Structural and electro-optical investigations of the smectic phase of chlorine-substituted banana-shaped compounds

Abstract

Six members of a new homologous series of achiral banana-shaped molecules have been synthesized and studied by optical microscopy, differential scanning calorimetry, NMR spectroscopy and X-ray diffraction. According to X-ray diffraction measurements on oriented samples, four homologues form an XB2 phase behaviour. From electro-optical studies the spontaneous polarization and the tilt angle could be measured. An orientational order parameter of 0.8 was determined by 13C NMR and this is nearly independent of the temperature. NMR investigations also give information about the real conformation of the molecules in the XB2 phase. Dielectric measurements indicate that the rotation around the molecular long axis is clearly hindered because of the packing of the bent molecules within the smectic layers. which exhibits antiferroelectric switching