Electron transporting compounds

Compounds comprising an aza-dibenzo moiety and a condensed aromatic moiety having at least three benzene rings are provided. In particular, the compounds may comprise an azadibenzofuran, azadibenzothiophene, or azadibenzoselenophene joined directly or indirectly to an anthracene. The compounds may be used in the electron transport layer of organic light emitting devices to provide devices with improved properties.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs). More specifically, the present invention relates to phosphorescent materials comprising an aza-dibenzo moiety and a condensed aromatic moiety having at least three benzene rings. These materials may be used in OLEDs to provide devices having improved performance.

BACKGROUND

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)3, which has the structure:

SUMMARY OF THE INVENTION

Compounds comprising an aza-dibenzo moiety and a condensed aromatic moiety having at least three benzene rings are provided. The compounds have the formula Ar(LiDi)n.

Ar contains a condensed aromatic ring having at least three benzene rings and the condensed aromatic ring has a triplet energy lower than 440 nm. Ar is optionally further substituted. L is a single bond or a bivalent linking group. n is at least 1. i is an indexing variable that identifies n structures for Liand Dithat may be the same or different for different values of i. Each Liis independently a single bond or a bivalent linking group. Each Diindependently has the structure:

In one aspect, the compound has the formula:

In another aspect, the compound has a formula selected from the group consisting of:

In one aspect, each Diis independently selected from the group consisting of:

In one aspect, L is a single bond. In another aspect, each Liis independently selected from the group consisting of:

In one aspect, Ar is selected from the group consisting of:

In one aspect, n is 1. In another aspect, n is greater than 1 and each Dihas the same structure. In yet another aspect, n is greater than 1 and at least two Dihave different structures. In a further aspect, n is 2.

Preferably, the compound has the formula:

Specific, non-limiting examples of the compounds comprising an aza-dibenzo moiety and an aromatic moiety having extended conjugation are provided. In one aspect, the compound is selected from the group consisting of:

A first device comprising an organic light emitting device is also provided. The organic light emitting device comprises an anode, a cathode, and an organic layer that is disposed between the anode and the cathode. The organic layer comprises a compound having the formula Ar(LiDi)n.

Ar contains a condensed aromatic ring having at least three benzene rings and the condensed aromatic ring has a triplet energy lower than 440 nm. Ar is optionally further substituted. L is a single bond or a bivalent linking group. n is at least 1. i is an indexing variable that identifies n structures for Liand Dithat may be the same or different for different values of i. Each Liis independently a single bond or a bivalent linking group. Each Diindependently has the structure:

The various specific aspects discussed above for compounds having the formula Ar(LiDi)nare also applicable to the compounds having formula Ar(LiDi)nwhen used in a first device. In particular, specific aspects of Ar, L, n, Di, X1-X9, R, R′1, R′2, R1-R6, Formula I, Formula II, Formula III, Formula IV, Formula V and Formula VI of the compounds having the formula Ar(LiDi)n, as discussed above, are also applicable to a compound having the formula Ar(LiDi)nthat is used in the first device.

Specific, non-limiting examples of devices comprising the compounds disclosed herein are provided. In one aspect, the compound used in the first device is selected from the group consisting of Compound 1-Compound 65.

In one aspect, the organic layer is a non-emissive layer and the compound is a non-emissive compound. In another aspect, the organic layer is an electron transport layer and the compound is an electron transport material. In yet another aspect, the electron transport layer is doped with an n-type conductivity dopant. In one aspect, the n-type conductivity dopant is a compound containing Li, Na, K, Rb, or Cs. Preferably, the n-type conductivity dopant is selected from the group consisting of LiF, CsF, NaCl, KBr, and LiQ.

In another aspect, the organic layer further comprises an emissive compound that is a transition metal complex having at least one ligand selected from the group consisting of:

Each of R′a, R′band R′cmay represent mono, di, tri, or tetra substituents. Each of R′a, R′band R′care independently selected from a group consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl, or heteroaryl. Two adjacent substituents may form into a ring.

In one aspect, the first device is a consumer product. In another aspect, the first device is an organic light emitting device.

DETAILED DESCRIPTION

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

Various materials have been reported for use in the electron transport layer (ETL) of OLEDs. For example, anthracene-benzimidazole compounds, azatriphenylene derivatives, anthracene-benzothiazole compounds, and metal 8-hydroxyquinolates are all commonly used electron transporting materials. Table 1 summarizes several commonly used electron transporting materials.

Even though many materials have been reported for use as an ETL material, the development a device with low operating voltage and good stability has remained problematic. Alq is a commonly used ETL material, but Alq has limitations for use in OLEDs. While Alq may have good stability, devices comprising Alq may have high operating voltage due to low electron mobility. Anthracene compounds with benzimidazole substituents have also been reported as ETL materials. See, e.g., U.S. Pat. No. 6,878,469 and US20090179554. However, these compounds may also have limitations when used as an ETL material in a device. Introducing electron deficient heterocycles, such as benzimidazole, oxadiazole, triazole, triazine, and pyridine, may increase electron affinity thereby resulting in good electron transporting properties and lowered device voltage, but often these compounds provide reduced device lifetime, too.

It is very difficult to predict whether the additional of electron deficient groups will result in improved device properties. For example, devices comprising an anthracene compound with a benzimidazole substituent may have reasonable device lifetime and operating voltage, as compared to devices using Alq as an ETL material; however, devices that use these electron deficient heterocyclic compounds in the ETL often have very short lifetimes. For example, devices using 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBi) as the ETL material have good efficiency, but very poor lifetime. Therefore, it is very difficult to predict which compounds may provide a low operating voltage and a long device lifetime.

Azadibenzofurans, azadibenzothiophenes, and azadibenzoselenophenes have been used as building blocks for host materials in phosphorescent OLEDs. See, JP2008074939. These materials have lower LUMOs, i.e., better electron affinity, than the corresponding dibenzofurans, dibenzothiophenes, and dibenzoselenophenes. It is believed that the electron affinity of these aza heterocyclic compounds may be advantageously used in ETL materials.

The compounds provided herein comprise an aromatic moiety with condensed aromatic rings with a low triplet energy and an aza-dibenzo moiety. By combining the aza-dibenzo moiety, e.g., azadibenzofuran, azadibenzothiophene, and azadibenzoselenophene, and the aromatic moiety, e.g., anthracene, in a compound, the result is ETL materials providing low voltage and good device stability. In particular, the compounds provided herein include anthracene compounds substituted with azadibenzofuran, azadibenzothiophene, or azadibenzoselenophene. These compounds may be used as ETL materials in OLEDs to provide devices with lower operating voltage while maintaining good device stability. Without being bound by theory, it is believed that the aza-dibenzo moiety of the compound improves device voltage by reducing the LUMO and the aromatic moiety having a low triplet energy, i.e., higher conjugation, improves device stability by delocalizing and destabilizing the electron.

Compounds comprising an aza-dibenzo moiety and a condensed aromatic moiety having at least three benzene rings are provided. The compounds have the formula Ar(LiDi)n.

Ar contains a condensed aromatic ring having at least three benzene rings and the condensed aromatic ring has a triplet energy lower than 440 nm. Ar is optionally further substituted. L is a single bond or a bivalent linking group. n is at least 1. i is an indexing variable that identifies n structures for Liand Dithat may be the same or different for different values of i. Each Liis independently a single bond or a bivalent linking group. Each Diindependently has the structure:

In one aspect, the compound has the formula:

In another aspect, the compound has a formula selected from the group consisting of:

In one aspect, each Diis independently selected from the group consisting of:

In one aspect, L is a single bond. In another aspect, each Liis independently selected from the group consisting of:

In one aspect, Ar is selected from the group consisting of:

In one aspect, n is 1. In another aspect, n is greater than 1 and each Dihas the same structure. In yet another aspect, n is greater than 1 and at least two Dihave different structures. In a further aspect, n is 2.

Preferably, the compound has the formula:

Specific, non-limiting examples of the compounds comprising an aza-dibenzo moiety and an aromatic moiety having extended conjugation are provided. In one aspect, the compound is selected from the group consisting of:

A first device comprising an organic light emitting device is also provided. The organic light emitting device comprises an anode, a cathode, and an organic layer that is disposed between the anode and the cathode. The organic layer comprises a compound having the formula Ar(LiDi)n.

Ar contains a condensed aromatic ring having at least three benzene rings and the condensed aromatic ring has a triplet energy lower than 440 nm. Ar is optionally further substituted. L is a single bond or a bivalent linking group. n is at least 1. i is an indexing variable that identifies n structures for Liand Dithat may be the same or different for different values of i. Each Liis independently a single bond or a bivalent linking group. Each Diindependently has the structure:

The various specific aspects discussed above for compounds having the formula Ar(LiDi)nare also applicable to the compounds having formula Ar(LiDi)nwhen used in a first device. In particular, specific aspects of Ar, L, n, i, Li, Di, X1-X9, R, R′1, R′2, R1-R6, Formula I, Formula II, Formula III, Formula IV, Formula V and Formula VI of the compounds having the formula Ar(LiDi)n, as discussed above, are also applicable to a compound having the formula Ar(LiDi)nthat is used in the first device.

In one aspect, the compound has the formula:

In another aspect, the compound has a formula selected from the group consisting of:

In one aspect, each Diis independently selected from the group consisting of:

In one aspect, L is a single bond. In another aspect, each Liis independently selected from the group consisting of:

In one aspect, Ar is selected from the group consisting of:

In one aspect, n is 1. In another aspect, n is greater than 1 and each Dihas the same structure. In yet another aspect, n is greater than 1 and at least two Dihave different structures. In a further aspect, n is 2.

Preferably, the compound has the formula:

Specific examples of devices comprising the compounds disclosed herein are provided. In one aspect, the compound used in the first device is selected from the group consisting of Compound 1-Compound 65.

In one aspect, the organic layer is a non-emissive layer and the compound is a non-emissive compound. In another aspect, the organic layer is an electron transport layer and the compound is an electron transport material. In yet another aspect, the electron transporting layer is doped with an n-type conductivity dopant. In one aspect, the n-type conductivity dopant is a compound containing Li, Na, K, Rb, or Cs. Preferably, the n-type conductivity dopant is selected from the group consisting of LiF, CsF, NaCl, KBr, and LiQ.

In another aspect, the organic layer further comprises an emissive compound that is a transition metal complex having at least one ligand selected from the group consisting of:

Each of R′a, R′band R′cmay represent mono, di, tri, or tetra substituents. Each of R′a, R′band R′care independently selected from a group consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl, or heteroaryl. Two adjacent substituents may form into a ring.

In one aspect, the first device is a consumer product. In another aspect, the first device is an organic light emitting device.

Combination with Other Materials

A hole injecting/transporting material to be used in embodiments of the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but are not limited to: a phthalocyanine or porphryin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and sliane derivatives; a metal oxide derivative, such as MoOx; a p-type semiconducting organic compound, such as 1, 4, 5, 8, 9, 12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but are not limited to the following general structures:

k is an integer from 1 to 20; X1to X8is CH or N; Ar1has the same group defined above.

M is a metal, having an atomic weight greater than 40; (Y1-Y2) is a bidentate ligand, Y1 and Y2are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y1-Y2) is a 2-phenylpyridine derivative.

In another aspect, (Y1-Y2) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc+/Fc couple less than about 0.6 V.

The light emitting layer of the organic EL device in some embodiments of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant.

Examples of metal complexes used as hosts are preferred to have the following general formula:

M is a metal; (Y3-Y4) is a bidentate ligand, Y3and Y4are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y3-Y4) is a carbene ligand.

R1to R7is independently selected from the group consisting of hydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X1to X8is selected from CH or N.

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one aspect, the compound used in the HBL contains the same molecule used as host described above.

In another aspect, the compound used in the HBL contains at least one of the following groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integer from 1 to 3.

In one aspect, the compound used in the ETL contains at least one of the following groups in the molecule:

R1is selected from the group consisting of hydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

Ar1to Ar3has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X1to X8is selected from CH or N.

In another aspect, the metal complexes used in the ETL contain, but are not limited to, the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any of the above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 2 below. Table 2 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

EXPERIMENTAL

Compound Examples

Synthesis of Compound 1

Synthesis of 2-(9,10-di(naphthalen-2-yl)anthracen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

2-bromo-9,10-di(naphthalen-2-yl)anthracene (4.75 g, 9.32 mmol), 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi(1,3,2-dioxaborolane) (3.08 g, 12.12 mmol), potassium acetate (1.830 g, 18.65 mmol) and dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.153 g, 0.373 mmol) were mixed in 400 mL of dioxane. The mixture was bubbled with nitrogen for 20 minutes. Pd2(dba)3(0.085 g, 0.093 mmol) was added. The reaction was heated up to 90° C. overnight. The reaction was stopped and filtered through Celite. Solvent was evaporated, coated on Celite and a column was run with 10% ethyl acetate and hexanes. The solid was then recrystallized from 100 mL of ethanol. Yellowish solid 2-(9,10-di(naphthalen-2-yl)anthracen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3.8 g, 6.83 mmol, 73.2% yield) was collected by filtration.

Synthesis of Compound 1

Device Examples

All device examples were fabricated by high vacuum (<10−7Torr) thermal evaporation. The anode electrode is 800 Å of indium tin oxide (ITO). The cathode consisted of 10 Å of LiF followed by 1000 Å of Al. All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H2O and O2) immediately after fabrication, and a moisture getter was incorporated inside the package.

The organic stack of the Device Examples consisted of sequentially, from the ITO surface, 100 Å of Compound A as the hole injection layer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the hole transporting layer (HTL), 300 Å of Host 1 doped with Compound A as the emissive layer (EML), 50 Å of Host 1 as the blocking layer (BL), and 450 Å of Compound 1 or Compound 1 doped with LiQ as the electron transport layer (ETL).

The Comparative Device Example was fabricated similarly to the Device Examples, except Alq was used as the ETL.

As used herein, the following compounds have the following structures:

Particular compounds for the ETL of an OLED are provided. These compounds may lead to devices having particularly good properties. The device structures are provided in Table 3, and the corresponding device data is provided in Table 4. Cmpd. is an abbreviation of compound. Comp. is an abbreviation of comparative. Ex. is an abbreviation of example.

Device Examples 1 and 2 showed green PHOLEDs with Compound 1 or Compound 1 doped with LiQ as the ETL. Comparative Example 1 used Alq as the ETL. As can be seen from the tables, Device Examples 1 and 2 with Compound 1 or Compound 1 doped with LiQ as the ETL, respectively, had similar efficiency and device lifetime as compared with Comparative Device Example 1 with Alq as the ETL. However, the device operating voltage of Device Example 1 was lower than the operating voltage of Comparative Example 1, i.e., 7.8 V compared to 8.1 V. The operating voltage of Device Example 2 was even further decreased to 6.2 V. Therefore, devices comprising an inventive compound as the ETL may maintain good lifetime and efficiency and have lowered device voltage.