A Dynamic Hydrogen-Bonded Azo-Macrocycle for Precisely Photo-Controlled Molecular Encapsulation and Release

A light-responsive system constructed from hydrogen-bonded azo-macrocycles demonstrates precisely controlled propensity in molecular encapsulation and release process. A significant decrease in the size of the cavity is observed in the course of the E→Z photoisomerization based on the results from DFT calculations and traveling wave ion mobility mass spectrometry. These macrocyclic hosts exhibit a rare 2:1 host-guest stoichiometry and guest-dependent slow or fast exchange on the NMR timescale. With the slow host-guest exchange and switchable shape change of the cavity, quantitative release and capture of bipyridinium guests is achieved with the maximum release of 68 %. This work underscores the importance of slow host-guest exchange on realizing accurate release of organic cations in a stepwise manner under light irradiation. The light-responsive system established here could advance further design of novel photoresponsive molecular switches and mechanically interlocked molecules.

Pillararene-Based Two-Component Thixotropic Supramolecular Organogels: Complementarity and Multivalency as Prominent Motifs

Rationally designed two-component supramolecular organogels based on multiple chemical interactions between percarboxylato- and peramino-pillararenes are described. Mixing low concentration solutions (<1 % w/v) of decacarboxylato-pillar[5]arene (1) with decaamino-pillar[5]arenes (2 b-d) affords, rapidly and without heating, organogels displaying an exceptional combination of properties. These supramolecular organogels, the characteristics of which are tunable, were found to be thixotropic and thermally stable, with T_gel values in some cases exceeding the boiling point of the embedded solvent. It is demonstrated that both structural complementarity and multivalency are important determinants in the gelation process of these attractive soft materials.

The cytochrome c–cyclo[6]aramide complex as a supramolecular catalyst in methanol

A hydrogen-bonded aromatic amide macrocycle forms a host–guest complex with cytochrome c, which acts as a supramolecular catalyst for the oxidation of benzhydrol even at low temperatures.

Liquid-crystalline mesogens based on cyclo[6]aramides: distinctive phase transitions in response to macrocyclic host-guest interactions

Producing macrocyclic mesogens that are responsive to guest encapsulation presents a significant challenge. Cyclo[6]aramides, a type of macrocycle with a hydrogen-bond-constrained backbone, exhibit thermotropic lamellar, discotic nematic, hexagonal, and rectangular columnar mesophases over a considerably wide temperature range, including at room temperature. Additionally, cyclo[6]aramides show unusual mesophase transitions from lamellar to hexagonal columnar phase mediated by macrocyclic host-guest (H-G) interactions between the macrocycles and alkylammonium salts. The phase transition, triggered by an organic guest engaging in H-G interactions with a macrocyclic cavity, provides a novel strategy for manipulating the properties of liquid-crystalline materials. The crystal structure of a homologous cyclo[6]aramide reveals a disk-shaped, near-planar molecular backbone that facilitates intermolecular π-π stacking and leads to columnar assembly.

Cyclo[6]aramide-Tropylium Charge Transfer Complex as a Colorimetric Chemosensor for Differentiation of Intimate and Loose Ion Pairs

Shape-persistent iso-C16-cyclo[6]aramide (1) was found to form a charge-transfer (CT) complex with aromatic carbonium tropylium (Tr(+)). The resulting CT complex was evidenced by both experimental results and theoretical calculations. Particularly, dibutylammonium salt with PF6(-) as the counterion can extrude Tr(+) from the CT complex, but it cannot do so with Cl(-), thereby offering a visual approach to identify organic intimate ion pairs and loose ion pairs.