Liquid-crystalline Metallomacrocycles Composed of Bis(hydroxypyridono)toluene Ligand and Cu²⁺ Ions

A series of π-extended chelating scaffolds incorporating two hydroxypyridone moieties were synthesized. X-ray crystallographic analysis revealed that a bis(hydroxypyridono)toluene ligand possessed a unique π-extended structure and exhibited efficient phase segregation from the aliphatic chains attached at the heterocyclic nitrogen. The bis-bidentate ligand formed a metal-coordination-induced macrocycle with Cu²⁺ ions. During the complexation, a spectral change in the visible region was induced. Furthermore, the successful development of a liquid crystal of the metallomacrocycle with appropriate side chains was achieved. Examples of liquid-crystalline macrocycles formed via metal-mediated self-assembly are still rare. Among them, the macrocycle described in this paper showed an obvious hexagonal columnar phase reflecting the three-fold symmetric planar structure of the mesogenic metal complex.