Organic electroluminescent device

Abstract

The present invention relates to an organic electroluminescent device comprising an anode, a cathode, an emission layer, an undoped electron transport layer comprising a first matrix compound, and an electron injection layer comprising a second matrix compound and an alkali organic complex and/or alkali halide, wherein the undoped electron transport layer and the electron injection layer are arranged between the emission layer and the cathode, wherein the reduction potential of the first matrix compound is less negative than, the reduction potential of 9,10-di(naphthalen-2-yl)anthracene and more negative than the reduction potential of 4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl, wherein the reduction potential in both cases is measured against Fc/Fc.sup.+ in tetrahydrofurane; and the dipole moment of the first matrix compound is selected ≥0 Debye and ≤2.5 Debye and the dipole moment of the second matrix compound is selected >2.5 and <10 Debye.

Claims

1. Organic electroluminescent device comprising an anode, a cathode, an emission layer, an undoped electron transport layer comprising a first matrix compound, and an electron injection layer comprising a second matrix compound and an alkali organic complex and/or alkali halide, wherein the undoped electron transport layer and the electron injection layer are arranged between the emission layer and the cathode, wherein the reduction potential of the first matrix compound is less negative than the reduction potential of 9,10-di(naphthalen-2-yl)anthracene and more negative than the reduction potential of 4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl, wherein the reduction potential in both cases is measured against Fc/Fc.sup.+ in tetrahydrofurane; wherein the dipole moment of the first matrix compound is selected 0 Debye and ≤2.5 Debye and the dipole moment of the second matrix compound is selected >2.5 and <10 Debye; the emission layer is in direct contact with the undoped electron transport layer; the emission layer comprises an emission layer host; and the off-set between the reduction potential of the emission layer host and the reduction potential of the first matrix compound is ≥0.1 and ≤0.3 V; wherein the first matrix compound is selected from the following compounds or derivatives thereof, the compounds being dibenzo[c,h]acridine, dibenzo[a,j]acridine, benzo[c]acridine, triaryl borane compounds, 2-(benzo[d]thiazol-2-yl)phenoxy metal complex, triazine, benzothienopyrimidine, or mixtures thereof; wherein the second matrix compound is selected from the following compounds or derivatives thereof, the compounds being phosphine oxide, benzimidazole, phenanthroline, or mixtures thereof; and wherein the alkali organic complex is a lithium organic complex and/or the alkali halide is lithium halide.

2. Organic electroluminescent device according to claim 1, wherein the first matrix compound comprises a triaryl borane compound of formula (I) ##STR00106## wherein R.sup.1, R.sup.3 and R.sup.7 are independently selected from a group consisting of H, D, C.sub.1-C.sub.16 alkyl and C.sub.1-C.sub.16 alkoxy; R.sup.2, R.sup.4, R.sup.5 and R.sup.6 are independently selected from a group consisting of H, D, C.sub.1-C.sub.16 alkyl, C.sub.1-C.sub.16 alkoxy and C.sub.6-C.sub.20 aryl; Ar.sup.0 is selected from substituted or unsubstituted C.sub.6-C.sub.20 aryl, wherein, in case that Ar.sup.0 is substituted, the substituents are independently selected from a group consisting of D, C.sub.1-C.sub.12 alkyl, C.sub.1-C.sub.16 alkoxy and C.sub.6-C.sub.20 aryl; and Ar.sup.1 is selected from substituted or unsubstituted C.sub.6-C.sub.20 arylene, wherein, in case that Ar.sup.1 is substituted, the substituents are independently selected from a group consisting of D, C.sub.1-C.sub.12 alkyl, C.sub.1-C.sub.16 alkoxy and C.sub.6-C.sub.20 aryl; and Ar.sup.2 is selected from a group consisting of H, D, substituted or unsubstituted C.sub.6-C.sub.40 aryl and C.sub.5-C.sub.40 heteroaryl.

3. Organic electroluminescent device according to claim 1, wherein the first matrix compound comprises a dibenzo[c,h]acridine compound of formula (II) ##STR00107## and/or a dibenzo[a,j]acridine compound of formula (III) ##STR00108## and/or a benzo[c]acridine compound of formula (IV) ##STR00109## wherein Ar.sup.3 is independently selected from C.sub.6-C.sub.20 arylene; Ar.sup.4 is independently selected from unsubstituted or substituted C.sub.6-C.sub.40 aryl; and in case that Ar.sup.4 is substituted, the one or more substituents may be independently selected from the group consisting of C.sub.1-C.sub.12 alkyl and C.sub.1-C.sub.12 heteroalkyl.

4. Organic electroluminescent device according to claim 1, wherein the first matrix compound comprises a triazine compound of formula (V) ##STR00110## wherein Ar.sup.5 is independently selected from unsubstituted or substituted C.sub.6-C.sub.20 aryl or Ar.sup.5.1-Ar.sup.5.2, wherein Ar.sup.5.1 is selected from unsubstituted or substituted C.sub.6-C.sub.20 arylene and Ar.sup.5.2 is selected from unsubstituted or substituted C.sub.6-C.sub.20 aryl or unsubstituted and substituted C.sub.5-C.sub.20 heteroaryl; Ar.sup.6 is selected from unsubstituted or substituted C.sub.6-C.sub.20 arylene; Ar.sup.7 is independently selected from a group consisting of substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, the aryl and the heteroaryl having 6 to 40 ring-forming atoms; x is selected from 1 or 2, wherein in case that Ar.sup.5 is substituted the one or more substituents may independently be selected from C.sub.1-C.sub.12 alkyl and C.sub.1-C.sub.12 heteroalkyl; and in case that Ar.sup.7 is substituted, the one or more substituents may be independently selected from C.sub.1-C.sub.12 alkyl and C.sub.1-C.sub.12 heteroalkyl, and from C.sub.6-C.sub.20 aryl.

5. Organic electroluminescent device according to claim 1, wherein the first matrix compound comprises benzothienopyrimidine compound substituted with C.sub.6-C.sub.40 aryl, C.sub.5-C.sub.40 heteroaryl and/or C.sub.1-C.sub.12 alkyl groups.

6. Organic electroluminescent device according to claim 1, wherein the alkali organic complex is a compound of formula (VII) ##STR00111## wherein M is an alkali metal ion, each of A.sup.1-A.sup.4 is independently selected from substituted or unsubstituted C.sub.6-C.sub.20 aryl or substituted or unsubstituted C.sub.2-C.sub.20 heteroaryl.

7. Organic electroluminescent device according to claim 1, wherein the thickness of the undoped electron transport layer is at least two times the thickness of the electron injection layer.

8. Organic electroluminescent device according to claim 1, wherein the emission layer comprises a fluorescent blue emitter.

9. Organic electroluminescent device according to claim 8, wherein the organic electroluminescent device is a fluorescent blue device.

10. Organic electroluminescent device according to claim 9, wherein the emission layer further comprises an anthracene matrix compound substituted with C.sub.6-C.sub.40 aryl, C.sub.5-C.sub.40 heteroaryl and/or C.sub.1-C.sub.12 alkyl groups.

11. Organic electroluminescent device according to claim 3, wherein Ar.sup.3 is phenylene, biphenylene, or fluorenylene.

12. Organic electroluminescent device according to claim 3, wherein Ar.sup.4 is phenyl, naphthyl, anthranyl, pyrenyl, or phenanthryl.

13. Organic electroluminescent device according to claim 4, wherein Ar.sup.6 is phenylene, biphenylene, terphenylene, or fluorenylene.

14. Organic electroluminescent device according to claim 4, wherein Ar.sup.7 is phenyl, naphthyl, phenantryl, fluorenyl, terphenyl, pyridyl, quinolyl, pyrimidyl, triazinyl, benzo[h]quinolinyl, or benzo[4,5]thieno[3,2-d]pyrimidine.

15. Organic electroluminescent device according to claim 5, wherein the first matrix compound comprises 2-phenyl-4-(4′,5′,6′-triphenyl-[1,1′:2′,1″:3″,1′″-quaterphenyl]-3′″-yl)benzo[4,5]thieno[3,2-d]pyrimidine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, of which:

(2) FIG. 1 shows a graph where power efficiency in lm/W is plotted against (a) the off-set in reduction potential between the EML host and the first matrix compound in Volt (primary x-axis) and (b) the reduction potential of the first matrix compound measured against Fc/Fc.sup.+ in tetrahydrofurane in Volt (secondary x-axis).

(3) FIG. 2 is a schematic sectional view of an organic electroluminescent device, according to an exemplary embodiment of the present invention.

(4) FIG. 3 is a schematic sectional view of an organic electroluminescent device, according to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION

(5) Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The exemplary embodiments are described below, in order to explain the aspects of the present invention, by referring to the figures.

(6) Herein, when a first element is referred to as being formed or disposed “on” a second element, the first element can be disposed directly on the second element, or one or more other elements may be disposed there between. When a first element is referred to as being formed or disposed “directly on” a second element, no other elements are disposed there between.

(7) FIG. 1 is a graph wherein the power efficiency in lm/W is plotted (a) against off-set between reduction potential of the EML host and reduction potential of the first matrix compound in Volt (primary x-axis) and (b) the reduction potential of the first matrix compound measured against Fc/Fc.sup.+ in tetrahydrofurane in Volt (secondary x-axis). As can be clearly seen, a small off-set in reduction potential of the EML host and the first matrix compound leads to low power efficiency. Additionally, a very large off-set between reduction potential of the EML host and first matrix compound results in low power efficiency. A polar first matrix compound also leads to poor performance. Surprisingly, it was found that the power efficiency is significantly increased if a small off-set in reduction potential between the EML host and first matrix compound is present and the first matrix compound is a polar compound.

(8) FIG. 2 is a schematic sectional view of an organic electroluminescent device (OLED) 100, according to an exemplary embodiment of the present invention. The OLED 100 includes a substrate 110, a first electrode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an emission layer (EML) 150, an undoped electron transport layer (ETL) 161. The undoped electron transport layer (ETL) 161 is formed directly on the EML 150. The electron injection layer (EIL) 180 is formed directly on the ETL. A cathode 190 is disposed on the electron injection layer 180.

(9) FIG. 3 is a schematic sectional view of an OLED 100, according to another exemplary embodiment of the present invention. FIG. 3 differs from FIG. 2 in that the OLED 100 of FIG. 3 comprises a hole blocking layer (HBL) 155.

(10) In the description above the method of manufacture an OLED of the present invention is started with a substrate 110 onto which an anode 120 is formed, on the anode 120, an hole injection layer 130, hole transport layer 140, an emission layer 150, optional a hole blocking layer 155, at least one electron transport layer 161, at least one electron injection layer 180, and a cathode 190 are formed, in that order or the other way around.

(11) While not shown in FIG. 2 and FIG. 3, a sealing layer may further be formed on the cathodes 190, in order to seal the OLEDs 100. In addition, various other modifications may be applied thereto.

(12) Hereinafter, one or more exemplary embodiments of the present invention will be described in detail with, reference to the following examples. However, these examples are not intended to limit the purpose and scope of the one or more exemplary embodiments of the present invention.

EXAMPLES

(13) A variety of dipole moments and reduction potentials of representative examples of the first matrix compounds were measured. The results are summarized in the below table 4.

(14) TABLE-US-00004 TABLE 4 Dipole moments and reduction potentials of representative examples of the first matrix compound Reduction potential Dipole against Com- moment/ Fc/Fc+ in pound Name Structure Debye THF/V ETM-1  Tri(naphthalen- 1-yl)borane 0.14 −2.31 ETM-7  bis(2- methylnaphthalen- 1-yl)(3- (phenanthren- 9- yl)phenyl) borane 0.18 −2.35 ETM-14 7-(3-(pyren-1- yl)phenyl)dibenzo [c,h]acridine 1.80 −2.26 ETM-16 7-(3-(pyridin- 4- yl)phenyl) dibenzo [c,h]acridine 2.26 −2.27 ETM-17 14-(3-(pyren-1- yl)phenyl) dibenzo[a,j] acridine 2.50 −2.3  ETM-36 7-(3-(pyren-1- yl)phenyl) benzo[c]acridine 2.13 −2.2  ETM-28 2-(3- (phenanthren- 9-yl)-5- (pyridin-2- yl)phenyl)-4,6- diphenyl-1,3,5- triazine 1.76 −2.17 ETM-27 2,4-diphenyl-6- (5″′-phenyl- [1,1′:3′,1″:3″,1″′: 3″′,1″″- quinque- phenyl]-3-yl)- 1,3,5-triazine 0 0.2  −2.19 ETM-25 2-([1,1′- biphenyl]-3- yl)-4-(3′-(4,6- diphenyl-1,3,5- triazin-2-yl)- [1,1′-biphenyl]- 3-yl)-6-phenyl- 1,3,5-triazine 0.13 −2.24 ETM-26 2-(3′-(4,6- diphenyl-1,3,5- triazin-2-yl)- [1,1-biphenyl]- 3-yl)-4- phenylbenzo [4,5]thieno[3,2- d]pyrimidine 2.0  −2.20 ETM-31 2-phenyl-4- (4′,5′,6′- triphenyl- [1,1′:2′,1″:3″,1′″- quaterphenyl]- 3′″- yl)benzo[4,5] thieno[3,2- d]pyrimidine 1.6  −2.23 ETM-32 7,12- diphenylbenzo[k] fluoranthene (CAS 16391-62-1) 0.13 −2.2  ETM-33 3,9- di(naphthalen- 2-yl)perylene (CAS 959611- 30-4) 0.12 −2.1 

(15) A variety of dipole moments of representative examples of the second matrix compounds were calculated. The results are summarized in the below Table 5.

(16) TABLE-US-00005 TABLE 5 Dipole moments of representative examples of the second matrix compound Com- Dipole pound Name Structure moment/Debye EIM-19 1,2-diphenyl-1H- benzo[d]imidazole 3.75 EIM-20 Triphenylphosphine oxide 3.97 EIM-21 4,7-diphenyl-1,10- phenanthroline 3.65 EIM-16 9-phenyl-9′- (quinazolin-2-yl)- 9H,9′H-3,3′- bicarbazole 3.2/1.65*.sup.) EIM-17 4-(2-naphthalenyl)-2- [4-(3- quinolinyl)phenyl]- benzo[h]quinazoline 00 3   EIM-18 4-(naphthalen-1-yl)- 2,7,9- triphenylpyrido[3,2- h]quinazoline 01 3.81 *.sup.)Two conformers with a difference of 1 kJ/mol difference in total energy. Therefore, both conformers are present at room temperature.
Synthetic Procedures

Synthesis of Compound ETM-3 ([1,1′:4′,1″-terphenyl]-3-ylbis(2-methylnaphthalen-1-yl)borane)

(17) ##STR00102##

1. Tetrakis(3-bromophenyl)stannane Stage 1

(18) Sn(m-C.sub.6H.sub.4Br).sub.4: 1,3-Dibromobenzene (5.89 g, 24.97 mmol) was dissolved in 60 mL of ether and cooled to −50° C. Then 16.2 mL of a 1.6 M solution of nBuLi (26.00 mmol) in hexane was added dropwise. After having been stirred for 120 min the reaction mixture was cooled to −78° C., and 0.73 mL (6.25 mmol) of SnCl.sub.4 was added dropwise. After the mixture was stirred for 12 h at ambient temperature, 20 mL of 1 M HCl was added, and the product was extracted with ether (3×70 mL). The organic phase was washed with H.sub.2O and dried with MgSO.sub.4. After removal of the solvent in vacuo, 30 mL of cold MeOH was added to the resulting oil and the mixture was stirring at 0-5° C. The precipitate was filtered and washed with cold MeOH (1×3 mL). After drying in vacuo Sn(m-C.sub.6H.sub.4Br) was obtained as a colorless crystalline powder (3.70 g, 5.00 mmol, 80% yield). M.p. 119-120° C. IR (ATR): U=1553, 1456, 1382, 1188, 1081, 996, 771, 715, 681, 643 cm.sup.−1. .sup.1H NMR (400 MHz, CDCl.sub.3): δ=7.64-7.62 (m, 4H), 7.61-7.56 (m, 4H), 7.44 (d, .sup.3J(H—H)=7.3 Hz, 4H), 7.32 (t, .sup.3J(H—H)=7.6 Hz, 4H) ppm; .sup.13C NMR (100 MHz, CDCl.sub.3): δ=139.1 (.sup.2J(.sup.119Sn—C)=41.8 Hz, CH), 138.8 (.sup.1J(.sup.119Sn—C)=528.2 Hz, Sn—C), 135.2 (.sup.2J(.sup.119Sn—C)=35.2 Hz, CH), 133.0 (.sup.4J(.sup.119Sn—C)=11.0 Hz, CH), 130.7 (.sup.3J(.sup.119Sn—C)=55.0 Hz, CH), 124.2 (Br—C) ppm. MS: [M].sup.+ (0.1%) 739.7, [M-Br].sup.+ (0.1%) 660.8, [M-C.sub.6H.sub.4Br].sup.+ (20%) 584.8, [M-2C.sub.6H.sub.4Br].sup.+ (7%) 429.8, [M-3C.sub.6H.sub.4Br].sup.+ (27%) 274.9, PhSn (100) 196.9.

2. (3-Bromophenyl)dichloroborane Stage 2

(19) To a 50 mL (50.00 mmol) of 1M solution of BCl.sub.3 in hexane at −78° C. was added 7.43 g (10.00 mmol) of Sn(m-C.sub.6H.sub.4Br).sub.4 and the resulting mixture was stirring 1 h at −78° C. and 2 d at r.t. After removal of volatiles (hexane, SnCl.sub.4 and excess of BCl.sub.3) with membrane pump (70-75° C. oil bad, 40 mbar), the residue was distilled in vacuo at 105-110° C. (oil bad)/0.2 mbar giving 7.06 g (29.70 mmol, 75%) of (3-bromophenyl)dichloroborane.—.sup.1H-NMR (400 MHz, CDCl.sub.3): δ=7.37 (t, J=7.8 Hz, 1H), 7.77 (ddd, J=7.8, 2.1, 1.1 Hz, 1H), 8.06 (ddd, J=7.8, 2.1, 1.1 Hz, 1H), 8.24 (dd, J=2.1, 1.1 Hz, 1H) ppm. .sup.13C NMR (100 MHz, CDCl.sub.3): δ=139.3 (CH), 137.8 (CH), 137.6 (B—C), 135.2 (CH), 129.9 (CH), 122.9 (Br—C) ppm. .sup.11B NMR (192 MHz, CDCl.sub.3) δ=54.9 ppm.

3. (3-Bromophenyl)bis(2-methylnaphthalen-1-yl)borane Stage 3

(20) To a solution of 4.00 g (3.60 g of pure compound, 16.00 mmol) 90% 1-bromo-2-methylnaphthalene in 80 ml of diethyl ether at −78° C. was added drop wise in 15 min 11 mL (17.6 mmol) 1.6 M nBuLi. After stirring at −78° C. for 1 h and at 0° C. for 2 h to the resulting mixture cooled to −78° C. was added in 5 min at vigorous stirring 2.02 g (8.50 mmol) (3-bromophenyl)dichloroborane. After stirring for 1 h at −78° C. the cooling bad was removed and reactions mixture was stirring additionally over night at ambient temperature, then cooled to 5° C. and quenched with 5 drops of cone. HCl. Ether was removed in vacuo, the residue was mixed with water (100 mL), extracted with CHCl.sub.3 (3×70 mL), organic lay was washed with water and dried with calcium chloride. Borane Stage 3 was purified by a silica gel column chromatography using petrol ether as eluent to give a light yellow solid (1.65 g, 3.67 mmol, 45%). M.p. 157-158° C. IR (ATR): U=1592, 1505, 1421, 1389, 1225, 1192, 808, 743, 604, 510, 503 cm.sup.−1. .sup.1H NMR (600 MHz, CDCl.sub.3) δ=7.86-7.79 (m, 4H), 7.61-7.53 (m, 4H), 7.37-7.28 (m, 5H), 7.18-7.11 (m, 3H), 2.24 (s, 6H, Me) ppm. .sup.13C NMR (150 MHz, CDCl.sub.3): δ=148.4 (br s, B—C.sub.Phenyl), 141.9 (br s, 2C, B—C.sub.Naphthyl), 139.6 (2Cq), 139.2 (CH), 135.9 (2Cq), 135.6 (CH), 135.3 (CH), 131.8 (Cq), 131.7 (Cq), 130.1 (CH), 130.0 (CH), 129.9 (CH), 129.5 (CH), 129.4 (CH), 129.1 (CH), 129.0 (CH), 128.5 (CH), 128.4 (CH), 125.5 (2CH), 124.5 (2CH), 122.9 (C—Br), 23.8 (Me), 23.6 (Me) ppm. .sup.11B NMR (192 MHz, CDCl.sub.3) δ=74.3 ppm. MS: [M].sup.+ (12%) 448; [M-(1-methylnaphthalene)].sup.+ (17%) 306; [M-(1-methylnaphthalene)-Br].sup.+ (12%) 227; [1-methylnaphthalene)].sup.+ (28%) 142.

4. [1,1′:4′,1″-terphenyl]-3-ylbis(2-methylnaphthalen-1-yl)borane Compound ETM-3

(21) A mixture of borane Stage 3 (90 mg, 0.20 mmol), Pd(PPh.sub.3).sub.4 (12 mg, 5 mol. %, 0.01 mmol), 1,1′-biphenyl]-4-ylboronic acid (48 mg, 0.24 mmol), Na.sub.2CO.sub.3 (64 mg, 0.60 mmol) and 1 mL water in toluene (15 mL) was degassed by N.sub.2 bubbling for 15 min. The reaction mixture was then heated to 105-110° C. and monitored via TLC until complete, typically 8-12 h. After removal of the solvent, the residue was diluted with 10 mL water, acidified with 3 drops conc. HCl, extracted with CHCl.sub.3 (3×20 mL), the organic lay was washed with water and dried with calcium chloride. Compound ETM-3 was purified by a silica gel column chromatography using petrol ether as eluent to give a white solid (51 mg, 0.098 mmol, 49%). M.p. 180-181° C. Tg 87° C. IR (ATR): U=1591, 1506, 1420, 1384, 1224, 1189, 811, 740, 606, 512, 505 cm.sup.−1. .sup.1H NMR (400 MHz, CDCl.sub.3) δ=7.85 (d, J=8.3 Hz, 4H), 7.79-7.65 (m, 5H), 7.60-7.53 (m, 4H), 7.49-7.39 (m, 5H), 7.38-7.31 (m, 5H), 7.18 (d, J=7.6 Hz, 1H), 7.14 (d, J=7.5 Hz, 1H), 2.31 (s, 3H, Me), 2.30 (s, 3H, Me) ppm. .sup.13C NMR (100 MHz, CDCl.sub.3): δ=146.2 (br s, B—C.sub.Phenyl), 142.5 (br s, 2C, B—C.sub.Naphthyl), 140.6 (Cq), 140.1 (Cq), 140.0 (Cq), 139.9 (Cq), 139.5 (2Cq), 136.6 (CH), 136.2 (Cq), 136.1 (Cq), 136.0 (CH), 131.8 (Cq), 131.7 (Cq), 131.3 (CH), 129.9 (CH), 129.8 (2CH), 129.7 (CH), 129.2 (2CH), 128.8 (2CH), 128.6 (CH), 128.5 (CH), 128.4 (CH), 127.5 (2CH), 127.4 (2CH), 127.3 (CH), 127.0 (2CH), 125.3 (2CH), 124.4 (2CH), 23.9 (Me), 23.7 (Me) ppm. MS: [M].sup.+ (35%) 522; [M-(1-methylnaphthalene)].sup.+ (98%) 380; [M-(1-methylnaphthalene)-Ph+2H].sup.+ (100%) 306; [1-methylnaphthalene)].sup.+ (72%) 142.

Synthesis of Compound ETM-7 (bis(2-methylnaphthalen-1-yl)(3-(phenanthren-9-yl)phenyl)borane)

(22) ##STR00103##

(23) A mixture of (3-bromophenyl)bis(2-methylnaphthalen-1-yl)borane (Stage 3) (2.00 g, 4.45 mmol), Pd(PPh.sub.3).sub.4 (0.26 mg, 5 mol. %, 0.22 mmol), phenanthren-9-ylboronic acid (1.19 g, 5.36 mmol), Na.sub.2CO.sub.3 (1.40 g, 13.21 mmol) and 22 mL water in toluene (306 mL) was degassed by N.sub.2 bubbling for 1 h. The reaction mixture was then heated to 110° C. and monitored via TLC until complete (29 h). After cooling to room temperature, the two phases were separated and the organic layer was washed with water (4×200 mL). Additionally, the organic layer was stirred twice with NaDTC (2×15 min) to remove palladium residues. After washing once more with water, the organic layer was dried with calcium chloride. The raw product was purified by column chromatography using hexane/ethylacetate 98:2 as eluent to give a white solid (950 mg, 1.74 mmol, 40%). HPLC-MS 97%, GC-MS 99.6% (m/z 546), Tg 102° C. (from DSC 10 K/min), no melting point observed. .sup.1H NMR (500 MHz, CD.sub.2Cl.sub.2) δ 8.78 (d, 1H), 8.68 (d, 1H), 7.93-7.82 (m, 6H), 7.82-7.76 (d, 1H), 7.76-7.70 (m, 1H), 7.68 (s, 1H), 7.66-7.55 (m, 6H), 7.55-7.48 (m, 1H), 7.48-7.39 (m, 2H), 7.39-7.33 (m, 2H), 7.33-7.22 (m, 3H), 2.38 (s, 3H, Me), 2.35 (s, 3H, Me) ppm. .sup.13C NMR (125 MHz, CD.sub.2Cl.sub.2): δ=146.5 (br, a B—C.sub.phenyl), 143.1 (br, s, B—C.sub.naphthyl), 141.0, 140.2 (d, J=7.3 Hz), 139.6, 139.0, 136.8 (d, J=11.4 Hz), 134.9, 132.6 (d, J=3.8 Hz), 132.0, 131.3, 131.0, 130.6, 130.4, 129.7, 129.1, 129.0, 128.1, 127.4, 127.2 (d, J=8.0 Hz), 127.0, 126.9, 125.9 (d, J=6.2 Hz), 125.1 (d, J=1.7 Hz), 123.4, 123.0, 24.2 (CH.sub.3), 23.9 (CH.sub.3) ppm.

(24) Other compounds, mentioned herein, were prepared accordingly. A person skilled in the art will understand that the specific reaction conditions for preparing the respective compounds may be slightly modified on basis of the general knowledge of this person to prepare the respective compounds.

(25) General Procedure for Fabrication of OLEDs

(26) For bottom emission devices, Examples 1 to 5 and comparative examples 1 to 4, a 15 Ω/cm 2 glass substrate (available from Corning Co.) with 100 nm ITO was cut to a size of 50 mm×50 mm×0.7 mm, ultrasonically cleaned with isopropyl alcohol for 5 minutes and then with pure water for 5 minutes, and cleaned again with UV ozone for 30 minutes, to prepare a first electrode.

(27) Then, 92 wt.-% of a hole transport matrix doped with 8 wt.-% and 8 wt.-% of 2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) was vacuum deposited on the ITO electrode, to form a HIL having a thickness of 10 nm. Then, the hole transport matrix was vacuum deposited on the HIL, to form a HTL having a thickness of 120 nm. For Examples 1 to 3 and Comparative examples 1 to 4 Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) was used as hole transport matrix. For Examples 4 and 5, N4,N4″-di(naphthalen-1-yl)-N4,N4″-diphenyl-[1,1′:4′,1″-terphenyl]-4,4″-diamine (CAS 139255-16-6) was used as hole transport matrix.

(28) Then 97 wt.-% of ABH113 (Sun Fine Chemicals) as EML host and 3 wt.-% blue dopant were deposited on the HTL, to form a blue-emitting EML with a thickness of 20 nm. For Examples 1 to 3 and Comparative examples 1 to 4, NUBD370 (Sun Fine Chemicals) was used a blue dopant. For Examples 4 and 5, NUBD005 (Sun Fine Chemicals) was used a blue dopant.

(29) Then the undoped electron transport layer (ETL) is formed by depositing a matrix compound according to Example 1 to Example 5 and Comparative examples 1 to 4, see Table 6. Then the electron injection layer (EIL) is formed by deposing 2-(4-(9,10-di(naphthalen-2-yl)anthracen-2-yl)phenyl-1-phenyl-1H-benzo[d]imidazole (CAS 561064-11-7) doped with 30 wt.-% LiQ (Comparative Example 1) or 3-Phenyl-3H-benzo[b]dinaphtho[2,1-d:1′,2′-f]phosphepine-3-oxide (EIM-11), doped with 30 wt.-% Lithium tetra(1H-pyrazol-1-yl)borate (Li-1) (Example 1 to 5 and Comparative examples 2 to 4) to form a layer as specified in Table 6. The cathode was evaporated at ultra-high vacuum of 10.sup.−7 mbar. Therefore, a thermal single co-evaporation of one or several metals was performed with a rate of 0, 1 to 10 nm/s (0.01 to 1 Å/s) in order to generate a homogeneous cathode with a thickness of 5 to 1000 nm. The cathode was formed from 100 nm aluminum.

(30) The OLED stack is protected from ambient conditions by encapsulation of the device with a glass slide. Thereby, a cavity is formed, which includes a getter material for further protection.

(31) To assess the performance of the inventive examples compared to the prior art, the current efficiency is measured under ambient conditions (20° C.). Current voltage measurements are performed using a Keithley 2400 sourcemeter, and recorded in V. At 10 mA/cm.sup.2 for bottom emission and 15 mA/cm.sup.2 for top emission devices, a calibrated spectrometer CAS140 from Instrument Systems is used for measurement of CIE coordinates and brightness in Candela. Lifetime LT of the device is measured at ambient conditions (20° C.) and 15 mA/cm.sup.2, using a Keithley 2400 sourcemeter, and recorded in hours. The brightness of the device is measured using a calibrated photo diode. The lifetime LT is defined as the time till the brightness of the device is reduced to 97% of its initial value.

(32) The light output in external efficiency EQE and power efficiency (lm/W efficiency) are determined at 10 mA/cm.sup.2 for bottom emission devices and 15 mA/cm.sup.2 for top emission devices.

(33) To determine the efficiency EQE in % the light output of the device is measured using a calibrated photodiode.

(34) To determine the power efficiency in lm/W, in a first step the luminance in candela per square meter (cd/m2) is measured with an array spectrometer CAS140 CT from Instrument Systems which has been calibrated by Deutsche Akkreditierungsstelle (DAkkS). In a second step, the luminance is then multiplied by π and divided by the voltage and current density.

(35) In bottom emission devices, the emission is predominately Lambertian and quantified in percent external quantum efficiency (EQE) and power efficiency in lm/W.

(36) In top emission devices, the emission is forward directed, non-Lambertian and also highly dependent on the micro-cavity. Therefore, the external quantum efficiency (EQE) and power efficiency in lm/W will be higher compared to bottom emission devices.

(37) Technical Effect of the Invention

(38) Bottom Emission Devices

(39) The beneficial effect of the invention on the performance of bottom emission devices can be seen in Table 6.

(40) TABLE-US-00006 TABLE 6 Voltage, external quantum efficiency (EQE) and power efficiency (PEff) of bottom emission OLEDs measured at 10 mA/cm.sup.2 wt.-% d (ETL)/ Li organic d (EIL)/ V at 10 EQE*.sup.2/ PEff*.sup.3/ ETL nm EIL complex*.sup.1 nm mA/cm.sup.2/V % lm/W Comparative ADN 36 EIM-1:LiQ 30 3 5.6 6 3.2 example 1 Comparative ADN 36 EIM-11:Li-1 30 3 3.2 4.5 4.1 example 2 Comparative Formula 36 EIM-11:Li-1 30 3 4.8 3.5 2 example 3 (A) Comparative EIM-9 36 EIM-11:Li-1 30 3 5.3 4.6 2.4 example 4 Example 1 ETM-3 36 EIM-11:Li-1 30 3 3.25 5.4 4.85 Example 2 ETM-1 36 EIM-11:Li-1 30 3 3.35 6.4 6.1 Example 3 ETM-28 36 EIM-11:Li-1 30 3 3.8 7.3 5.3 Example 4 ETM-15 36 EIM-11:Li-1 30 3 3.2 7.3 5.7 Example 5 ETM-34 36 EIM-11:Li-1 30 3 3.3 6.8 4.9 *.sup.1the wt.-% of the matrix compound MX and the wt.-% of the lithium organic complex are in total 100 wt.-% based on the weight of the EIL. *.sup.2detecting the light output efficiency with a calibrated photo diode. *.sup.3calculated lm/W efficiency based on the luminance in cd/m.sup.2, voltage in Volt and current density in mA/cm.sup.2.

(41) In comparative Example 1, Table 6, anthracene compound ADN (9,10-di(naphthalen-2-yl)anthracene, CAS 122648-99-1) is tested as first matrix compound.

(42) ##STR00104##

(43) The reduction potential is −2.44 V against Fc/Fc.sup.+ in tetrahydrofurane and the dipole moment is 0.01 Debye. The reduction potential and LUMO level of the first matrix compound are the same as of the EML host. The EIL comprises benzimidazole compound EIM-1 and lithium organic complex LiQ. The power efficiency is 3.2 lm/W (Table 6).

(44) In comparative Example 2, first matrix compound ADN is tested with an EIL comprising phosphine oxide compound EIM-11 and lithium organic complex Li-1. The power efficiency is improved to 4.1 lm/W.

(45) In comparative Example 3, triazine compound 4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl (CAS 266349-83-1) of formula (A) is tested as first matrix compound.

(46) ##STR00105##

(47) The reduction potential is −2.03 V against Fc/Fc.sup.+ in tetrahydrofurane and the dipole moment is 0.03 Debye. The EIL composition is selected the same as in comparative example 2. The power efficiency is reduced to 2 lm/W. Clearly, a very large off-set in reduction potential and LUMO of the EML host compared to the ETL matrix has a detrimental effect on power efficiency.

(48) In comparative Example 4, phosphine oxide compound EIM-9 with a reduction potential of −2.2 V against Fc/Fc.sup.+ in tetrahydrofurane is tested as ETL matrix. The dipole moment of this compound is 4 Debye. Therefore, this compound is a polar compound in the sense of the present invention. The EIL composition is selected the same as in comparative examples 2. The power efficiency is reduced compared to comparative example 2, 2.4 V against 4.1 V for comparative example 2 (Table 6). Even though the off-set in reduction potential between the EML matrix and ETL matrix is within the desired range, the high dipole moment of the ETL matrix compound results in low power efficiency.

(49) In Example 1, Table 6, triaryl borane compound ETM-3 is tested with the same EIL composition as in comparative example 2. The reduction potential of ETM-3 is −2.33 V against F/Fc.sup.+ in tetrahydrofurane and the dipole moment is <2.5 Debye. The power efficiency is improved from 4.1 to 4.85 lm/W.

(50) In Example 2, a triaryl borane compound with a deeper LUMO compared to Example 1 is tested. The reduction potential of ETM-1 is −2.31 V against Fc/Fc.sup.+ in tetrahydrofurane and the dipole moment is 0.14 Debye. The power efficiency is further improved from 4.85 to 6.1 lm/W.

(51) In Example 3, triazine compound ETM-28 is tested with the same EIL composition as in comparative example 2. The reduction potential is −2.17 V against Fc/Fc.sup.+ in tetrahydrofurane and the dipole moment is 1.76 Debye. The power efficiency is improved from 4.1 lm/W in comparative example 2 to 5.3 lm/W in Example 3.

(52) In Example 5, dibenzo[c,h]acridine compound ETM-15 is tested with the same EIL composition as in comparative example 2. The reduction potential is −2.26 V against Fc/Fc.sup.+ in tetrahydrofurane and the dipole moment is between 1.5 and 2 Debye. The power efficiency is improved from 4.1 lm/W in comparative example 2 to 5.7 lm/W in Example 5.

(53) In Example 6, tris(2-(benzo[d]thiazol-2-yl)phenoxy)aluminum metal complex ETM-34 is tested with the same EIL composition as in comparative example 2. The reduction potential is −2.21 V against Fc/Fc.sup.+ in tetrahydrofurane and the dipole moment is ≤2.5 Debye. The power efficiency is improved from 4.1 lm/W in comparative example 2 to 4.9 lm/W in Example 6.

(54) In summary, a significant improvement in power efficiency (lm/W efficiency) has been achieved for a wide range of first matrix compound classes with a reduction potential less negative than the reduction potential of 9,10-di(naphthalen-2-yl)anthracene (CAS 122648-99-1) and more negative than the reduction potential of 4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl (CAS 266349-83-1) and a dipole moment between ≥0 Debye and ≤2.5 Debye.

(55) Another aspect is directed to an organic light-emitting diode (OLED) comprising more than one emission layer (EML) 150, for example two, three or four emission layers may be present. An organic light-emitting diode (OLED) comprising more than one emission layer is also described as a tandem OLED or stacked OLED.

(56) Another aspect is directed to a device comprising at least one organic light-emitting diode (OLED). A device comprising organic light-emitting diodes (OLED) is for example a display or a lighting panel.

(57) The features disclosed in the foregoing description, in the claims and the accompanying drawing may, both separately or in any combination, be material for realizing the invention in diverse forms thereof.