Columnar liquid-crystalline metallomacrocycles.

We report synthesis of novel macrocyclic molecules and their metal complexes as well as their thermotropic columnar liquid-crystalline behavior. The macrocyclic ligands were prepared size-selectively based on dynamic covalent chemistry. X-ray study of a model macrocycle with short alkyl chains revealed that they were discrete and highly symmetric, with an inner vacant cavity of 9 Å diameter enclosed by a 56π planar ring composed of four bis(salicylidene)-o-phenylenediamine (salphen) moieties alternating with four carbazoles. Ni(2+) and Cu(2+) ions were incorporated into the four salphen ligands and formed square-planar metal complexes inside the macrocycles. From the structural and thermal analyses via X-ray diffraction measurements, differential scanning calorimetry, and polarized optical-microscopic observations, it was revealed that the macrocyclic ligand and its metal complexes self-assembled into columnar liquid-crystalline phases depending on the temperature and displayed a highly fluid character over a wide range of temperatures. The peripheral alkyl chains were influential in controlling the temperature range and flowability of the liquid-crystalline phases, and the range of the liquid-crystalline temperature of the metallo-macrocycles was significantly higher than those of the metal-free macrocycles. To the best of our knowledge, these are the first examples of thermotropic columnar liquid crystals of macrocyclic metal complexes with a large hollow area.