Spiropyran, chromene and spirooxazine, mélange á trois: Molecular logic systems through selective and reversible deactivation of photochromism mediated by CO2 gas

We report a new expanded molecular logic system based upon combinations of spiropyrans, spirooxazines and chromenes, whereby the photochromism of some molecules can be selectively preserved while reversibly deactivating the photochromism of others. The non-photochromic molecules can be reversibly activated by CO₂ gas. It was found that the photochromic effect of spiropyrans, in general, and one spirooxazine (with a hydroxyl group on the naphtho-ring) could be reversibly deactivated by DBU, while a chromene and an unsubstituted spirooxazine remained photochromic in the system under the same conditions. The presence of protic solvent was necessary for the deactivation of some of these photochromic molecules and hence it was used as an additional sensitizer in the system. This afforded the expansion of stimuli for molecular logic operations and allowed combinations of the benign stimuli of UV, visible light, CO₂, and CO₂ depleted with protic and aprotic solvents. This effect provided the mechanism for molecular logic systems that do not suffer from the usual problems of dilution effects and hence become truly reversible. This is highly significant when designing molecular switches to perform logic operations.     

Comment on the matrix effect on photochromism of spiropyrans in bulk polymers

Summary The photochromic behaviour of spiropyran derivatives dissolved in a polymer matrix or incorporated in the backbone of bulk polymers is discussed. The deviations from first order kinetics of the thermal decolouration in glassy specimen are attributed to both influences of local free volume and of different merocyanine isomers during the decolouration reaction. The application of the free volume theory in terms of a WLF-equation is proven for the first time in these systems and conclusions are drawn on chain segmental mobility.     

Photochromic effect of transparent lead-free ferroelectric KSr2Nb5O15 ceramics

Transparent KSr₂Nb₅O₁₅ (KSN) lead-free ferroelectric ceramics have been synthesized via modified pressureless sintering method. A significant photochromic effect was observed for the transparent KSN ceramics prepared without rare-earth dopant modification. The piezoelectric properties depend on the grain orientations were investigated. The optical transmittance of the KSN ceramics is greater than 40% in the wavelength range of 530–800 nm. After NUV irradiation, the absorbance was enhanced by more than 40% in a broad visible range (more than 79%). The absorbance returned to the initial value after a thermal bleaching process. The results of the cycling tests and response experiments showed the stability and saturation of the photochromic effect. In addition, the possible photochromic mechanism of the KSN ceramics is discussed and the photochromic centers are identified. This transparent KSN ceramics exhibits an obvious photochromic effect and is a potential candidate materials for optical data storage and information recording applications.     

Preparation and photochromic properties of waterborne polyurethane containing spirooxazine groups

Two novel photochromic spirooxazines, SO 1 and SO 3, were successfully prepared and characterized by Fourier transform infrared spectroscopy (FTIR), ¹H-NMR, and mass spectrometry with electrospray ionization (ESI-MS). SO 1 was doped and grafted with waterborne polyurethane (WPU) to afford D₁-WPU and G₁-WPU. D₃-WPU was prepared by doping SO 3 with waterborne polyurethane. FTIR spectra indicated that SO 1 was grafted onto waterborne polyurethane successfully. Scanning electron microscopy proved that spirooxazines of D-WPU can be effectively dispersed in a waterborne polyurethane matrix, and spirooxazines of G-WPU are evenly distributed in the copolymer. The results showed that the light transmittance of modified waterborne polyurethane films decreased compared with pure waterborne polyurethane films, but the water resistance and tensile strength were better. Ultraviolet–visible spectra demonstrated that the thermal stability of spirooxazine derivatives improved significantly after being modified. The fading rate constant of the D₃-WPU film (k = 0.0079 s^-1) during the discoloration process decreased 9.77 times in contrast to SO 3 in ethanol, which showed that the thermal stability of spirooxazine in WPU film was obviously enhanced. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47067.     

Electrochromic properties of polycrystalline thin films of tungsten trioxide prepared by chemical vapour deposition

The electrochromic properties of polycrystalline thin films of tungsten trioxide prepared by chemical vapour deposition were studied using cyclic voltametry and chronoamperometry measurements. Two kinds of films were investigated depending on the conditions of preparation. Although the composition of the layers obtained after pyrolysis of W(CO)₆ is influenced by the presence of oxygen flow, the final annealing of these products leads to the same polycrystalline structure. Electrochromic properties have been investigated in acid and hydro-organic electrolytes. Cyclic voltametry shows that both colouration and bleaching of the films are associated with electrochemical reactions. The optical efficiencies and the response times were studied in both media and compared with amorphous WO₃ thin films prepared by vacuum evaporation. Best results have been obtained in acid electrolyte for films prepared by pyrolysis of W(CO)₆ in the presence of oxygen flow. We also observed that cycling greatly enhanced the response time. Current injection during colouration was found to depend strongly on time and to be mainly controlled by the resistance of the electrolyte at short times (f<200 ms).     

Preparation of UV-cured spironaphthooxazine/silica/polyacrylate photochromic hard coatings on plastic substrates

Hard coatings exhibiting photochromic properties were prepared by UV-curing of formulations that incorporated surface-modified silica nanoparticles, hexa-functional curing agent, and organic dye (spironaphthooxazine) on poly(methyl methacrylate) (PMMA) substrates. Spectroscopic studies of the coatings indicated effective photochromic activities over the visible range in response to UV irradiation (365 nm). The color density and bleaching performance were found to depend on the silica and dye contents in the coatings; generally, increasing either quantity could increase the color density and raise the initial bleaching rate, and yet it took a longer time to completely bleach the coatings. Furthermore, the coatings were very hard (8H), attached perfectly (5B) on the substrate, and were much more wear-resistant than pure PMMA against the CS-10 abradant.     

Al-Pillared clay for cottonseed oil bleaching: An optimization study

In this study, Al-pillared white bentonite (Ordu-Unye, Turkey) was used for cottonseed oil bleaching. Pillaring process parameters were optimized in terms of bleaching efficiency as the bleaching capacity of cottonseed oil. The initial cation concentration, hydrolyzing agent ratio, and thermal treatment temperature were chosen as major process parameters. Pillared clays were characterized by FTIR and differential thermal analysis. The bleaching efficiency of bentonite increased from 11.8 to 17.5% by acid activation and to 33.5% by further Al pillaring. The optimal pillaring process conditions for cottonseed bleaching were an initial concentration of AICl₃, of 0.5 M, a OH⁻/Al³⁺ molar ratio of 0.3, and a thermal treatment temperature of 700°C.     

Enhanced photochromism of heteropolyacid/polyvinylpyrolidone composite film by TiO2 doping

Novel composite film was synthesized by TiO₂ doping into phosphomolybdic acid (PMoA)/polyvinylpyrrolidone (PVP) system. The influence of TiO₂ doping on its microstructure and photochromic properties was investigated via atomic force microscopy, transmission electron microscope, Fourier transform infrared spectroscopy (FT‐IR), ultraviolet–visible spectra, and X‐ray photoelectron spectroscopy (XPS). After TiO₂ doping, the surface of TiO₂/PMoA/PVP composite film changed to rough from smooth, and the particle size significantly increased. The FT‐IR results verified that the basic structure of PMoA and PVP were not destroyed in the composite films. The non‐bonded interaction between the acid and polymer was strengthened by TiO₂ doping. Irradiated with UV light, composite films changed from colorless to blue. The TiO₂/PMoA/PVP composite film exhibited a strong photochromic effect and faster bleaching reaction than that of PMoA/PVP film. XPS results indicated that the amount of PMoA in photo‐reductive reaction was increased after TiO₂ doping, which resulted in the photochromic efficiencies enhanced. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41583.     

Lichtinduzierte Polymer- und Polymerisationsreaktionen, 47. Photopolymersysteme mit α-sulfonyldesoxybenzoinen als initiatoren

α-Sulfonyl deoxybenzoines are formed by the reaction of desylchloride with sodium arylsulfinates in good preparative yields. The photolysis of these compounds proceeds with quantum yields of about Φ_in = 0.50. Compared to other photoinitiators, α-sulfonyl deoxybenzoines polymerize methylmethacrylate in acetonitrile solution with moderate polymerization quantum yields only. On the contrary, the yellowing of cured polyester resins using these compounds as photoinitiators is much smaller.     

Curing of epoxy systems at sub‐glass transition temperature

Three epoxy‐amine thermoset systems were cured at a low ambient temperature. Evolution of the reaction kinetics and molecular structure during cure at the sub‐glass transition temperature was followed by DSC and chemorheology experiments. The effect of vitrification and the reaction exotherm on curing and final mechanical properties of the epoxy thermosets was determined. Thermomechanical properties of the low‐temperature cured systems depend on the reaction kinetics and volume of the reaction mixture. Curing of the fast‐reacting system in a large volume (12‐mm thick layer) resulted in the material with T_g exceeding the cure temperature by 70–80°C because of an exothermal temperature rise. However, the reaction in a too large volume (50‐mm layer) led to thermal degradation of the network. In contrast, thin layers (1.5 mm) were severely undercured. Well‐cured epoxy thermosets could be prepared at sub‐T_g temperatures by optimizing reaction conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3669–3676, 2006     

On the photochromic activity of some diphenyl-3H-naphtho[2,1-b]pyran derivatives: Synthesis,NMR characterisation and spectrokinetic studies

The synthesis, NMR and mass spectrometric characterisation of a several novel compounds of the naphthopyran family containing either halogen or phosphonate substituents are reported. All of the compounds exhibited photochromic properties in solution and their thermal bleaching after exposure to polychromatic light was monitored using UV–vis spectrophotometry. The bleaching of the merocyanines from these compounds involved two first-order processes, the first of these being more relevant than the second. The effects of substituents upon bleaching kinetics are discussed.     

Reversible luminescence modulation of Ho‐doped K0.5Na0.5NbO3 piezoelectrics with high luminescence contrast

A significant luminescence modulation behavior based on photochromic reactions was observed in Ho³⁺‐doped (Na_0.52K_0.48)_0.92Li_0.08NbO₃ ceramics, fabricated by the conventional solid‐state reaction method. Under visible light irradiation (407 nm) for 20 second, the samples changed pale gray from initial pale green, and returned to their original color by a thermal stimulus of 230°C for 10 minutes, showing typical photochromic phenomenon. Under 453 nm excitation, the samples exhibited strong green emission at 551 nm. Interestingly, their green emission intensity can be effectively tailored by controlling photochromic reaction processes (irradiation wavelength and time), and the luminescent modulation ratio (ΔR_t) reaches up to 77%. And, the ΔR_t value has no any obvious degradation after 10 cycles by alternating visible light irradiation and thermal stimulus, showing excellent reversibility. These results make it potential applications in many fields as a kind of multifunctional material.     

One‐Pot Synthesis of Polyfunctionalized 4H‐Chromenes and Dihydrocoumarins Based on Copper(II) Bromide‐Catalyzed C?C Coupling of Benzylic Alcohols with Ketene Dithioacetals

The synthesis of polyfunctionalized 4H‐chromenes 3 and dihydrocoumarins 4 has been developed from the same substrates. Catalyzed by copper(II) bromide (0.3 equiv.), the reactions of the easily available ketene dithioacetals 1 with 2‐(hydroxymethyl)phenols 2 lead to 4H‐chromenes 3 in high to excellent yields in dichloromethane solvent, whereas, 3,4‐trans‐disubstituted dihydrocoumarins 4 are obtained in high yields with high diastereoselectivities by prolonging the reaction time or changing the solvent from dichloromethane to acetonitrile.     

Synthesis and photochromic properties of a dithiazolylindole

A novel photochromic 2,3-dithiazolylindole has been synthesized and its photochromic properties was elucidated. This compound showed reversible photochromism both in solution and in a crystal with no spontaneous bleaching under dark conditions. The photocyclization quantum yield of the dithiazolylindole was as high as 83% in hexane, suggesting the photoreactive conformation was stabilized through intramolecular interactions. X-ray crystal structure analysis revealed that the dithiazolylindole adopted the photoreactive conformation with quasi-C₂ symmetry around the hexatriene moiety in the crystalline state. This conformation was assisted by presumed intramolecular CH/N hydrogen bonding between the central N-methylindole and the side-chain thiazolyl units in combination with steric interactions between methyl groups at the reactive center carbons. The suggestion of intramolecular hydrogen bonding in solution was also supported by a ¹H NMR variable temperature study.     

Stretchable photochromic hydrous TiO2-embedded glycerol-poly(dimethylsiloxane) film for rewritable information storage

Photoreversible, color-changing films have great potential in various optical applications. In this study, we developed a photochromic film by embedding droplets of metatitanic acid (hydrous TiO₂) and glycerol in commercially available poly(dimethylsiloxane) (PDMS) silicone elastomers. Benefiting from the electron–hole pair scavenging abilities of glycerol, the resulting film exhibited rapid photoresponse, high photoreversible stability, excellent antiaging capability, and remarkable stretchability. The degree of color changes upon ultraviolet (UV) irradiation was effectively controlled by adjusting both the concentration of hydrous TiO₂ (1–20 wt%) and UV irradiation time (5–30 min), thereby increasing total color-changing ability (ΔE). High-resolution patterns could be repetitively printed, erased, and rewritten (≥20 times) with no significant loss of clarity. After a 30-day exposure to ambient air, there were no significant aging effects in the photochromic ability of the films, thus demonstrating promising potential as rewritable films for information storage.     

Textile applications of photochromic dyes. Part 2: factors affecting the photocoloration of textiles screen‐printed with commercial photochromic dyes

The performance of five commercial photochromic dyes applied by screen printing on textiles was evaluated using a colour measurement methodology which has previously been established and validated. Printing as disperse dyes on polyester gives the strongest photochromic effect when the dye is located near the surface. However, the dyes are applied more effectively using an adaptation of a pigment printing method. Several factors influencing the photochromic properties of the printed textiles were evaluated. The ultraviolet reflecting properties of cotton give a higher level of photocoloration than on polyester. In the dyes studied, the spirooxazines show slightly faster colour development and fade much more rapidly than the naphthopyrans, and the latter show a residual colour after fading. The effect of the ultraviolet irradiation wavelength profile on the photochromic response may be correlated with the ultraviolet absorption spectra of the dyes.     

Tuning Photoswitchable Dual-Color Fluorescence from Core-Shell Polymer Nanoparticles

Core-shell polymeric nanoparticles (NPs) containing photoswitchable spiropyrans (SP) and spirooxazines (SO) within the cores were fabricated. Fluorescence photoswitching studies revealed that the substituent groups on the photochromic SP/SO structures exerted significant influence on the fluorescence photoswitching behaviors of the as-prepared polymeric NPs, such as the reversibly interchangeable fluorescence color and the photoswitching kinetics. The electron-releasing and electron-withdrawing abilities of the substituent groups are believed to play important roles in controlling the electron configuration of the photochromic component and therefore be responsible for the tunable dual-color photoswitching performance.     

基于光控二芳基乙烯的手性向列相液晶体系研究进展

光控手性分子开关结合到液晶材料体系中,可以有效利用其光诱导的手性变化,实现远程光刺激液晶材料的自组装螺旋超结构。二芳基乙烯（DAE）是一类新型的、有前景的光致变色分子,作为智能光响应开关,在手性向列相液晶材料体系中表现出优异的性能。本文重点围绕结构设计,总结了一系列具备不同螺旋扭曲力（HTP）的手性DAE分子及其在液晶自组装螺旋结构中所产生的特定性能,如光可逆宽范围调控和光控手性反转。该类光控DAE手性向列相液晶体系在手性调控、光学显示、可调谐激光等领域具有巨大的应用潜力。最后讨论了该领域面临的挑战和机遇,并指出了未来可能的发展方向。     

Mechanism for the catalytic exchange of methane with deuterium on Pt(111) surfaces

The reaction of methane with deuterium on Pt(111) single crystals was studied using thermal programmed desorption (TPD) under ultra-high vacuum conditions. Methyl groups, believed to result from the dissociative adsorption of methane under catalytic conditions, were deposited directly by thermal decomposition of methyl iodide. TPD experiments after coadsorption with deuterium show that methane formation occurs in very high yields. Furthermore, the desorbing molecules display a bimodal distribution very similar to that obtained under atmospheric pressures, with maxima for CH₃D and CD₄. This distribution can be explained by a competition between two surface reactions, namely, direct incorporation of hydrogen in methyl groups and methylene formation followed by rapid interconversion to methylidyne before final hydrogenation to methane. We found that the rates for both reactions depend linearly on the coverage of methyl groups, but while the hydrogenation rate is also proportional to the coverage of deuterium, in the case of multiple H-D exchange an almost zero order dependence at low temperatures slowly becomes first order as the reaction temperature is increased. The activation energies for CH₃D and CD₄ formation were estimated to be 17.0 and 6.5 kcal/mol respectively even though the reaction rates displayed comparable values because of a compensation effect in the preexponential factors. Finally, the relative yields for CH₂D₂, CHD₃ and CD₄ are close to the equilibrium values, a result that is consistent with the proposed methylene-methylidyne interconversion step in our mechanism.     

基于光控二芳基乙烯的手性向列相液晶体系研究进展

光控手性分子开关结合到液晶材料体系中,可以有效利用其光诱导的手性变化,实现远程光刺激液晶材料的自组装螺旋超结构。二芳基乙烯（DAE）是一类新型的、有前景的光致变色分子,作为智能光响应开关,在手性向列相液晶材料体系中表现出优异的性能。本文重点围绕结构设计,总结了一系列具备不同螺旋扭曲力（HTP）的手性DAE分子及其在液晶自组装螺旋结构中所产生的特定性能,如光可逆宽范围调控和光控手性反转。该类光控DAE手性向列相液晶体系在手性调控、光学显示、可调谐激光等领域具有巨大的应用潜力。最后讨论了该领域面临的挑战和机遇,并指出了未来可能的发展方向。