Abstract Influence of the electric field upon alignment of molecules in ferro- and antiferroelectric phases has been studied for two fluoro-substituted compounds exhibiting antiferroelectric phase at room temperature. Two different relaxation processes have been revealed in the ferroelectric as well as antiferroelectric phase. Low temperature value of spontaneous polarization is ca. 130 nC/cm2 for both substances studied. The substances align very well in the external electric field — a mono-domain of the ferroelectric SmC* phase can be obtained in about 3.5 hours.