Effect of Magnetic and Electric Field on the Orientation of Rare-Earth-Containing Nematics.

We report rare-earth-containing metallomesogens with newly synthesized ligands represented by the ß-diketone 1-(4-(4-propylcyclohexyl)phenyl)octane-1,3-dione (CPDk3-5) and the Lewis base 5,5'-bis(heptadecyl)-2,2'-bipyridine (bpy17-17). The stoichiometry of the complexes is [Ln(CPDk3-5)3bpy17-17], where Ln is a trivalent rare-earth ion (La, Sm, Eu, Gd, Tb, Dy, Ho, Tm, and Yb). Although the ligands themselves do not form any mesophase, the respective metal complexes produce nematic and smectic A phases. The mesogenic rare-earth complexes were characterized by NMR, MS, POM, DSC, X-ray diffraction, magnetic susceptibility measurements, and dielectric spectroscopy. The metal complexes display a remarkably large magnetic anisotropy in the mesophase. These nematic liquid crystals can, therefore, be easily aligned by an external low-threshold magnetic field.

Light propagation in chiral media with large pitch.

Light propagation in uniaxial chiral media with large pitch is studied. In these systems there are forbidden zones for extraordinary beams, which lead to effective reflection on zone boundaries and to wave damping inside the forbidden zone. We analyze the vicinities of the turning points and the transition of an extraordinary wave through the forbidden zone. Narrow forbidden zones with merging turning points are studied in detail. The transition through the forbidden zone is studied experimentally in nematic liquid crystal doped with a chiral addition. There is a good agreement between experimental results and theoretical calculations.