Pleochroic dyes and electro-optical displays therewith

In an electro-optical device wherein an electrical field is imposed or withdrawn from action on a cell comprising liquid crystalline material having dissolved therein a pleochroic dye between transparent electroded glass plates, the improvement wherein the liquid crystalline material has dielectrically positive anisotropy and comprises at least one nematic liquid crystalline material having dielectrically positive anisotropy and the dissolved pleochroic dyes has the general formula:

• ##STR42## wherein substituent (NRR') and Q may be in positions 1 through 8, Q is F, Cl, NO.sub.2, NH.sub.2, NH(Alk), OH,
• x is 0, 1, 2, 3,
• m is 1 or 2,
• R is H,
• R' is cyclohexyl, bicyclohexyl or --(CH.sub.2).sub.p --Ar
• where
• p is 0, 1 or 2 and Ar is aryl of 6 to 10 carbon atoms substituted in the 4 position by --NHCOCH.sub.3, CN, C.sub.b H.sub.2b+1, --OC.sub.n H.sub.2n+1, cyclohexyl, 4--(Alk)--cyclohexyl or ##STR43## where y is 0 or 1 Y is CH.sub.2, O, S, or OCH.sub.2
• Z is H, NO.sub.2, CN, --C.sub.n H.sub.2n+1, --OC.sub.n H.sub.2n+1, F, Cl,
• and, when y is 0, X can also be --C.sub.6 H.sub.5, and
• wherein Ar can be substituted in from 0 to 2 further positions by CN, --C.sub.n H.sub.2n+1, --OC.sub.n H.sub.2n+1, NH.sub.2, or OH, provided that when p is 1 or 2 Ar can be unsubstituted aryl, and
• when m is 2, the substituent R and R' taken together with N to which R is attached can alternatively be ##STR44## where X is NO.sub.2, CN, --C.sub.n H.sub.2n+1, --OC.sub.n H.sub.2n+1, or N(Alk).sub.2,
• n is 1 to 20,
• b is 2 to 20;
• provided that when p is 1 or 2 b can be 1 to 20, and
• Alk is alkyl of 1-8 carbon atoms.