| abstract |
Liquid crystal compositions having positive dielectric anisotropy comprise at least one nematic liquid crystal material having positive dielectric anisotropy and are characterized by containing a pleochroic dye of the general formula: <IMAGE> wherein a is 1 or 0; provided that when a = 1, n = 0 m is an integer from 1 to 4, R represents -CH3, -OCH3 or -H, and Y represents, independently, -NH2, -NO2, -OH, -Cl or -F, and when a = 0, Y represents, independently, -NH2, -NO2 or -OH; Q is independently, <IMAGE> or <IMAGE> and is present only in one or more of positions 1, 4, 5 and 8; R' and R'' independently represent hydrogen or a nonionic substituent; m is 0, 1 or 2; n is an integer from 1 to 4; and m + n is 4 or less; provided, that when Q is <IMAGE> then n = 2, m = 0, and S-Q is present only in positions 1 and 4, 1 and 5, 1 and 8, 4 and 5 or 5 and 8. The compositions are used in electro-optical devices, e.g. displays. |