Banana-shaped Liquid Crystal Research Articles

Dimorphism SmA-B2 in bent-core mesogens with perfluorinated terminal chains

Several banana-shaped liquid crystal materials with perfluorinated terminal chains have been synthesized. A dimorphism SmA-B2 was proved by X-ray studies and electro-optical measurements. The unusual ratio d/L (d = layer spacing, L = molecular length) and the unexpected behaviour of the layer spacing at the phase transition SmA > B2 can be interpreted by a change of the packing of the bent molecules.

Novel sulphur-containing banana-shaped liquid crystal molecules

In this preliminary report we present the mesomorphic properties and electro-optic investigations of three new 'banana-shaped' mesogens. The materials are structurally similar to Niori's the original bent-core materials but possess alkylthio substituents in place of alkoxy substituents. Microscopic investigations revealed an unusual 'spiral-domain texture', similar to that observed in the 'B7' phase of related materials. Further investigations support our earlier observations that the materials display antiferroelectric switching in this phase, in two of the new materials studied. The nature of this phase, in comparison with the 'switchable' (B2) and 'chiral-domain' (B4) phases of the original materials, is discussed.

Smectic Mesophases Formed by Banana-Shaped Molecules

Liquid crystals composed of bent molecules exhibit smectic-like phases including und-ulated or two-dimensional ones which are unlike the smectic phases fromed from normal calamitic molecules [1]. These phases are not miscible with any smectic phases of calamitic compounds, which emphasizes their distinctness, although it must be remembered that immiscibility is not a criterion for a new phase type. Until the true character of these phases is established, it has been proposed (Workshop on Banana-shaped Liquid Crystals, December 1997, Berlin) that the phases be labelled with the code letters B1…B7 in the sequence of the their discovery.

Designing banana-shaped liquid crystals without Schiff's base units: m-terphenyls, 2,6-diphenylpyridines and V-shaped tolane derivatives

This paper reports attempts to obtain (anti)ferroelectric switchable achiral banana-shaped molecules without Schiff's base units. For this purpose we have synthesized novel V-shaped molecules consisting of rigid angular central units [1,3-disubstituted benzene, 2,7-disubstituted naphthalene, 1,3-diphenylbenzene, 2,6-diphenylnitrobenzene, 2,6-diphenylpyridine, 1,3-bis(phenylethynyl)benzene, 1-phenyl-3-(phenylethynyl)benzene] connected via ester linkages to two rigid cores (1,4-disubstituted benzenes, biphenyls, 2-phenylpyrimidines, phenylbenzoates). Most compounds have rather high melting points. Only molecules with seven aromatic rings show liquid crystalline properties. Two-dimensional modulated smectic phases (rectangular columnar phases) were found for molecules with phenylbenzoate rigid units. Intercalated fluid smectic phases were detected for the corresponding 2-phenylpyrimidine derivatives. For the first time in the case of banana-shaped molecules a nematic phase was observed for a 2′-nitro-m-terphenyl-4,4″-diyl bisbenzoate. However, none of the synthesized compounds exhibit the typical texture of the (anti)ferroelectric switchable mesophases, known from the Schiff's base derivatives.

A novel class of non-chiral banana-shaped liquid crystals with ferroelectric properties

The first banana-shaped molecules without Schiff-base units, with broad regions of a ferroelectric switchable liquid crystalline phase and low melting points, have been obtained.