Photochemically induced isothermal phase transition in polymer liquid crystals with mesogenic phenyl benzoate side chains. 2. Photochemically induced isothermal phase transition behaviors

The design and preparation of azobenzene-containing polymers showing a large photoinduced change in refractive index, and their applications to rewritable Raman-Nath and Bragg holograms are reviewed. Optically transparent films with a thickness of 4200 lm have been prepared with random copolymers, which contain photoresponsive and amplifying components in the side chain. Various azobenzene chromophores are used as the photoresponsive component. Cyanobiphenyl and tolane moieties are incorporated as the amplifying component, which enhances the change in refractive index triggered by the azobenzene. When two writing beams are made to overlap in the film, a periodic change in refractive index is induced, and an incident probe beam is diffracted at B100% diffraction efficiency. The recorded holograms can be erased by thermal treatment or by photoirradiation with a single writing beam. Angular multiplicity is discussed from the viewpoint of high-density information storage. Keywords: azobenzene; grating; hologram; liquid crystal; refractive index INTRODUCTION Holograms, in which we can observe natural three-dimensional (3D) images without eyeglasses, have been of great interest from the viewpoint of 3D television. [1][2][3] In addition, other photonic applications such as holographic memory, optical switch and waveguide have been proposed. [3][4][5][6][7][8][9] The holograms can be categorized into two types: (1) Raman-Nath type and (2) Bragg type. The Raman-Nath hologram recorded in a thin film causes multiple diffraction of an incident beam, leading to low diffraction efficiency (o34%). On the other hand, the Bragg hologram shows a single diffraction, which enables 100% diffraction efficiency. Furthermore, angular multiplicity can be used in the Bragg hologram. Therefore, thick films are suitable for holograms with high diffraction efficiency. The diffraction efficiency also depends on a photoinduced change in refractive index of the film. If materials in which a large change in refractive index can be induced by light can be prepared, the performances parameters such as diffraction efficiency, response and multiplicity of the holograms can be enhanced. How can we induce the change in refractive index efficiently? In an isotropic material, the change in refractive index by photoirradiation is rather small and the efficiency is not high. In addition, the material is theoretically polarization inactive. On the other hand, an anisotropic material could show birefringence. By controlling their molecular alignment by photoirradiation, a large change in refractive index and high diffraction efficiency can be obtained. Furthermore, an anisotropic material shows polarization activity. Therefore, we can expect the fabrication of high-performance holograms by photoinduced alignment of anisotropic molecules.

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“…Ikeda et al 4,[41][42][43][44] prepared various azobenzene-containing LC polymers and investigated their photoresponsive behavior (Figure 2). …”

Section: Photoinduced Change In Molecular Alignment In Lcsmentioning

confidence: 99%

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

Shishido

2010

Polym J

165

108

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“…If even a small number of azomolecules are distributed in an LC phase, trans-cis isomerization can destabilize the phase by lowering the nematic-to-isotropic phase transition temperature (Eich and Wendorff, 1990). This enables fast isothermal photocontrol of phase transitions (Kato et al, 1996;Hayashi et al, 1995;Ikeda and Tsutsumi, 1995;Ikeda et al, 1990). Since these modulations are photoinitiated, it is straightforward to create patterns (Shannon et al, 1994).…”

Section: Classes Of Azobenzene Systemsmentioning

confidence: 99%

“…The azo chromophores act as mesogens and their photoalignment becomes transferred to the LC host. A very small azo content (a few mol% [Ikeda et al, 1990]) can lead to orientational control of LC domains. This is an excellent example of amplification of the azomolecular motion.…”

Section: Domain Motionmentioning

confidence: 99%

Azobenzene Polymers for Photonic Applications

Yager¹,

Barrett²

2008

Smart Light‐Responsive Materials

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“…[4][5][6] Azobenzene groups in polymer matrices have been studied in many application. [7][8][9][10] A variety of polymers were used in host/guest, [11][12][13] main-chain, 14 and side-chain 15,16 systems. Among them, side-chain poly(methylmethacrylate) (PMMA) would be the most famous structure because of the facile synthesis for functional monomers and polymers therefrom.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Photoisomerization Properties of Polynorbornenes with Azobenzene Chromophores

Kang

Shin

et al. 2002

Bulletin of the Korean Chemical Society

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We successfully synthesized the addition-type polynorbonenes (PNB) exhibiting photochromic properties and excellent thermal stability. Three norbornene-based monomers with different azobenzene moiety (R=NO 2 , H, OCH 3 ) were synthesized by transesterification method. The corresponding PNB copolymers were synthesized by transition metal-catalyzed addition polymerization method, and characterized by GPC, UV-Vis spectroscopy, NMR, and thermal analysis. For comparison of the photochromic properties depending on the rigidity of polymer backbone, we prepared the polymethylmethacrylate (PMMA) copolymer with the corresponding azobenzene moiety. We investigated the photoisomerization behavior by means of optical muitichannel analyzer with Xe lamp as well as real-time UV-Vis spectroscopy with high-pressure mercury lamp. Among three PNB copolymers, a polymer with azobenzene (R=H) was the most adaptable for observation of photoisomerization behavior. It was found that the rate of photoisomerization and relaxation depended on the structure of azobenzene chromophore, rather than that of polymer backbone.

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Photochemically induced isothermal phase transition in polymer liquid crystals with mesogenic phenyl benzoate side chains. 2. Photochemically induced isothermal phase transition behaviors

Cited by 196 publications

References 7 publications

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

Azobenzene Polymers for Photonic Applications

Synthesis and Photoisomerization Properties of Polynorbornenes with Azobenzene Chromophores

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