| abstract |
New compositions based on yellow azo dyes and new compositions of liquid crystals containing them. The yellow azo dye composition, which is provided with terminal ester groups, has the following general formula: (FORMULA) in which R and R 'represent an alkyl or a substituted alkyl having at least 4 carbon atoms, an aryl, arylalkyl, substituted aryl or substituted arylalkyl. When yellow dichroic azo dyes are used alone, or in combination with other dyes, as recipient or donor crystalline material, they form a novel composition which can be used in liquid crystal displays. Method for improving the black coloring of dichroic dyes for use in black liquid crystal displays, in which a coloring composition comprising a mixture of dichroic dyes of different colors and containing at least one yellow dichroic azo dye is added to a receiving liquid crystal material. The mixture of dichroic dyes of different colors must absorb radiation in the spectrum range of about 400-700 nm in order to produce the substantially black coloration that is used in black liquid crystal displays. |