Mechanically interlocked molecules are likely candidates for the design and synthesis of artificial molecular machines. Although polyrotaxanes have already found niche applications in exotic materials with specialized mechanical properties, efficient synthetic protocols to produce them with precise numbers of rings encircling their polymer dumbbells are still lacking. We report the assembly line–like emergence of poly[n]rotaxanes with increasingly higher energies by harnessing artificial molecular pumps to deliver rings in pairs by cyclical redox-driven processes. This programmable strategy leads to the precise incorporation of two, four, six, eight, and 10 rings carrying 8+, 16+, 24+, 32+, and 40+ charges, respectively, onto hexacationic polymer dumbbells. This strategy depends precisely on the number of redox cycles applied chemically or electrochemically, in both stepwise and one-pot manners.

One ring threaded by two other rings to form a non-intertwined ternary ring-in-rings motif is a challenging task in noncovalent synthesis. Constructing multicolor photoluminescence systems with tunable properties is also a fundamental research goal, which can lead to applications in multidimensional biological imaging, visual displays, and encryption materials. Herein, we describe the design and synthesis of binary and ternary ring-in-ring(s) complexes, based on an extended tetracationic cyclophane and cucurbit[8]­uril. The formation of these complexes is accompanied by tunable multicolor fluorescence outputs. On mixing equimolar amounts of the cyclophane and cucurbit[8]­uril, a 1:1 ring-in-ring complex is formed as a result of hydrophobic interactions associated with a favorable change in entropy. With the addition of another equivalent of cucurbit[8]­uril, a 1:2 ring-in-rings complex is formed, facilitated by additional ion–dipole interactions involving the pyridinium units in the cyclophane and the carbonyl groups in cucurbit[8]­uril. Because of the narrowing in the energy gaps of the cyclophane within the rigid hydrophobic cavities of cucurbit[8]­urils, the binary and ternary ring-in-ring(s) complexes emit green and bright yellow fluorescence, respectively. A series of color-tunable emissions, such as sky blue, cyan, green, and yellow with increased fluorescence lifetimes, can be achieved by simply adding cucurbit[8]­uril to an aqueous solution of the cyclophane. Notably, the smaller cyclobis­(paraquat-p-phenylene), which contains the same p-xylylene linkers as the extended tetracationic cyclophane, does not form ring-in-ring(s) complexes with cucurbit[8]­uril. The encapsulation of this extended tetracationic cyclophane by both one and two cucurbit[8]­urils provides an incentive to design and synthesize more advanced supramolecular systems, as well as opening up a feasible approach toward achieving tunable multicolor photoluminescence with single chromophores.

The development of synthetic receptors that recognize carbohydrates in water with high selectivity and specificity is challenging on account of their structural complexity and strong hydrophilicity. Here, we report on the design and synthesis of two pyrene-based, temple-shaped receptors for the recognition of a range of common sugars in water. These receptors rely on the use of two parallel pyrene panels, which serve as roofs and floors, capable of forming multiple [C−H•••π] interactions with the axially oriented C−H bonds on glycopyranosyl rings in the carbohydratebased substrates. In addition, eight polarized pyridinium C−H bonds, projecting from the roofs and floors of the temple receptors toward the binding cavities, form [C−H•••O] hydrogen bonds, with the equatorially oriented OH groups on the sugars located inside the hydrophobic cavities. Four para-xylylene pillars play a crucial role in controlling the distance between the roof and floor. These temple receptors are highly selective for the binding of glucose and its derivatives. Furthermore, they show enhanced fluorescence upon binding with glucose in water, a property which is useful for glucose-sensing in aqueous solution.

We report the encapsulation of free-base and zinc porphyrins by a tricyclic cyclophane receptor with subnanomolar binding affinities in water. The high affinities are sustained by the hydrophobic effect and multiple •π] stacking surfaces between the substrate porphyrins and the receptor. We discovered two co-conformational isomers of the 1:1 complex, where the porphyrin is orientated differently inside the binding cavity of the receptor on account of its tricyclic nature. The photophysical properties and chemical reactivities of the encapsulated porphyrins are modulated to a considerable extent by the receptor. Improved fluorescence quantum yields, redshifted absorptions and emissions, and nearly quantitative energy transfer processes highlight the emergent photophysical enhancements. The encapsulated porphyrins enjoy unprecedented chemical stabilities, where their D/H exchange, protonation, and solvolysis under extremely acidic conditions are completely blocked. We anticipate that the ultrahigh stabilities and improved optical properties of these encapsulated porphyrins will find applications in single-molecule materials, artificial photodevices, and biomedical appliances.

The recognition and separation of anions attracts attention from chemists,m aterials scientists,a nd engineers. Employing exo-binding of artificial macrocycles to selectively recognizea nions remains ac hallenge in supramolecular chemistry.W er eport the instantaneous co-crystallization and concomitant co-precipitation between [PtCl 6 ] 2À dianions and cucurbit[6]uril, which relies on the selective recognition of these dianions through noncovalent bonding interactions on the outer surface of cucurbit[6]uril. The selective [PtCl 6 ] 2À dianion recognition is driven by weak [PtÀCl•••HÀC] hydrogen bonding and [Pt À Cl•••C = O] ion-dipole interactions.T he synthetic protocol is highly selective.R ecognition is not observed in combinations between cucurbit[6]uril and six other Pt-and Pd-or Rh-based chloride anions.W ea lso demonstrated that cucurbit[6]uril is able to separate selectively [PtCl 6 ] 2À dianions from amixture of [PtCl 6 ] 2À ,[PdCl 4 ] 2À ,and [RhCl 6 ] 3À anions.T his protocol could be exploited to recover platinum from spent vehicular three-wayc atalytic converters and other platinum-bearing metal waste.

A new family of fluorescent thiophene and thienothiophene-containing squaraine dyes is described with tunable wavelengths that cover the absorption/emission range of 600–800 nm. The deep-red and near-infrared fluorescent compounds were easily prepared by simple synthesis and purification methods. Spectral studies showed that each squaraine was rapidly encapsulated by a tetralactam macrocycle, with nanomolar affinity in water, to produce a threaded supramolecular complex with high chemical stability, increased fluorescence quantum yield, and decreased fluorescence quenching upon dye self-aggregation. Energy transfer within the supramolecular complex permitted multiplex emission. That is, two separate dyes with fluorescence emission bands that match the popular Cy5 and Cy7 channels, could be simultaneously excited with a beam of 375 nm light. A broad range of practical applications is envisioned in healthcare diagnostics, microscopy, molecular imaging, and fluorescence-guided surgery.

A neutral tetralactam macrocycle was prepared in a few minutes in one pot and at high concentration using commercially available starting materials. NMR titration studies in DMSO revealed an anion affinity order of F– > AcO– > Cl– > Br–. The receptor affinity for F– is very high due in part to formation of a self-complementary dimer comprised of two “saddle shaped” complexes. An X-ray crystal structure showed that the two F– ions within the dimer are separated by 3.39 Å. The electrostatic penalty for this close proximity is compensated by attractive interactions provided by the surrounding tetralactam molecules. Reactivity experiments showed that stabilization of F– as a supramolecular complex abrogated its capacity to induce elimination and substitution chemistry. This finding raises the idea of using tetralactam macrocycles to stabilize fluoride-containing liquid electrolytes within redox devices such as room-temperature fluoride-ion batteries. A lipophilic version of the tetralactam macrocycle was prepared and used to extract F– from water into a chloroform layer with high efficiency. The favorable extraction is due to the architecture of the extracted dimeric complex, with all the polarity located within the core of the self-associated dimer and all the nonpolar functionality on the exterior surface.

We report the molecular recognition of the Au(CN) 2 − anion, a crucial intermediate in today's gold mining industry, by α-cyclodextrin. Three X-ray single-crystal super-structuresKAu(CN) 2 ⊂α-cyclodextrin, KAu(CN) 2 ⊂(α-cyclodextrin) 2 , and KAg(CN) 2 ⊂(α-cyclodextrin) 2 demonstrate that the binding cavity of α-cyclodextrin is a good fit for metal-coordination complexes, such as Au(CN) 2 − and Ag(CN) 2 − with linear geometries, while the K + ions fulfill the role of linking αcyclodextrin tori together as a result of [K + •••O] ion−dipole interactions. A 1:1 binding stoichiometry between Au(CN) 2 − and α-cyclodextrin in aqueous solution, revealed by 1 H NMR titrations, has produced binding constants in the order of 10 4 M −1 . Isothermal calorimetry titrations indicate that this molecular recognition is driven by a favorable enthalpy change overcoming a small entropic penalty. The adduct formation of KAu(CN) 2 ⊂α-cyclodextrin in aqueous solution is sustained by multiple [C−H•••π] and [C−H•••anion] interactions in addition to hydrophobic effects. The molecular recognition has also been investigated by DFT calculations, which suggest that the 2:1 binding stoichiometry between α-cyclodextrin and Au(CN) 2− is favored in the presence of ethanol. We have demonstrated that this molecular recognition process between α-cyclodextrin and KAu(CN) 2 can be applied to the stripping of gold from the surface of activated carbon at room temperature. Moreover, this stripping process is selective for Au(CN) 2 − in the presence of Ag(CN) 2 − , which has a lower binding affinity toward α-cyclodextrin. This molecular recognition process could, in principle, be integrated into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.