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ABSTRACT:We investigated the photoreaction of the side chain type liquid crystalline polymers with a chalcone derivative in the side chain. The polymer films were irradiated with linearly polarized UV (LPUV) light (350 nm) under different conditions. The photodimerization of the chalconyl moieties would mainly occur due to a decrease in the peak assigned to the chalconyl moiety by UV-vis spectroscopy measurements. The extent of the photoreaction in the liquid crystalline (LC) state is larger than that in the solid state after spin-coating and in the locked-in LC state after annealing. The LC cell was fabricated from the polymer film irradiated with LPUV light to examine the alignment properties of low molar mass LC molecules on them. A mixture of low molecular liquid crystal with the dichroic dye was filled in the LC cell. The low molecular liquid crystal was easily aligned parallel to the electric vector of the incident exposed LPUV light in the LC cell with the polymer film irradiated in the LC state.KEY WORDS Chalcone / Liquid Crystalline Polymer / Photodimerization / Photoalignment / The alignment of liquid crystalline (LC) molecules plays an important role for liquid crystalline displays (LCDs). The rubbing process has been mainly employed for the uniaxial orientation of the LC molecules. However, the rubbing process has many disadvantages for LCDs such as generation of electrostatic charge and dust. Therefore, many methods of alignment technique for LC molecules are focused on rubbing free methods. Photoalignment procedure is recognized as one of rubbing free methods and is investigated as one of candidates that overcome the generation of electrostatic charge and dust for the rubbing process. 1,2 Photoalignment procedure is based on photochemical reactions such as photoisomerization, photodimerization (photocrosslinking) and photodecomposition. With respect to photoisomerization, polymers containing an azobenzene derivative were intensively investigated. [3][4][5] The reversible photoreaction of the azobenzene moieties in the polymer induced a reversible change in the alignment direction of low molecular weight LC molecules. Generally photodimerization of photosensitive groups in the polymer was employed to obtain a stable alignment of low molecular weight LC molecules.Photodimerization of the cinnamoyl chromophore in the polymer film have been studied in detail. The polymer films containing dimerized moiety of cinnamoyl group have been investigated as a photoalignment material by many researches. 2, 6-10 Schadt et al. have obtained the alignment film by photodimerization of cinnamoyl group in the poly(vinyl 4-methoxycinnamate). LC molecules in the LC cell were aligned perpendicular to the electric vector of the incident LPUV light. 6 Alignment behavior of LC molecules would be easily improved by the liquid crystalline polymer surface where mesogenic groups are aligned. Kawatsuki et al. had reported alignment properties of side chain type liquid crystalline polymers with the cinnamoyl groups as an alignmen...

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We synthesized two kinds of side chain type polymers containing chalconyl moieties to investigate the alignment's capability of photo-crosslinked polymer films. One is methacrylate type polymer having the chalconyl moiety in the side chain, and the other is imide type polymer. A smectic phase was exhibited for the methacrylate type polymers, while no mesophases were observed for the imide type polymer. These polymer films were irradiated with linearly polarized UV (LPUV) light (350 nm) under different conditions. The liquid crystalline (LC) cell was fabricated from the polymer film irradiated with LPUV light to examine the alignment properties of low molecular liquid crystal on the film. A mixture of a low molecular liquid crystal and a dichroic dye was filled in the LC cells. Alignment behavior of the low molecular liquid crystal was discussed by the dichroic ratio of the dichroic dye in the LC cell.