The Effect on Mesomorphic Properties of Substituting a Sulfur for the Ether Oxygen Atom in the Ester Linkage of 4-Alkylphenyl-4′-Alkyl or Alkoxybenzoates

A variety of homologs of 4-alkylbenzenethio-4′-alkyl or alkoxybenzoates in which the 4′-alkoxy group is C7-C14, the 4′-alkyl group is C7-C12 and the 4-alkyl group is C5-C8 or C10 were prepared and their mesomorphic properties studied by microscopy, DSC and X-ray diffraction. A comparison is made of the mesomorphic properties in the thio- and oxy-esters and the effect on mesomorphic properties of replacing the ether oxygen atom in the ester linkage with a sulfur atom. The types of smectic phases observed are discussed; two apparently new biaxial smectic phases were found in the alkoxy-alkyl series. Relationships between mesomorphic and thermodynamic properties with molecular structure are discussed.