Photoisomerization Of Azobenzene Group Research Articles

Bent-core liquid crystals joining the ethylene-oxide/lithium ion tandem: Ionic conductivity and dielectric response towards new electrolytes for energy applications

We report the dielectric and conductivity response of three materials containing bent-core and tetra(ethylene-oxide) moieties, and their complexes doped with lithium triflate salts, as new potential nanostructured electrolytes. Whilst the pristine bent-core compounds do not show mesomorphism, the doped materials display smectic mesophases inside indium tin oxide cells assisted by the selective solvation of the lithium ions in the ethylene-oxide blocks. The dielectric response of the materials in the high-frequency range is controlled by the chemical composition of the bent-core structure, and the presence of lithium ions promotes direct current conductivity at low frequencies, in the σdc ∼ 10-5 S cm−1 range, which can be enhanced to σdc ∼ 10-4 S cm−1 via trans-to-cis photoisomerization of azobenzene groups. The dynamic and dual character of these materials (responding to low and high frequency electrical fields), the formation of ferroelectric crystals capable to store energy, and their interactions with light, will be applied to develop new energy devices.

Back Cover

The development of azobenzene‐containing polymers (azopolymers) opens up an avenue for controlling their properties and functions with light. These polymers show shape changes and mechanical responses under the stimulation of light via photoisomerization of azobenzene groups. Herein, this report focuses on the growing research on moving polymers via photoisomerization, including their moving mechanisms and various applications. More details are discussed in the article by Wu et al. on page 1019—1022.image

Moving Polymers via Photoisomerization

Photoresponsive materials, which can adapt their states and shapes upon light irradiation, have attracted worldwide attention in the past decades. The development of azobenzene‐containing polymers (azopolymers) opens up an avenue for controlling their properties and functions with light. These polymers show shape changes and mechanical responses under the stimulation of light via photoisomerization of azobenzene groups. Herein, this report focuses on the growing research on moving polymers via photoisomerization, including their moving mechanisms and various applications.

Liquid Crystalline Copolymers Containing Sulfonic and Light-Responsive Groups: From Molecular Design to Conductivity.

In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). By using a cascade of reversible addition-fragmentation chain polymerisations, RAFT, we have tailored different side-chain polymeric structures by controlling monomer composition (MeOAzB/AMPS/MMA) and configuration. We have yielded simultaneous liquid crystalline behaviour and appreciable conductivity in polymers with low concentrations of polar acid groups, by the formation of smectic phases in narrow aggregates. The light-responsiveness of the polymers, via reversible trans-to-cis photoisomerization of azobenzene groups, and the local activation of conductivity at relatively low temperatures, opens the possibility to prepare polymer electrolytes for energy conversion and storage, whose conductivity could be controlled and optimised by external stimuli, including light irradiation.

Azobenzene-functionalized polymers by ring-opening metathesis polymerization for high dielectric and energy storage performance

Block copolymers with push–pull azobenzene pendants and core–shell nanostructures exhibited high and regulated dielectric constants by photoisomerization of azobenzene groups, low dielectric loss, and high energy density.

Switchable biphotonic holographic recording in an azobenzene liquid crystal film

Biphotonic holographic recording through the competition of linearly polarized laser beams with wavelengths of 532 nm and 632.8 nm was investigated in an azobenzene liquid crystal film. With the irradiation of 532 nm excitation light as a switch, holographic gratings were able to be turned on and off. It was found that diffraction behaviors of the recorded gratings were strongly dependent on not only the polarization angle between the recording light and excitation light, but also the sample temperature. Formation processes and diffraction properties of biphotonic holographic gratings were discussed based on the photoisomerization of azobenzene groups. Besides, biphotonic polarization holographic recording was also achieved by means of adjusting the polarization states of recording light and the diffraction characteristics were analyzed in terms of Jones matrices.

Frontispiece: Photoinduced Liquefaction of Azobenzene‐Containing Polymers

Photoisomerization of azobenzene groups in the polymer results in solid-to-liquid transition (see the Frontispiece graphic). Photoinduced liquefaction of azopolymers shows potential applications in healing, lithography, transfer printing, and others. The possible mechanisms, remaining challenges and potential applications of photoinduced liquefaction of azopolymers are described after the fundamentals of photoresponsive azopolymers are presented. For more details, see the Minireview by W. Tian, S. Wu and P. Weis on page 6494 ff.

Photo Induced Membrane Separation for Water Purification and Desalination Using Azobenzene Modified Anodized Alumina Membranes.

Water purification and desalination to produce end-use water are important agendas in 21st century, because the global water shortage is becoming increasingly serious. Those processes using light energy, especially solar energy, without the consumption of fossil fuels are desired for creating sustainable society. For these earth-friendly water treatments, nanoporous materials and membranes are expected to provide new technologies. We have reported before that the repetitive photo isomerization of azobenzene groups between the trans and cis isomers induced by the simultaneous irradiation of UV and visible lights accelerates the molecular movement of nearby molecules in nanoporous materials. After further studies, we recently found that the permeation of water through azobenzene modified anodized alumina membranes as a photo responsive nanoporous membrane was achieved by the simultaneous irradiation of UV and visible lights, while no water penetration occurred under no light, only single UV or visible light. The photo induced permeation of water was promoted by the vaporization of water with the repetitive photo isomerization of azobenzene. This membrane permeation achieved the purification of water solutions, because dye molecules and a protein dissolved in aqueous solutions were not involved in the photo induced penetrated water. When 3.5% of sodium chloride solution as model seawater was employed for this membrane separation, the salt content of the permeated water was less than 0.01% to accomplish the complete desalination of seawater.

Synthesis and Electrooptical Properties of Metal-Containing Azopolymers. The Influence of Steric Factors on the Electro-Optical Effect in Polycomplexes of Azobenzene Derivatives with Cobalt

We propose new structures of metal-containing azopolymers with changeable electro-optical properties in consequence of different coordination metal ions. The new monomers – 4-methacroyloxy-(4′-carboxy-3′-hydroxy)-azobenzene, 4-methacroyloxy-2′-carboxy-azobenzene and their complexes with Co and polymers based of these ones are synthesized. The influence of the electric field on the absorption spectra of new metal-containing azopolymers films are investigated. Electro-optical properties of polymeric films is determined by the re-orientation of dipole moments of azobenzene groups photo induced by polarized light in the electric field. Increase of structural inflexibility by the photo isomerization of azobenzene groups decrease the electro-optical effect value.

Grating inscription in picosecond regime in thin films of functionalized DNA

Polymers containing azo-benzene groups are useful holographic recording materials. In these materials the efficient mixed amplitude and phase gratings, frequently accompanied with photoinduced-surface relief gratings, can be inscribed with polarized laser light. The light-induced trans-cis-trans photoisomerization of azo-benzene groups is responsible for optical anisotropy in such systems. The aim of the present work is to study the dynamics of grating inscription in Disperse Red 1 doped deoxyrbonucleic acid- hexadecyltrimethylammonium material (DR1-DNACTMA) using 16 ps laser pulses (532 nm, 1.3 mJ). Results are compared with that obtained for other polymeric matrices loaded with DR1. The dynamics of the grating growth, due to repeated pulses from picosecond laser with 10 Hz repetition rate, was probed by measuring the intensity of the first order of diffraction of a cw He-Ne. We report results in function of the light polarization of writing beams. In this paper we present the first results of the grating inscription in functionalized DNA (in the picosecond pulse regime).

Different shapes of spherical vaterite by photo-induced cis–trans isomerization of an azobenzene-containing polymer in a mixture of dimethyl sulfoxide and water

We studied the crystallization of CaCO3 by the photoisomerization of azobenzene groups in poly[1-[4-[3-carboxy-4-hydroxyphenylazobenzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) in a mixture of dimethyl sulfoxide and water at 30°C. The products were characterized by scanning electron microscopy (SEM), FT-IR, and powder X-ray diffraction (XRD) analysis. We observed that the different shapes of spherical vaterite particles were produced by the changes of configuration and polarity of the azobenzene groups in the polymer which resulted from photo-induced isomerization. The results indicate that the nucleation of primary particles of CaCO3 was inhibited by in situ photo-induced cis–trans isomerization of PAZO. Therefore, we suggest that the shapes of the spherical vaterite can be effectively modified by photoisomerization of the azobenzene groups in the polymer at the initial stage of CaCO3 crystallization.

Photoinduced textural and optical changes in a cholesteric copolymer with azobenzene-containing side groups

Textural changes induced by UV irradiation of planarly oriented films of a cholesteric copolymer were investigated. The copolymer is composed of photosensitive ethoxyazobenzene and chiral cholesterol-containing side groups, and displays a chiral nematic phase with a left-handed helical supramolecular structure in the temperature range 84–128°C. UV light with a wavelength of 365 nm leads to a deformation of the planar texture at temperatures higher than 100°C and to a reduction of the absorbance peak for left-handed circularly polarized light. Polarizing optical microscopy revealed the formation of a focal-conic texture in the irradiated regions. The texture induced by irradiation is very stable but the initial planarly oriented state can be recovered by mechanical stress. The observed phenomenon is attributed to the E–Z photoisomerization of azobenzene groups leading apparently to the formation of a thin isotropic layer in the films which in turn causes a destabilization of the planar texture. At temperatures below 100°C the textural transformations are accompanied by small shifts of the selective reflection maxima to longer wavelengths. The kinetics of the observed phenomenon were studied in detail and the influence of different parameters, such as light intensity and temperature, examined.