Chunying Duan

Homochiral metal-organic frameworks for heterogeneous asymmetric catalysis.

Homochiral crystallizations of two enantiomeric metal-organic frameworks (MOFs) Ce-MDIP1 and Ce-MDIP2 were achieved by using L- or D-BCIP as chiral inductions, respectively, where the chiralities were characterized by solid state CD spectra. Ce-MDIPs exhibit excellent catalytic activity and high enantioselectivity for the asymmetric cyanosilylation of aromatic aldehydes; the homochiral Cd-TBT MOF having L-PYI as a chiral adduct exhibits stereochemical catalysis toward the Aldol reactions.

A Color‐Tunable Europium Complex Emitting Three Primary Colors and White Light

The manufacture of new full-color displays is one of the main tasks in flat-panel display systems and lighting technology. Different applications place different demands on emitted light: in some cases a white-light source is needed, and in others pure colors are necessary. Thus, white emission should ideally be composed of three (blue, green, and red) or two (blue and yellow) primary colors and cover the whole visible range from 400 to 700 nm, and the emitter should have the ability to emit the primary colors simultaneously with equal intensities to produce white light and the pure colors separately in a tunable way. Considerable interest exists for such color-tunable materials, which can be used to define or modify environments, moods, and brands. Traditional methods of such white light generation typically rely on mixing various primary colors from different emitting materials. An alternative approach for the generation of efficient (white) light sources is to use a single-component emitter, which can have advantages such as greater stability, better reproducibility, no phase separation, and simpler fabrication processes. 8] Although a few materials show white-light emission as a single-emitting component, none has been reported to produce well-separated blue, green, and red emissions beside white light. Since energy transfer typically quenches one or more of the emission pathways and thereby restricts the transitions that define the output spectrum, the design of color tunable single-component emitters requires readily tailorable different fluorophores and fine-tuning of the energy-transfer processes between the different fluorophores. On the other hand, lanthanide-containing materials, which exhibit excellent sharp-emission luminescence properties with suitable sensitization, have attracted considerable interest and been effectively used in designing white-emitting nanoparticles. With judiciously chosen red(Eu, Pr, Sm), green(Tb, Er), and blue-emissive (Tm , Ce, Dy) ions doped in an suitable host, it is possible to obtain phosphors which emit across the entire visible spectrum with high color purity. Specifically, an Eu-containing singlecomponent complex has been reported to offer white-light emission in a carefully designed system which only allows partial energy transfer between the sensitizing fluorophore and the Eu center. Herein we report the design and synthesis of a new fluorophore that exhibits tunable emission of three primary colors (blue, green, and red) and white light, by combining an Eu moiety as the origin of red light with an organic ligand that comprises a blue-emitting coumarin fluorophore and a green-emitting Rhodamine 6G fluorophore. Coumarin-Rhodamine CR1 was synthesized by reaction of 7-diethylamino-2-oxo-2H-chromen-3-carboxylic chloride and N-(Rhodamine-6G)lactamethylenediamine and recrystallized from ethanol as yellow crystals. Single-crystal X-ray structural analysis confirms the coexistence of two fluorophores in CR1 (Supporting Information Figure S1), whereby the Rhodamine 6G moiety is in a luminescence-inactive ringclosed tautomeric form. Europium compound CR1-Eu (1) was prepared by refluxing ligand CR1 and [Eu(tta)3] in THF (tta = 1,1,1-trifluoro-3-(2-thenoyl)acetone) and purified by recrystallization as an amorphous yellow powder. Elemental analysis and H NMR spectroscopic characterization suggest the chemical formula [Eu(tta)2(CR1)2](tta) for 1 (Figure 1).

Recognition preference of rhodamine-thiospirolactams for mercury(II) in aqueous solution.

This work presents the design, syntheses, photophysical properties and Hg(2+)-binding of the red-emitting rhodamine derivatives RS1, RS2, and RS3 with different coordination ability and different spatial effects that derived from rhodamine thiohydrazone chromophores and respective carboxaldehydes (benzaldehyde, pyridine-2-carboxaldehyde, ferrocenecarboxaldehyde). Chemosensors RS2 and RS3 afford turn-on fluorescence enhancement and display high brightness in water with the EC(50) for Hg(2+) of 0.5 ppb. The fluorescence intensities are nearly proportional to the amount of Hg(2+) at ppb level, when employing 100 nM probes in water. The fluorescence responses of these two chemosensors are Hg(II) specific, and the probes are selective for Hg(II) over alkali, alkaline earth metals, divalent first-row transition metal ions, and Group 12 congeners Zn(II) and Cd(II), as well as heavy metals Pb(II) and Ag(I). X-ray crystal structure analyses exhibit the thioether derivative of the spirolactone in these compounds. Hg(II)-specific binding in water would make the opening of the spirolactam ring and consequently causes the appearance of strong absorption at visible range, and the obvious and characteristic color change from colorless to pink. Compared to the thioamides, the improved selectivity for Hg(2+) is attributed to the poorer coordination affinity of the thioether over other interference metal ions.

Amplifying the Red-Emission of Upconverting Nanoparticles for Biocompatible Clinically Used Prodrug-Induced Photodynamic Therapy

A class of biocompatible upconverting nanoparticles (UCNPs) with largely amplified red-emissions was developed. The optimal UCNP shows a high absolute upconversion quantum yield of 3.2% in red-emission, which is 15-fold stronger than the known optimal β-phase core/shell UCNPs. When conjugated to aminolevulinic acid, a clinically used photodynamic therapy (PDT) prodrug, significant PDT effect in tumor was demonstrated in a deep-tissue (>1.2 cm) setting in vivo at a biocompatible laser power density. Furthermore, we show that our UCNP–PDT system with NIR irradiation outperforms clinically used red light irradiation in a deep tumor setting in vivo. This study marks a major step forward in photodynamic therapy utilizing UCNPs to effectively access deep-set tumors. It also provides an opportunity for the wide application of upconverting red radiation in photonics and biophotonics.

Dye-Sensitized Core/Active Shell Upconversion Nanoparticles for Optogenetics and Bioimaging Applications.

Near-infrared (NIR) dye-sensitized upconversion nanoparticles (UCNPs) can broaden the absorption range and boost upconversion efficiency of UCNPs. Here, we achieved significantly enhanced upconversion luminescence in dye-sensitized core/active shell UCNPs via the doping of ytterbium ions (Yb(3+)) in the UCNP shell, which bridged the energy transfer from the dye to the UCNP core. As a result, we synergized the two most practical upconversion booster effectors (dye-sensitizing and core/shell enhancement) to amplify upconversion efficiency. We demonstrated two biomedical applications using these UCNPs. By using dye-sensitized core/active shell UCNP embedded poly(methyl methacrylate) polymer implantable systems, we successfully shifted the optogenetic neuron excitation window to a biocompatible and deep tissue penetrable 800 nm wavelength. Furthermore, UCNPs were water-solubilized with Pluronic F127 with high upconversion efficiency and can be imaged in a mouse model.

An Amide-Containing Metal–Organic Tetrahedron Responding to a Spin-Trapping Reaction in a Fluorescent Enhancement Manner for Biological Imaging of NO in Living Cells

Metal-organic polyhedra represent a unique class of functional molecular containers that display interesting molecular recognition properties and fascinating reactivity reminiscent of the natural enzymes. By incorporating a triphenylamine moiety as a bright blue emitter, a robust cerium-based tetrahedron was developed as a luminescent detector of nitronyl nitroxide (PTIO), a specific spin-labeling nitric oxide (NO) trapper. The tetrahedron encapsulates molecules of NO and PTIO within the cavity to prompt the spin-trapping reaction and transforms the normal EPR responses into a more sensitively luminescent signaling system with the limit of detection improved to 5 nM. Twelve-fold amide groups are also functionalized within the tetrahedron to modify the hydrophilic/lipophilic environment, ensuring the successful application of biological imaging in living cells.

Metal–Organic Polymers Containing Discrete Single-Walled Nanotube as a Heterogeneous Catalyst for the Cycloaddition of Carbon Dioxide to Epoxides

The cycloaddition of carbon dioxide to epoxides to produce cyclic carbonates is quite promising and does not result in any side products. A discrete single-walled metal-organic nanotube was synthesized by incorporating a tetraphenyl-ethylene moiety as the four-point connected node. The assembled complex has a large cross-section, with an exterior wall diameter of 3.6 nm and an interior channel diameter of 2.1 nm. It features excellent activity toward the cycloaddition of carbon dioxide, with a turnover number of 17,500 per mole of catalyst and an initial turnover frequency as high as 1000 per mole of catalyst per hour. Only minimal decreases in the catalytic activity were observed after 70 h under identical reaction conditions, and a total turnover number as high as 35,000 was achieved. A simple comparison of relative porous MOFs suggested that the cross-section of the channels is an important factor influencing the transport of the substrates and products through the channel.

Field-induced slow relaxation of magnetization in a tetrahedral Co(II) complex with easy plane anisotropy

The mononuclear Co(II) complex CoBr (dmph = 2,9-dimethyl-1,10-phenanthroline) was obtained and X-ray structurally characterized as a distorted tetrahedron environment that is responsible for the moderately strong positive anisotropy of high spin Co(II). In combination with variable-field magnetic susceptibility data at low temperature, high-field electron paramagnetic resonance (HF-EPR) spectroscopy reveals the presence of easy-plane anisotropy (D > 0) in complex CoBr. Slow magnetic relaxation effects were observed for CoBr in the presence of a dc magnetic field. At very low temperatures, ac magnetic susceptibility data show the magnetic relaxation time, τ, to be temperature-independent, while above 2.4 K thermally activated Arrhenius behavior is dominated with Ueff = 22.8(8) cm(-1) and τ0 = 3.7(5) × 10(-10) s. Upon dilution of the complex within a matrix of the isomorphous compound ZnBr, ac susceptibility data reveal the individual molecular nature of the slow magnetic relaxation and indicate that the quantum tunneling pathway observed at low temperatures is likely mediated by intermolecular dipolar interactions.

Structural and Catalytic Performance of a Polyoxometalate-Based Metal−Organic Framework Having a Lanthanide Nanocage as a Secondary Building Block

A polyoxometalate-based lanthanide-organic framework was achieved using the {[Ho(4)(dpdo)(8)(H(2)O)(16)BW(12)O(40)] (H(2)O)(2)}(7+) nanocage as a secondary building block for the heterogeneous catalysis of phosphodiester cleavage in an aqueous solution.

Homochiral Crystallization of Metal–Organic Silver Frameworks: Asymmetric [3+2] Cycloaddition of an Azomethine Ylide

Metal–organic frameworks (MOFs) are hybrid solids with infinite network structures built from organic bridging ligands and inorganic connecting nodes. Besides the potential applications in many diverse areas, MOFs are ideally suited for catalytic conversions, because they can impose sizeand formselective restriction through readily fine-tuned channels and pores, thus providing precise knowledge about the pore structure and the nature and distribution of catalytically active sites. In particular, analogues of homogeneous asymmetric catalysts can be synthetically incorporated into MOFs, thus resulting in the incorporation of the selectivity of these single-site catalysts into micropores, and thereby enhancing the shape-, size-, and enantioselectivities of catalytic reactions in comparison to those performed in homogeneous solution. While recent progress in MOFbased asymmetric catalysis has proved that these emerging catalysts provide a new exciting opportunity for the synthesis of enantiopure compounds, including chiral drugs and fine chemicals, privileged asymmetric metal catalysts or organocatalysts that are incorporated into the nodes of frameworks are still quite limited. The 1,3-dipolar cycloaddition of azomethine ylides with electron-deficient olefins is an extremely versatile process to form highly substituted chiral pyrrolidines, which provide an important motif with widespread applications to the synthesis of biologically active compounds and natural products. The cycloaddition reaction is also one of the most fascinating transformations and has inspired much research interest in the development of asymmetric catalytic variants. The configuration of the four new stereogenic centers of the product could be established in one step with complete atom economy. Recently, elegant studies in this field have shown that chiral silver(I) and copper(I) bisdentate imine complexes are adequate homogeneous catalysts to afford the corresponding cycloadducts in good yields and high enantioselectivities. Like for other precious-metal-catalyzed reactions, it is highly desirable to incorporate chiral metal complexes that are able to generate a metallodipole within the nodes of frameworks, thus resulting in efficient catalytic activity with the catalysts being recyclable and reusable to minimize the metal trace in the product. By incorporating three pyridine–imine bidentate chelators into a triphenylamine fragment, we realized the homochiral crystallization of silver-based MOFs by using cinchonine or cinchonidine as chiral templates. We envisioned that the distorted tetrahedral silver(I) centers within the framework would not only act as chiral nodes to connect these ligands, but also be asymmetric catalytic sites for the 1,3dipolar cycloaddition reactions. We also postulated that the twist configurations of the three phenyl rings attached to one nitrogen atom might exhibit atropisomeric chirality in the solid state, thus facilitating the chiral transfer between the silver centers and finally leading to the formation of chiral MOFs. In the meantime, the coordination intermediate that corresponds to cinchonine moieties is expected to be useful for controlling the absolute chirality of the silver centers, such as those observed in the asymmetric catalytic reactions. The ligand tris(4-(1-(2-pyridin-2-ylhydrazono)ethyl)phenyl) amine (TPHA; Scheme 1), was readily prepared by reaction of tris(4-acetylphenyl)amine with 2-hydrazinylpyridine in a molar ratio of 1:3. Reaction of TPHAwith AgBF4 in methanol afforded new compound Ag-TPHA. Single-crystal structure analysis showed that Ag-TPHA crystallizes in the chiral space group I213 (Figure 1). [12] The silver(I) atom is positioned at a 21 fold axis and is coordinated by two identical bidentate chelators from two different ligands in a distorted tetrahedral geometry. The dihedral angle between the bidentate chelating rings is 49.4(6)8. The ligand is positioned at a three-fold axis to three bridged silver ions through its bidentate chelators. It adopts an atropisomeric chirality with a torsion angle of about 74.5(5)8 between the pair of the phenyl rings. In this case, the Schiff base ligands could be viewed as three connecting nodes, the silver atoms worked as directional connectors. Accordingly, the homochiral frame-