Macrocycles are molecular entities that display a combination of molecular recognition and complexation properties with vital implications for host-guest/supramolecular chemistry. Since the accidental discovery of the crown ethers by Pedersen half a century ago, the chemistry of wholly synthetic macrocycles for structure-specific, highly selective, host-guest complexation has experienced rapid development. While the structural diversity and host-guest chemistry of the original macrocycles are well-known, new derivatives of them are being investigated continuously and reported on today in order to improve their recognition properties as well as to unleash new opportunities in supramolecular chemistry. In this Review, we survey the recent developments of the chemistry of naturally occurring cyclodextrins, along with a variety of synthetic flexible and rigid macrocycles that have drawn their inspiration from Pedersen's ground-breaking discovery of crown ethers in the mid-1960s.

The wavelength determines whether DNA is captured in a light‐responsive ternary supramolecular complex or released (see scheme). The reversible binding of DNA is triggered by a photoisomerization, which switches the complex from a multivalent to a monovalent binding mode.

The reversible in situ formation of a self-assembly building block (naphthalenediimide (NDI)-dipeptide conjugate) by enzymatic condensation of NDI-functionalized tyrosine (NDI-Y) and phenylalanine-amide (F-NH2) to form NDI-YF-NH2 is described. This coupled biocatalytic condensation/assembly approach is thermodynamically driven and gives rise to nanostructures with optimized supramolecular interactions as evidenced by substantial aggregation induced emission upon assembly. Furthermore, in the presence of di-hydroxy/alkoxy naphthalene donors, efficient charge-transfer complexes are produced. The dynamic formation of NDI-YF-NH2 and electronic and H-bonding interactions are analyzed and characterized by different methods. Microscopy (TEM and AFM) and rheology are used to characterize the formed nanostructures. Dynamic nanostructures, whose formation and function are driven by free-energy minimization, are inherently self-healing and provide opportunities for the development of aqueous adaptive nanotechnology.

Supramolecular glue: The photoinduced isomerization of difunctional azobenzenes can be used to induce and reverse the molecular recognition and adhesion of bilayer vesicles made up of cyclodextrin (CD) molecules. The molecular basis of this light‐responsive supramolecular glue is the cis–trans isomerization of the azobenzene (see picture; black circles CD, green trans‐azobenzene, red cis‐azobenzene).

Peptide self-assembly provides a useful approach to control the organization of functional molecular components, as relevant to future opto-electronic or photonic nanostructures. In this article, we report on the discovery of efficient energy transfer nanostructures using a dynamic combinatorial library (DCL) approach driven by molecular self-assembly, demonstrating an enhanced self-selection and amplification of effective energy transfer nanostructures from complex mixtures of dipeptide derivatives. By taking advantage of an enzyme-catalysed fully reversible amide formation reaction, we show how gelation shifts the equilibrium in favour of the formation of short aromatic dipeptide derivatives in the DCL system, as confirmed by reversed-phase high pressure liquid chromatography (HPLC), fluorescence emission spectroscopy, atomic force microscopy (AFM), transmission force microscopy (TEM) and circular dichroism (CD) spectroscopy. This approach enabled us to identify a two-component donor-acceptor hydrogel, which forms within minutes and exhibits efficient energy transfer