Chiral liquid crystalline m-nitrotolans and tolans: synthesis and mesomorphic properties

Two homologous series, 4'-(4-n-alkoxybenzoyloxy)-4-substituted 3-nitrotolan s (Ia-d) acid 4'-( 4-n-alkoxybenzoyloxy)-4-substituted tolans (IIa-c), with substituents (S)-2-methyl-1-butyl and n-alkyl, were synthesized by Sonogas hira's coupling. Their mesomorphic behaviour is reported. The thermal stabi lity of the series II is higher than that of series I. Series I melting poi nts and clearing points are lower than those of series II. None of the chir al 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 e nantiotropic smectic C phase is seen. All compounds have a nematic or chole steric phase, and two homologues of series II present a monotropic smectic C phase with mosaic texture. The mesophases were characterized using optica l polarized light microscopy and differential scanning calorimetry.