First oxadiazole-functionalized terbium(III) beta-diketonate for organic electroluminescence

Synthesis, infrared and fluorescence spectra of lanthanide complexes with a new amide-based 1,3,4-oxadiazole derivative

A new amide-based 1,3,4-oxadiazole derivative ligand 2,5-bis[2-(N,N-diethyl-1'-oxopropylamide)phenyl]-1,3,4-oxadiazole (L) and its complexes, Ln(NO3)3L (Ln=La, Eu, Gd, Tb, Er), were synthesized. The complexes were characterized by elemental analysis, infrared spectra and conductivity. The lanthanide ions were coordinated by O atoms from CO. The fluorescence properties of Eu(NO3)3L and Tb(NO3)3L in the solid state and in different solvents were investigated. Under the excitation of UV light, these complexes exhibit characteristic fluorescence of europium and terbium ions. The solvent factors influencing the fluorescent intensity were discussed.

Synthesis, Structural Characterization, and Electrophosphorescent Properties of Rhenium(I) Complexes Containing Carrier-Transporting Groups

Two novel diimine rhenium(I) carbonyl complexes with the formula [Re(CO)(3)(L)Br], where L = 1-(4-5'-phenyl-1,3,4-oxadiazolylbenzyl)-2-pyridinylbenzoimidazole (1) and 1-(4-carbazolylbutyl)-2-pyridinylbenzoimidazole (2), have been successfully synthesized and characterized by elemental analysis, (1)H NMR, and IR spectra. Their electrochemical, photophysical, and electroluminescent behaviors, along with the X-ray crystal structure analysis of 2, are also described. White electrophosphorescent devices were fabricated using 1 and 2 as emitters. The devices based on carbazole-containing (hole-transporting group) 2 with the structure ITO/m-MTDATA (30 nm)/NPB (20 nm)/2:CBP (8%, 30 nm)/Bphen (20 nm)/Alq(3) (20 nm)/LiF (0.8 nm)/Al (200 nm) exhibit Commission Internationale de L'Eclairage coordinates of x = 0.34, y = 0.33 with a maximum brightness of 2300 cd/m(2) at 580 mA/cm(2). When a brightness of 1500 cd/m(2) appears at 230 mA/cm(2), the devices based on 10 wt % 2 still possess 56% of the maximum efficiency which appeared at 2.7 mA/cm(2). These performances are among the best reported for devices using Re(I) complexes as emitters. By comparison of the electroluminescent properties of the devices based on 1 and 2, we conclude that the introduction of the carbazole group into the ligand improves the performance of 1-doped devices.

The synthesis and properties of Iridium(iii)-cored dendrimers with carbazole peripherally functionalized β-diketonato dendrons

A simple convergent synthetic approach has been developed for the synthesis of iridium(III)-cored dendrimers with carbazole peripherally functionalized beta-diketonato dendrons. The zeroth- to third-generation green-emitting dendrimers were synthesized by reacting the corresponding beta-diketonato dendrons with iridium(III) dimer under mild conditions with good yields, respectively. This approach proved to be modular, and could be used to prepare blue-green-emitting and red-emitting dendrimers with the same beta-diketonato dendrons only by using different cyclometallating ligands. The resulting dendritic ligands and iridium(III)-cored dendrimers were well characterized. Their photoluminescent properties both in solution and in the solid state were tested. It was found that all the dendrimers retained the photophysical properties of the corresponding small analogues with high emission quantum yields (0.06-0.30). Preliminary results indicated that these dendrimers functionalized carbazole units exhibited distinct light-harvesting potential, resulting in a strong intense emission from the iridium core of the dendrimers.

Lanthanide-based emitting materials in light-emitting diodes

Since the description of efficient electroluminescence from aluminium tris(hydroxyquinoline) in the mid 1980s, interest in new complexes and polymers with luminescence properties as emitting layers in light-emitting diodes has steadily increased. Recently, Ln(III) ion complexes have gained in importance for this type of application. Here we review some of the seminal work in the area, along with new developments in the field. The photophysical characterization of complexes of lanthanide ions both in solution and in the solid state allows the determination of which of the complexes might be successfully utilized as emitting layers in light-emitting diodes for display applications. However, the architecture of the device is also of major importance, to allow for good charge transport and recombination and thus obtain pure colors and high emission quantum efficiency.

Ag(I) and Cu(II) Discrete and Polymeric Complexes Based on Single- and Double-Armed Oxadiazole-Bridging Organic Clips

Four new oxadiazole-bridging ligands (L1-L4) were designed and synthesized by the reaction of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole with isonicotinoyl chloride and nicotinoyl chloride, respectively. L1 and L3 are unsymmetric single-armed ligands (4- or 3-pyridinecarboxylate arm), and L2 and L4 are symmetric double-armed ligands (4- or 3-pyridinecarboxylate arms). Nine new complexes, [Ag(L1)]PF6.CH3OH (1), [Ag(L1)]ClO4.CH3OH (2), Cu(L2)(NO3)2.2(CH2Cl2) (3), [Cu(L2)2](ClO4)2.2(CH2CCl2) (4), Cu(L2)Cl2 (5), [Cu4(L3)2(H2O)2](L3)4(ClO4)4 (6), [Ag(L4)(C2H5OH)]ClO4 (7), [Ag(L4)(C2H5OH)]BF4 (8), and [Ag(L4)(CH3OH)]SO3CF3 (9), were isolated from the solution reactions based on these four new ligands, respectively. L1, L2, and L3 act as convergent ligands and bind metal ions into discrete molecular complexes. In contrast, L4 exhibits a divergent spacer to link metal ions into one-dimensional coordination polymers. New coordination compounds were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the luminescent and electrical conductive properties of these new compounds were investigated.

Polyaryl Ether Dendrimer with a 4-Phenylacetyl-5-pyrazolone-based Terbium(III) Complex as Core: Synthesis and Photopysical Properties

A series of novel dendritic beta-diketone ligands, 1-phenyl-3-[G-n]-4-phenylacetyl-5-pyrazolone (n = 0-3, G stands for polyaryl ether), were synthesized by introducing Fréchet-type dendritic branches. The corresponding Tb3+-cored dendritic complexes were characterized by X-ray crystallography, elemental analysis, ESI mass spectra, and FT-IR spectra. These dendritic complexes, prepared from aqueous solution, exhibit high stability. Interestingly, the study of photophysical properties shows that the luminescence quantum yields of the dendritic Tb-complexes increase from 0.1 to 2.26% with an increase of the dendritic generation from 0 to 3. Importantly, an "energy-reservoir effect" was observed in the dendritic system using the method based on the resonance energy transfer from these complexes to rhodamine 6G. With the increase of the dendritic generation, the metal-centered luminescence quantum yield was almost the same, and the energy transfer (phi(transfer)) from the ligand to Tb(3+) increased. Further measurements of the triplet state and oxygen quenching of these dendritic complexes verify that this enhancement of the energy transfer (phi(transfer)) is attributed to both an "antenna effect" and a "shell effect".

Silver(I) Coordination Polymers Based on A Nano-Sized Bent Bis(3-acetylenylphenyl-(4-cyanophenyl))oxadiazole Ligand: The Role of Ligand Isomerism and the Templating Effect of Polyatomic Anions and Solvent Intermediates

One nanosized oxadiazole bridging ligand, bis(3-acetylenylphenyl-(4-cyanophenyl))oxadiazole (L11), was designed and synthesized by the reaction of bis(3-iodophenyl)oxadiazole with 4-cyanophenylacetylene via a Sonogashira-Hagihara cross-coupling reaction. Eight Ag(I)-L11 coordination polymers with one-, two-, or three-dimensional structures have been successfully prepared by the reaction of L11 with various Ag(I) salts in solution. New coordination polymers were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. All new complexes contain silver heteroatom cluster-connecting nodes, and the L11 ligand is "doubling up" in the frameworks. In this Ag(I)-L11 system, the conformation of L11 is versatile because of the conformational rotation around the central oxadiazole moiety and depends greatly on the counterion and solvent system used in the formation of the complexes. In addition, the luminescence property and host-guest chemistry of some complexes were investigated primarily.

Di- and Tetranuclear Metal Complexes with Phenoxo Bridges: Synthesis, Structures, and Photoluminescent and Electroluminescent Properties

Dinuclear and tetranuclear copper 2,6-bis(2-hydroxyphenyl)pyridine (H(2)L) complexes Cu2(L)2(py)2 (1) and Cu4(L)4(DMF) (2) were synthesized. The complexes 1 and 2 were characterized by elemental analyses, mass spectrometry, and single-crystal X-ray diffraction analyses. 1 crystallizes in the monoclinic space group P2(1)/n with a = 13.330(2) Angstroms, b = 9.361(1) Angstroms, c = 14.676(1) Angstroms, beta = 100.94(1) degrees, V = 1798.1(3) Angstroms(3), and Z = 2. 2 crystallizes in the monoclinic space group P2(1)/n with a = 13.360(1) Angstroms, b = 14.884(1) Angstroms, c = 15.462(2) Angstroms, beta = 97.50(4) degrees, V = 3048.4(1) Angstroms(3), and Z = 2. Tetranuclear zinc complex Zn4(L)4(py)4 (3) was prepared and characterized by X-ray diffraction. 3 crystallizes in the triclinic space group P with a = 13.770(1) Angstroms, b = 15.465(1) A, c = 16.409(2) Angstroms, alpha = 88.877(9) degrees, beta = 88.035(4) degrees, gamma = 82.956(3) degrees, V = 3465.6(5) Angstroms(3), and Z = 2. The di- and tetranuclear complexes 1-3contain phenoxo bridges. 1 is a dinuclear complex with two Cu(II) centers, two py ligands, and two L ligands, and each L ligand donates its pyridyl ring and one of the phenolate groups to one metal and shares the other phenolate group between both metals, affording a Cu(2)(mu-O)(2) core. 2, in contrast, is a tetranuclear complex with four Cu(II) centers and four L ligands. Two of the L ligands have the same coordination mode as 1, and the other two L ligands donate their pyridyl rings to one metal and share both phenolate groups between four metals, resulting in three four-membered Cu2(mu-O)2 rings, which joined each other and showed great distortion from planarity. 3 is a tetranuclear complex with four Zn(II) centers, four pyridine ligands, and four L ligands, and the L ligands have the same coordination modes as those of 2. Single-crystal X-ray analysis showed that hydrogen-bonding and pi-pi stacking interactions exist in complexes 1 and 2 resulting in two- and three-dimensional molecular arrangements, and the parallel arrangement of the ligand in the crystal of complex 3 resulted in a close inter- and intramolecular pi-pi interactions. Investigation of the crystals, as well as an amorphous thin film and powder of 3, by photoluminescence (PL) allowed the effect of the molecular packing on the emission properties to be elucidated. Furthermore, the electroluminescent (EL) properties of 3 were examined by fabricating a multilayer device with structure of [ITO/NPB/(ZnL)(n)/Alq3/LiF/Al] (NPB = N,N'-bis(alpha-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine, Alq3 = tris(8-hydroxyquinolinato)aluminum).

A series of luminescent lanthanide–cadmium–organic frameworks with helical channels and tubes

Lanthanide (Ln) oxides and cadmium (Cd) salts as sources of metals provided the first series of luminescent Ln-Cd-organic frameworks, [LnCd(imdc)(SO4)(H2O)3].0.5H2O (Ln = Tb, Eu, Dy, Gd, Er, Yb, Y, Nd, Pr; H3imdc = 4,5-imidazoledicarboxylic acid), in which the Ln atoms are linked by imdc ligands with skew coordination orientation, resulting in novel hetero-metallic-organic frameworks with left-/right-handed helical tubes (L1/R1) and channels (L2/R2) along the b axis.

Tuning the Triplet Energy Levels of Pyrazolone Ligands to Match the 5D0 Level of Europium(III)

Three pyrazolone-based ligands, namely 1-phenyl-3-methyl-4-(1-naphthoyl)-5-pyrazolone (HL1), 1-phenyl-3-methyl-4-(4-dimethylaminobenzoyl)-5-pyrazolone (HL2), and 1-phenyl-3-methyl-4-(4-cyanobenzoyl)-5-pyrazolone (HL3), were synthesized by introducing electron-poor or electron-rich aryl substituents at the 4-position of the pyrazolone ring. Their corresponding europium complexes Eu(LX)3(H2O)2 and Eu(LX)3(TPPO)(H2O) (X = 1-3) were characterized by photophysical studies. The characteristic Eu(III) emission of these complexes with at most 9.2 x 10(-3) of fluorescent quantum yield was observed at room temperature. The results show that the modification of ligands tunes the triplet energy levels of three pyrazolone-based ligands to match the 5D0 energy level of Eu3+ properly and improves the energy transfer efficiency from antenna to Eu3+, therefore enhancing the Eu(III) emission intensity. The highest energy transfer efficiency and probability of lanthanide emission of Eu(L1)3(H2O)2 are 35.1% and 2.6%, respectively, which opens up broad prospects for improving luminescent properties of Eu(III) complexes by the modification of ligands. Furthermore, the electroluminescent properties of Eu(L1)3(TPPO)(H2O) were also investigated.

Organometallic Coordination Polymers Generated from Bent Bis(acetylenylphenyl)oxadiazole Ligands and Ag(I) Salts

Two new bent oxadiazole bridging benzoacetylene ligands 2,5-bis(4-ethynylphenyl)-1,3,4-oxadiazole (L9) and 2,5-bis(3-ethynylphenyl)-1,3,4-oxadiazole (L10) were synthesized. The coordination chemistry of them with various inorganic Ag(I) salts has been investigated. Seven new coordination polymers were prepared by solution reactions and fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. [Ag2(L9)](SO3CF3)2 (1) (triclinic, P; a =10.292(4), b = 10.794(4), c = 11.399(5) A; alpha = 98.894(5), beta = 102.360(6), gamma = 90.319(5) degrees ; Z = 2), [Ag(L9)]SbF6 (2) (orthorhombic, Cmca; a = 19.059(9), b = 12.922(6), c = 15.609(7) A; Z = 8), [Ag(L9)]BF4 (3) (orthorhombic, Cmca; a = 19.128(3), b = 12.6042(18), c = 28.003(4) A; Z = 16), [Ag(L9)]ClO4 (4) (monoclinic, P2(1)/c; a = 8.5153(16), b = 19.722(4), c = 10.320(2) A; beta = 105.307(3) degrees ; Z = 4), [Ag(L10)]SO3CF3 (5) (triclinic, P; a = 9.0605(13), b = 10.4956(15), c = 10.8085(16) A; alpha = 101.666(2), beta = 109.269(2), gamma = 100.944(2) degrees ; Z = 2), [Ag(L10)(H2O)(0.5)]BF4.0.5H2O (6) (monoclinic, C2/m; a = 32.180(6), b = 17.027(3), c = 8.1453(15) A; beta = 102.541(3) degrees ; Z = 8), and {[Ag2(L10)2(H2O)](ClO4)2}.o-xylene (7) (monoclinic, P2(1)/c; a = 8.1460(10), b = 17.326(2), c = 30.345(4) A; beta = 97.71 degrees ; Z = 4) were obtained by the combination of L9 and L10 with various Ag(I) salts in a benzene/methylene chloride mixed solvent system. In addition, the luminescent and electrical conductive properties of these new compounds were investigated.

Efficient electroluminescence from new lanthanide (Eu3+, Sm3+) complexes

The syntheses, structures, and electroluminescent properties are described for two new lanthanide complexes Ln(HFNH)3phen [HFNH = 4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)hexane-1,3-dione; phen = 1,10-phenanthroline; Ln = Eu3+ (1), Sm3+ (2)]. Both complexes exhibit bright photoluminescence at room temperature (RT) due to the characteristic emission of Eu3+ and Sm3+ ion. Several devices using the two complexes as emitters were fabricated. The performances of these devices are among the best reported for devices using europium complex and samarium complex as emitters. The device based on 1 with the structure ITO/TPD (50 nm)/1:CBP (10%, 40 nm)/BCP (20 nm)/AlQ (30 nm)/LiF (1 nm)/Al (200 nm) exhibits the maximum brightness of 957 cd/m2, current efficiency of 4.14 cd/A, and power efficiency of 2.28 lm/W with a pure red Eu3+ ion emission. Especially, at the high brightness of 200 cd/m2, the device of 1 still has a high current efficiency of 2.15 cd/A. The device of 2 with a three-layer structure of ITO/TPD (50 nm)/2 (50 nm)/BCP (20 nm)/LiF (1 nm)/Al (200 nm) gives the maximum brightness of 42 cd/m2, current efficiency of 0.18 cd/A. By the comparison of the electroluminescent properties of devices based on Eu(TTA3phen (TTA = 2-thenoyltrifluoroacteonate) and 1, we conclude that the polyfluoration on the alkyl group of the ligand and the introduction of the long conjugate naphthyl group into the ligand improve the efficiency of 1-doped devices, especially at high current densities.

Organometallic Silver(I) Supramolecular Complexes Generated from Multidentate Furan-Containing Symmetric and Unsymmetric Fulvene Ligands and Silver(I) Salts

One new conjugated symmetric fulvene ligand L1 and two new unsymmetric fulvene ligands L2 and L3 were synthesized. Five new supramolecular complexes, namely Ag2(L1)3(SO3CF3)3 (1) (1, monoclinic, P2(1)/c; a = 12.702(3) A, b = 26.118(7) A, c = 13.998(4) A, beta = 96.063(4) degrees, Z = 4), [Ag(L1)]ClO4 (2) (monoclinic, C2/c; a = 17.363(2) A, b = 13.2794(18) A, c = 13.4884(18) A, beta = 100.292(2) degrees, Z = 8), [Ag(L1)(C6H6)SbF6] x 0.5C6H6 x H2O (3) (monoclinic, P2(1)/c; a = 6.8839(11) A, b = 20.242(3) A, c = 18.934(3) A, beta = 91.994(3) degrees, Z = 4), Ag(L2)(SO3CF3) (4) (triclinic, P1; a = 8.629(3) A, b = 10.915(3) A, c = 11.178(3) A, alpha = 100.978(4) degrees, beta = 91.994(3) degrees, gamma = 105.652(4) degrees, Z = 2), and Ag(L3)(H2O)(SO3CF3) (5) (triclinic, P1; a = 8.914(5) A, b = 10.809(6) A, c = 11.283(6) A, alpha = 69.255(8) degrees, beta = 87.163(9) degrees, gamma = 84.993(8) degrees, Z = 2) were obtained through self-assembly based on these three new fulvene ligands in a benzene/toluene mixed-solvent system. Compounds 1-5 have been fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The results indicate that the coordination chemistry of new fulvene ligands is versatile. They can adopt either cis- or trans-conformation to bind soft acid Ag(I) ion through not only the terminal -CN and furan functional groups but also the fulvene carbon atoms into organometallic coordination polymers or discrete complexes. In addition, the luminescent properties of L1-L3 and their Ag(I) complexes were investigated preliminarily in EtOH and solid state.