A dye compound suitable for use in solution with a liquid crystal material is characterized by one of the following formulae: ##STR1## (III) a derivative of (I) or (II) containing one or more simple lateral substituents or bridging groups on the benzene rings: ##STR2## where n.sub.1, n.sub.2, n.sub.3 are integers in the range 0 to 4, A is azo or azoxy, X is cyano, or nitro and Y.sub.1 and Y.sub.2 are one of the following: hydrogen, alkoxy, arylalkoxy or N.sub.R.sbsb.2.sup.R.sbsp.1 where R.sub.1 and R.sub.2 are alkyl, substituted alkyl or alkylene groups.