Pyridinium-based ionic liquid crystals with terminal fluorinated pyrrolidine

A new class pyridinium-based liquid crystals with an extended fluorinated pyrrolidine were synthesized. These compounds show a wide mesophase range and are stable to high temperatures after an introduction of a fluorinated pyrrolidine to the terminal end. Their properties were modified by varying alkyl substituents on the pyridinium ring. The mesophase behavior was affected by altering the configuration of the terminal fluorinated heterocycle. For a comparison, the analogs 5a–5c with an extended fluorinated azepine were also synthesized. The terminal seven-membered 3,3,4,4,5,5,6,6-octafluoroazepane formed an “L” shape. The twisted L configuration significantly impacted the liquid crystal behavior of 5a–5c, resulting from steric hindrance. The structures of 3b were investigated using single crystal X-ray diffraction analysis.