Patent Application
20080030125
In the drawings:
A light-emitting device possesses a substrate 1 and, mounted on it, at least one anode 2, a light-emitting layer 4 and a cathode 6. In order to improve the efficiency of a light-emitting device, it may, as
The substrate 1 is preferably a transparent glass plate or a transparent plastic plate. The plastic plate may contain polyethylene terephthalate (PET), for example. The anode 2 is preferably transparent and may contain p-doped silicon, indium-doped tin oxide (ITO) or antimony-doped tin oxide (ATO), for example. The anode 2 ideally contains ITO. The anode 2 is not structured, it possesses a flat design. The cathode 6 may contain a metal, such as aluminum, copper, silver or gold, an alloy or n-doped silicon, for example. It may be preferable for the cathode 6 to possess two or more conductive layers. It may be particularly preferable for the cathode 6 to possess a first layer made from an alkaline-earth metal, such as calcium or barium, or from an alkali halide, such as LiF or lithium benzoate, and a second layer made from aluminum. The cathode 6 may be structured and, for example, possess a number of parallel strips of the conductive material(s). Alternatively,-the cathoder;6 may not be structured and may have a flat design.
The anode 2 is bordered by a first hole-transporting layer 3 which simplifies the injection and transport of the holes into the device. Suitable materials for the hole- transporting layer 3 are, for example, triaryl amine, diaryl amine, tristilbene amine or a mix. of polyethylene dioxythiophene (PDOT) and poly(styrene sulphonate).
Positioned between the cathode 6 and the light-emitting layer 4 there is an electron-transporting layer 5, which may possess tris-(8-hydroxy-quinolato)-aluminum (Alq3), 1,3,5-tris-(1-phenyl-1H-benzimidazole-2-yl)benzole (TPBI) or low-electron heterocycles, such as 1,3,4-oxadiazoles or 1,2,4-triazoles.
The light-emitting layer 4 contains one or more of the new iridium complexes as light-emitting material.
The iridium complexes IrL3 in accordance with the invention are neutral and non-ionic. At least two of the three ligands L are a dibenzoquinoline. Alternatively, all three of the ligands L are a dibenzoquinoline. The ligands L are preferably identical dibenzoquinohnes. However, they may also be different.
Dibenzoquinolines are quinolines to which two other benzole rings are condensed. Examples of suitable dibenzoquinolines are dibenzo[f,h]quinoline (dbzq), dibenzo[c,f]quinoline, dibenzo[c,d,e]quinoline or dibenzo[f,g]quinoline. All these dibenzoquinolines are large, rigid ligands with good complexing properties. Dibenzo[f,h]quinoline is the preferred ligand on account of its sterics.
The dibenzoquinolines can additionally possess other substituents R. Each ring can possess one or more substituents R which influence the electronic properties of the dibenzoquinoline and, thus, of the later iridium complex.
The substituents R1, R2, R3, etc. may, for example, contain linear or branched C1-C8-alkyl groups, C2-C6-alkenyl groups, C3-C8-cycloalkyl groups, C1-C6-alkinyl groups, aryl groups, heteroaryl groups, C1-C6-heterocycloalkyl groups, amines, phosphates, phosphine groups, phosphine oxide groups, halogens, sulphate groups, sulphonate groups, sulphone groups, carboxylates, C2-C6-alkoxyl groups, phosphate groups, etc. The substituents R1, R2, R3, etc. may be identical or different.
If the iridium complex contains two dibenzoquinolines as ligands L, the third ligand L is preferably the anion of a 1.3-diketone derivatives:
The substituents R1 and R2 etc. may, for example, contain linear or branched C1-C8-alkyl groups, C2-C6-alkenyl groups, C3-C8-cycloalkyl groups, C1-C6-aikinyl groups, aryl groups, heteroaryl groups, C1-C6-heterocycloalkyl groups, amines, phosphates, phosphine groups, phosphine oxide groups, halogens, sulphate groups, sulphonate groups, sulphone groups, carboxylates, C2-C6-alkoxyl groups, phosphate groups, etc. The substituents R1 and R2 may be identical or different.
The third ligand L is preferably selected from the following group: pentane-2,4-dionate (acac), 2,2,6,6-tetramethyl-3,5-heptane dionate (thd), 7,7-dimethyl-1,1,1,2,2,3,3-heptafluorine-4,6-octane dionate (fod), 1,1,1,5,5,5-hexafluoropentane-2,4-dionate (hfa), 4,4,4-trifluorol-(2-thienyl)butane-1,3-dionate (ttfa), 1,3-diphenyl propane-1,3-dionate (dbm), 4,4,4-trifluorine-1-(2-naphthyl)butane-1,3-dionate (tfnb) and 4,4,4-trifluoro-1-(1-napthyl)butane-1,3-dionate. They are all well known ligands with good complexing properties. Pentane-2,4-dionate (acac) is the ligand which is most preferred.
A preferred iridium complex is Ir(dibenzo[f,h]quinoline)2(pentane-2,4-dionate).
Another preferred iridium complex is Ir(dibenzo[f,h]quinoline)3.
Both complexes emit light with a wavelength of λ<600 nm. Complex IV emits light with a wavelength λmax of 595 nm (in methyl-THF) while complex III emits lights with a wavelength λmax of 545 nm (in methyl-THF).
Given the fact that, as has been indicated above, the human eye is most sensitive at a wavelength of 555 nm, light-emitting devices with complex III and/or complex IV in the light-emitting layer 4 exhibit favorable energy-efficiency.
It is surprising to note that a shift in emission wavelength λmax of 50 nm as achieved by simply varying a ligand, for example by replacing a dibenzo[f,h]chinoline with pentane-2,4-dionate.
It is also advantageous that, given their structural similarity, complexes III and IV also possess similar physical properties, thereby simplifying the manufacture and operation of a light-emitting device which contains two or more iridium complexes in accordance with the invention in the light-emitting layer 4. Undesired chemical interactions between two different complexes, such as ligand exchange reactions, make no difference here either. This is particularly advantageous in the case of devices which emit white light because the light-emitting layer 4 in them contains several light-emitting materials, which emit in the three primary colors for example.
In order to produce complexes in accordance with the invention with three dibenzoquinolines as ligand L, an iridium salt, such as IrCl3 or Ir(acac)3 is converted with the corresponding dibenzoquinoline in a suitable solvent.
The synthesis of von Ir(dbzq)3 led to a fac/mer isomer mix in the case of all synthesis pathways. The prefixes fac- and mer- indicate that there are three identical ligands immediately adjacent to one another in octahedral coordination compounds with different ligands.
In this case, while the complexes with three identical dibenzoquinolines as ligands L possess three identical ligands, each of the dibenzoquinolines has two different coordination sites: One coordinates a dibenzoquinoline via the nitrogen to the iridium(III) cation, and a covalent bond between a C-atom on one of the aromatic rings and the Ir(III) cation. This means in arguments to the contrary that only dibenzoquinolines which can form an N—Ir and a C—Ir bond can be used as ligands.
fac/mer isomerism exists in these complexes in terms of the close proximity between the three identical coordination sites.
In order to produce complexes in accordance with the invention with two dibenzoquinolines as ligands L, the dichiorine-bridged dimer (dibenzoquinohne)2Ir(μ-Cl)2(dibenzoquinoline)2 is produced first, based on IrCI3. The dichlorine-bridged dimer (dibenzoquinoline)2Ir(μ-Cl)2(dibenzoquinoline)2 is then converted into the required iridium complex with the third ligand, for example a 1,3-diketone derivative, such as pentane-2,4-dione, in the presence of a base.
Vacuum separation is used to obtain thin films of the iridium complexes in accordance with the invention which possess good electroluminescent properties. By- varying the ligands L or substituents R in the dibenzoquinolines, the electroluminescent properties of the light-emitting.materials can be finely coordinated.
The iridium complexes can be used on their own (accounting for 100% of the total weight of the light-emitting layer 4) or embedded in a matrix comprising hole or electron-transporting material in the light-emitting layer 4. The quantity of iridium complex is preferably>10% (of the total weight of the light-emitting layer 4). The choice of matrix material depends on the requirements of the iridium complex. For example, the matrix may contain 4,4′,4″-tri(N-carbazolyl)triphenyl amine (TCTA), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or 1,3,5-tris-(1-phenyl-1H-benzimidazole-2-yl)benzole (TPBI).
The following embodiments are examples and are intended to illustrate the invention, but not limit it.
Synthesis of the dichlorine-bridged dimer (dbzq)2Ir(μ-Cl)2(dbzq)2
250 mg of IrCI3.3H2O and 407 mg of dibenzo[f,h]quinoline (dbzq) were dissolved in a mixture of 2-ethoxy ethanol (20 ml) and water (7 ml) and were heated and refiuxed for 24 hours. After cooling down to room temperature, the yellow deposit which was obtained was centrflged off, washed with ethanol (60 ml) and acetone (60 ml) and dried.
370 mg (77%) of the dichiorine-bridged dimer was obtained in the form of a yellow powder.
Synthesis of Ik(dbzq)2(acac) starting off from (dbzq)2Ir(μ-Cl)2(dbzq)2
(dbzq)2Ir(μ-Cl)2(dbZq)2 was heated and refiuxed for 20 hours with 2.5 equivalent acetyl acetonate and 400 mg of sodium carbonate in 2-ethoxy ethanol. The obtained orange-colored deposit was centrifuiged off, washed with water, n-hexane, diethyl ether and ethanol. The yield of raw product was between 70 and 75%.
The raw product was cleaned in silica gel (CH2CI2/n-hexane/diethyl ether) by means of column chromatography.
1H-NMR (CDCI3): δ=1.80 (s, 6H, 2CH3), 5.29 (s, 1H, CH), 6.33 (d, J=7.3 Hz, 2H,. CH arom.), 6.97 (t, 2H, CH arom.), 7.61 (dd, J=7.7 Hz, J=5.4 Hz, 2H, CH arom.), 7.66 to 7.72 (m, 4H, CH arom.), 7.86 (d, J=8.0 Hz, 2H, CH arom.), 8.56 to 8.60 (m, 2H, CH arom.), 8.64 to 8.67 (m, 2H, CH arom.), 8.87 to 8.91 (m, 4H, CH.atom.).
The complex obtained, Ir(dbzq)2(acac), emits light at a wavelength λmax of 545 nm (in fnethyl THF). The emission spectrum is shown in
Synthesis of Ir(dbzq)3
53 mg of iridium(III)acetyl acetonate and 250 mg of dibenzo[f,h]quinoline were added to 5 ml of degassed ethylene glycol. The suspension obtained was heated and refiuxed for 60 hours. After cooling down to room temperature, the reaction mixture was added to 10 ml of 1N HCl. Following 5 minutes stirring, the orange-colored, crystalline deposit was filtered off, washed with 5 ml of iN HCl and water and dried.
The product was dissolved in dichioromethae, filtered through silica gel and dried.
The 1H-NMR spectrum showed that the product contains mer- and fac- isomers from the complex, whereby the share of iner-isomers is larger.
The mixture offac/mer-isomers in the complex Ir(dbzq)3 emits light at a wavelength λmax of 595 nm (in methyl TBF). The emission spectrum is shown in
Synthesis of Ir(dbzq)3 starting off from Ir(dbzq)2(acac)
258 mg of Ir(dbzq)2(acac) and 119 mg of dibenzo[f,h]quinoline were heated for 24 hours at 220° C. in 5 ml of glycerine. After cooling down to room temperature, the reaction mixture was diluted with water, and the deposit was centrifuged off. Following repeated washing with methanol, the deposit was dried in the vacuum.
This 1H-NMR spectrum also showed that the product contains met- and fac- isomers from the complex, whereby the share of mer-isomers is larger.
A 150 nm thick layer of ITO, serving as an anode 2, was applied to a transparent substrate 1 made from glass. A 30 nm thick layer of a-NPD, serving as a hole-transporting layer 3, was applied to the anode 2 by means of spin-coating. A light-emitting layer 4 made from Ir(dbzq)2(acac), embedded in TCTA, was applied to the hole-transporting layer 3. The light-emitting layer 4 was 30 nm thick. A 40 nm thick layer of TPBI, serving as an electron-transporting layer 5, was applied to the light-emitting layer 4. A 151 nrm thick cathode 6 comprising a 1 nm thick first layer of lithium benzoate and a 150 nm thick second layer of aluminum were applied to the electron-transporting layer 5.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03104258.3 | Nov 2003 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB04/52328 | 11/8/2004 | WO | 00 | 2/20/2007 |
