Chiral liquid crystalline m-nitrotolans and tolans: synthesis and mesomorphic properties (original) (raw)

Two homologous series, 4¾ -(4-n-alkoxybenzoyloxy)-4-substituted 3-nitrotolans (Ia-d) and 4¾ -(4-n-alkoxybenzoyloxy)-4-substituted tolans ( IIa-c), with substituents (S)-2-methyl-1-butyl and n-alkyl, were synthesized by Sonogashira's coupling. Their mesomorphic behaviour is reported. The thermal stability of the series II is higher than that of series I. Series I melting points and clearing points are lower than those of series II. None of the chiral tolans or m-nitrotolans have an enantiotropic smectic C phase. When the chiral chains are changed to n-alkyl groups in compounds Ia,b and IIa, an enantiotropic smectic C phase is seen. All compounds have a nematic or cholesteric phase, and two homologues of series II present a monotropic smectic C phase with mosaic texture. The mesophases were characterized using optical polarized light microscopy and diOE erential scanning calorimetry.

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