Three-Dimensional Manipulation of an Azo Polymer Liquid Crystal with Unpolarized Light

Wu, Yiliang; Ikeda, Tomiki; Zhang, Qijin

doi:10.1002/(sici)1521-4095(199903)11:4<300::aid-adma300>3.0.co;2-y

Cited by 101 publications

(73 citation statements)

References 8 publications

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“…Therefore, azobenzene molecules are reoriented according to the incident NP light direction (Figure 12b). 109,110 In contrast, photocrosslinkable materials exhibiting reorientation parallel to E generate the three-dimensional molecular reorientation via slantwise p-polarized LP light exposure (Figure 13a). 73,74 For example, Figure 13b plots the angular dependence of the retardation of a 31 (m = 6) film exposed to slantwise LP light (45°with p-polarization) and subsequent annealing.…”

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confidence: 99%

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Kawatsuki¹

2011

Chemistry Letters

116

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Photosensitive materials for photoalignment of liquid crystals (LCs) and photoinduced molecular reorientation are described, especially focusing on azobenzene-containing materials and photocrosslinkable polymers. All the materials generate photoinduced optical anisotropy by means of linearly polarized (LP) light exposure. The large optical anisotropy is induced when the axis-selective photoreaction is accompanied by molecular reorientation. Ç IntroductionDue to practical applications of the alignment layer of functional materials such as low-molecular-weight liquid crystals (LCs), photoalignment and photoinduced molecular reorientation of photosensitive films have received much attention. 13 Additionally, these films have been investigated for molecularly oriented birefringent devices due to the absence of mechanical damage, absence of electric charge, and patterning ability.13 Photoinduced optical and physical anisotropies can be generated in a photoreactive polymeric film by light exposure because the photoreaction changes the inherent refractive index of the molecules. Irradiating with linearly polarized (LP) light causes the photosensitive molecules parallel to the polarization (E) of LP light (y axis) to preferentially photoreact (Figure 1). This axis-selective photoreaction leads to optical anisotropy (birefringence) between the y axis and xz plane if the photoreaction changes the inherent refractive indices of the molecules.To obtain uniaxial alignment of LCs on thin polymeric films, the LC photoalignment layer should exhibit optical or physical anisotropy. Under this circumstance, a large molecular orientation of the film is unnecessary. The anisotropic interaction between the photoalignment layer and LC molecules induces uniaxially oriented LC molecules.1 Because the axis-selective photoreaction induces a small change in the refractive index of the photoalignment layer, 4 a thick film is necessary for optically anisotropic devices such as a birefringent film. Consequently, a large optical anisotropy in the photoreacted film is generated when molecular reorientation occurs during an anisotropic photoreaction. 3Various types of materials that undergo an axis-selective photoreaction to generate photoinduced optical anisotropy have been investigated, including azobenzene-containing polymers 2,57 and photocrosslinkable polymers. 1,3,4 For the azobenzene molecules, axis-selective photoisomerization is generated when the film is irradiated with linearly polarized (LP) light (Figure 2a). Similarly, irradiating with LP ultraviolet (LPUV) light induces both axis-selective [2 + 2] photo/cycloaddition (photocrosslinking) reaction and photoisomerization for cinnamic ester derivatives (Figure 2b). Low-molecular LC molecules easily align on these anisotropically photoreacted films. When an axis-selective photoreaction occurs without generating molecular reorientation, the photoinduced birefringence (¦n) is less than 0.01. 4 An anisotropic photoreaction combined with molecular motion may generate a large optica...

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Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Kawatsuki¹

2011

Chemistry Letters

116

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“…This means that non-photo-crosslinked mesogenic groups may control the inclination direction of the mesogenic groups for film P3, similarly to the slantwise LP light exposure of azobenzene-containing PLC films. [17,18] The inclination of the out-of-plane reorientation can be evaluated by a conoscopic observation as shown in Fig. 6.…”

Section: Three-dimensional Molecular Orientationmentioning

confidence: 99%

Three-Dimensional Orientation of Mesogenic Moieties in Photo-Cross-Linkable Copolymer Liquid Crystals by Irradiation with Polarized Light.

Kawatsuki

Furuso

Goto

et al. 2002

J. Photopol. Sci. Technol.

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Three kinds of methacrylate polymer liquid crystals (PLCs); a copolymer PLC (PLC) substituted with a photo-cross-Linkable 4-(4'-methoxycinnamoyl)oxybiphenyl (MCB) side group and a 4-methoxybiphenyl (4MB) side group (P1), a CPLC with a MCB side group and a 4-cyanobiphenyl (4CN) side group (P2) , and a PLC with a photocross-linkable 4-cinnamoyloxybiphenyl side group (P3), are synthesized . The thin films of these polymers are applied to a birefringent film by irradiation with linearly polarized ultraviolet (LPUV) light and subsequent annealing. Due to axis-selective photo-crosslinking, a small negative optical anisotropy is observed for all CPLCs after exposure to LPUV light. Thermal treatment in the liquid crystalline temperature range for Pl causes in-plane reorientation and results in an in-plane order parameter of 0.71 . In contrast, outof-plane reorientation is generated for P2 and P3. Three-dimensional molecular reorientation and inclined out-of-plane reorientation can be controlled by adjusting the exposure angle. The inclination direction is dependent on the type of the liquid crystalline phase and the side group.

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“…[1][2][3][4][5][6][7][8][9][10][11] For the LC polymers, LC polymers with azobenzene group as a photoisomerizable group 8,[12][13][14][15][16] or cinnamoyl group as a photocyclodimerizable group [17][18][19][20][21] have been mainly studied on photoalignment after linearly polarized ultraviolet (LPUV) light irradiation or on thermal alignment after the anisotropic photoreaction. In these reports, spacer lengths of alkylene groups, 5,15,19,20 compositions of non-photosensitive comonomers, 6,17,19,21 and comonomer units 8,19,22 as structural factors of the photosensitive LC polymers were focused on the orientational order and directions, i.e.…”

Section: Introductionmentioning

confidence: 99%

High in-plane alignment of liquid crystalline methacrylate copolymers bearing photoreactive 2-styrylpyridine and mesogenic 4-methoxybiphenyl groups

et al. 2010

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This paper describes the thermally enhanced in-plane alignment and other properties of liquid crystalline (LC) copolymers (1, 2, and 3) consisting of a methacrylate with a 2-styrylpyridine side group as a photocyclodimerizable group and a methacrylate with a methoxy biphenyl side group as a mesogenic group. 1 H NMR spectroscopy indicated that the contents of the photoreactive monomer unit in copolymers 1, 2, and 3 were 0.65, 0.46 and 0.19 (mole fraction), respectively. The copolymers in the film showed a transmittance of 92% at wavelengths > 450 nm, even at 100 o C, as well as thermal stability up to approximately 360 o C. Copolymers 1 and 2 gave a nematic texture at 155 and 150 o C, respectively, while copolymer 3 showed a smectic texture at 130 o C. The copolymer films aligned parallel to the linearly polarized UV(LPUV) light after LPUV light irradiation and subsequent thermal annealing. The respective in-plane order parameters of copolymers 1, 2, and 3 in the film at 315 nm were 0.65 at 0.001 J/cm 2 , 0.59 at 0.01 J/cm 2 , and 0.48 at 0.025 J/cm 2 by the same treatment in the LC temperature ranges. This suggests that the photoreactive LC copolymers not only have high optical transparency and good thermal stability but also have controllable, high in-plane alignment with the contents of the photoreactive monomer unit.

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Three-Dimensional Manipulation of an Azo Polymer Liquid Crystal with Unpolarized Light

Abstract: Micro-electron diffraction measurements were obtained with a different TEM instrument that is not ªhigh-resolutionº, therefore diffraction from an individual crystallite is not presented with the corresponding image.

Cited by 101 publications

References 8 publications

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Three-Dimensional Orientation of Mesogenic Moieties in Photo-Cross-Linkable Copolymer Liquid Crystals by Irradiation with Polarized Light.

High in-plane alignment of liquid crystalline methacrylate copolymers bearing photoreactive 2-styrylpyridine and mesogenic 4-methoxybiphenyl groups

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