INTERMOLECULAR INTERACTIONS IN MIXTURES OF DICHROIC DYES WITH N-ALKYL-4(4-ISOTHIOCYANATOPHENYL)BICYCLO[2,2,2] OCTANES

On the basis of the polarized absorption spectra, the guest order para meter as a function of temperature for five dichroic azo dyes dissolve d in four members (pentyl to octyl) of the homologous series of yl-4-( 4-isothiocyanatophenyl)bicyclo[2,2,2]octanes has been evaluated. Moreo ver, the influence of the dichroic dye addition on the nematic-isotrop ic phase transition temperature has been examined. The relation betwee n the molecular geometry of the guest, its orientation efficiency in t he nematic host and the clearing temperature of the azo dye-liquid cry stal mixtures has been determined. The experimental results have been compared in some detail with calculations performed on the basis of th e mean field theory for binary mixtures.