Photoluminescent Studies Research Articles

Tetranuclear homo- (ZnII4and CdII4) and hetero-metal (ZnII2TbIII2and CdII2TbIII2) complexes with a pair of carboxylate ligands in a rare η2:η2:μ4-bridging mode: syntheses, structures and emission properties

Four tetranuclear complexes involving both homo- and hetero-metal combinations, viz. [Zn(II)(2)L(2)(μ(4)-PhCOO)(2)Zn(II)(2)(hfac)(2)] (1), [Cd(II)(2)L(2)(μ(4)-PhCOO)(2)Cd(II)(2)(hfac)(2)] (2), [Zn(II)(2)L(2)(μ(4)-PhCOO)(2)Tb(III)(2)(hfac)(4)] (3), and [Cd(II)(2)L(2)(μ(4)-PhCOO)(2)Tb(III)(2)(hfac)(4)] (4) have been prepared following a single-pot synthesis protocol using N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine (H(2)L) as a primary ligand. Both benzoate and hexafluoroacetylacetonate (hfac(-)), used here as ancillary ligands, play crucial roles in generating a tetranuclear core with high thermodynamic stability. Oxygen atoms of each carboxylate moiety bind all the four metal centers together in a rare η(2):η(2):μ(4)-bridging mode as confirmed by X-ray crystallography. In the homo-metallic complexes (1 and 2), the metal centers are all lying in a square plane, each occupying a corner, and remain connected together by oxygen bridges forming octagonal metallacrowns. These structures remain intact in solution as confirmed by (1)H NMR spectroscopy and photoluminescent studies. In the hetero-metal complexes (3 and 4), the metal centers are arrayed in alternate positions of the tetranuclear core. The Tb(III) centers have eight coordinate bi-capped trigonal prismatic coordination environments with different degrees of distortions. The all oxygen O(8) core surrounding each Tb(III) center is devoid of solvent molecules that make fluorescent emission from these molecules (3 and 4) quite interesting. The hfac(-)-based (1)(π-π*) emissions observed in 1 and 2 are quenched in 3 and 4. These sensitized Tb(III) emissions [(5)D(4)→(7)F(j); j = 6, 5, 4, and 3] are influenced by the local environments surrounding the 4f-metal center. The lifetime for the luminescence decay of 3 ((5)D(4)→(7)F(5) transition) is about 1.5 times longer than that of 4 in all the solvents studied at 298 K.

Syntheses, structures, photoluminescence and magnetic properties of four-connected lanthanide–tricarboxylate coordination polymers

Ten novel lanthanide-based coordination polymers {[LnL(H2O)2]·H2O}n (Ln = Pr (1), Nd (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Yb (9), and Lu (10), H3L = 2-(carboxylmethoxy)terephthalic acid), have been successfully synthesized through hydrothermal reactions of corresponding Ln(OH)3 with semirigid tricarboxylate H3L ligands. Compounds 1 and 2 are isostructural, containing a 3D porous framework built of carboxylate-bridged layers with 66-topology, while 3–10 display the same 2D double-layer structure based on binuclear Ln2O2 units with 43·63-topology. The PXRD and TGA prove their phase purity and high thermal stability, respectively. Photoluminescent studies indicate the efficient energy transfer from L3− ligand to Ln3+ ions, exhibiting the typical intense emissions of corresponding Ln3+ ions in the visible region. The magnetic exchange interactions also are studied in compounds 4–7 for their short O bridges between Ln3+ ions, and the results show that there may be ferromagnetic interactions in 4–6, while in 7 the interactions cannot be distinctly deduced from the curves due to the nature of the Ho3+ ions. Furthermore, compound 6 displays slow magnetization relaxation, exhibiting single-molecule magnetic behavior.

Structural Diversity and Properties of Coordination Polymers Built from a Rigid Octadentenate Carboxylic Acid

By using a semi-rigid tetracarboxylate ligand 5,5′-(1,4-phenylenebis(methylene))bis(oxy)diisophthalic acid (H4L), three novel coordination polymers were synthesized solvothermally and characterized by single-crystal X-ray diffraction, thermogravimetric, photoluminescent and gas adsorption studies. Compound [Zn(H2L)(H2O)2] (1) is a two-dimensional (2D) network with sql/Shubnikov topology built from the 4-connecting Zn2(OOC)2 cluster and bridging ligand H2L2−. Compound [Co2(H3L)2(H2L)(H2O)2]·5H2O (2) is a one-dimensional (1D) zigzag chain-like polymer made of 2-connecting ligand H2L2− and Co2O6(H2O)4 clusters, which form a 3D network through hydrogen bonding interactions. [Cd3(L)2]·(H3O)2(H2O)(DMF)4 (3) possesses a rare (4,8)-connected flu (CaF2) net built from 8-connecting Cd3 clusters and 4-connecting L ligands. In three complexes, the ligand H4L exhibits diverse coordination configurations and modes owing to its flexibility. Upon excitation at room temperature, complexes 1 and 3 exhibit strong violet and blue emissions, respectively. N2 gas adsorption measurements at 77 K showed that compound 3 possesses permanent porosities.

Structure and Photoluminescent Properties of B3+-Doped (Y0.9Dy0.1)InGe2O7 Phosphor

A color-tunable, near-white-light-emitting, B3+-doped (Y0.9Dy0.1)InGe2O7 phosphor was synthesized using a solid-state reaction, and its structure and luminescent properties were determined. X-ray powder diffraction patterns showed that all of the diffraction peaks can be attributed to the monoclinic YInGe2O7 crystal structure for B3+ ion concentration up to 5 mol.%, and that the optimal concentration for B3+ doping is 3 mol.%. In the photoluminescent studies, increasing the B3+ ion concentration caused the intensities of both the excitation and emission peaks to increase and then decrease. In addition, the color tone changes gradually, from the near-white-light region, through greenish, and finally to yellowish. This change is caused by a decrease in the symmetry of the local structure around the Dy3+ ion when the B3+ ion in the host reaches the optimum concentration for the H3BO3 flux of 3 mol.%. When the B3+ content is increased further, the distinct difference in ionic radius between the lattice atoms and the substituent atoms causes the lattice to become distorted and the crystallinity of the (Y0.9Dy0.1)InGe2O7 phosphor to decrease.

Tailor-Made Zinc Uranyl Diphosphonates from Layered to Framework Structures

Hydrothermal reactions of zinc uranyl acetate and 1-hydroxyethylidenediphosphonic acid (H4L) with 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), 1H-benzo[d]imidazole (bi), or 1-phenyl-1H-imidazole (pi) resulted in the formation of four new zinc uranyl compounds, namely, [Zn2(phen)2(UO2)2(L)2(H2O)3]·3H2O (ZnUP-1), Zn2(bipy)2(UO2)2(L)2(H2O)2 (ZnUP-2), (Hbi)[Zn0.5(UO2)2(L)(H2L)(H2O)3]·3H2O (ZnUP-3), and (Hpi)[Zn(UO2)2(H2O)4(L)(HL)]·H2O (ZnUP-4). These four structures all comprise uranyl diphosphonate layers formed by UO7 pentagonal bipyramids and PO3C tetrahedra. Such layers are further connected by Zn-centered polyhedra by sharing oxygens from phosphonate groups. For ZnUP-1 and ZnUP-2, the zinc atoms are terminally coordinated by phen and bipy molecules, respectively, resulting in two-dimensional (2-D) hybrid materials. In ZnUP-3 and ZnUP-4, the uranyl phosphonate layers are joined together by Zn–O polyhedra forming three-dimensional (3-D) frameworks. The structures of ZnUP-3 and ZnUP-4 contain large channels along the a-axis with apertures around 3.4 × 13.3 and 4.4 × 12.2 Å2, respectively. Protonated templates exist in the channels, filling the space and compensating the negative charge of the anionic frameworks. Photoluminescent studies reveal that ZnUP-1 and ZnUP-2 exhibit the characteristic vibronically coupled charge-transfer based UO22+ emission.

Three open-framework coordination polymers with new topological structures built on two tripod ligands

By using flexible tricarboxylate 4,4′,4″-(((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(oxy))tribenzoic acid (H3L) and multiimidazole 1,3,5-tri(imidazo-1-ylmethyl)-2,4,6-trimethylbenzene (titb) ligands simultaneously, three novel coordination polymers [M3L2(titb)2]·2H2O·2.5DMF (M=Co,1; Zn, 2; Cd, 3) were synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, thermogravimetric and photoluminescent studies. The three compounds are isomorphous and possess a three-dimensional (3D) framework built from 2D sheets of L3− ligands and M ions, and 1D chains of titb ligands and M ions. Topological analyses showed that they exhibit a novel (3,3,4,4) four-nodal 3D net constructed from two 4-connecting metal, and two 3-connecting L3− and titb nodes. Compounds 2 and 3 are photoluminescent upon excitation at room temperature.

Dual-Emission from a Single-Phase Eu–Ag Metal–Organic Framework: An Alternative Way to Get White-Light Phosphor

A new bifunctional NTB (tris(benzimidazol-2-ylmethyl)amine)-type ligand incorporating coordination discriminable tripodal benzimidazolyl and monodentate pyridyl groups, tris((pyridin-3-ylmethyl)benzoimidazol-2-ylmethyl)amine (3-TPyMNTB), has been prepared to assemble 4d–4f heterometallic three-dimensional metal–organic frameworks (MOFs) in a stepwise route: (1) direct reaction of 3-TPyMNTB with Ln(ClO4)3 affords monomeric complexes [Eu(3-TPyMNTB)2](ClO4)3·2.5MeCN (1-Eu) and [Gd(3-TPyMNTB)2](ClO4)3·2MeCN·2CHCl3 (1-Gd), and (2) assembly of the precursors 1-Eu and 1-Gd with AgClO4 gives rise to infinite MOFs [EuAg3(3-TPyMNTB)2(H2O)(MeCN)](ClO4)6·4MeCN (2-Eu-Ag) and [GdAg3(3-TPyMNTB)2(H2O)(MeCN)](ClO4)6·4MeCN (2-Gd-Ag), respectively. In monomer 1-Eu, the ligand shows an antenna effect to transfer absorbed energy to Eu3+ center to emit characteristic red luminescence, while in 4d–4f heterometallic MOF 2-Eu-Ag, the ligand centered emission is resensitized by Ag+ ions to generate dual emissions, coming up with the direct white-light emission from a single crystal. The detailed photoluminescent study has been carried out in both solid state and solution to elucidate the emission nature.

Solvothermal synthesis, structure and characterization of 1D chain and 2D layered rare earth sulfates in the presence of cyclic diamines

Abstract Three new rare earth sulfates were solvothermally synthesized and characterized by X-ray diffraction, elemental analysis, thermogravimetric, and photoluminescent studies. Compounds [(NH4)(C6N2H12)][Ln(SO4)3] (Ln Eu, 1; Gd, 2) were synthesized in the solvent of DMA with 1,4-diazabicyclo-[2,2,2]-octane (DABCO) as a structure-directing agent (SDA), which are isomorphous and adopt a two-dimensional layered structure with 8-membered rings made of LnO8 polyhedra and SO4 tetrahedra. The protonated DABCO molecules lie between the layers while the ammonium cations are located within the layers. Compound [(C4N2H12)1.5][Er(SO4)3(H2O)] (3) was synthesized in the mixed solvent of water and ethanol with piperazine (PIP) as a SDA. The structural analyses showed that 3 is constructed from ErO9 polyhedra and SO4 tetrahedra to form a one-dimensional chained structure with edge-sharing 4-membered rings. The protonated PIP molecules and coordination H2O molecules form extensive intra- and inter-chain hydrogen bonding to generate a 3-dimensional supramolecular network. The three compounds exhibit good thermal stability. Compound 1 exhibits intense red luminescence upon excitation owing to the Eu3+ ion.

Capacitive properties of low potential electro-polymerized polyfluorene and activated carbon composite electrode

Polyfluorene (PF) film has been successfully electropolymerized at lower potential (0.91 V vs. Ag/AgCl) in the mixed electrolyte of boron trifluoride diethyl etherate and trifluoroacetic acid. The PF film is characterized to have about 10 repeat units and no presence of ketonic defect site. UV-vis and photoluminescent spectral studies indicate that the PF film is blue light emitting. From cyclic voltammetry and galvanostatic charge-discharge tests in 1 M lithium perchlorate/acetonitrile electrolyte, the polyfluorene/activated carbon electrode shows a specific capacitance of 227.1 F g−1 (per active layer mass) and reversible redox reaction at the potential of 1.4 V in a three electrode configuration. An asymmetric electrochemical capacitor based on this composite electrode and activated carbon electrode exhibits a specific energy of 14.7 Wh kg−1 (per active layer mass). These results indicate that electrochemically prepared polyfluorene could be used as energy storage component for electrochemical application.

Citric based sol–gel synthesis and luminescence characteristics of CaLa2ZnO5:Eu3+phosphors for blue LED excited white LEDs

A novel class of orange–red phosphors namely CaLa2ZnO5 (CLZ) doped with Eu3+ ions were prepared by adopting citrate based sol–gel method. Those were thoroughly characterized by means of XRD, SEM, Tg-DTA, photoluminescent (PL) spectral profiles. PL studies reveal that its emission intensity strongly depends on sintering temperature as well as the dopant ion (Eu3+) concentration. Eu3+ ion doped CaLa2ZnO5 phosphor has a strong excitation at 468nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The influence of the preparation method on the luminescence property was studied by comparing the emission performance of phosphors prepared by sol–gel and solid-state reaction methods along with a commercial red phosphor Y2O2S:Eu3+. Thus, the intense red emission (5D0→7F2) of the Eu3+ doped CLZ phosphors under blue excitation suggests them to be a potential candidate for the production of white light by blue LEDs.

The influence of Eu 3+ doping on photoluminescent properties of red emitting phosphor YInGe 2O 7:Eu 3+ by microwave assisted and conventional sintering method

This paper describes an investigation of the crystalline morphology and photoluminescent properties of YInGe 2O 7 powders doped with different Eu 3+ concentrations using microwave assisted sintering and conventional sintering. X-ray powder diffraction analysis confirmed the formation of monoclinic YInGe 2O 7 structure as YInGe 2O 7:Eu 3+ powders were sintered at 1200 °C in microwave furnace for 1 h, and the raw material phase of Y 2O 3 was observed when Eu 3+ concentration was below 30 mol%. Scanning electron microscopy showed microwave assisted sintering results in smaller particle size and more uniform grain size distribution. In the photoluminescent (PL) studies, the concentration quenching effect was observed under the excitation at 393 nm, but not under the excitation at CTS band. The 5D 0→ 7F 2 transition (620 nm), exhibits a non-exponential decay behavior as YInGe 2O 7:Eu 3+ powders were sintered by microwave with the Eu 3+ concentration higher than 50 mol%.

Binding interaction of bioactive imidazole with bovine serum albumin—A mechanistic investigation

A novel Y-shaped imidazole derivative 4-((E)-2-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)vinyl)phenol has been synthesized and characterised by IR, UV–vis, mass and NMR spectral techniques. The mutual interaction of this imidazole derivative (DPTIV) with bovine serum albumin (BSA) was investigated using photoluminescent studies. The fluorescence quenching mechanism of BSA by DPTIV was analyzed and the binding constant has been calculated. The binding distance between DPTIV and BSA was obtained based on the theory of Forester's non-radiation energy transfer. The effect of some common ions on the binding constant between DPTIV and BSA was also examined.

Syntheses, Structures, and Luminescent Properties of Two Novel Coordination Polymers with Poly-Carboxylate and N-Heterocyclic Ligands

Two novel metal–organic coordination polymers {[Pb(CIPT)(1,4-BDC)]·2H2O}n1 and {[Zn2(IPDT)2(1,4-BDC)2(H2O)].3H2O}n2 [CIPT = 2-(3-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, 1,4-BDC = terephthalic acid, IPDT = 4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-2,6-dimethoxyphenol] were obtained from hydrothermal reaction and characterized by elemental analysis, thermogravimetric (TG) analysis, IR and single-crystal X-ray diffraction. Both of the two coordination polymers exhibit one-dimensional (1D) infinite chain structures through non-covalent interactions, and the existence of hydrogen bonds interactions lead the 1D chain to 2D layer structures. It is noteworthy that the existence of hydrogen bonds reinforces the structural stability of the complexes 1 and 2, which can be proved by TG analysis. The photoluminescent study of coordination polymer 1 shows that it exhibits fluorescent emission band at 637 nm, which is red-shifted by 46 nm relative to the free ligand CIPT.

In Situ Synthesis, X-Ray Structure, Fluorescence and Theoretical Investigations of [Cu2Cl4][(C2H5)2-4,4'-Bipyridine

A novel N,N'-diethyl-4,4'-bipyridine copper complex, [Cu2Cl4][(C2H5)2-4,4'-bipyridine] (1), has been obtained in situ through a solvothermal reaction and structurally characterised by X-ray diffraction. Complex 1 comprises discrete Cu2Cl4 moieties and (C2H5)2-4,4'-bipyridine molecules interlinked via hydrogen bonding interactions to give a three-dimensional supramolecular open framework. Photoluminescent study shows that the complex exhibits an emission in the green region. Theoretical study reveals that the emission is attributed to the π → π* charge-transfer interaction of the (C2H5)2-4,4'-bipyridine moieties.

Spectroellipsometric and photoluminescent studies of SnO x nanostructures doped with Sm ions

We present results on the photoluminescence and optical properties of SnO x nanocrystals as a function of their size. Samariums ions are incorporated in SnO x nanostructures to huge improve their photoluminescence efficiency. We have performed photoluminescent, ellipsometrical, atomic force microscopy, and structural studies of these nanocrystals and found them to be a direct semiconductor with a gap of ≈3.6 eV. The origin of the observed photoluminescence has been discussed. The doping of lanthanide atoms in semiconductor nanocrystals expands the range of possibilities offered by such materials, allowing them to be modified to meet specific requirements in electronic and optoelectronic applications.

In Situ Synthesis, Structure, Photoluminescence and Theoretical Study of [Cu(2-PyCOOH)2(H2O)2]Cl2

A new pyridine-2-carboxylic acid complex, [Cu(2-PyCOOH)2(H2O)2]Cl2, has been prepared in situ through a hydrothermal reaction and its structure comprises discrete [Cu(2-PyCOOH)2(H2O)2]2+ cations and chloride anions which are interlinked via hydrogen bonding interactions to give a 3-D supramolecular motif. Photoluminescent study shows that the complex exhibits an emission in the blue region. Theoretical studies reveal that the emission can be ascribed to metal-to-ligand charge transfer.

In situ formation of an unprecedented 3D microporous CuCN coordination polymer based on a semirigid tetrahedral linker

An unprecedented three-dimensional (3D) coordination polymer [Cu4(CN)4(tpom)]n (tpom = tetrakis(4-pyridyloxymethylene)methane) (1) was solvothermally prepared and characterized by single-crystal X-ray diffraction, IR, TGA, adsorption and photoluminescent studies. Compound 1 is constructed from a 1D CuCN chain and a tetrahedral ligand tpom, in which the CN ligand was in situ generated by the C―C bond cleavage of acetonitrile molecule under solvothermal conditions. Compound 1 possesses a three-fold interpenetrating framework with ths-z type of rod packing topology. It exhibits relatively high thermal stability up to 330 °C and weak photoluminescent emissions at room temperature. The gas absorption studies revealed that 1 can selectively adsorb 0.8 wt% H2 at 77 K and 1 atmospheric pressure.

Solvent-Induced Synthesis of Zinc(II) and Manganese(II) Coordination Polymers with a Semirigid Tetracarboxylic Acid

By using a semirigid quadricarboxylate ligand 5,5′-(biphenyl-4,4′-diylbis(methylene))bis(oxy)diisophthalic acid (H4L), four novel coordination polymers were obtained solvothermally and characterized by single-crystal X-ray diffraction, thermogravimetric, photoluminescent and gas adsorption studies. Compound [Zn2(L)]·CH3CN, 1, is a three-dimensional (3D) framework built from one-dimensional (1D) rod-shaped Zn–O–C secondary building units (SBUs) that are linked together by the 4-connecting L ligands to give rod packing of pcu type and elliptical channels of 7.7 × 8.4 Å2. Compound [Zn4(L)2(H2O)4]·5H2O, 2, possesses a 3D open framework with a doubly interpenetrated sra net built from 4-connecting Zn2(OOC)4 unit and L ligand. Compound [Mn2(L)(H2O)2]·2H2O, 3, is built from trigonal–bipyramidal binuclear Mn2(OOC)3 units and octadentate L ligands, forming a binodal 5,5-connected 43.66.8 net. Compound [Mn(H2L)(DMA)(H2O)]·(DMA)(H2O), 4, is a two-dimensional (2D) layered structure made of 4-connecting mononuclear Mn atoms and half-deprotonated L ligands. N2 gas adsorption measurements at 77 K showed that compounds 1, 2, and 4 possess permanent porosities.

Displacement Reaction Using Ibuprofen in a Mixture of Bioactive Imidazole Derivative and Bovine Serum Albumin—a Fluorescence Quenching Study

The mutual interaction of imidazole derivative (PIPP) with bovine serum albumin (BSA) was investigated using photoluminescent studies. The fluorescence quenching mechanism of BSA by PIPP was analyzed and the binding constant was calculated. The binding distance between PIPP and BSA was obtained based on the theory of Forester's non-radiation energy transfer. Displacement experiments were performed by using ibuprofen to identify PIPP binding site in BSA. The effect of some common ions on the binding constant between PIPP and BSA was also examined.

Optical absorption and photoluminescent studies of cerium-doped cobalt tungstate nanomaterials

This paper deals with optical absorption and photoluminescence properties of nanorange (22–65 nm) luminescent materials Co1−xCexWO4 (where x = 0.01, 0.015, 0.02, 0.025 and 0.03) sintered in air at various temperatures. These compounds were prepared by the solution-based co-precipitation method and characterized by x-ray powder diffraction and thermal analysis. Optimum conditions for high luminescence emission were obtained.