Organic electroluminescent materials and devices

Heteroleptic cyclometallated complexes having a 6-membered ring cyclometallated to the metal, as shown in Formula (I), are provided:wherein ring A and ring B are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; wherein L1 is BR, NR, PR, O, S, Se, C═O, S═O, SO2, CRR′, SiRR′, or GeRR; wherein Z1 and Z2 are independently carbon or nitrogen; wherein at least one of Z1 and Z2 is carbon; whereinis a bidentate ligand selected from the group consisting of:wherein R1, R2, Ra, Rb, Rc, and Rd may represent mono, di, tri, or tetra substitution, or no substitution; wherein R1, R2, R, R′, Ra, Rb, Rc, and Rd are each independently selected from various substituents; and wherein n is 1 or 2. Devices, such as organic light emitting devices (OLEDs) that comprise phosphorescent light emitting materials are also provided.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs). More specifically, the invention relates to phosphorescent light emitting materials that may have improved electron stability.

BACKGROUND

SUMMARY OF THE INVENTION

A new type of light emitting material is provided, which include heteroleptic complexes having a cyclometallated 6-membered ring, as shown in Formula (I), below:

is a bidentate ligand selected from the group consisting of:

In some such embodiments,

where the variables have the definitions provided above.

In some such embodiments, A-L1-B is

where the variables have the definitions provided above. In some such embodiments, L1is CRR′, wherein R and R′ are alkyl. In some further such embodiments, CRR′ is C(CH3)2.

In some such embodiments A-L1-B is

In some embodiments, the ring A is an imidazole ring, which may be substituted as indicated, and Z1is nitrogen.

In some such embodiments A-L1-B is

In some embodiments,

Heteroleptic complexes are provided, where the complexes are selected from the group consisting of:

A device is also provided. The device may include an anode, a cathode, and an organic layer disposed between the anode and the cathode, where the organic layer comprises a heteroleptic complex of any of the foregoing embodiments.

The invention is not limited to any particular type of device. In some embodiments, the device is a consumer product. In some embodiments, the device is an organic light emitting device (OLED). In other embodiments, the device comprises a lighting panel.

In some embodiments, the organic layer of the device is an emissive layer. In some such embodiments, the heteroleptic complex is an emissive dopant. In some other embodiments, the heteroleptic complex is a non-emissive dopant.

In some embodiments, the organic layer of the device further comprises a host.

In some such embodiments, the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan, wherein any substituent in the host is an unfused substituent independently selected from the group consisting of CnH2n+1, OCnH2n+1, OAr1, N(CnH2n+1)2, N(Ar1)(Ar2), CH═CH—CnH2n+1, C≡C—CnH2n+1, Ar1, Ar1—Ar2, and CnH2n—Ar1, or the host has no substitutions, wherein n is from 1 to 10, and wherein Ar1and Ar2are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof. In some such embodiments, the host is a compound selected from the group consisting of:

and combinations thereof.

In some other embodiments, the host comprises a metal complex.

In some other embodiments, the host comprises at least one of the chemical groups selected from the group consisting of carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.

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.

Heteroleptic complexes having at least one ligand forming a 6-membered ring when cyclometallated to the metal are provided. The inclusion of the cyclometallated 6-membered ring in the complex can provide higher triplet energy, can boost the metal-centered (MC) state compared to the (N,N), (O,O), or (N,O) coordination modes, and can lead to a lower energy LUMO, which improves electron stability. Further, the inclusion of the cyclometallated 6-membered ring can sometimes promote interligand charge transfer and can possibly broaden the emission spectrum of the material, making it suitable for white light applications.

A new type of light emitting material is provided, which include heteroleptic complexes having at least one cyclometallated 6-membered ring, as shown in Formula (I), below:

is a bidentate ligand selected from the group consisting of:

In some such embodiments,

where the variables have the definitions provided above.

In some such embodiments, A-L1-B is

where the variables have the definitions provided above. In some such embodiments, L1is CRR′, wherein R and R′ are alkyl. In some further such embodiments, CRR′ is C(CH3)2.

In some such embodiments A-L1-B is

In some embodiments, the ring A is an imidazole ring, which may be substituted as indicated, and Z1is nitrogen.

In some such embodiments A-L1-B is

In some embodiments,

Heteroleptic complexes are provided, where the complexes are selected from the group consisting of:

A device is also provided. The device may include an anode, a cathode, and an organic layer disposed between the anode and the cathode, where the organic layer comprises a heteroleptic complex of any of the foregoing embodiments.

The invention is not limited to any particular type of device. In some embodiments, the device is a consumer product. In some embodiments, the device is an organic light emitting device (OLED). In other embodiments, the device comprises a lighting panel.

In some embodiments, the organic layer of the device is an emissive layer. In some such embodiments, the heteroleptic complex is an emissive dopant. In some other embodiments, the heteroleptic complex is a non-emissive dopant.

In some embodiments, the organic layer of the device further comprises a host.

In some such embodiments, the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan, wherein any substituent in the host is an unfused substituent independently selected from the group consisting of CnH2n+1, OCnH2n+1, OAr1, N(CnH2n+1)2, N(Ar1)(Ar2), CH═CH—CnH2+1, Ar1, Ar1—Ar2, and CnH2n—Ar1, or the host has no substitutions, wherein n is from 1 to 10, and wherein Ar1and Ar2are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof. In some such embodiments, the host is a compound selected from the group consisting of:

In some other embodiments, the host comprises a metal complex.

In some other embodiments, the host comprises at least one of the chemical groups selected from the group consisting of carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, compounds disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

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

Examples of metal complexes used in HIL or HTL include, but not limit to the following general formula:

M is a metal, having an atomic weight greater than 40; (Y5-Y6) is a bidentate ligand, Y5and Y6are 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, (Y5-Y6) is a 2-phenylpyridine derivative.

In another aspect, (Y5-Y6) 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.

In addition to the host materials described above, the device may further comprise other host materials. Examples of such other 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. While the Table below categorizes host materials as preferred for devices that emit various colors, any host material may be used with any dopant so long as the triplet criteria is satisfied.

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.

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

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.

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

(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 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 1 below. Table 1 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

EXPERIMENTAL

Calculation and Measurement of Decrease in LUMO Level

DFT calculations with the Gaussian software package at the B3LYP/cep-31g functional and basis set and cyclic voltammetry (CV) measurements in DMF solution with 0.1 M NBu4PF6were carried out for two heteroleptic complexes of Formula (I) and two homoleptic complexes. TABLE 2 below shows the calculated values for the HOMO and the LUMO, and shows the respective oxidation and reduction values for the CV measurement. The CV measurements used ferrocene as a reference. The LUMO energies for the tris(cyclometallated) complexe Compound W and Compound X are closer to the vacuum level and therefore harder to reduce, with reduction potentials of −2.90 V and −3.10 V, respectively. It has been unexpectedly discovered that for the inventive compounds, the reduction potentials are further from the vacuum level and therefore the complexes are easier to reduce. To wit, Compound 59 has a reduction potential of −2.73 V (compared to −3.10 V in the comparative Compound X). Likewise, Compound 1 has a reduction potential of −2.75 V, compared to −2.90 V in the comparative Compound W. Without being bound by theory, it is believed that large negative reduction potentials can lead to instabilities in the OLED devices and the inability to trap charge well in the emissive layer. The inventive compounds presented here remove the instabilities associated with large reduction potentials and allow for better charge trapping in the emissive layer.

In addition, the HOMO energy levels for the inventive compounds are further from the vacuum level, making the compounds more difficult to oxidize. Compound 59 has an oxidation potential of 0.29 V while the comparative Compound X has an oxidation potential of 0.05 V. Likewise, Compound 1 has an oxidation potential of 0.41 V while the comparative Compound W has an oxidation potential of 0.20 V. Without being bound by theory, it is believed that small oxidation potentials can lead to instabilities due oxidative agents (e.g., oxygen) in the OLED devices and can lead to hole trapping exclusively by the emitting species, therefore reducing the emissive lifetime. The inventive compounds presented here remove the instabilities associated with small reduction potentials and allow for better charge trapping in the emissive layer.

Photoluminescence measurements further showed an unexpected advantage of incorporating a 6-membered metallocyclic ring into the complexes. As shown inFIG. 4below, broadening and red-shifting of the photoluminescence spectra was observed in inventive complexes Compound 1 and Compound 59 when compared to comparative complex Compound X.

Table 3 below shows the numerical values from the photoluminescence spectrum. Compound 1 shows a 54 nm red shift from comparative Compound X, while Compound 59 shows a more pronounced red shift of 78 nm. In addition, Compound 1 exhibits a broad emission spectrum with Full-Width Half Maximum (FWHM) of 104 nm compared to comparative Compound X with FWHM of 72 nm, while inventive Compound 59 is further broadened to FWHM of 116 nm. Such a broadening of the photoluminescence spectrum is advantageous in certain emissive displays, such as the production of white light wherein broadband emission is desired.

Photoluminescence (PL) spectra were recorded for each of Compounds 1, 59, and X.FIG. 4shows the PL spectra for the three compounds superimposed onto the same graph. Compounds 1 and 59 show broader spectra compared to the homoleptic Compound X. Such broader PL spectra indicate that the compounds may be more beneficial for use in white light applications.

Compound Examples

Some of the heteroleptic complexes were synthesized as follows.

Synthesis of Compound 59

Synthesis of 2-(1-phenylethyl)pyridine

A 100 mL round-bottomed flask was charged with phenyllithium (1.8 M, 59 mL, 106 mmol) and cooled to 0° C. 2-Benzylpyridine (17.1 mL, 106 mmol) was dissolved in 55 mL ether and added dropwise to the reaction mixture over 30 min. at 0° C. The reaction mixture was stirred for 2.5 h at 0° C. before iodomethane (6.6 mL, 106 mmol) was added dropwise at 0° C. The reaction mixture was then stirred at room temperature for 16 h before being poured into cold saturated ammonium chloride solution and extracted by ethyl acetate. The organic portion was subjected to column chromatography (85:15 hexane:THF) to yield 18 g (92%) of 2-(1-phenyl-ethyl)pyridine.

Synthesis of 2-(2-phenylpropan-2-yl)pyridine

A 100 mL round-bottomed flask was charged with phenyllithium (1.8 M, 59 mL, 106 mmol) and cooled to 0° C. 2-(1-phenylethyl)pyridine (19.5 g, 106 mmol) was dissolved in 55 mL ether and added dropwise to the reaction mixture over 30 min. at 0° C. The reaction mixture was stirred for 2.5 h at 0° C. before iodomethane (6.6 mL, 106 mmol) was added dropwise at 0° C. The reaction mixture was then stirred at room temperature for 16 h before being poured into cold saturated ammonium chloride solution and extracted by ethyl acetate. The organic portion was subjected to column chromatography (85:15 hexane:THF) to yield 16 g (75%) of 2-(2-phenylpropan-2-yl)pyridine.

Synthesis of Compound 59

In a 50 mL round bottom flask was charged the iridium complex (0.5 g, 0.49 mmol) and 2-(2-phenylpropan-2-yl)pyridine (0.5 g, 2.5 mmol) and 8 drops of dichlorobenzene. The reaction mixture was heated to 200° C. for 21 h and, after cooling, subjected to column chromatography (80:20 hexane:THF) to 100 mg (20%) of Compound 59 as a yellow solid.

Synthesis of Compound 1

In a 50 mL round bottom flask was charged the iridium dimer complex (0.5 g, 0.24 mmol), silver(I) triflate (0.12 g, 0.48 mmol), DCM (10 mL) and methanol (10 mL). The reaction mixture was stirred for 3 h at room temperature, filtered and the filtrate evaporated to dryness. To the residue was added 2-(2-phenylpropan-2-yl)pyridine (0.32 g, 1.63 mmol) and 8 drops of dichlorobenzene. The reaction mixture was heated to 200° C. for 19 h and, after cooling, the crude mixture was subjected to column chromatography on silica gel (80:20 hexane:THF) to give 49 mg (16%) of Compound 1 as a yellow solid.