A novel blue-emitting Ir(III) complex with short excited state lifetime: Synthesis,structure, photophysical property,and electrophosphorescence performance

In this paper, we synthesize a triphenylamine-derived cyclometalating ligand of (4-benzothiazol-2-yl-phenyl)-diphenyl-amine (referred as BPDA) and its corresponding Ir(III) complex of (BPDA)₂Ir(acac) (acac=acetylacetone). The photophysical property, molecular structure, thermal property and electroluminescence performance of (BPDA)₂Ir(acac) are investigated in detail. It is found that (BPDA)₂Ir(acac) is an efficient emitter with high thermal stability and short excited state lifetime. The emission of (BPDA)₂Ir(acac) changes from deep blue (417 nm) to bluish green (500 nm) upon addition of different solvents. We also investigate its electrophosphorescence performance. A maximum electroluminance of 8820 cd/m² peaking at 494 nm is achieved, with the highest device efficiency of 1.72 cd/A.     

Synthesis and photophysics of a new deep red soluble phosphorescent iridium(III) complex based on chlorine-methyl-substituted 2,4 diphenyl quinoline

A new iridium complex with a chlorine-methyl-substituted 2,4 diphenyl quinoline, (Cl-MDPQ) ligand has been synthesized. The synthesized iridium metal complex, Ir(Cl-MDPQ)₂(acac) where Cl-MDPQ=chlorine-methyl substituted, 2,4 diphenyl quinoline, acac=acetyl acetone is characterized by employing different techniques such as mass spectrometry, ¹H NMR, DTA/TGA, XRD, and FTIR. The molecular structures of Cl-MDPQ and Ir(Cl-MDPQ)₂(acac) complexes are confirmed by the FTIR spectra. Strong singlet metal-to-ligand charge-transfer (¹MLCT) and triplet metal-to-ligand charge-transfer (³MLCT) absorption peaks at 353 and 437 nm in tetrahydrofuran (THF) are reported in the synthesized complex, respectively. A deep red emitting Ir(Cl-MDPQ)₂(acac) complex at 662 nm is promising for flexible organic devices.     

Mono(pyridine-N-oxide) analog of DOTA as a suitable organic reagent for a sensitive and selective fluorimetric determination of Ln(III) ions

The mono(pyridine-N-oxide) analog of the H₄dota macrocylic ligand, H₃do3a-py^NO, is capable of forming thermodynamically stable and kinetically inert Ln(III) complexes. Its Eu(III) and Tb(III) complexes display a strong long-lived fluorescence as a result of the antenna effect of the pyridine-N-oxide fluorophore in the reagent. It is shown that H₃do3a-py^NO can be used as a fluorogenic reagent for the determination of Eu(III) and Tb(III) at pH 6.5 and c_L=1 mM. At an excitation wavelength of 286 nm, the emission maxima are 615 nm (Eu(III)-complex), and 547 nm (Tb(III)complex). Detection limits are at concentrations around 1.0 μM and linearity of the method spans over 2 orders of magnitude. The method was applied to artificial and real samples (spiked mineral waters, extracts from cathode ray tube luminophore dust) and gave satisfactory results. The method is simple, rapid, and hardly interfered by other metal ions.     

Evidence for Strong Mixing Between the LC and MLCT Excited States in Some Heteroleptic Iridium (III) Complexes

The synthesis, structure and photophysical properties of series of new luminescent cyclometalated Iridium (III) complexes are reported. The cyclometalated ligand used here is 2-aryl imidazole and the auxiliary ligand is acetyl acetone (acac). The crystal structure of the complex (dmdpi)₂Ir(acac) (5) show that the Iridium(III) ion resides in a distorted octahedral environment. All complexes exhibit bright photoluminescence (PL) at room temperature and (fpdmdmpi)₂Ir(acac) 4 has a high solution PL quantum efficiency of 0.56. The role played by electron releasing and electron withdrawing substituents of the 2-arylimidazole ligands towards the stability of HOMO and how the substituent influences the luminescent behaviour are discussed. Furthermore those substituents have effect on the contribution to mixing between ³(π-π*) and ³(MLCT) for the lowest excited states.     

Synthesis, Crystal Structure and Photoluminescence of a Cyclometalated Iridium(III) Coumarin Complex

In this paper a new cyclometalated iridium(III) coumarin complex, Ir(III)bis(3-(2-benzothiazolyl)coumarinato N,C⁴)(acetylacetonate) (Ir(L)₂(acac)), was synthesized and characterized. X-ray crystallography demonstrated that the iridium(III) ion is hexacoordinated by two C atoms and two N atoms from 3-(2-benzothiazolyl)coumarinato ligands and two O atoms from acac ligand, displaying distorted octahedral coordination geometry. The Ir(L)₂(acac) complex has good thermal stability with less than 2 % weight-reduction occurring at 300 °C, and exhibits strong reddish orange emission. The results shown that Ir(L)₂(acac) is useful for fabrication organic light-emitting diodes.     

Microwave Assisted Synthesis of a New Triplet Iridium(III) Pyrazine Complex

采用微波辅助加热方法,2,3-二苯基吡嗪(DPP)与水合三氯化铱(IrCl₃·3H₂O)反应制备了[Ir(DPP)₃],通过¹H NMR、元素分析和质谱方法对配合物结构进行了表征,并研究了配合物的吸收光谱和光致发光光谱. 结果表明,配合物Ir(DPP)₃在382和504 nm处存在单重态¹MLCT(金属到配体的电荷跃迁)和三重态³MLCT的吸收;在573 nm 处有较强的金属配合物三重态的磷光发射.     

Synthesis and characterization of phosphorescent iridium complexes of 6-chloro-3-phenylpyridazine and 3-chloro-6-(3′-methoxy-phenyl)-4-methyl-pyridazine

The preparation and photophysics of organometallic Ir(III) complexes with 3-phenylpyridazine (H6Clppdz) and its derivative are reported. IrCl₃ · nH₂O reacts with H6Clppdz, and 3-chloro-6-(3^′-methoxyphenyl)-4-methyl-pyridazine (MCOMppdz) to give the corresponding chloride-bridged dimers, (6Clppdz)₂Ir(μ-Cl)₂Ir(6Clppdz)₂ and (MCOMppdz)₂Ir(μ-Cl)₂Ir(MCOMppdz)₂ in good yields. These chloride-bridged dimers are cleaved with 2-pyrazinecarboxylic acid (Hpyzc), 2-picolinic acid (Hpic), acetylacetone (Hacac), and 2,2,6,6-tetramethyl-3,5-heptanedione (Htmd) to give the corresponding monomer, (6Clppdz)₂Ir(pyzc), (6Clppdz)₂Ir(pic), (6Clppdz)₂Ir(acac), (6Clppdz)₂Ir(tmd), (MCOMppdz)₂Ir(acac), and (MCOMppdz)₂Ir(tmd), respectively. The complexes show bright orange to red luminescence at room temperature and the emission wavelenghts are affected by the ancillary ligands as well as cyclometalating ligands (593–664 nm).     

An organic electrophosphorescent device driven by all-organic thin-film transistor using photoacryl as a gate insulator

Organic electrophosphorescent devices have been intensively investigated for using in full-color flat-panel display. Since the quantum efficiency of electrophosphorescent device decreases rapidly as the luminance increases, it is desirable to operate the electrophosphorescent display with active matrix rather than passive matrix. Here we report the study of driving electrophosphorescent diode with all-organic TFT. We obtained the maximum power luminance that was obtained about 90 cd/m². Turn-on voltage is approximately 10 V. Field effect mobility, threshold voltage, and on–off current ratio in 0.5-μm thick gate dielectric layer were 0.13 cm²/V s, −7 V, and 10⁶ A/A. The structure of electrophosphorescent diode is ITO/TPD/BCP:Ir(ppy)₃/BCP/Alq₃/Li:Al/Al. In organic TFT, photoacryl is used as an insulator and pentacene as an active layer.     

A study on the characteristics of OLEDs using Ir complex for blue phosphorescence

Several iridium-based complexes were investigated as phosphorescent dopants. They achieved about 100% internal quantum efficiency, due to utilization of both singlet and triplet excitons in the radiative processes. We have fabricated phosphorescent OLEDs with 8% Ir(ppz)₃ as a triplet emissive dopant in various host materials. CBP, which has an efficiency of 0.20 cd/A, is the best host material. Furthermore, we synthesized metal-organic phosphor complexes based on Ir with different ligands as to (Im)₂Ir(acac), (Im-R)₂Ir(acac), and Ir(ppz)₂(acac).     

Photoluminescence characterization of a novel red-emitting phosphor In2(MoO4)3:Eu3+ for white light emitting diodes

The red-emitting phosphor In₂(MoO₄)₃:Eu³⁺ with cubic crystal structure was synthesized by a conventional solid-state reaction technique and its photoluminescence properties were investigated. The prepared phosphor can be efficiently excited by ultraviolet (395 nm) and blue (466 nm) light. The emission spectra of the phosphor manifest intensive red-emitting lines at 612 nm due to the electric dipole ⁵D₀→⁷F₂ transitions of Eu³⁺. The chromaticity coordinates of x=0.63, y=0.35 (λ_ex=395 nm) and x=0.60, y=0.38 (λ_ex=466 nm) are close to the standard of National Television Standard Committee values (NTSC) values. The concentration quenching of In₂(MoO₄)₃:Eu³⁺ is 40 mol% and the concentration self-quenching mechanism under 466 nm excitation was the dd intereaction. As a result of the strong emission intensity and good excitation, the phosphor In₂(MoO₄)₃:Eu³⁺ is regarded as a promising red-emitting conversion material for white LEDs.     

An organic electroluminescent device made from a gadolinium complex

A gadolinium ternary complex, tris(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) (phenanthroline) gadolinium [Gd(PMIP)₃(Phen)] was synthesized and used as a light emitting material in the organic electroluminescent (EL) devices. The triple layer device with a structure of indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) (20 nm)/Gd(PMIP)₃(Phen) (80 nm)/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (bathocuproine or BCP) (20 nm)/Mg: Ag(200 nm)/Ag(100 nm) exhibited green emission peaking at 535 nm. A maximum luminance of 230 cd/m² at 17 V and a peak power efficiency of 0.02 lm/w at 9 V were obtained.     

Phosphorescent iridium(III) complexes with hetero (C ˆN) ligands

In order to improve luminescence efficiency, it is necessary to design a phosphorescent material which is capable of transferring the excited energy without triplet–triplet (T–T) annihilation. For this purpose, new types of metal complexes were designed with different species of (C ˆN) ligands. Herein, Ir(ppy)₂(piq), Ir(ppy)₂(piq-F) and Ir(ppy)₂(piq-CF₃) were designed and prepared, where ppy, piq, piq-F and piq-CF₃ represent 2-phenylpyridine, 1-(phenyl)isoquinoline, 1-(4′-fluorophenyl)isoquinoline and 1-(4′-trifluoromethylphenyl)isoquinoline, respectively. These Ir(III) complexes having two different ligands (hetero-Ir complexes) are expected to have a high luminescence efficiency by intramolecular energy transfer from the energy absorbing ligand to the luminescent ligand leading to a decrease in quenching or energy deactivation. To compare luminescent characteristics of these hetero-Ir complexes, homo-Ir complexes Ir(ppy)₃, Ir(piq)₃, Ir(piq-F)₃ and Ir(piq-CF₃)₃ were prepared and investigated photophysically.     

Synthesis,photoluminescence and intramolecular energy transfer model of a dysprosium complex

The energy of the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as their energy gaps, and the singlet and triplet state energy levels of 4-benzoylbenzoic acid (HL=4-BBA) and triphenylphosphine oxide (TPPO) were calculated with the Gaussian03 program package. The singlet state and triplet state energy levels were also estimated from the UV–vis absorption spectra and phosphorescence spectra. The results suggest that the calculated values approximately coincided with the experimental values. A Dy(III) complex was synthesized with 4-BBA as primary ligand and TPPO as neutral ligand. The structure of the complex was characterized by elemental analysis, ¹H NMR spectrometry, and FTIR spectrometry. TG–DTG analysis indicates that the complex kept stable up to 305 °C. The photoluminescence properties were studied by fluorescence spectrometry. The results show that Dy(III) ion sensitized by 4-BBA and TPPO emitted characteristic peaks at 572 nm (⁴F_9/2–⁶H_13/2) and 480 nm (⁴F_9/2–⁶H_15/2), and its Commission Internationale de L'Eclairge coordinates were calculated as x=0.33 and y=0.38, being located in the white range. Intermolecular energy transfer process was discussed and energy transfer model was also proposed.     

Spectral structure of barium–phosphate–silicate phosphor Ba10(PO4)4(SiO4)2:EuM+

The new apatite–silicate phosphor doped with Eu ions in Ba₁₀(PO₄)₄(SiO₄)₂ matrix was synthesized through solid-state reaction. It was found that the as-synthesized phosphor displayed apparent mixture of band and line emission peaks giving rise to pseudo white light. The narrow emission bands peaking at 410 nm can be assigned to the 4f⁶5d→4f⁷(⁸S_7/2) transition of Eu²⁺ ions, and the other band at 507 nm is ascribed to anomalous fluorescent emission. One group of line emission peaking at 595 nm and 613 m were due to the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The occurrence of photostimulated luminescence and discrete emission lines in violet (410 nm), green (507 nm) and red (595 nm and 613 nm) colors indicate that this material has potential application in fields of white-light-emitting.     

Structural,optical and electrical properties of europium picrate tetraethylene glycol complex as emissive material for OLED

A new europium complex [Eu(Pic)₂(H₂O)(EO4)](Pic)·0.75H₂O was synthesized and used as the emission material for the single layer device structure of ITO/EO4–Eu–Pic/Al, using a spin-coating technique. Study on the optical properties of the [Eu(Pic)₂(H₂O)(EO4)](Pic)·0.75H₂O complex where EO4=tetraethylene glycol and Pic=picrate anion, had to be undertaken before being applicable to the study of an organic light emitting diode (OLED). The electrical property of an OLED using current–voltage (I–V) measurement was also studied. In complex, the Eu(III) ion was coordinated with the EO4 ligand as a pentadentate mode, one water molecule, and with two Pic anions as bidentate and monodentate modes, forming a nine-coordination number. The photoluminescence (PL) spectra of the crystalline complex in the solid state and its thin film showed a hypersensitive peak at 613.5–614.9 nm that assigned to the ⁵D₀→⁷F₂ transition. A narrow band emission from the thin film EO4–Eu–Pic was obtained. The typical semiconductor I–V curve of device ITO/EO4–Eu–Pic/Al showed the threshold and turn on voltages at 1.08 and 4.6 V, respectively. The energy transfer process from the ligand to the Eu(III) ion was discussed by investigating the excitation and PL characteristics. Effect of the picrate anion on the device performance was also studied.     

Efficient red light phosphorescence emission in simple bi-layered structure organic devices with fluorescent host-phosphorescent guest system

Highly efficient red phosphorescent devices comprising a simple bi-layered structure using tris(1-phenylisoquinoline)iridium (Ir(piq)₃) doped in a narrow band-gap fluorescent host material, bis(10-hydroxybenzo [h] quinolinato)beryllium complex (Bebq₂) are reported. The driving voltage to reach 1000 cd/m² is 3.5 V in Bebq₂:Ir(piq)₃ red phosphorescent device. With a dopant concentration of as low as 4%, the current and power efficiency values of 8.41 cd/A and 7.34 lm/W are obtained in this PHOLEDs, respectively. External quantum efficiency (EQE) of 14.5% is noticed in this red phosphorescent device, promising to high brightness applications.     

Synthesis and photoluminescence properties of YVO4:Eu3+, Al3+ phosphor

The Y_0.95?xAl_xVO₄:5%Eu³⁺ (0≤x≤0.1) phosphors were successfully synthesized by solid state reaction at 900 °C for 6 h, and their luminescence properties were investigated under UV and VUV excitation. Monitoring at 619 nm, a strong broad absorption was enhanced by co-doping of Al³⁺ into the YVO₄:Eu³⁺ lattices at 256 nm under UV excitation. The VUV excitation spectra also showed the enhanced excitation bands at about 156 and 200 nm. Under 254 or 147 nm excitation, it was found that Y_0.95?xAl_xVO₄:Eu³⁺(0≤x≤0.1) phosphors showed strong red emission at about 619 nm corresponding to the electric dipole ⁵D₀^–7F₂ transition of Eu³⁺. The improvement of luminescence intensity of YVO₄:Eu³⁺ was also observed after partial substituting Y³⁺ by Al³⁺ and the optimal luminescence intensity appeared with incorporation of 2.5 mol% Al³⁺.     

Surface oxides of Ir(111) prepared by gas-phase oxygen atoms

The Ir(111) surface is oxidized with gas-phase oxygen atoms under vacuum condition to achieve an oxidation level beyond its saturation coverage for chemisorption. Two surface oxides, rutile IrO₂ of (100) domain and corundum Ir₂O₃ of (001) domain, have been grown at 550 K with different oxygen exposure of 3.6 × 10⁵ L and 7.2 × 10⁵ L respectively. The temperature programmed desorption (TPD) experiment of rutile IrO₂(100) shows its desorption curve (at 4 K s^? 1) peaks at 750 K, followed by a long tail of less pronounced desorption features. On the other hand, TPD of corundum Ir₂O₃(001) displays a symmetric trace, peaking at 880 K. Carbon monoxide titration experiments show that adsorbed CO reduces corundum Ir₂O₃(001) at 400 K, but CO does not adsorb on rutile IrO₂(100) and no reduction reaction occurs. Evidently, among the two surface oxides, corundum Ir₂O₃(001) involves in catalysis of carbon monoxide oxidation, while rutile IrO₂(100) does not. The formation of two surface oxides is also compared, we conclude that the atom arrangement favors Ir₂O₃(001) at the oxide/metal interface.     

Upconversion photoluminescence properties of SrY2(MoO4)4:Er3+/Yb3+ phosphors synthesized by a cyclic microwave-modified sol–gel method

SrY_2−x(MoO₄)₄:Er³⁺/Yb³ phosphors with doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2 and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by a cyclic microwave-modified sol–gel method, and the upconversion photoluminescence properties have been investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of 1–3 μm. Under excitation at 980 nm, SrY₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited a strong 525-nm, weak 550-nm emission bands in the green region, and a very weak 655-nm emission band in the red region. The possible mechanism of the green and red emissions was discussed in detail under consideration of a two-photon process. The Raman spectra of the particles indicated the presence of strong peaks at both higher and lower frequencies.     

Luminescence properties of Eu3+ and Sm3+ coactivated Gd(III) tungstate phosphor for light-emitting diodes

Rare-earth ions coactivated red phosphors Gd_0.2RE_1.8(WO₄)₃ (RE=Eu³⁺ and Sm³⁺) were synthesized by conventional solid-state reaction using boric acid as a flux agent. The samples were characterized by X-ray diffractometer (XRD), energy-dispersive X-ray spectrometer (EDS) and luminescence spectrometer (LS). The results showed that the Eu–Sm system exhibits higher emission intensity than those of the Eu single-doped system and Sm separate-doped system under ultraviolet (UV) radiation. Samarium(III) ions are effective in broadening and strengthened absorptions around 400 nm. Furthermore, it exhibits enhanced luminescence emission. when the mole ratio of boric acid is about 0.16, the luminescence capability is optimum. Two strongest lines at ultraviolet (394 nm) and blue (465 nm) in excitation spectra of these phosphors match well with the output wavelengths of UV and blue GaN-based light-emitting diodes (LEDs) chips.