Synthesis of diphenyl-diacetylene-based nematic liquid crystals and their high birefringence properties

Synthesis of Some Novel Aromatic Alkynyl Silanes: Mesomorphic Characterization of Ethynyl-Substituted Rod-Shaped Molecules

“…Compound 6 was used for Sonogashira homo-coupling reaction to obtain compound 7, which was subjected to reduction with 5% palladium on charcoal and hydrogen gas at atmospheric pressure and room temperature to get 8 with flexible n-butyl spacer. The chemical structures were confirmed by comparison with the corresponding literature [12,13].…”

“…Yield = 1.26 g (73%). (6) [12]. To the 1-(4 -n-pentyloxyphenyl)-2-trimethylsilylacetylene (1 g, 0.38 mmol) was added potassium carbonate (1.0 g, 0.76 mmol) in cold methanol at ambient temperature.…”

“…[12,13] To a solution of dry pyridine (5 mL) and methanol (5 mL) was added 1-ethynyl-4-(pentyloxy)benzene (0.250 g, 1 mmol) and copper acetate (0.601 g, 2.5 mmol) under argon atmosphere. The resultant reaction mixture was refluxed at 80…”

“…Liquid crystals consisting of a rigid and linear molecular framework with extended π -conjugated electronic structure of difluoroterphenyl core with short and bulky trimethylsilyl terminal groups provide stability to the mesophase [6]. The pyrimidinylphenyldiacetylenes [7], azotolanes [8,9], 1,4-bis(phenylethynyl)benzene [10], 1,4-bis(2-naphthyl)-1,3-butadiynes [11], and high birefringence property having diphenyl-diacetylene-based nematogens [12] are also reported. Alkyl-substituted oligo(p-phenylene)ethynylenes [13] and 1,2-(4,4-dialkoxyaryl)acetylene with solid polymorphism [14,15] and mesomorphism showing triptycene derivatives [16] have been achieved using different synthetic routes and in the presence of different concentrations of palladium catalysts.…”

Polar structure of disclination loops in nematic liquid crystals probed by second-harmonic-light scattering

“…1. They comprise examples from three classes of thermotropic compounds: polar and nonpolar rodlike mesogens -4-Cyano-4'-pentylbiphenyl or 5CB and 1-heptyl-4-[4-(4-heptylphenyl)buta-1,3-diyn-1-yl]benzene or C7 [17], respectively -as well as a bow shaped (bent-core) nematic compound -4-chloro-1,3-phenylenebis-4-[4-(9-decenyloxy)benzoyloxy]benzoate [18], which we simply designate BCN. This BCN and closely related compounds exhibit unusual properties -including shortrange smectic-C-like molecular correlations [19], nonNewtonian flow behavior [20], unusual viscoelastic anisotropy [21], and large electromechanical coupling [22] -even though their macroscopic orientational order is of the conventional (uniaxial) type.…”