SYNTHESIS AND PHASE BEHAVIOR OF SUPRAMOLECULAR LIQUID CRYSTALS OF ROD­ SHAPED MOLECULES

Abstract

Two series of compounds of the type 4-pyridylazophenyl-4'-substituted benzoates were prepared. The first, In, is a homologous series that bears terminal alkoxy group with a length varies between 10 and 18 carbons. The terminal substituent, X, in the second series, Ia.e, is a compact polar group that alternatively changes from CH30, CH3, H, Br, and N02• Structures of compounds prepared were confirmed via infrared spectroscopy, mass spectra, NMR, and elemental analyses, and their mesophase behavior investigated by differential scanning calorimetry, DSC, and polarized-light microscopy, PLM. The results obtained showed that, almost, all members of the first series (In) are mesomorphic possessing SmC as the only mesophase observed, while those of series Ia.e are non-mesomorphic. Supramolecular complexes were prepared, and characterized for their mesophase behavior, from each of the individual members of both series, In and Ia-e, using two series of 4-substituted benzoic acids, namely, 4-alkoxybenzoic acids, lim, having an alkoxy chain varies between 10 and 18 carbon atoms, and 1Ia-f that beers a polar substituent changes again between CH30, CH3, H, Br, N02 and CN. Using two types of substituents on both sides of the supramolecular complexes, one comes to prepare four groups of hydrogen-bonded complexes, namely: 1. Group A in which both components of the complex bear an alkoxy group of varying chain length. In this case, both complementary components are mesomorphic. n. Group B in which only the pyridine-based component, In, that bears an alkoxy group is mesomorphic, while the acid component, 1Ia-f, bearing a compact polar substituent, Y, is not. iii. Group C is substituted in an opposite manner in which the acid component, lim, is mesomorphic while the pyridine-based component, Ia-e, is not. iv. In Group D, both components bear a compact polar substituent, X or Y, and consequently, none of them is mesomorphic. Binary phase diagrams, covering the whole composition ranges, were constructed for group C complexes, aiming to investigate the effect of polar substituent, of the base side, on the extent and stability of the supramolecular phases induced by intermolecular hydrogen bonding. In each group of supramolecular complexes, bearing the same alkoxy, or polar substituent, the mesophase-isotropic transition temperatures, Tc, were correlated with the polarizability anisotropy of bonds to the substituent X or Y. The results were discussed in terms of mesomeric and polarizability effects.