ORDER PARAMETERS OF DYES IN A BIPHENYL-TERPHENYL LIQUID-CRYSTAL MIXTURE

The order parameters of a number of azo- and anthraquinonoid dyes dissolved in a eutectic liquid crystal mixture composed of derivatives of 4-cyanobiphenyl- and 4-cyano-p-terephenyl (Type E7, B. D. H. Chemicals Ltd. ) have been determined spectrometrically. Orientation was achieved using rubbed polyvinyl alcohol coated cells. A good correlation was found between order parameter and molecular structure, allowing order parameters to be predicted for other dyes based on the monazo-chromophore. Azo-dyes exhibited a marked red shift relative to the color of the dye in slightly polar isotropic solvents, whereas anthraquinonoid dyes showed little change. The results are interpreted in terms of charge transfer perturbations arising from dipole-interactions between guest and host molecules.