Supramolecular materials, dynamic materials by nature, are defined as materials whose components are bridged via reversible connections and undergo spontaneous and continuous assembly/disassembly processes under specific conditions. On account of the dynamic and reversible nature of noncovalent interactions, supramolecular polymers have the ability to adapt to their environment and possess a wide range of intriguing properties, such as degradability, shape-memory, and self-healing, making them unique candidates for supramolecular materials. In this critical review, we address recent developments in supramolecular polymeric materials, which can respond to appropriate external stimuli at the fundamental level due to the existence of noncovalent interactions of the building blocks.

Introduction 7399 2. Synthesis of Rotaxanes Based on Various Macrocycles 7400 2.1. Crown Ethers 7401 2.1.1. Bis(m-phenylene)-32-crown-10 and Crown Ethers with Larger Sizes 7401 2.1.2. Dibenzo-24-crown-8 7402 2.1.3. Benzo-21-crown-7 7406 2.1.4. Crown Ether-Based Cryptands 7407 2.2. Cyclodextrins 7410 2.3. Cucurbiturils 7413 2.3.1. Cucurbit[6]uril 7413 2.3.2. Cucurbit[7]uril 7414 2.3.3. Cucurbit[8]uril 7415 2.4. Calixarenes 7416 2.4.1. Calix[4]arenes as Linkers or Stoppers 7416 2.4.2. Calix[5]arenes and Calix[6]arenes as Wheels 7416 2.4.3. Heterocalix[n]arenes or Calix[n]heteroarenes 7417 2.5. Pillararenes 7418 2.5.1.

Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-1-3) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-2 was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics.

Light-emitting materials, especially those with tunable wavelengths, attract considerable attention for applications in optoelectronic devices, fluorescent probes, sensors and so on. Many species evaluated for these purposes either emit as a dilute solution or on aggregation, with the former often self-quenching at high concentrations, and the latter falling dark when aggregation is disrupted. Here we preserve emissive behaviour at both low- and high-concentration regimes for two discrete supramolecular coordination complexes (SCCs). These tetragonal prismatic SCCs are self-assembled on mixing a metal acceptor, Pt(PEt3)2(OSO2CF3)2, with two organic donors, a pyridyl-decorated tetraphenylethylene and one of two benzene dicarboxylate species. The rigid organization of these fluorescence-active ligands imparts an emissive behaviour to dilute solutions of the resulting assemblies. Furthermore, on aggregation the prisms exhibit variable-wavelength visible-light emission, including rare white-light emission in tetrahydrofuran. The favourable photophysical properties and solvent-dependent aggregation behaviour provide a means to tune emission wavelengths.

Supramolecular gels are a fascinating class of soft materials. Their gelators can self-assemble into nano- or micro-scale superstructures, such as fibers, ribbons, sheets and spheres in an appropriate solvent, thereby resulting in the formation of 3D networks. The dynamic and reversible nature of the non-covalent interactions that contribute to the formation of these network structures together gives these supramolecular gels the inherent ability to respond to external stimuli. However, the dynamic nature of supramolecular gels, which endows them with unique properties, makes their characterization diversified at the same time. Therefore, we present here a review summarizing various methods for characterizing supramolecular gels, including nuclear magnetic resonance spectroscopy, computational techniques, X-ray techniques, microscopy techniques, dynamic light scattering, thermal analysis, and rheology. Based on the gelation mechanisms and influencing factors of supramolecular gels, suitable and sufficient characterization methods should be carefully employed to make full use of their respective advantages to better investigate these materials.

A cross-linked supramolecular polymer network gel is designed and prepared, which shows reversible gel-sol transitions induced by changes in pH, temperature, cation concentration, and metal co-ordination. The gel pore size is controlled by the amount of cross-linker added to the system, and the material can be molded into shape-persistent, free-standing objects with elastic behavior. These features are all due to the dynamically reversible host-guest complexation and good mechanical properties of the cross-linked polymer network. No single organogel has previously been reported to possess all of these features, making this supramolecular gel an unprecedentedly intelligent soft material.

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Supramolecular polymers constructed by orthogonal self-assembly based on host-guest and metal-ligand interactions are attracting increasing attention currently because of their interesting properties and potential applications. Host-guest interactions impart these polymers with good selectivity and convenient enviro-responsiveness, and metal-ligand interactions endow them with various coordination geometries, strong yet tunable coordination binding abilities, as well as magnetic, redox, photophysical, and electrochromic properties. Therefore, supramolecular polymers constructed by orthogonal host-guest and metal-ligand interactions have wide applications in the fields of soft matter, fluorescence sensing, heterocatalysis, electronics, gas storage, etc. In this critical review, we will address the recent development of supramolecular polymeric systems involving metal-ligand interactions and host-guest molecular recognition. Specifically, we classify the related supramolecular polymers depending on the types of macrocyclic hosts, and highlight their intriguing properties originating from the elegant combination of host-guest complexation and metal centers.