Reversible Trans-cis Isomerization Research Articles

Modulation of room temperature emission characteristics of heteroleptic ruthenium-terpyridine complexes via aggregation

In this work, we have thoroughly investigated the modulation of room temperature luminescence characteristics of our recently reported stilbene-appended heteroleptic Ru(II)-terpyridine complexes of the type, [(tpy-PhCH3)Ru(tpy-pvp-X)](ClO4)2, wherein X =naphthalene, anthracene, and pyrene moiety via aggregation through the use of appropriate solvent mixtures. Taking profit of the polyaromatic motif, the complexes display both aggregation-induced emission quenching as well as emission augmentation, depending upon nature of the solvent mixtures. By virtue of the presence of stilbene unit, the complexes undergo trans–cis isomerization upon irradiation of light. We have previously investigated the reversible trans–cis isomerization of the non-aggregated form of the complexes upon alternative treatment of visible and UV light. In the present study, we have also undertaken the trans → cis photoisomerization of the aggregated forms of the complexes. The rate constant and quantum yield of photoisomerization in the aggregated form of the complexes are also estimated and compared with their non-aggregated counterparts.

Light-Triggered Reversible Swelling of Azobenzene-Containing Block Copolymer Worms via Confined Deformation Prepared by Polymerization-Induced Self-Assembly.

Stimuli-responsive block copolymer nanoparticles (NPs) have received close attention in recent years owing to their tremendous application potential in smart materials. Azobenzene-containing NPs are widely studied due to the advantages of light as a stimulus and fast reversible trans-cis isomerization of azobenzene chromophores. However, the inefficient preparation process and difficult reversible transformation of morphologies limit their development. Herein it is demonstrated that the light-triggered reversible swelling behavior of wormlike NPs with high azobenzene content could be realized via confined deformation. These worms are prepared in large quantities via polymerization-induced self-assembly based on the copolymerization of 11-(4-(4-butylphenylazo)phenoxy)undecyl methacrylate (MAAz) and N-(methacryloxy)succinimide (NMAS) monomers. Upon UV/visible light irradiation, the reversible deformation of worms is achieved when the feed molar ratio of NMAS/MAAz is relatively high or via crosslinking using diamines, which leads to the reduction of the photoisomerization efficiency. The diameter variation of the worms is influenced by the amount and types of crosslinkers. Moreover, the scalability of this strategy is further proved by the fabrication of photo- and reductant-responsive crosslinked worms. It is expected that this study not only provides a new route to affording reversible photoresponsive NPs but also offers a unique insight into the reversible photodeformation mechanism of azobenzene-containing NPs.

A switchable zinc-based metal organic framework for the light triggered absorption and release of organic dyes

Due to its adjustable pore structure, the metal–organic frameworks (MOFs) have attracted much attention in the treatment of organic dye molecules in wastewater. However, the general tuning of the pore channels of MOFs is mainly by changing the chain length of the organic ligands and metal nodes. This approach not only limits the types of MOFs, but also limits the treatment of a large number of dye methylene blue (MB) and methyl orange (MO) dye molecules in the wastewater. Hence, we synthesized photoresponsive Zn-AzDC/TPA MOF as adsorbents to adsorb and release organic dye molecules in a photo-controlled manner. The photoresponsive Zn-AzDC/TPA was prepared using a mixed ligand strategy, in which the azobenzene carboxylic acid derivative (AzDC) served as a photoresponsive ligand and terephthalic acid (TPA) served as a non-active ligand in coordination with zinc ion. The optical and structural properties of the synthesized Zn-AzDC/TPA was characterized by UV–vis, FT-IR, PXRD, SEM, TEM, TGA, and pore analysis. Interestingly, it was found that the photoresponsive AzDC unit of Zn-AzDC/TPA demonstrated reversible trans–cis isomerization under the alternating UV and visible light, resulting in reversible changes in the pore size of the Zn-AzDC/TPA. Its photoresponse properties can trapp and release dye molecules under light-driven conditions. This result provides a new direction for the application of photoresponsive MOF and also lays a foundation for the study of diversified optically responsive materials.

Luminescent Ruthenium-Terpyridine Complexes Coupled with Stilbene-Appended Naphthalene, Anthracene, and Pyrene Motifs Demonstrate Fluoride Ion Sensing and Reversible Trans-Cis Photoisomerization.

A new family of luminescent heteroleptic Ru(II)-terpyridine complexes coupled with stilbene-appended naphthalene, anthracene, and pyrene motifs is reported. Each of the complexes features moderately intense emission at room temperature having a lifetime of 16.7 ns for naphthalene and 11.4 ns for anthracene, while a substantially elevated lifetime of 8.3 μs was observed for the pyrene derivative. All the three complexes display a reversible couple in the positive potential window due to Ru2+/Ru3+ oxidation but multiple reversible and/or quasi-reversible peaks in the negative potential domain because of the reduction of the terpyridine moieties. All the complexes selectively sense F- among the studied anions via the intermediary of different noncovalent interactions. The interaction event is monitored through absorption, emission, and 1H and 19F NMR spectroscopy. Additionally, upon utilizing the stilbene motif, reversible trans-cis isomerization of the complexes has been undertaken upon alternate treatment of visible and UV light so that the complexes can act as potential photomolecular switches. We also carried out the anion sensing characterization of the cis form of the complexes. Theoretical calculation employing density functional theory is also executed for a selective complex (naphthalene derivative) to elucidate different noncovalent interactions that are operative during the complex-fluoride interplay.

Fabrication and Enzymatic Disorganization of Multiresponse Worm-Like Micelles.

How to fabricate multiresponse worm-like micelles (WLMs) and the corresponding green disposal is still challenging. A strategy of fabricating the surfactant-based WLMs that can respond simultaneously to light, heat, and pH was developed by using triple-response sodium (E)-2-(4-(phenyldiazenyl)phenoxy) acetate (AzoNa) and butyrylcholinesterase (BChE)-hydrolyzable palmitoylcholine bromide (PCB). Under the optimal molar ratio of AzoNa to PCB (∼0.5), the PCB-AzoNa WLMs formed with a maximum zero-shear viscosity (η0) value of about 2.1 × 105 mPa·s and an average diameter (D) of 4.1 ± 0.6 nm under conditions of 37 °C and pH 7.4. After irradiated with 365 nm UV light for 80 min, AzoNa underwent the trans-to-cis transition, by which the PCB-AzoNa WLMs was destroyed; however, the PCB-AzoNa WLMs could be reformed upon the irradiation of 455 nm blue light for 18 h or heating at 70 °C for 45 min due to the cis-to-trans isomerization of AzoNa. When pH changed from 7.4 to 2.0, the PCB-AzoNa WLMs was destroyed rapidly because of the conversion of AzoNa to the acid form of AzoH, whereas the PCB-AzoNa WLMs could be reformed after pH was restored to 7.4. The multiple responsiveness of the PCB-AzoNa WLMs was reversible due to the reversible trans-cis isomerization or protonation of AzoNa. Besides, the average D values of light, heat, and pH-regenerated PCB-AzoNa WLMs were 4.2 ± 0.7, 4.0 ± 0.7, and 4.0 ± 0.6 nm, respectively. Finally, the PCB-AzoNa WLMs could be enzymatically disorganized under conditions of 37 °C and pH 7.4 due to the BChE-catalyzed hydrolysis of PCB. We hope that the fabrication and enzymatic disorganization strategies for PCB-based multiresponse WLMs presented here will find potential applications in the formulation of antimicrobial household and personal care products containing PCB and in the green disposal of viscous waste containing PCB.

Synthesis and cis-trans kinetics of an azobenzene-based molecular switch for light-responsive silica surfaces

Light-responsive materials design is an attractive research field that stimulates demand for the synthesis of novel molecular photoswitches. The novel photoswitches should be capable of being attached to a desired surface in order to provide it with light-responsive properties. The switchback to its ground state is expected to be gradual, with the possibility of acceleration. This study presents a comprehensive description of a chemical route to a molecular photoswitch based on an azobenzene derivative with a trifluoromethoxy group and a long alkyl chain. The photoswitch is capable of modifying submicrometer silica particles and silicon wafers as models of curved and flat surfaces, respectively. The thermal relaxation times of the synthesized azobenzene were studied in three different solvents: ethanol, chloroform, and toluene. The results reveal a significantly delayed relaxation process lasting for several days. This observation is found to be related to the polarity of the solvents used. To characterize the extensive thermal relaxation process, a methodology including the use of white-light pulses to accelerate cis-trans isomerization is suggested. The white light spectrum used in pulses affects thermal relaxation but does not alter the relaxation time extrapolated to zero. The density of the photoswitch molecules attached to particles varies from 0.7 to 1.7 molecules/nm2 as the initial amount of azobenzene in the reaction increases. Surface-attached photoswitches demonstrate reversible cis-trans isomerization behavior when exposed to UV and white light irradiation. A 14° contact angle change is observed when flat surfaces modified with photoswitches are irradiated with UV light.

Photochromic Azobenzene Inverse Opal Film toward Dynamic Anti-Fake Pattern.

Azobenzene mesogens have garnered considerable research attention in the realm of photo-responsive materials due to their reversible trans-cis isomerization. In this paper, we demonstrate an azobenzene inverse opal film synthesized via photo-polymerization from a SiO2 opal template. The proposed design exhibits intriguing optical properties, including dynamic fluorescent features, distinct fluorescent enhancement, and an anti-fake micropattern with a switchable structure color. This work holds significant importance for advancing the development of novel optical devices.

Reversible photo-controllable surface wettability of epoxy-polyurethane smart coating

Light-responsive materials, in which a rapid and reversible response can be achieved, are of particular interest for several technological applications. The transformation of external stimuli into mechanical energy is very promising in the field of molecular motors and energy convertors. Azobenzene chromophores undergo photon-driven reversible cis-trans isomerization. In these stimuli-responsive materials, reversible molecular motion can be responsible for switching surface properties, such as surface wettability. In this work, the authors synthesized a fluorinated epoxy - isocyanate thermosetting coating (EPUF) modified with an azobenzene derivative (AZO). The increase in AZO content on the surface by migration during synthesis, as a consequence fluorine presence, leads to changes in the surface hydrophobicity, when UV light is used as a stimulus. First, polyurethane precursors (PUs) based on isophorone diisocyanate (IPDI), a fluorinated diol, and AZO were synthesized. Size-Exclusion Chromatography (SEC), Fourier Transform Infrared Spectroscopy (FTIR), and Ultraviolet-Visible Spectroscopy (UV) techniques were used to characterize the precursors. The polyurethane – epoxy reaction obtained allowed to prepare AZO modified epoxy networks. The resulting materials were characterized using different techniques. Fluorinated and pristine networks were compared. The changes in contact angle, roughness, and mechanical behavior by UV irradiation were analyzed. The reversible photo-induced switching of the surface properties of the fluorine-AZO modified coatings renders them potentially useful for multiple technological applications, in which cycling surface properties are of great use.

Flexible Azo-Polyimide-Based Smart Surface with Photoregulatable Surface Micropatterns: Toward Rewritable Information Storage and Wrinkle-Free Device Fabrication

Stimulus-sensitive materials are of great fascination in surface and interface science owing to their dynamically tunable surface properties and/or morphologies. Herein, we have synthesized an azobenzene-containing polyimide (azo-PI) with enhanced chain flexibility for the fabrication of photosensitive surface patterns on a film/substrate wrinkle system or wrinkle-free devices. The phototriggered cis-trans isomerization kinetics of azobenzene groups in the novel azo-PI with various chain structures were systematically investigated. On the basis of the characteristics of stress relaxation that azobenzene reversible cis-trans isomerization induces in the wrinkled azo-PI film/substrate system, a variety of rewritable visual surface patterns with high resolution and a long legibility time (>30 days) could be easily constructed via visible-light irradiation, enabling the wrinkled azo-PI surfaces to be used as rewritable information storage media. Meanwhile, because of the visible-light irradiation strategy, these photoresponsive surfaces could find potential application in the fabrication of wrinkle-free flexible devices. This study not only sheds light on the influence of the azo-polymer chain structure on its photoresponsive behavior but also provides a versatile strategy for realizing tailor-made smart surface patterns on multilayer functional devices.

Synthesis and characterization of photo-responsive azobenzene side-chain liquid crystalline polystyrenes with a mesogenic phase of wide temperature range

Polystyrenes (PSs) that provide photochemical stability are commonly used as the chromophore macromolecular carriers. Herein, PS-based alternating copolymers, i.e., alt-P(D-SiH/Ip), alt-P(D-2SiH/Ip) and alt-P(D-SiH/St), are synthesized through anionically copolymerized Si–H functionalized 1,1-diphenylethylene (DPE-SiH/2SiH) with isoprene (Ip)/styrene (St). Anionically polymerized (4-vinylphenyl)-dimethyl-silane is used as the uniform hydrosilylated PS, i.e., Uni.-P(St-SiH). A series of photo-responsive azobenzene side-chain liquid crystalline PSs combine the above PS-based main chains and the mesogenic moiety composed of azobenzene (Azo) and cholesterol (Chol) groups, i.e., Azo-Chol (M), via the hydrosilylation. The polarized optical microscopic (POM) morphologies and thermal properties of Azo-Chol (M) and Azo-Chol-PSs are studied. As desired, they produce the cholesteric phase of wide temperature range due to the PSs and Chol-groups. Moreover, the photo-responsive behavior irradiated under UV-light of different wavelengths are quantitatively evaluated by time-dependent UV–Vis spectroscopy. Azo-Chol-PSs undergo rapid and reversible trans-cis isomerization under the alternating irradiation of UV and visible light. The trans-to-cis isomerization efficiency under 365 nm UV-light is over that under 290–320 nm UV-light, while over 80% of cis-to-trans efficiency can be realized under 400–500 nm Vis-light irradiation This work would provide guidelines for the effective design of photo-responsive anisotropic materials.

Anisotropic fluid with phototunable dielectric permittivity

Dielectric permittivity, a measure of polarisability, is a fundamental parameter that dominates various physical phenomena and properties of materials. However, it remains a challenge to control the dielectric permittivity of materials reversibly over a large range. Herein, we report an anisotropic fluid with photoresponsive dielectric permittivity (200 < ε < 18,000) consisting of a fluorinated liquid-crystalline molecule (96 wt%) and an azobenzene-tethered phototrigger (4 wt%). The reversible trans-cis isomerisation of the phototrigger under blue and green light irradiation causes a switch between two liquid-crystalline phases that exhibit different dielectric permittivities, with a rapid response time (<30 s) and excellent reversibility (~100 cycles). This anisotropic fluid can be used as a flexible photovariable capacitor that, for example, allows the reversible modulation of the sound frequency over a wide range (100 < f < 8500 Hz) in a remote manner using blue and green wavelengths.

Light-controllable chiral dopant based on azo-fragment: synthesis and characterisation

ABSTRACT We present the synthesised chiral dopant 2-[(2-isopropyl-5-methylcyclohexyl)oxy]-2-oxoethyl 4-{(E)-[4-(decyloxy)phenyl]diazenyl}benzoate (ChD-3501), consisting of azo- and aliphatic fragments together with a chiral centre based on l-menthol as a reversible light-controllable chiral dopant. To assess the effects of UV–vis irradiation and temperature in the isotropic and liquid crystalline (LC) states, we studied the spectral kinetics of ethanol solution of ChD-3501, as well as induction of the cholesteric helix when it was dissolved in nematic LC (E7) as a chiral dopant. The concentration dependence of the helical pitch of the induced cholesterics was studied by means on Grandjean–Cano method, and the helical twisting power of ChD-3501 in the nematic host E7 was determined. The reversible trans-cis isomerisation of chiral dopant ChD-3501 in E7 under UV–vis irradiation was studied, and it has been found that the storage of the cis-isomer at certain constant temperature also leads to the reversible isomerisation. Possible applications of the studied system are discussed.

Azobenzene-Semicarbazone Enables Optical Control of Insect Sodium Channels and Behavior.

Photopharmacology uses molecular photoswitches to establish control over the action of bioactive molecules. The application of photopharmacology in the research of invertebrate sodium channels has not been investigated. Here we report several photochromic ligands of metaflumizone. One ligand, termed ABM04, underwent reversible trans-cis isomerization under ultraviolet or blue light irradiation. cis-ABM04 had excellent larvicidal activity against mosquito larvae with an LC50 value of 4.39 μM and showed insecticidal activity against Mythimna separata with an LC50 value of 7.19 μM. However, trans-ABM04 was not found to have biological activity. ABM04 (10 μM) can induce depolarization of dorsal unpaired median neurons and enable the real-time photoregulation of mosquito larval behavior. The precise regulation of invertebrate sodium channels is realized for the first time, which provides a new strategy for the basic and accurate research of invertebrate sodium channels.

Light-Driven Polarity Switching of the Chromatographic Stationary Phase with Photoreversibility.

Regrettably, conventional chromatographic columns have immutable polarity, resulting in requirements of at least two columns with polarity difference and sophisticated mechanical switching valves, which hinders the development of "micro-smart" multidimensional tandem chromatography. In this work, light-driven polarity switching was realized in a single capillary column based on the reversible trans-cis isomerization of 4-[3-(triethoxysilyl)propoxy]azobenzene as the stationary phase under light irradiation, with the change in dipole moment. As a result, the stationary phase offers precise and dynamic control of polarity based on the cis-trans azobenzene ratio, which depends on irradiation wavelength and time. Thus, the continuous adjustment of polarity enables diversified chromatographic separation modes, for example, step-polarity gradient and polarity-conversion separation modes, taking advantage of the superior freedom of polarity switching in time and spatial dimensions. The photosensitive column also shows good reproducibility of polarity photoreversibility and high separation efficiency. The present study might offer brand new insight into developing miniaturization and intellectualization of multidimensional chromatography via designing smart responsive switching valves or stationary phases, besides mechanical means.

β-Cyclodextrin-Modified Mesoporous Silica Nanoparticles with Photo-Responsive Gatekeepers for Controlled Release of Hexaconazole

In the present research, photo-responsive controlled-release hexaconazole (Hex) nanoparticles (Nps) were successfully prepared with azobenzene (Azo)-modified bimodal mesoporous silica (BMMs), in which β-cyclodextrin (β-CD) was capped onto the BMMs-Azo surface via host–guest interactions (Hex@BMMs/Azo/β-CD). Scanning electron microscopy (SEM) confirmed that the nanoparticles had a spherical structure, and their average diameter determined by dynamic light scattering (DLS) was found to be 387.2 ± 3.8 nm. X-ray powder-diffraction analysis and N2-adsorption measurements indicated that Hex was loaded into the pores of the mesoporous structure, but the structure of the mesoporous composite was not destroyed. The loading capacity of Hex@BMMs/Azo/β-CD nanoparticles for Hex was approximately 27.3%. Elemental components of the nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS) and electron dispersive spectroscopy (EDS). Ultraviolet–visible-light (UV–Vis) absorption spectroscopy tests showed that the azophenyl group in BMMs-Azo undergoes effective and reversible cis-trans isomerization under UV–Vis irradiation. Hex@BMMs/Azo/β-CD Nps exhibited excellent light-sensitive controlled-release performance. The release of Hex was much higher under UV irradiation than that in the dark, which could be demonstrated by the bioactivity test. The nanoparticles also displayed excellent pH-responsive properties, and the sustained-release curves were described by the Ritger–Peppas release kinetic model. BMMs nanocarriers had good biological safety and provided a basis for the development of sustainable agriculture in the future.

Liquid‐Phase Super Photoactuator through the Synergetic Effects of a Janus Structure and Solvent/Thermal/Photo Responses

AbstractAzobenzene actuator has attracted wide research attention in the fields of soft robots, artificial muscles, etc., owing to the typical photoresponsive material based on its reversible trans–cis isomerization. However, it remains challenging to enhance the actuation performance of azobenzene actuators through simple methods and can work in complex and variable environments. In contrast to complex molecular functional design, this study presents a Janus azobenzene inverse opal actuator: one side of a monodomain azobenzene polymer and the other side of a polydomain azobenzene inverse opal structure. The proposed design can significantly enhance the photoactuation performance in the liquid phase based on the synergetic effects of the Janus structure and the plastic influence of solvent/thermal/photo responses on the polymer segment. Promising applications of photo‐driven ring rolling in the liquid phase are demonstrated. The results of this study are of great significance for the design and fabrication of novel‐type azobenzene actuators in the liquid phase.

Light-Enabled Reversible Shape Transformation of Block Copolymer Particles

Confined self-assembly of block copolymers (BCPs) is effective to manipulate various shapes of particles. In emulsion confined self-assembly, reversibly light-trigged switchable BCP particles are extremely expected, yet rarely reported. Herein, a novel strategy is developed to realize reversibly light-responsive shape-transformation of BCP particles by constructing functional surfactants with light-active azobenzene (azo) groups in the confined self-assembly of BCPs within emulsion droplet. Ultraviolet and visible lights can reversibly modulate the amphiphilicity and interfacial affinity of the surfactants to different blocks, triggering the reversible microphase structure transformation of BCP particles with high temporal-spatial resolution. We can realize shape and morphological transitions of BCP particles from onion-shaped spherical particles to striped ellipsoids and, ultimately, to inverse onion-like particles by ultraviolet irradiation. More importantly, this shape transformation is reversible by the irradiation of visible light, attributed to the reversible trans-cis isomerization of azo groups. We also demonstrate that the light-triggered shape transformation of BCP particles can be employed in a controllable drug release through a noncontacted and programmed manner, showing promising potential in clinic and biomedicine.

A visible light-controllable Rho kinase inhibitor based on a photochromic phenylazothiazole.

Rho-associated coiled-coil-containing protein kinase (ROCK) is a serine-threonine kinase whose inhibitors are useful for the regulation of the actomyosin system. Here, we developed a photoswitchable ROCK inhibitor based on a phenylazothiazole scaffold. The reversible trans-cis isomerization by visible light stimuli enabled us to manipulate ROCK activities in vitro and in cells.

Azobenzene-diamides as Photopharmacological Ligands for Insect Ryanodine Receptor.

Photoresponsive ligands are powerful tool compounds for studying receptor function with spatiotemporal resolution. However, to the best of our knowledge, such a ligand is not available for the ryanodine receptor (RyR). Herein, we present a photochromic ligand (PCL) for insect RyR by decorating chlorantraniliprole (CHL) with photoswitchable azobenzene (AB). We demonstrated that one potent ligand, named ABCHL13, shows light-induced reversible trans-cis isomerization and 3.5-fold insecticidal activity decrease toward oriental armyworm (Mythimna separata) after UV-light irradiation, that is, trans-ABCH13 has higher activity than the cis-ABCH13. ABCHL13 enables optical control over intracellular Ca2+ release in dorsal unpaired median (DUM) neurons of M. separata and American cockroach (Periplaneta americana) and cardiac function of P. americana. Our results provide a first photopharmacological toolkit that is applicable to light-dependent regulation of RyR and heart beating.

Reversible Solid-State Isomerism of Azobenzene-Loaded Large-Pore Isoreticular Mg-CUK-1

A large-pore version of Mg-CUK-1, a water-stable metal-organic framework (MOF) with 1-D channels, was synthesized in basic water. Mg-CUK-1L has a BET surface area of 2896 m2 g-1 and shows stark selectivity for CO2 sorption over N2, O2, H2, and CH4. It displays reversible, multistep gated sorption of CO2 below 0.33 atm. The dehydrated single-crystal structure of Mg-CUK-1L confirms retention of the open-channel structure. The MOF can be loaded with organic molecules by immersion in hot melts, providing single crystals suitable for X-ray diffraction. trans-Azobenzene fills the channels in a 2 × 2 arrangement. Solid-state UV-vis spectroscopy reveals that azobenzene molecules undergo reversible trans-cis isomerization, despite being close-packed; this surprising result is confirmed by DFT-simulated UV-vis spectra.