Tetraphenylethylene-Based Hydrogen-Bonded Organic Frameworks (HOFs) with Brilliant Fluorescence.

By synergistically employing four key strategies: (I) introducing tetraphenylethylene groups as the central core unit with aggregation-induced emission (AIE) properties, (II) optimizing the π-conjugated length by extending the building block branches, (III) incorporating flexible groups containing ethylenic bonds, and (IV) applying crystal engineering to attain dense stacking mode and highly twisty conformation, we successfully synthesized a series of hydrogen-bonded organic frameworks (HOFs) exhibiting exceptional one/two-photon excited fluorescence. Notably, when utilizing the fluorescently superior building block L2, HOF-LIFM-7 and HOF-LIFM-8 exhibiting high quantum yields (QY) of 82.1 % and 77.1 %, and ultrahigh two-photon absorption (TPA) cross-sections of 148959.5 GM and 123901.1 GM were achieved. These materials were successfully employed in one and two-photon excited lysosome-targeting cellular imaging. It is believed that this strategy, combining building block optimization and crystal engineering, holds significant potential for guiding the development of outstanding fluorescent HOF materials.

One/Two-Photon-Excited ESIPT-Attributed Coordination Polymers with Wide Temperature Range and Color-Tunable Long Persistent Luminescence.

The multiple metastable excited states provided by excited-state intramolecular proton transfer (ESIPT) molecules are beneficial to bring temperature-dependent and color-tunable long persistent luminescence (LPL). Meanwhile, ESIPT molecules are intrinsically suitable to be modulated as D-π-A structure to obtain both one/two-photon excitation and LPL emission simultaneously. Herein, we report the rational design of a dynamic CdII coordination polymer (LIFM-106) from ESIPT ligand to achieve the above goals. By comparing LIFM-106 with the counterparts, we established a temperature-regulated competitive relationship between singlet excimer and triplet LPL emission. The optimization of ligand aggregation mode effectively boost the competitiveness of the latter. In result, LIFM-106 shows outstanding one/two-photon excited LPL performance with wide temperature range (100-380 K) and tunable color (green to red). The multichannel radiation process was further elucidated by transient absorption and theoretical calculations, benefiting for the application in anti-counterfeiting systems.

Thermally Activated Fluorescence vs Long Persistent Luminescence in ESIPT-Attributed Coordination Polymer.

Excited-state intramolecular proton transfer (ESIPT) molecules demonstrating specific enol-keto tautomerism and the related photoluminescence (PL) switch have wide applications in displaying, sensing, imaging, lasing, etc. However, an ESIPT-attributed coordination polymer showing alternative PL between thermally activated fluorescence (TAF) and long persistent luminescence (LPL) has never been explored. Herein, we report the assembly of a dynamic Cd(II) coordination polymer (LIFM-101) from the ESIPT-type ligand, HPI2C (5-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazol-1-yl)isophthalic acid). For the first time, TAF and/or color-tuned LPL can be achieved by controlling the temperature under the guidance of ESIPT excited states. Noteworthily, the twisted structure of the HPI2C ligand in LIFM-101 achieves an effective mixture of the higher-energy excited states, leading to ISC (intersystem crossing)/RISC (reverse intersystem crossing) energy transfer between the high-lying keto-triplet state (Tn(K*)) and the first singlet state (S1(K*)). Meanwhile, experimental and theoretical results manifest the occurrence probability and relevance among RISC, ISC, and internal conversion (IC) in this unique ESIPT-attributed coordination polymer, leading to the unprecedented TAF/LPL switching mechanism, and paving the way for the future design and application of advanced optical materials.

High-Temperature and Dynamic RGB (Red-Green-Blue) Long-Persistent Luminescence in an Anti-Kasha Organic Compound.

Organic LPL (long-persistent luminescence) materials have sparked extensive research interest due to the ultralong-lived triplet states. Although numerous organic LPL materials have been reported, most of the triplet emission was static and monotonous. Therefore, LPL materials with dynamic triplet emission are urgently required. A triamino-s-triazine derivative 1 with dynamic LPL was fabricated. The single-crystal structure shows that the abundant intermolecular interactions and small free volume restrict the molecular motion and avoid the quenchers. Spectral and theoretical calculations upheld the existence of multiple excited states in 1, and the migration of electrons between multiple excited states is very sensitive to external stimuli. By modulating the stimulus, the residence of electrons in different triplet states can be manipulated to achieve RGB LPL. Importantly, blue LPL was achieved by manipulating the anti-Kasha emission. And the red LPL can still be observed at high temperature.

One and Two-Photon Excited Fluorescence Optimization of Metal-Organic Frameworks with Symmetry-Reduced AIEgen-Ligand.

By designing a tetraphenylethylene (TPE)-based AIEgen-ligand with reduced symmetry, we obtained two alkaline-earth metal-based MOFs (LIFM-102 and LIFM-103) with dense packing structures and low porosity as proved by single-crystal X-ray diffraction and CO2 sorption data. Excitingly, the desolvated MOFs with rigid environment and reduced lattice free solvent exhibit high quantum yields (QY, 64.9 % and 79.4 %) and excellent two-photon excited photoluminescence (TPA cross-sections, 2946.6 GM and 2899.0 GM), while maintaining the external-stimuli-responsive properties suitable for anticounterfeit fields. The effect of ligand conformation was validated by comparing the structure and fluorescence properties of the samples before and after desolvation and further verified by theoretical calculations. This work expands the study on TPE-cored materials to symmetry-reduced ligand and might bring forward novel structures and excellent photoluminescent properties in the future.

Conformational Regulation of Multivalent Terpyridine Ligands for Self-Assembly of Heteroleptic Metallo-Supramolecules.

A two-ligand system composed of the predesigned multivalent and complementary terpyridine-based ligands was exploited to construct heteroleptic metallo-supramolecules and to investigate the self-assembly mechanism. Molecular stellation of the trimeric hexagon [Cd6L23] gave rise to the exclusive self-assembly of the star hexagon [Cd18L16L33] through complementary ligand pairing between the ditopic and octatopic tectons. To understand how the intermolecular heteroleptic complexation influenced the self-assembly pathway, the star hexagon was truncated into two triangular fragments: [Cd12L13L43] and [Cd12L13L53]. In the self-assembly of [Cd12L13L43], the conformational movements of hexatopic ligand L4 could be regulated by L1 to promote the subsequent coordination event, which was the key step to the successful multicomponent self-assembly. In contrast, the formation of [Cd12L13L53] was hampered by the geometrically mismatched intermediates.

Multicomponent Metallo-Supramolecular Nanocapsules Assembled from Calix[4]resorcinarene-Based Terpyridine Ligands.

Tetrafunctionalized calix[4]resorcinarene cavitands commonly serve as supramolecular scaffolds for construction of coordination-driven self-assembled capsules. However, due to the calix-like shape, the structural diversity of assemblies is mostly restricted to dimeric and hexameric capsules. Previously, we reported a spontaneous heteroleptic complexation strategy based on a pair of self-recognizable terpyridine-based ligands and CdII ions. Building on this complementary ligand pairing system, herein three types of nanocapsules, including a dimeric capsule, a Sierpinski triangular prism, and a cubic star, could be readily obtained through dynamic complexation reactions between a tetratopic cavitand-based ligand and various multitopic counterparts in the presence of CdII ions. The dimeric capsular assemblies display the spacer-length-dependent self-sorting behavior in a four-component system. Moreover, the precise multicomponent self-assembly of a Sierpinski triangular prism and a cubic star possessing three and six cavitand-based motifs, respectively, demonstrates that such self-assembly methodology is able to efficiently enhance architectural complexity for calix[4]resorcinarene-containing metallo-supramolecules.

The Gigantic {Ni36Gd102} Hexagon: A Sulfate-Templated "Star-of-David" for Photocatalytic CO2 Reduction and Magnetic Cooling.

Gigantic coordination molecules assembled from a large number of metal ions and organic ligands are structurally and functionally challenging to characterize. Here we show that a heterometallic cluster [Ni36Gd102(OH)132(mmt)18(dmpa)18(H2dmpa)24(CH3COO)84(SO4)18(NO3)18(H2O)30]·Br6(NO3)6·(H2O)x·(CH3OH)y, (1, x ≈ 130, y ≈ 60), shaped like a "Star of David", can be synthesized using a "mixed-ligand" and "sulfate-template" strategy. In terms of metal nuclearity number, 1 is the second largest 3d-4f cluster to date. In the solid state, 1 is porous after removing the lattice guests. The N2 adsoption experiment reveals that the BET and Langmuir surface areas are 299.8 and 412.0 cm2 g-1, respectively. CO2 adsorption at 298 K gives the amount of 45 cm3 g-1 for 1. More importantly, 1 is soluble in common organic solvents and exhibits high solution stability revealed by high resolution MALDI-TOF mass spectroscopy, small-angle X-ray scattering (SAXS), and low-dose transmission electron microscopy. The solubility and the potential open metal sites owing to the labile coordinating components prompted us to investigate the photocatalytic properties of 1, which displays high selectivity and efficiency for reduction of CO2 to CO with turnover number and turnover frequency of 29700 and 1.2 s-1, respectively. These values are higher than most catalysts working under the same conditions, presumably due to the strong Ni-CO2 binding effect. In addition, the large percentage of Gd(III) in 1 leads to a large magnetic entropy change (41.3 J·kg-1·K-1) at 2.0 K for ΔH = 7 T.

Iron-Based Metal-Organic Framework System as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions.

The fabrication of highly efficient and sustainable electrocatalysts used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is exceedingly challenging and warranted for overall water splitting. In this work, we successfully synthesized a series of metal-organic frameworks (MOFs), namely, as Fe2M-MOF (M = Fe, Co, Ni, Zn, Mn; H4L = 3,3,5,5'-azoxybenzenetetracarboxylic acid) under a simple and mild condition, in which the Fe3 cluster as a basic building unit was replaced by the second kind of metal center; at the same time, a redox-active organic linker was adopted. The Fe2M-MOF system as a multifunctional catalyst realizes great improvement of the OER and HER performances. Among of them, the Fe2Co-MOF catalyst exhibits an extremely low overpotential of 339 mV at a current density of 10 mA cm-2 and a very small Tafel slope of 36.2 mV dec-1 in an alkaline electrolyte for OER. This result has far exceeded the commercial catalyst IrO2. Meanwhile, Fe2Zn-MOF manifests excellent HER activity with a small overpotential of 221 mV at 10 mA cm-2 and a low Tafel slope of 174 mV dec-1. In addition, the good long-term stability for these catalysts can be evaluated under working conditions. Systematic investigations are used to explain the enhanced electrocatalytic mechanism. In conclusion, we provide a simple and effective strategy for the preparation of multifunctional catalysts for energy conversion applications based on a pristine MOF material with redox-active metal centers and organic linkers.

Tetraphenylethylene(TPE)-Containing Metal-Organic Nanobelt and Its Turn-on Fluorescence for Sulfide (S2-).

A metal-organic supramolecular nanobelt was synthesized by quantitative self-assembling terpyridine-functionized tetraphenylethylene (TPE) and Cd2+, which only showed a weak emission both in solution or aggregated state. Nevertheless, nanobelt complex could be transferred to a fluorescence turn-on sensor to S2- by taking advantage of the structural transformation from nanobelt to its fluorescent ligand.

Precise Self-Assembly of Molecular Four- and Six-Pointed Stars.

A novel metal-organic ligand (MOL 2) has been prepared by linking two V-shaped bis-terpyridines with one X-shaped tetrakis-terpyridine through the stable connectivity. The complexation between MOL 2, X-shaped tetrakis-terpyridine, and Zn2+ gave rise to a supramolecular C6-symmetrical six-pointed star quantitatively. In addition, a mixture of MOL 2, K-shaped tetrakis-terpyridine, and Zn2+ afforded a C2-symmetrical four-pointed star. These metallo-supramolecular architectures were adequately characterized by NMR, ESI-MS, TWIM-MS, and TEM analyses.

Metallaoctahedron Derived from the Self-Assembly of Tetranuclear Metal-Organic Ligands.

Construction of 3D terpyridine-based metallopolyhedra remains challenging because of the linear coordination geometry of ⟨tpy-MII-tpy⟩ connectivity. A progressive strategy is made by assembling tetranuclear terpyridyl metal-organic ligands to afford a novel regular octahedron, whose structure was established by NMR, electrospray ionization mass spectrometry, traveling-wave ion-mobility mass spectrometry, atomic force microscopy, and transmission electron microscopy. This strategy provides an efficient method for the construction of 3D terpyridine-based metallopolyhedra.

Molecular Lemniscates from Organic-Metal Terpyridine-Based Self-Assembly and Host-Guest Recognition.

The intricate discrete supramolecular architectures via two or more noncovalent interactions are very attractive for chemists. In this paper, a series of homomeric metallo-supramolecular lemniscates were prepared in nearly quantitative yields by assembling either dialkylammonium salt- or benzo-21-crown-7 (B21C7)-containing terpyridyl metallo-organic ligands with Zn2+. Furthermore, the heteromeric analogue could be obtained through two ways: (1) the cooperative interaction of coordination-driven self-assembly and host-guest recognition and (2) the transformation from homodimers to heterodimers driven by host-guest interaction. These supramolecules were characterized by nuclear magnetic resonance (NMR), diffusion-ordered NMR spectroscopy, electrospray ionization mass spectrometry, and two-dimensional (2D) ion-mobility mass spectrometry.

Geometrically Complementary Self-Assembly of a Hexarhomboid Architecture from Two Ruthenium(II)-Organic Building Blocks.

A shape-persistent metallosupramolecular multirhomboid that inlays a hexarhomboid polygon in a three-lobed flat structure was prepared by means of coordination-driven self-assembly. The key ligands were synthesized by a "reaction on complex" strategy that becomes accessible to troublesome metalloorganic ligand L3. The formation here consists of four different starting components and two metal ions. Complementarity of the shape and size drives molecular puzzling and results in the multicomponent, quantitative self-assembled construct.

Truncated Sierpinski Triangular Assembly from a Molecular Mortise-Tenon Joint.

The amalgamation of different components into a giant and intricate structure that makes quantitative and spontaneous assembly through molecular design is indispensable but challenging. To construct novel metallo-supramolecular architectures, here we present an architectural design principle based on multicomponent self-assembly. Using a carefully designed hexatopic terpyridine-based metallo-organic ligand (MOL), [Ru2T2K], we report on the formation of supramolecular trapezoid Zn5[Ru2T2K]V2, hollow hexagon Zn15[Ru2T2K]3K3, and giant star-shaped supramolecule Zn18[Ru2T2K]3[Ru2X2V]3, all of which were assembled by one-pot, nearly quantitative assembly of [Ru2T2K] with the ditopic 60°-directed bisterpyridine V, tetrakisterpyridine K, and MOL [Ru2X2V], respectively. The complementary ligands were selected on the basis of the size- and shape-fit principles, actually similar to the mortise-tenon joint that aligns and locks the two complementary wood components. This strategy is expected to open the door to sophisticated designer supramolecules and nonbiological materials. The multivalent connections within the mutual ligands give rise to the formation of stable assemblies, which are unambiguously characterized by NMR, ESI-MS, TWIM-MS, and TEM analyses.

Micelles Protect Intact Metallo-supramolecular Block Copolymer Complexes from Solution to Gas Phase during Electrospray Ionization.

Supramolecular diblock copolymers using metal-ligand coordination can be synthesized under ambient conditions by delicate design of the end groups of the homopolymer chains. However, mass spectrometric analysis of such metallo-supramolecular copolymers is challenging. One of the reasons is the nonpolarity of the polymer chains, making it hard to disperse the complexes in electrospray ionization (ESI)-friendly environments. The other difficulty is the noncovalent nature of such copolymers, which is easily disrupted during the ionization. Here, we demonstrate that the intact metallo-supramolecular diblock copolymers can be maintained sufficiently during the ESI process in aqueous solution within micelles. The high-resolution mass spectrometric evidence revealed that the surfactant molecules effectively protect the noncovalent binding of the complexes into gaseous ions. Intriguingly, surfactant molecules were sufficiently detached away from the copolymer complexes, giving unambiguous mass spectra that were predominated by intact diblock copolymers. This ESI-based approach allowed us to investigate the relative bond strengths of metal-to-ligand complexation using collision-induced dissociation (CID) in the ion trap mass spectrometry. Conformational features and collision cross sections of the copolymers were thus obtained using subsequent ion mobility spectrometry mass spectrometry (IMS-MS). Remarkable environment-dependent conformations of the denoted diblock copolymers were found using this mass spectrometric platform.

Functional and structural characterization of a ß-glucosidase involved in saponin metabolism from intestinal bacteria.

Saponins are natural glycosides widely used in medicine and the food industry. Although saponin metabolism in human is dependent on intestinal microbes, few involving bacteria enzymes have been identified. We cloned BlBG3, a GH3 ß-glucosidase from Bifidobacterium longum, from human stool. We found that BlBG3 catalyzes the hydrolysis of glycoside furostanol and ginsenoside Rb1 at higher efficiency than other microbial ß-glucosidases. Structural analysis of BlBG3 in complex with d-glucose revealed its three unique loops, which form a deep pocket and participate in substrate binding. To understand how substrate is bound to the pocket, molecular docking was performed and the binding interactions of protobioside with BlBG3 were revealed. Mutational study suggested that R484 and H642 are critical for enzymatic activity. Our study presents the first structural and functional analysis of a saponin-processing enzyme from human microbiota.

A Dual-Functional Luminescent MOF Sensor for Phenylmethanol Molecule and Tb3+ Cation.

A highly luminescent porous metal-organic framework Cd3(L)2.5(4-PTZ)(DMF)3, labeled as NBU-9, has been designedly synthesized based on Cd(NO3)2·4H2O and mixed ligands of 4-(1 H-tetrazol-5-yl)pyridine (4-HPTZ) with N-coordinated sites and thiophene-2,5-dicarboxylic acid (H2L) with heteroatomic (S) ring and carboxylate groups in N, N-dimethylformamide (DMF) at 100 °C for 3 days. The interesting result is that this compound NBU-9 can be also obtained via the mixed raw materials of Cd(NO3)2·4H2O, 4-cyanopyridine, NaN3, and H2L under solvothermal condition at a higher temperature of 140 °C for 3 days, involving in situ ligand synthesis of 4-HPTZ. Its structure was indentified by single-crystal X-ray study, powder X-ray diffraction, element analysis, and TGA results. Structural analysis shows that the three-dimensional framework of NBU-9 contains cubic channels of 9.59 × 10.26 Å2 covered by a large number of open S- and O-coordinated sites and can be simplified into a 8-connected uninodal eca net with high potential solvent accessible volumes of 34.1%. Its luminescent properties demonstrate that NBU-9 as a multifunctional sensory material realizes the selective detection for the phenylmethanol molecule on the basis of fluorescence quenching mechanism and effectively sensitizing the visible emitting of the Tb3+ cation based on luminescence enhancement.

Self-Assembly and Catalytic Reactivity of BINOL-Bridged Bis(phenanthroline) Metallocages.

Upon treatment with ZnII ions, a series of BINOL-bridged bis(phenanthroline) ligands was self-assembled into [M2L3] metallocages, which were carefully characterized by NMR spectroscopy and ESI-MS spectrometry. Among them, a racemic mixture of the BINOL-bridged bis(phenanthrolines) underwent chiral self-sorting to afford two homochiral metallocages. The narcissistic self-sorting process of the metallocages was observed in the complexation reaction of the constitutionally isomeric bis(phenanthrolines) with varying connection positions. Moreover, the endo hydroxyl-functionalized metallocage [Zn2{( S)-L2OH}3] exhibited catalytic activity and substrate selectivity for the Knoevenagel condensation reactions of aromatic tricarbaldehydes with malononitrile.

Ascidiaceibacter salegens gen. nov., sp. nov., isolated from an ascidian.

An aerobic, Gram-stain negative, rod-shaped, non-motile bacterium, designated as strain HQA918T, was isolated from an ascidian, Botryllus schlosseri, which was collected from the coast of Weihai in the north of the Yellow Sea, in China. The strain grew optimally at 28-30 °C, at pH values 7.0-8.0, and in the presence of 1.0-3.0% (w/v) sodium chloride (NaCl). A phylogenetic analysis based on 16S rRNA gene sequences showed that strain HQA918T can be affiliated with the family Flavobacteriaceae in the phylum Bacteroidetes, with 92.7% similarity to its close relatives. The major fatty acids identified were iso-C15:0, iso-C15:0 3-OH, and summed feature 3 (iso-C15:0 2-OH and/or C16:1ω7c). The major polar lipids were phosphatidylethanolamine, one unidentified aminolipid, and five unidentified polar lipids. The G+C content of the genomic DNA was 44.1 mol%. On the basis of the phylogenetic, genotypic, phenotypic, and chemotaxonomic data, this organism should be classified as a representative of a novel genus, for which the name Ascidiaceibacter gen. nov. is proposed. The type species is Ascidiaceibacter salegens sp. nov. (type strain HQA918T = KCTC 52719T = MCCC 1K03259T).