Structure and properties of organic liquid crystals

Organic liquid crystals (LCs), both in the monomeric and polymeric state, are capable of self organisation because of the anisotropic shape of their molecules. By suitable molecular engineering it is thus possible to induce interesting physical properties like ferroelectricity, second harmonic generation (SHG) and photoconductivity. For a deeper understanding it is necessary to gain insight into the relationship between molecular characteristics (electronic charge distribution, dipole moments, hyperpolarisabilities, molecular conformation), structural relations (symmetry relations, space groups, defects) and the above physical propertiesFor structure analysis electron diffraction patterns from different crystallographic zones with many higher orders of diffraction are required. Unfortunately a characteristic feature of LCs is their loss of all higher order reflections and a change in symmetry. Furthermore, LCs give rise to specific defects, which give important information about the elastic energy density of the system. These can only be characterised by a phase contrast imaging method in which the small angle spatial frequencies are transferred by the electron microscope phase transfer function.