Photoisomerization Of Azobenzene Research Articles

Azobenzene-Bridged Expanded “Texas-sized” Box: A Dual-Responsive Receptor for Aryl Dianion Encapsulation

We report an expanded "Texas-sized" molecular box (AzoTxSB) that incorporates photoresponsive azobenzene bridging subunits and anion recognition motifs. The shape of this box can be switched through light induced E ↔ Z photoisomerization of the constituent azobenzenes. This allows various anionic substrates to be bound and released by using different forms of the box. Control can also be achieved using other environmental stimuli, such as pH and anion competition.

Preparation of azobenzene-intercalated kaolinite and monitoring of the photoinduced activity

AbstractSystems consisting of layered structures and photoactive molecules have been studied extensively. The structures of resulting complexes may be controlled by UV–Vis radiation, which subsequently affects their materials properties. This study describes a synthesis route for obtaining a photoresponsive kaolinite intercalation compound. The material was prepared by co-intercalating azobenzene and benzylalkylammonium chlorides into a methoxy form of kaolinite. The resultant materials possessed large basal spacing values in the range of 45–55 Å. The UV–Vis and Fourier-transform infrared spectroscopy analyses confirmed the reversible photoisomerization of azobenzene upon exposure to UV and Vis radiation. This phenomenon was significantly influenced by the type and amount of co-intercalated molecules. Upon multiple trans–cis conversions, the azobenzene partially evaporated. For the first time, a kaolinite-based material was prepared that exhibited photochromic behaviour upon UV and Vis irradiation.

Rationally designed azobenzene photoswitches for efficient two-photon neuronal excitation

Manipulation of neuronal activity using two-photon excitation of azobenzene photoswitches with near-infrared light has been recently demonstrated, but their practical use in neuronal tissue to photostimulate individual neurons with three-dimensional precision has been hampered by firstly, the low efficacy and reliability of NIR-induced azobenzene photoisomerization compared to one-photon excitation, and secondly, the short cis state lifetime of the two-photon responsive azo switches. Here we report the rational design based on theoretical calculations and the synthesis of azobenzene photoswitches endowed with both high two-photon absorption cross section and slow thermal back-isomerization. These compounds provide optimized and sustained two-photon neuronal stimulation both in light-scattering brain tissue and in Caenorhabditis elegans nematodes, displaying photoresponse intensities that are comparable to those achieved under one-photon excitation. This finding opens the way to use both genetically targeted and pharmacologically selective azobenzene photoswitches to dissect intact neuronal circuits in three dimensions.

Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator

Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm3+ or Er3+ as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < λem < 480 nm (for Tm3+, three and four photon induced emission) or 525 nm < λem < 545 nm (for Er3+, two photon induced emission), respectively. Especially for UCNPs containing Tm3+ a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (λex = 976 nm) in the presence of the Tm3+-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR.

Photocontrollable Wrinkle Morphology Evolution on Azo-Based Multilayers for Hierarchical Surface Micropatterns Fabrication.

Inspired by nature, comprehensive understanding and ingenious utilization of the self-organized wrinkling behaviors of the sandwiched multilayer bonded on substrates are important for engineering and/or functional laminated devices design. Herein, we report a facile and effective strategy to regulate the wrinkles morphology evolution and the resultant hierarchical surface micropatterns on azobenzene-based laminated multilayers by visible-light irradiation. Revealed by systematic experiments, the photocontrolled dynamic wrinkle evolutions are triggered by the reversible photoisomerization of azobenzene in the top azopolymer film and are strongly dependent on the intermediate photoinert layers (e.g., polystyrene and oxygen plasma-induced SiO x layer) with the wrinkle-reinforcing effect or the stress relaxation acceleration effect. Interestingly, large-area well-defined hierarchical surface wrinkle patterns could be fabricated on the multilayers upon selective exposure. In the unexposed region, the wrinkles evolved into highly oriented patterns, whereas in the exposed region, they were fully erased or evolved into smaller-wavelength wrinkles. This study not only sheds light on the morphological evolution of the wrinkling laminated composites in engineering and nature but also paves a new avenue to conveniently and controllably realize the hierarchical stimulus-responsive surface patterns.

Photoresponsive Halogen-Bonded Liquid Crystals: The Role of Aromatic Fluorine Substitution

A new strategy for controlling the liquid crystalline and photophysical properties of supramolecular mesogens assembled via halogen bonding is reported. Changing the degree of fluorination at the halogen-bond donor of the supramolecular liquid crystal allows for the fine-tuning of the halogen bond strength and thereby provides control over the temperature range of the mesophase. At least three fluorine atoms have to be present to ensure efficient polarization of the halogen-bond donor and the formation of a mesophase. In addition, it was found that stilbazole acceptors are superior to their azopyridine counterparts in promoting stable liquid crystalline phases. The halogen-bond-driven supramolecular liquid crystals between fluorinated azobenzenes and stilbazole/azopyridine acceptors show a rich variety of photoinduced processes driven by azobenzene photoisomerization, dictated not only by the photochemical properties of the molecular components but also by the difference between the operation temperature ...

A photoregulated split aptaswitch for small molecules with improved sensitivity.

Here we show the design of a photoregulated split aptaswitch (PSA) for the challenging small-molecule biorecognition and its sensing application. The PSA specifically binds with the target in a binary reaction, and can easily rule out false positive signals by azobenzene photoisomerization, exhibiting an approximately 50-fold improved sensitivity over a control assay.

A NIR-triggered gatekeeper of supramolecular conjugated unimicelles with two-photon absorption for controlled drug release.

A near-infrared (NIR)-sensitive gated assembly of supramolecular conjugated unimicelles based on robust host-guest recognition between a β-cyclodextrin-grafted hyperbranched conjugated polymer and azobenzene-functionalized poly(ethylene glycol) was constructed. Utilized as a drug carrier, these unimicelles exhibited controlled drug release through the NIR-triggered photoisomerization of azobenzene in cancer cells via a two-photon excited fluorescence resonance energy transfer (TP-FRET) approach, leading to efficient cancer therapy.

A supramolecular chain of dimeric Dy single molecule magnets decorated with azobenzene ligands.

We report the synthesis, ab initio calculations, magnetic and optical characterization of a DyIII-based dimeric compound named DyAZO. The dimers self-organize into a supramolecular chain decorated with photo-isomerizable azobenzene ligands. DyAZO displays single-molecule magnet (SMM) behavior. However, ab initio calculations highlight a quite strong admixture of MJ states of the 6H15/2 level of DyIII ions, the presence of low-lying excited MJ states and antiferromagnetic Dy-Dy dipolar coupling. This favors zero-field fast tunneling. Accordingly the Dy-doped analogue YDyAZO (5.5% Dy doping) displays enhanced magnetic relaxation with a hysteresis that is observed at 0.5 K. The influence of the cis- to trans-isomerization of the decorating azobenzene ligand on magnetic properties has been tested for both solid samples and solutions of DyAZO and YDyAZO. This provides hints for the synthesis of future Dy-based photo-isomerizable molecules.

Supramolecular Control of Azobenzene Switching on Nanoparticles.

The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene's hydrophobic nature, most of these examples have been realized only in organic solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-soluble. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amount of azobenzene on the functionalized nanoparticles. Molecular dynamics simulations helped us to identify two distinct supramolecular architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aqueous solubilities. Azobenzenes adsorbed on these water-soluble nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aqueous media and, in the long run, in biological environments.

Reversible Photocontrol of Thrombin Activity by Replacing Loops of Thrombin Binding Aptamer using Azobenzene Derivatives.

The photoisomerization of azobenzenes provides a general means for the photocontrol of many important biomolecular structures and organismal functions. For temporal and spatial control activity of thrombin binding aptamer (TBA) by light, azobenzene derivatives were carefully selected as light-triggered molecular switches to replace TT loops and the TGT loop of TBA to reversibly control enzyme activity. These molecules interconverted between the trans and cis states under alternate UV and visible light irradiation, which consequently triggered reversible formation of G-quadruplex morphology. In addition, we investigated the impact of three azobenzene derivatives on stability, thrombin binding ability, and anticoagulant properties. The result showed that 4,4'-bis(hydroxymethyl)azobenzene at the TGT loop position significantly photoregulated affinity to thrombin and blood clotting in human plasma, which provided a successful strategy to control blood clotting in human plasma and a further evidence for design of TBA analogues with pivotal positions of modifications.

A novel photosensitive dual-sensor for simultaneous detection of nucleic acids and small chemical molecules

Sensors that can rapidly and specifically detect nucleic acids and chemical molecules can revolutionize the diagnosis and treatment of diseases by allowing molecular-level informations to be used during the routine medicines. In this study, we demonstrated a novel dual-sensor that can be used to simultaneously detect any nucleic acids and chemical molecules whose binding aptamers can be found or synthesized. In the developed dual-sensor, the specifically designed PTG (a photosensitive azobenzene derivative carrying one photoisomerizable azobenzene moiety, one threoninol terminal and one guanidinium terminal) molecules are introduced into the unwinding region of two T7 promoters, and two DNA bubbles are introduced upstream of the two T7 promoters. Without the target, the indicating gene in the dual-tensor would not be expressed since the binding with RNAPs (RNA polymerases) cannot melt the T7 promoter for the indicating gene due to the integration of the DNA double strands via the PTG molecules, manifesting the absence of the target nucleic acid and chemical molecule. While with the presence of the target nucleic acid and/or chemical molecule, the indicating gene would be expressed as the T7 promoter contained in the enlarged DNA bubble can be melted and transcribed by the bound RNAPs as the enlarged DNA bubble can help the separation of the two DNA strands, demonstrating the existence of target nucleic acid and/or chemical molecule.

Manipulating azobenzene photoisomerization through strong light\u2013molecule coupling

The formation of hybrid light–molecule states (polaritons) offers a new strategy to manipulate the photochemistry of molecules. To fully exploit its potential, one needs to build a toolbox of polaritonic phenomenologies that supplement those of standard photochemistry. By means of a state-of-the-art computational photochemistry approach extended to the strong-coupling regime, here we disclose various mechanisms peculiar of polaritonic chemistry: coherent population oscillations between polaritons, quenching by trapping in dead-end polaritonic states and the alteration of the photochemical reaction pathway and quantum yields. We focus on azobenzene photoisomerization, that encompasses the essential features of complex photochemical reactions such as the presence of conical intersections and reaction coordinates involving multiple internal modes. In the strong coupling regime, a polaritonic conical intersection arises and we characterize its role in the photochemical process. Our chemically detailed simulations provide a framework to rationalize how the strong coupling impacts the photochemistry of realistic molecules.

Reconfigurable photoactuator through synergistic use of photochemical and photothermal effects

A reconfigurable actuator is a stimuli-responsive structure that can be programmed to adapt different shapes under identical stimulus. Reconfigurable actuators that function without control circuitry and are fueled remotely are in great demand to devise adaptive soft robotic devices. Yet, obtaining fast and reliable reconfiguration remains a grand challenge. Here we report a facile fabrication pathway towards reconfigurability, through synergistic use of photochemical and photothermal responses in light-active liquid crystal polymer networks. We utilize azobenzene photoisomerization to locally control the cis-isomer content and to program the actuator response, while subsequent photothermal stimulus actuates the structure, leading to shape morphing. We demonstrate six different shapes reconfigured from one single actuator under identical illumination conditions, and a light-fueled smart gripper that can be commanded to either grip and release or grip and hold an object after ceasing the illumination. We anticipate this work to enable all-optical control over actuator performance, paving way towards reprogrammable soft micro-robotics.

Isosbestic Points Do Not Always Work as the Measure to Determine the Oneness of a Reaction as Exemplified by the Photoisomerization of Azobenzene Tethered to Polymer Chains

Even though two isosbestic points are generated in UV-induced changes in UV-vis absorption spectra of films of a polymethacrylate with azobenzene side chains, the corresponding fourth-order derivative spectra disclose the presence of H-aggregate so that the dual process comprised of UV-induced disaggregation and E/Z photoisomerization of non-aggregated species are involved.

Multi-arm azobenzene liquid crystal based on cholic acid: synthesis and mesophase properties

ABSTRACTA new series of multi-arm liquid crystals (D1–D5) based on cholic acid as the chiral core and ω-[4-(p-substituted azobenzeneoxy carbonyl]valeric acid (B1–B5) as the mesogenic arms were designed and synthesised. All the mesogenic arms and the multi-arm liquid crystals were structurally well-characterised using elementary analysis (EA), 1H NMR and FT-IR. The photochemical properties were determined by UV spectra. The optical rotations were measured by Automatic Polarimeter. The phase behaviours were investigated by means of polarised optical microscopy, X-ray diffraction and differential scanning calorimetry, while the effect of the terminal groups of azobenzene on mesogenic and photochemical properties were discussed. The results demonstrated that the mesogenic arms exhibited nematic phase except B3. The multi-arm compounds showed chiral nematic except D3. Cholic acid played an important role in inducing chiral nematic of the multi-arm liquid crystals. Tm or Ti of B1–B5 and D1–D5 are influenced by the effect of electrical effects of the terminal groups and the molecular shapes. Furthermore, the multi-arm compounds exhibited well light sensitivity, owning the photoisomerisation of the tran-form azobenzene to the cis-form azobenzene. λmax of D1–D5 displayed blue shift first and then red shift with the different electrical effects of the terminal groups of mesogenic arms.

Unpolarized light-induced alignment of azobenzene by scanning wave photopolymerization

Controlling the alignment of various functional molecules is important for the development of many next-generation, high-performance optical devices. However, there are some limitations in inducing molecular alignment using the current methods. We report herein the alignment control of azobenzene in a polymer film by a simple, new alignment-patterning technique based on a scanning wave photopolymerization (SWaP) concept. In this technique, molecular alignment was induced by the spatiotemporal control of the non-polarized light. A photoisomerizable azobenzene molecule, Disperse Red 1 (DR1), was doped into the photopolymerizable mixture, and it was successfully aligned along the direction of the neighboring mesogens; the alignment was induced by SWaP with unpolarized light. The alignment behavior showed that the degree of photoisomerization of the doped azobenzene moieties was proportional to the light intensity, and the unidirectional alignment of DR1 was achieved through optimization of the photopolymerization conditions. This finding indicates that SWaP could be employed as a novel and simple fabrication process for preparing a wide variety of highly functional optical devices requiring alignment control. The alignment of azobenzene molecule was induced by a new-alignment-patterning technique based on a scanning wave photopolymerization (SWaP) concept with unpolarized light. This finding indicates that SWaP could be employed as a novel and simple fabrication process for preparing a wide variety of highly functional optical devices requiring alignment control.

Azobenzene Molecular Machine: Light-Induced Wringing Gel Fabricated from Asymmetric Macrogelator.

To develop light-triggered wringing gels, an asymmetric macrogelator (1AZ3BP) was newly synthesized by the chemically bridging a photoisomerizable azobenzene (1AZ) molecular machine and a biphenyl-based (3BP) dendron with a 1,4-phenylenediformamide connector. 1AZ3BP was self-assembled into a layered superstructure in the bulk state, but 1AZ3BP formed a three-dimensional (3D) network organogel in solution. Upon irradiating UV light onto the 3D network organogel, the solvent of the organogel was squeezed and the 3D network was converted to the layered morphology. It was realized that the metastable 3D network organogels were fabricated mainly due to the nanophase separation in solution. UV isomerization of 1AZ3BP provided sufficient molecular mobility to form strong hydrogen bonds for the construction of the stable layered superstructure. The light-triggered wringing gels can be smartly applied in remote-controlled generators, liquid storages, and sensors.

QM/MM Studies on Photoisomerization Dynamics of Azobenzene Chromophore Tethered to a DNA Duplex: Local Unpaired Nucleobase Plays a Crucial Role.

The photoresponsive azobenzene-tethered DNAs have received growing experimental attention because of their potential applications in biotechnology and nanotechnology; however, little is known about the initial photoisomerization of azobenzene in these systems. Herein we have employed quantum mechanics/molecular mechanics (QM/MM) methods to explore the photoisomerization dynamics of an azobenzene-tethered DNA duplex. We find that in the S1 state the trans-cis photoisomerization path is much steeper in DNA than in vacuo, which makes the photoisomerization much faster in the DNA environment. This acceleration is primarily caused by complex steric interactions between azobenzene and the nearby unpaired thymine nucleobase, which also change the photoisomerization mechanism of azobenzene in the DNA duplex.

Performance of TDDFT with and without spin-flip in trajectory surface hopping dynamics: cis–trans azobenzene photoisomerization

Time-dependent density functional theory (TDDFT) with and without a spin-flip scheme is extensively compared in on-the-fly trajectory surface hopping molecular dynamics with a global switching (GS) algorithm. The simulation is performed for cis-trans azobenzene photoisomerization following the excitation to the S1(nπ*) state that is involved in a conical intersection (CI) between ground and first excited states. This CI is found correctly to be a single-cone (artificial double-cone) structure computed by the TDDFT method with (and without) spin-flip. Nevertheless, simulated quantum yields and lifetimes are in very good agreement; 0.43 and 63 fs (0.34 and 62 fs) for cis-to-trans isomerization, and 0.11 and 2200 fs (0.13 and 1040 fs) for trans-to-cis isomerization, by TDDFT with (and without) a spin-flip scheme. Distributions of excited-state decay, hopping spots and products, as well as typical trajectories have similar patterns and behaviors with and without spin-flip. The global switching trajectory surface hopping method is demonstrated to be well suited to TDDFT on-the-fly dynamic simulation with and without spin-flip. For comparison, previous simulations with the CASSCF method and Tully's fewest-switches trajectory surface hopping method are also addressed.