Supramolecular liquid crystals of amide functionalized imidazolium salts

Liquid crystalline 1-acetamido-3-alkylimidazolium bromide, hexafluorophosphate and tetrafluoroborate salts with 3-alkyl chains of carbon number n = 10, 12, 14, 16 and 18 were prepared. The single crystal structure of the PF6- salt of n = 12 self-organizes to form a framework of a hydrogen bonded ribbon polymer. The mesomorphic behaviors of these compounds were studied by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction. The presence of extended hydrogen bonding interactions in these acetamidoimidazolium salts allows them to have a wide temperature range of the mesophase. Anions have a profound effect on the phase transition temperature, suggesting that both ionic and hydrogen bonding interactions play dominant roles in the mesomorphic behavior of these liquid crystalline compounds.