Recent developments in aromatic azo polymers research

Abstract

The photochemical and thermal cis-to-trans isomerization of aromatic azo groups covalently bonded within polymers and its practical consequences as well as some other recent applications are reviewed. The kinetics and mechanism of the isomerization of azo polymers are briefly presented, and then several recent developments in azo polymers research are discussed. They include liquid crystallinity, nonlinear optical properties, monolayer assemblies, and the lightinduced birefringence and dichroism. Some of the phase transitions of liquid-crystalline azo polymers can be induced photochemically by the azo groups isomerization. Second-order optical nonlinearity can be obtained in polymers with donorand acceptor-substituted azo groups. Using the Langmuir-Blodgett technique, azo polymer monolayers can be built and used as "command surfaces" of liquid-crystal films. The light-induced birefringence is a reorientation phenomenon which is a consequence of the trans-cis-trans isomerization. Future possible applications for a variety of practical devices, such as display devices, optical modulators, optical waveguides, holography, and reversible optical storage are mentioned.

Responsive behavior of 4-(N-maleimido)azobenzene in polymers with aromatic main chain and side chain linked units

“…Their potential use in optics or optoelectronics, such as for information storage, optical switching devices, surface relief gratings, nonlinear optics, etc has been motive the attention of the researchers and end users. [1][2][3][4][5][6][7][8][9][10] Large area of applications of azobenzene compounds is possible due to both its photoinduced properties and wide variety of the systems that it contained. Azobenzene chromophore has unique optical and photochemical properties.…”

“…Several approaches were used to insert azobenzene chromophores into polymer matrices: randomly incorporation (guest-host structures), binding to main or side chains, or formation of thin-layer structures like Langmuir-Blodgett films. [2][3][4][5][13][14][15] Azobenzene-containing polymers have been investigated with regard to different phenomena associated with the photochromic nature of the azobenzene moiety. Their conformational modifications induced by photo-or thermal isomerization of the azobenzene chromophore give the possibility to control some physical and chemical properties of the materials including viscosity, solubility, pH, refractive index, conductivity, dielectric permittivity, mechanical properties, etc.…”

“…Their conformational modifications induced by photo-or thermal isomerization of the azobenzene chromophore give the possibility to control some physical and chemical properties of the materials including viscosity, solubility, pH, refractive index, conductivity, dielectric permittivity, mechanical properties, etc. [1][2][3]12,16 Doping azobenzene compounds into polymer matrices is a convenient inclusion technique. Besides opportunity to use a presynthetized polymer the development of doped azobenzene systems become interesting for studying the behavior of chromophore and owing to the actual tendency to obtain composites with very small content of active component.…”

Photophysics, Photochemistry, and Photo-optical Effects in Polymer Solids

“…Photochemical reactions have potential applicability to photo-optical switching devices, because they change the electronic structure of the molecules and the density of the system (22)(23)(24)(25). The change in refractive indices and the anisotropy of PMMA (poly(methyl methacrylate)) films containing DAAB (pKiimethylaminoazobenzene) were measured during polarized-light-induced photoisomerization, and the possibility as a photo-optical controlling material was examined (26).…”

Azobenzene Polymers for Photonic Applications

“…1.4). The thermal backrelaxation is agreed to be via rotation, whereas for the photochemical isomerization, both mechanisms appear viable (Xie et al, 1993). Historically, the rotation mechanism (as necessarily occurs in stilbene) was favored for photoisomerization, with some early hints that inversion may be contributing (Gegiou et al, 1968).…”