| abstract |
Compounds of the formula <IMAGE> I wherein X2 is a single covalent bond or -COO-; X1 is a single covalent bond, -COO-, -CH2CH2- or when X2 is -COO-, X1 also can be p-C6H4-, p-C6H4-CH2CH2-, -CH2CH2-p-C6H4, p-C6H4-COO- or -COO-p-C6H4; ring A is a benzene ring or trans-1,4-cyclohexylene; ring B is a benzene ring or when X2 is -COO- and X1 is a single covalent bond, -COO- or -CH2CH2-, ring B also can be trans-1,4-cyclohexylene; Z1, Z2 and Z3 individually are hydrogen or when positioned on a benzene ring which is not linked directly with a further ring via a single covalent bond, Z1, Z2 and Z3 also can be halogen, cyano or methyl; Y2 is cyano, nitro, 2,2-dicyanovinyl or when Y1 is hydrogen Y2 also can be 2,2-dicyano-1-methylvinyl; Y1 is halogen, cyano, C1-C3-alkyl or, when X1 includes a benzene ring of -COO- or Y2 is nitro or at least one of Z1 and Z2 is other than hydrogen, Y1 also can be hydrogen; and R1 is C1-C12-alkyl or when positioned on a benzene ring R1 also can be C1-C12-alkoxy, their manufacture and use in liquid crystalline mixtures are described. |