By utilizing a simple memristor-based convolutional neural network, one can easily realize handwritten digit recognition. After 10 epochs of training, numeral recognition accuracy can reach up to 96.21%.

Development of Spiropyran Immobilization and Characterization Protocols for Reversible Photopatterning of SiO2 Surfaces.

Spiropyran is a dynamic organic compound that is distinguished by its reversible conversion between two forms: the colorless closed spiropyran (SP) form and the purple open merocyanine (MC) form. Typically triggered by UV light and reversed by visible light, spiropyran-functionalized surfaces offer reversible conversion in properties including color, polarity, reactivity, and fluorescence, making them applicable to diverse applications in chemical sensors, biosensors, drug delivery, and heavy metal extraction. While spiropyran has been successfully incorporated into various material platforms with SiO2 surfaces, its application on flat surfaces has been limited due to surface area constraints and a lack of standardized evaluation methods, which largely depend on the integration approach and substrate type used. In this study, we systematically review the existing literature and categorize integration methods and substrate types first and then report on our experimental work, in which we developed a streamlined three-step immobilization protocol, which includes surface activation, amination with (3-aminopropyl) triethoxysilane (APTES), and subsequent functionalization with carboxylic spiropyran (SP-COOH). Using SiO2 surfaces as a demonstration, we have also established a robust characterization protocol, consisting of contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and fluorometric analysis. Our results evaluate the newly developed immobilization protocol, demonstrating effective activation and optimal amination using a 2% APTES solution, achieved in 5 min at room temperature. Fluorescence imaging provided clear contrast between the SP and the MC forms. Furthermore, we discuss limitations in the surface density of functional groups and steric hindrance and propose future improvements. Our work not only underscores the versatility of spiropyran in surface patterning but also provides optimized protocols for its immobilization and characterization on SiO2 surfaces, which may be adapted for use on other substrates. These advancements lay the groundwork for on-chip sensing technologies and other applications.

90% Yield Production of Spiropyran Covalently Grafted MXene‐Based RRAM Devices for Optoelectronic Dual‐Response Switching

AbstractOver 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.

Construction of photo-responsive lignin as a broad-spectrum sunscreen agent

Lignin has potential to serve as promising sunscreen agents as it has good ultraviolet (UV) absorption and antioxidant properties. However, the weak absorption capacity of lignin in the long-wave UV region (UVA, 320–400 nm) limits its further development. In this work, a spiropyran-modified lignin (DLSP) with photo-responsive property was prepared by in-situ construction of spiropyran (SP) structure in the demethylated lignin (DL). Due to the presence of SP moiety, the absorption of DLSP in the UVA region was significantly improved. Under UV irradiation, its absorption peak was redshifted as unconjugated SP form isomerized to conjugated merocyanine (MC) form, and the UVA/UVB ratio increased from 0.62 to 0.74. The free-radical scavenging ability of lignin could protect SP from photodegradation, which provided DLSP excellent fatigue resistance. DLSP were blended into creams to investigate its sunscreen performance. Results indicated that DLSP exhibited radiation-enhanced sunscreen performance, the sun protection factor (SPF) of cream containing 10 wt% of DLSP improved from 20 to 67 after 8 h of UV irradiation. Moreover, DLSP showed low skin penetration and good biocompatibility. These results provide a useful guideline for the rational design of sunscreens with special functionalities.

Single- and Double-Pulse Laser Kinetic Spectroscopy of Indoline Spiropyran

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.

Photoresponsive Spiropyran and DEGMA-Based Copolymers with Photo-Switchable Glass Transition Temperatures.

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 = 365nm), 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.

Electrochemical investigation of a photochromic spiropyran containing a pyrrolidinofullerene moiety

Reversible transformations of a hybrid molecule based on [60]fullerene and a spiropyran moiety under conditions of combined photo- and electrochemical exposure were found. It has been established that the electrochemical oxidation of the UV-photoinduced colored form of the hybrid spiropyran in solution significantly accelerates the discoloration process and does not affect the fullerene part of the hybrid molecule. The research results are promising for designing a photo-electrochromic device that modulates electromagnetic radiation in the visible range of the spectrum.

Enaminoketones - functional derivatives based on 7-hydroxy-3′,3′-dimethyl-3′<i>H</i>-spiro[chromen-2,1′-isobenzofuran]-8-carbaldehyde with aromatic amines. physicochemical studies and biological activity

This research focuses on studying derivatives of 2-oxaindane spiropyran by its condensation with aromatic amines. The results showed that all the synthesized compounds are enaminoketones form in both solution and solid state. This is explained by the fact that during the formation of Schiff bases, the proton of the 7-hydroxyl group of the benzopyran part migrates to the azomethine nitrogen, which leads to the transition of the cyclic form of spiropyran into the corresponding enaminoketone. In the DMSO solution, the enaminoketones dynamic equilibrium of the E , Z -isomeric forms were observed. The structure of enaminoketone based on 3,4-dimethylaniline was proved by the X-ray diffraction method. The synthesized compounds were studied for their in vitro anticancer activity against human hepatocellular carcinoma (HepG2), breast carcinoma (MCF-7), lung cancer (A549), and carcinoma cells (KB). Enaminoketone with R = 3,4-СH3Ph is characterized by the highest activity, with IC50 values of 13.38 μM (KB). The results in vitro antioxidant activity test using 1,1-diphenyl-2-picrylhydrazyl (DPPH) indicated that enaminoketones were inactive.

Spiropyran-Based Soft Substrate with SPR, Anti-Reflection and Anti-NRET for Enhanced Visualization/Fluorescence Dual Response to Metal Ions.

The photoluminescence of modified spiropyran on solid surfaces is poor, and the fluorescence intensity of its MC form is weak, which affects its application in the field of sensing. In this work, a PMMA layer containing Au nanoparticles and a spiropyran monomolecular layer are coated on the surface of a PDMS substrate with inverted micro-pyramids successively by means of interface assembly and soft lithography, and the overall structure is similar to insect compound eyes. The anti-reflection effect of the bioinspired structure, the SPR (surface plasmon resonance) effect of the Au nanoparticles and the anti-NRET (non-radiation energy transfer) effect of the PMMA isolation layer raise the fluorescence enhancement factor of the composite substrate vs. the surface MC form of spiropyran to 5.06. In the process of metal ion detection, the composite substrate can achieve both colorimetric and fluorescence response, and the detection limit for Zn2+ can reach 0.281 μM. However, at the same time, the lack of the ability to recognize specific metal ions is expected to be further improved by the modification of spiropyran.

Oxazine as an efficient precursor for the development of photochromic spiropyrans

Spiropyran derivatives were synthesized through an alternate synthetic route that passed through a photochromic [1,3]-oxazine. The structures of the new spiropyran derivatives were established with the assistance of spectroscopic methods and single-crystal X-ray crystallography. The photochemistry of the spiropyran derivatives was investigated using a suitable wavelength of UV and visible light. Density functional theory (DFT) was exploited as a predictive tool to understand the unique organic transformation, which supported the conversion of photochromic oxazine into the spiropyran through consideration of the stability of the intermediates, transition state, and H-bonds. A comparison of solvation energies calculated for different isomers suggested greater solvation of colored isomers of oxazine structure as compared to the colored isomers of spiropyran form.

Binuclear coordination complex of open merocyanine form of photochromic spiropyran with MnII(hfac)2 having high spin (S = 5) ground state

The interaction of 1,3,3-trimethylindolino-β-naphthopyrylospiran (TMI-NPS) with manganese(ii) hexafluoroacetylacetonate yields crystals of {MnII(hfac)2 (μ2-TMI-NPS)}2 (1) in which Mn(ii) atoms are bridged by oxygen atoms of ring-opened TMS-BPI into the dimer.

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental-Theoretical Approach to Photophysical Properties and Self-Assembly.

This joint experimental-theoretical work focuses on molecular and photophysical properties of the spiropyran-containing amphiphilic molecule in organic and aqueous solutions. Being dissolved in tested organic solvents, the system demonstrates positive photochromism, i.e., upon UV stimulus the colorless spiropyran form is transformed into colorful merocyanine isomer. However, the aqueous solution of the amphiphile possesses a negative photochromism: the orange-red merocyanine form becomes thermodynamically more stable in water, and both UV and vis stimuli lead to the partial or complete photobleaching of the solution. The explanation of this phenomenon is given on the basis of density functional theory calculations and classical modeling including thermodynamic integration. The simulations reveal that stabilization of merocyanine in water proceeds with the energy of ca. 70 kJ mol, and that the Helmholtz free energy of hydration of merocyanine form is 100 kJ mol lower as compared to the behavior of SP isomer in water. The explanation of such a difference lies in the molecular properties of the merocyanine: after ring-opening reaction this molecule transforms into a zwitterionic form, as evidenced by the electrostatic potential plotted around the opened form. The presence of three charged groups on the periphery of a flat conjugated backbone stimulates the self-assembly of merocyanine molecules in water, ending up with the formation of elongated associates with stack-like building blocks, as shown in molecular dynamics simulations of the aqueous solution with the concentration above critical micelle concentration. Our quantitative evaluation of the hydrophilicity switching in spiropyran/merocyanine containing surfactants may prompt the search for new systems, including colloidal and polymeric ones, aiming at remote tuning of their morphology, which could give new promising shapes and patterns for the needs of modern nanotechnology.

DFT modeling of indoline spiropyrans with a cationic substituent in the gas phase

Isomeric forms of indoline spiropyrans show unusual behavior compared with similar compounds, according to experimental data. DFT modeling for gas phase was made to consider the simplest case without environmental effects, which revealed the intramolecular reasons for occurrence of ring opening reaction depending on the particular structure of the compound. The questions of charge redistributions, the changes of geometry and chemical bonds in the structures are also discussed.

Grafting parameters and surface free energy components of photosensitive poly(methacrylated spiropyran) brushes

Poly(methacrylated spiropyran) (P(MMASP)) brushes on silicon wafers were synthesized using the interface-mediated RAFT polymerization of methacrylated spiropyran (MMASP) monomers to determine their grafting density and surface free energy changes during photoinitiation. The grafting parameters of P(MMASP) layers such as the grafting density (σ), the radius of gyration (Rg ) and average distance between polymer chains (D) were calculated. It is found that 1.25 P(MMASP) chains covered per nm2 area of wafers, and the distance between chains was 1.0 nm which is smaller than doubled Rg , 1.1 nm. Thus, P(MMASP) chains overlapped each other and forced themselves to stretch away from the interface. We evaluated the surface free energy components of P(MMASP) brushes during photo initiation. Van Oss-Good method was used to calculate the surface free energy components of brushes. It is found that spiropyran (SP)-merocyanine (MC) system significantly influenced the surface energy components of P(MMASP) brushes. The electron acceptor and electron donor surface free energies of SP and MC form of P(MMASP) brushes were found as and respectively. It is concluded that MC form of P(MMASP) brushes possess high base character; whereas, SP forms have low base character.

A substituted benzothiazolinic merocyanine derivative as a reversible, selective, colorimetric and fluorescent probe for HSO4− in aqueous solution

A benzothiazolinic bromide salt of merocyanine form of spiropyran has been synthesized through a coupling reaction between a (3-(2-carboxyethyl)benzo[d]thiazol-3-ium) bromide and 2‑hydroxy-1-naphthaldehyde. The structure of the salt was examined using IR, NMR, and HR-MS techniques. Due to the zwitterionic nature and H-bond formation ability of the product, its affinity towards toxic anions was investigated in 50% aq. MeCN at pH 7.4. The zwitterionic benzothiazolinic bromide salt selectively detected the presence of HSO4−ion in the solution by showing a color change from purple to yellow and displayed a spectral change (hypsochromic shift) in both absorption and fluorescence spectra. The dynamic light scattering and scanning electron microscope studies were utilized to study the aggregation of the merocyanine salt. Moreover, the aggregation was observed to be controlled by light. The 1H NMR studies confirmed the displacement of bromide by HSO4− ion. The computational studies provided details of the complex and conformation stability at the molecular level. To explain the observed absorption spectra further, electronic excitation parameters were calculated using time-dependent density functional theory (TD-DFT).

Spectral study of the structure and properties of complexes of unsubstituted indoline spiropyran with aluminum ions

The methods of absorption electronic and NMR spectroscopy were used to study the processes of complexation during the interaction of molecules of unsubstituted indoline spiropyran with aluminum salts. The mechanism of formation and structure of complexes of two types has been established. Negative photochromism of the complex of the merocyanine form of spiropyran with aluminum ions was found. The stability of metal complexes to the action of various agents has been investigated. Keywords: photochromism, spiropyrans, metal complexes, aluminum salts, electron spectroscopy, NMR spectroscopy.

Spiropyran Photoisomerization Dynamics in Multiresponsive Hydrogels.

Light-responsive, spiropyran-functionalized hydrogels have been used to create reversibly photoactuated structures for applications ranging from microfluidics to nonlinear optics. Tailoring a spiropyran-functionalized hydrogel system for a particular application requires an understanding of how co-monomer composition affects the switching dynamics of the spiropyran chromophore. Such gels are frequently designed to be responsive to different stimuli such as light, temperature, and pH. The coupling of these influences can significantly alter spiropyran behavior in ways not currently well understood. To better understand the influence of responsive co-monomers on the spiropyran isomerization dynamics, we use UV-vis spectroscopy and time-dependent fluorescence intensity measurements to study spiropyran-modified hydrogels polymerized from four common hydrogel precursors of different pH and temperature responsivity: acrylamide, acrylic acid, N-isopropylacrylamide, and 2-(dimethylamino)ethyl methacrylate. In acidic and neutral gels, we observe unusual nonmonotonic, triexponential fluorescence dynamics under 405 nm irradiation that cannot be explicated by either the established spiropyran-merocyanine interconversion model or hydrolysis. To explain these results, we introduce an analytical model of spiropyran interconversions that includes H-aggregated merocyanine and its light-triggered disaggregation under 405 nm irradiation. This model provides an excellent fit to the observed fluorescence dynamics and elucidates exactly how creating an acidic internal gel environment promotes the fast and complete conversion of the hydrophilic merocyanine speciesto the hydrophobic spiropyran form, which is desired in most light-sensitive hydrogel actuators. This can be achieved by incorporating acrylic acid monomers and by minimizing the aggregate concentration. Beyond spiropyran-functionalized gel actuators, these conclusions are particularly critical for nonlinear optical computing applications.

Photochromic spiropyran-based liquid crystals

We present a new type of light responsive self-assembling structures based on a spiropyran photoswitchable unit. The spiropyran central part was modified by functional groups, which enabled the connection of two structurally different elongating parts. Two series of compounds were prepared with reversed orientation of the ester as a linkage group in the molecular core. The properties of the target materials were studied by differential scanning calorimetry and polarized light optical microscopy, which confirmed the presence of a nematic phase for most of the materials. In case of a trifluromethyl-substituted compound, a sequence of nematic – smectic A – smectic C phase was detected and confirmed by X-ray diffraction analysis. The photochromic properties of compounds were studied in solution as well as in mesophases. In the condensed state, UV light-induced switching from the spiropyran form to the merocyanine dye led to isothermal transition from the liquid crystalline phase to the isotropic liquid.

Reversible Adhesion Switching Using Spiropyran Photoisomerization in a High Glass Transition Temperature Polymer

Previous work has shown that photoisomerization of dopant molecules in a polystyrene film can either enhance or suppress its adhesion to a polar glass surface (Mostafavi, S. H. Macromolecules 2018, 51, 2388−2394; Mostafavi, S. H. Macromolecules 2019, 52, 6311–6317). In this paper, a different polymer host, Zeonex (ZX), is used in conjunction with the photochrome spiropyran. Nonpolar ZX has a higher glass transition temperature that makes it resistant to nanoscale mechanical deformations, while the spiropyran (SP) → merocyanine (MC) photoisomerization is a reversible reaction with a large polarity change. Ultraviolet light isomerizes SP to the polar MC form, increasing both the shear and pull-off adhesion forces to a clean glass surface by a factor of 5. Visible irradiation switches it back to the nonpolar SP form and returns the film back to its original weak adhesion, in contrast to the previously studied polystyrene films. The ability of visible light to switch off the polymer–glass adhesion is harnessed to make a light-controlled payload release device as well as to accelerate the polymer film delamination rate in water by a factor of 100. The kinetics of the water delamination, as well as the origin of residual adhesion after switching back to the SP form, are investigated. This work demonstrates how light-controlled noncovalent adhesion can be used as a solvent-free method to remove protective coatings or to disassemble structures.