Aromatic disazo dyes and liquid-crystalline materials containing these dyes

An azo dye of the formula:

• ##STR37## wherein:
• X is a 5-membered heterocyclic ring selected from the group consisting of oxadiazole, thiadiazole, thiazole, an oxadiazole ring substituted by C.sub.1 -C.sub.12 alkyl, C.sub.2 - or C.sub.3 -alkyl substituted by hydroxy, C.sub.1 -C.sub.12 alkoxy, phenyl or phenoxy, phenylmethyl, C.sub.5 -C.sub.7 -cycloalkyl, phenyl, or phenyl substituted by C.sub.1 -C.sub.12 -alkyl, phenylmethyl, phenylethyl, C.sub.1 -C.sub.12 -alkoxy, phenoxy, phenylmethoxy, C.sub.1 -C.sub.12 -alkanoyloxy, benzoyloxy, phenyl, diphenyl, cyclohexyl, 4-(C.sub.1 -C.sub.7 -alkylcyclohexyl), carboxylic ester or chlorine, C.sub.1 -C.sub.12 -alkylthio, C.sub.5 -C.sub.7 -cycloalkylthio, phenylmethylthio substituted by C.sub.1 -C.sub.12 -alkyl, phenylmethyl, phenylethyl, C.sub.1 -C.sub.12 -alkoxy, phenoxy, phenylmethoxy, C.sub.1 -C.sub.12 alkanoyloxy, benzoyloxy, phenyl, diphenyl, cyclohexyl, 4-(C.sub.1 -C.sub.7 -alkylcyclohexyl), carboxylic ester or chlorine, or 2-phenylethylthio, a thiadiazole ring substituted by C.sub.1 -C.sub.12 -alkyl, C.sub.2 - or C.sub.3 -alkyl substituted by hydroxyl, C.sub.1 -C.sub.12 -alkoxy, phenyl or phenoxy, phenylmethyl, C.sub.5 -C.sub.7 -cycloalkyl, phenyl, or phenyl substituted by C.sub.1 -C.sub.12 -alkyl, phenylmethyl, phenylethyl, C.sub.1 -C.sub.12 -alkoxy, phenoxy, phenylmethoxy, C.sub.1 -C.sub.12 alkanoyloxy, benzoyloxy, phenyl, diphenyl, cyclohexyl, 4-(C.sub.1 -C.sub.7 -alkylcyclohexyl), carboxylic ester or chlorine, C.sub.1 -C.sub.12 -alkylthio, C.sub.5 -C.sub.7 -cycloalkylthio, phenylmethylthio substituted by C.sub.1 -C.sub.12 -alkyl, phenylmethyl, phenylethyl, C.sub.1 -C.sub.12 -alkoxy, phenoxy, phenylmethoxy, C.sub.1 -C.sub.12 -alkanoyloxy, benzoyloxy, phenyl, diphenyl, cyclohexyl, 4-(C.sub.1 -C.sub.7 -alkylcyclohexyl), carboxylic ester or chlorine, or 2-phenylethylthio or a thiazole ring substituted by C.sub.1 -C.sub.4 -alkyl, phenyl, phenyl substituted by C.sub.1 -C.sub.4 -alkyl, chlorine or bromine, C.sub.5 -C.sub.7 -cycloalkyl or C.sub.1 -C.sub.8 -alkoxycarbonyl;
• Y is a radical of the formula:
• ##STR38## the rings, A, B and C are each independently unsubstituted, or ring A is substituted by chlorine, bromine, cyano, methyl, ethyl, methoxy, ethoxy or hydroxyl, or ring B is substituted by chlorine, bromine, methyl, ethyl, methoxy, ethoxy, acetylamino, propionylamino or ring B is a naphthyl ring, or ring C is substituted by chlorine, bromine, methyl, ethyl, methoxy, ethoxy, acetylamino, propionylamino or ring C is a naphthyl ring;
• R.sup.1 and R.sup.2 are each independently hydrogen, C.sub.1 -C.sub.12 alkyl, cyclohexyl, 2-phenylethyl, 2-cyanoethyl, 2-hydroxyethyl, 2-acetoxyethyl, 2-butyryloxyethyl, allyl, phenylmethyl, 4-butylphenylmethyl, 4-cyclohexylphenylmethyl or 4-(4'-butylcyclohexyl)-phenylmethyl;
• or R.sup.1 and R.sup.2, together with a nitrogen atom to which they are both bound, are piperidino, pyrrolidino or morpholino;
• R.sup.3 is C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkyl interrupted by oxygen, C.sub.5 -C.sub.7 cycloalkyl, phenylmethyl, 2-phenylethyl, 4-(C.sub.1 -C.sub.12 -alkyl)-phenylmethyl, 4-cyclohexylphenylmethyl, 4-(4'-C.sub.1 -C.sub.7 -alkyl-cyclohexyl)-phenylmethyl, 4'-(C.sub.1 -C.sub.12 -alkoxy)-phenylmethyl, 4-phenoxyphenylmethyl, 4-phenylmethyloxyphenylmethyl, 4-(C.sub.1 -C.sub.12 -alkanoyloxy)-phenylmethyl, benzoyloxyphenylmethyl or 4-caproyloxyphenylmethyl;
• and
• R.sup.4 is hydrogen, C.sub.1 -C.sub.4 alkyl or cyclohexyl.