Unexpected liquid crystalline behaviour of three-ring bent-core mesogens: bis(4-subst.-phenyl) 2-methyl-iso-phthalates

Abstract

Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155 ) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138 in the SmA and about 146 in the nematic phase). Dielectric and SHG measurements give evidence that in the SmA phase a polar structure can be induced by application of an electric field which disappears in the isotropic liquid phase. The electric field not only leads to a slight textural change even in the SmA phase but also polar-type electric current response (P S about 200 nC cm À2 ) is observed. This unusual electrooptical behaviour is discussed on the basis of the orientation of polar clusters formed by the bent molecules. In the paper we not only attempt to characterize the mesophases and to describe their physical properties, but we also show that these types of molecules represent the borderline between bent-shaped and calamitic liquid crystals.

Banana-calamitic Dimers: Further Variations of the Bent-core Mesogenic Unit

“…For example, the B 5 phase and crystalline polar phases have been first reported for bent-core mesogens and liquid crystalline behaviour have been described for methyl substituted three-ring bent-core molecules. [67][68][69] The enlargement of the bent-core mesogenic part by insertion of a further benzoyloxy unit yields compounds with high mesophase stability. Surprisingly, the appearance of a nematic phase is supported, mostly in combination with a columnar one.…”

3,5-diarylisoxazoles: A New Entry to Soft Crystal Phase

“…Bent-shaped molecules are also founded in 5-membered heterocyclic if the bending angle varies between about 135 • and 160 • . In this sense molecules with this bending angle are more elongated in comparison to the 1,3-phenylene derivatives where the bending angle is 120 • caused by the meta-substitution [4]. Typical mesophase formed by calamitic molecules, e.g N, SmA and SmC are observed when the bending angle increase to about 140 • or more.…”

“…146-147 • C; 1 H NMR (300 MHz, CDCl 3 ) δ 7.85 (m, 2H), 7.74 (m, 2H), 7.16 (m, 2H), 7.09 (m, 2H), 6.70 (s, 1H), 1.41 (s, 9H); 13 C NMR (75.5 MHz, CDCl 3 ) δ 170.5, 163.7 (d, 1 J C-F = 249.7 Hz), 162.0, 157.6, 128.7 (d, 3 J C-F = 8. 6 Hz),126.8,125.4 (d,4 J C-F = 3.1 Hz), 124.0, 122.2, 116.0 (d, 2 J C-F = 21.8 Hz),96.4,79.5,28.9.…”

Ethylenedioxythiophene as a novel central unit for bent-core liquid crystals

“…Initially, we designed and synthesised EDOTbased three-ring bent-core molecules as shown in Scheme 1, where the central EDOT core is flanked by alkyl or alkoxy-substituted phenyl rings. These compounds were found to be non-LC, which is not much surprising as three-ring structures are usually not conducive for BC LCs [24,25]. To enhance the length:width ratio, we added one phenyl ring each side to generate five-ring structure.…”