The π–π interactions enhanced in salicylaldimines and salicylaldazines

Abstract

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.