Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes.

Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds. Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4'-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N'-dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and could be extended to additional research on flexible applications.

Luminescence color tuning of the iridium complexes by interligand energy transfer (ILET) with ancillary ligands for organic light emitting diode.

The series of new iridium complexes, Ir(C--N)2(LX), (main ligand, C--N = the anion of 2-phenylpyridine (ppy), 4-difluoro-2-phenylpyridine (F2-ppy) and 4-methyl-2,3-diphenylquinoline (4-Me-2,3-dpq); ancillary ligand, LX = 2-(2-hydroxyphenyl)benzoxazolate (BOX) and 2-(2-hydroxyphenyl)benzothiazolate (BTZ)) were prepared and their luminescence properties were investigated. We expected that the relative energy levels of the main ligands and ancillary ligands in the complexes could determine the possibility of interligand energy transfer (ILET) in the complexes and thereby luminescence properties. As the main ligands, F2-ppy, ppy and 4-Me-2,3-dpq, which have drastically different energy gap between the HOMO and LUMO energy levels, were chosen and their complexes were synthesized. BOX and BTZ were chosen as the ancillary ligands which can form a stable 6-membered metallacycle with the iridium center. The iridium complexes showed various emission ranges from 510 to 643 nm, depending upon the relative energy levels of their main and ancillary ligands. The studies of photoabsorption, electrochemistry, photoluminescence and electroluminescence revealed that ILET might contribute to absorption and luminescence process of the iridium complexes containing the ppy-based ligands and BOX.

Orange phosphorescent iridium complexes chelated with phenylbenzothiazolate derivatives for white organic light-emitting diodes.

For the application to white organic light-emitting diodes (OLEDs), the iridium complexes containing phenylbenzothiazolate derivatives as main ligands were prepared and their photophysical properties were investigated. We introduced a series of substituted 2-phenylbenzothiazolate (pbt) ligands to the iridium complexes. Variation of the substituent (R) in the ligand backbones could lead to the emission color tuning of the complexes. As ancillary ligands, the anions of 2,3-diphenyl-4-methyl-quinoline-C2,N (4-Me-2,3-dpq) and phenylpyridine (ppy) were chelated to the iridium center to complete 6-coodinate complexes. The iridium complexes prepared herein are Ir(pbt-R)2(4-Me-2,3-dpq) (pbt-R = 2-(4-R-phenylbenzothiazolate (R = H, OCH3, F); 4-Me-2,3-dpq = 2,3-diphenyl-4-methyl-quinolinate-C2,N) and Ir(pbt-R)2(ppy) (ppy = 2-phenylpyridinate). The PL spectra of the iridium complexes showed yellow to orange emission at 540-595 nm with some variation in luminescence maxima depending on the ancillary ligand rather than on the substituents of the main ligands. The electrochemical characteristics of the complexes were also investigated with cyclic voltammetry and the resulting energy gaps between HOMOs and LUMOs were consistent with the PL maxima. The electroluminescence (EL) properties of the new iridium complexes were studied as possible phosphors for the application to orange and white OLEDs.

Synthesis and luminescence properties of iridium complexes chelated with coumarin ligands.

According to a recent report, the organic light-emitting diodes (OLEDs) using the iridium complexes of coumarin derivatives as emissive dopants are highly efficient and stable. Unlike the other Ir(III) phopsphorescent dopants, these coumarin-based Ir(III) complexes can effectively trap and transport electrons in the emissive layer. We have prepared a series of phosphorescent cyclometalated Ir(III) complexes containing 3-(2-pyridinyl)coumarin (pc) as an ancillary ligand. The new heteroleptic iridium complexes, Ir(C--N)2(pc) (CAN = 2-(2,4-difluorophenyl)pyridine (F2-ppy), 2-phenylpyridine (ppy) and 2-phenylquinoline (pq)) were characterized by 1H NMR and mass spectrometer. As main ligands, F2-ppy, ppy and pq were employed, which should have the drastically different ligand molecular orbital energy levels. The iridium complexes showed various emission ranges from 560 to 610 nm, depending upon the relative energy levels of their main and ancillary ligands. The photoabsorption, photoluminescence and electroluminescence of the complexes were studied. We also investigated the electrochemical properties of the iridium complexes to compare the HOMO and LUMO energy levels of these phosphorescent materials.

Highly efficient blue- and white-organic light-emitting diode based on dual recombination zones with a charge control layer.

Highly efficient blue phosphorescent organic light-emitting diodes are investigated using iridium(Ill) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2']picolinate doped in N,N'-dicarbazolyl-3,5-benzene (mCP) with a charge control layer (CCL) as the dual recombination zone (DRZ) system. DRZ with CCL was used to form a broad recombination zone and exciton confinement within each emission zone. Holes and electrons can be easily transported through the CCL, which were a mixed p-type mCP and n-type 2,2',2"-(1,3,5-benzenetryl) tris(1-phenyl)-1H-benzimidazol, for controlling the carrier movement. The CCL can play a role in triplet exciton blocking as expected from high triplet energy levels as well. Additionally, a white organic light-emitting diode was fabricated using a new phosphorescent orange emitter: bis[2-(2,4-difluorophenyl)pyridinato]iridium 2-(2-hydroxyphenyl)benzothia zolate doped in DRZ. The white device showed a maximum luminous efficiency of 23.15 cd/A, a maximum external quantum efficiency of 9.56%, and a maximum power efficiency of 13.37 lm/W. It also showed white emission with CIEx,y coordinates of (x = 0.33, y = 0.41) at 8 V.

Phosphorescence color tuning of oxadiazole-based iridium(III) complexes for organic light emitting diode.

The new heteroleptic iridium complexes bearing 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenolate (ODZ), were synthesized and characterized for application to organic light-emitting diodes (OLEDs). As main ligands (C^N), the anions of 2-phenylpyridine (ppy), 2-phenylquinoline (pq) and 2-(2,4-difluorophenyl)pyridine (F2-ppy) were chelated to the iridium center and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenolate (ODZ) was introduced as an ancillary ligand for luminescence modulation of their iridium complexes. We expected that the relative energy levels of the main and ancillary ligands in the complexes could lead to emission color tuning and luminous efficiency improvement by possible inter-ligand energy transfer (ILET). The photoabsorption, photoluminescence and electroluminescence of the complexes were studied. Ir(F2-ppy)2(ODZ), Ir(ppy)2(ODZ) and Ir(pq)2(ODZ) exhibited the photoluminescence maxima between 505-610 nm at room temperature in CH2Cl2, depending on both main and ancillary ligands. The longer pi conjugation in the cyclometallating pq ligands leads to the bathochromic shift in luminescence of their iridium complexes. The electroluminescent properties of the complexes were influenced by ILET.

Introduction of the benzoquinoline ancillary ligand to the iridium complexes for organic light-emitting diodes.

The new iridium complexes, Ir(C^N)2(bq), (C^N = ppy, F2-ppy, 2,3-dpqx-F2 or 4-Me-2,3-dpq) were prepared and their luminescence properties were investigated, where ppy, F2-ppy, 2,3-dpqx-F2, 4-Me-2,3-dpq and bq represent 2-phenylpyridine, 2-(4',6'-difluorophenyl)-pyridine, 2,3-bis (4'-fluorophenyl)quinoxaline, 4-methyl-2,3-diphenylquinoline and 10-hydroxybenzoquinoline ligands, respectively. We expected that the relative energy levels of the main ligands (C^N) and ancillary ligand, bq, in the complexes could determine the possibility of interligand energy transfer (ILET) in the complexes and thereby luminescence properties. The main ligands, F2-ppy and 2,3-dpqx-F2, which have drastically different energy gaps between the HOMO and LUMO energy levels were chosen and their complexes were synthesized. The photoabsorption, photoluminescence and electroluminescence of the complexes were studied. Ir(ppy)2(bq), Ir(F2-ppy)2(bq) Ir(2,3-dpqx-F2)2(bq) and Ir(4-Me-2,3-dpq)2(bq) exhibited the luminescence maxima between 600-694 nm and their efficiencies were affected by the main ligands. While Ir(ppy)2(bq) and Ir(F2-ppy)2(bq) showed relatively high luminous efficiencies (> 10 cd/A), Ir(2,3-dpqx-F2)(bq) had poor luminous efficiency (0.30 cd/A). The electrochemical properties were studied to support ILET in the ppy-based iridium complexes. Their luminescence performances were compared with those of the complexes containing acetylacetonate (acac) ancillary ligand which are not allowed to have ILET.

The new iridium complexes involving pyridylpyridine derivatives for the saturated blue emission.

To obtain a saturated blue phosphorescent material with a good color purity, we have synthesized the new blue emitting iridium complexes with 2, 6-difluoro-3-(4-methylpyridin-2-yl)pyridine (4-Me-dfpypy) as a main ligand. We expected that the LUMO energy levels of the complex might increase upon introduction of an electron donating group such as a methyl group to the pyridyl moieties of the ligand, leading to a wide energy gap of the complex to give the saturated blue emission. We have also introduced a variety of the ancillary ligands to the iridium center to compare the effect of the ancillary ligards on the emission of their complexes. The resulting iridium complexes, Ir(4-Me-dfpypy)3, Ir(4-Me-dfpypy)2(acac), Ir(4-Me-dfpypy)2(pic) and Ir(4-Me-dfpypy)2(trzl-CH3) where acac, pic, and trzl-CH3 represent acetylacetonate, picolinate, and 2-(5-methyl-2H-1,2,4-triazol-3-yl) pyridinate, respectively exhibited the blue emission at 451, 447, 440 and 425 nm in CH2Cl2 solution. The organic light emitting device (OLED) employing homoleptic Ir(4-Me-dfpypy), as the blue dopant was prepared and their electroluminescence was investigated. Ir(4-Me-dfpypy)3 exhibited the blue emission of CIE coordinates (0.22, 0.32).

Highly efficient and stable white organic light emitting diode base on double recombination zones of phosphorescent blue/orange emitters.

We demonstrated efficient and stable white phosphorescent organic light-emitting diodes (OLEDs) with double-emitting layers (D-EMLs), which were comprised of two emissive layers with a hole transport-type host of N,N'-dicarbazolyl-3,5-benzene (mCP) and a electron transport-type host of 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) with blue/orange emitters, respectively. We fabricated two type white devices with single emitting layer (S-EML) and D-EML of orange emitter, maintaining double recombination zone of blue emitter. In addition, the device architecture was developed to confine excitons inside the D-EMLs and to manage triplet excitons by controlling the charge injection. As a result, light-emitting performances of white OLED with D-EMLs were improved and showed the steady CIE coordinates compared to that with S-EML of orange emitter, which demonstrated the maximum luminous efficiency and external quantum efficiency were 21.38 cd/A and 11.09%. It also showed the stable white emission with CIE(x,y) coordinates from (x = 0.36, y = 0.37) at 6 V to (x = 0.33, y = 0.38) at 12 V.

Efficient phosphorescent white organic light-emitting diodes using Ir(4-Me-2,3-dpq)2(przl-C6H4F) as a red emitter.

We demonstrated white organic light-emitting diodes (WOLED) using the iridium bis(4-methyl-2,3-phenylquinolinato-N,C2) fluorophenylpyrazolonate complex (Ir(4-Me-2,3-dpq)2(przl-C6H4F)) as a phosphorescent red dopant and iridium bis[(4,6-difluorophenyl)-pyridinato-N,C2] picolinate (Flrpic) as a phosphorescent blue dopant. The WOLED with Ir(4-Me-2,3-dpq)2(przl-C6H4F) had better exciton confinement in emitting layer and indicated smaller movement of exciton than the WOLED with iridium bis(2-phenylquinoline) acetylacetonate (Ir(2-pq)2(acac)) as phosphorescent red dopant. The optimized WOLED had a peak external quantum efficiency of 7.16%, current efficiency of 11.84 cd/A, and Commission Internationale de l'Eclairage (CIE(x,y)) coordinates of (0.35, 0.32). The WOLED also exhibited the minimal change with delta CIE(x,y) coordinates of +/- (0.01, 0.00) from 100 to 4000 cd/m2.

New blue phosphorescent iridium complexes containing phenylpyridine and triazole ligands: synthesis and luminescence studies.

The synthesis and luminescence of iridium(III) complexes containing new phenylpyridine (C(see test for symbol)N) ligands, 4-Me-4'-F-ppy, 4-Me-4'-CF3-ppy and 4-OMe-4'-CF3-ppy, were studied. These ligands were designed for development of the blue light-emitting iridium complexes by introducing the electron-withdrawing group (F, CF3) and the electron-donating group (Me, OMe) at the para positions of the phenyl and pyridine ligand rings, respectively. As an ancillary ligand, trzl-CMe3 was employed where trzl-CMe3 represents 2-(5-tert-butyl-2H-1,2,4-triazol-3-yl)pyridine. The resulting iridium complexes, Ir(4-Me-4'-F-ppy)2(trzl-CMe3), Ir(4-OMe-4'-CF3-ppy)2 (trzl-CMe3) and Ir(4-Me-4'-CF3-ppy)2(trzl-CMe3) exhibited the blue emission at 472, 484 and 494 nm in CH2Cl2 solution, respectively. Ir(4-Me-4'-F-ppy)2(trzl-CMe3) showed the most hypsochromic shift in photoluminescence (PL) among the complexes prepared herein. In the electroluminescence (EL) spectra, Ir(4-Me-4'-F-ppy)2(trzl-CMe3) and Ir(4-Me-4'-CF3-ppy)2(trzI-CMe3) exhibited the luminescence peak at 437 nm and 496 nm, respectively. In the aspect of blue emission color purity, Ir(4-Me-4'-F-ppy)2(trzl-CMe3) had the CIE coordinates of (0.176, 0.143), very close to the saturated standard blue emission.

Synthesis and photophysical studies of iridium complexes of new 2,3-diphenylquinoxaline derivatives for organic light-emitting diodes.

For the application to organic light-emitting diodes (OLEDs), the new iridium complex containing 2,3-diphenylquinoxaline (dpqx) derivatives as a ligand were prepared. Variation of the substituents in the dpqx ligand backbone of the complex led to tuning of the emission color. The complexes, Ir(2,3-dpqx-F2)2(acac), Ir(6-F-2,3-dpqx-F2)2(acac) and Ir(6-F-2,3-dpqx-(OMe)2)2(acac) were formed from the two-step reactions of the corresponding ligand with IrCl3 x H2O. In the photoluminescence (PL) spectra, Ir(2,3-dpqx-F2)2(acac), Ir(6-F-2,3-dpqx-F2)2(acac) and Ir(6-F-2,3-dpqx-(OMe)2),(acac) exhibited the luminescence peak at 631 nm, 638 nm and 645 nm, respectively. The OLEDs employing these compounds as a dopant were prepared and their electroluminescence was investigated. In the electroluminescence (EL) spectra, Ir(2,3-dpqx-F2)2(acac), Ir(6-F-2,3-dpqx-F2)2(acac) and Ir(6-F-2,3-dpqx-(OMe)2)2(acac) exhibited the luminescence peak at 630 nm, 644 nm and 667 nm, respectively. The Commission Internationale de L'Eclairage (CIE) coordinates of Ir(2,3-dpqx-F2)2(acac), Ir(6-F-2,3-dpqx-F2)2(acac) and Ir(6-F-2,3-dpqx-(OMe)2)2(acac) were (0.684, 0.311), (0.675, 0.313) and (0.697, 0.289), respectively.