Pillar[n]arenes: from synthesis, host-guest chemistry to self-assembly properties and applications

Abstract

The study of chemistry based on macrocyclic host is always an important aspect in supramolecular chemistry. As a new class of supramolecular macrocyclic hosts after crown ethers, cyclodextrins, calixarenes, and cucurbiturils, pillar[n]arenes, are useful and interesting macrocyclic compounds that present a hydrophobic core sandwiched between two functionalizable rims. Their syntheses, conformational mobility, derivatization, host-guest complexation, self-assembly in water or organic solvents and applications have been widely explored recently. They have been described as "a new class of macrocycles for supramolecular chemistry". In this review, we provide a comprehensive overview of pillararene chemistry, summarizing our results along with related studies from other researchers. We describe strategies for the synthesis, isomerization, and functionalization of pillararenes. We also discuss their host-guest properties, their self-assembly into micelles, vesicles, microtubes, supramolecular polymers, and other nanomaterials. The hydroxyl groups of the pillararenes can be modified at all positions or selectively on one or two positions. Through a variety of functionalizations, researchers have developed many pillararene derivatives that exhibit very interesting host-guest properties both in organic solvents and in aqueous media. Guest molecules include electron acceptors such as viologen derivatives and (bis)imidazolium cations and alkyl chain derivatives such as n-hexane, alkanediamines, n-octyltrimethyl ammonium, and neutral bis(imidazole) derivatives. These host-guest studies have led to the fabrication of (pseudo)rotaxanes, poly(pseudo)rotaxanes, supramolecular dimers or polymers. At last, pillararenes applied in molecular recognition, artificial transmembrane proton channels, fluorescent sensors, TNT adsorption, catalysis, biological detoxification, nanoparticles and other areas.