L C, 2003, V. 30, N. 5, 603–610 Novel liquid crystals based on [1]benzothieno[3,2-b][1]benzothiophene BEDR ˇ ICH KOS ˇ ATA, VA ´ CLAV KOZMIK, JIR ˇ I ´ SVOBODA* Department of Organic Chemistry, Institute of Chemical Technology, Technicka ´ 5, CZ-166 28 Prague 6, Czech Republic VLADIMI ´ RA NOVOTNA ´ , PR ˇ EMYSL VANE ˇ K and MILADA GLOGAROVA ´ Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Prague 8, Czech Republic (Received 30 September 2002; in final form 18 December 2002; accepted 17 January 2003 ) Four series of new [1]benzothieno[3,2-b][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmC* A phase just below the SmA phase. The SmA–SmC* A phase transition has been studied using DSC and dielectric spectroscopy. In the SmC* A phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain. 1. Introduction 2,7-dicarboxylic acid, a tetracyclic fused system, exhibit liquid crystalline properties. Long chain saturated and The majority of liquid crystals contain a rigid 1,4-substituted phenylene-based moiety as the mesogenic unsaturated esters were further studied [21] and it was found that due to the relatively large, flat and fully aromatic group in their core [1]. When this moiety is replaced with a five-membered heterocyclic system, for example system having a high polarizability, the liquid crystalline phases exhibit interesting charge transport properties. thiophene, the geometry of the mesogen is changed, and this has a pronounced influence on mesomorphic phase These properties were attributed to the p-stacking of the aromatic cores which supports a lamello–columnar formation. The sulphur atom also changes the polarity of the local bonds and the polarizability of the mesogenic ordering. The term ‘sanidics’ was suggested for such mesogens instead of the more usual ‘calamitics’. group. Thus, the convenient combination of one or more phenylene and/or thiophene units connected by polar Our interest in the chemistry of fused heterocyclic compounds [22–25] and their application in materials functional groups and spacers has led to the design of various nematogens [2–5] and smectogens exhibiting chemistry [26, 27] led us to develop methods for the introduction of alkyl and acyl groups into the [ 1 ] benzo- ferro-, ferri- and antiferro-electric phases [6–10]. Liquid crystalline bi- [11, 12], ter- [3, 7, 13], oligo- and poly- thieno[3,2-b][1]benzothiophene ( 1 ) core, see scheme 1 [28]. These methods enabled us to synthesize series of thiophenes [8, 9, 14, 15] have also been studied and have found application in the design of new photonic, and derivatives of heterocycle 1 with long acyl and alkyl chains attached in positions 2 and 7, i.e. along the long conductive polymers and in molecular devices. Fused thiophene-based cores, for example, benzothiophene [16] axis of the molecule. To continue our search for new liquid crystalline molecules, here we report the syntheses and thienothiophene [17], have also been incorporated in liquid crystalline molecules, although, high transition and physical studies of achiral and chiral derivatives of heterocycle 1 with the aim to broaden our knowledge temperatures and a destabilization of mesomorphic properties were observed. On the other hand, we have of materials based on such a single ring system. found [18, 19] that even higher fused heterocycles can be successfully used in the design of new ferroelectric 2. Experimental materials. Recently [20] it was shown that simple 2.1. Characterization esters of [1]benzothieno[3,2-b][1]benzothiophene- The melting points of crystalline intermediates were determined using a Leica VM TG block. Elemental analyses were carried out on a Perkin-Elmer 2400. IR *Author for correspondence; e-mail: jiri.svoboda@vscht.cz L iquid Crystals ISSN 0267-8292 print/ISSN 1366-5855 online © 2003 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/0267829031000097484