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^-4J/m ², which is of the same magnitude as the anchoring of the rubbed Pl 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