Xin-Ming Wang

Effects of solvents and temperature on the luminescence properties of Cd-isonicotinic acid frameworks based on mono-, bi-, and trinuclear cluster units

In this work, we present the synthesis of three novel 3D Cd(II) coordination polymers, {[Cd(IN)2]·H2O}n (1), [Cd2(IN)2(SO4)(DMF)2]n (2) and {[Cd3(IN)5.5]·0.5OH−}n (3) (HIN = isonicotinic acid). Coordination polymers 1 and 2 were obtained via solvothermal reactions. The synthesis of coordination polymer 3 was realized by a simple temperature induced single crystal to single crystal transition from 1. Single-crystal X-ray diffraction analyses revealed that 1–3 exhibit three different structural types: 1 displays a (6,3)-connected rtl net with the Schlafli symbol (4·62)2 (42·610·83) constructed from mononuclear [CdO4N2] clusters with the help of HIN. 2 is defined as a 6-connected pcu net with the Schlafli symbol {412·63} which is built from binuclear [Cd2(SO2)2] clusters and HIN linkers. 3 can be regarded as a 9-connected ncd net with the Schlafli symbol {36·422·58}, which consists of paddlewheel trinuclear [Cd3(O2C)5] clusters and a bridging HIN. Coordination polymers 1–3 display luminescence with emission maxima containing deep blue, blue, light blue and green at 298 K or 77 K both in solvents (polarity: DMF > CH3OH > CH2Cl2) and in the solid state. The lifetime of all the molecules is in microsecond scale.

Tunable luminescence from rare 2D Ga(III)/In(III) coordination polymers coexisting with three different conjugated system aromatic ligands

Two rare 2D Ga/In-based coordination polymers in which one metal center coexists with three distinct aromatic ligands were synthesized. Helical channels along the 21 screw axis are exhibited to form a hcb net. The compounds exhibit tunable fluorescence from blue, green, white to yellow light by varying the temperature and solvents.

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).

Tunable Luminescence and Application in Dye-Sensitized Solar Cells of Zn(II)/Hg(II) Complexes: Methyl Substitution-Induced Supramolecular Structures Based on (E)-N-(6-Methoxypyridin-2-ylmethylene)arylamine Derivatives

Using Schiff-base ligands (E)-N-(6-methoxypyridin-2-yl)(CH═NAr) (where Ar = C6H5, L1; 2-MeC6H4, L2; 2,4,6-Me3C6H2, L3), six Zn(II)/Hg(II) complexes, namely, [ZnL1Cl2] (Zn1), [HgL1Cl2] (Hg1), [ZnL2Cl2] (Zn2), [HgL2Cl2] (Hg2), [ZnL3Cl2] (Zn3), and [HgL3Cl2] (Hg3) have been synthesized under solvothermal conditions. The structures of six complexes have been established by X-ray single-crystal analysis and further physically characterized by EA, FT-IR, (1)H NMR, and ESI-MS. The crystal structures of these complexes indicate that noncovalent interactions, such as hydrogen bonds, C-H···Cl, and π···π stacking, play essential roles in constructing the resulting supramolecular structures (1D for Hg3; 2D for Zn2, Hg2; 3D for Zn1, Hg1, and Zn3). Upon irradiation with UV light, the emission of complexes Zn1-Zn3 and Hg1-Hg3 could be finely tuned from green (480-540 nm) in the solid state to blue (402-425 nm) in acetonitrile solution. It showed that the ligand and metal cation can influence the structures and luminescence properties of complexes such as emission intensities and maximum wavelengths. Since these ligands and complexes could compensate for the absorption of N719 in the low-wavelength region of the visible spectrum and reduce charge recombination of the injected electron, the ligands L1-L3 and complexes Zn3/Hg3 were employed to prepare cosensitized dye-sensitized solar cells devices for investigating the influences of the electron-donating group and coordination on the DSSCs performance. Compared to DSSCs only being sensitized by N719, these prepared ligands and complexes chosen to cosensitize N719 in solar cell do enhanced its performance by 11-41%. In particular, a DSSC using L3 as cosensitizer displays better photovoltaic performance with a short circuit current density of 18.18 mA cm(-2), corresponding to a conversion efficiency of 7.25%. It is much higher than that for DSSCs only sensitized by N719 (5.14%).

Structure variations of a series of lanthanide complexes constructed from quinoline carboxylate ligands: photoluminescent properties and PMMA matrix doping

A series of lanthanide complexes with formulae {[KEu(Hqlc)(qlc)(H2O)6(OH)]2+·2Cl−}n (1·Eu), {[Eu(qlc)2(phen)(H2O)2]+·Cl−}·CH3CN (2·Eu), [Eu(qlc)2(phen)(NO3)]·H2O (3·Eu), [Ln(qlc)2(H2O)4]·(qlc)·(H2O) (Ln = Eu(4·Eu), Sm(5·Sm), Gd(6·Gd), Tb(7·Tb), Dy(8·Dy), Ho(9·Ho)) (Hqlc = quinoline-3-carboxylic acid, phen = 1,10-phenanthrolin) are synthesized under solvo(hydro)thermal conditions and characterized by single-crystal X-ray diffraction, infrared spectra, elemental analysis, and powder X-ray diffraction. Complex 1 exhibits two-dimensional (6,3)-connected hcb networks and possesses a stable structure through typical O/C–H⋯Cl intermolecular hydrogen bonds. Complexes 2–4 display three diverse dimer structures, due to the synergistic effect from coordination modes of Hqlc ligand and anion effect. Complexes 5–9 are isostructural with complex 4. Eu-complexes 1–4 could provide intense and bright characteristic 5D0 → 7FJ red luminescence under UV excitation in the solid state at 298 K and 77 K. In complexes 2 and 3, the coordinate phen ligand could play the antenna role in the energy transfer process. Therefore, the luminescence lifetimes of complexes 2 (779.62 and 792.65 μs) and 3 (947.21 and 1095.59 μs) are longer than those of complexes 1 (456.93 and 499.33 μs) and 4 (283.70 and 46 469 μs) in the solid state at 298 K and 77 K. Complexes 5, 7 and 8 exhibit characteristic Sm3+, Tb3+ and Dy3+ ion luminescence. Furthermore, through controlling the concentration of complexes 3 and 4 in poly(methyl methacrylate) (PMMA), a series of 3–PMMA and 4–PMMA hybrid materials are obtained, respectively. They all display strong and characteristic red luminescence emissions at a concentration of 8%. Compared with 3 and 4, the luminescence intensities and luminescence lifetimes of 3–PMMA and 4–PMMA are increased, due to the replacement of water molecules by PMMA.

Multifunctional Zn(II)/Cd(II) metal complexes for tunable luminescence properties and highly efficient dye-sensitized solar cells

We design two novel d10 metal complexes [Zn(3-qlc)2]n (Zn1), [Cd(3-qlc)2]n (Cd1) (3-Hqlc = quinoline-3-carboxylic acid), which display similar 2D layer structures, and further form 3D 6-connected primitive cubic (pcu) network topology via π⋯π stacking interactions with the point symbol {412·63}. Complexes Zn1 and Cd1 exhibit tunable luminescence and photovoltaic properties as a new type of multifunctional materials. Zn1 and Cd1 show tunable luminescence from blue to green by varying the temperature in the solid state. Whats more, both of them exhibit excellent aggregation-induced emission (AIE) properties in DMSO/water mixtures. Encouraged by the UV-visible absorption in an ethanol solution result, Zn1 and Cd1 can be considered as co-sensitizers in combination with N719 to investigate their effect on enhancing the dye-sensitized solar cells (DSSCs) performance. Zn1 and Cd1 could overcome the deficiency in the ruthenium complex N719 absorption in the ultraviolet and blue-violet region, offsetting competitive visible light absorption of I3− and reducing the charge recombination of injected electrons. After being co-sensitized with Zn1 and Cd1, the devices co-sensitized by Zn1/N719 and Cd1/N719 yield an overall efficiency of 7.75% and 7.70%, which are 44.59% and 43.66% higher than that of the device sensitized only by N719 (5.36%).

An insight into the controllable synthesis of Cd(II) complexes with a new multifunctional ligand and its application in dye-sensitized solar cells and luminescence properties

Based on a new design of 4-cyanobenzyl-based 1,2,4-triazole ligand 4-(1,2,4-triazolylmethyl) cyanobenzene (TMCB), a series of cadmium complexes 1–5′ from a mononuclear to three-dimensional (3D) structure have been synthesized through hydro(solvo)thermal reactions; they were generally formulated as [Cd(TMCBA)2]n (1), [Cd(TMCB)(1,4-bda)(H2O)]n (2), {[Cd2(TMCB)4(1,4-bda)2(H2O)2]n·3H2O}n (3), {[Cd(TMCB)4(H2O)2]·(NO3)2·(H2O)2}n (4), [Cd1.5(1,4-bda)1.5(DMF)2]2n (5) and [Cd1.5(1,4-bda)1.5(DMF)2]2n (5′) (TMCBA = 4-(1,2,4-triazolylmethyl) benzoic acid, which is formed from the hydrolysis of TMCB; 1,4-H2bda = 1,4-benzenedicarboxylic acid; the difference between two genuine supramolecular isomers of 5 and 5′ is the use of TMCB as the additive agent for the reaction). Complexes 1–5′ exhibit tunable luminescence with emission maxima containing deep blue, blue, light blue, green and deep green region at 298 K or 77 K in both different solvents (polarity: DMSO > CH3OH > CHCl3) and solid state. Interestingly, the good thermal stability accompanied by their compensated adsorption to ruthenium complex N719 in the region of low wavelength, enabled 1 and 4 to serve as co-sensitizers in combination with N719 in dye sensitized solar cells (DSSCs). After co-sensitization with N719, the overall conversion efficiency of 1 and 4 were found to be 7.68% and 6.85%, which are 40.40% and 25.23% higher than that for DSSCs only sensitized by N719 (5.47%) under the same conditions, respectively. The improvement in efficiency is attributed to the fact that complexes 1 and 4 overcome the deficiency of N719 absorption in the low wavelength region of ultraviolet and blue-violet, offset competitive visible light absorption of I3− and reduce charge recombination due to the formation of an effective cover layer of the dye molecules on the TiO2 surface. As a result, the synthesized complexes are promising candidates as co-adsorbents and co-sensitizers for highly efficient DSSCs.

Novel bright blue emissions IIB group complexes constructed with various polyhedron-induced 2-[2′-(6-methoxy-pyridyl)]-benzimidazole derivatives

Five IIB group complexes, [ZnL1Cl2] (1), {[CdL1Cl2]}2 (2), [Cd(L1)2(NO3)2]·H2O (3), [HgL1Cl2] (4), and [ZnL2Cl2] (5) [L1 = 1-[2-(6-methoxy-2-pyridylmethyl)]-2-[2-(6-methoxy-pyridyl)]benzimidazole; L2 = 2-[2-(6-methoxypyridyl)]benzimidazole] have been synthesized and structurally characterized by elemental analysis, IR spectroscopy, 1H NMR, 13C NMR and X-ray single-crystal analyses. The structural investigations testify that the ionic radius and counterions (Cl− and NO3−) cooperatively affect the coordination mode of central metal. As small and medium radii, four-coordinated Zn2+ (1 and 5) and five-coordinated Cd2+ (2) possess tetrahedron and trigonal bipyramid geometries, respectively. Though Hg2+ (4) has a larger radius, its three-coordinated geometry is trigonal planar in order to eliminate repulsive forces. Further observations illustrate that Cd2+ (3) is bound to two ligands L1 when NO3− is the counter anion, forming seven-coordinated monocapped trigonal prismatic geometry. Complexes 1–5 display bright blue luminescence with the emission maxima (λmax) ranging from 399 to 499 nm at 298 K, depending on the N,N′-chelating ligand-centered π* → π transition. Upon cooling to 77 K, the complexes show rich structured emission profiles compared to those at 298 K. The emission lifetimes of L and 1–5 are on the microsecond scale. The emission efficiency of 1–5 is shown by quantum yields ranging from 0.23 to 0.40. Complexes 1–5 offer a good insight into the opportunities in the utilization of blue materials for application and function.

A blue-green-emitting 3D supramolecular compound: synthesis, crystal structure and effect of solvents and temperature on the luminescent properties

A blue-green-emitting three-dimensional supramolecular compound (C10O2N2H8)(C9O7H6) (1) was synthesised under hydrothermal conditions and structurally characterised by elemental analysis, IR spectrum, 1H NMR and single-crystal X-ray diffraction. The crystal belongs to triclinic system with P 1¯ space group. The crystal structure is stabilised by O–H…O, O–H…N hydrogen bonds and π–π interactions (π–π stacking distance is 3.282 Å). Compound 1 exhibits intense green luminescence in solid state at 298 K (λem = 546 nm). In addition, absorption and fluorescence characteristics of compound 1 have been investigated in different solvents (DMSO, CH3CN and CH3OH). The results show that compound 1 exhibits a large red shift in both absorption and emission spectra as solvent polarity increases (polarity: DMSO>CH3CN>CH3OH), indicating a change in dipole moment of compound 1 upon excitation. Although the emission spectra of compound 1 in CH3OH are close to it in dimethyl sulfoxide (DMSO), it is revealed that the luminescence behaviour of compound 1 depends not only on the polarity of environment but also on the hydrogen bonding properties of the solvent. Meanwhile, temperature strongly affects the emission spectra of compound 1. Emission peaks of compound 1 were blue shift at 77 K than those at 298 K in both solid state (ca. 142 nm) and solution (ca. 6–23 nm), which was due to the non-radiative transition decreases at low temperature. Moreover, the quantum yield and fluorescence lifetime of compound 1 were also measured, which increased with increasing polarity of solvent, lifetime in DMSO at 298 K (τ1 = 0.92 μs, τ2 = 8.71 μs) was the longest one in solvents (298 K: τ1 = 0.87–0.92 μs, τ2 = 7.50–8.71 μs; 77 K: τ1 = 0.72–0.90 μs, τ2 = 6.88–7.45 μs), which was also shorter than that in solid state (298 K: τ1 = 1.13 μs, τ2 = 7.50 μs; 77 K: τ1 = 0.97 μs, τ2 = 8.97 μs). This was probably because of the weak polarity environment of compound 1 in solid state.

Direct observation of a fast single-crystal-to-single-crystal transformation from a CuII-framework to a CuI-chain mediated by ascorbic acid

With the help of ascorbic acid as reductant, an exceedingly rare example of a visible single-crystal-to-single-crystal transformation from a CuII-framework to a CuI-chain under mild conditions has been observed, which involves the metal valence tautomerism and restructuring of bonds. The two compounds exhibit the properties of solvatochromism and luminescence aggregation-induced-emission towards CH3OH, respectively.