Organic electroluminescent material that emits in the red region of the spectrum

 

(57) Abstract:

The invention relates to an electroluminescent material, which can be used for the manufacture of organic electroluminescent displays. The electroluminescent material consists of an electronic an injecting layer, an active luminescent layer of an organic substance with a fluorescent additive, hole-transport layer and the transparent hole an injecting layer and the organic luminescent substance layer material contains bis(2-oxybenzone-4-tertbutylamine)zinc (II), and as a fluorescent additive is a dye Nile red in an amount of from 0.1 to 5 wt.%. Technical result: the material is characterized by photo - and electroluminescence in the red region of the spectrum, 632 km 3 C.p. f-crystals, 1 Il.

The invention relates to electroluminescent material containing an organic fluorescent substance.

Known organic electroluminescent materials (OSM) containing an anode, an organic hole-nictheroy and hole-transport layer, an active luminescent layer, electron transport layer, and electron-an injecting layer and a cathode, in which the efficient photoluminescence spectra [L. J. Rothberg, A. J. Lovinger, Status of and prospects for organic electroluminescence. J. Mater. Res. Vol.11, N l2, p.3174-3187 (1996)].

One of the goals for improving the properties of OLM is color management radiation emitted by the device. This task can be solved by various methods. So, apply external to OALM light-absorbing filters [Japan Patent N 10012383, 16.01.98, the Japan Patent N 06132081, 13.05.94], external fluorescent filters in which the filter material absorbs radiation of OALM and emits light with a different wavelength [Japan Patent N 09213478, 15.08.97, the Japan Patent N 09204982, 15.08.97, the Japan Patent N 09115668, 02.05.97] . Promising is the use of fluorescent additives included in the low concentration directly in the composition of the active luminescent layer OELM [C. W. Tang, S. A. Van Slyke, C. H. Chen, Electroluminescence in doped organic thin films. J. Appl.Phys. V. 65, p.3610 (1989), the Japan Patent N 09082473, 28.03.97, the Japan Patent N 08078163, 22.03.96, the Japan Patent N 07220871, 18.08.95, the Japan Patent N 07142169, 02.06.95, Z. Shen, P. E. Burrows, V. Bulovic, S. R. Forrest, M. E. Thompson, Three color, tunable, organic light emitting devices. Science, v.276, p.2009-2011 (1997), U.S. Patent N4356429, Europatent N 0669387 A1, IPC6FROM 09 TO 11/06, 24.02.94]. Typically, the luminescent layer consists of an organic matrix material (host), capable of receiving and transferring the injected holes and electrons, and fluoresce to use any active material, previously used as fluorescent in OALM, such as derivatives and stilbene in the form of thin films [US Patent N 4356429] . They can act as optical amplifiers. The most frequent 8-oksikhinolinata metals [C. W. Tang, S. A. Van Slyke, C. H. Chen, Electroluminescence in doped organic thin films. J. Appl.Phys. V. 65, p. 3610 (1989); Z. Shen, P. E. Burrows, V. Bulovic, S. R. Forrest, M. E. Thompson, Three color, tunable, organic light emitting devices. Science, v.276, p.2009-2011 (1997); Europatent N 0669387 A1, IPC6FROM 09 TO 11/06, 24.02.94]. All of these materials emit light in response to electron-hole recombination. By introducing a matrix material (host) of a small amount of fluorescent material, it is possible to modify the emitted light. To select the fluorescent material, it is important that he had a less negative reduction potential than the potential of the matrix. In addition, the energy gap (the difference in energy levels between the highest filled molecular orbital, HOMO, and the lower free orbital, LUMO) of the fluorescent material must be narrower than the matrix material. As a fluorescent material applied coumarins [C. W. Tang, S. A. Van Slyke, C. H. Chen, Electroluminescence in doped organic thin films. J. Appl. Phys. V. 65, R. 3610 (1989); Japan Patent N 09082473, 28.03.97] , phthalocyanines [Europatent N 0669387 A1, IPC6C 09 K 11/06, aetsa not enough full color conversion - in addition to the light with the wavelength corresponding to the fluorescent dye, it is saved as the radiation corresponding to the matrix material [C. W. Tang, S. A. Van Slyke, C. H. Chen, Electroluminescence in doped organic thin films. J. Appl.Phys. V. 65, p. 3610 (1989); Europatent N 0669387 A1, IPC6FROM 09 TO 11/06, 24.02.94].

The closest to the technical nature of the present device is of OALM consisting of electron-an injecting layer (cathode) (alloy Mg-Ag 10: 1), an active luminescent layer, hole - transport layer (layer consisting of a polyp-vinylcarbazole and a layer of copper phthalocyanine) and hole-an injecting layer (anode) (In2O3-SnO2), in which the active luminescent layer includes at less than 3 wt.% fluorescent phthalocyanine compound capable of emitting in the field 660-780 nm, and as a primary fluorescent substance layer is used Tris(8-) aluminum, Alq3emitting in the green spectral region [Europatent N 0669387 A1, IPC6C 09 K 11/06, 24.02.94]. The structure on the basis of such a layered material with magnesium phthalocyanine as a fluorescent additive has a red electroluminescence with a peak at 692 nm, but there is also a green electroluminescence of the basic substance is their stable electroluminescent material with radiation in the red region of the spectrum due to the efficient energy conversion, absorbed the main fluorescent substance layer, the excitation energy of the impurity fluorescent substances.

The problem is solved by the fact that according to the invention the electroluminescent material consisting of electron-an injecting layer, an active luminescent layer of an organic substance with a fluorescent additive, hole-transport layer and a transparent hole-an injecting layer, as the basic substance luminescent layer contains not previously described in the literature compound bis(2-oxybenzone-4 - tertbutylamine)zinc(II), Zn(OB-BA)2formula

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characterized by photo - and electroluminescence in the green region of the spectrum (545 nm), and as a fluorescent additive contains a dye Nile red (7 diethylamino-3,4-benzobisoxazole)

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in the amount of from 0.1 to 5 wt.%. Such material is characterized by photo - and electroluminescence in the red region of the spectrum (632 nm) due to the nonradiative transfer of energy absorbed main substance, Zn(OB-BA)2for fluorescent additive, Nile red, with the subsequent emission of molecules Nile red. At concentrations below 0.1 wt.% in the spectrum of the residual IIA.

As the hole-transport layer material may contain derivatives of diphenylamine (TRA), such as N, N'-diphenyl-N,N'-(m-tolyl)benzidine (TPD), 4,4', 4"-tricarbonylchromium (TSTA), oligomers TRA. Preferably offer the electroluminescent material as a hole-transport layer contains a mixture of oligomers of triphenylamine (PTA) formula

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where n= 8-9, when the molecular-mass distribution: MP = 2332 (about 9 units), Mw = 3586 and polydispersity Mw/Mn=1.54, with a high glass transition temperature 185oC, which ensures the stability of the material by maintaining the morphology of the hole-transport layer even at elevated temperatures. In the case of an insufficiently high temperature vitrification warming up when the device leads to a change in the electrical transport properties of the layer due to changes in morphology and, consequently, the loss of the electroluminescence device, i.e. the loss of life of the device. These drawbacks are eliminated when using the PTA.

As a transparent hole-an injecting layer material may contain mixed oxide In2O3-SnO2, translucent film of gold or conductive polymers, such as polyaniline, polyethylenimine square 20 - 25 Ohms, as it has high transparency and high mechanical strength.

As the cathode injects layer material may contain various metals and alloys: Al, Ca, Mg, Al:Li, Mg:Ag. Preferably the material contains an alloy of Mg:Ag composition Ag-10 wt.%, Mg - 90 wt.%, since the use of this alloy allows a reduction of the potential barrier at the metal - organic layer and, consequently, increases the brightness of the electroluminescence.

Example 1.

Synthesis of ligand 2-oxybenzone-4-tertbutylamine

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Into a flask of 100 ml equipped with a reflux condenser, was placed of 2.44 g (0.02 mol) of salicylic aldehyde, 2,98 g (0.02 mol) 4-tertbutylamine and 30 ml of methanol. To the mixture was added 0.5 ml of acetic acid and boiled under reflux for 1 hour. Then drove at atmospheric pressure, the basic amount of methanol (20-25 ml), was added 50 ml of toluene and drove most of the solvent (35-40 ml), the residue was dissolved in 15 ml of hexane, the solution was cooled to -10oC. the Precipitated yellow precipitate, which was filtered off, washed with cold (-10oC) hexane (2-3 ml). Received 3.12 g of product with a yield of 62% of theoretical. TPL= 93-94oC. the CLASS="ptx2">

Synthesis of chelate bis(2-oxybenzone-4-tertbutylamine) zinc (II), Zn(OB-BA)2< / BR>
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In a flask with a volume of 200 ml, provided with a mechanical stirrer, addition funnel and reflux condenser, was placed 2,53 g (0.01 mol) 2-oxybenzone-4-tertbutylamine and 20 ml of methanol. The mixture was heated in an argon atmosphere until complete dissolution of the ligand (50oC) was added a solution of 0.56 g (0.01 mol) of potassium hydroxide in 4 ml of methanol. After 10 min under continuous stirring was added dropwise to 0.68 g (0,005 mol) of anhydrous zinc chloride dissolved in 5 ml of methanol. The mixture was stirred at a temperature of about 50oC for 1 hour. It was formed precipitate of a complex of zinc and potassium bromide. After cooling the reaction mixture to 10oC the precipitate was filtered off, washed with n-hexane, and water. Dried in vacuum over calcium chloride. Received 2,03 g of product with a yield of 71% of theoretical. TPL=257-258oC. Elemental analysis. Found, %: C: 78.80; H: 6.35; N: 4.93. Brutto-formula C34H36N2O2Zn. Calculated, %: C 71,64; H 6,37; N 4,92.

In the IR spectrum contains absorption bands with maxima (cm-1) (tablet KBR): 3080 SL, 3058 SL, 3022 SL, 2962, 2904 SL, 2866 SL, 1612 O., 1590 O., 1556, 1512, 1465 O., 1444, 1403 Wed, 113 SL, 869 Wed, 841 Wed, 834 Wed, 821 SL, 790 SL, 763, 757, 744 Wed, 735 CL, 646 O. SL, 623 SL, 598 Wed, 559 Wed, 547 SL, SL 524, 504 SL, 485 SL, SL 479. Qualitative denote the intensities of the bands in the IR spectra: acting with - very strong, s - strong, Wed - medium, SL - weak, acting with very weak. The presence of bands of stretching vibrations of C-H in the region of 3000 - 3100 cm-1and bands of vibrations of double bond C=C in the field 1500-1600 cm-1confirms the existence of a system of interconnected relations of the carbon-carbon bonds.

Absorption maxima in the UV region for film of Zn(OBBA)2deposited at 285oC: 238,312,406 nm. In the photoluminescence spectrum of this film (excitation radiation 406 nm) is observed emission with a maximum at 540 nm and a width of 150 nm.

Example 2. Spectral properties of films of Zn(OBBA)2and a mixture of Zn(OBBA)2(99%) + Nile red (1%).

Zn(OBBA)2(synthesized according to example 1) is dissolved in chloroform and applied by centrifuging on a quartz plate in the form of a film thickness of 0.05-0.1 μm (film 1). Zn(OBBA)2and Nile red (Aldrich Chem. Co) in the ratio of 99:1 (by weight) is dissolved in chloroform and applied by centrifuging on a quartz plate in the form of a film thickness of 0.05-0.1 μm (film 2). For films 1 and 2 is measured absorption spectra, spinouts on the spectral sensitivity of the setup.

Film 1 (as deposited film in example 1) was observed absorption spectrum with maxima 312 and 406 nm (drawing, curve 1) and photoluminescence in the green spectral region with a maximum of 540 nm and a width of 150 nm (drawing, curve 2; exciting line 406 nm). Excitation spectrum of the photoluminescence film 1, measured in the field 320-600 nm (shown on drawing circles) coincides with the absorption spectrum of this film: contains the line 406 nm, and the edge of the strip 312 nm.

Film 2 in the absorption spectrum are also observed maxima 312 and 406 nm, related to Zn(OBBA)2in addition, there is a weak maximum of 556 nm, associated with the uptake of Nile red (drawing, curve 3). In the spectrum of the photoluminescence film 2 is observed only red radiation with a maximum of 632 nm, associated with the luminescence of Nile red ( drawing, curve 4, a stimulating line 406 nm). Band radiation Zn(OBBA)2540 nm in the spectrum of the photoluminescence film 2 is not observed. Excitation spectrum of the photoluminescence film 2 as shown in the drawing, x) coincides with the absorption spectrum of this film and contains bands 406 and 312 nm corresponding to the absorption of Zn(OBBA)2and a weak band 556 nm corresponding to the absorption Helskog and Zn(OBBA)2and radiates only molecules Nile red. This indicates efficient nonradiative energy transfer from molecules Zn(OBBA)2to molecules Nile red. Thus, in the system Zn(OBBA)2(99%) + Nile red (1%) green radiation of the basic substance luminescent layer, Zn(OBBA)2, completely extinguished due to nonradiative energy transfer to the molecules of the fluorescent additive, Nile red, and is saved only red radiation of this Supplement.

Example 3. The electroluminescent material is ITO/OTA/Zn(OBBA)2/ Mg:Ag

Use a glass substrate with a transparent layer of a mixed oxide of indium and tin, In2O3-SnO2with the resistance of a square 20-25 Ohms, which by centrifuging from a solution in toluene put a layer of PTA thickness of 0.05 - 0.1 μm. Then by evaporation in a vacuum at a temperature of about 285oC and a base pressure of 5 10-6mm RT.article put the active layer is Zn(OBBA)2thickness of 0.02-0.05 micron. The sample is placed in a vacuum installation VUP-4, pump out in a dynamic mode to vacuum 5 10-6mm RT.article and sprayed metal electrode by evaporation of an alloy containing magnesium (90%) and silver (10%). The thickness of the metal is radiation with brightness, proportional to the current to a voltage of 11.8 V and a current density of 2 mA/cm2the achieved brightness of 480 CD/m2.

Example 4. The electroluminescent material is ITO/PTA/Zn(OB-BA)2(99%) + Nile red (l%)/Mg:Ag.

Use a glass substrate with a transparent layer In2O3-SnO2with the resistance of a square 20-25 Ohms, which by centrifuging from a solution in toluene put a layer of PTA thickness of 0.05 - 0.1 μm. Then by centrifuging from a solution in chloroform is applied to the active layer Zn(OBBA)2(99%) + Nile red (1%) with a thickness of 0.02-0.05 microns (as in example 2). The sample is placed in a vacuum installation VUP-4, pump out in a dynamic mode to vacuum 510-6mm RT.article and sprayed metal electrode by evaporation of an alloy containing magnesium (90%) and silver (10%). The thickness of the metal electrode is about 0.1 μm. The area of the illuminated surface of 4-5 mm2. Received ELU emits red light with a brightness proportional to the current to a voltage of 11 V and a current density of 30 mA/cm2when this is achieved brightness of 0.4 CD/m2.

Sources of information

1. L. J. Rothberg, A. J. Lovinger, Status of and prospects for organic electroluminescence. J. Mater.Res. Vol.11, N l2, p. 3174-3187 (1996).

2. Pathé>/P>5. The Japan Patent N 09204982, 15.08.97.

6. The Japan Patent N 09115668, 02.05.97.

7. The Japan Patent N 06215874, 15.08.94.

8. The Japan Patent N 06203963, 22.07.94.

9. C. W. Tang, S. A. Van Slyke, C. H. Chen, Electroluminescence in doped organic thin films. J. Appl.Phys. V. 65, R. 3610 (1989).

10. The Japan Patent N 09082473, 28.03.97.

11. The Japan Patent N 08078163, 22.03.96.

12. The Japan Patent N 07220871, 18.08.95.

13. The Japan Patent N 07142169, 02.06.95.

14. Z. Shen, P. E. Burrows, V. Bulovic, S. R. Forrest, M. E. Thompson, Three color, tunable, organic light emitting devices. Science, v.276, p.2009-2011 (1997).

15. U.S. patent N 4356429.

16. Europatent N 0669387 A1, IPC6FROM 09 TO 11/06, 24.02.94.

1. The electroluminescent material consisting of e an injecting layer, an active luminescent layer of an organic substance with a fluorescent additive, hole-transport layer and the transparent hole an injecting layer, characterized in that as an organic fluorescent substance layer material contains bis(2-oxybenzone-4-tertbutylamine)zinc (II) formula

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and as fluorescent additive contains a dye Nile red in an amount of from 0.1 to 5 wt.%.

2. The electroluminescent material under item 1, characterized in that it as a hole-the RNO-mass distribution: Mn = 2332, Mw = 3586 and polydispersity Mw/Mn = 1.54.

3. The material under item 1, characterized in that as the hole-an injecting layer contains a mixed oxide In2O3-SnO2with the electrical resistance of a square of 20 to 25 Ohms.

4. The material under item 1, characterized in that as electroconductive layer contains an alloy of Mg and Ag composition Ag-10 wt.%, Mg - 90 wt.%.

 

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2 cl, 1 tbl, 13 ex

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