Optical anisotropy of liquid-crystal lanthanide complexes

Refractive and optical anisotropy indices have been measured for a number of liquid-crystal lanthanide complexes with different counter ions, ligands, and complexing agents. The optical anisotropy of the complexes is found to range from 0.002 to 0.09, i.e., to be one to two orders of magnitude smaller than that of classical calamitic liquid crystals. Analysis of the chemical structure of mesogenic complexes showed that the complexes containing counter ions with sizes much smaller than the ligand sizes and mixed-ligand complexes containing less than five ligands exhibit the largest optical anisotropy. The optical anisotropy of other mixed-ligand complexes with a large number of ligands is much smaller. The reason is the different degrees of anisometry of complexes and, as a consequence, the difference in the polarizability anisotropy and, correspondingly, the optical anisotropy of the mesophase.