Open versus Closed Polyaromatic Nanocavity: Enhanced Host Abilities toward Large Dyes and Pigments

Abstract Host functions of polyaromatic nanocavities were revealed by using an M 2 L 4 molecular cage and capsule. On the basis of the previously reported M 2 L 4 capsule with a closed polyaromatic cavity, a new M 2 L 4 cage (as a mixture of the isomers) was prepared by the quantitative assembly of two metal ions and four desymmetrized bispyridine ligands with a single polyaromatic panel. The obtained, open nanocavity of the cage exhibited enhanced binding abilities toward large dyes and pigments in water. For example, two molecules of coumarin dyes were bound in the nanocavity and showed strong whitish emission (up to Φ F =34 %). Furthermore, metallopigments, the sizes of which are larger than the inner cavities of the cage and capsule, were bound only in the open polyaromatic nanocavity of the cage to give water‐soluble 1:1 host–guest complexes.