High-Yield Diastereoselective Synthesis of Planar Chiral [2]- and [3]Rotaxanes Constructed from per-Ethylated Pillar[5]arene and Pyridinium Derivatives

Multistimuli Sensitive Behavior of Novel Bodipy-Involved Pillar[5]arene-Based Fluorescent [2]Rotaxane and Its Supramolecular Gel

Fluorescent [2]rotaxane BC12P5 is successfully constructed with 1,4-diethoxypillar[5]arene as wheel over a long alkyl axle with Bodipy chromophore as one stopper for the first time. NMR spectra clearly reveal its molecular shuttle nature triggered by multiple external stimuli including solvent polarity and temperature. In particular, the fluorescence nature introduced into [2]rotaxane BC12P5 renders it a good sensor for the external stimuli. Nevertheless, the supramolecular gel successfully fabricated from this novel rotaxane system via self-assembly in dimethyl sulfoxide (DMSO) also shows reversible gel-sol phase transition upon multiple external stimuli such as heating/cooling, shaking/resting, or the addition of different anions. Interestingly, exposure of the supramolecular gel film to HCl or ammonia vapor induces the change in the film fluorescence intensity, endowing this system with a potential application in gas detecting.

Mechanically selflocked chiral gemini-catenanes

Mechanically interlocked and entangled molecular architectures represent one of the elaborate topological superstructures engineered at a molecular resolution. Here we report a methodology for fabricating mechanically selflocked molecules (MSMs) through highly efficient one-step amidation of a pseudorotaxane derived from dual functionalized pillar[5]arene (P[5]A) threaded by α,ω-diaminoalkane (DA-n; n=3-12). The monomeric and dimeric pseudo[1]catenanes thus obtained, which are inherently chiral due to the topology of P[5]A used, were isolated and fully characterized by NMR and circular dichroism spectroscopy, X-ray crystallography and DFT calculations. Of particular interest, the dimeric pseudo[1]catenane, named 'gemini-catenane', contained stereoisomeric meso-erythro and dl-threo isomers, in which two P[5]A moieties are threaded by two DA-n chains in topologically different patterns. This access to chiral pseudo[1]catenanes and gemini-catenanes will greatly promote the practical use of such sophisticated chiral architectures in supramolecular and materials science and technology.

Catenanes: fifty years of molecular links

Half a century after Schill and Lüttringhaus carried out the first directed synthesis of a [2]catenane, a plethora of strategies now exist for the construction of molecular Hopf links (singly interlocked rings), the simplest type of catenane. The precision and effectiveness with which suitable templates and/or noncovalent interactions can arrange building blocks has also enabled the synthesis of intricate and often beautiful higher order interlocked systems, including Solomon links, Borromean rings, and a Star of David catenane. This Review outlines the diverse strategies that exist for synthesizing catenanes in the 21st century and examines their emerging applications and the challenges that still exist for the synthesis of more complex topologies.

Enantiopure pillar[5]arene active domains within a homochiral metal-organic framework

Enantiopure struts containing pillar[5]arenes incorporating planar chirality have been linked together with Zn4O clusters in order to create metal-organic frameworks that include homochiral active domains and so have the potential to act as a solid support in chiral chromatography.

Diastereoselective cyclization of an aminobenzoic acid derivative and chiroptical properties of triple-stranded helical bis(phenylethynyl)benzene

Diastereoselective cyclic trimerization of 2,5-dibromo-4-hexylaminobenzoic acid followed by a Sonogashira–Hagihara coupling reaction constructed the triple-stranded helical structure of bis(phenylethynyl)benzene units.

Potential 129Xe-NMR biosensors based on secondary and tertiary complexes of a water-soluble pillar[5]arene derivative

We report on the first secondary and tertiary complexes of the pillar[5]arene derivative with xenon in water. We show that the chemical shift of the encapsulated xenon provides information on the type of the formed complex suggesting that has the potential to be used as a platform for NMR biosensors.

Pillar[5]arene-based nonionic polyrotaxanes and a topological gel prepared from cyclic host liquids

We synthesize nonionic polymer-based polyrotaxanes by click reactions in pillar[5]arene-based cyclic host liquids and a topological gel by a metathesis reaction.

A pillar[5]arene and crown ether fused bicyclic host: synthesis, guest discrimination and simultaneous binding of two guests with different shapes, sizes and electronic constitutions

A pillar[5]arene- and crown ether-based bicyclic host molecule binds two guest species selectively by its two independent cyclic host subunits.

Pillar[5]- and pillar[6]arene-based supramolecular assemblies built by using their cavity-size-dependent host–guest interactions

We discuss various pillar[5]- and pillar[6]arene-based supramolecular assemblies built using their host–guest interactions.

Diastereoselective synthesis of a [2]catenane from a pillar[5]arene and a pyridinium derivative

A [2]catenane composed of a pillar[5]arene wheel and a pyridinium derivative was synthesized for the first time.

Induction of motion in a synthetic molecular machine: effect of tuning the driving force

Rotaxane molecular shuttles were studied in which a tetralactam macrocyclic ring moves between a succinamide station and a second station in which the structure is varied. Station 2 in all cases is an aromatic imide, which is a poor hydrogen-bond acceptor in the neutral form, but a strong one when reduced with one or two electrons. When the charge density on the hydrogen-bond-accepting carbonyl groups in station 2 is reduced by changing a naphthalimide into a naphthalene diimide radical anion, the shuttling rate changes only slightly. When station 2 is a pyromellitimide radical anion, however, the shuttling rate is significantly reduced. This implies that the shuttling rate is not only determined by the initial unbinding of the ring from the first station, as previously supposed. An alternative reaction mechanism is proposed in which the ring binds to both stations in the transition state.

Photoreversible switching of the lower critical solution temperature in a photoresponsive host-guest system of pillar[6]arene with triethylene oxide substituents and an azobenzene derivative

A new water-soluble thermoresponsive pillar[6]arene with triethylene oxide groups was synthesized. The pillar[6]arene showed lower critical solution temperature behavior in aqueous solution. Its clouding point was photoreversibly switched based on a photoresponsive host-guest system. The trans form of an azobenzene guest formed a stable 1:1 complex with the pillar[6]arene. Complexation increased the clouding point. Irradiation with UV light induced a conformation change for the azobenzene guest from the trans to cis form, and dethreading occurred because of a size mismatch between the cis form and the pillar[6]arene cavity. This dethreading decreased the clouding point. The photoresponsive host-guest system was reversible, and the clouding point could be switched by alternating irradiation with UV or visible light. We demonstrated photoresponsive reversible clear-to-turbid and turbid-to-clear transitions for the solution based on the reversible switching of the clouding point using the photosensitive host-guest system.