Kazuaki Kudo

Command surfaces 12 [1]. Factors affecting in-plane photoregulation of liquid crystal alignment by surface azobenzenes on a silica substrate

Abstract In-plane alignment of nematic liquid crystals was regulated by polarized-light-irradiation of a cell assembled with a silica plate, the surface of which was modified by attaching 4-hexyl-4′-hexyloxyazobenzene at its o-position through surface silylation. The photoisomerizability of the chemisorbed azo-chromophore was affected by their surface density and the nature of photoinactive co-modifiers. The efficiency of the photoregulation of liquid crystal alignment was optimized by two-dimensional dilution of the chromophore with ethyltriethoxysilane (ETS) or 3-aminopropyltriethoxysilane (ATS). As a result, favourable procedure was to modify a silica surface with a crude azo-silylating reagent contaminated by ATS. The rate of the photoinduced reorientation of liquid crystals was followed by monitoring the alteration of the alignment direction of a dichroic dye dissolving in a mesophasic layer upon exposure to linearly polarized light. Exposure energy for the in-plane reorientation of a liquid crystal ...

Command surfaces 14 [1]. Photoregulation of in-plane alignment of a liquid crystal by the photoisomerization of stilbenes chemisorbed on a substrate silica surface

Abstract Stilbenes were attached to a quartz surface at their 2-position by silylation through a spacer to determine the capability to regulate an azimuthal alignment of a nematic liquid crystal by irradiation with linearly polarized light. Liquid crystal molecules aligned perpendicular to the direction of polarization plane of the actinic light, just as in the case of surface azobenzenes. The efficiency of the photoregulation was influenced by excitation wavelength and hence related with an E/Z isomeric ratio in a photostationary state. The irradiation with 260 nm polarized light resulting in the E-isomer as a major component in the photostationary state gave better optical quality of a photoaligned texture when compared with 330 nm irradiation, suggesting that the orientation of liquid crystals is induced by the rod-like E-isomer. Discussion was made on the possibility of the role of phenanthrenes, which were formed upon prolonged irradiation, in the liquid crystal photoalignment.

Command surfaces 15 [1]. Photoregulation of liquid crystal alignment by cinnamoyl residues on a silica surface

Abstract The surface of a silica substrate plate was modified with a cinnamate moiety having a triethoxysilyl group at the ortho-position through a spacer. The plate was employed to assemble a cell filled with a nematic liquid crystal and exposed to linearly polarized 259 nm light to obtain homogeneous alignment. The direction of the alignment was perpendicular to an electric vector of the actinic light. On the contrary, the exposure of the cell to polarized light at 330 nm did not result in homogeneous alignment while the actinic light caused the disappearance of the chromophore. This wavelength effect on the azimuthal photoalignment suggests that the surface-assisted liquid crystal orientation is triggered by the reorientation of the E-isomer of the cinnamate group. This is in marked contrast to a proposed mechanism of a photoalignment by a thin film of a poly(vinyl cinnamate) derivative (Schadt et al., 1993, Jpn J. appl. Phys., 31, 2155); homogeneous alignment is induced by the axially selective photod...

Autocatalytic Decomposition of A β-Tosyloxy-Ketone Acetal as an Acid Amplifier

Abstract By the action of a small amount of an acid, 2-phenyl-2-(2-tosyloxyethyl)-1,3-dioxolane decomposed to give p-toluenesulfonic acid resulting in the proliferation of acid molecules. The decomposition manner was stepwise in solution state and autocatalytic in polymer film. The sensitivity of an acid-catalyzed photoimaging material was enhanced by 10 times upon the addition of the above compound due to the acid proliferation.

Photoregulation of Liquid Crystal Alignment by Photoisomerizable Molecular Layers

Abstract Linearly polarized UV light irradiation of a nematic liquid crystal cell assembled with a quartz plate surface-modified with a stilbene caused reversible reorientation of liqquid crystal molecules.

Surface-assisted formation of anisotropic dye molecular films

Abstract Dichroic dye layers were fabricated by spin coating of an aqueous dye solution on a thin film of an azobenzene polymer which was exposed to linearly polarized light in advance. The effect of polymer thickness on the dichroism and surface morphology of the dye layers were described.

Morphological Observation of Photoisomerizable Monolayers of Azobenzene Derivatives on Water Surface

Abstract Brewster angle microscopic (BAM) study was successfully achieved for photoresponsive monolayers composed of poly(vinyl alcohol) derivatives bearing an azobenzene (Az) side chain. BAM observation revealed clear differences in the morphological and theological properties between the trans- and cis-isomerized monolayers. The deformation process was also monitored under UV irradiation, which correspondingly visualized the magnitude of expansion stemmed from the difference in the methylene spacer length of the amphiphilic Az polymer.

Photochromic Behavior of Thin Films of Polymehacrylate Substituted with Laterally Attached Azobenzenes Displaying Liquid Crystal Alignment Photocontrol

Abstract Photo-and thermal isomerization of poly[2-(2-methacryloyoxy)azobenzene] derivatives was investigated both in solution and in film state. In the photo-induced trans-cis isomerization, the rate in film slate was smaller than that in solution. The kinetics of the thermal back reaction was proved to depend on the copplymerization ratio of the polymer. Linearly polarized light (LPL) irradiation of a thin film of the polymer induced dichroism of the film. The degree of the dichroism was related to the Tg of the polymers. In-plane alignment of nematic liquid crystals (LCs) was regulated by photodichroic thin films. Heat treatment of a film before irradiation was a important factor for the photoregulation.

PHOTOSENSITIVE CHARACTERISTICS OF POLY(METHACRYLATES) CONTAINING BENZYLIDENEPHTHALIMIDINE MOIETIES ON THE SIDE CHAIN

Abstract Photosensitive polymethacrylates having benzylidenephthalimidine(BPI) moiety on the side chains were synthesized. Upon photoirradiation of the polymer film, there occurred two kinds of photoreactions; the E/Z photoisomerization and [2+2] cycloaddition. The cycloaddition of BPI units of polymers resulted in the crosslinking of the polymer chains. The quantum yield for the photocrosslinking reaction was estimated from gelation experiment. Irradiation of the film with linearly polarized UV light induced a dichroism of BPI. Linearly polarized UV light irradiation of a nematic liquid crystals (LCs) cell assembled with a glass plate surface-modified with a Poly[N-(2-methacryloyloxy)ethyl-p-methoxy benzylidenephthalimidine] film brought about the homogeneous alignment.