Novel glass-forming liquid crystals. III Helical sense and twisting power in chiral nematic systems

Abstract Based on nematic and chiral precursors comprising of acetylenic, phenyl, naphthyl and terminal cyano groups in conjugation and cyclohexane as the central core, a series of novel nematic and chiral nematic glass-forming liquid crystals with a T g ≧ = 60°C were synthesized for an investigation of handedness and helical twisting power, HTP, as functions of chemical structure. Three chiral building blocks with a single asymmetric carbon centre were employed: (S)-(−)-1-phenylethanol, (S)(−)-α-methyl-2-naphthalenemethanol, and (S)-(−)-1-phenylethylamine, were all found to yield a left-handed cholesteric mesophase. With reference to (S)-(−)-1-phenylethanol, the HTP value was found to be nearly doubled in the presence of a strong anchoring plane furnished by a naphthyl group surrounding the asymmetric carbon centre, but reduced by one third in the presence of intermolecular hydrogen bonding through the amide group. All these observations were properly accounted for by a molecular interaction model of a s...