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(S)-(+)-4 - [(4-(1-methylheptyloxycarbonylphenyl) thiocarbonylphenyl]-decyloxybenzoate (in short 10.OPOSMH) was studied by complementary methods. The substance shows rich polymorphism. In addition to ferroelectric and antiferroelectric smectic C * phases it possesses three ferrielectric sub-phases. Phase transitions between the phases were revealed by dierential scanning calorimetry and static dielectric permittivity measurements. The aim of this paper was to study phase transitions and dierences in dielectric spectra shown by dierent phases. Collective and molecular dynamics of all phases shown by 10.OPOSMH will be discussed in terms of theoretical models. Dielectric spectra of antiferroelectric phase show two characteristic dielectric relaxation modes: one connected with the molecular process (reorientation around the short axis) and the other originating from uctuations of antiferroelectric order parameters.

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1,3-Phenylene bis{4- [(4-dodecyloxybenzoyl) sulfanyl] benzoate} (12OSOR) possessing banana-like achiral molecules has been studied by complementary methods to investigate linear dielectric as well as antiferroelectric properties of its B 2 phase. To this end, the following experimental methods were used: differential scanning calorimetry, polarizing microscopy, dielectric spectroscopy and reversal current method. As found, 12OSOR compound with bent-core molecules exhibits only B 2 phase that happens to be antiferroelectric. Dielectric spectra have been measured using the dielectric spectrometer based on Agilent 4294A impedance analyzer. The measurements have been done using HG 5 mm cells (giving homogeneous orientation) with gold electrodes. Thermal, dielectric, and electro-optic properties of 12OSOR are discussed.