Elena Prudnikova

Synthesis and properties of azo dye aligning layers for liquid crystal cells

The synthesis and properties of azo dyes that can be used for photoaligning liquid crystals (LCs) have been investigated. The structures and the synthetic procedure for the azo dyes are presented. The photoaligning of azo dyes takes place purely due to the reorientation of the molecular absorption oscillators perpendicular to the UV light polarization. The qualitative model for the phenomenon in terms of the rotational diffusion of the azo dye molecules in the field of the polarized light is discussed. The order parameters S = -0.4 (80% of the maximum absolute value S m = -0.5) were measured from the polarized absorption spectra at the wavelength 372 nm. A temperature stable pretilt angle of 5.3° was obtained by a two-step exposure of the azo dye film using normally incident polarized light followed by oblique non-polarized light. The azimuthal anchoring energy of the photoaligned substrate was Aϕ , 10−4 J m−2, which is the same as the anchoring of the rubbed polyimide (PI) layer. The voltage holding ratio value of a photoaligned LC cell was found to be even higher than for a rubbed PI layer, which enables the applications of azo dyes as aligning layers in active matrix liquid crystal displays. The thermal stability of the photoaligned azo dye layers is sufficiently high, but UV stability has to be improved, e.g. by polymerization. A new LCD aligning technology based on polymerized azo dye layers is envisaged.

P‐104: Aligning Layers Using Azo Dye Derivatives for Liquid Crystal Devices

The photo-induced alignment of an azo dye film and liquid crystal (LC) alignment on it are discussed for the liquid crystal display applications. Considerable dichroism is induced in the azo dye SD1 film not only by polarized UV light but also by obliquely incident non-polarized UV light irradiation. It was found that sulfo groups in the azo dye molecule play an important role in the LC alignment on the film. Large pretilt of LC on the photo-aligned film was achieved simultaneously, because the azo dye molecules can be easily reoriented out of the film plane by obliquely incident non-polarized light irradiation. In order to improve stability of the photo-aligned film, a monomer derived from the azo dye was synthesized. After thermal polymerization, the film of it also exhibit good photo-alignment properties. Improvement of durability against light exposure and moisture was observed in the LC cell using it.

New photo-aligning and photo-patterning technology: superthin internal polarizers, retarders, and aligning layers

The photo-aligning materials based on azodye layers are proposed. The azodye aligning layers enable (i) high order parameter; (ii) excellent alignment quality of LCD with a high contrast ratio; (iii) temperature stability, suitable for LCD manufacturing; (iv) perfect adhesion and high voltage holding ratio due to the specific molecular groups (v) pretilt angle generation. The azodye layers can be used to fabricate thin internal patterned (pixelated) polarizers with different local orientations of the absorption axis and/or absorption colors. Our new methods allow to produce defect-free highly uniform alignment of lyotropic LC or iodine-doped azodye layers themselves with a fine resolution of the polarization pattern. The photo-aligned internal polarizers are cost-effective and enable new LCDs with excellent electro-optical response, including good viewing angles and high brightness. We prepared an internal phase retarder using UV-cured photo-polymerized material. 4-(6- acryloyloxyhexyloxy) benzoic acid had been synthesized and the synthesis procedure was modified for a better yield. We had shown that by applying an electric or magnetic field, the director deformation of the liquid crystalline monomer could be in-situ UV-cured for the optimal phase compensation generation.

Azo-dye aligning layers for liquid-crystal cells

The photo-induced alignment of liquid crystal onto a photochemical stable azo-dye film was studied for liquid-crystal display (LCD) applications. The photo-aligning of azo dye takes place due to the pure reorientation of the molecular absorption oscillators perpendicular to the UV-light polarization. The order parameters S = -0.4 (80% of the maximum absolute value S m = -0.5) was measured at a wavelength of 372 nm from the polarized absorption spectra. The temperature-stable pretilt angle of 5.3° was obtained by a two-step exposure of azo-dye film using normally incident polarized light followed by oblique non-polarized light. The azimuthal anchoring energy of the photo-aligned substrate was A φ > 10 -4 J/m 2 , which is of the same magnitude as the anchoring of the rubbed PI layer. The VHR value of the photo-aligned LC cell was also found to be very high (98-99%) at room temperature and more than 95% at T= 80°C. The thermal stability of the photo-aligned azo-dye layers is sufficiently high, while UV stability has to be improved, e.g., by polymerization. The new LCD aligning technology based on photochemical stable azo-dye layers is envisaged.

38.2: Azodye Aligning Layers for Liquid Crystal Cells

The photo-induced alignment of liquid crystal onto a photochemical stable azo dye film is studied for the liquid crystal display (LCD) applications. The photo-aligning of azo dye takes place due to the pure reorientation of the molecular absorption oscillators perpendicular to the UV-light polarization. The order parameters S= −0.4 (80% of the maximum absolute value Sm= −0.5) was measured at the wavelength of 372 nm from the polarized absorption spectra. The temperature stable pretilt angle of 5.3° was obtained by a two-step exposure of azo- dye film using normally incident polarized light followed by oblique non-polarized light. The azimuthal anchoring energy of the photo-aligned substrate was Aɛ> 10−4 J/m2, which is of the same magnitude as the anchoring of the rubbed PI layer. VHR value of the photo-aligned LC cell was also found to be very high (98–99%) at room temperature and more than 95% at T=80°C. The thermal stability of the photo-aligned azo-dye layers is sufficiently high, while UV-stability has to be improved e.g. by polymerization. The bright perspectives for the new LCD aligning technology are envisaged.

45.3: Azo Dye Materials for the Alignment of Liquid Crystal

In this paper, the photo-induced alignment of liquid crystal on an azo dye film is discussed for the liquid crystal display (LCD) applications. This is a non-contact technique to align the liquid crystals so that the dust particles and static charges generated by the rubbing process can be eliminated. To prepare for the photo-alignment layer, the azo dye film is exposed to a linearly polarized or non-polarized light. As a result of the dipole absorption, the photo-induced molecular distribution is non-uniform and has an angular dependence. Consequently, since the dispersion forces between the dye and the liquid crystal molecules dominate, the induced orientation of the liquid crystal molecules is possible. The oblique incidence of the light exposure will also favour a non-zero pretilt angle. We find that the order parameter associated with the aligned liquid crystal medium is high, and very good contrast has been measured in the Twist Nematic (TN) LCD.