Liquid Crystals ISSN 0267-8292 print/ISSN 1366-5855 online # 2003 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/02678290310001622506 New antiferroelectric liquid crystalline materials containing a keto group and two lactate groups VE ˇ RA HAMPLOVA ´ , ALEXEJ BUBNOV*, MIROSLAV KAS ˇ PAR, VLADIMI ´ RA NOVOTNA ´ , YVETA LHOTA ´ KOVA ´ and MILADA GLOGAROVA ´ Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague, Czech Republic (Received 14 March 2003; in final form 16 June 2003; accepted 21 July 2003 ) New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC* A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro- optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases. 1. Introduction Since the discovery of the antiferroelectric SmC* A phase for MHPOBC [1], it has been observed in many substances. Antiferroelectric liquid crystals are still of great interest not only due to their application potential but also on a fundamental level because of the anticlinic structure of the phase. The relationships between their molecular structure and physical properties are not clearly understood. In designing new liquid crystal molecules, we must remember that their mesogenic behaviour is influenced not only by the structure of the rigid molecular core but also by the chiral part of the molecule. Using the lactate unit as the basis of the chiral segment has yielded many materials having a rather broad ferroelectric phases [2–6]. Materials containing two lactate units have been described in just a few papers [7–9] although some of these showed the antiferroelectric phase. Recently, two new series of liquid crystalline materials containing two lactate units in the chiral part of the molecule were synthesized and studied [7]. These com- pounds show the paraelectric SmA phase, the ferro- electric SmC* phase and a hexatic phase. Some of these, specifically those having three chiral centres, also exhibit the antiferroelectric SmC* A phase. More recently, two series of new ferroelectric liquid crystalline materials containing a keto group in the core and one lactate unit have been described [10]. In these materials, the transverse dipole moment near the chiral centre becomes dominant due to the weakening of the longitudinal molecular dipole moment. These com- pounds show a wide ferroelectric SmC* phase with rather high values of spontaneous polarization down to room temperatures [10]. In the present work, we attempted to combine the promising chiral segment containing two lactate units with a keto group in the core with the aim of obtaining a broad antiferroelectric phase with high values of spontaneous polarization, such a material could meet application demands. The general formula of the materials studied, which are denoted as KLLm/n, is: 2. Synthesis The general procedure for the preparation of the KLLm/n homologues is shown in the scheme. The synthesis of the keto acids 1 has been described recently [10]. The synthesis of compounds 2 and 3 was described in detail in [7]. All chiral centres have (S) configuration. The final KLLm/n products were prepared by the reaction of 10 mmol of phenol 3 and 10 mmol of mesogenic acid 1 in 100 ml of dichloro- methane after the addition of 15 mmol of N,N’– dicyclohexylcarbodiimide. The mixture was stirred for 12 h at room temperature. The crude product was chromatographed on silica gel (Kieselgel 60, Merck) *Author for correspondence; e-mail: bubnov@fzu.cz LIQUID CRYSTALS,VOL. 30, NO. 12, DECEMBER 2003, 1463–1469