Materials for organic electroluminescent devices

Abstract

The present invention relates to compounds of the formula (1) which are suitable for use in electronic devices, in particular organic electroluminescent devices, and to electronic devices which comprise these compounds.

Claims

1. An organic electroluminescent device (OLED) comprising a compound of the formula (2A), ##STR00062## where the following applies to the symbols and indices used: R.sup.1 stands on each occurrence, identically or differently, for H, D, F, CN, a straight-chain alkyl groups having 1 to 10 C, where one or more H atoms may be replaced by D or F; R.sup.2 stands on each occurrence, identically or differently, from the group consisting of F, CN, a straight-chain alkyl, alkoxy or thioalkyl groups having 1 to 20 C atoms or a branched or a cyclic alkyl, alkoxy or thioalkyl groups having 3 to 20 C atoms, each of which may be substituted by one or more radicals R.sup.3, where in each case one or more non-adjacent CH.sub.2 groups may be replaced by R.sup.3C═CR.sup.3, C═C, C═O, P(═O)(R.sup.3), SO, SO.sub.2, O, S or CONR.sup.3 and where one or more H atoms may be replaced by D or F, an aromatic or heteroaromatic ring systems having 5 to 30 aromatic ring atoms, which may in each case be substituted by one or more radicals R.sup.3, or an aryloxy groups having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R.sup.3; R.sup.3 stands on each occurrence, identically or differently, for H, D, F, Cl, Br, I, CHO, CN, N(Ar).sub.2, C(═O)Ar, P(═O)(Ar).sub.2, S(═O)Ar, S(═O).sub.2Ar, NO.sub.2, Si(R.sup.4).sub.3, B(OR.sup.4).sub.2, OSO.sub.2R.sup.4, a straight-chain alkyl, alkoxy or thioalkyl groups having 1 to 40 C atoms or branched or cyclic alkyl, alkoxy or thioalkyl groups having 3 to 40 C atoms, each of which may be substituted by one or more radicals R.sup.4, where in each case one or more non-adjacent CH.sub.2 groups may be replaced by R.sup.4C═CR.sup.4, C≡C, Si(R.sup.4).sub.2, Ge(R.sup.4).sub.2, Sn(R.sup.4).sub.2, C═O, C═S, C═Se, P(═O)(R.sup.4), SO, SO.sub.2, O, S or CONR.sup.4 and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO.sub.2, an aromatic or heteroaromatic ring systems having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R.sup.4, or an aryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R.sup.4, where two adjacent substituents R.sup.3 may form a mono- or polycyclic, aliphatic ring system or aromatic ring system, which may be substituted by one or more radicals R.sup.4; R.sup.4 stands on each occurrence, identically or differently, for H, D, F, Cl, Br, I, CN, a straight-chain alkyl, alkoxy or thioalkyl groups having 3 to 20 C atoms, where in each case one or more non-adjacent CH.sub.2 groups may be replaced by SO, SO.sub.2, O, S and where one or more H atoms may be replaced by D, F, Cl, Br or I, or an aromatic or heteroaromatic ring system having 5 to 24 C atoms; Ar is on each occurrence, identically or differently, and aromatic of heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case also be substituted by one or more radicals R.sup.4; n is on each occurrence equal to 1 and wherein the OLED comprising the compound of the formula (2A), is employed as an electron-acceptor material in a hole-injection layer.

2. A formulation comprising at least one compound according to claim 1 and at least one solvent.

3. The OLED according to claim 1, wherein the compound is employed as the electron-acceptor material in the hole-injection layer as pure material, or in combination with one or more further compounds, where a proportion of the compound according to claim 1 is then comprised between 50.0 and 99.9% by vol. if the compounds are applied from a gas phase and 50.0 and 99.9% by weight if the compounds are applied from solution.

4. The OLED according to claim 3, wherein the OLED further comprises at least one hole-transport layer and at least one emitting layer, where the hole-transport layer is located between the hole-injection layer and the emitting layer.

5. The OLED according to claim 3, wherein the hole-injection layer comprising the compound has a thickness layer of from 0.5 nm to 50 nm.

6. The OLED according to claim 1, wherein the compound is employed as a p-dopant in a hole-transporting layer selected from a hole-injection layer, a hole-transport layer and an electron-blocking layer.

7. The OLED according to claim 1, wherein the compound is of the formula: ##STR00063##

Description

WORKING EXAMPLES

A) Synthesis Examples

Example 1 (E1) 2-(12-oxo-2,9-bis(trifluoromethoxy)indeno[1,2-a]fluoren-7-ylidene)malononitrile

a) Dimethyl 4,4″-bis(trifluoromethoxy)-[1,1′:3′,1″-terphenyl]-2,2″-dicarboxylate

(1) ##STR00044##

(2) Methyl 2-bromo-5-(trifluoromethoxy)benzoate (63.5 g, 212.4 mmol), 1,3-phenylenediboronic acid (16.0 g, 96.5 mmol) and K.sub.3PO.sub.4 (88.9 g, 386.1 mmol) are dissolved in toluene (700 ml)/ethanol (420 ml)/water (280 ml) under argon. The solution is degassed and Pd(PPh.sub.3).sub.4 (5.57 g, 4.83 mmol) is added. The mixture is heated up to 60° C. over night. After cooling to room temperature, the solution is poured into water (300 ml) with vigorous stirring. The layers are separated and the aqueous layer is extracted with toluene (2×100 ml) and dichloromethane (100 ml). The combined organic layers are washed with brine (150 ml) and dried over MgSO.sub.4. The solvent is evaporated in vacuo. The crude product is purified via silica column chromatography using ethyl acetate/heptane (1:4) as eluent. The product is obtained as yellow glue (51.3 g, quant. with some impurities).

(3) 1H NMR (CDCl.sub.3, 500 MHz): δ=3.69 (s, 6H, COOCH.sub.3), 7.21-7.22 (m, 1H, H-2′), 7.30 (dd, 2H, .sup.3J=7.3 Hz, .sup.4J=1.7 Hz, H-5,5″), 7.37-7.40 (m, 2H, H-4′,6′), 7.41-7.45 (m, 3H, H-6,6″, H-5), 7.71 (d, 2H, .sup.4J=1.6 Hz, H-3,3″) ppm GC-MS (EI, 70 eV)=514 (60%), 451 (100%), 423 (25%), 326 (20%)

b) 2,9-bis(trifluoromethoxy)indeno[1,2-a]fluorene-7,12-dione

(4) ##STR00045##

(5) Dimethyl 4,4″-bis(trifluoromethoxy)-[1,1′:3′,1″-terphenyl]-2,2″-dicarboxylate (51.3 g, 99.8 mmol) is dissolved in conc. H.sub.2SO.sub.4 (400 ml). The mixture is stirred at room temperature for 1 h, then heated up to 50° C. over night. The temperature is increased to 70° C. until TLC shows complete consumption of the starting material. After cooling to room temperature, the reaction mixture is poured into iced water. A voluminous yellow precipitate is formed. The solid is filtered off and is washed with water, ethanol and heptane. The crude material is dried in vacuo at 60° C. over night. It is filtered over silica using DCM and DCM+10% methanol as eluent. The crude product (39.55 g, 87.8 mmol, 88%) is used in the next reaction without further purification.

(6) TLC: Rf(product)=0.55, (silica, DCM/heptane 3:1)

(7) 1H NMR (CDCl.sub.3, 500 MHz): δ=7.44 (dd, 1H, .sup.3J=8.2 Hz, .sup.4J=1.5 Hz, H-3), 7.48 (dd, 1H, .sup.3J=8.2 Hz, .sup.4J=1.5 Hz, H-10), 7.54 (d, 1H, .sup.3J=7.3 Hz, H-5), 7.59-7.60 (m, 1H, H-1), 7.63-7.64 (m, 1H, H-8), 7.69 (d, 1H, .sup.3J=8.2 Hz, H-4), 7.88 (d, 1H, .sup.3J=7.4 Hz, H-6), 8.95 (d, 1H, .sup.3J=8.2 Hz, H-11) ppm GC-MS (EI, 70 eV)=450 (100%), 325 (40%), 200 (15%)

c) 2-(12-oxo-2,9-bis(trifluoromethoxy)indeno[1,2-a]fluoren-7-ylidene)malononitrile (E1)

(8) ##STR00046##

(9) Crude material of 2,9-bis(trifluoromethoxy)indeno[1,2-a]fluorene-7,12-dione (39.55 g, 87.8 mmol) is dissolved in pyridine (1500 ml) under argon. Malononitrile (34.8 g, 527 mmol) is added and the reaction mixture is heated up to 65° C. over night. After cooling to room temperature the reaction mixture is diluted with dichloromethane and 1 M HCl. The layers are separated and the aqueous layer is extracted with dichloromethane. The combined organic layers are dried over MgSO.sub.4 and the solvent is removed in vacuo. The crude product (63.3 g) is obtained as red solid. The material is further purified via silica column chromatography using heptane and dichloromethane (1:2) as eluent. The isolated product fraction is recrystallized from heptane/dichloromethane. E1 (6.3 g, 12.6 mmol, 14%) is obtained as fluffy orange solid. The material is sublimed for further purification.

(10) TLC: Rf(E1)=0.46, (silica, ethyl acetate/heptane 1:2)

(11) 1H NMR (CDCl.sub.3, 500 MHz): δ=7.46 (dd, 1H, .sup.3J=8.1 Hz, .sup.4J=1.5 Hz, H-3), 7.51 (dd, 1H, .sup.3J=8.5 Hz, .sup.4J=1.1 Hz, H-10), 7.55 (d, 1H, .sup.3J=8.1 Hz, H-5), 7.62 (s, 1H, H-1), 7.71 (d, 1H, .sup.3J=8.5 Hz, H-4), 8.35 (s, 1H, H-8), 8.66 (d, 1H, .sup.3J=8.0 Hz, H-6), 9.18 (d, 1H, .sup.3J=8.4 Hz, H-11) ppm

(12) MS (ESI+): m/z=499 (M+H.sup.+)

Example 2 (E2) 2-(12-oxo-2,9-bis(trifluoromethoxy)indeno[1,2-a]fluoren-7-ylidene)malononitrile

(13) ##STR00047##

(14) E1 (50 mg, 0.10 mmol) and malononitrile (0.13 g, 2.01 mmol) are dissolved in pyridine (4 ml). The reaction mixture is heated to 100° C. for 24 h. After cooling to room temperature, aqueous HCl (1 M) is added. The red precipitate is filtered off and is washed with water, little DCM and heptane.

(15) E2 is obtained as red powder.

(16) TLC: Rf(E2)=0.05, (silica, ethyl acetate/heptane 1:2)

(17) MS (EI+): m/z=546 (M*.sup.+)

Examples 3 to 16 (E3 to E-16)

(18) Following compounds can be obtained in analogy by using the same synthetic procedure as described for E1 (E3-E9) and E2 (E10-E16):

(19) ##STR00048##

(20) ##STR00049## ##STR00050## ##STR00051##

B) Device Examples

(21) The data for various devices are presented in Examples below (see Tables 1 to 2). The substrates used are glass plates coated with structured ITO (indium tin oxide) with a thickness of 50 nm.

(22) Freshly cleaned substrates are transferred into the evaporation tool. Here the substrates are either preconditioned with oxygen plasma for 130 s and afterwards treated with argon plasma for 150 s (Oxygen_Argon) or only preconditioned with oxygen plasma for 130 s (Oxygen).

(23) Afterwards several organic layers are deposited by physical vapour deposition.

(24) The thickness of the layers is determined by reference experiments, where thick layers of roughly 100 nm organic material are deposited. The thickness is measured during the evaporation by a thin-film thickness monitor, based on quartz crystal microbalance, e.g. Inficon. The organic layer is protected by evaporation of a thin aluminium film on top. Then the real thickness of the organic layer is measured by a surface profiler, e.g. K-LA-Tencor P7. The tooling factor of the thin-film monitor is adapted in a way that the film thickness of the surface profiler and the thin film monitor is the same.

(25) The devices basically have the following layer structure: substrate/hole-injection layer (HIL)/hole-transport layer (HTL) and finally a cathode. The cathode is formed by an aluminium layer with a thickness of 100 nm. The precise structure of the devices is shown in table 1. The materials required for the production of the devices are shown in table 5.

(26) All materials are applied by thermal vapour deposition in a vacuum chamber. An expression such as HTM1: HIM1 (5%) here means that material HTM1 is present in the layer in a proportion by volume of 95% and HIM1 is present in the layer in a proportion of 5%. Analogously, other layers may also consist of a mixture of two or more materials.

(27) The OLEDs are characterised by standard methods. For this purpose, the electroluminescence spectra and the external quantum efficiency (EQE, measured in percent) as a function of the luminous density, calculated from current/voltage/luminous density characteristic lines (IUL characteristic lines) assuming Lambert emission characteristics. The expression EQE @10 mA/cm.sup.2 denotes the external quantum efficiency at an operating current density of 10 mA/cm.sup.2. LT90 @ 60 mA/cm.sup.2 is the lifetime until the OLED has dropped from its initial luminance of i.e. 5000 cd/m.sup.2 to 90% of the initial intensity, i.e. to 4500 cd/m.sup.2 without using any acceleration factor. The data for the various OLEDs containing inventive and comparative materials are summarised in table 2 and 4.

(28) TABLE-US-00001 HIL HTL Cathode Thickness/ Thickness/ Thickness/ Ex. Plasma nm nm mm V1 Oxygen_Argon HATCN HTM1 Al 5 nm 100 nm 100 nm V2 Oxygen — HTM1 Al 100 nm 100 nm V3 Oxygen — HTM2 Al 100 nm 100 nm V4 Oxygen — HTM3 Al 100 nm 100 nm V5 Oxygen — HTM4 Al 100 nm 100 nm E1 Oxygen_Argon HIM1 HTM1 Al 5 nm 100 nm 100 nm E2 Oxygen_Argon HIM1 HTM1 Al 2 nm 100 nm 100 nm E3 Oxygen_Argon HIM1 HTM2 Al 2 nm 100 nm 100 nm E4 Oxygen_Argon HIM1 HTM3 Al 2 nm 100 nm 100 nm E5 Oxygen_Argon HIM1 HTM3 Al 3 nm 100 nm 100 nm E6 Oxygen_Argon HIM1 HTM3 Al 4 nm 100 nm 100 nm E7 Oxygen_Argon HIM1 HTM3 Al 5 nm 100 nm 100 nm E8 Oxygen_Argon HIM1 HTM4 Al 2 nm 100 nm 100 nm E9 Oxygen_Argon HIM1 HTM4 Al 3 nm 100 nm 100 nm E10 Oxygen_Argon HIM1 HTM4 Al 4 nm 100 nm 100 nm E11 Oxygen_Argon HIM1 HTM4 Al 5 nm 100 nm 100 nm E12 Oxygen HIM1 HTM1 Al 2 nm 100 nm 100 nm E13 Oxygen HIM1 HTM1 Al 3 nm 100 nm 100 nm E14 Oxygen HIM1 HTM1 Al 4 nm 100 nm 100 nm E15 Oxygen HIM1 HTM1 Al 5 nm 100 nm 100 nm E16 Oxygen HIM1 HTM2 Al 2 nm 100 nm 100 nm E17 Oxygen HIM1 HTM2 Al 3 nm 100 nm 100 nm E18 Oxygen HIM1 HTM2 Al 4 nm 100 nm 100 nm E19 Oxygen HIM1 HTM2 Al 5 nm 100 nm 100 nm E20 Oxygen HIM1 HTM3 Al 2 nm 100 nm 100 nm E21 Oxygen HIM1 HTM3 Al 3 nm 100 nm 100 nm E22 Oxygen HIM1 HTM3 Al 4 nm 100 nm 100 nm E23 Oxygen HIM1 HTM3 Al 5 nm 100 nm 100 nm E24 Oxygen HIM1 HTM4 Al 2 nm 100 nm 100 nm E25 Oxygen HIM1 HTM4 Al 3 nm 100 nm 100 nm E26 Oxygen HIM1 HTM4 Al 4 nm 100 nm 100 nm E27 Oxygen HIM1 HTM4 Al 5 nm 100 nm 100 nm

(29) TABLE-US-00002 U U @ 10 mA/cm.sup.2 @ 100 mA/cm.sup.2 Ex. [V] [V] V1 1.5 2.3 V2 8.1 11.1 V3 10.8 14.5 V4 7.1 9.5 V5 5.8 8.2 E1 1.8 5.4 E2 1.8 3.4 E3 2.9 6.1 E4 1.4 2.3 E5 1.4 2.3 E6 1.4 2.4 E7 1.4 3.0 E8 1.4 2.5 E9 1.4 2.5 E10 1.4 2.4 E11 1.6 3.6 E12 1.5 2.3 E13 1.5 2.1 E14 1.5 2.1 E15 1.5 2.2 E16 1.7 2.5 E17 1.7 2.7 E18 1.7 2.5 E19 1.7 2.7 E20 1.4 2.3 E21 1.4 2.3 E22 1.4 2.2 E23 1.4 2.3 E24 1.4 2.8 E25 1.3 2.2 E26 1.3 2.2 E27 1.4 2.5

(30) TABLE-US-00003 HIL HTL EBL EML ETM Cathode Thickness/ Thickness/ Thickness/ Thickness/ Thickness/ Thickness/ Ex. nm nm nm nm nm nm E28 HIM1 HTM3 HTM1 SMB; SEB (3%) ETM; LiQ (50%) Al 3 nm 175 nm 10 nm 20 nm 30 100 nm

(31) TABLE-US-00004 U EQE LT90 @ 10 mA/cm.sup.2 @ 10 mA/cm.sup.2 @ 60 mA/cm.sup.2 Ex. [V] [%] h E28 4.0 6.0 140

(32) TABLE-US-00005 TABLE 5 Structures of the materials used 0

Examples

(33) Devices with the structures shown in table 1 are produced. Table 2 shows the performance data of the examples described. The devices are hole-only devices in which HATCN and HIM1 are used as the hole injection layer (HIL). It can be shown, that very low voltages can be obtained with thin layers of HIM1, also in combination with deeper HOMO level HTMs, such as HTM2.

(34) Furthermore, it can be shown that HIM1 also gives very low voltage, good efficiency and good lifetime in a blue device (E28).