Photoisomerization Of Azobenzene Moiety Research Articles

Sunlight-Driven Smart Windows with a Wide Temperature Range of Optical Switching Based on Chiral Nematic Liquid Crystals.

Photoresponsive liquid crystals are promising materials for sunlight-driven smart windows, which can automatically change their optical states in response to sunlight and control energy flow between the inside and outside of a building. Herein, liquid-crystalline systems are developed that show a transparent-scattering transition upon irradiation with sunlight in a wide temperature range. Push-pull azobenzenes with axial chirality have been newly developed as photochromic chiral dopants to allow changes in mesostructures of liquid crystals in response to sunlight. To realize optical switching, photochromic and photoinert chiral compounds with opposite handedness of helical twisting are doped in liquid crystals. This liquid crystalline sample with a compensated nematic phase is transparent in its initial state. Upon irradiation with sunlight, this sample transforms to a scattering state due to the formation of helical mesostructures along with photoisomerization of azobenzene moieties and the change in the helical twisting power. After the cease of irradiation, the sample reverts to the transparent state through thermal back isomerization of azobenzene moieties. This system significantly improves the operating temperature range of sunlight-driven smart windows based on liquid crystals: the transparent-scattering transition is observed at 4-42 °C. The present mechanism allows development of autonomous and wireless smart windows adaptable to various environments.

Azobenzene Functionalized Organic Covalent Frameworks: Controlled Morphologies and Photo‐Regulated Adsorption

AbstractCovalent organic frameworks (COFs) containing azobenzene building blocks carry great potential for use in intelligent storage, separation, chemical sensing, and catalysis due to their intriguing photo‐responsiveness. However, azobenzene units are often exploited as the linkers to form the framework of COFs, thereby restricting their molecular motion and photoisomerization. Herein, a simple yet robust template‐free solvothermal strategy is reported to yield azobenzene‐dangled COFs (Azo‐COFs) with their azobenzene moieties suspending within the pores. The crystallinity, specific surface area, and morphology of Azo‐COFs can be conveniently tailored by changing the ratio of amine to aldehyde monomers. Notably, the Azo‐COFs provide sufficient free space for the reversible trans‐to‐cis isomerization of the dangled azobenzene units inside the pores, thus reversibly regulating surface wettability of Azo‐COFs. The adsorption capacity of Azo‐COFs toward organic dye molecules is increased by 3.7‐fold when irradiated with ultraviolet light, which can be ascribed to the intelligent closing/opening of molecular gates rendered by photoisomerization of azobenzene moieties. As such, the ability to photoregulate the adsorption of Azo‐COFs highlights their significance in functioning as smart porous nanomaterials for applications in cargo release, molecular sieves, ion transport, energy conversion systems, and environmental remediation.

Light-Triggered Reversible Swelling of Polymeric Spheres via Surfactant-Free RAFT Emulsion Polymerization-Induced Self-Assembly.

Responsive photonic crystals (RPCs) assembled by monodisperse colloidal particles have attracted enormous interest recently due to their tremendous applications in smart devices. Their structural colors can be determined by particle sizes. However, the lack of a reliable way to tune the sizes in situ limits their development. Herein, we present an efficient route to solve this problem through the fabrication of spherical polymeric particles with light-triggered reversible swelling behavior via surfactant-free reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization-induced self-assembly (PISA). Amphiphilic macro-RAFT agents containing azobenzene groups were synthesized and subsequently employed to mediate the polymerization of methyl methacrylate. Uniform submicron spheres were obtained by modulating solid contents and other parameters. Benefiting from the photoisomerization of azobenzene moieties, the particle sizes expanded and contracted upon alternative ultraviolet/visible-light irradiation accordingly. This strategy will be a supplement to the emulsion PISA and especially give aid to the progress of the RPC materials.

Automated adherent cell elimination by a high-speed laser mediated by a light-responsive polymer

Conventional cell handling and sorting methods require manual labor, which decreases both cell quality and quantity. To purify adherent cultured cells, cell purification technologies that are high throughput without dissociation and can be utilized in an on-demand manner are expected. Here, we developed a Laser-induced, Light-responsive-polymer-Activated, Cell Killing (LiLACK) system that enables high-speed and on-demand adherent cell sectioning and purification. This system employs a visible laser beam, which does not kill cells directly, but induces local heat production through the trans-cis-trans photo-isomerization of azobenzene moieties. Using this system in each passage for sectioning, human induced pluripotent stem cells (hiPSCs) maintained their pluripotency and self-renewal during long-term culture. Furthermore, combined with deep machine-learning analysis on fluorescent and phase contrast images, a label-free and automatic cell processing system has been developed by eliminating unwanted spontaneously differentiated cells in undifferentiated hiPSC culture conditions.

Photomechanical Motion of Liquid-Crystalline Fibers Bending Away from a Light Source

A series of photomechanical fibers was fabricated with a thermal drawing method by using liquid-crystalline random copolymers containing azobenzene and biphenyl groups in side chain. After being post-cross-linked under mild conditions, these fibers showed photoinduced bending motion away from the light source even though homogeneous alignment of mesogens was observed along the drawing direction. This abnormal photoinduced deformation of the obtained fibers is far different from previously reported light-directed motions about liquid-crystalline fiber and film materials. The interesting photomechanical deformation can be ascribed to the surface volume expansion caused by photoisomerization of azobenzene moieties. Then the photoinduced bending behaviors of these fibers containing different azobenzene concentrations and cross-linking densities were systematically investigated, suggesting that the location of photoresponsive azobenzene played an important role in deciding their photomechanical behaviors. This...

Photoinduced Deformation of Rigid Azobenzene-Containing Polymer Networks

Photoresponsive poly(amide acid) (PAA) gels containing multiple azobenzene units in a rigid aromatic backbone were synthesized. A centimeter-long cantilever made up of the photoresponsive PAA gel exhibited reversible bending motions upon blue (442 nm) and visible light (>490 nm) irradiation. The network structure in the PAA gels during alternating photoirradiation of blue and visible light was characterized using in situ scanning microscopic dynamic light scattering (SMILS), which revealed reversible mesh-size changes synchronized with the photoisomerization of azobenzene moieties. The photomechanical responses of the PAA gel were likely due to photoinduced contracting and stretching motions of the polymer backbone. A numerical calculation of photon absorptions revealed that photoisomerization in a very thin layer of the surface (∼40 μm) generated large macroscopic motion and large strain in the gel cantilever. The photoresponsive capability is, however, reduced or eliminated when the PAA gels are transfo...

Fabrication of Multilayer Film Type Laser Devices Containing Azobenzene Polymer and Control of Polarized Laser Emission

We prepared multi-bilayered films consisting of methacrylate polymer having azobenzene side chain groups (PMAz6Mc), polyvinyl alcohol and lasing dye. We investigated effects of molecular orientation of azobenzene moieties on the lasing behavior by measuring laser emission of the multi-bilayered films with/without polarized visible light irradiation to cause trans-cis-trans photoisomerization of azobenzene moieties. After irradiation of the polarized visible light, significant dependence of polarization direction of the laser emission intensity was observed, corresponding to the change in the molecular orientation of azobenzene moieties.

Building a Nanostructure with Reversible Motions Using Photonic Energy

Recently, the specific hybridization of DNA molecules has been used to construct self-assembled devices, such as the mechanical device to mimic cellular protein motors in nature. Here, we present a new light-powered DNA mechanical device based on the photoisomerization of azobenzene moieties and toehold-mediated strand displacement. This autonomous and controllable device is capable of moving toward either end of the track, simply by switching the wavelength of light irradiation, either UV (365 nm) or visible (>450 nm). This light-controlled strategy can easily solve one main technical challenge for stepwise walking devices: the selection of routes in multipath systems. The principle employed in this study, photoisomerization-induced toehold length switching, could be further useful in the design of other mechanical devices, with the ultimate goal of rivaling molecular motors for cargo transport and macroscopic movement.

Synthesis and Characterization of Photochromic Copolymer Grafting Azoaromatic Chromospheres on Pullulan

Preparation of photochromic copolymer grafting 4-(4-nitro phenylazo)-1-naphthol units on a pullulan molecular surface has been accomplished. Surface modification was carried out in aqueous solution by an inverse emulsion polymerization method. Polymerization products were characterized by IR, SEM, XRD and TG-DTA. UV-vis spectroscopy has been used to monitor the photoisomerization of azobenzene moieties on a pullulan molecular surface. The results indicated that functional copolymer has a better photochromism property than its corresponding azobenzene moieties, reflecting the macromolecular backbone of pullulan should actively affect the photoisomerization of azoaromatic moieties.

Photocontrolled Self-Assembly and Disassembly of Block Ionomer Complex Vesicles: A Facile Approach toward Supramolecular Polymer Nanocontainers

A new concept of designing a photocontrollable supramolecular polymer nanocontainer through the electrostatic association between an azobenzene-containing surfactant (AzoC10) and a double-hydrophilic block ionomer, poly(ethylene glycol)-b-poly(acrylic acid) (PEG(43)-PAA(153)), is described. Such a block ionomer complex can self-assemble in aqueous solution and form vesicle-like aggregates, which are composed of a poly(ethylene glycol) corona and a poly(acrylic acid) shell associated with azobenzene-containing surfactant. The photoisomerization of azobenzene moieties in the block ionomer complex can reversibly tune the amphiphilicity of the surfactants, inducing the disassembly of the vesicles. Such block ionomer complex vesicles are further evaluated as nanocontainers capable to encapsulate and release guest solutes on demand controlled by light irradiation. For example, the vesicles encapsulating the fluorescein sodium display clear spherical images observed by fluorescence microscopy. However, such fluorescence-marked images disappear after releasing the solute from the vesicles triggered by the UV light. Such novel materials are of both basic and practical significance, especially as prospective nanocontainers for cargo delivery.

Contrast Viscosity Changes upon Photoirradiation for Mixtures of Poly(acrylic acid)-Based α-Cyclodextrin and Azobenzene Polymers

Polymer-polymer interactions were investigated for mixtures of a poly(acrylic acid) (pAA) carrying azobenzene (pC12Azo) and two kinds of pAA carrying alpha-cyclodextrin (CD), in which CDs are attached to the main chain through the 3- and 6-positions in CD (p3alphaCD and p6alphaCD, respectively), using several techniques, such as viscosity and NMR measurements. Viscosity data exhibited contrast changes upon UV irradiation: thinning (p3alphaCD/pC12Azo) and thickening (p6alphaCD/pC12Azo). NOESY spectra confirmed that the contrast viscosity changes were ascribable to differences in how CD moieties interact with pC12Azo after photoisomerization of azobenzene moieties from trans to cis: dissociation of inclusion complexes (p3alphaCD/pC12Azo) and formation of interlocked complexes (p6alphaCD/pC12Azo).

Multi-functional polypyrrole nanofibers via a functional dopant-introduced process

This paper reports a functional dopant-introduced route to synthesize polypyrrole (PPy) nanofibers (60–100 nm in average diameter) in the presence of p-hydroxyl-azobenzene sulfonic acid ( p-OH-ABSA) as a functional dopant. The nanofibers show a high conductivity (120–130 S/cm) and photoisomerization, which resulted from proton doping and photoisomerization of azobenzene moiety, respectively. Static and dynamic light scattering as well as freeze-fracture replication transmission electron microscope measurements (FFRTEM) showed that the self-assembled cylindrical micelles act as “soft-templates” during the formation of the nanofibers. Influence of polymerization conditions, such as the type of oxidant, the rate of oxidant addition, the concentration of reactants and polymerization time, on the fibrous morphology of PPy-( p-OH-ABSA) has been investigated. The characterizations of molecular structure, photoisomerization and electrical properties have been carried out. The method described in this study provides a simple and inexpensive route to prepare multi-functional nano-structured conducting polymers.

Photoreactivity in Self-Assembled Monolayers Formed from Asymmetric Disulfides Having para-Substituted Azobenzenes

Asymmetric dialkyl disulfides with a para-substituted azobenzene (i.e., 4-substituted 4‘-(12-(dodecyldithio)dodecyloxy)azobenzenes) produced photoresponsive self-assembled monolayers (SAMs) on gold (111) surfaces. Infrared reflection absorption (IR-RA) spectroscopy and reflection ultraviolet (UV) and visible (vis) light absorption spectroscopy gave information on the molecular orientational order of the adsorbates in the SAMs. The photoreactivity was investigated using dynamic contact-angle measurements with a Wilhelmy-type surface balance. The structure and photoreactivity of the SAMs were dependent on the substituent at the para position of an azobenzene moiety. Relatively ordered structures in the methylene parts and the photoisomerization of azobenzene moieties were observed for the SAMs formed from the hexyl- and the nonsubstituted azobenzene disulfides. However, a less-ordered SAM structure was seen for the cyanoazobenzene disulfide SAM, and the photoresponse is rather unstable.