Bilayer Packing of the Nematogen Molecules in the Induced Smectic a Phase

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Abstract
A dynamic intermolecular associates in structure of the smectic A phase induced by mixing of two nematogens 4-pentyloxy-4″ cyanobiphenyl (1, high polar), and hexyloxyphcnylic ester of nonylbenzoic acid (2, low polar) have been discovered with aid of 13C-NMR spectroscopy. They ate connected by means of dipole-dipole interaction between CO- and CN-groups, and dispersion forces between complementary packed aryl fragments. An analysis of the 13C chemical shifts and of the 13C spin-lattice relaxation times, T1, confirms the bilayer model of the molecular packing for induced SmA phase. By formation of such associates the carbonyl group of 2 continually exchanges a partner because of lateral diffusion. Moreover the aromatic ring of the COOAr group is situated normally to the layer plane between two biphenyl aromatic rings of compound 1. This fact facilitates the co-operative rotation of the aromatic rings of interacting molecules within bilayer.