Pretilt Angle of Liquid Crystals Induced by Photo-Aligned Films of Polyimide Containing Azobenzene in the Backbone Structure(<Special Section>Electronic Displays)

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We have investigated the pretilt angle of liquid crystal (LC) molecules induced by photo-alignment films of polyimide (Azo-PI) containing azobenzene in the backbone structure. To generate finite pretilt angles, the Azo-PI film with inclined alignment of the backbone structure was prepared by a double light-exposure method. In this method the corresponding polyamic acid (Azo-PAA) film was first exposed to linearly polarized ultraviolet/visible (UV/VIS) light (LP-light) at normal incidence, and then oblique angle irradiation of unpolarized UV/VIS light (UP-light) was performed in the plane of incidence perpendicular to the polarization direction of the LP-light. Repeated photo-isomerization reactions of azobenzene induce the alignment of the Azo-PAA backbone structure. By thermally imidizing the photo-treated film we obtained a thermally and optically stable Azo-PI film. The orientational distribution of the Azo-PI backbone structure was determined by measuring the polarized infrared absorption spectra as a function of the sample rotation angle and the angle of incidence. The pretilt angle of LC molecules was determined by a crystal rotation method. We found that the average inclination angle of the Azo-PI backbone structure increased with the UP-light exposure. The pretilt angle of LC molecules, measured from the surface plane, also increased with the UP-light exposure. We succeeded in generating a pretilt angle of 3°. The relation between the LC pretilt angle and the average inclination angle of the Azo-PI backbone structure is discussed.
社団法人電子情報通信学会の論文
2004-11-01

Pretilt Angle of Liquid Crystals Induced by Photo-Aligned Films of Polyimide Containing Azobenzene in the Backbone Structure(<Special Section>Electronic Displays)

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