On the supramolecular packing of bent-shaped molecules: the influence of the central bent-core on the liquid crystalline behaviour

Abstract

Two series of bent-shaped molecules have been synthesized and their supramolecular self-organization at variable temperature has been studied. The majority of these bent-compounds form liquid crystalline phases and the mesomorphic behaviour of them has been fully characterized by polarised optical microscopy, calorimetry, X-ray diffraction and dielectric techniques. A series of bis-4-n-tetradecyloxybenzoyloxybenzoates derived from naphthalene, resulting in a change of the bending angle, have proved that when these cores bend around 1201, a polar lamellar packing (SmC a P A ) can be induced, whereas when the angle was around 601, an orthogonal lamellar arrangement (SmA) that responded to an electric field, are found to occur. Liquid-crystal order can also be achieved over a significant range of temperatures by using appropriate bis-4,4 0 -disubstituted phenylene derivatives (-Ar-X-Ar-). Groups such as -CO-, SO-and -CH 2 -connecting the aromatic rings induce the SmC a P A phase while a sulfide group (-S-) leads to columnar order. Further, the formation of isotropic textures as chiral conglomerates or a field-induced phase transition have also been observed as unusual properties of the self-organizations of these compounds.

The SmA phase of a bent-core V-shaped compound: structure and electric-field response

“…Under an electric field, no switching is observed when applying fields up to the damage threshold (25 V/µm). Some samples could resist fields as large as 30V/µm [10]. At these high fields, the texture darkens indicating a tendency toward homeotropic orientation.…”

“…In this work we present an exhaustive study of the structural properties of the phases of one V-shaped compound whose synthesis and a preliminary characterisation study have been published previously [10]. In particular we have obtained some results on the molecular packing it presents in the SmA and crystalline phases.…”

Smectic A–hexagonal columnar–B7 phase transition of acute-angle bent-core molecules

“…One controversial example is related to acute-angle bent-core molecules comprising a 2,3-naphthalene core with ester-type side wings. These molecules have been reported as switchable by Choi et al 17,18 but non-switchable by Ros et al 19,20 in the smectic phase. Thus, we believe a species of acute-angle bent-core mesogens can be an ultimate example that lies on the line between the banana-like and calamitic LC properties.…”

New cholesteryl containing bent core liquid crystals

“…17 The 4-{[4-(alkyloxy)phenyl]azo}benzoic acids 18 and the 4-[4-(alkyloxy)benzoyloxy]benzoic acids 19 were obtained by adapting literature data. Cholesteryl 6-bromohexanoate was synthesized accordingly to a literature procedure.…”