Photochromic Groups Research Articles

Ionic Hydrogen-Bonded Organic Frameworks with a Two-Photon Synergistic Color Change and Their Information Encryption Applications.

Photochromic hydrogen-bonded organic frameworks (HOFs) can introduce different luminescent functional groups to achieve synergistic controlled multiple color change properties, which are in great demand for diverse information encryption applications. We report in this paper switchable photochromic and photoluminescent dual luminescent functional group HOFs constructed with synergistic effects by N,N'-bis(2-phenylalanine)-1,4,5,8-naphthalenediimine (H2PheNDI) and benzenecarboximidamide 4,4'-azobis(hydrochloride) (AZBH). The crystal powder of iHOF-41 is orange-red in color, which can be changed to black under the irradiation of a 365 nm ultraviolet (UV) light source for 15 min. The photoisomerization rate of the crystal solution under continuous UV irradiation for 5 h was close to 99%. The composite membranes can achieve the properties of photochromism and photoluminescence when they are discolored under 365 nm UV irradiation and, at the same time, excite red bright fluorescence. This work achieves the construction of HOFs based on switching biluminescent functional groups and explores the synergistic mechanism of the photoisomerization process and photochromism as well as its practical application in information encryption.

Exciting Novel Polyaspartates: Design, Synthesis, and Photo-Responsive Behavior in Solution and Lyotropic Liquid Crystalline Phase Upon Irradiation with Visible Light.

Many polypeptides form stable, helical secondary structures enabling the formation of lyotropic liquid crystalline (LLC) phases. Contrary to the well-studied polyglutamate, their counterparts based on polyaspartates exhibit a much lower helix inversion barrier. Therefore, the helix sense is not solely dictated by the chirality of the amino acid used, but additionally by the nature and conformation of the polymer sidechain. In this work, polymers responsive to irradiation with visible light are designed achieving conformational transitions from helix-to-coil and helix-to-helix. The synthesis and the application as LLC mesogens of several (co-)polyaspartates bearing ortho-fluorinated azobenzene (FAB) as a photochromic group are presented. Many of the obtained polymers undergo changes in their secondary structure upon E-Z-isomerization of the FAB-containing sidechain. Of special interest are copolymers that exhibit photo-responsive helix inversion without loss of their helical secondary structure. These copolymers form stable LLC phases in helicogenic solvents, where the effect of photo-switching on the macroscopic behavior is studied by NMR spectroscopy. Especially, the irradiation of the different LLC phases of the helix inversion polymers displays a change in the LLC order experienced by the solvent. These peculiar properties are promising for future applications as photo-responsive alignment media for structure elucidation in NMR.

Effects of hydrogen bonding on photo-responsive behavior of healable azobenzene-containing polyurea elastomers

Photo-responsive polymers, obtained by incorporation of photochromic azobenzene groups into polymer, can display reversible photoactuation behavior. However, the damage can cause a reduction in their service scope or service lifetime. It remains a challenge to design healable and reprocessable azobenzene-containing polymers. The polyaddition of isophorone diisocyanate (IPDI) with p-diaminoazobenzene (DAAB) and amino-terminated poly(propylene glycol) (D2000) was performed to prepare the main-chain polyurea elastomer. The hydrogen bonding between urea groups can enhance self-healing of polyurea elastomer, but its influence on photo-responsive behavior of polyurea elastomer is not clear. The proportion of ordered hydrogen bonds was regulated by changing azobenzene content and the ratio of hard/soft segments. The ordered hydrogen bonds played a fundamental role in the maximum peak intensity of polyurea, while they had no direct effect on the photo-responsive efficiency of polyurea. This study provides a feasible way to obtain healable and reprocessable azobenzene-containing polymers.

Large Thermally Irreversible Photoinduced Shift of Selective Light Reflection in Hydrazone-Containing Cholesteric Polymer Systems.

Stimuli responsive liquid crystalline polymers are a unique class of so-called "smart" materials demonstrating various types of mesomorphic structures easily controlled by external fields, including light. In the present work we synthesized and studied a comb-shaped hydrazone-containing copolyacrylate exhibited cholesteric liquid crystalline properties with the pitch length of the helix being tuned under irradiation with light. In the cholesteric phase selective light reflection in the near IR spectral range (1650 nm) was measured and a large blue shift of the reflection peak from 1650 nm to 500 nm was found under blue light (428 or 457 nm) irradiation. This shift is related to the Z-E isomerization of photochromic hydrazone-containing groups and it is photochemically reversible. The improved and faster photo-optical response was found after copolymer doping with 10 wt % of low-molar-mass liquid crystal. It is noteworthy that both, the E and Z isomers of hydrazone photochromic group are thermally stable that enable to achieve a pure photoinduced switch without any dark relaxation at any temperatures. The large photoinduced shift of the selective light reflection, together with thermal bistability, makes such systems promising for applications in photonics.

Effect of Photochromic Contact Lens Wear on Indoor Visual Performance and Patient Satisfaction.

IntroductionTo quantitatively assess visual performance and patient satisfaction during photochromic contact lens (CL) wear in an indoor environment.MethodsThis observational study comprised 82 eyes of 41 healthy subjects (mean age ± standard deviation, 21.7 ± 0.7 years) who had no ophthalmic diseases except for refractive errors at Kitasato University in 2021. We prospectively compared visual acuity, kinetic visual acuity, functional (time-dependent) visual acuity, the maintaining rate of visual acuity, the response time, contrast sensitivity function, higher-order aberrations, and patient satisfaction score for overall vision in such subjects during photochromic and non-photochromic CL wear in such an environment.ResultsThe kinetic visual acuity at 30 km/h was 0.32 ± 0.21 and 0.41 ± 0.24 in the photochromic and non-photochromic CL groups, respectively (p = 0.008). The kinetic visual acuity at 60 km/h was 0.32 ± 0.21 and 0.41 ± 0.24, respectively (p = 0.034). The functional visual acuity was 0.00 ± 0.21 and 0.05 ± 0.25, respectively (p = 0.030). The average response time was 1.19 ± 0.15 s and 1.23 ± 0.15 s, respectively (p = 0.029). The patient satisfaction score for overall visual performance was 4.22 ± 0.11 and 3.59 ± 0.68, respectively (p < 0.001). Otherwise, we found no significant differences in visual acuity, the maintaining rate, higher-order aberrations, or contrast sensitivity function (p = 0.116, p = 0.053, p = 0.371, or p = 0.943). We found no apparent complications such as ocular discomfort, superficial punctate keratitis, conjunctival injection, or infectious keratitis during the observation period.ConclusionsAccording to our experience, the photochromic CL showed good visual quality, especially in terms of kinetic and functional visual acuities and subsequent high patient satisfaction, even in an indoor environment, suggesting its viability of visual correction not only in daily activities but also in indoor sports activities.

Effective Photocatalytic Initiation of Reactive Oxygen Species by a Photoactive Covalent Organic Framework for Oxidation Reactions

Reactive oxygen species (ROS) play a vital role in both chemistry and physiology. Developing effective photocatalysts becomes a feasible approach to trigger the generation of ROS. Herein, a photosensitive covalent organic framework (COF) was rationally designed and constructed by incorporating the photoactive triphenylamine moieties into its skeleton, characterizations of which not only showed the success formation of the highly crystalline and stable framework, but also revealed the photoactive property derived from triphenylamine-based building block. Electron paramagnetic resonance measurements displayed that the COF was an effective photocatalyst for generating ROS with one unpaired electron, that is, superoxide radical anion (O2• –). Subsequently, its high efficiency, selectivity, and reusability in photocatalytic aerobic oxidation of sulfides confirmed that the COF is a promising photocatalyst in the applications of ROS-involved reactions, demonstrating that precisely embedding organic photochromic groups into COFs could be a powerful strategy to fabricate metal-free heterogeneous photocatalysts for targeted reactions.

A Mononuclear Iron(II) Spin-Crossover Molecule Decorated by Photochromic Azobenzene Group.

Aiming at constructing photoresponsive spin crossover (SCO) behavior, herein we designed a new ligand Abtz (Abtz = (E)-N-(4-((E)-phenyldiazenyl)phenyl)-1-(thiazol-4-yl)methanimine) which was decorated by a photochromic azobenzene group. Based on this photochromic ligand, a mononuclear Fe(II) SCO molecule [Fe(Abtz)3](BF4)2·(EAC)2 (1, EAC = ethyl acetate) was successfully synthesized and showed a complete one-step SCO behavior. Under continuous UV light and blue-light exposure, the cis–trans photoisomerization of both ligand Abtz and compound 1 in the liquid phase was confirmed through UV–Vis spectra. Moreover, the 1H-NMR spectra of Abtz reveal a trans–cis conversion ratio of 37%. Although the UV–Vis spectra reveal the photochromic behavior for 1 in the solution phase, the SCO behavior in the liquid state is absent according to the variable-temperature Evans method, suggesting the possible decomposition. Moreover, in the solid state, the cis–trans photoisomerization of both Abtz and 1 was not observed, due to the steric hindrance.

Photopharmacology of Ion Channels through the Light of the Computational Microscope.

The optical control and investigation of neuronal activity can be achieved and carried out with photoswitchable ligands. Such compounds are designed in a modular fashion, combining a known ligand of the target protein and a photochromic group, as well as an additional electrophilic group for tethered ligands. Such a design strategy can be optimized by including structural data. In addition to experimental structures, computational methods (such as homology modeling, molecular docking, molecular dynamics and enhanced sampling techniques) can provide structural insights to guide photoswitch design and to understand the observed light-regulated effects. This review discusses the application of such structure-based computational methods to photoswitchable ligands targeting voltage- and ligand-gated ion channels. Structural mapping may help identify residues near the ligand binding pocket amenable for mutagenesis and covalent attachment. Modeling of the target protein in a complex with the photoswitchable ligand can shed light on the different activities of the two photoswitch isomers and the effect of site-directed mutations on photoswitch binding, as well as ion channel subtype selectivity. The examples presented here show how the integration of computational modeling with experimental data can greatly facilitate photoswitchable ligand design and optimization. Recent advances in structural biology, both experimental and computational, are expected to further strengthen this rational photopharmacology approach.

Azobenzene-isoxazoline as photopharmacological ligand for optical control of insect GABA receptor and behavior.

Photopharmacology is a fast-growing photonics-based technology, which realizes the high-resolution regulation of drugs in time and space through light. The purpose of this research was to introduce photochromic groups into the isoxazoline structure to realize the regulation of γ-Aminobutyric acid receptors (GABARs) targeting insect behavior. Azobenzene-Fluralaner analogs ABF02, ABF03 and ABF04 have been proven to have larvicidal activity against mosquito larvae. Cis-ABF03 had excellent larvicidal activity against mosquito larvae with a median lethal concentration (LC50 ) value of 1.63, which was better than that of trans-ABF03 (LC50 =3.90). In particular, ABF03 also showed insecticidal activity against Mythimna separata. Further experiments showed that ABF03 (1μm) induced depolarization of dorsal unpaired median neurons after ultraviolet light irradiation, enhanced affinity to the receptor, and blocked ligand-gated chloride channels of GABARs. ABF03 (1μm) realized the real-time photoregulation of the behavior of mosquito larvae, which indicated that the synthesized ligand can complete the binding and off-target action of drugs and targets in vivo under the regulation of light. Azobenzene-Isoxazoline as photopharmacological ligand was synthesized and evaluated for optical control of insect GABARs and behavior for the first time. ABF03 completed the differential regulation of cockroach neurons and the real-time reversible regulation of insect behavior. The establishment of photochromic ligands provides a new strategy for basic and convenience-oriented research on GABARs in invertebrates. © 2021 Society of Chemical Industry.

The Unusual Photochromic and Hydrochromic Switching Behavior of Cellulose-Embedded 1,8-Naphthalimide-Viologen Derivatives in the Solid-State.

Stimuli-responsive chromic materials such as photochromics, hydrochromics, thermochromics, and electrochromics have a long history of capturing the attention of scientists due to their potential industrial applications and novelty in popular culture. However, hybrid chromic materials that combine two or more stimuli-triggered color changing properties are not so well known. Herein, we report a design strategy that has led to a series of emissive 1,8-naphthalimide-viologen dyads which exhibit unusual dual photochromic and hydrochromic switching behavior in the solid-state when embedded in a cellulose matrix. This behavior manifests as reversible solid state fluorescence hydrochromism upon changes in atmospheric relative humidity (RH), and reversible solid state photochromism upon generation of a cellulose-stabilized viologen radical cation. In this design strategy, the bipyridinium unit serves as both a water-sensitive receptor for the hydrochromic fluorophore-receptor system, and a photochromic group, capable of eliciting its own visible colorimetric response, generating a fluorescence quenching radical cation with prolonged exposure to ultraviolet (UV) light. These dyes can be inkjet-printed onto cellulose paper or drop-cast as cellulose powder-based films and can be unidirectionally cycled between three different states which can be characteristically visualized under UV light or visible light. The material's photochromism, hydrochromism, and underlying mechanism of action was investigated using computational analysis, dynamic vapor sorption/desorption isotherms, electron paramagnetic resonance spectroscopy, and variable humidity UV-Vis adsorption and fluorescence spectroscopies.

Incorporating Photochromic Triphenylamine into a Zirconium-Organic Framework for Highly Effective Photocatalytic Aerobic Oxidation of Sulfides.

A zirconium-based metal-organic framework (MOF) was successfully constructed via solvothermal assembly of a triphenylamine-based tricarboxylate ligand and Zr(IV) salt, the structure simulation of which revealed that it possesses a two-dimensional layered framework with a relatively rare dodecnuclear Zr12 cluster as the inorganic building unit. The inherent photo-responsive property derived from the incorporated photochromic triphenylamine groups combined with its high stability makes the constructed MOF an efficient heterogeneous photocatalyst for the oxidation of sulfides, which is a fundamentally important reaction type in both environmental and pharmaceutical industries. The photocatalytic activity of the constructed MOF was first investigated under various conditions with thioanisole as a representative sulfide substrate. The MOF exhibited both high efficiency and selectivity on aerobic oxidation of thioanisole in methanol utilizing molecular oxygen in air as the oxidant under blue light irradiation for 10 h. Its high photocatalytic performance was also observed when extending the sulfide substrate to diverse thioanisole derivatives and even a sulfur-containing nerve agent simulant (2-chloroethyl ethyl sulfide). The high photocatalytic efficiency and selectivity to a broad set of sulfide substrates make the triphenylamine-incorporating zirconium-based MOF a highly promising heterogeneous photocatalyst.

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Synthesis and radical copolymerization of 2‐(4‐((4‐isocyanophenyl)diazenyl)phenoxy)ethyl‐3‐phenylacrylate with maleic anhydride

AbstractA monomer containing a photochromic group was synthesized by condensation of 4‐(2‐hydroxyethyloxy)‐4‐cyanoazobenzene with cinnamoyl chloride. The structure and composition of the monomer were established by FTIR, UV–Vis, 1H NMR spectroscopy, and elemental analysis. The values of chemical shifts, multiplicity, and integrated intensity of 1H signals in one‐dimensional NMR spectra of the monomer were determined, and the homo‐ and heteronuclear interactions were found. The crystal structure of 4‐(2‐hydroxyethyloxy)‐4‐cyanoazobenzene was established using X‐ray diffraction analysis. A copolymer containing photochromic mesogenic fragment was synthesized by radical copolymerization of 2‐(4‐((4‐isocyanophenyl)diazenyl)phenoxy)ethyl‐3‐phenylacrylate with maleic anhydride.

Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains

Multi-stimuli-responsive field-effect transistors (FETs) with organic/polymeric semiconductors have received increasing attention. Herein, we report a novel strategy for fabricating multi-stimuli-r...

Light- and temperature-responsive micellar carriers prepared by spiropyran-initiated atom transfer polymerization: Investigation of photochromism kinetics, responsivities, and controlled release of doxorubicin

Stimuli-responsive block copolymer assemblies are a significant class of smart materials extensively studied for advanced applications such as drug- and gen-delivery systems. Different types of light- and temperature-responsive polymer assemblies containing photochromic spiropyran chain end groups, temperature-responsive poly (N-isopropylacrylamide) (PNIPAM) block, and hydrophobic poly (methyl methacrylate) (PMMA) block were developed. These amphiphilic block copolymers with the ability of self-assembly to micellar structures were synthesized using spiropyran-initiated atom transfer radical polymerization. Regarding the hydrophilic fraction (0.5<fphilic), the amphiphilic block copolymers were self-assembled to spherical micelles in aqueous media as confirmed by TEM images. The size of these polymer assemblies was changed in response to temperature changes and also UV light (365 nm) irradiation. The results of UV–Vis spectroscopy display that photochromic behavior, the kinetics of spiropyran (SP) to merocyanine (MC) and MC to SP isomerizations were significantly affected by the polarity of the polymer blocks in neighboring of the spiropyran chain end group. The lower critical solution temperature (LCST) of PNIPAM shows a shift from 26.5 to 37.5 °C after isomerization of the SP to MC, as a result of increase of its polarity and water-solubility. The doxorubicin (DOX) release can be controlled by pH, temperature, and light by using of multi-responsive block copolymer micelles as smart drug carriers. The release efficiency was reached to 60–85% at pH 5.3, 80–90% at temperatures of above LCST of PNIPAM (40 °C), and also 90–100% under UV irradiation after 48 h. The results display that stimuli-responsive polymer assemblies based on amphiphilic block copolymers containing spiropyran chain end groups are applicable in smart drug-delivery systems, and offer controlling over drug-release by different triggers, such as light irradiation, pH variation, and temperature changes.

The Effects of Side Chains on the Charge Mobilities and Functionalities of Semiconducting Conjugated Polymers beyond Solubilities.

Recent decades have witnessed the rapid development of semiconducting polymers in terms of high charge mobilities and applications in transistors. Significant efforts have been made to develop various conjugated frameworks and linkers. However, studies are increasingly demonstrating that the side chains of semiconducting polymers can significantly affect interchain packing, thin film crystallinity, and thus semiconducting performance. Ways to modify the side alkyl chains to improve the interchain packing order and charge mobilities for conjugated polymers are first discussed. It is shown that modifying the branching chains by moving the branching points away from the backbones can boost the charge mobilities, which can also be improved through partially replacing branching chains with linear ones. Second, the effects of side chains with heteroatoms and functional groups are discussed. The siloxane-terminated side chains are utilized to enhance the semiconducting properties. The fluorinated alkyl chains are beneficial for improving both charge mobility and air stability. Incorporating H bonding group side chains can improve thin film crystallinities and boost charge mobilities. Notably, incorporating functional groups (e.g., glycol, tetrathiafulvalene, and thymine) into side chains can improve the selectivity of field-effect transistor (FET)-based sensors, while photochromic group containing side chains in conjugated polymers result in photoresponsive semiconductors and optically tunable FETs.

Synthesis and application of reversible fluorescent photochromic molecules based on tetraphenylethylene and photochromic groups

In molecules with both AIE and photochromic properties, light exchange between absorption and fluorescence is reversible under alternating UV/visible treatment.

Low-temperature nematic phase in azo functionalised reactive hockey stick mesogens possessing lateral methyl group

We report, the design, synthesis and mesomorphic behaviour of new hockey stick mesogens containing photochromic azo group and a reactive double bond. The structure of the compounds resemble the hockey stick due to unequal distribution of the phenyl rings in the two arms of the molecule and possess a reactive 4-n-undecenyloxy chain attached at short arm of the bent-core molecule, while the elongated arm consists of a small methoxy group and photochromic azo linkage between two phenyl rings. All the compounds exhibit a wide-range of enantiotropic nematic phase at low temperature. The photo-responsive behaviour of nematic phase was characterized by polarising optical microscopy with in situ white light irradiation. Upon irradiation, the nematic phase almost completely disappeared in about 20s. We have also investigated the effect of the position of methyl group substitution at the outer phenyl ring of the elongated arm of the molecule on the nematic phase of azo functionalised compounds. Our theoretical calculations predict that different position of methyl group does not bring any significant change in reactivity profile, electronic properties and spectroscopic properties. Irrespective of the position of a methyl group, trans conformation has slightly greater stability as well as less reactivity than cis conformation.

Metal-Organic Nanosheets Step into the Spotlight

In this issue of Chem, Moorthy and co-workers show that integrating photochromic groups into metal-organic frameworks introduces the potential to make responsive functional materials. However, the systems are responsive to light only when separated into two-dimensional nanosheets.

Photoswitchable phospholipid FRET acceptor: Detergent free intermembrane transfer assay of fluorescent lipid analogs

We have developed and characterized a novel photoswitchable phospholipid analog termed N-nitroBIPS-DPPG. The fluorescence can be switched on and off repeatedly with minimal photobleaching by UV or visible light exposure, respectively. The rather large photochromic head group is inserted deeply into the interfacial membrane region conferring a conical overall lipid shape, preference for a positive curvature and only minimal intermembrane transfer. Utilizing the switchable NBD fluorescence quenching ability of N-nitroBIPS-DPPG, a detergent free intermembrane transfer assay system for NBD modified lipids was demonstrated and validated. As NBD quenching can be turned off, total NBD associated sample fluorescence can be determined without the need of detergents. This not only reduces detergent associated systematic errors, but also simplifies assay handling and allows assay extension to detergent insoluble lipid species.