Host-Guest Chemistry of Porphyrins in Liquid Crystalline Macrocycles

Abstract

Structurally well-defined macrocyclic molecules have great potential to accommodate specific guest molecules in the hollow. Recently, we have reported a series of macrocycles which are composed of four carbazoles connected with four salphen ligands1, four dibenzothiophenes connected with four salen ligands2, or four diindrocarbazoles connected with four salphen ligands3 (MC1, MC2 and MC3, respectively). The macrocycles with appropriate peripheral alkyl chains and their tetranuclear metal complexes with square planar metal ions showed thermotropic columnar liquid crystalline properties1,2. These macrocycles stacked to form columns inside the fluid materials. Especially, the giant macrocycle MC3 contained a square hollow with a diagonal of 2.5 nm. This giant macrocycle has the largest inner cavity among known discrete shape-persistent macrocycles that exhibit thermotropic LC properties. The size and shape of the hollow structure make it interesting for molecular inclusion applications. For example, MC3 molecule can accommodate a tetrapyridylporphyrin inside the hollow to afford a planar conjugate, and the conjugate showed liquid crystalline behavior. Reference: [1] S. Kawano, Y. Ishida, and K. Tanaka, J. Am. Chem. Soc. 2015, 137, 2295.[2] Kawano, S.; Hamazaki, T.; Suzuki, A.; Kurahashi, K.; Tanaka, K. Chem. Eur. J. 2016, 22, 15674-15683.[3] Kawano, S.; Kato, M.; Somiya, S.; Nakayama, M.; Onoe, J.; Tanaka, K. Angew. Chem. Int. Ed. 2018, 57, 167–171. Figure 1