Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine

Influence of counterion on the mesomorphic behavior and photophysical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine [Display omitted] •ILC pyridinium salts derived from 4-hydroxypyridine were prepared and studied.•N-3,4,5-tridodecyloxybenzyl-4-pyridone shows a monotropic Colh phase.•Bulkier counterions (BF4- or PF6-) destabilize the LC phase.•3,4,5-Tridodecyloxybenzyl pyridinium bromide salt shows two LC columnar phases. A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56°C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br−) with other counterions (NO3-,BF4- and PF6-) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed.