Calix[3]carbazole: One-Step Synthesis and Host–Guest Binding

Reversible encapsulation and release of fullerenes using calix[n]phenoxazines

This investigation presents the synthesis of butyl-decorated calix[n]phenoxazines of varying sizes by kinetic control and the ring-expansion of calix[3]phenoxazine, which uniquely exhibits distinct binding affinities for fullerenes C60 and C70. Calix[3]phenoxazine demonstrates a higher binding affinity for cationic ammonium, which can be reversibly deprotonated and protonated, enabling the reversible release and reloading of fullerenes. This system holds potential for applications in fullerene extraction and separation.

The synthesis and application of o-carborane-based macrocyclic arenes

Two o-carborane-hybridized macrocyclic arenes have been synthesized via Friedel-Crafts alkylation of carborane diaryl derivatives. The single-crystal X-ray diffraction analysis clearly revealed their cavity structure and intermolecular interaction force. These novel macrocycles exhibited aggregation-induced luminescence and intramolecular charge transfer properties and also significant selectivity towards nitro explosive compounds. This work provided a method for the synthesis of hybridized macrocyclic arenes.

Window[1]resorcin[3]arenes: A Novel Macrocycle Able to Self-Assemble to a Catalytically Active Hexameric Cage

The hexameric resorcin[4]arene capsule has been utilized as one of the most versatile supramolecular capsule catalysts. Enlarging its size would enable expansion of the substrate size scope. However, no larger catalytically active versions have been reported. Herein, we introduce a novel class of macrocycles, named window[1]resorcin[3]arene (wRS), that assemble to a cage-like hexameric host. The new host was studied by NMR, encapsulation experiments, and molecular dynamics simulations. The cage is able to bind tetraalkylammonium ions that are too large for encapsulation inside the hexameric resorcin[4]arene capsule. Most importantly, it retained its catalytic activity, and the accelerated conversion of a large substrate that does not fit the closed hexameric resorcin[4]arene capsule was observed. Thus, it will help to expand the limited substrate size scope of the closed hexameric resorcin[4]arene capsule.

Prism[2]dihydrophenazines: Synthesis, Configurational Analysis, and Supramolecular Tessellation through Exo-Wall Interactions

Macrocyclic arenes have gained considerable attention for their structural diversity and widespread applications. In this research, a new kind of macrocyclic arenes, namely prism[2]dihydrophenazines (anti-P2P20, syn-P2P20, and P2P22), composed of two dihydrophenazine derivatives subunits bridged by methylene groups, were conveniently synthesized by AlCl3-catalyzed one-pot condensation in 1,2-dichloroethane. Both anti-P2P20 and its isomer syn-P2P20 exhibited flexible and convertible conformation with narrow cavity, while P2P22 possessed rigid and rhombic-like skeleton due to the more steric hindrance on subunits. In addition, the selection of electron-deficient guest was found to influence the outside binding behavior of syn-P2P20. Fantastic regular supramolecular tessellation was fabricated by tiling of syn-P2P20 with tetrafluoro-1,4-benzoquinone (TFB) through the exo-wall interactions. Using 1,5-difluoro-2,4-dinitrobenzene (DFN) as a linker, only the regular 2D network superstructure with periodic units in a plane was obtained through cocrystallization. This work not only reports the construction of supramolecular tessellations by using prism[2]dihydrophenazines as building blocks, but also provides a new perspective for the design of macrocyclic arenes and fabrication of 2D supramolecular materials.

A calix[3]carbazole-based cavitand: synthesis, structure and its complexation with fullerenes

A calix[3]carbazole-based cavitand was conveniently synthesized. It was found that the cavitand with adjustable conformation could show excellent complexation with fullerenes C60 and C70 in both solution and the solid state. Moreover, the crystal structures of the host-guest complexes show that the cavitand can stack into channel-like architectures, in which fullerenes are orderly arranged inside.

Modular Synthesis of Biphen[n]arenes Directed by Five-Membered Heterocycles

Modular synthesis of novel biphen[n]arenes (n = 2-4) with customizable heterocycle blocks, functional skeletons, binding sites, and topological structures could be facilely achieved through the rational design and replacement of reaction modules (furan and thiophene), functional modules (substituted benzene, biphenyl, and naphthalene), and linking modules (methylene). These biphen[n]arenes were characterized by NMR, HRMS, and X-ray crystalline diffraction, complemented by DFT calculations. Their photophysical properties were thoroughly studied.

Recent advances in the synthesis and applications of macrocyclic arenes

Macrocyclic arenes including calixarenes, resorcinarenes, cyclotriveratrylene, pillararenes and so on have emerged as highly attractive synthetic macrocyclic hosts due to their unique structures, facile functionalization, and broad range of applications. In recent years, there has been growing interest in the development of novel macrocyclic arenes composed of various aromatic building blocks bridged by methylene groups, which have found applications in various research areas. Consequently, the development of novel macrocyclic arenes has become a frontier and hot topic in supramolecular and macrocyclic chemistry. In this review, we feature the recent advances in the synthesis and applications of novel macrocyclic arenes that have emerged in the last decade. The general synthetic strategies employed for these macrocyclic arenes are systematically summarized, and their wide applications in molecular recognition and assemblies, molecular machines, biomedical science and functional materials are highlighted.

N-Embedded Cubarene: A Quadrangular Member of the Macrocycle Family

Despite the large number of synthetic macrocycles, the cubarenes, the quadrangular-shaped macrocyclic arenes, remain less investigated, possibly due either to synthetic challenges or to the lack of suitable building blocks. In this paper, a N-embedded cubarene (cub[4]indolocarbazole) is facilely synthesized by FeCl₃·6H₂O-catalyzed cyclization in dichloromethane. The endo cavity of cub[4]indolocarbazole can bury quaternary ammonium salts in an intramolecular manner, whereas the intermolecular interaction between its exo walls with Cu²⁺ generates two-dimensional supramolecular tessellation.

3,6-Carbazoylene Octaphyrin (1.0.0.0.1.0.0.0) and Its Bis-BF2 Complex

3,6-Carbazole precursors were used to prepare an octaphyrin. The conformation and electronic structure of the system could be modulated through trifluoroacetate (TFA) protonation and BF₂ complexation. The resulting nonaromatic macrocyclic complexes, 2-2TFA and 2-2BF₂, displayed noteworthy photophysical properties. For instance, the diprotonated species 2-2TFA showed a strong panchromic absorption up to 800 nm, while the bis-BF₂-chelated dipyrromethene (BODIPY)-like complex 2-2BF₂ exhibited an intense visible absorption feature (ε_535nm = 2.1 × 10⁵ M^-1 cm^-1), as well as a relatively red-shifted emission at 640 nm characterized by a large Stokes shift. It was found that 2-2BF₂ could be used to construct a high-quality organic microlaser that functions under optical pumping. The present study highlights the potential utility of expanded porphyrins as possible laser dyes.

Synthesis of a large-cavity carbazole macrocycle for size-dependent recognition

A large-cavity carbazole macrocycle (1) is reported through condensation of a long and rigid monomer and paraformaldehyde. 1 exhibits highly selective binding of large-sized tetra(n-propyl) ammonium cation 3⁺. The complexation of 3⁺ by 1 is counter anion-dependent, where Cl^- gives the highest association constant of 3010 ± 230 M^-1.

Macrocyclic host molecules with aromatic building blocks: the state of the art and progress

Macrocyclic host molecules play the central role in host-guest chemistry and supramolecular chemistry. The highly structural symmetry of macrocyclic host molecules can meet people's pursuit of aesthetics in molecular design, and generally means a balance of design, synthesis, properties and applications. For macrocyclic host molecules with highly symmetrical structures, building blocks, which could be described as repeat units as well, are the most fundamental elements for molecular design. The structural features and recognition ability of macrocyclic host molecules are determined by the building blocks and their connection patterns. Using different building blocks, different macrocyclic host molecules could be designed and synthesized. With decades of developments of host-guest chemistry and supramolecular chemistry, diverse macrocyclic host molecules with different building blocks have been designed and synthesized. Aromatic building blocks are a big family among the various building blocks used in constructing macrocyclic host molecules. In this feature article, the recent developments of macrocyclic host molecules with aromatic building blocks were summarized and discussed.

Xanthene[n]arenes: Exceptionally Large, Bowl-Shaped Macrocyclic Building Blocks Suitable for Self-Assembly

A new class of macrocycles denoted as "xanthene[n]arenes" was synthesized. In contrast to most other macrocycles, they feature a conformationally restricted bowl shape due to the attached alkyl groups at the linking methylene units. This facilitates the synthesis of cavitands and the self-assembly to molecular capsules via noncovalent interactions. The derivatization potential of the novel macrocycles was demonstrated on the xanthene[3]arene scaffold. Besides a deep cavitand and an oxygen-embedded zigzag hydrocarbon belt[12]arene, a modified macrocycle was synthesized that self-assembles into a hydrogen-bonded tetrameric capsule, demonstrating the potential of xanthene[n]arenes as a new set of macrocyclic building blocks.

Saucer[n]arenes: Synthesis, Structure, Complexation, and Guest-Induced Circularly Polarized Luminescence Property

Macrocycles denoted as saucer[n]arenes (n=4,5) were easily synthesized by the one-pot condensation of 2,7-dimethoxynaphthalene (2,7-DMN) and paraformaldehyde in the presence of TFA or catalytic BF₃ ⋅OEt₂ . With 1,1-dimethylpiperidin-1-ium as the template, saucer[4]arene was selectively obtained. Crystal structures show that saucer[n]arenes are all composed of 2,7-DMN moiety bridged by the methylene groups at 1,6-positions: all of the 7-methoxy groups lie on one face, and all of the 2-methoxy groups lie on the other. Saucer[n]arenes exhibit strong fluorescence properties with the quantum yields of 19.6 % and 23.4 %. They form 1:1 complexes with ammonium salts in both solution and solid state (association constant up to 10⁵  M^-1 in CDCl₃ ). Chiral quaternary ammonium salts can induce the chirality of the dynamically racemic inherently chiral saucer[n]arenes in solution, and thus show mirror-imaged circular dichroism signals and circularly polarized luminescence (CPL) properties.

Hydrated cation-π interactions of π-electrons with hydrated Li+, Na+, and K+ cations

Cation-π interactions are essential for many chemical, biological, and material processes, and these processes usually involve an aqueous salt solution. However, there is still a lack of a full understanding of the hydrated cation-π interactions between the hydrated cations and the aromatic ring structures on the molecular level. Here, we report a molecular picture of hydrated cation-π interactions, by using the calculations of density functional theory (DFT). Specifically, the graphene sheet can distort the hydration shell of the hydrated K+ to interact with K+ directly, which is hereafter called water-cation-π interactions. In contrast, the hydration shell of the hydrated Li+ is quite stable and the graphene sheet interacts with Li+ indirectly, mediated by water molecules, which we hereafter call the cation-water-π interactions. The behavior of hydrated cations adsorbed on a graphene surface is mainly attributed to the competition between the cation-π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated cations adsorbed onto the graphene surface.

Preparation of a Multicarbazole-Based Nanocapsule Capable of Largely Modulating Guest Spectroscopic Properties in Water

A nanocapsule composed of multiple carbazole panels (ca. 12 panels) was quantitatively generated from bent carbazole-based amphiphiles in water. Unlike previously reported macrocycles and coordination cages bearing several carbazole panels, the resultant nanocapsule displays enhanced emissivity and improved electrochemical stability as compared with the monomeric amphiphile. The spectroscopic properties of substituted coumarin and boron-dipyrromethene dyes can be modulated upon encapsulation by the nanocapsule in water. In the cavity, a highly blue-shifted absorption band is observed from largely twisted coumarin dyes and two absorption bands are found from boron-dipyrromethene dimers stacked in an unusual L-shaped fashion. Moreover, the encapsulated dimers exhibit unique excimer-like emission.

Aryl carbazole-based macrocycles: synthesis, their remarkably stable radical cations and host–guest complexation with fullerenes

Herein, we have designed and synthesized a series of aryl carbazole-based macrocycles and their stable radical cation species and interesting fullerene recognition were systematically investigated.

Ketocalix[3]carbazole: facile synthesis, rigid conformation and baicalin-selective sensing

Ketocalix[3]carbazole, a facilely synthesized rigid “basket” capable of sensing baicalin.

One-step synthesis of methylene-bridged bis-carbazole and evaluation of its antitumor activity and G-quadruplex DNA binding property

Most reported carbazolyl G-quadruplex DNA (G4-DNA) ligands possess a rigid structure rather than a flexible one. The conformationally flexible ligands are paid much less attention. In this study, we report a novel class of non-rigid methylene-bridged biscarbazolyl ligand and their G4-DNA binding properties. Moreover, the antitumor activities of all these oligomers have been evaluated. The results show that this family of oligomers could be facilely synthesized via solely one step. Among them, compound 2, the bis-carbazole derivative, displays the best antitumor activity and IC₅₀ values against HT-29, HepG2, A375 and MCF-7 cells are 0.69, 5.09, 3.15 and 3.8 μ mol/L, respectively. Although conformationally flexible, 2 is still capable of binding to as well as stabilizing G4-DNA via π-π stacking interaction. Moreover, 2 selectively binds to G4-DNA over duplex DNA. The current study enriches the category of carbazolyl G4-DNA ligands and paves the way for the search of more efficient G4-DNA ligands and antitumor leads.

Supramolecular catalytic synthesis of a novel bis(salicylaldehyde hydrazone) ligand for ratiometric recognition of AT-DNA

Hydrazone bond formation under physiological conditions remains challenging. In this study, bis(salicylaldehyde hydrazone) was synthesized using supramolecular catalysis under physiological conditions and its AT-DNA ratiometric sensing properties were identified.

New opportunities in synthetic macrocyclic arenes

This feature article summarizes the latest research progress in the design and development of new synthetic macrocyclic arenes.

Rational synthesis of benzimidazole[3]arenes by CuII-catalyzed post-macrocyclization transformation

A new series of calix[n]arene analogues, benzimidazole[3]arenes, was rationally synthesized by Cu^II-catalyzed post-macrocyclization transformation of a tris(o-phenylenediamine) macrocycle, and fully characterized by NMR, MS, and single-crystal X-ray diffraction (XRD) analyses.

A new series of calix[n]arene analogues, benzimidazole[3]arenes, was rationally synthesized by Cu^II-catalyzed post-macrocyclization transformation of a tris(o-phenylenediamine) macrocycle, and fully characterized by NMR, MS, and single-crystal X-ray diffraction (XRD) analyses. The resulting syn- and anti-benzimidazole[3]arenes have a bowl-shaped and a warped structure, respectively, in their crystalline states, and both display a dynamic inversion behavior in solution. This modification resulted in strong fluorescence due to the generated benzimidazole moieties. The mechanistic study of the post-macrocyclization transformation demonstrated that the formation of both benzimidazole[3]arenes was catalyzed, via triimine intermediates, by Cu^II ions in air through oxidation and cyclization of the tris(o-phenylenediamine) macrocycle.

Supramolecular Recognition of Three Way Junction DNA by a Cationic Calix[3]carbazole

DNA three-way junctions (TWJ-DNA) are intermediate structures in DNA replication and/or recombination. They play very important roles in biological processes, but more subtle functions are still unknown due partially to the lack of a fluorescent ligand. In this study, a cationic calix[3]carbazole (2) has been synthesized and its properties of interacting with TWJ-DNA have been evaluated by UV/Vis and fluorescence spectroscopy, circular dichroism (CD), gel electrophoresis, and ¹ H NMR studies. The results show that 2 binds to the central hydrophobic cavity of TWJ-DNA. Moreover, it could selectively bind to TWJ-DNA over duplex and quadruplex DNA. Furthermore, 2 possesses the capability of serving as the TWJ-DNA probe as its trap-II excimer emission is turned on by TWJ-DNA.

One-pot, highly efficient, cavity controllable synthesis and binding properties of carbazole-based macrocycles with sulfonamide linkages

A new type of carbazole-based sulfonamide macrocycle was synthesized efficiently in one single step.

Regioselective Synthesis of Methylene-Bridged Naphthalene Oligomers and Their Host-Guest Chemistry

In this research, we report the regioselective synthesis of methylene-bridged naphthalene oligomers from 2,6-dialkoxyl naphthanene and paraformaldehyde by using p-TsOH as the catalyst and CH₂Cl₂ as the solvent. The structures were characterized by NMR spectroscopy and X-ray crystallography. Their host-guest chemistry with organic cations was studied, and optimal naphthalene numbers in the oligomers were revealed for different guests. In addition, the reason for the unsuccessful synthesis of methylene-bridged naphthalene macrocycles was discussed.

Calix[3]carbazole: A C3-symmetrical receptor for barium ion

The binding ability of calix[3]carbazole (1) to metal ions has been investigated. It is found that 1 could serve as a non crown ether based, C₃-symmetrical receptor for Ba²⁺ via the marriage of cation-π and cation-dipole interactions. FID assay further illustrates that 1 could selectively interact with Ba²⁺ over Pd²⁺. A possible binding mechanism for [1-Ba²⁺] complex is proposed.

Synthesis of benzo[6]urils and their selective interactions with bipyridines

Benzo[6]urils bearing hydroxymethyl or methyl groups have been synthesized with a facile method, and their supramolecular interactions with bipyridine guests have been investigated.

Calixarenes with naphthalene units: calix[4]naphthalenes and hybrid[4]arenes

A facile, one-step synthesis of new calix[4]naphthalenes and the conformational and complexation properties of the homomacrocycles and the hybrid macrocycle are presented.