Query: azobenzene;

title: Facile Synthesis of Self Assembled NiFe Layered Double Hydroxide Based Azobenzene Composite Films with Photoisomerization and Chemical Gas Sensor Performances
abstract: Two kinds of layered double hydroxide (LDH) Langmuir composite films containing azobenzene (Azo) groups were successfully prepared by Langmuir Blodgett (LB) technology. Then, an X ray diffractometer (XRD) a transmission electron microscope (TEM) and an atomic force microscope (AFM) were used to investigate the structures of NiFe LDH and the uniform morphologies of the composite LB films. The photoisomerization and acid base gas sensor performances of the obtained thin film samples were tested by infrared visible (FTIR) spectroscropy and ultraviolet visible (UV vis) spectroscropy. It is proved that the Azo dye molecules in the composite film are relatively stable to photoisomerization. In addition, the prepared composite films have high sensing sensitivity and good recyclability for acid base response gases. The present research proposes a new clue for designing thin film materials for chemical gas response with good stability and sensitivity.

title: Computational Design and Synthesis of a Deeply Red Shifted and Bistable Azobenzene
abstract: We computationally dissected the electronic and geometrical influences of ortho chlorinated azobenzenes on their photophysical properties. X ray analysis provided the insight that trans tetra ortho chloro azobenzene is conformationally flexible and thus subject to molecular motions. This allows the photoswitch to adopt a range of red shifted geometries, which account for the extended n p* band tails. On the basis of our results, we designed the di ortho fluoro di ortho chloro (dfdc) azobenzene and provided computational evidence for the superiority of this substitution pattern to tetra ortho chloro azobenzene. Thereafter, we synthesized dfdc azobenzene by ortho chlorination via 2 fold C H activation and experimentally confirmed its structural and photophysical properties through UV vis, NMR, and X ray analyses. The advantages include near bistable isomers and an increased separation of the n p* bands between the trans and cis conformations, which allows for the generation of unusually high levels of the cis isomer by irradiation with green/yellow light as well as red light within the biooptical window.

title: Enhanced CO2 capture in nitrogen enriched microporous carbons derived from Polybenzoxazines containing azobenzene and carboxylic acid units
abstract: In this study, we prepared nitrogen doped microporous carbons (NMCs) from two different benzoxazine monomers (AMBZ, AEBZ) each containing both azobenzene and carboxylic groups, through a simple and environmentally friendly process of ring opening polymerization (ROP) calcination, and KOH activation. We synthesized the AMBZ and AEBZ monomers through Mannich condensations of 4,4' diaminodiphenylmethane (M) and 4,4' diaminodiphenyl ether (E) respectively, with paraformaldehyde and 4 (4 hydroxphenylazo)benzoic acid (Azo COOH) Differential scanning calorimetry (DSC) revealed that the thermal curing temperatures of AMBZ and AEBZ (both ca. 230 degC) were lower than that of a typical Pa type benzoxazine monomer (263 degC) suggesting that the azobenzene and COOH units acted as promoters and catalysts for the ROP of the benzoxazine units. In addition, after ROP of the benzoxazine units of AMBZ and AEBZ, the polymers PAMBZ and PAEBZ, respectively, displayed high glass transition temperatures (Tg) and high thermal stability, as evidenced using DSC and thermogravimetric analysis (TGA) due to their greater cross linking densities. We used Brunauer Emmett Teller analysis, TGA, wide angle X ray diffraction, transmission electron microscopy, Raman spectroscopy, and X ray photoelectron spectroscopy to examine the specific surface areas, porous structures, chemical compositions, and thermal stabilities of the resulting KOH activated NMCs PAMBZ A and PAEBZ A. The CO2 capture abilities and thermal properties of these two highly nitrogen doped microporous carbons, synthesized from polybenzoxazine (PBZ) resins containing azobenzene and COOH groups, were excellent when compared with those of other N doped porous carbons derived from other PBZ matrices.

title: Azobenzene assisted exfoliation of 2D covalent organic frameworks into large area, few layer nanosheets for high flux and selective molecular separation membrane
abstract: The porous 2D covalent organic nanosheets (CONs) membrane has become a new generation of membrane material due to its ultrahigh permeation flux. The main challenge in fabricating CONs membrane is how to exfoliate covalent organic frameworks (COFs) into large scale, few layer nanosheets. Herein, we presented a simple and economical azobenzene template approach for exfoliating 2D COFs into large nanosheets and achieved fabrication of ultrathin CONs membrane successfully. Three COFs with different skeleton structures were chosen to explore the influencing factors for effective exfoliating. We found that the compatibility between azobenzene molecules and COFs skeleton structure was the key point for exfoliation. When the COF skeleton matching with the azobenzene molecular structure, COFs can be easily exfoliated into larger scale CONs than nanosheets prepared by conventional exfoliation methods. The as exfoliated nanosheets membrane showed a higher water flux (596 L m2 h 1 bar 1) than a graphene oxide (GO) membrane (4.3 L m2 h 1 bar 1) and high rejection of dye molecules, due to the nano channels perpendicular to the surface of the membrane.

title: Kinetics of photo isomerization of azobenzene containing surfactants.
abstract: We report on photoisomerization kinetics of azobenzene containing surfactants in aqueous solution. The surfactant molecule consists of a positively charged trimethylammonium bromide head group, a hydrophobic spacer connecting via 6 to 10 CH2 groups to the azobenzene unit, and the hydrophobic tail of 1 and 3CH2 groups. Under exposure to light, the azobenzene photoisomerizes from more stable trans to metastable cis state, which can be switched back either thermally in dark or by illumination with light of a longer wavelength. The surfactant isomerization is described by a kinetic model of a pseudo first order reaction approaching equilibrium, where the intensity controls the rate of isomerization until the equilibrated state. The rate constants of the trans cis and cis trans photoisomerization are calculated as a function of several parameters such as wavelength and intensity of light, the surfactant concentration, and the length of the hydrophobic tail. The thermal relaxation rate from cis to trans state is studied as well. The surfactant isomerization shows a different kinetic below and above the critical micellar concentration of the trans isomer due to steric hindrance within the densely packed micelle but does not depend on the spacer length.

title: Photodeformable Azobenzene Containing Liquid Crystal Polymers and Soft Actuators.
abstract: Photodeformable liquid crystal polymers (LCPs) that adapt their shapes in response to light have aroused a dramatic growth of interest in the past decades, since light as a stimulus enables the remote control and diverse deformations of materials. This review focuses on the growing research on photodeformable LCPs, including their basic actuation mechanisms, the various deformation modes, the newly designed molecular structures, and the improvement of processing techniques. Special attention is devoted to the novel molecular structures of LCPs, which allow for easy processing and alignment. The soft actuators with various deformation modes such as bending, twisting, and rolling in response to light are also covered with the emphasis on their photo induced bionic functions. Potential applications in energy harvesting, self cleaning surfaces, sensors, and photo controlled microfluidics are further illustrated. The existing challenges and future directions are discussed at the end of this review.

title: Reversible redox chemistry in azobenzene based organic molecules for high capacity and long life nonaqueous redox flow batteries
abstract: Redox active organic molecules have drawn extensive interests in redox flow batteries (RFBs) as promising active materials, but employing them in nonaqueous systems is far limited in terms of useable capacity and cycling stability. Here we introduce azobenzene based organic compounds as new active materials to realize high performance nonaqueous RFBs with long cycling life and high capacity. It is capable to achieve a stable long cycling with a low capacity decay of 0.014% per cycle and 0.16% per day over 1000 cycles. The stable cycling under a high concentration of 1 M is also realized, delivering a high reversible capacity of ~46 Ah L 1. The unique lithium coupled redox chemistry accompanied with a voltage increase is observed and revealed by experimental characterization and theoretical simulation. With the reversible redox activity of azo group in p conjugated structures, azobenzene based molecules represent a class of promising redox active organics for potential grid scale energy storage systems. Organic molecules are promising active materials for nonaqueous redox flow batteries (RFBs) but suffer from poor cycling stability. Here, the authors introduce azobenzene based molecules as new type of highly soluble and stable active materials to realize high capacity and long life nonaqueous RFBs.

title: Light responsive and self healing behavior of azobenzene based supramolecular hydrogels.
abstract: Multi component supramolecular hydrogels are gaining increasing interest as stimuli responsive materials. To fully understand and possibly exploit the potential of such complex systems, the hierarchical structure of the gel network needs in depth investigations across multiple length scales. We show that a thorough structural and rheological study represents a crucial pillar for the exploitation of this class of functional materials.  Supramolecular hydrogels are prepared by self assembly of hexadecyltrimethylammonium bromide (CTAB) and azobenzene 4,4' dicarboxylic acid (AZO) in alkaline aqueous solution. The CTAB/AZO concentration was varied from ph 0.25 to 4 wt% keeping the CTAB:AZO molar ratio fixed at 2:1. The systems were thoroughly studied through a combination of X ray scattering, microscopy, rheological and spectroscopic analyses.  The CTAB/AZO solutions form a self supporting gel with nanofibrillar structure below ~30 degC. The critical gelation concentration is phc 0.45 wt% Above this threshold, the gel elasticity and strength increase with CTAB/AZO content as (ph phc)1. The hydrogels exhibit self healing ability when left at rest after a stress induced damage. Moreover, the light induced isomerization of the AZO moieties provides the gel with light responsiveness. Overall, the multi stimuli responsiveness of the studied CTAB/AZO hydrogels makes them a solid starting point for the development of sensors for mechanical vibrations and UV/visible light exposure.

title: Efficient chemoselective hydrogenation of nitrobenzene to aniline, azoxybenzene and azobenzene over CQDs/ZnIn2S4 nanocomposites under visible light
abstract: Efficient production of amino azo and azoxy aromatics is important in chemical industries. In this manuscript, we reported that controllable chemoselective hydrogenation of nitrobenzene to produce aniline, azoxybenzene and azobenzene was realized over CQDs/ZnIn2S4 nanocomposite under visible light via simply regulating the reaction medium including the alkalinity and the hydrogen source. An optimized production of aniline was obtained over 3.0 wt% CQDs/ZnIn2S4 nanocomposite in a reaction medium of TEOA: MeOH (1:1) while a strong alkaline reaction medium promote N N coupling to produce azoxybenzene and azobenzene. In addition, azoxybenzne is the intermediate to form azobenzene during the hydrogenation of nitrobenzene, in which a strong hydrogen source like TEOA is indispensable for the transformation. This study not only demonstrated a noble metal free photocatalytic system for visible light induced efficient and controllable chemoselective hydrogenation of nitrobenzene to produce aniline, azobenzene and azoxybenzene, but also highlights the great potential of photocatalysis in organic syntheses.

title: Optically tunable microresonator using an azobenzene monolayer
abstract: Photoswitchable organic molecules can undergo reversible structural changes with an external light stimulus. These optically controlled molecules have been used in the development of smart polymers, optical writing of grating films, and even controllable in vivo drug release. Being the simplest class of photoswitches in terms of structure, azobenzenes have become the most ubiquitous, well characterized, and implemented organic molecular switch. Given their predictable response, they are ideally suited to create an all optically controlled switch. However, fabricating a monolithic optical device comprised solely from azobenzene while maintaining the photoswitching functionality is challenging. In this work, we combine integrated photonics with optically switchable organic molecules to create an optically controlled integrated device. A silica toroidal resonant cavity is functionalized with a monolayer of an azobenzene derivative. After functionalization, the loaded cavity Q is above 100,000. When 450 nm light is coupled into cavity resonance, the azobenzene isomerizes from trans isomer to cis isomer, inducing a refractive index change. Because the resonant wavelength of the cavity is governed by the index, the resonant wavelength changes in parallel. At the probe wavelength of 1300 nm, the wavelength shift is determined by the duration and intensity of the 450 nm light and the density of azobenzene functional groups on the device surface, providing multiple control mechanisms. Using this photoswitchable device, resonance frequency tuning as far as sixty percent of the cavity free spectral range in the near IR is demonstrated. The kinetics of the tuning are in agreement with spectroscopic and ellipsometry measurements coupled with finite element method calculations.