Methylation driven molecular packing difference at the smectic phases of a series of pyridinium-based chiral ionic liquid crystals

A series of pyridinium-based chiral ionic liquid crystals were designed and synthesized. All of them exhibit enantiotropic smectic phases. The methylation on the pyridine ring not only decreases the melting point and clearing point, but also drives structural transitions from bilayer molecular packing structures to interdigitated monolayer ones at the smectic A and C phases. Due to entropy increase, the clearing point of the liquid crystal derived from 2-methylpyridine is higher than that derived from 3-methylpyridine, and then that derived from 4-methylpyridine.