Para-Bridged Macrocyclic Host Molecules Pillar[5]arenes: Their Synthesis and Application for Supramolecular Materials

In 2008, we reported a new class of macrocyclic hosts and named “Pillar[5]arenes”. They combine the advantages and aspects of traditional hosts and have a composition similar to those of typical calix[n]arenes. Pillar[5]arenes have repeating units connected by methylene bridges at the para-position, and thus they have a unique symmetrical pillar architecture differing from the basket-shaped structure of meta-bridged calix[n]arenes. Pillar[5]arenes show high functionality similar to cyclodextrins, and can capture electron accepting guest molecules within their cavity similarly to cucurbit[n]urils. In this review, the synthesis, structure, rotation, host-guest properties, planar chirality and functionality of pillar[5]arenes are discussed, along with pillar[5]arene-based supramolecular architectures.