Organic Red Electro-Luminescent Device Including A Hetrocyclic Emitter

Description

Summary of Invention

[0017] The objective of the invention was to make available an organic, red electro-luminescent device with improved quantum efficiency and improved long term stability and at the same time to develop new luminescent compounds and new doping agents for known luminescent compounds for the luminescent layer, especially for AlQ3. A further objective was readying new compounds.

[0018] The organic electro-luminescent device consists, in the simplest case, of an interlaminar bonding in accordance with Fig. 1, designed with a metal electrode 1 (cathode), a luminescent layer 2, which in addition to an organic luminescent compound, which is in particular AlQ3, contains at least one organic doping agent of a hole transport layer 3 which contains an organic hole transport compound, a transparent conductive anode 4, as well as a support 5 of glass or a similar transparent material.

[0019] The characteristics of this device can be optimized by a different type of construction of the electro-luminescent device, as for example according to Figures 2 and 3.

[0020] In accordance with the invention, the electro-luminescent device consists of a hole transport layer and a luminescent layer between two conductive electrodes, whereby at least one electrode is transparent, characterized in that the luminescent layer contains, as a doping agent for a luminescent compound, at least one compound of general formula I

wherein R1 to R12 are identical or different, and indicate hydrogen, straight chain or branched C1-C6 alkyl, aralkyl, aryl or substituted aryl; R1 and R2 and/or R3 and R4 and/or R4 and R5 and/or R5 and R11 and/or R8 and R5 and/or R4 and R12 can form, preferably, a 5 or 6 member alicyclic, heterocyclic or aromatic ring; R5 can furthermore be hydrogen, OH, OR5, N,N-di-(C1-C6)alkylamino, acetylamino or a halogen; R6 and R7 together can form an alicyclic or heterocyclic ring; A1 and A2 are identical or different and are -CN, -NO2 or -COOR10; R1, R2, R3, R4 and/or R8 can, moreover be halogens, especially fluorine; X is -CH, -CR11 or N; and Y is O, -NH, -NR12, S or Se.

[0021] One invention design consisting of a luminescent layer contains at least one compound in which the substituents R1 and R2 or R3 and R4 or R1 and R2 and R3 and R4 form a carbocyclic 5 or 6 member ring as doping substance or mixed with additional other doping substances for luminescent compounds.

[0022] Another invention design consisting of a luminescent layer contains, as a doping agent for a luminescent compound or mixed with additional doping agents of a different type for luminescent compounds, at least one compound of general formula II:

wherein R1, R2, R5 to R7 could be equal to or various H, straight chain or branched C1-C6-alkyl, especially isopropyl or tert butyl; R1 and R2 can form an alicyclic, heterocyclic or aromatic, preferably 5 or 6 member ring; R1, R2, R5, R6, R7 can be equal to or various aryl or substituted aryl; R5 can be equal to OH, OR5, N,N-dialkylamino (C1-C6), acetylamino, or a halogen; R6 and R7 can jointly form an alicyclic or heterocyclic ring; A1, A2 can be equal to or various CN, NO2 or COOR5; R8 is H, straight chained or branched C1-C6 or aryl; X is equal to CH, CR5 or N; Y is equal to O, NH, NR8, S or Se.

[0023] An additional invention design consisting of a luminescent layer as doping agent for luminescent compounds or mixed with further doping agents of a different type for luminescent compounds, contains at least one compound of general formula III:

wherein R1, R2, R5 to R7 can be equal to or various H, straight chain or branched C1-C6 Alkyl, especially isopropyl or tert butyl; R1 and R2 can form an alicyclic, heterocyclic or aromatic, preferably 5 or 6 member ring; R1, R2, R5, R6, R7 can be equal to or various aryl or substituted aryl; R5 can be equal to OH, OR8, N,N-dialkylamino (C1-C6), acetylamino, or a halogen; R6 and R7 can jointly form an alicyclic or heterocyclic ring; A1, A2 can be equal to or various CN, NO2 or COOR8; R8 is H, straight chained or branched C1-C6 or aryl; X is equal to CH, CR5 or N; and Y is equal to O, NH, NR8, S or Se.

[0024] A further invention design consisting of a luminescent layer contains, as doping agent for a luminescent compound or mixed with further doping agents of a different type, at least one compound of general formula IV:

wherein R3 to R7 can be equal to or various H, straight chain or branches C1-C6 alkyl, especially isopropyl or tert butyl; R3 and R4 can form an alicyclic, heterocyclic or aromatic, preferably 5 or 6 member ring; R5, R6, R7 can be equal to or various aryl or substituted aryl; R5 can be equal to OH, OR8, N,N-dialkylamino (C1-C6), acetylamino, or a halogen; R6 and R7 can jointly form an alicyclic or heterocyclic ring; A1, A2 can be equal to or various CN, NO2 or COOR8; R8 is H, straight chained or branched C1-C6 or aryl; X is equal to CH, CR5 or N; Y is equal to O, NH, NR8, S or Se.

[0025] An additional invention design consisting of a luminescent layer, as a doping agent or mixed with additional doping agents for luminescent compounds of a different type, contains at least one compound of general formula V:

R5 to R7 can be equal to various aryl, substituted aryl, hydrogen, straight chain or branched C1-C6 aryl; R5 in particular can be isopropyl or tert butyl; R5 can be equal to OH, OR8, N,N-dialkylamino (C1-C6), acetylamino, or a halogen; R6 and R7 can jointly form an alicyclic or heterocyclic ring; A1, A2 can be equal to or various CN, NO2 or COOR8; R8 is H, straight chained or branched C1-C6 or aryl; X is equal to CH, CR5 or N; Y is equal to O, NH, NR8, S or Se.

[0026] When R1, R2, R5 or R7 have the meaning of aryl, it is preferably cyclohexyl or phenyl. Preferably 1 to 3 substituents for this are in particular C1-C6 alkyl, special methyls, isopropyls or tert butyls.

[0027] If R6 and R7 form a heterocyclic ring, a preferred hetero-atom is O. Further hetero-atoms can be N or S.

[0028] A further invention design consisting of a luminescent layer, as a doping agent or mixed with further doping agents for luminescent compounds of a different type, contains at least one compound for which A1 and A2 mean -CN in each case.

[0029] Preferably, the residual R1 to R12 in the meaning of C1-C6 alkyl represent methyl, isopropyl or tartan butyl in any given case.

[0030] An additional invention design according to the invention, consisting of a concentration of a doping agent mixed with another doping agent, according to the invention, or with a known doping agent of luminescent substances in the luminescent layer can be varied in the range between 0.1% by weight and 50% by weight in relation to the total weight of all doping agents.

[0031] Furthermore, it is preferable that the luminescent layer contains AlQ3 as a luminescent compound.

[0032] It was found that the new and known compounds recently used in electro-luminescent devices in the concentration range of > 1% by weight to 8% by weight, preferably >1 to 5% by weight, and specifically 1.5-3% by weight in relation to the weight of the organic luminescent compound AlQ3 generate a very efficient pure red light alone or together with AlQ3.

[0033] Objects of the invention are also new compounds of general formula I

wherein R1 to R12 are equal to or different and mean hydrogen, straight chain or branched C1-C6 alkyl, aralkyl, aryl or substituted aryl; R1 and R2 and/or R3 and R4 and/or R4 and R5 and/or R5 and R11 and/or R8 and R5 and/or R4 and R12 can form a preferably 5 or 6 member alicyclic, heterocyclic or aromatic ring; R5 can furthermore be hydrogen, OH, OR9, N,N-di-(C1-C6)alkylamino, acetylamino or halogen; R6 and R7 together can form an alicyclic or heterocyclic ring; A1 and A2 are identical or different and are -CN, -NO2 or -COOR8; X is -CH, -CR11 or N; and Y is O, -NH, -NR12, S or Se, provided that Y is not S if X means N and R5 means aryl.

[0034] The device to be used in accordance with the invention is produced according to the state of the art technology in that one, first of all, installs the anode as a transparent conductive layer of indium-tin oxide (ITO) in a layer thickness from 10 nm to 200 nm on a stable glass substrate. Immediately before applying the organic layers, this ITO layer, especially following long storage, is to be treated in an ultrasound bath successively with pure acetone and methanol. After blowing off insoluble particles with a beam of vaporization capable CO2 ice crystals, the layer is subsequently additionally treated with an oxygen plasma, whereby organic impurities are burned and eliminated.

[0035] Likewise according to the state of the art technology, one can manufacture the hole transport layer 3 (HTL) using the spin coating technique. The hole transport layer 3 consists in this case, for example, of a molecular dispersion of N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), in poly-(N-vinylcarbazole) (PVK) or a suitable polycarbonate in the proportion by weight of 1:1, whereby the ratio of hole transport material to hole transporting binding agents or also to an insulating binding agent, such as, for example, polycarbonate, can be varied in wide range. First a clear solution of PVK/TPD is produced, according to generally known principles, in an organic solvent or solvent mixture, as for example, methylene chloride in a dissolving vessel while stirring under inert gas at room temperature. The electrically conductive transparent substrate is subsequently coated by means of a spin coating device to the extent that the hole transport layer 3 possesses, following drying at 250C to 400 C under inert gas, for example, in a vacuum drying chamber, a dry layer thickness from 50 to 80 nm. It should be mentioned that the hole transport layer 3 according to the state of the art technology, preferably consisting of N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) or N,N'-biphenyl-N,N'-bis-(1-naphthyl)-benzidine (1-NPB), can also be vapor deposited on the conductive support.

[0036] Subsequently, a compound described in accordance with the invention can be applied under a high vacuum individually or also as a mixture with other types of doping agents using the co-vapor deposition technique together with the luminescent compound, for example, together with AlQ3. Here the concentration of the doping agent or also of a doping agent mixture in relation to the overall amount of material to be vaporized can come to between 1% by weight and 5% by weight, especially with a concentration between 1.5% by weight and 3% by weight in the case where AlQ3 is used as a luminescent substance to emit a red light.

[0037] The concentration of the other type of doping agent in the case where a mixture of doping agents is used can here, according to the purpose for using the electro-luminescent device, be varied in a wide range, for example between 0.1% by weight and 50% by weight in relation to the overall amount of all doping agents.

[0038] Surprisingly, with the accomplishment of the objective of the invention, it was found that, as a collateral effect, the organic electro-luminescent device emits white light in the event of an "underdoping" of the luminescent compound, especially with an "underdoping" of AlQ3 with the doping agents used in accordance with this invention.

[0039] Underdoping exists when the doping agent is co-vaporized alone or mixed with other types of doping agents in a concentration between 0.1% and 1% by weight, especially between 0.2% and 0.8% by weight in relation to the overall amount of material to be vaporized.

[0040] Without interim ventilation, the metal cathode 1 is finally applied by vaporization of LiF or Li benzoate and Al, usually in a proportion of 10:1 (0.7 nm Li benzoate + 100 nm Al). But other metals or alloys, or other proportions of metals or alloys, can also be used.

[0041] One will obtain very efficient red electro-luminescent devices when, in the luminescent layer 2, preferably in the following compounds 1 to 18 in the table, they are used as new, previously unknown doping agents, individually or also mixed with other suitable doping agents for doping AlQ3 or other luminescent compounds (the proportion of doping substances of the same time can here be freely selected):

1TABLE I1

[0042]

2

7

[0043]

3

13

[0044] One moreover will obtain very efficient red luminescent devices if the new doping agents or also mixtures of these with another type of doping agent (for example, dyes according to US-A 4,769,292) are co-vaporized for manufacturing the luminescent layer, such as with a 1,2 or 1,3-substituted quadratic acid dye.

[0045] Dyes which in accordance with the invention are used as doping agents for luminescent compounds are known as such and described in DE-A-2,831,054 and elsewhere for producing images according to a photoelectrophoretic procedure.

[0046] With these procedures, charged particles are transported in an electric field through graphic exposure of an electrically charged device containing a dye which then supplies a positive or negative image of the pattern. This method is of a completely different type in relation to the manufacture of electro-luminescent devices with dyes used in accordance with the invention and therewith not tangent.

[0047] The general manufacturing method of compounds of this dye is disclosed in US-A-2,965,486.

[0048] The following examples should serve to explain the invention in greater detail, whereby the invention is not only restricted to these.

Brief Description of Drawings

[0049] In the drawings,

[0050] Fig. 1Depicts a simple layer structure of an electro-luminescent device

[0051]
Fig. 2 Shows the layer structure with an additional electron transport layer

[0052]
Fig. 3 Illustrates the layer structure with an additional hole transport layer

[0053]
Fig. 4 Represents the layer structure with an additional hole injection layer.

Detailed Description

[0054] In the drawings, U shows the voltage applied between the corresponding electrodes.

Example of a Synthesis

[0055] The manufacture of the dyes to be used takes place preferably in a "stew reaction" according to the known methods (see US-A-2985486 of US-A-5908581) on basis of a reactive 2-methyl-4H-pyran-4-onanes by condensation, first with malonitrile in acetic acid anhydride and, in a subsequent reaction with appropriate hetero-aromatic aldehydes without isolation of the 4-dicyanomethylene-2-methyl-4-pyrans first forming. The hetero-aromatic aldehydes necessary for the synthesis and their fundamental substances are obtained according to known reaction procedures in accordance with S. Scheithauer et al. in Z. Chem. 8(1968) 182; Hartmann, H. J. Prakt. Chem. 36 (1967) 50; Liebscher, J. Houben Weyl, Methods of Organic Chemistry Vol. E 8b, Stuttgart 1995 and Organikum, Basic Practical Organic Chemistry Course, 13th edition, VEB German Sciences Publishing Company, Berlin 1974.

Example 1

[0056] Pursuant to Fig 1, a hole transport layer (HTL) 3 is applied on a glass support 5 coated with ITO (indium-zinc oxide) 4 by spin coating a solution of N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-benzidine mixed with poly-(N-vinyl carbazole) 1:1 (parts by weight) in dichloromethane. After drying the layer under inert gas at a temperature between 250C and 400 C, the layer thickness becomes 50 nm. Then the luminescent layer 2 is applied to the obtained hole transport layer 3 in a high vacuum (10-5 hPa) by co-vaporization of AlQ3 and the purified dye 1 in a concentration of 1.8% by weight in relation to AlQ3. Subsequently the metal cathode 1 is applied to the 60 nm thick luminescent layer 2 by vaporization of LiF and Al (0.7 nm LiF + 100 nm Al).

[0057] To measure the electro-luminescence, a controllable tension between 1 and 20 V is applied between the ITO and metal electrode. The electro-luminescent device so obtained shows a luminance up to 400 cd/m2 at 12.5 V. The emitted light is free from concurrent emissions of AlQ3 in the region around 530 nm and shows visually a pure red color tone.

Example 2

[0058] Vapor deposit a hole transport layer (HTL) 3 of N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-benzidine to a glass support 5 in accordance with Fig. 1 coated with ITO (indium-tin oxide) 4 in a layer thickness of 50 nm in a high vacuum (10-5 hPa). Then apply the luminescent layer 2 to the hole transport layer 3 obtained by co-vaporization of AlQ3 and the purified dye 1 in a concentration of 2.2% by weight in relation to AlQ3. The thickness of the vapor deposited luminescent layer 2 comes to 60 nm. Subsequently metal cathode 1 is applied by vaporization of Li benzoate and Al (0.7 nm Li benzoate + 100 nm Al).

[0059] To measure the electro-luminescence, a controllable tension between 1 and 20 V is applied between the ITO and metal electrode. The electro-luminescent device so obtained shows a luminance up to 450 cd/m2 at 12.5 V. The emitted light is free from concurrent emissions of AlQ3 in the region around 530 nm and shows visually a pure red color tone.

Example 3

[0060] Vapor deposit a hole transport layer (HTL) 3 of 4,4',4"-tris-(N-1-naphthyl)-N-phenyl-amino)-triphenylamine to a glass support 5 coated with ITO (indium-tin oxide) 4 in accordance with Fig. 2 in a layer thickness of 55 nm in a high vacuum (10-5 hPa). Apply the luminescent layer 2 to the hole transport layer 3 so obtained by co-vaporization of AlQ3 and the purified dye 1 in a concentration of 1.8% by weight in relation to AlQ3. The thickness of the vapor deposited luminescent layer 2 comes to 40 nm. Then apply to this layer 10 nm AlQ3 as electron transport layer 6. Subsequently apply metal cathode 1 by vaporization of Li benzoate and Al (0.7 nm Li benzoate + 100 nm Al).

[0061] To measure the electro-luminescence, a controllable tension between 1 and 20 V is applied between the ITO and metal electrode. The electro-luminescent device so obtained shows a luminance up to 1000 cd/m2 at 12.5 V. The emitted light is free from concurrent emissions of AlQ3 in the region around 530 nm and shows visually a pure red color tone.

Example 4

[0062] Sequentially vapor deposit a 5 nm thick hole injection layer of CuPC, a hole transport layer (HTL) 3b of 4,4',4"-tris-(N-(1-naphthyl)-N-phenyl-amino)-triphenyl amine to a purified glass support 5 coated with ITO (indium-tin oxide) 4 in accordance with Fig. 4 in a layer thickness of 55 nm and an additional hole transport layer 3a of N,N'-biphenyl-N,N'-bis-(1-naphthyl) benzidine (1-NPB) in a layer thickness of 5 nm in a high vacuum (10-5 hPa). Then apply the luminescent layer 2 to the hole transport layers 3a, 3b by co-vaporization of AlQ3 and purified dye 1 in a concentration of 2.2% by weight in relation to AlQ3. The thickness of the vapor deposited luminescent layer 2 comes to 40 nm. Then vapor deposit 5 nm of AlQ3as an electron transport layer 6 to this layer. Subsequently apply metal cathode 1 by vaporization of Li benzoate and Al (0.7 nm Li benzoate + 100 nm Al).

[0063] To measure the electro-luminescence, a controllable tension between 1 and 15 V is applied between the ITO and metal electrode. The electro-luminescent device so obtained shows a luminance up to 2050 cd/m2 at 14.0 V. The emitted light is free from concurrent emissions of AlQ3 in the region around 530 nm and shows visually a pure red color tone.

Example 5

[0064] Apply luminescent layer 2 by co-vaporization of AlQ3 and dye 1 to hole transport layers 3a, 3b analogously to the layer structure of example 4, whereby this is used in a concentration of only 0.7% by weight (underdoping) in relation to AlQ3. One will obtain an electro-luminescent device which alternatively emits white light when a voltage of 17 V is applied between ITO and metal electrode.

Example 6

[0065] Vapor deposit a 5 nm thick hole injection layer of CuPC, a hole transport layer (HTL) 3b of 4,4',4"-tris-(N-(1-naphthyl)-N-phenyl-amino)-triphenylamine to a purified glass support 5 coated with ITO (indium-tin oxide) 4 in accordance with Fig. 4 in a layer thickness of 55 nm and a further hole transport layer 3a of 1-NPB in a layer thickness of 5 nm in a high vacuum (10-5 hPa) one after the other. Then apply the luminescent layer 2 to the hole transport layers 3a, 3b so obtained by co-vaporization of AlQ3 and the purified dye 2 in a concentration of 2.5% by weight in relation to AlQ3. The thickness of the vapor deposited luminescent layer 2 amounts to 40 nm. Then vapor deposit on this layer 5 nm of AlQ3 as an electron transport layer 8. Subsequently apply metal cathode 1 by vaporization of Li benzoate and Al (0.7 nm Li benzoate + 100 nm Al).

[0066] To measure the electro-luminescence, a controllable tension between 1 and 15 V is applied between the ITO and metal electrode. The electro-luminescent device so obtained shows a luminance of up to 2200 cd/m2 at 13.8 V. The emitted light is free from concurrent emissions of AlQ3 in the region around 530 nm and shows visually a pure red color tone.

Claims

1. Electro-luminescent device, consisting of a hole transport layer and a luminescent layer between two conductive electrodes, whereby at least one electrode is transparent, characterized in that the luminescent layer contains as a luminescent compound or doping agent for a luminescent compound at least one compound of general formula I 25
2. Device according to claim 1, characterized in that the luminescent layer contains as a doping agent or mixed with additional other doping agents for luminescent compounds in particular a compound in which the substitutents R1 and R2 or R3 and R4 or R1 and R2 and R3 and R4 form a carbocyclic 5 or 6 member ring.
3. Device according to claim 1, characterized in that the luminescent layer contains, as doping agent or mixed with additional different types of doping agents for luminescent compounds at least one compound of general formula II: 26
4. Device according to claim 1, characterized in that the luminescent layer contains, as a doping agent or mixed with additional different types of doping agents for luminescent compounds, at least one compound of general formula III: 27
5. Device according to claim 1, characterized in that the luminescent layer contains, as doping agent or mixed with additional, different types of doping agents for luminescent compounds, at least one compound of general formula IV: 28
6. Device according to claim 1, characterized in that the luminescent layer contains, as doping agent or mixed with additional, different types of doping agents for luminescent compounds, at least one compound of general formula V: 29
7. Device according to one of claims 1, characterized in that the radicals R1 to R12 represent in any given case methyl, isopropyl or tert butyl in the meaning of C1-C6 alkyl.
8. Device according to one of claims 1, characterized in that the concentration of a doping agent or a doping agent mixture in the luminescent layer is between 1% by weight and 5% by weight, especially between 1.5% by weight and 3% by weight in relation to the amount of luminescent substance, especially in relation to AlQ3.
9. Device according to one of claims 1, characterized in that the luminescent layer preferably contains AlQ3 as the luminescent compound.
10. Device according to claim 8, characterized in that it generates a pure red light emission.
11. Device according to one of claims 1, characterized in that the luminescent layer contains as a doping agent or mixed with additional, different types of doping agents for luminescent compounds, at least one compound for which A1 and A2 in each case mean -CN.
12. Device according to one of claims 1, characterized in that the concentration of a doping agent mixed with a doping agent of a different type for luminescent substances is varied in the luminescent layer in the range between 0.1% by weight and 50% by weight in relation of the overall weight of all doping agents.
13. Device according to one of claims 1, characterized in that the concentration of doping agents lies in the range from 0.1 to 1% by weight in relation to the weight of the luminescent compound AlQ3, preferably 0.1-0.8% by weight, and in that it generates a white light when AlQ3 is used as the luminescent compound.
14. Compounds of general formula I 30

Organic Red Electro-Luminescent Device Including A Hetrocyclic Emitter

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