Novel antiferroelectric liquid crystals with a phenylpiperazine moiety in the mesogenic core structure

A novel series of antiferroelectric liquid crystalline compounds having a p henylpiperazine unit and a biphenyl or a phenyl moiety in the core structur e was synthesized using the optically active alcohols 2-methyl octanol and 1,1,1-trifluoromethyl octanol. Most of the compounds exhibited enantiotropi c SmCA*, SmC* and SmA mesophases. The phase transition temperatures, respon se times, spontaneous polarizations and the field-transmittance hysteresis loops were monitored. These data were compared with those of the MHPOBC com pounds, which represent the most conventional cope structure of the bipheny l/phenyl combination. The replacement of the biphenyl moiety, with the phen ylpiperazine unit, reduced the isotropization temperature as well as the Sm CA*-SmC transition point. It was found that some of the new compounds, whic h consisted of an octyl or a nonyl terminal chain with a 2-methyloctyl 2-fl uorophenylcaboxylate group in the core structure, could have a potential ap plication in display devices. Some work an blends of these compounds is als o described.