Liquid crystal dyestuffs and electro-optic devices incorporating same

Abstract

Novel dyes of the formula ##STR1## wherein X is --NH, --NCH.sub.3, --S or --O; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 independently at each occurrence can be hydrogen, fluoro, chloro, bromo, alkoxy, cyano, nitro, --N(R).sub.2 wherein R is alkyl or two of R.sub.1 to R.sub.4 together can be part of an aromatic ring; R.sub.5 and R.sub.6 are hydrogen, fluoro, chloro, bromo or lower alkyl; and R.sub.7 is hydrogen, fluoro, chloro, bromo, alkoxy, cyano, nitro, --N(R.sub.2), ##STR2## HYDROGEN, FLUORO, CHLORO, BROMO, ALKOXY, CYANO, NITRO, DI-ALKYLAMINO, ##STR3## can be added to known liquid crystal compositions to impart color to the mixtures and to improve contrast of a liquid crystal electro-optic device containing such mixtures.