Synthesis and Photophysical Properties of Ternary β-Diketonate Europium(III) Complexes Incorporating Bipyridine and its Derivatives

Two new octa-coordinated ternary europium(III) complexes of the type [Eu(btfa)3(Br2-bpy)] (Eu-1) and [Eu(btfa)3(PhE2-bpy)] (Eu-2) (where btfa = 4,4,4-trifluoro-1-phenyl-1,3-butanedione, Br2-bpy = 5,5'-dibromo-2,2'-bipyridine, PhE2-bpy 5,5'-bis(phenylethynyl)-2,2'-bipyridine) together with a previously reported complex [Eu(btfa)3(bpy)] (Eu-3) have been synthesized. The complexes have been characterized by analytical and spectroscopic methods. The photophysical properties of the complexes have also been analyzed both experimentally and theoretically. The contribution of each ligand to the sensitized Eu(III) photoluminescence (PL) has been analyzed and is discussed. An energy transfer (ET) mechanism is proposed and discussed for the sensitized Eu(III) emission using experimental and theoretical data. The Eu(III) complex incorporating the parent bpy showed impressive performance as a double-emitting layer (EML) red organic light emitting diodes (R-OLEDs)

Single component white-OLEDs derived from tris(β-diketonato) europium(iii) complexes bearing the large bite angle N^N 2-(4-thiazolyl)benzimidazole ligand

Two new organo-europium complexes (OEuCs) [Eu(tfac)3(TB-Im)] (Eu1) [Eu(hfac)3(TB-Im)] (Eu2) incorporating fluorinated (hexafluoroacetylacetone; Hhfaa) or hemi-fluorinated (trifluoroacetylacetone; Htfac) β-diketones together with the large bite angle N^N ligand (2-(4-thiazolyl)benzimidazole; TB-Im) have been synthesized and characterized. The structure of the complexes has been established by single crystal X-ray diffraction (SC-XRD) analysis and shows that the coordination sphere is composed of a EuO6N2 core (octacoordinated). Continuous shape measures (CShMs) revealed that the geometry around Eu(III) is trigonal dodecahedral with approximate D2d-symmetry. Efficient red emission is observed for both the complexes in solution with a fairly large photoluminescence quantum yield (PLQY (QLEu) = 39.00–47.00%). Furthermore, by utilizing the experimental photoluminescence (PL) data and theoretical modelling employing density functional theory (DFT) in conjunction with LUMPAC, energy transfer (ET) and back energy transfer rates were calculated, and an ET mechanism for the sensitized PL is proposed and discussed in detail. Finally, the complexes were used as an emitting layer (EML) to fabricate 20 organic light emitting diodes (OLEDs) by varying the doping concentration. Interestingly, both the complex-based OLEDs at 4 wt% doping concentration display white electroluminescence (EL) with the brightness (B) = 100.5–364.1 cd m−2 at very low turn-on voltage (Vturn-on) = 3.9–4.6 V. The overall electroluminescence performance of Eu1 and Eu2 is higher than that of the reported europium based single component white-OLEDs

Bimetallic Pt(II)-bipyridyl-diacetylide/Ln(III) tris-diketonate adducts based on a combination of coordinate bonding and hydrogen bonding between the metal fragments: syntheses, structures and photophysical properties

The luminescent Pt(II) complex [Pt(4,4'-Bu-t(2)-bipy){CC-(5-pyrimidinyl)}(2)] (1) was prepared by coupling of [Pt(4,4'-Bu-t(2)-bipy)Cl-2] with 5-ethynyl-pyrimidine, and contains two pyrimidinyl units pendant from a Pt(H) bipyridyl diacetylide core; it shows luminescence at 520 nm which is typical of Pt(II) luminophores of this type. Reaction with [Ln(hfac)(3)(H2O)(2)] (hfac = anion of hexafluoroacetylacetone) affords as crystalline solids the compounds [1 center dot {Ln(hfac)(3)(H2O)}{Ln(hfac)(3)(H2O)(2)}] (Ln = Nd, Gd, Er, Yb), in which the {Ln(hfac)(3)(H2O)} unit is coordinated to one pyrimidine ring via an N atom, whereas the {Ln(hfac)(3)(H2O)(2)} unit is associated with two N atoms, one from each pyrimidine ring of 1, via N center dot center dot center dot HOH hydrogen-bonding interactions involving the coordinated water ligands on the lanthanide centre. Solution spectroscopic studies show that the luminescence of 1 is partly quenched on addition of [Ln(hfac)(3)(H2O)(2)] (Ln = Er, Nd) by formation of Pt(II)/Ln(III) adducts in which Pt(II)-> Ln(III) photoinduced energy-transfer occurs to the low-lying f-f levels of the Ln(Ill) centre. Significant quenching occurs with both Er(Ill) and Nd(III) because both have several f-f states which match well the (MLCT)-M-3 emission energy of 1. Time-resolved luminescence studies show that Pt(II)-Er(III) energy-transfer (7.0 x 10(7) M-1) is around three times faster than Pt(II)-> Nd(III) energy-transfer (approximate to 2 x 10(7) M-1) over the same distance because the luminescence spectrum of l overlaps better with the absorption spectrum of Er(111) than with Nd(III). In contrast Yb(111) causes no significant quenching of 1 because it has only a single f-f excited level which is a poor energy match for the Pt(II)-based excited state

Dicopper(I) Complexes Incorporating Acetylide-functionalized Pyridinyl-based Ligands::Synthesis, Structural and Photovoltaic Studies

Heteroaryl incorporated acetylide-functionalized pyridinyl ligands (<b>L1–L6</b>) with the general formula Py-CC-Ar (Py = pyridine and Ar = <i>thiophene-2-yl</i>, 2,2′<i>-bithiophene]-5-yl</i>, 2,2′<i>:5</i>′,2″<i>-terthiophene]-5-yl</i>, <i>thieno­[2,3-<i>b</i>]­thiophen-2-yl</i>, <i>quinoline-5-yl</i>, <i>benzo­[c]­[1,2,5]­thiadiazole-5-yl</i>) have been synthesized by Pd(0)/Cu­(I)-catalyzed cross-coupling reaction of 4-ethynylpyridine and the respective heteroaryl halide. Ligands <b>L1–L6</b> were isolated in respectable yields and characterized by microanalysis, IR spectroscopy, ¹H NMR spectroscopy, and ESI-MS mass spectrometry. A series of dinuclear Cu­(I) complexes <b>1</b>–<b>10</b> have been synthesized by reacting <b>L1–L6</b> with CuI and triphenylphosphine (PPh₃) (<b>R1</b>) or with an anchored phosphine derivative, 4-(diphenylphosphino) benzoic acid (<b>R2</b>)/2-(diphenylphosphino)­benzenesulfonic acid (<b>R3</b>), in a stoichiometric ratio. The complexes are soluble in common organic solvents and have been characterized by analytical, spectroscopic, and computational methods. Single-crystal X-ray structure analysis confirmed rhomboid dimeric structures for complexes <b>1</b>, <b>2</b>, <b>4</b>, and <b>5</b>, and a polymeric structure for <b>6</b>. Complexes <b>1</b>–<b>6</b> showed oxidation potential responses close to 0.9 V vs Fc^0/+, which were chemically irreversible and are likely to be associated with multiple steps and core oxidation. Preliminary photovoltaic (PV) results of these new materials indicated moderate power conversion efficiency (PCE) in the range of 0.15–1.56% in dye-sensitized solar cells (DSSCs). The highest PCE was achieved with complex <b>10</b> bearing the sulfonic acid anchoring functionality

Synthesis and spectroscopic properties of a fluorosensor for Zn2+ ions

The new Schiff base ligand L: (E)-N'-(pyridin-2-ylmethylene)acetohydrazide, was synthesized, and its reaction with Zn(II) ions form the complex: [ZnL2](ClO4)2, as confirmed by X-ray crystallography. This complex is stable in polar and non-polar solvents as proven by NMR. A significant enhancement in the fluorescence was observed from L upon coordination to Zn(II) ions over other transition metals such as Fe(II), Co(II), Ni(II), Cu(II), Cd(II) and Ag(I). These results suggest that L can be used as a selective flourosensor for the detection of Zn(II) ions

Dioxygen Binding by Cobalt(II) Complexes of 8,8'-bis(aminomethyl)-2,2'-biquinoline

A new series of Co(II) complexes of the type CoLX2 , where Lis a tetra-dentate ligand 8,8'-bis(aminomethyl)-2,2'-biquinoline  and X= SCN–, BF4–, I– or NO3– ,  have been synthesized and characterized. The complexes have magnetic moments in the range typical of a low-spin d7 Co(II) center. The interaction of these Co(II) complexes with dioxygen was studied by E.S.R. spectroscopy. A dicobalt(III) peroxo-bridged complex was formed in DMF solution, associated with the formation of an E.S.R.-silent solution compatible with the formation of low-spin d6 Co(III) species. Similar behavior was also observed for the interaction of these Co(II) complexes with dioxygen in the presence of ancillary ligands such as pyridine and 2-methylimidazole. The dioxygen complexes proved successful as oxygen carrier oxidation catalysts for tripehnylphosphine and 2,6-bis(t-butyl)phenol