Pillar[n]arenes (P[n]As) and their derivatives, consisting of (substituted) hydroquinone units linked by methylene bridges at para-positions, are new type of cyclophane hosts developed in 2008. Their intrinsic characteristics and properties, such as facile preparation and flexible modification, symmetrical and columnar architectures, very rigid and π-rich cavities, as well as intriguing and peculiar guest complexation capability, make them ideal building blocks for the fabrication of polymeric supramolecules. This Feature Article provides an overview of the construction of pillararene-based supramolecular polymers and covers recent research endeavors of the marriage between pillararene-based host–guest pairs and polymeric aggregates. These polymers are classified into two major classes according to the different types of guest species: (1) supramolecular polymers relying on pillararene-based cationic guest recognition; (2) supramolecular polymers relying on pillararene-based neutral guest recognition. The host–guest motifs, building strategies, topological architectures, stimuli-responsiveness and functionalities are comprehensively discussed.

Highly effective binding of neutral dinitriles by simple alkyl-substituted pillar[5]arenes and the formation of interpenetrated geometries are reported. The resulting host–guest complexes represent one of the most efficient recognition motifs based on pillararenes.

Since their discovery in 2008, pillar[n]arenes have been a popular family of macrocyclic arene hosts due to their accessible one-step synthesis, convenient functionalization, symmetrical prism structures and perfect cavity host–guest properties. Compared with other macrocyclic hosts, the most peculiar recognition behavior of pillararenes is the strong binding affinities of pillar[5]arenes (P5As) towards neutral guests in organic media, which is unfeasible for classic crown ethers and calixarenes. The intriguing properties have found extensive applications in many fields from supramolecular chemistry to materials science. This feature article provides a detailed summary of the molecular recognition of P5As and neutral guests, where the driving forces, binding mechanisms, and binding selectivities are comprehensively discussed. Furthermore, brief highlights of research progress in the functional applications based on the neutral guest⊂P5A motifs were also discussed, including the construction of complex topological superstructures (e.g. rotaxanes, catenanes and daisy chains), supramolecular polymers, and functional materials.

The complexation behavior of a series of paraquats (G1·2PF₆–G5·2PF₆) and bis(pyridinium) derivatives (G6·2PF₆–G14·2PF₆) with pillar[5]arene (P5A) host has been comprehensively investigated by ¹H NMR, ESI mass and UV-vis absorption spectroscopy. It is found that P5A forms 2 : 1 external complexes with N,N′-dialkyl-4,4′-bipyridiniums (G1–G4·2PF₆); while it forms 1 : 1 pseudorotaxane-type inclusion complexes with methylene [–(CH₂)_n–] linked bis(pyridinium) derivatives possessing appropriate chain lengths (n = 3–6, G7–G10·2PF₆). Host–guest association constants in dimethyl sulfoxide (DMSO) were determined, indicating G7–G10·2PF₆ axles form stable [2]pseudorotaxanes with P5A wheel in this very high polarity solvent and 1,4-bis(pyridinium)butane (G8·2PF₆) was the most suitable axle unit. Meanwhile, the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior. The introduction of pyridyls (G13·2PF₆) increases not only the K_a value (4.5 × 10²→7.4 × 10² M⁻¹), but also the charge transfer (CT) absorption (colorless→yellow). Furthermore, the solvent effects have also been investigated, showing they significantly influence the association strength during the course of host–guest complexation. Particularly, the K_a value of P5A–G13·2PF₆ in 1 : 1 (v:v) acetone-d₆ /DMSO-d₆ is enhanced by a factor of 7.3 compared with pure DMSO-d₆ (7.4 × 10²→5.4 × 10³ M⁻¹).

A simple bis(imidazolium) dication, 1,4-bis[N-(N′-hydroimidazolium)]butane, can act as a new template for formation of [2]pseudorotaxane with pillar[5]arene, in which the dethreading/rethreading process can be controlled by acid–base stimulus.

To design and exploit novel macrocyclic synthetic receptors is a permanent and challenging topic in supramolecular chemistry. Here we describe the one-pot synthesis, unique geometries and intriguing host–guest properties of a new class of supramolecular macrocycles – biphen[n]arenes (n = 3, 4), which are made up of 4,4′-biphenol or 4,4′-biphenol ether units linked by methylene bridges at the 3- and 3′- positions. The biphenarene macrocycles are conveniently accessible/modifiable and extremely guest-friendly. Particularly, biphen[4]arene is capable of forming inclusion complexes with not only organic cationic guests but also neutral π-electron deficient molecules. Compared with calixarenes, resorcinarenes, cyclotriveratrylenes and pillararenes with substituted mono-benzene units, the biphen[n]arenes reported here possess significantly different characteristics in both their topologic structures and their recognition properties, and thus can find broad applications in supramolecular chemistry and other areas.