Polymerizable discoticnematic triphenylene derivatives and their application to an optically anisotropic film

Abstract

A novel optically anisotropic film which consists of discotic liquid crystalline molecules aligned and fixed in hybrid mode was invented. The discotic liquid crystalline molecules are polymerizable discotic nematic liquid crystalline triphenylene derivatives. The film is exceedingly useful for improvement in viewing angle of TFT-TN LCD. In the TFT-TN LCD, calamitic liquid crystal molecules which have positive birefringence in refractive property are used. This anisotropy causes light leakage and results in narrow range of the viewing angle of the LCD. It is, therefore, considered that compensation for the positive birefringence by using a negative birefringent material is the essential means for achievement of the wide viewing angle. The triphenylene derivatives are chosen as one of negative birefringent materials. In our study, discotic nematic phase was the most suitable liquid crystalline phase for preparation of the optically anisotropic film. Discotic nematic phase was frequently shown by 2,3,6,7,10,11-hexa-(4-alkoxybenzoyloxy)triphenylene derivatives. Some modification of the alkoxy group brought disappearance of the discotic nematic phase. Introduction of an acryloyl group to the alkoxy group at the terminal position, however, did not cause the disappearance of the discotic nematic phase. 2,3,6,7,10,11-hexa-(4-alkoxybenzoyloxy)triphenylene molecules were able to align on an obliquely vapor deposited SiO film and organic alignment films in the monodomain discotic nematic phase. In this case, the layer of the discotic molecules contacted with the alignment film only on one side and on the other side it contacted with air. Retardation data by an ellipsometric measurement suggested that the molecules aligned in hybrid mode. In the case of the acryloyl derivatives, alignment of the molecules was able to be fixed by photopolymerization of acryloyl moieties. According to the abovementioned method, a novel optically anisotropic film was produced. If alignment of the discotic molecules can be freely controlled, a new area of optically anisotropic film will be produced. Copyright © 2000 John Wiley & Sons, Ltd.