Ke-Zhi Wang

Carbazole-functionalized europium complex and its high-efficiency organic electroluminescent properties

A complex tris(dibenzoylmethanato){1-ethyl-2-(N-ethyl-carbazole-yl-4) imidazo[4,5-f]1,10phenanthroline} europium(III) [Eu(DBM)3phencarz] functionalized by a hole-transport group carbazole was synthesized. Devices using this complex as emitter showed greatly enhanced performance benefited from the increased hole-transport properties and efficient energy transfer from carbazole to the central ions. A 58-nm-single-layer device gave a brightness of 20 cd/m2 at 15 V. The highest power efficiency of 2.7 lm/W at 5 V and 0.5 cd/m2 and the luminance exceeding 2000 cd/m2 at 20 V was obtained from a device with the configuration of ITO/TPD(20 nm)/Eu(DBM)3phencarz(40 nm)/BCP(20 nm)/AlQ(40 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm).

Syntheses, spectroscopic and crystal structural studies of novel imidazo[4,5-f]1,10-phenanthroline derivatives and their Eu(III) ternary complexes with dibenzoylmethane

Abstract Two novel ligands, 2-(4′-dimethylaminophenyl)imidazo[4,5-f]1,10-phenanthroline (L1) and 3-ethyl-2-(4′-dimethylaminophenyl)imidazo[4,5-f]1,10-phenanthroline (L2), and their europium(III) complexes with dibenzoylmethanate (DBM), Eu(DBM)3(L1) and Eu(DBM)3(L2), were synthesized and characterized by IR, UV–Vis and fluorescence spectroscopy, and thermogravimetric and differential thermal analyses (TG–DTA). The fluorescent intensity of Eu(DBM)3(L2) is 18 times that of Eu(DBM)3(L1). The crystal structures of Eu(DBM)3(L1) and L2 were determined by single crystal X-ray diffraction. Each europium atom is coordinated by six oxygen atoms of three bidentate DBM anions and two nitrogen atoms from one bidentate L1, forming a distorted square antiprism. Highly resolved fluorescence spectroscopy of Eu(DBM)3(L1) at 77 K revealed one Eu(III) site.

Ultralong Persistent Room Temperature Phosphorescence of Metal Coordination Polymers Exhibiting Reversible pH-Responsive Emission

Ultra-long-persistent room temperature phosphorescence (RTP) materials have attracted much attention and present various applications in illumination, displays, and the bioimaging field; however, the persistent RTP is generally from the inorganic phosphor materials to date. Herein, we show that the metal coordination polymers (CPs) could be new types of emerging long-lived RTP materials for potential sensor applications. First, two kinds of Cd-based CPs, Cd(m-BDC)(H2O) (1) and Cd(m-BDC)(BIM) (2) (m-BDC = 1,3-benzenedicarboxylic acid; BIM = benzimidazole), were obtained through a hydrothermal process, and the samples were found to exhibit two-dimensional layered structures, which are stabilized by interlayer C-H···π interaction and π···π interaction, respectively. The CPs show unexpected second-time-scale ultra-long-persistent RTP after the removal of UV excitation, and this persistent emission can be detected easily on a time scale of 0-10 s. The CPs also feature a tunable luminescence decay lifetime by adjusting their coordination situation and packing fashion of ligands. Theoretical calculation further indicates that the introduction of the second ligand could highly influence the electronic structure and intermolecular electron transfer toward tailoring the RTP of the CP materials. Moreover, CP 2 exhibits well-defined pH- and temperature-dependent phosphorescence responses. Therefore, this work provides a facile way to develop new type of CPs with steady-state and dynamic tuning of the RTP properties from both experimental and theoretical perspectives, which have potential applications in the areas of displays, pH/temperature sensors, and phosphorescence logic gates. On account of suitable incorporation of inorganic and organic building blocks, it can be expected that the ultra-long-persistent RTP CPs can be extended to other similar systems due to the highly tunable structures and facile synthesis routes.

Synthesis and electroluminescence properties of an organic europium complex

Abstract In order to develop new materials for red electroluminescent devices, a novel ligand, 2-phenyl-imidazo[4,5-f]1,10-phenanthroline (L), and an europium (III) complex with dibenzoylmethanate (DBM), Eu(DBM) 3 L, was synthesized. The crystal structure of Eu(DBM) 3 L was determined by single crystal X-ray diffraction. The crystal of Eu(DBM) 3 L belongs to orthorhombic, space group Pbca with cell dimensions of a =2.1655(6) nm, b =2.0834(5) nm, c =2.6469(7) nm, V =11.942(5) nm 3 , Z =8, D x =1.307 g/cm 3 . Each europium atom is coordinated with six oxygen atoms from three bidentate DBM anions and two nitrogen atoms from one bidentate L, forming a distorted square antiprism. The complex is easily evaporated and can be used as a red light emitting material. Upon improvement, the device with a structure of ITO/ N , N ′-diphenyl- N , N ′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) (40 nm)/Eu(DBM) 3 L (50 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine or BCP) (20 nm)/tris(8-hydroxyquinoline) aluminum (ALQ) (30 nm)/cathode gives off pure red light with luminance of 42 cd/m 2 at 16 V.

Layer-by-layer assembly of graphene oxide and a Ru(II) complex and significant photocurrent generation properties.

The multilayer films were fabricated by layer-by-layer electrostatically coassembling graphene oxide and a ruthenium complex of [Ru(bpy)2L](ClO4)2 {L = 2-(2,6-di(pyridin-2-yl)pyridine-4-yl)-1H-imidazo[4,5-f]-1,10-phenanthroline} and characterized using UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and cyclic voltammetry. The dependence of redox properties and cathodic photocurrents on the number of layers deposited and the photocurrent generation mechanism and polarity were studied in detail. The homogeneous growth and close packing of the two film-forming components, linear relationships of the dark cyclic voltometry peak currents and photocurrents vs number of layers deposited, and large cathodic photocurrent density of 4.1 μA/cm(2) for a four-layer film make this novel hybrid thin film promising applications ranging from molecular photovoltaic and photocatalytic molecular devices to photoelectrochemical sensing.

Lanthanide-pyridyl-2,5-dicarboxylate N-oxide frameworks with rutile topology

Four novel lanthanide-organic frameworks Ln(2,5-pdco)(CH3COO)(H2O) [Ln = La (1), Eu (2), Gd (3), Tb (4); 2,5-H2pdco = pyridyl-2,5-dicarboxylic acid N-oxide] have been synthesized and characterized. The coordination networks are similarly constructed viaLn2(μ-CH3COO)2 dinuclear secondary building units (SBUs), which are further linked by six 3-connected 2,5-pdco tectons to result in a novel 3D (3,6)-connected framework with rutile topology. Compound 2 shows the characteristic red emissions of Eu3+ at room temperature with the life time of 0.42(1) ms and emission quantum yield of 32.1%. The variable-temperature magnetic susceptibility studies indicate the presence of weak antiferromagnetic coupling between Gd3+ in 3 while weak ferromagnetic like one between Tb3+ in 4 through chelating-bridging acetate anions, despite their similar crystal structures.

Water cluster supported architecture of lanthanide coordination polymers with pyrazinetricarboxylic acid

The first examples of lanthanide coordination polymers with pyrazinetricarboxylic acid, [Ln(PZTA)(H2O)4]·2H2O (Ln = Eu(1), Gd (2), PZTA = pyrazine-2,3,5-tricarboxylate) and [Ln(PZTA)(H2O)2]·H2O (Ln = Er(3), Yb(4)) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. Structural analysis shows that complexes 1 and 2 are composed of 1-D lanthanide-pyrazinetricarboxylate (Ln-PZTA) framework and two types of water clusters while complexes 3 and 4 have 3-D Ln-PZTA framework with 1-D channel, at which a 1-D water cluster chain is located. This shows the effect of lanthanide contraction on the construction of the Ln-PZTA framework. The results of TG curves and PXRD display that the uncoordinated and coordinated water molecules are removed, the Ln-PZTA frameworks collapse, which shows that the water clusters play an important role in constructing Ln-PZTA frameworks in the title complexes.

Smart Luminescent Coordination Polymers toward Multimode Logic Gates: Time-Resolved, Tribochromic and Excitation-Dependent Fluorescence/Phosphorescence Emission

In this work, we propose that lanthanide cations (such as Eu3+ and Tb3+)-doped long-afterglow coordination polymers (CPs) can be an effective tool for designing multimode optical logic gates based on their tunable fluorescence/phosphorescence transformation and state-dependent emission. First, multicolor and white-light luminescence across the blue/green/yellow/red visible regions can be obtained by balancing the co-doping ratio of Eu3+/Tb3+ cations and suitable excitations. Additionally, a new tribochromic Eu-Cd-CP was developed based on the mechanism of a change in structural symmetry. Benefitting from long-afterglow, tribochromism, and excitation-dependent emission on the same luminescent CP, a new three-input and three-output logic gate was obtained. Therefore, this work not only provides detailed insights into the interesting fields of tribochromism and tunable photoemission, but also confirms that long-afterglow CPs can serve as a new platform for the construction of smart luminescent systems and multimode optical logic gates.

DNA Binding and Photocleavage Properties, Cellular Uptake and Localization, and in-Vitro Cytotoxicity of Dinuclear Ruthenium(II) Complexes with Varying Lengths in Bridging Alkyl Linkers.

Two new dinuclear Ru(II) polypyridyl complexes containing three and ten methylene chains in their bridging linkers are synthesized and characterized. Their calf thymus DNA-binding and plasmid DNA photocleavage behaviors are comparatively studied with a previously reported, six-methylene-containing analog by absorption and luminescence spectroscopy, steady-state emission quenching by [Fe(CN)6](4-), DNA competitive binding with ethidium bromide, DNA viscosity measurements, DNA thermal denaturation, and agarose gel electrophoresis analyses. Theoretical calculations applying the density functional theory (DFT) method for the three complexes are also performed to understand experimentally observed DNA binding properties. The results show that the two complexes partially intercalate between the base pairs of DNA. Cellular uptake and colocalization studies have demonstrated that the complexes could enter HeLa cells efficiently and localize within lysosomes. The in-vitro antitumor activity against HeLa and MCF-7 tumor cells of the complexes are studied by MTT cytotoxic analysis. A new method, high-content analysis (HCA), is also used to assess cytotoxicity, apoptosis and cell cycle arrest of the three complexes. The results show that the lengths of the alkyl linkers could effectively tune their biological properties and that HCA is suitable for rapidly identifying cytotoxicity and can be substituted for MTT assays to evaluate the cell cytotoxicity of chemotherapeutic agents.

Photoelectrochemical properties of electrostatically self-assembled multilayer films formed by a cobalt complex and graphene oxide.

The multilayer films consisting of graphene oxide and a cobalt complex were fabricated though electrostatic layer-by-layer self-assembly technique and characterized by UV-Vis absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and cyclic voltammetry. The results demonstrated that the hybrid films were successfully prepared and exhibited good electrochemical activity. The film was also subjected to photoelectrochemical studies and were found to exhibit large cathodic photocurrent density of 6.1 μA/cm(2) while irradiated with 100 mW/cm(2) polychromatic light (730 nm>λ>325 nm) at an applied potential of -0.4V versus saturated calomel electrode.