&lt;title&gt;Free and stimulated orientation of liquid crystals on azobenzene polymer films&lt;/title&gt;

Yaroshchuk, O.; Tereshchenko, A. G.; Lindau, J.; Böhme, Axel

doi:10.1117/12.239190

Cited by 8 publications

(3 citation statements)

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“…Changes in birefringence induced by irradiation with linearly polarized light at high temperatures were observed by Wang et al for liquid crystalline polymers with azobenzene side chains, though no clear mechanism has been provided. The successive out-of-plane reorientation occurs as a result of the repetition of photoisomerization in the same mechanism as that for the out-of-plane orientation induced by nonpolarized light to minimize light absorption …”

Section: Discussionmentioning

confidence: 99%

Factors Affecting In-Plane and Out-of-Plane Photoorientation of Azobenzene Side Chains Attached to Liquid Crystalline Polymers Induced by Irradiation with Linearly Polarized Light

2000

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Photoinduced orientational behavior of polymethacrylates with side chains (amorphous polymers, pMAz2 and C2MeO, and liquid crystalline polymers, C6MeO and C12MeO) with different alkylene spacer lengths (n ) 2, 6, 12) were investigated by means of polarized Fourier transform infrared (FT-IR) and UV-vis absorption spectroscopy. Being different from pMAz2, C2MeO showed high optical anisotropy due to in-plane orientation and the excellent thermostability even above T g, which can be explained in terms of potential liquid crystallinity to be able to have a tendency to form a well-ordered domain. We observed marked dependence of photoorientation processes on film temperatures of C6MeO. While in-plane orientation was generated in glassy state as well as at 76 °C, irradiation at 90 °C slightly lower than T SN (transition temperature between smectic and nematic phases) gave rise to the distinct transformation from in-plane orientation at the early stage to successive out-of-plane reorientation, which was accompanied by H-aggregation. This situation enabled ones to record optical images in a C6MeO film on the basis of the difference in birefringences between two orientational modes. The biaxial reorientation occurred also for C12MeO, though both in-plane and out-of-plane photoorientation occurred simultaneously at room temperature as well as elevated film temperatures.

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Section: Discussionmentioning

confidence: 99%

Factors Affecting In-Plane and Out-of-Plane Photoorientation of Azobenzene Side Chains Attached to Liquid Crystalline Polymers Induced by Irradiation with Linearly Polarized Light

2000

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“…Kawanishi et al suggested for the first time the photocontrol of tilt orientation of liquid crystals (LCs) by oblique nonpolarized UV irradiation of cells surface-modified with azobenzenes as a command surface. This work was followed by a report by Yoroshchuk et al who studied LC orientations on azobenzene polymer films exposed to UV light of perpendicular and inclined incidence. However, no clear indication was given to elucidate the relationship of molecular tilt orientation between LCs and surface azobenzenes.…”

Section: Introductionmentioning

confidence: 92%

Tilt Orientation of p-Methoxyazobenzene Side Chains in Liquid Crystalline Polymer Films by Irradiation with Nonpolarized Light

Han

Ichimura

2000

Macromolecules

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Unambiguous observation of the reorientation of azobenzene chromophores toward the propagation direction of the actinic light has been performed. Prolonged irradiation of a spin-coated film of liquid crystalline poly[6-{4-(4′-methoxyphenyl)azophenyloxy}hexyl methacrylate] (C6MeO) with 436 nm light for n-π* excitation led to a marked decrease of the π-π* absorption band. Spectral analysis in combination with conoscopic observation revealed that the reorientation of the azobenzene chromophores occurs in such a way that the longitudinal molecular axis of the azobenzene aligns in parallel with the propagation of light to form strong H-aggregates. The tilt orientation of the azobenzene was more readily achieved by irradiation with light at high temperatures near or above the glass transition temperature. Concerning the effect of spacer length on the three-dimensional orientation, the azobenzene groups showed a tendency to orient more homeotropically as the alkylene spacer length increases.

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“…An electrically excited molecule undergoes reversible E/Z photoisomerization to give preferentially in-plane reorientation toward the direction perpendicular to the electric vector of light, leading to photoinduced birefringence of polymer films doped with the azobenzene . On the other hand, irradiation with nonpolarized light results in spatial (three-dimensional) reorientation of azobenzene in such a way that the transition dipole moment aligns predominantly in parallel with a direction of light propagation to minimize light absorption. , This kind of optical anisotropy of polymers containing azobenzenes induced by irradiation with linearly polarized light as well as by oblique irradiation with nonpolarized light is markedly enhanced by heating of the systems when the polymers with azobenzene side chains are liquid crystalline. Studies on photoinduced reorientation of azobenzenes in polymer matrices reported so far have been carried out by visible light irradiation for n−π* excitation to lead to a photostationary state containing E -isomer as a major component. − …”

Section: Introductionmentioning

confidence: 99%

In-Plane and Tilt Reorientation of p-Methoxyazobenzene Side Chains Tethered to Liquid Crystalline Polymethacrylates by Irradiation with 365 nm Light

Han

Ichimura

2000

Macromolecules

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The generation of optical anisotropy induced by irradiation with linearly polarized 365 nm light and by oblique irradiation with nonpolarized 365 nm light and subsequent annealing was described for liquid crystalline polymethacrylates with p-methoxyazobenzene side chains. Exposure of the spincoated films of the polymers to linearly polarized UV light of 10-20 mJ/cm 2 doses and subsequent annealing at temperatures close to the glass transition temperatures (Tg) of the polymers led to a marked enhancement of azimuthal reorientation of the azobenzene to give birefringent films exhibiting excellent thermostability of the optical anisotropy. When the spin-coated films of the polymers were irradiated obliquely with nonpolarized 365 nm light of about 15 mJ/cm 2 dose and annealed subsequently, spatially manipulated reorientation of the azobenzene groups was realized, accompanied by the formation of H-aggregation. The orientational direction was controlled simply by the incident direction of UV light. The photogenerated optical anisotropy for both cases was considerably reduced or disappears when exposure doses exceed about 50 mJ/cm 2 . The mechanism for the thermally enhanced generation of optical anisotropy induced by both modes of photoirradiation was discussed on the basis of photoselective E-to-Z photoisomerization of the E-isomer with a transition dipole moment parallel to the electric vector of linearly polarized 365 nm light or perpendicular to the incident direction of nonpolarized UV light.

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<title>Free and stimulated orientation of liquid crystals on azobenzene polymer films</title>

Cited by 8 publications

References 0 publications

Factors Affecting In-Plane and Out-of-Plane Photoorientation of Azobenzene Side Chains Attached to Liquid Crystalline Polymers Induced by Irradiation with Linearly Polarized Light

Factors Affecting In-Plane and Out-of-Plane Photoorientation of Azobenzene Side Chains Attached to Liquid Crystalline Polymers Induced by Irradiation with Linearly Polarized Light

Tilt Orientation of p-Methoxyazobenzene Side Chains in Liquid Crystalline Polymer Films by Irradiation with Nonpolarized Light

In-Plane and Tilt Reorientation of p-Methoxyazobenzene Side Chains Tethered to Liquid Crystalline Polymethacrylates by Irradiation with 365 nm Light

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