Liquid crystalline behaviour of model compounds di-laterally substituted with different polar groups

Five groups of laterally di-substituted three-ring compounds, 4-(3'-fluoro phenylazo)-2-(or 3-) substituted phenyl-4'-alkoxybenzoates, were prepared and investigated for their mesophase formation and stability. Each group of compounds, which have in common a lateral fluorine atom on the first terminal ring, differs from each other by a second lateral group substituted on the central ring. The central group varies between the electron-donating (CH3) and electron-withdrawing (Cl and CN) groups, including the hydrogen (H). In each group of homologues, the number of carbons in the other terminal, alkoxy group varies between eight and 16 carbons. The study investigated the effect of the di-lateral substitution, as well as the spatial orientation of the central substituent, on the mesomorphic properties of the produced derivatives either in their pure or mixed states. Molecular formulae of the compounds prepared were confirmed via elemental analyses, IR, NMR and mass spectroscopy. The compounds prepared were characterised for their mesophase behaviour by differential scanning calorimetry (DSC), and the mesophases were identified by polarised light microscopy (PLM) and confirmed by miscibility with a standard smectic C (SmC) compound.