Pillar[5]- and pillar[6]arene-based supramolecular assemblies built by using their cavity-size-dependent host-guest interactions.

Pillar[n]arenes, which we first synthesized and named in 2008, are new pillar-shaped macrocyclic hosts. Pillar[n]arene homologues with n = 5-10 have already been synthesized, but the cyclic pentamers, i.e., pillar[5]arenes, and cyclic hexamers, i.e., pillar[6]arenes, have been most widely used because these can be obtained in good yields. To date, nearly all pillar[n]arene-based supramolecular assemblies have been constructed using pillar[5]- and pillar[6]arene scaffolds. In this feature article, we describe supramolecular assemblies built using host-guest interactions depending on the cavity sizes of pillar[5]- and pillar[6]arenes. We first discuss the effects of the type of substituents on the rims of pillar[5]- and pillar[6]arenes on their solubilities, functionalities and host-guest properties. We then discuss supramolecular assemblies based on their host-guest properties and pillar-shaped architectures.