Photochemically induced isothermal phase transition in polymer liquid crystals with mesogenic phenyl benzoate side chains. 1. Calorimetric studies and order parameters

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

163

108

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“…For example, functional main-chain LC polymers 5 have been prepared to exhibit electron conductivities and luminescence properties. 11,12 Photofunctional, 13,14 electro-active, [15][16][17][18] and ion-active [19][20][21][22][23][24] groups have been incorporated into the side chains of LC polymers. For example, LC polymers 6 and 7 bearing electroactive moieties are obtained by using π-conjugated molecules as mesogenic units.…”

Section: Introductionmentioning

confidence: 99%

Functional liquid-crystalline polymers and supramolecular liquid crystals

Kato

Uchida

Ichikawa

et al. 2017

Polym J

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The design and functions of liquid-crystalline (LC) polymers with classifying them into conventional-, supramolecular-, dendriticand network-type LC polymers are described. LC polymers show new functions as new devices in the field of energy and environment by incorporating mesogenic moieties exhibiting photonic, electronic and ionic functions. Supramolecular LC polymers show dynamic and unique properties because the mesogenic moieties are built with non-covalent interactions. Dendritic-type LC polymers exhibit liquid crystallinity by nanosegregation of aromatic and aliphatic moieties. Dendritic fork-like mesogens have also been prepared. A variety of nonmesogeic functional building blocks including fullerene, π-conjugated moieties, catenane, rotaxane and others can be incorporated into LC phases by attaching these dendritic moieties. LC networks are constructed in situ polymerization of polymerizable nematic or nanostructured liquid crystals. The specific characteristics of the LC networks have generated new research trends to develop well-defined polymers that exhibit optical, transport and separation properties. In these materials, through suitable design of LC monomers, the preservation of smectic, columnar and bicontinuous cubic phases has been successfully used for the development of membranes with one-dimensional, two-dimensional and three-dimensional nanostructures.

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“…Azobenzene derivatives are known to undergo cis/trans photo-isomerisation upon irradiation. There are two typical liquid crystalline systems in relating to the photo-cotnrol of the molecular orientation by means of photoisomerisation of azobenzene compounds: one is "photochemical phase transition" between a liquid crystalline phase and a random state [3][4][5] , the other is photoalignment between in-plane and out-of-plane structures, which is called command surface 1,6 . Very few papers have been published on spontaneous outof-plane molecular orientation of polymeric liquid crystals (PLCs) [7][8][9][10][11] .…”

Section: Introductionmentioning

confidence: 99%

Photo Alignment Behaviour of Polyethene Imine Having Cyano Azobenzene Side Chain

Kamruzzaman

Kurihara

2015

Dhaka Univ. J. Sci.

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New type of polyethene imine having cyano (-CN) side chain through six methylene spacer group (PEI6C) was successfully synthesised and characterised. The effect of reaction parameters on degree of substitution of PEI6C was also studied and the reaction conditions were optimised. Photochemical as well as photoorientational behaviour of the polymer were investigated. PEI6C in solid film exhibited photoresponsive properties upon irradiation with UV and visible light. PEI6C film also exhibited reversible molecular orientation from random state to out-of-plane and from out-of-plane to random state upon non-polarised visible and UV light irradiation.

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Photochemically induced isothermal phase transition in polymer liquid crystals with mesogenic phenyl benzoate side chains. 1. Calorimetric studies and order parameters

Cited by 187 publications

References 14 publications

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

Functional liquid-crystalline polymers and supramolecular liquid crystals

Photo Alignment Behaviour of Polyethene Imine Having Cyano Azobenzene Side Chain

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