Xi Du

Copper(I)-iodide based coordination polymers: bifunctional properties related to thermochromism and PMMA-doped polymer film materials

Poly(methyl methacrylate) (PMMA) films doped with Cu(I)-based imidazole derivative coordination polymers [Cu3I3(bib)1.5]n (1) and [Cu4I4(bix)2]n (2) [bib = 1,4-bis(1-imidazolyl)benzene and bix = 1,4-bis(imidazol-1-ylmethyl)benzene] were synthesized and their photophysical properties were studied. 1 and 2 were prepared by a solvothermal method and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy, 1H NMR, PXRD and thermal gravimetric analyses. Molecular structural analysis reveals that 1 exhibits a unique one-dimensional (1D) infinite triplex chain and 2 is built from a [Cu4I4]n cluster which possesses an interesting two-dimensional (2D) (4,4)-connected sql (square lattice) network. Detailed structural characterization of the supramolecular organization of 1 and 2 revealed overall three-dimensional (3D) interlinked networks driven by extensive π⋯π stacking interactions. Both 1 and 2 display remarkable narrow band emission with a smaller full width at half-maximum (FWHM) (77 K, 34.63 and 60.07 nm; 298 K, 121.95 and 126.83 nm) in the solid state at 77 K, which leads to excellent monochromaticity. The combination of such a narrow FWHM and the large red-shift of 62 nm from 298 K to 77 K endows 2 with a more prominent thermochromism effect than 1, with emissions strongly depending on temperature and tunable from yellow to red by changing the temperature from 298 K to 77 K. Here, the role of the [Cu4I4]n cluster in controlling the performance of thermochromic luminescence is highlighted. Meanwhile, 1 and 2 demonstrate stronger and longer lifetime yellow luminescence emissions at concentrations of 0.8% (τ = 156.62 μs) and 1.0% (τ = 92.28 μs) in poly(methyl methacrylate) (PMMA). Furthermore, development of easy-to-prepare hybrid materials 1–PMMA and 2–PMMA leads to bright yellow luminescence polymer film materials with outstanding thermal stability in daily applications (321 °C and 500 °C).

Assembly of one-, two-, and three-dimensional Ln(III) complexes constructed from a novel asymmetric tricarboxylic acid: synthesis, structure, photoluminescence and tunable white-light emission

By reacting an asymmetric semi-rigid V-shaped linker H3dpob (H3dpob = 3-(2′3′-dicarboxylphenoxy)benzoic acid) and Ln(NO3)3·6H2O, nine novel Ln-based luminescent materials, from 1D to 3D, namely {[Eu(dpob)(phen)]·H2O}n (1), {[Ln(Hdpob)(ox)0.5(H2O)2]}n (Ln = Eu(2), Sm(3), Gd(4), Tb(5)), {[Eu(dpob)(H2O)2]·0.5H2O}n (6), and {[Ln(dpob)(H2O)2]·mH2O}n (Ln = Eu(7), Gd(8), Tb(9), m = 0.5 for 7 and 9; m = 1 for 8) (phen = 1,10-phenanthroline; H2ox = oxalic acid) have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, infrared (IR) spectroscopy, elemental analysis, and PXRD. The crystal structures of 1–9 indicate that the coordination modes and coordination configuration of the H3dpob ligand play critical roles in the formation of the lanthanide architectures. Complexes 1–5 display multiple structures from double-stranded 1D chains to 4-connected 2D layers, through [Eu2(CO2)4] or [Eu2(CO2)2] dinuclear units with different auxiliary ligands. Complexes 6 and 7 are genuine supramolecular isomers which are induced by the concentration effect. 6 possesses a 2D kgd network with a Schlafli symbol of (43)2(46·66·83) built from 6-connected [Eu2(CO2)2] units and 3-connected H3dpob, which further connects to a (3,8)-connected tfz-d topology through O–H⋯O hydrogen bonds. 7 displays a 3D (3,6)-connected rtl network with the Schlafli symbol (4·62)2(42·610·83). Eu complexes 1, 2, 6, and 7 as well as Tb complexes 5 and 9 could provide intense and bright characteristic 5D0 → 7FJ/5D4 → 7FJ red/green luminescence under UV excitation in the solid state at 298 K and 77 K. The calculated singlet and triplet energies of H3dpob as well as phen and H2ox ligands indicate that these ligands act as antenna chromophores that are able to efficiently absorb and transfer energy to Ln(III) ions. In complexes 1, 2 and 5, ligand-to-metal energy transfer processes could occur in mixed ligands. However, these processes occurred in a single H3dpob ligand in complexes 6 and 7. With careful adjustment of the relative concentration of the lanthanide ions and by varying the excitation wavelengths of {[Gd0.92Eu0.04Tb0.04(dpob)(H2O)2]·0.5H2O}n (10), tunable yellow (CIE coordinate: 0.51, 0.40) to white-light (CIE coordinate: 0.33, 0.34) emission has been obtained.

Controlled Zn2+-Triggered Drug Release by Preferred Coordination of Open Active Sites within Functionalization Indium Metal Organic Frameworks

Drug delivery in target regions could make extraordinary progress in chemoselective therapies. A novel preferred coordination (PC) strategy referring to proactive interacting with open active sites to replace previous occupation by ion-exchange for controlling release of drug molecules is well-constructed. Two topological types of MOF-In1 (Schläfli symbol: (4,8)-connected of (410·615·83)(45·6)2) and MOF-In2 (Schläfli symbol: (4,4)-connected of (66)) show the specific way. Increasing node connectivity as well as the trapping of guest OH- anions, 5-fluorouracil (5-FU) is preferentially captured into the MOF-In1, which exhibits an outstanding loading capacity around 34.32 wt %. 19F NMR spectroscopy was further employed to investigate host-guest interaction and reveal the binding constant (Ka = 3.84 × 102 M-1). Meanwhile, the controlled release of 5-FU in a simulated human body with liquid phosphate-buffered saline solution by biofriendly Zn2+-triggered is realized. With an elevated Zn2+ concentration, the drug release will be enhanced. This efficient strategy for MOFs as multifunctional drug carrier opens a new avenue for biological and medical applications.

Novel Hydrogen-Bonding Cross-Linking Aggregation-Induced Emission: Water as a Fluorescent “Ribbon” Detected in a Wide Range

The development of efficient sensors for detection of the water content in a wide detection range is highly desirable for balance in many industrial processes and products. Presented herein are six novel different substituted Schiff base Zn(II) complexes, which exhibit the remarkable capability to detect traces of water in a wide linear range (most can reach 0-94%, v/v), low detection limit of 0.2% (v/v), and rapid response time of 8 s in various organic solvents by virtue of an unusual water-activated hydrogen-bonding cross-linking AIE (WHCAIE) mechanism. As a proof-of-concept, the WHCAIE mechanism is explained well by single X-ray diffraction, absorption spectra, fluorescence spectra, dynamic light scattering, 1H NMR spectra, and theoretical calculations. In addition, the molecules demonstrated their application for the detection of humidity (42-80%). These Schiff base Zn(II) complexes become one of the most powerful water sensors known due to their extraordinary sensitivity, fast response, and wide detection range for water.

Unusually Flexible Indium(III) Metal–Organic Polyhedra Materials for Detecting Trace Amounts of Water in Organic Solvents and High Proton Conductivity

Humidity-induced single-crystal transformation was observed in the indium metal-organic polyhedra [In2(TCPB)2]·2H2O (In1), where H3TCPB is 1,3,5-tri(4-carboxyphenoxy)benzene. When the humidity is above 58% relative humidity (RH) at room temperature, the neutral compound In1 could be successfully converted into the positively charged compound In1-H along with the color change from yellow to deep red, which also undergoes a reversible transformation into In1 driven by thermal dehydration. Notably, the color of In1 takes only 5 min to change under 58% RH at room temperature, which is much quicker than common desiccant bluestone. As the water content is increased from 0.0% to 0.2% in acetonitrile solvent, compound In1 exhibits rapid detection of trace amounts of water through turn-off luminescence sensing mechanism with a low detection limit of 2.95 × 10-4%. Because of the formation of extensive hydrogen-bonding network between the metal-organic polyhedra (MOPs) and surrounding guest OH- ions, compound In1-H, along with isostructural Ga1-H, displays excellent proton conductivity up to 2.84 × 10-4 and 2.26 × 10-4 S cm-1 at 298 K and 98% RH, respectively. Furthermore, the activation energies are found to be 0.28 eV for In1-H and 0.34 eV for Ga1-H. This method of incorporation of OH- ions to obtain high proton conductivity MOPs with low activation energy demonstrates the advantage of OH- ion conduction in the solid-state materials.

A highly sensitive turn-on ratiometric luminescent probe based on postsynthetic modification of Tb3+@Cu-MOF for H2S detection

The fabrication of luminescent materials with lanthanide cations encapsulated within MOF pores is currently of interest because luminescent materials are used in numerous applications. In this study, a distinctive strategy via postsynthetic modification (PSM) of a novel metal–organic framework [Cu(HCPOC)2]n (Cu1) (H2CPOC = 5-(4′-carboxyphenoxy)nicotinic acid) and terbium ions (Tb3+) for sensing hydrogen sulfide (H2S) is reported. The obtained composite Tb3+@Cu1 emits a weak typical Tb3+ ion emission and strong ligand-centred emission. Interestingly, H2S, as a strong electron donor, can strongly enhance the luminescence of Tb3+ through its superior affinity for Cu2+ ions. The composite Tb3+@Cu1 was designed as a luminescent turn-on ratiometric probe for H2S detection, showing high sensitivity and selectivity. The detection limit of Tb3+@Cu1 (1.20 μM) is far below that of Cu1 (13.25 μM). Moreover, a similar ligand, 5-(4′-carboxyphenyl)nicotinic acid (H2CPC), was used to synthesize a fascinating structure, [Cu5(CPC)2(HCPC)2(OH−)4]n (Cu2), which was quite similar to that of the famous semiconductor MoS2, with the advantageous support of an organic linker between layers, and it showed a band gap of 2.45 eV.

Highly Stable and Regenerative Metal–Organic Framework Designed by Multiwalled Divider Installation Strategy for Detection of Co(II) Ions and Organic Aromatics in Water

MOF-based sensors capable of effectively and stably detecting toxic species in water have attracted huge attention in terms of improving environmental monitoring levels and water quality. Combining the flexibility of structure and modifying of pore surface, a multiwalled divider installation (MWDI) strategy is proposed and used for property enhancement. We herein report three metal-organic frameworks (MOFs) 1-3 based on a C3 symmetry organic phosphonic ligand with topology increased from 3,6-connected to 3,8-connected. Among them, MOFs 1 and 2 with remaining binding sites and large pores display lower luminescence response to Co2+ than does the applying standard. Guided by the MWDI strategy, 3 with high rigid framework and triple molecular installer divided rhombic pore was achieved under top-down topological analysis as anticipated, which endows high sensitivity and rapid response to Co2+, contributed by the synergy from free activated sites and appropriate pore and molecular dividing effect. Particularly, the high stability of 3 in boiling solvent and acid/base solutions has been evidenced and explained by structural robustness and kinetic inertness. Moreover, 3 shows excellent detection ability toward trinitrophenol (TNP) over other aromatic analytes in water, attributing to the predomination of energy transfers. Of note is that the used framework can be in situ regenerated into a fresh one. That provides a promising strategy to prepare effective and economic luminescent sensors in a predictable way for property modification.

Self-assembly of two supramolecular indium(III) metal–organic frameworks for reversible iodine capture and large band gap change semiconductor behavior

Under self-assembly, a novel polydentate benzimidazole ligand 2-(quinoline-2-yl)-benzimidazole (2-QLBM) and two In(III) compounds, [In(2-Hqlca)2Cl3·3H2O] (1) and {[In(2-QLBM)(2-qlca)Cl2]2·CH3CN·2H2O} (2) (2-Hqlca = 2-quinolinecarboxylic acid) have been synthesized and characterized. Both the In(III) compounds are driven by noncovalent interactions to assemble into supramolecular metal–organic frameworks (MOFs). Considering 2-QLBM and 2-Hqlc ligands with different geometrical structures, compound 1 possesses a (66)-dia network with a channel diameter of about 1.856 A, and compound 2 displays a (3,4)-connected topology network with the Schlafli symbol of (63)(65·8), whose channel diameter is about 3.683 A. Owing to large voids in the framework, 2 can serve as a host for reversible encapsulation of iodine corresponding to the 1.52 molecules of iodine per formula unit with a fast response and high sensitivity. Upon irradiation with UV light, the two compounds display tunable fluorescence emission from blue to yellow by varying the temperature. Moreover, the absorption spectra demonstrate that the band gaps of compounds 1 and 2 are 3.71 and 3.58 eV, respectively. When adsorbing iodine into the framework, the host structure of 2 is relatively perturbed by the presence of guests and exerts a remarkable influence on the band size and gap state.

Lanthanide MOFs constructed based on a difunctional ligand with bimodal emission and Eu3+ doped Dy3+ materials: white emission and color tuning

Based on azabicyclo ligands, four 3D supramolecular lanthanide complexes have been synthesized through hydro(solvo)thermal reactions, generally formulated as [Dy(bipy) (NO3)3]2 (1·Dy), [Dy(bipy)2(NO3)3] (2·Dy), [Dy2(bpdc)3(DMF)(H2O)]2·(DMF)10(H2O) (3·Dy) and [Eu4(bpdc)6(CH3NH2)3(DMSO)(H2O)] (4·Eu) (Bipy = 2,2′-bipyridine; H2bpdc = 2,2′-bipyridine-5,5′-dicarboxylic acid, DMF = N,N-dimethylformamide), and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis and powder X-ray diffraction (PXRD). There are three kinds of hydrogen bonding, C2–H2A⋯O6, C4–H4A⋯O4 and C8–H8A⋯O8 along the a/c, b, c axis, respectively in complex 1·Dy. They connect the 1·Dy complex into a 3D 6-connected pcu supramolecular network. 2·Dy is connected into a 3D network with 8–connected bcu architecture by two kinds of hydrogen bonding: C2–H2A⋯O1 and C9–H9A⋯O3. In order to connect the polymer to form a 3D complex, H2bpdc has been chosen in the synthesis and design of the crystal. In the network of 3·Dy, two kinds of Dy(III) cations in different coordination models construct the different binuclear [Dy2O14(DMF)2] and [Dy2O12(H2O)2], and further form the (4,4,6)-connected 3D architecture. The isostructural complex 4·Eu has been synthesised simultaneously. The property of luminescence in solid state or different solvents of the four complexes has been studied in detail. The four complexes show the unique emission peaks of lanthanide cations. Futhermore, in 3·Dy and 4·Eu, the ligand shows a rare bimodal emission, which can sensitize the emission of europium cations as an “antenna effect”, and the shorter one keeps its blue emission though coordinated with Dy(III) cations. Based on the synthesis of green or red color materials, multicolored photoluminescence tuning has been studied in detail through growth of a series of bimetallic complexes, the crystal formula as [Dy2nEu′2−2n(bpdc)3(DMF)(H2O)] (M-1–M-9; 0 < n < 1). We achieved dichromatic fine-tuning among the triangle region of red, green and white. The linear dependence of the emissions has been analyzed, and the mathematical matrix model is useful to calculate the ratio and excitation wavelength for a given color in need.

Effect of noncovalent interactions on Ag(I)/Cu(II) supramolecular architecture for dual-functional luminescence and semiconductive properties

Four novel luminescent materials, namely, [Ag3(3,2′,3′-dpob)(bpy)]n (1·Ag), [Ag(3,3′,4′-H2dpob)(bpy)]n (2·Ag), [Ag3(3,2′,3′-Hdpob)(3,2′,3′-H2dpob)(bib)3·2H2O]n (3·Ag), and [Cu(3,2′,3′-Hdpob)(bib)·2H2O]n (4·Cu) [3,2′,3′-H3dpob = 3-(2′,3′-dicarboxylphenoxy)benzonic acid; 3,3′,4′-H3dpob = 3-(3′,4′-dicarboxylphenoxy)benzonic acid; bpy = 4,4′-bipyridine; bib = 1,4-bis(1-imidazoly)benzene] have been hydrothermally synthesized by mixed ligands and characterized using single crystal X-ray diffraction, infrared (IR), elemental analysis and thermogravimetric analysis (TGA). The crystal structures of four compounds indicate that the hydrogen bonding (O–H⋯O, C–H⋯O and C–H⋯π) and π⋯π stacking interactions play critical roles in the formation of the extended supramolecular array. 1·Ag displays a rare 3D compact structure with a 1D right-handed helical chain [–Ag1–CO2–Ag3–CO2–Ag1–]. 2·Ag and 3·Ag exhibit a 3D supramolecular architecture linked by intermolecular hydrogen bonds based on a 1D double-chain and 1D triple-chain, respectively. 4·Cu shows a 1D + 1D → 2D sheet, which is propagated to form an extended 3D structure with pcu (primitive cubic) topology via π⋯π stacking. The four compounds display remarkable narrow band emission with smaller full width at half-maximum (FWHM) (77 K, 97.91, 92.27, 72.98 and 77.96 nm; 298 K, 169.41, 241.98, 293.66 and 148.50 nm) in the solid state. The combination of such narrow FWHM and the red-shift from 298 K to 77 K endow them with a prominent thermochromic effect. It is worth noting that 2·Ag and 3·Ag display good aggregation-induced emission (AIE) properties. Both of them show very weak luminescence in dimethyl sulfoxide (DMSO, good solvent) while their intensities increased enormously with the addition of water (H2O, poor solvent) due to aggregation. In addition, adsorption spectra reveal their semiconductive nature (2.35 eV for 1·Ag and 2.91 eV for 3·Ag) and the role of Ag⋯Ag interactions in controlling the performance of semiconductive properties is highlighted.