New Synthetic Host Pillararenes: Their Synthesis and Application to Supramolecular Materials

In 2008, we reported a new class of macrocyclic hosts called “pillararenes.” They combine the advantages and aspects of traditional hosts and have a composition similar to those of typical calixarenes. Pillararenes have repeating units connected by methylene bridges at the para-position of benzene moieties, and thus they have a unique symmetric pillar architecture differing from the basket-shaped structure of calixarenes bridged at the meta-position of benzene moieties. Pillararenes show high functionality similar to cyclodextrins and can capture electron-accepting guest molecules within their cavity similarly to cucurbiturils. In this account, the synthesis, structure, and host–guest properties are discussed, along with pillararene-based supramolecular architectures.