U-shaped dimeric liquid crystals derived from phthalic acid

Details of the transitional properties of four homologous series of U-shaped liquid crystal materials, the benzene-1,2-di-(4-carboxyalkoxybenzylide-4'-n-alkylanilines), are presented. The spacers incorporate 3 to 6 methylene units, whilst terminal aliphatic chain lengths are varied from 1 to 12 units. Members of the two homologous series with an odd number of methylene units in the spacer form nematic and smectic phases as a function of terminal chain length. Materials with an even number of methylene units in the spacer are purely smectogenic, and in both series the first two homologues form only smectic B phases. For all four series the higher homologues show the phase sequence S-F/I-S-C-S-A-I. X-ray diffraction studies have shown that these smectic phases are composed of molecules arranged in bilayers.