The π-π interactions enhanced in salicylaldimines and salicylaldazines

Four new series of salicylaldazines 1 and salicylaldimines 2-4 were prepared, characterized and their mesomorphic properties were studied. The structures of all compounds were identified and confirmed by spectroscopic techniques such as ¹H, ¹³C NMR, MS and elemental analysis. Three single crystallographic structures of compounds 1a (n=3, 6) and 2 (n=3) were determined by X-ray analysis in order to correlate the molecular structures with the formation of mesophases. Crystallographic data indicated that the better mesomorphic properties might be controlled by CH-π, π-π or/and H-bonds in such system. Except for crystalline compounds 4, all other compounds 1-3 showed mesomorphic behavior of nematic, smectic A or/and smectic C phases, which were characterized by differential scanning calorimetry, optical polarizing microscope and X-ray diffraction experiments. All compounds 1-4 showed yellow-green photoluminescence in THF occurred at 519-521 nm.