Banana-shaped mesogens derived from 2,7-dihydroxynaphthalene and 1,3-dihydroxybenzene: novel columnar mesophases

Abstract

The synthesis and mesomorphic properties of a number of compounds belonging to different homologous series and derived from 2,7-dihydroxynaphthalene are described. In addition, several compounds derived from 1,3-dihydroxybenzene have also been synthesized for comparison. All these compounds are relatively stable esters of E-p-n-alkoxycinnamic acids and E-p-n-alkoxy-α-methylcinnamic acids which are incorporated in the arms of these bent-core compounds. Many of these compounds show interesting mesophases including a novel antiferroelectric columnar phase with a rectangular lattice. Direct transitions from a rectangular columnar B₁ phase, an antiferroelectric B₂ phase, and an intercalated B₆ phase to a nematic phase have also been obtained. In addition, a direct transition from a novel columnar phase with an oblique lattice to a nematic phase has also been observed for the first time. The X-ray diffraction pattern of an oriented sample of the mesophase with an oblique lattice exhibited by a bent-core material has been reported for the first time. The possibility of a mesophase with a pseudo hexagonal lattice has also been demonstrated in bent-core compounds. The nematic phase has been obtained exclusively in compounds derived from 2,7-dihydroxynaphthalene. The influence of the central core as well as that of a fluorine substituent on the phenyl rings in the sidearms of these bent-core compounds has also been examined. The mesophases have been characterized using conventional techniques.