Molecular structure and smectic properties: the substituent effect on the smectic A phase in biphenyl ester systems

Abstract

The substituent effect on the thermal properties of smectic A phase for two related compounds; 4-octyloxybiphenyl-4-yl 4-Y-benzoates and 4-Y-phenyl 4-octyloxybiphenyl-4′-carboxylate with Y = N(CH₃)₂, OH, OCH₃, CH₃, C₆H₅, SCH₃, H, CHO, halogens, COCH₃, SO₂CH₃, CO₂CH₃, CN and NO₂, has been examined. The smectic A–nematic transition temperature (T_SA–N) and the ratio of T_SA–N to the nematic–isotropic transition temperature are discussed in terms of Hammett's constants for the substituents and change in polarity around the ester group and the substituent. The non-ideal solution behaviour of T_SA–N in binary phase diagrams consisting of methoxy and cyano derivatives is also examined.