Synthesis and photo physical study of iridium complex of new pentafluorophenyl-substituted ligands

New iridium complexes, [Ir(dpq)₂(acac), Ir(PF-dpq)₂(acac) and Ir(PF-dpq-5F)₂(acac)] (dpq = 2,4-diphenylquinoline, dpq-5F = 2-(3′-fluorophenyl)-4-phenylquinoline), PF-dpq-5F = 2-(3-fluoro-phenyl)-6-pentafluorophenyl-4-phenylquinoline and acac = acetylacetonate) have been synthesized and characterized for efficient red organic light-emitting diodes (OLEDs). In order to improve the luminescence efficiency by preventing self-quenching and to tune photoluminescence (PL) and electroluminescence (EL) spectra to a longer wavelength, dpq ligand was fluorinated by -PF and -F moieties. However, the iridium complex of PF-dpq-5F underwent a weak MLCT transition because of the weak coupling between the 5d orbital of the iridium atom and HOMO of the substituted ligand. Thus, the maximum luminous efficiencies of the device using Ir(dpq)2(acac), Ir(PF-dpq)₂(acac) and Ir(PF-dpq-5F)₂(acac) are 4.36 cd/A, 6.04 cd/A and 4.35 cd/A, respectively.     

Magneto-optical Kerr-effect studies on copper oxide thin films produced by atomic layer deposition on SiO2

This work demonstrates the sensitivity of magneto-optical Kerr-effect (MOKE) spectroscopy to ultra-thin nonmagnetic films using the example of copper oxide. The films with an effective thickness between 0.6 nm and 6 nm are produced by atomic layer deposition (ALD) on silicon oxide substrates based on the Cu(I) β-diketonate precursor [(ⁿBu₃P)₂Cu(acac)] (acac = acetylacetonate) at a process temperature of 120 °C. The copper oxide films exhibit magneto-optical activity in the spectral ranges around 2.6 eV and above 4 eV. The evolution of the spectral features as a function of the number of ALD cycles is simulated numerically using the dielectric function and the Voigt constant of Cu₂O as input parameters. The comparison between experimental and simulated MOKE spectra strengthens the conclusion drawn from spectroscopic ellipsometry studies that the thin film optical constants differ markedly from the bulk ones.     

Magnetic behavior of cobalt oxide films prepared by pulsed liquid injection chemical vapor deposition from a metal-organic precursor

Thin films of cobalt oxide were prepared by the pulsed liquid injection chemical vapor deposition technique from metal-organic precursor. By using a β-diketonate complex of cobalt, namely cobalt (II) acetylacetonate (Co(acac)₂) as the precursor, oxygen as the reactant and argon as the carrier gas, cobalt oxide films 100 nm in thick were deposited onto Si (100) substrates at 650 °C in about 40 min. According to the characterization by X-ray diffraction and atomic force microscopy, smooth and polycrystalline films, consisting exclusively of the Co₃O₄ phase, were deposited. Magnetic properties, such as saturation magnetization, the remanence, the coercivity, the squareness ratio and the switching field distribution, were extracted from the hysteresis loop. Cobalt oxide films with coercivities of 6.61 mT, squareness ratio of 0.2607 and saturation magnetization of 12.17 nA m², corresponding to a soft magnetic material, were achieved.     

Optical and structural characteristics of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films synthesized from yttrium acetylacetonate

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)₃). The decomposition of Y(acac)₃ was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)₃. The rest of the complex is then dissociated or degraded partially until Y₂O₃ is obtained in the final step with the presence of carbon related residues. Then the Y(acac)₃ was used to synthesize Y₂O₃ thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase.     

Fill factor enhancement of organic solar cells based on a wide bandgap phosphorescent material and C60

Planar heterojunction organic solar cells using wide bandgap phosphorescent material bis[2-(4-tertbutylphenyl)benzothiazolato-N,C^2'] iridium (acetylacetonate) [(t-bt)₂Ir(acac)] as electron donor and fullerene (C₆₀) as electron acceptor were fabricated. A large open circuit voltage of 0.94 V was achieved due to low highest occupied molecular orbital level of (t-bt)₂Ir(acac). The effect of different hole transport layers and substrate heating were investigated to improve fill factor. It is shown that the open circuit voltage is strongly influenced by the interface energy barrier, whereas the fill factor is mainly limited by the charge carrier transport properties in active materials. The fill factor was significantly improved by either using hole transport layer with high carrier mobility or increasing the hole mobility of (t-bt)₂Ir(acac). A power conversion efficiency of 2.10% under AM 1.5 solar illumination at an intensity of 100 mW/cm² was achieved by heating the substrate during the deposition of active materials.     

Color tuning of red phosphorescence: New iridium complexes containing fluorinated 2,3-diphenylquinoxaline ligands

The new iridium complexes containing a derivative of 2,3-diphenylquinoxaline as an emitting ligand were synthesized, and their photophysical properties were investigated. The complexes prepared in this study were bis(6-F-2,3-di(p-fluorophenyl) quinoxalinato)iridium acetylacetonate (Ir(6-F-2,3-dpqx-F₂)₂(acac)) and bis(6-F-2,3-di(p-fluorophenyl)quinoxalinato)iridium pyrazolonates (Ir(6-F-2,3-dpqx-F₂)₂(przl1) and Ir(6-F-2,3-dpqx-F₂)₂(przl2)). Their photoluminescence maxima appeared at 638, 632 and 630 nm, respectively. The electroluminescence study revealed that the CIE coordinates of the devices containing Ir(6-F-2,3-dpqx-F₂)₂(acac) and Ir(6-F-2,3-dpqx-F₂)₂(przl2) as a light-emitting dopant were (0.675, 0.313) and (0.685, 0.310), respectively, very close to those of the saturated standard red emission.     

High efficiency red organic light-emitting diodes using a phosphorescent iridium complex doped into a hole-blocking material

We demonstrate high-efficiency red electrophosphorescent organic light-emitting devices (OLEDs) by doping a red-emitting iridium complex, Bis[7-methyl-1-p- tolyisoquinolinato-N,C²′]-iridium(III)(acetylacetonate) [(7-mtiq)₂Ir(acac)], into a hole-blocking material, 4-biphenyloxolato aluminum(III)bis(2-methyl-8- quinolinato)4-phenylphenolate. Both the phosphorescent characteristics of (7-mtiq)₂Ir(acac) and the electroluminescence mechanisms of OLEDs are investigated in this study. The Commission Internationale de L'Eclairage coordinates of (0.66, 0.34) is very close to the National Television System Committee standard red point (0.66, 0.33). With a dopant concentration of about 4%, a maximum luminance of 31317 cd/m² and a luminous efficiency of 21.6 cd/A have been obtained.     

Mass spectrometric study of the thermodynamic properties of mixed-ligand Mn(III) complexes

We have synthesized Mn(thd)₃ (thd = dipivaloylmethane, or 2,2,6,6-tetramethyl-3,5-heptanedione) and evaluated its enthalpy of sublimation (89.0 ± 7.0 kJ/mol) and its saturated vapor pressure as a function of temperature from mass spectrometry data. Exchange reactions between Mn(acac)₃ (acac = acetylacetonate, or 2,4-pentanedione) and Mn(thd)₃ have been performed using an in situ technique. We have calculated the enthalpies of the exchange reactions and the enthalpies of formation of Mn(acac)₂(thd) and Mn(acac)(thd)₂ in the vapor phase: −1417.5 ± 15.0 and −1590.6 ± 15.0 kJ/mol, respectively.     

The composition,structure and electronic properties of thermally prepared iridium dioxide films

The composition, structure and electronic properties of thermally prepared iridium oxide films are studied depending on the preparation conditions, and particularly, on the composition of iridium complexes in the starting solutions of Ir chlorides. The starting solutions and the thermal treatment products of both the films and iridium hydroxides produced from Ir(IV) and Ir(III) chloride solutions were characterized. The data of IR and XPE spectroscopy, electron microscopy and diffraction analysis have shown that the films are the products of incomplete dehydration of hydrated iridium dioxide (HID) and are mixtures of phases of anhydrous crystalline IrO₂ and amorphous or crystalline HID, identical to hydroxides in composition. The different compositions of starting solutions affect the chemical composition and structure of HID, thus determining also the differences in the structure and composition of the films by the following parameters: the degree of crystallinity, the crystallites' size and orientation, the composition of the crystalline and amorphous phases, the surface area and electronic properties.     

Study on energy relation between blue and red emissive layer of organic light-emitting diodes by inserting spacer layer

In this paper, energy relation between blue emissive layer (blue-EML) and red emissive layer (red-EML) in organic light-emitting diodes based on blue-emitting and red-emitting phosphorescent dopants, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (Firpic) and bis(2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C3′)iridium(acetylacetonate) (Btp₂Ir(acac)), was studied. Two phosphorescent dopants, Firpic and Btp₂Ir(acac), were co-doped in the single emissive layer, and the results exhibit complete energy transfer from Firpic to Btp₂Ir(acac). Then, Firpic and Btp₂Ir(acac) were doped into blue-EML and red-EML, separately. By inserting 4,4′-bis(N-carbazolyl)biphenyl (CBP) spacer between blue- and red-EML, energy relation between blue- and red-EML was researched. The results of this work reveal that, CBP spacer may strengthen energy transfer between blue- and red-EML. The reason is that CBP triplets at blue-/red-EML interface can transfer their energies to both CBP molecules of red-EML and Firpic molecules of blue-EML in spacer-without devices, while CBP triplets in the spacer can transfer their energies only to CBP molecules of red-EML. Therefore, energy flow from blue- to red-EML is strengthened because of the avoidance of energy transfer from CBP triplets in the spacer to Firpic molecules of blue-EML, leading to the relative enhancement of red emission in CBP-spacer devices.     

Hafnium and zirconium tetramethylnonanedionates as new MOCVD precursors for oxide films

New bulky Zr and Hf β-diketonates (2,2,8,8-tetramethyl-4,6-nonanedionates, tmnd) were synthesized and characterized by elemental analyses, ¹H NMR, FT-IR and mass spectrometry. A volatile copper compound Cu(tmnd)₂, an intermediate product of ligand synthesis, was isolated and characterized as well. The M(tmnd)₄ (M=Zr, Hf) compounds were tested as precursors for MOCVD of ZrO₂ and HfO₂ films. Preferentially (001)/(010)/(100) textured and in-plane oriented films of monoclinic oxides have been deposited by pulsed liquid injection MOCVD on R plane sapphire. Smooth films could be grown, especially on sapphire and at low temperature (500 °C). The films on Si(100) were polycrystalline and had rougher surface. XPS study showed 3–4 and 7–8 at.% of carbon in HfO₂ and ZrO₂ films, respectively. Zr(tmnd)₄ and Hf(tmnd)₄ lead to significantly higher growth rates of ZrO₂ and HfO₂ films at low temperature than conventional Zr(thd)₄ and Hf(thd)₄ precursors (thd=2,2,6,6-tetramethyl-3,5-heptanedionate) and are attractive precursors for oxide films.     

Impedance spectroscopy measurements of charge carrier mobility in 4,4'-N,N'-dicarbazole-biphenyl thin films doped with tris(2-phenylpyridine) iridium

The charge carrier mobility of green phosphorescent emissive layers, tris(2-phenylpyridine) iridium [Ir(ppy)₃]-doped 4,4'-N,N'-dicarbazole-biphenyl (CBP) thin films, has been determined using impedance spectroscopy (IS) measurements. The theoretical basis of mobility measurement by IS rests on a theory for single-injection space-charge limited current. The hole mobilities of the Ir(ppy)₃-doped CBP thin films were measured to be 10^− 10–10^− 8 cm²V^− 1 s^− 1 in the 2–7 wt.% Ir(ppy)₃-doped CBP from the frequency dependence of both conductance and capacitance. These hole mobility values are much lower than those of the undoped CBP thin films (~ 10^− 3 cm²V^− 1 s^− 1) because the Ir(ppy)₃ molecules act as trapping centers in the CBP host matrix. These mobility measurements in the Ir(ppy)₃-doped CBP thin films provide insight into the hole injection process.     

一种新型红色磷光材料的合成及光物理性能研究

以2-甲基苯并噻唑、苯甲醛为原料,通过与三氯化铱配合,得到一种新型红色金属铱(Ⅲ) E-2-苯乙烯基苯并噻唑(SBT)乙酰丙酮(acac)配合物(SBT)2Ir(acac).通过质谱、核磁、红外光谱对其结构进行了表征,并对其光致发光性能进行了研究.研究结果表明:配合物(SBT)2 Ir(acac)在428和471nm处的紫外吸收属于单线态和三线态金属铱到配体的电荷转移吸收(1MLCT和3MLCT);在632nm处有强的金属配合物三线态磷光发射;(SBT)2Ir(acac)金属配合物的EHOMO=-4.8 eV,ELUMO=-2.5eV,磷光量子效率Φ (SBT)2Ir(acac) =0.19.(SBT)2Ir(acac)可能是一种极有潜力的电致磷光材料.     

Synthesis and luminescence of a new phosphorescent iridium(III) pyrazine complex

The synthesis and luminescent study of a new iridium pyrazine complex are reported. The iridium complex [Ir(MDPP)2(acac)] (MDPP=5-methyl-2,3-diphenylpyrazine, acac=acetylacetone) shows strong ¹MLCT (singlet metal-to-ligand charge-transfer) and ³MLCT (triplet metal to ligand charge-transfer) absorption at 386 and 507 nm, respectively. Organic light emitting device (OLED) with a configuration of ITO / NPB (30 nm) / NPB: 7% (wt.) Ir(MDPP)₂(acac) (25 nm) / BCP (10 nm) / Alq₃(30 nm) / Mg : Ag (mass ratio 10 : 1)120 nm / Ag(10 nm) exhibits an external quantum efficiency of 6.02% (power efficiency 9.89 lm W^− 1 ) and a maximum brightness of 78,924 cd m^− 2. The device also shows high color purity with a maximum peak at 576 nm without any shoulder.     

Efficient red-emitting phosphorescent iridium(III) complexes of fluorinated 2,4-diphenylquinolines

Ir(β) complexes of fluorinated dpqs(dpq-3-F, dpq-4-CF₃) as a cyclometallated ligand were prepared and their photonic properties were investigated, where dpq-3-F and dpq-4-CF₃ represent 2-(3-fluoro-phenyl)-4-phenylquinoline and 4-phenyl-2-(4-trifluoromethylphenyl)quinoline, respectively. Fluorinated dpq derivatives were introduced to the iridium complexes to increase the efficiency compared to Ir(dpq)₂(acac) which was recently reported to have emission wavelength of 614 nm with quantum efficiency of 0.14. These fluorinated ligands and their Ir(III) complexes were computationally calculated by ab initio methods to support our experimental results. It was found that the Ir complex containing dpq-3-F ligands exhibits the largest emission efficiency with maximum emission peak at 593.5 nm. The result of ab initio calculation using the time-dependent density functional theory (TD-DFT) showed that the strong ³MLCT transition of the complex occurs due to the strong coupling between the 5d orbital of the Ir atom and the highest occupied molecular orbitals (HOMOs) of these ligands.     

A photochemical method for the preparation of indium oxide and indium-cobalt oxides thin films

Indium oxide and indium-cobalt oxide thin films have been successfully prepared by direct UV irradiation of amorphous films of β-diketonate complexes on Si(1 0 0) substrates. Deposited films were characterized by X-ray diffraction, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The surface morphology of the films, examined by atomic force microscopy and scanning electron microscopy, revealed that mixed indium-cobalt oxide films are much smoother than In₂O₃ films, with rms surface roughness of 7.24 and 26.1 nm, respectively.     

High-efficiency white organic light-emitting devices with a non-doped yellow phosphorescent emissive layer

Highly efficient phosphorescent white organic light-emitting devices (PHWOLEDs) with a simple structure of ITO/TAPC (40 nm)/mCP:FIrpic (20 nm, x wt.%)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C²′] iridium (acetylacetonate) (tbt)₂Ir(acac) (y nm)/Bphen (30 nm)/Mg:Ag (200 nm) have been developed, by inserting a thin layer of non-doped yellow phosphorescent (tbt)₂Ir(acac) between doped blue emitting layer (EML) and electron transporting layer. By changing the doping concentration of the blue EML and the thickness of the non-doped yellow EML, a PHWOLED comprised of higher blue doping concentration and thinner yellow EML achieves a high current efficiency of 31.7 cd/A and Commission Internationale de l'Eclairage coordinates of (0.33, 0.41) at a luminance of 3000 cd/m² could be observed.     

Synthesis and phosphorescent properties of the copolymers of N-vinylcarbazole,methyl methacrylate and iridium complex

The copolymers containing carbazole unit and iridium complexes, such as (Ir(bpy)₂Cl, Ir(mbpy)₂Cl and Ir(Brbpy)₂Cl, were synthesized via radical copolymerization of N-vinylcarbazole, methyl methacrylate and iridium complex. The synthesized copolymers were characterized by FT-IR, UV-Vis absorption spectroscopy and photoluminescence (PL) spectroscopy, respectively. According to the results, the copolymers (Ir(Brbpy)₂Cl/PVK and Ir(mbpy)₂Cl/PVK) exhibit yellow phosphorescence with an emission peak at around 553 nm under UV-visible light in the solid state. The results also reveal almost complete energy transfer from the host carbazole segments to the guest Ir complex in the copolymer film when the Ir content reaches 1.0 wt.%. The synthesized copolymers are good candidates as blue or yellow phosphorescent materials for PLED applications.     

Nuclear microanalysis of amorphous As2Se3 films modified with Ln(thd)3 (Ln = Eu, Tb)

The compositions of amorphous As₂Se₃ thin films modified with the Ln(thd)₃ (Ln = Eu, Tb) complexes have been determined by nuclear microanalysis using deuterons provided by an electrostatic accelerator: Rutherford backscattering spectroscopy and nuclear reaction analysis. The rare-earth, oxygen, and carbon contents have been determined as functions of the initial concentration of the complex. The films have been also characterized by IR spectroscopy. Analysis of the nuclear microanalysis and IR spectroscopy results suggests that, in the modified films, the rare-earth atoms retain their local environment, in contrast to thin films of amorphous hydrogenated silicon.     

Heteroleptic tris-cyclometalated iridium(III) complexes with phenylpridine and diphenylquinoline derivative ligands

The synthesis and photophysical study of efficient phosphorescent heteroleptic tris-cyclometalated iridium(III) complexes having two different (C^N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet-triplet (T-T) annihilation, new heteroleptic tris-cyclometalated iridium complexes, Ir(ppy)₂(dpq), Ir(ppy)₂(dpq-3-F) and Ir(ppy)₂(dpq-CF₃), are designed and prepared where ppy, dpq, dpq-3-F and dpq-CF₃ represent 2-phenylpyridine, 2,4-diphenylquinoline, 2-(3-fluorophenyl)-4-phenylquinoline, and 4-phenyl-2-(4-(trifluoromethyl)phenyl)quinoline, respectively. Ppy ligands and dpq derivatives can act as a source of energy supply. When new heteroleptic tris-cyclometalated iridium complex, Ir(ppy)₂(dpq-3-F) is placed in the lowest excited state, the excitation energy is neither quenched nor deactivated but quickly intermolecularly transferred from two ppy ligands to one luminescent dpq-3-F ligand. Such transfer can occur because the triplet energy level of Ir(ppy)₃ is higher than that of Ir(dpq-3-F)₃ and because Ir(dpq-3-F)₃ was known to have a shorter lifetime than that of Ir(ppy)₃. As a result, Ir(ppy)₂(dpq-3-F) shows strong emission band at 620 nm from dpq-3-F ligand in the end. Thus it allows more reddish luminescent color and improves the luminescence by the decrease of quenching or energy deactivation by decreasing the number of the luminescent ligand. To analyze luminescent mechanism, we calculated these complexes theoretically by using computational method.