Search Results (207)

Photochromic compounds have attracted much attention for their potential applications in photo-actuators, optoelectronic devices and optical recording techniques. This interest is driven by their key photochemical and photophysical properties, which can be reversibly modulated by light irradiation. Among them, diarylethene compounds have garnered extensive investigation due to their excellent thermal stability of both open- and closed-form isomers, robust fatigue resistance, high photocyclization quantum yield and good photochromic performance in both solution and solid phases. However, a notable limitation in expanding the utility of diarylethene compounds is the necessity for ultraviolet light to induce their photochromism. This requirement poses challenges, as ultraviolet light can be detrimental to biological tissues, and its penetration is often restricted in various media. This review provides an overview of design strategies employed in the development of visible-light-responsive diarylethene compounds. These design strategies serve as a guideline for molecular design, with the potential to significantly broaden the applications of all-visible-light-activated diarylethene compounds in the realms of materials science and biomedical science. Full article

Photochromic inks have shown disadvantages, such as poor durability and high cost. Self-healable hydrogels have shown photostability and durability. Herein, a viologen-based covalent polymer was printed onto a paper surface toward the development of a multi-stimuli responsive chromogenic sheet with thermochromic, photochromic, and vapochromic properties. Viologen polymer was created by polymerizing a dialdehyde-based viologen with a hydroxyl-bearing dihydrazide in an acidic aqueous medium. The viologen polymer was well immobilized as a colorimetric agent into a polyvinyl alcohol (PVA)/tricarboxy cellulose (TCC)-based self-healable hydrogel. The viologen/hydrogel nanocomposite films were applied onto a paper surface. The coloration measurements showed that when exposed to ultraviolet light, the orange layer printed on the paper surface switched to green. The photochromic film was used to develop anti-counterfeiting prints using the organic hydrogel composed of a PVA/TCC composite and a viologen polymer. Reversible photochromism with strong photostability was observed when the printed papers were exposed to UV irradiation. A detection limit was monitored in the range of 0.5–300 ppm for NH_3(aq). The exposure to heat (70 °C) was found to reversibly initiate a colorimetric change. Full article

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. Full article

The operation of bacteriorhodopsin (BR) from the archaeon Halobacterium salinarum is based on the photochromic reaction of isomerization of the chromophore group (the retinal protonated Schiff base, RPSB) from the all-trans to the 13-cis form. The ultrafast dynamics of the reverse 13-cis → all-trans photoreaction was studied using femtosecond transient absorption spectroscopy in comparison with the forward photoreaction. The forward photoreaction was initiated by photoexcitation of BR by pulse I (540 nm). The reverse photoreaction was initiated by photoexcitation of the product K₅₉₀ at an early stage of its formation (5 ps) by pulse II (660 nm). The conversion of the excited K₅₉₀ to the ground state proceeds at times of 0.19, 1.1, and 16 ps with the relative contributions of ~20/60/20, respectively. All these decay channels lead to the formation of the initial state of BR as a product with a quantum yield of ~1. This state is preceded by vibrationally excited intermediates, the relaxation of which occurs in the 16 ps time range. Likely, the heterogeneity of the excited state of K₅₉₀ is determined by the heterogeneity of its chromophore center. The forward photoreaction includes two components—0.52 and 3.5 ps, with the relative contributions of 91/9, respectively. The reverse photoreaction initiated from K₅₉₀ proceeds more efficiently in the conical intersection (CI) region but on the whole at a lower rate compared to the forward photoreaction, due to significant heterogeneity of the potential energy surface. Full article

The doping process is a unique method of changing the microstructure of a material, influencing its mechanical, thermal, and optical properties. Typically, the doping process is carried out via chemical reagents. In this work, we present a “green” method of doping photochromic TiO₂ via low-temperature plasma. The doping agent was the electrode material that was sputtered during plasma burning. The process of electrode sputtering is confirmed by the emission spectroscopy data of the plasma zone and the mass loss of the electrodes. The doping process was confirmed by X-ray, Raman spectroscopy, and XPS analyses. The role of the dopant nature and the action of diaphragm discharge in improving the photochromic properties of titanium dioxide is considered. Full article

This study explores the modeling, design, simulation, and testing of a new composite material designed for high-strength and high-temperature resistance in in-space optical mining, examining its properties at both the polymer and atomic/molecular levels. At the polymer level, the investigation includes mechanical and thermal performance analyses using COMSOL Multiphysics 6.1, employing layerwise theory, equivalent single layer (ESL) theory, and a multiple-model approach for mechanical modeling, alongside virtual thermal experiments simulating laser heating. Experimentally, porous Polyaniline (PANI) films are fabricated via electrochemical polymerization, with variations in voltage and deposition time, to study their morphology, optical performance, and electrochemical behavior. At the atomic and molecular levels, this study involves modeling the composite material, composed of Nomex, Kevlar, and Spirooxazine-Doped PANI, and simulating its behavior. The significance of this work lies in developing a novel composite material for in-space optical mining, integrating it into optical mining systems, and introducing innovative thermal management solutions, which contribute to future space exploration by improving resource efficiency and sustainability, while also enhancing the understanding of PANI film properties for in-space applications. Full article

Ionic liquid crystals (ILCs), a class of soft matter materials whose properties can be tuned by the wise pairing of the cation and anion, have recently emerged as promising candidates for different applications, combining the characteristics of ionic liquids and liquid crystals. Among those potential uses, this review aims to cover chromogenic ILCs. In this context, examples of photo-, electro- and thermochromism based on ILCs are provided. Furthermore, thermotropic and lyotropic ionic liquid crystals are also summarised, including the most common chemical and phase structures, as well as the advantages of confining these materials. This manuscript also comprises the following main experimental techniques used to characterise ILCs: Differential Scanning Calorimetry (DSC), Polarised Optical Microscopy (POM) and X-Ray Powder Diffraction (XRD). Chromogenic ILCs can be interesting smart materials for energy and health purposes. Full article

The art of dyeing textiles has a long history, as natural dyes have been used since prehistoric times. With the development of synthetic dyes in the 19th century, the focus shifted from natural to synthetic dyes due to their superior properties. Recently, however, interest in natural dyes has increased again due to environmental and health concerns. Among industrial dyes, heterocyclic dyes, especially azo dyes, are of great importance due to their color brilliance and fastness. This review examines the synthesis, application, and analysis of azo dyes, especially heterocyclic dyes. It deals with monoazo, diazo, and polyazo dyes and highlights their structures, synthesis methods, and fastness properties. In addition, the ecological impact of azo dyes and practical solutions for their synthesis and application are discussed. Full article

The recyclable paper based on photochromic materials not only reduces the pollution in the paper manufacture process, but also reduces the pollution caused by the use of ink, which receives wide attention. In this paper, a series of phosphomolybdic acid–phosphotungstic acid/ZnO/polyvinylpyrrolidone (PMoA-PWA/ZnO/PVP) hybrid films, which had different ratio of PMoA/PWA, was prepared by the ultrasonic composite method. The results indicated that the hybrid film prepared when the ratio of PMoA to PWA was 3 had the best photochromic performance. In this system, ZnO was the photosensitizer, while PMoA/PWA was the chromophore. The photochromic mechanism of the PMoA-PWA/ZnO/PVP hybrid film was based on the photogenerated electron transfer mechanism. ZnO generated photoelectron under the excitation of visible light, then PMoA and PWA obtained the photoelectron and produced photoreduction reaction to generate heteropolyblue. The visible light photochromic paper was prepared by loaded PMoA-PWA/ZnO/PVP hybrid film (A₃) on A4 paper. Application tests showed that the prepared paper had extremely stable, excellent and reversible visible light photochromic properties, whether it was printing patterns or words, and could replace ordinary paper to realize the reuse of paper. Full article

Tungsten oxide (WO₃) is known for its photochromic properties, making it useful for smart windows, displays, and sensors. However, its small bandgap leads to rapid recombination of electron–hole pairs, resulting in poor photochromic performance. This study aims to enhance the photochromic properties of WO₃ by synthesizing hexagonal tungsten oxide via hydrothermal synthesis, which increases surface area and internal hydrates. Titanium oxide (TiO₂) was adsorbed onto the tungsten oxide to inject additional charges and reduce electron–hole recombination. Additionally, polyvinylpyrrolidone (PVP) was used to improve dispersion in organic solvents, allowing for the fabrication of high-quality films using the doctor blade method. Characterization confirmed the enhanced surface area, crystal structure, and dispersion stability. Reflectance and transmittance measurements demonstrated significant improvements in photochromic properties due to the composite structure. These findings suggest that the introduction of TiO₂ and PVP to tungsten oxide effectively enhances its photochromic performance, broadening its applicability in various advanced photochromic applications. Full article

Photochromic polycaprolactone (PCL) nanofibers were prepared through electrospinning. Various factors, including the solvent system, the concentration of PCL, the viscosity of the solution, and the electrical conductivity, influence the morphology of PCL nanofibers. A binary solvent system can dissolve PCL, control fiber structure and morphology, and allow solvent evaporation. The photochromic properties of electrospun membranes based on PCL and diethienylethene (DTE) were assessed using the CM-3610a spectrophotometer. The study showed that incorporating DTE into the membrane enables photochromic performance, with the photochromic reaction being reversible. The analysis of the color-change kinetics showed that the mechanism of photo cycling during colorization was linked to the amplitude of the fast and slow mechanisms, which depended on the formulation tested. The study showed that the photoreversion of the membrane under visible illumination occurs according to first-order kinetics. This work presented the design and manufacturing of photochromic membranes through electrospinning, which offers rapid color change rates, adjustable color fade times, superior reversibility, and reproducibility over at least 10 cycles. The thermochromic properties are proportional to the DTE concentration used, making it possible to obtain color variations with a delta E of 13 and 38 for concentrations ranging from 0.95 to 11.4 wt.%. Full article

A visible-light photochromic hybrid film was synthesized based on combining phosphomolybdic acid (PMoA) with the polythiophene (PTh) matrix. The microstructure and photochromic properties of the materials were analyzed through atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectra (UV-vis). According to FTIR spectra, the geometries of PMoA and PTh were well preserved in hybrid film and there exists a strong interaction at the interface of PMoA and PTh. The XPS spectra revealed the change in the chemical microenvironment and the reduction of Mo⁶⁺ atoms in the photoreduction reaction. Under visible light irradiation, the composite film changed from transparent to blue and deepened gradually, generating heteropoly blue. The hybrid film also shows reversibility in the presence of oxygen. The results indicated that the photochromic reaction was inconsistent with photoinduced electron transfer mechanism. Full article

In daily life, counterfeit and substandard products, particularly currency, medicine, food, and confidential documents, are capable of bringing about very serious consequences. The development of anti-counterfeiting and authentication technologies with multilevel securities is a powerful means to overcome this challenge. Among various anti-counterfeiting technologies, fluorescent anti-counterfeiting technology is well-known and commonly used to fight counterfeiters due to its wide material source, low cost, simple usage, good concealment, and simple response mechanism. Spiropyran is favored by scientists in the fields of anti-counterfeiting and information encryption due to its reversible photochromic property. Here, we summarize the current available spiropyran-based fluorescent materials from design to anti-counterfeiting applications. This review will be help scientists to design and develop fluorescent anti-counterfeiting materials with high security, high performance, quick response, and high anti-counterfeiting level. Full article

In recent years, significant advancements have been made in the research of photoswitchable probes. These probes undergo reversible structural and electronic changes upon light exposure, thus exhibiting vast potential in molecular detection, biological imaging, material science, and information storage. Through precisely engineered molecular structures, the photoswitchable probes can toggle between “on” and “off” states at specific wavelengths, enabling highly sensitive and selective detection of targeted analytes. This review systematically presents photoswitchable fluorescent and colorimetric probes built on various molecular photoswitches, primarily focusing on the types involving photoswitching in their detection and/or signal response processes. It begins with an analysis of various molecular photoswitches, including their photophysical properties, photoisomerization and photochromic mechanisms, and fundamental design concepts for constructing photoswitchable probes. The article then elaborates on the applications of these probes in detecting diverse targets, including cations, anions, small molecules, and biomacromolecules. Finally, it offers perspectives on the current state and future development of photoswitchable probes. This review aims to provide a clear introduction for researchers in the field and guidance for the design and application of new, efficient fluorescent and colorimetric probes. Full article

Gelatin films are very versatile materials whose properties can be tuned through functionalization with different systems. This work investigates the influence of WO₃ nanoparticles on the swelling, barrier, mechanical, and photochromic properties of gelatin films. To this purpose, polyvinylpirrolidone (PVP)-stabilized WO₃ nanoparticles were loaded on gelatin films at two different pH values, namely, 4 and 7. The values of swelling and solubility of functionalized films displayed a reduction of around 50% in comparison to those of pristine, unloaded films. In agreement, WO₃ nanoparticles provoked a significant decrease in water vapor permeability, whereas the decrease in the values of elastic modulus (from about 2.0 to 0.7 MPa) and stress at break (from about 2.5 to 1.4 MPa) can be ascribed to the discontinuity created by the nanoparticles inside the films. The results of differential scanning calorimetry and X-ray diffraction analysis suggest that interaction of PVP with gelatin reduce gelatin renaturation. No significant differences were found between the samples prepared at pH 4 and 7, whereas crosslinking with glutaraldehyde greatly influenced the properties of gelatin films. Moreover, the incorporation of WO₃ nanoparticles in gelatin films, especially in the absence of glutaraldehyde, conferred excellent photochromic properties, inducing the appearance of an intense blue color after a few seconds of light irradiation and providing good resistance to several irradiation cycles. Full article