Ester-functionalized pillar[6]arene as the gas chromatographic stationary phase with high-resolution performance towards the challenging isomers of xylenes, diethylbenzenes, and ethyltoluenes

This work presents the first example of the utilization of polar ester group functionalized pillar[6]arene (P6A-C10-OAc) as a stationary phase for capillary gas chromatographic (GC) separations. The statically coated P6A-C10-OAc column showed a high column efficiency of 5393 plates/m and moderate polar nature. Its resolving capability and retention behaviors were investigated for a mixture of 20 analytes and more than a dozen isomers from apolar to polar in nature. As evidenced, the P6A-C10-OAc column achieved high-resolution separations of all the analytes and good inertness. Importantly, it exhibited distinctly advantageous performance for high resolution of the challenging isomers of xylenes, diethylbenzenes, ethyltoluenes, and halobenzenes over the commercial HP-5 (5% phenyl dimethyl polysiloxane), HP-35 (25% phenyl dimethyl polysiloxane), and PEG-20M (polyethylene glycol) columns.

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

Pillar[n]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral inversion. These advantages have enabled the high-yield synthesis and rational design of pillar[n]arene-based mechanically interlocked molecules (MIMs). In particular, new types of pillar[n]arene-based MIMs that can dynamically convert between interlocked and unlocked states through unit rotation have been produced. The highly symmetrical pillar-shaped structures of pillar[n]arenes result in simple NMR spectra, which are useful for studying the motion of pillar[n]arene wheels in MIMs and creating sophisticated MIMs with higher-order structures. The creation and application of polymeric MIMs based on pillar[n]arenes is also discussed.

CPL on/off control of an assembled system by water soluble macrocyclic chiral sources with planar chirality

Herein, we report the synthesis and planar chiral properties of a pair of water-soluble cationic pillar[5]arenes with stereogenic carbons. Interestingly, although units of the molecules were rotatable, only one planar chiral diastereomer existed in water in both cases. As a new type of chiral source, these molecules transmitted chiral information from the planar chiral cavities to the assembly of a water-soluble extended π-conjugated compound, affording circularly polarized luminescence (CPL). The chirality transfer process and resulting CPL were extremely sensitive to the feed ratio of the chiral pillar[5]arenes owing to the combined action of their planar chirality, bulkiness, and strong binding properties. When a limited amount of chiral source was added, further assembly of the extended π-conjugated compound into helical fibers with CPL was triggered. Unexpectedly, larger amounts of chiral source destroyed the helical fiber assemblies, resulting in elimination of the chirality and CPL properties from the assembled structures.

Readily obtained pillar[5]arenes with pure planar chirality enabled CPL on/off control of an assembled system by varying the feed ratio.

Neutral Isocyanide-Templated Assembly of Pillar[5]arene [2] and [3]Pseudorotaxanes

Unprecedented pillar[5]arene–isocyanide pseudorotaxane inclusion complexes are reported. Extensive 1H-NMR experiments reveal remarkably strong binding affinities of alkyl diisocyanide guests (Ka >105 M-1 in CDCl3) by pillar[5]arenes. Characterised by multinuclear 1H...

Supramolecular Engineering of Efficient Artificial Light-Harvesting Systems from Cyanovinylene Chromophores and Pillar[5]arene-Based Polymer Hosts

Enhanced emission and adjustable wavelength for single luminogen systems are highly desirable in the scope of photoluminescent materials. Herein, a supramolecular strategy has been proposed for supramolecular assembly-induced enhanced emission and valid emission manipulation by fabricating an amphiphilic copolymer host material with pillar[5]arene units as the side chains, whereby cyanovinylene-based (CV) derivatives are anchored to the polymer hosts via host-guest interactions. The guest-bearing copolymers can further form luminescent supramolecular polymer nanoparticles (SPNs). Remarkably, the as-prepared SPNs exhibit dramatic emission enhancement and tunable fluorescence wavelength, ascribing to the synergetic effects involving the restriction of intramolecular motions and the prevented excimer formation for CV moieties, as endowed by host-guest interactions and the entanglement of the polymer chains. Furthermore, the SPNs can be established as efficient artificial light-harvesting systems via the inclusion of Nile red into the particles for broadened emission spectra. As a proof-of-concept study, the use of pillar[5]arene-containing polymer hosts largely facilitates the emission enhancement and wavelength adjustment for the inherent luminogens, setting the basis for the supramolecular design of highly tunable luminescent systems.

Pillar[5]arene-Based [2]Rotaxane: Synthesis, Characterization, and Application in a Coupling Reaction

Mechanically interlocked molecules are a class of smart supramolecular species because of their interesting topological structure and application in various areas, such as biology and nanoscience. In this work, we used "multicomponent reaction" to fabricate a new [2]rotaxane based on pillar[5]arene from different small-sized molecules. The molecular structure of the obtained [2]rotaxane R was confirmed by ¹H and ¹³C NMR, high-resolution electrospray ionization mass spectrometry, two-dimensional nuclear Overhauser effect spectroscopy, and density functional theory studies. Interestingly, the [2]rotaxane-based organometallic cross-linked catalyst (Pd@R) was easily constructed via the coordination between triazole groups and Pd(NO₃)₂. Pd@R proved to be a good catalyst for the Suzuki-Miyaura coupling reaction with excellent stability and repeatability.

Pertosylated pillar[5]arene: self-template assisted synthesis and supramolecular polymer formation

A facile synthesis of decatosylate pillar[5]arene 1 is reported in excellent yield (>70%). The high yield is attributed to a self-template effect of the pendant tosylate arms. The X-ray crystal structure shows the formation of a linear supramolecular polymer, stabilised by intermolecular pillar[5]arene-tosylate inclusion complexes. These polymeric arrays persist in solution and form rod-like microfibril nanostructures evidenced by SEM.

Host-Guest Complexations Between Pillar[6]arenes and Neutral Pentaerythritol Derivatives

It is demonstrated that three kinds of neutral pentaerythritol derivatives possess promising host-guest complexations with pillar[6]arenes both in solution and in the solid state. The inclusion structures were characterized by NMR spectroscopy and X-ray crystallography. The complexation properties in different solvents were also investigated.

Preparation of a mechanically interlocked polymer from a linear supramolecular polymer

We transformed a linear supramolecular polymer into a mechanically interlocked polymer by photoisomerization.

Efficient Aggregation-Induced Emission Manipulated by Polymer Host Materials

Linear copolymer hosts bearing a number of pillar[5]arene dangling side chains are synthesized for the facile construction of highly emissive supramolecular polymer networks (SPNs) upon noncovalently cross-linking with a series of tetraphenyethylene (TPE)-based tetratopic guests terminated with different functional groups through supramolecular host-guest interactions. An extremely high fluorescence quantum yield (98.22%) of the SPNs materials is obtained in tetrahydrofuran (THF) by fine-tuning the parameters, and meanwhile supramolecular light-harvesting systems based on spherical supramolecular nanoparticles are constructed by interweaving 9,10-distyrylanthracene (DSA) and TPE-based guest molecules of aggregation-induced emission (AIE) with the copolymer hosts in the mixed solvent of THF/H₂ O. The present study not only illustrates the restriction of the intramolecular rotations (RIR)-ruled emission enhancement mechanism regulated particularly by macrocyclic arene-containing copolymer hosts, but also suggests a new self-assembly approach to construct high-performance light-harvesting materials.

A dimethoxypillar[5]arene/azastilbene host-guest recognition motif and its applications in the fabrication of polypseudorotaxanes

Pillar[n]arenes, known as the fifth generation of host macrocycles since 2008, have become a popular topic over the past ten years. Until now, the studies of pillar[n]arenes were mainly focused on pillar[5]arenes owing to their easy synthesis and high yields. In particular, 1,4-dimethoxypillar[5]arene (DMP5), which shows a simple structure, efficient synthesis and high yield, has played important roles in the construction of various advanced supramolecular architectures. However, DMP5 has only displayed host-guest binding properties towards some guests. Therefore, the investigation of the host-guest chemistry of DMP5 should be able to greatly promote the development of pillararene chemistry. Herein, a photosensitive azastilbene derivative was chosen as a neutral guest to study the host-guest binding and stimuli-responsive behavior with DMP5. In addition, the binding behavior of DMP5 towards a series of analogous neutral guest molecules was investigated to study the driving forces of the host-guest interaction between DMP5 and the azastilbene guest. Moreover, the [2]pseudorotaxane based on DMP5 and the azastilbene guest was used to construct a polypseudorotaxane via metal coordination.

Spacer Length-Independent Shuttling of the Pillar[5]arene Ring in Neutral [2]Rotaxanes

For a series of neutral [2]rotaxanes consisting of a pillar[5]arene ring and axles possessing two stations separated by flexible spacers of different lengths, the free energies of activation for the ring shuttling between the stations were found to be independent of the spacer length. The constitution of the spacer affects the activation energies: replacement of CH₂ groups by repulsive oxygen atoms in the axle increases the barrier. The explanation for the observed length‐independence lies in the presence of a barrier for re‐forming the stable co‐conformation, which makes the ring travel back and forth along the thread in an intermediate state.

Construction of [2]rotaxane-based supramolecular polymers driven by wheel-stopper π⋯π interactions

A new strategy for supramolecular polymerization is designed and presented, which is based on the wheel-stopper charge-transfer interactions of [2]rotaxanes.

Novel rare earth fluorescent supramolecular polymeric assemblies constructed by orthogonal pillar[5]arene-based molecular recognition, Eu(iii)-coordination and π–π donor–acceptor interactions

Linear rare earth fluorescent supramolecular polymer is easily constructed by pillar[5]arene-based molecular interaction.

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as "pillar[n]arenes". Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host-guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host-guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in the field and inspire discoveries concerning pillar[n]arene chemistry.

Efficient complexation between pillar[5]arenes and neutral guests: from host–guest chemistry to functional materials

This feature article covers the molecular recognition of pillar[5]arenes and neutral guests, and its application in making supramolecular structures, polymers and functional materials.

Redox-responsive host–guest system using redox-active pillar[5]arene containing one benzoquinone unit

Pillar[5]arene with one benzoquinone formed weak complex with a guest, while pillar[5]arene containing one hydroquinone strongly captured the guest.

Pillararene-based supramolecular polymers: from molecular recognition to polymeric aggregates

Pillar[n]arenes (P[n]As) and their derivatives, consisting of (substituted) hydroquinone units linked by methylene bridges at para-positions, are new type of cyclophane hosts developed in 2008. Their intrinsic characteristics and properties, such as facile preparation and flexible modification, symmetrical and columnar architectures, very rigid and π-rich cavities, as well as intriguing and peculiar guest complexation capability, make them ideal building blocks for the fabrication of polymeric supramolecules. This Feature Article provides an overview of the construction of pillararene-based supramolecular polymers and covers recent research endeavors of the marriage between pillararene-based host-guest pairs and polymeric aggregates. These polymers are classified into two major classes according to the different types of guest species: (1) supramolecular polymers relying on pillararene-based cationic guest recognition; (2) supramolecular polymers relying on pillararene-based neutral guest recognition. The host-guest motifs, building strategies, topological architectures, stimuli-responsiveness and functionalities are comprehensively discussed.

Host–guest complexation of pillar[6]arenes towards neutral nitrile guests

The binding behavior of a series of nitrile derivatives by ethylated pillar[6]arene is described; this work represents the first example of complexation of neutral guests by pillar[6]arenes.

Novel pseudo[2]rotaxanes constructed by the self-assembly of dibenzyl tetramethylene bis-carbamate derivatives and per-ethylated pillar[5]arene

Novel pseudo[2]rotaxanes based on per-ethylated pillar[5]arene and neutral guests G1/G7 were successfully constructed. Particularly, the pseudo[2]rotaxane constructed from per-ethylated pillar[5]arene and G7 showed photoresponsive properties.

An unprecedented porphyrin-pillar[5]arene hybrid ditopic receptor

A porphyrin-pillar[5]arene hybrid host compound with a ditopic receptor nature was synthesized for the first time, which combines a neutral 1,4-bis(imidazol-1-yl)butane guest by means of its two active centers to form a stable supramolecular complex.

A cross-linked supramolecular polymer constructed from pillar[5]arene and porphyrine via host–guest interactions

A novel supramolecular polymer, DMeP5@TImPor, was successfully constructed via host–guest interactions between the host molecule, bis-(methoxy-pillar[5]arene) (DMeP5), and the guest molecule, 5,10,15,20-tetrakis{butoxy-4-(1H-imidazol-1-yl)}porphyrine (TImPor).

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.