CREATED USING THE RSC ARTICLE TEMPLATE (VER. 3.1) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS ARTICLE TYPE www.rsc.org/xxxxxx | XXXXXXXX This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00 | 1 Nematic-polar columnar phase sequence in new bent-shaped liquid crystals based on 7-hydroxynaphthalene-2-carboxylic acid core. Michal Kohout, a Jiří Svoboda, a Vladimíra Novotná,* b Damian Pociecha, c Milada Glogarová b and Ewa Gorecka c 5 Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X First published on the web Xth XXXXXXXXX 200X DOI: 10.1039/b000000x Mesomorphic properties of new bent-shaped liquid crystals based on 7-hydroxynaphthalene-2- carboxylic acid are presented. The central unit of the molecular core was also modified by 10 substitution of chlorine atom or methyl group. Texture and calorimetric studies and for selected compounds electrooptical, X-ray and dielectric measurements were performed. For long homologues the lamellar B 2 phase was observed, while for shorter homologues two-dimensional columnar phases were found built of layer fragments with the electron density modulation plane perpendicular to polarization direction. Based on X-ray patterns two types of modulated polar 15 columnar phases were distinguished, having oblique or orthogonal centered crystallographic unit cell and differing in relative position of neighboring layer fragments. For some homologues above these phases also the nematic phase was formed, which has not been observed so far. Introduction Bent-shaped mesogens have developed into an important field 20 of liquid crystals and their general structure-property relationships have been recognized and generalized in recent reviews. 1-5 Materials with a non-symmetrical molecular structure that differed in the type and length of the terminal chain, linking groups and their orientation, number and type 25 of aromatic rings, lateral substitution in the arms and all these factors in respect to the central unit, have also been studied. A simple way to escape the symmetrical molecular structure of the bent-shaped materials utilized two different functionalities bound to the central core, such as amino and carboxylic 30 groups 6-8 and more usually hydroxylic and carboxylic groups, 9-12 derivatization of which forms the final non- symmetrical mesogen. As a consequence, materials with reversed orientation of ester group(s) are formed. In a series of five ring bent-core mesogens the influence of all the 35 possible orientation of the linking ester units was studied 13 for non-substituted central phenyl-core and it was found that orientation of the ester group strongly affects the transition temperatures and the type of the formed phases. Theoretical calculations showed 14 that the orientation of the ester units 40 influences flexibility of the molecular branches, local and overall dipole moments, all these factors in turn have a pronounced effect on the flexibility and polarity of the isomers in electric field. One can expect the bent-shaped molecules preferably 45 form a flat layer structure. Besides, several 2-D structures exist and their structure can be described as a ripple phase with layers divided into molecular blocks. 15 If the density modulation plane is perpendicular to the polarization vector, the nomenclature of the B 1Rev phase is used. Layer fragments can create the centred 50 rectangular (B 1Rev phase) or oblique lattice (B 1RevTilted phase). In our previous research we have dealt with five ring bent- shaped mesogens based on naphthalene-2,7-diol central core with ester and/or imino linking groups. 16-19 We have prepared symmetrical as well as non-symmetrical mesogens with different 55 length of the terminal chains and type of the lateral substitution on the central naphthalene core and obtained a variety of B-type phases in a broad temperature interval. In addition, in a series of hockey-stick mesogens, despite their bend shape, we have established formation of calamitic-like nematic and smectic 60 phases. 20 In all so far studied naphthalene-based compounds all ester and/or imino linking groups are oriented in a symmetrical way. The presented paper contributes to the broad issue discussed above. We report synthesis of laterally substituted difunctional 7- 65 hydroxynaphthalene-2-carboxylic acid, a new model of central core for design and synthesis and mesomorphic study of three series of nonsymmetrical bent-shaped materials I-III. We show the role of direction of the ester linkage group for mesomorphic properties in such type of central core with various substitutions. 70 Experimental Synthesis As it was discussed above, bent-shaped materials with non- symmetrical molecular structure can be derived from a central core carrying two different functionalities, such as hydroxylic 75 and carboxylic groups. In this respect, the studied bent shaped materials are derived from 7-hydroxynaphthalene-2- carboxylic acids 1 (X = H), and are laterally substituted by a chlorine atom in compounds 2 (X = Cl) and by methyl group in 3 (X = CH 3 ). Nonsubstituted acid 1 was obtained by a 80 slightly modified procedure reported 21,22 starting with the commercially available 2,7-dihydroxynaphthalene (scheme 1). One of its hydroxylic groups was first substituted with triphenylphosphine dibromide at 280 °C to 7-bromo- naphthalene-2-ol (4). In the next step, the bromo atom of 4 85 was substituted with CuCN to form nitrile 5, base catalyzed hydrolysis of which gave rise to acid 1. The hydroxylic group in 1 was then protected by benzylation with benzyl bromide through dibenzyl derivative 6, its hydrolysis afforded protected acid 7. To our best knowledge, chloro- 2, and 90 methyl substituted central core 3 have not been reported in the literature yet, and original procedures were elaborated. Synthesis of chloro acid 2 started with methyl ester 8,