Dichroic liquid crystal composition with 4,4-bis (substituted naphthylazo)azobenzene dichroic dyes

A dichroic dye dissolved in a nematic liquid crystal host material of positive dielectric anisotropy and imparting a blue color thereto, said dichroic dye-nematic liquid crystal mixture having a high degree of photostability;

• said dye being a 4,4'-Bis-(substituted naphthylazo)azobenzene with a general chemical formula:
• ##STR5## wherein the substituents at bonds R and R', are coordinately selected for a desired set of an approximate order parameter (S) and an approximate wavelength (.lambda..sub.Max.) of maximum absorption in accordance with the following table:
• ______________________________________ Dye R R' S .sup..lambda. Max. (nm.) ______________________________________ a NHCH.sub.3 H 0.75 595 b NHC.sub.2 H.sub.5 H 0.72 598 c NH.sub.2 NH.sub.2 0.74 595 ##STR6## 0.72 610 e ##STR7## 0.72 605 ______________________________________
• the approximate order parameter and approximate maximum absorption wavelength being measured with said dye dissolved in a host material consisting of a mixture of 70% by weight of p-pentylphenyl 2-chloro-4-(p-pentyl-benzoyloxy)benzoate, and 30% by weight of an ester mixture composed approximately of 50-60% by weight of 4'-n-pentylphenyl ester of anisic acid, 25-35% by weight of 4'-n-pentylphenyl ester of 4-hexyloxybenzoic acid, and 10-15% by weight of (2'-cyano-4'-butylphenyl) ester of 4-(hexanoyloxybenzoyloxy)benzoic acid.