Ionic liquid crystals derived from 4-hydroxypyridine

Abstract

Monoalkylation of 4-hydroxypyridine gave either neutral N-alkyl-4-pyridones or 4-alkoxypyridines depending on the site (N or O) of alkylation. Further alkylation of these two neutral compounds yielded ionic liquid crystals (ILCs) of N-alkyl-4-alkoxypyridinium bromide, having two long alkyl chains. Alternatively, simple protonation of the two neutral compounds with HCl also induced the formation of ILCs of N-alkyl-4-hydroxypyridinium chloride or 4-alkoxypyridinium hydrochloride. Crystal structures of two different types of ionic liquid crystals and one neutral compound were determined via single crystal X-ray diffraction. Mesophase properties were examined by the technique of differential scanning calorimetry, polarized optical microscopy, and powder X-ray diffractometry. Anions influence the structure and stability of the mesophase in the dialkylated compounds. The self-assembly behavior of some typical compounds in solution was studied using the technique of NMR diffusion order spectroscopy. Finally, stable Au nanoparticles stabilized by a pyridinium salt were prepared and characterized.