Chiral (S) 4-(1-methylheptyloxycarbonyl)phenyl 4'-(omega -trifluoroethoxyalcoxy)biphenyl-4-carboxylates and 4'-(omega -trifluoro-butanoyloxyalcoxybiphenyl)carboxylates were prepared and their phase transitions and the temperature dependence of the smectic layer spacings, tilt angle, spontaneous polarization, threshold and switching times for the antiferroelectic - ferroelectric transition were measured.