Steric and Geometrical Frustration Generate Two Higher-Order CuI12L8 Assemblies from a Triaminotriptycene Subcomponent.

The use of copper(I) in metal-organic assemblies leads readily to the formation of simple grids and helicates, whereas higher-order structures require complex ligand designs. Here, we report the clean and selective syntheses of two complex and structurally distinct CuI12L8 frameworks, 1 and 2, which assemble from the same simple triaminotriptycene subcomponent and a formylpyridine around the CuI templates. Both represent new structure types. In T-symmetric 1, the copper(I) centers describe a pair of octahedra with a common center but whose vertices are offset from each other, whereas in D3-symmetric 2, the metal ions form a distorted hexagonal prism. The syntheses of these architectures illustrate how more intricate CuI-based complexes can be prepared via subcomponent self-assembly than has been possible to date through consideration of the interplay between the subcomponent geometry and solvent and electronic effects.

Enhancing the Toughness and Strength of Polymers Using Mechanically Interlocked Hydrogen Bonds.

The energy dissipative features of hydrogen bonds under conditions of mechanical strain have provided an ongoing incentive to explore hydrogen bonding units for the purpose of controlling and customizing the mechanical properties of polymeric materials. However, there remains a need for hydrogen bond units that (1) possess directionality, (2) provide selectivity, (3) dissipate energy effectively, and (4) can be incorporated readily into polymeric materials to regulate their mechanical properties. Here, we report mechanically interlocked hydrogen bond units that incorporate multiple hydrogen bonds within a [2]catenane structure. The conformational flexibility and associated spatial folding characteristics of the [2]catenane units allow for molecular scale motion under external stress, while the interlocked structure serves as a pivot that maintains the directionality and selectivity of the resultant hydrogen bonding units. When incorporated into polymers, these interlocked hydrogen bond motifs serve to strengthen and toughen the resulting materials. This study not only presents a novel hydrogen bond unit for creating polymeric materials with improved mechanical properties but also underscores the unique opportunities that mechanically interlocked hydrogen bond structures may provide across a diverse range of applications.

Stereocontrolled Self-Assembly of a Helicate-Bridged CuI12L4 Cage That Emits Circularly Polarized Light.

Control over the stereochemistry of metal-organic cages can give rise to useful functions that are entwined with chirality, such as stereoselective guest binding and chiroptical applications. Here, we report a chiral CuI12L4 pseudo-octahedral cage that self-assembled from condensation of triaminotriptycene, aminoquinaldine, and diformylpyridine subcomponents around CuI templates. The corners of this cage consist of six head-to-tail dicopper(I) helicates whose helical chirality can be controlled by the addition of enantiopure 1,1'-bi-2-naphthol (BINOL) during the assembly process. Chiroptical and nuclear magnetic resonance (NMR) studies elucidated the process and mechanism of stereochemical information transfer from BINOL to the cage during the assembly process. Initially formed CuI(BINOL)2 thus underwent stereoselective ligand exchange during the formation of the chiral helicate corners of the cage, which determined the overall cage stereochemistry. The resulting dicopper(I) helicate corners of the cage were also shown to generate circularly polarized luminescence.

Metal Ions Trigger the Gelation of Cysteine-Containing Peptide-Appended Coordination Cages.

We report a series of coordination cages that incorporate peptide chains at their vertices, prepared through subcomponent self-assembly. Three distinct heterochiral tripeptide subcomponents were incorporated, each exhibiting an L-D-L stereoconfiguration. Through this approach, we prepared and characterized three tetrahedral metal-peptide cages that incorporate thiol and methylthio groups. The gelation of these cages was probed through the binding of additional metal ions, with the metal-peptide cages acting as junctions, owing to the presence of sulfur atoms on the peripheral peptides. Gels were obtained with cages bearing cysteine at the C-terminus. Our strategy for developing functional metal-coordinated supramolecular gels with a modular design may result in the development of materials useful for chemical separations or drug delivery.

Supramolecular Modulation of Tumor Microenvironment through Pillar[5]arene-Based Host-Guest Recognition to Synergize Cancer Immunotherapy.

Despite the tremendous breakthrough of immunotherapy, the low response rate and resistance of immune checkpoint inhibitors (ICIs) toward solid tumors occur frequently. A highly hypoxic tumor microenvironment (TME) provides tumor cells with high concentrations of HIF-1α and polyamines to evade immune cell destruction. Reprogramming of an immunogenic TME has exhibited a brilliant future to boost immunotherapeutic performances. Herein, a supramolecular nanomedicine (TAPP) is developed on the basis of host-guest molecular recognition and metal coordination, showing the capability to remodel the immunosuppressive TME. Tamoxifen (Tmx) and Fe3+ are encapsulated into TAPP to achieve the combination of chemotherapy and chemodynamic therapy (CDT). Tmx directly downregulates HIF-1α, and a pillar[5]arene-based macrocyclic host successfully eliminates polyamines in tumors. Enhanced immunogenic cell death is achieved by Tmx and Fe3+, and the therapeutic efficacy is further synergized by immune checkpoint blockade (ICB) therapy. This supramolecular reprogramming modality encourages cytotoxic T lymphocyte infiltration, achieving pre-eminent immune response and long-term tumor suppression.

Substrate-Responsive Pillar[5]arene-Based Organic Room-Temperature Phosphorescence.

Room-temperature phosphorescence (RTP) is a photophysical phenomenon typically associated with a long-lived emission that can be detected by the unaided eye. Several natural proteins display RTP, as do certain artificial polymers. In both cases, the RTP is ascribed to effective intramolecular through-space electronic communication. However, small molecules with internal electronic communication that enable RTP are relatively rare. Herein, we describe an alkyl halide-responsive RTP system consisting of a meta-formylphenyl-bearing pillar[5]arene derivative that supports effective through-space charge transfer (TSCT) within the pillararene cavity. Treatment with bromoethane, a heavy atom-containing guest for the pillar[5]arene host, serves to enhance the emission. An isomeric para-formylphenyl-bearing pillar[5]arene system proved ineffective in producing an RTP effect. Quantum chemical calculations based on single-crystal X-ray diffraction analyses provided insights into the structural determinants governing TSCT between the 1,4-dimethoxybenzene donor units and the formylphenyl groups of the pillar[5]arene, as well as the associated energy gaps and intersystem crossing channels. We believe that the present system and the associated mechanistic analysis provide the foundation for design of new small molecule with tunable RTP features.

Pillararene-Induced Intramolecular Through-Space Charge Transfer and Single-Molecule White-Light Emission.

The fabrication of single-molecule white-light emission (SMWLE) materials has become a highly studied topic in recent years and through-space charge transfer (TSCT) is emerging as an important concept in this field. However, the preparation of ideal TSCT-based SMWLE materials is still a big challenge. Herein, we report a bifunctional pillar[5]arene (TPCN-P5-TPA) with a linear donor-spacer-acceptor structure and aggregation-induced emission (AIE) property. The bulky pillar[5]arene between the donor and acceptor induces a twisted conformation and a non-conjugated structure, resulting in intramolecular TSCT. In addition, the AIE feature and pillar[5]arene cavity endow TPCN-P5-TPA with responsiveness to viscosity and polar guests, by which the TSCT emission is triggered. The combination of blue locally-excited state emission and yellow TSCT emission of TPCN-P5-TPA generates SMWLE. Therefore, we provide a new and versatile strategy for the construction of TSCT-based SMWLE materials.

Synthetic Macrocycle Nanopore for Potassium-Selective Transmembrane Transport.

Reproducing the structure and function of biological membrane channels, synthetic nanopores have been developed for applications in membrane filtration technologies and biomolecular sensing. Stable stand-alone synthetic nanopores have been created from a variety of materials, including peptides, nucleic acids, synthetic polymers, and solid-state membranes. In contrast to biological nanopores, however, furnishing such synthetic nanopores with an atomically defined shape, including deliberate placement of each and every chemical group, remains a major challenge. Here, we introduce a chemosynthetic macromolecule-extended pillararene macrocycle (EPM)-as a chemically defined transmembrane nanopore that exhibits selective transmembrane transport. Our ionic current measurements reveal stable insertion of individual EPM nanopores into a lipid bilayer membrane and remarkable cation type-selective transport, with up to a 21-fold selectivity for potassium over sodium ions. Taken together, direct chemical synthesis offers a path to de novo design of a new class of synthetic nanopores with custom transport functionality imprinted in their atomically defined chemical structure.

Cyclization-Promoted Ultralong Low-Temperature Phosphorescence via Boosting Intersystem Crossing.

Ultralong organic phosphorescence holds great promise as an important approach for optical materials and devices. Most of phosphorescent organic molecules with long lifetimes are substituted with heavy atoms or carbonyl groups to enhance the intersystem crossing (ISC), which requires complicated design and synthesis. Here, we report a cyclization-promoted phosphorescence phenomenon by boosting ISC. N-butyl carbazole exhibits a phosphorescence lifetime (τp) of only 1.45 ms and a low phosphorescence efficiency in the solution state at 77 K due to the lack of efficient ISC. In order to promote its phosphorescence behavior, we explored the influence of conjugation. By linear conjugation of four carbazole units, possible ISC channels are increased so that a longer τp of 2.24 s is observed. Moreover, by cyclization, the energy gap between the singlet and triplet states is dramatically decreased to 0.04 eV for excellent ISC efficiency accompanied by increased rigidification to synergistically suppress the nonradiative decay, resulting in satisfactory phosphorescence efficiency and a prolonged τp to 3.41 s in the absence of any heavy atom or carbonyl group, which may act as a strategy to prepare ultralong phosphorescent organic materials by enhancing the ISC and rigidification.

Azobenzene-Based Macrocyclic Arenes: Synthesis, Crystal Structures, and Light-Controlled Molecular Encapsulation and Release.

Azobenzene (azo)-based macrocycles are highly fascinating in supramolecular chemistry because of their light-responsiveness. In this work, a series of azo-based macrocyclic arenes 1, 2, 3, and 4, distinguished by the substituted positions of azo groups, is rationally designed and synthesized via a fragment-cyclization method. From the crystal and computed structures of 1, 2, and 3, we observe that the cavity size of these azo-macrocycles decreases gradually upon E→Z photoisomerization. Moreover, light-controlled host-guest complexations between azo-macrocycle 1 and guest molecules (7,7,8,8-tetracyanoquinodimethane, terephthalonitrile) are successfully achieved. This work provides a simple and effective method to prepare azo-macrocycles, and the light-responsive molecular-encapsulation systems in this work may further advance the design and applications of novel photo-responsive host-guest systems.

Chemoresponsive Supramolecular Polypseudorotaxanes with Infinite Switching Capability.

Chemoresponsive supramolecular systems with infinite switching capability are important for applications in recycled materials and intelligent devices. To attain this objective, here a chemoresponsive polypseudorotaxane is reported on the basis of a bis(p-phenylene)-34-crown-10 macrocycle (H) and a cyano-substituted viologen guest (G). H and G form a [2]pseudorotaxane (H⊃G) both in solution and in the solid state. Upon addition of AgSF6 , a polypseudorotaxane (denoted as [H⋅G⋅Ag]n ) forms as synergistically driven by host-guest complexation and metal-coordination interactions. [H⋅G⋅Ag]n depolymerizes into a [3]pseudorotaxane (denoted as H2 ⋅G⋅Ag2 ⋅acetone2 ) upon addition of H and AgSF6 , while it reforms with successive addition of G. The transformations between [H⋅G⋅Ag]n and H2 ⋅G⋅Ag2 ⋅acetone2 can be switched for infinite cycles, superior to the conventional chemoresponsive supramolecular polymeric systems with limited switching capability.

Selective Separation of Methylfuran and Dimethylfuran by Nonporous Adaptive Crystals of Pillararenes.

The separation of 2-methylfuran (MeF) and 2,5-dimethylfuran (DMeF) mixtures is very important in the chemical industry. Herein, we offer a novel strategy for the separation of MeF and DMeF using nonporous adaptive crystals (NACs) of perethylated pillar[5]arene (EtP5), perethylated pillar[6]arene (EtP6), perbromoethylated pillar[5]arene (BrP5), and perbromoethylated pillar[6]arene (BrP6). We find that the crystals of EtP6 and BrP5 show remarkable selectivities for MeF in a 50:50 (v/v) MeF:DMeF mixture vapor, yielding purities of 94.0 and 96.3%, respectively. Single-crystal structures reveal that these different selectivities come from the different thermodynamic stabilities and binding modes of the host-guest complexes. Cycling experiments demonstrate that these crystals can be reused more than five cycles without loss of performance.

Self-Assembly of Porphyrin-Based Metallacages into Octahedra.

Despite rapid progress in recent years, it has remained challenging to prepare well-defined metal-organic complex-based suprastructures. As a result, the physicochemical mechanisms leading to their geometrical complexity remain perplexing. Here, a porphyrin-based metallacage was used as a building block to construct octahedra via self-assembly, and the mechanism for the evolution of the metallacages into octahedra was disclosed by both experiments and theoretical simulations.

Formation of Planar Chiral Platinum Triangles via Pillar[5]arene for Circularly Polarized Luminescence.

Chiral metal-organic complexes hold great promise as new functional materials that exhibit unique stereochemical and optical properties. Here, we report the formation of optically pure pillar[5]arene-based platinum chiral metallacycles. By coordination with 60° and 90° Pt(II) acceptors, planar chiral platinum triangles were self-assembled efficiently and characterized by multiple spectroscopic techniques. Optical studies indicated that these metallacycles had chiral properties: pS enantiomers showed a negative Cotton effect, and pR enantiomers exhibited a positive Cotton effect. In addition, these metallacycles also exhibited circularly polarized luminescence.

Pillararene Host-Guest Complexation Induced Chirality Amplification: A New Way to Detect Cryptochiral Compounds.

The contradiction between the rising demands of optical chirality sensing and the failure in chiral detection of cryptochiral compounds encourages researchers to find new methods for chirality amplification. Inspired by planar chirality and the host-guest recognition of pillararenes, we establish a new concept for amplifying CD signals of cryptochiral molecules by pillararene host-guest complexation induced chirality amplification. The planar chirality of pillararenes is induced and stabilized in the presence of the chiral guest, which makes the cryptochiral molecule detectable by CD spectroscopy. Several chiral guests are selected in these experiments and the mechanism of chiral amplification is studied with a non-rotatable pillararene derivative and density functional theory calculations. We believe this work affords deeper understanding of chirality and provides a new perspective for chiral sensing.

Dual-Emissive Platinum(II) Metallacage with a Sensitive Oxygen Response for Imaging of Hypoxia and Imaging-Guided Chemotherapy.

Imaging of hypoxia in vivo helps with accurate cancer diagnosis and evaluation of therapeutic outcomes. A PtII metallacage with oxygen-responsive red phosphorescence and steady fluorescence for in vivo hypoxia imaging and chemotherapy is reported. The therapeutic agent and diagnostic probe were integrated into the metallacage through heteroligation-directed self-assembly. Nanoformulation by encapsulating the metallacage into nanoparticles greatly enhanced its stability the in physiological environment, rendering biomedical applications feasible. Apart from enhanced red phosphorescence upon hypoxia, the ratio between red and blue emissions, which only varies with intracellular oxygen level, provides a more precise standard for hypoxia imaging and detection. Moreover, in vivo explorations demonstrate the promising potential applications of the metallacage-loaded nanoparticles as theranostic agents for tumor hypoxia imaging and chemotherapy.

Alkyl Chain Length-Selective Vapor-Induced Fluorochromism of Pillar[5]arene-Based Nonporous Adaptive Crystals.

Developing new vapochromic fluorescent sensing materials with selectivity is in great demand due to serious air pollution caused by volatile organic compounds. Here we report the first nonporous adaptive crystals with vapor-induced fluorochromism. The emission of anthracene conjugated pillar[5]arene P5en crystals blue shifts from bright yellow to green upon exposure to vapors of linear alkyl ketones with alkyl chain length selectivity. Powder and single crystal X-ray diffraction analyses reveal the relationship between vapor-induced crystal structural transformation and fluorochromism. After exposure to 2-butanone, 2-pentanone, and 2-hexanone, the anthracene groups in P5en exist as monomers in the solid state, while after exposure to heptanone and octanone, the anthracene groups instead aggregate as excimers in the solid state. By solid-state NMR and thermogravimetric analysis, we further find that the size fit between ketone molecules and interspaces in P5en crystals lead to the alkyl chain length selectivity. This work provides a new strategy to design vapochromic fluorescent crystalline materials and crystalline transformation systems.

Spontaneous Formation of a Cross-Linked Supramolecular Polymer Both in the Solid State and in Solution, Driven by Platinum(II) Metallacycle-Based Host-Guest Interactions.

The recent progress in platinum(II) coordination-driven supramolecular polymers has had a substantial effect on the design of functional soft materials. However, the prospect of realizing polymerization induced by platinum(II) metallacycle-based host-guest interactions has received little attention until recently. Here we report the realization of supramolecular polymerization driven by platinum(II) metallacycle-based host-guest interactions both in the solid state and in solution. On the basis of the disclosed polymerization mechanism, we present a new strategy for the preparation of platinum(II) metallacycle-based supramolecular polymers.

Controllable Self-Assembly of Macrocycles in Water for Isolating Aromatic Hydrocarbon Isomers.

A series of purely organic macrocycles and catenanes can be self-assembled by condensing a cationic bisaldehyde compound with a series of dihydrazide linkers in weakly acidic water. On one hand, the macrocycles could be generated as the predominant products under the condition of low concentration or less polar media. In the presence of a guest template, these macrocycles could even be obtained in close to quantitative yields, allowing them to be isolated as pure solid products without the need for chromatographic purification. On the other hand, [2]catenanes could be obtained as the major products in more concentrated solutions or more polar media where hydrophobic effects are enhanced. Once purified, both macrocycles and catenanes exhibit remarkable kinetic stability in both the solid state and neutral aqueous solution at room temperature. By means of selective host-guest recognition, one of the macrocyclic products is capable of resolving a pair of hydrocarbon isomers, namely phenanthrene and anthracene, which have similar properties and can hardly be separated by commonly used approaches.

Formation of Linear Side-Chain Polypseudorotaxane with Supramolecular Polymer Backbone through Neutral Halogen Bonds and Pillar[5]arene-Based Host-Guest Interactions.

Linear side-chain polypseudorotaxane with supramolecular polymer backbone was assembled by neutral halogen bonds (XB) and pillar[5]arene-based host-guest interactions in solution and in the solid state. The formation of the halogen-bonded supramolecular polymer backbone and side-chain polypseudorotaxane in solution was characterized by 1 H NMR spectroscopy, diffusion ordered NMR spectroscopy and scanning electron microscopy experiments. Furthermore, the solid-state structures of these two highly organized supramolecular architectures were provided by single-crystal X-ray analysis.