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Study of the effect of a heterocyclic ring end group and an azomethane linkage on mesomorphism

ABSTRACT A novel homologous series RO-C6H4-COO-C6H4-N = CH-C5H4N of liquid crystalline Schiff base esters has been synthesized and studied with a view to correlating molecular structure to the liquid crystal properties on the basis of molecular rigidity and flexibility. All 12 members of series are either monotropic (C1, C3, C5) or enantiotropic (C2, C4, C6 to C16) nematic with the absence of smectogenic character throughout the series. Transition temperatures and LC behavior of the series were determined using an optical polarizing microscope equipped with a heating stage. Transition curves (Cr-N or Cr-I and N-I or I-N) behave in the normal established manner as depicted in a phase diagram. An odd–even effect is exhibited by the N-I transition curve up to the C8 homologue.