Organometallic compounds and their applications

Abstract

Organometallic compound with the structural formula as shown in Formula III: where XY is a monoanionic bidentate ligand of type OO or CN that is not identical to the ligand on the left-hand side; wherein R1-R4 are independently selected from hydrogen, deuterium, substituted or unsubstituted C1-C8 alkyl, or substituted or unsubstituted C3-C20 cycloalkyl, wherein the substitution can be by deuterium, F, Cl, Br or C1-C4 alkyl, and wherein at least one of R3 and R4 is not hydrogen; where Z is selected from O, S, C(R)2, where R is independently selected from substituted or unsubstituted C1-C10 alkyl groups.

Description

Technical field

[0001] The present invention relates to the technical field of organic electroluminescence, in particular to an organic luminescence material suitable for organic electroluminescence devices, especially to an organic metal compound and its application to organic electroluminescence devices. State of the art

[0002] Currently, organic electroluminescent devices (OLEDs), a new generation of display technologies, are gaining increasing attention in the display and lighting industries, and their application prospects are very broad. However, compared to market requirements, the luminous efficacy, drive voltage, and lifetime of OLED devices need to be further enhanced and improved.

[0003] In general, the basic structure of an OLED device consists of an organic functional material film with various functions sandwiched around a metal electrode. Driven by an electric current, holes and electrons are injected from the cathode and anode, respectively. After traveling a certain distance, these holes and electrons assemble within the light-emitting layer and are released as light or heat, thus generating OLED luminescence.

[0004] However, organic functional materials are a central component of organic electroluminescence devices. The thermal stability, photochemical stability, electrochemical stability, quantum yield, film formation stability, crystallinity, and color saturation of the material are the main factors that influence the performance of the device.

[0005] In general, functional organic materials include fluorescent and phosphorescent materials. Fluorescent materials are typically low-molecular-weight organic materials that generally only utilize 25% singlet luminescence, resulting in relatively low luminescence efficiency. However, due to the spin-orbit coupling effect caused by the heavy-atom effect of the phosphorescent material, the energy of the 75% triplet exciton can also be utilized in addition to the 25% singlet state, thus improving the light yield. Compared to fluorescent materials, however, phosphorescent materials have a slower onset, and their thermal stability, lifetime, and color saturation need to be improved, which is a challenging area. Various organometallic compounds have been developed as phosphorescent materials.For example, patent CN107973823 discloses a class of quinoline iridium compounds, but the color saturation and device performance of such compounds, particularly the luminescence efficiency and device lifetime, need improvement. Patent CN106459114 discloses a class of iridium compounds coordinated with diketone ligands, but these compounds have a high sublimation temperature and poor color saturation; in particular, the device performance is not ideal and needs further improvement. Additional phosphorescent compounds are disclosed in documents EP 2 940 098 A1 and US 2016 / 0 111 661 A1. Content of the present invention

[0006] One object of the present invention is to provide a phosphorescent compound. The compounds have the advantages of a low sublimation temperature, high light and electrochemical stability, high color saturation, high luminescence efficiency, and a long device lifetime, and can be used in organic electroluminescent devices. In particular, it can be used as a red luminescent dopant in the OLED industry.

[0007] Organometallic compound with the structural formula as shown in Formula III: where XY is a monoanionic bidentate ligand of type OO or CN that is not identical to the ligand on the left.

[0008] R1-R4 are independently selected from hydrogen, deuterium, substituted or unsubstituted C1-C8 alkyl, or substituted or unsubstituted C3-C20 cycloalkyl, wherein the substitution can be by deuterium, F, Cl, Br or C1-C4 alkyl, and wherein at least one of R3 and R4 is not hydrogen.

[0009] Z is O, S, C (R)2, where R is independently selected from substituted or unsubstituted C1-C10 alkyl.

[0010] The preferred compound XY is a 1,3-diketone compound.

[0011] The following connections are preferred:

[0012] One object of the present invention is also to provide a phosphorescent OLED material containing the above compounds.

[0013] One object of the present invention is also to provide an OLED device that incorporates the above compounds.

[0014] The material according to the invention not only has the advantages of a low sublimation temperature, high photoelectrochemical stability, high color saturation, high luminescence efficiency, and a long device lifetime. As a phosphorescent material, the material according to the invention can convert the excited triplet state into light, thus improving the luminescence efficiency of the organic electroluminescence device and reducing energy consumption. Detailed descriptions

[0015] The following embodiments are provided only to facilitate understanding of the technical invention and should not be regarded as specific limitations of the present invention.

[0016] The raw materials and solvents involved in the synthesis of the compounds in the present invention are purchased from suppliers known to technicians in this field, such as Alfa and Acros. Example 1:

[0017] Synthesis of common intermediates: Synthesis of compound 2:

[0018] Compound 1 (27.2 g, 0.12 mol, 1.2 eq), 1-chloroisoquinoline (16.3 g, 0.1 mol, 1.0 eq) and Cs2CO3 (97.5 g, 0.3 mol, 3.0 eq) and Pd (dppf) Cl2 (3.655 g, 0.05 mol, 0.05 eq) were placed in a flask and 1 L of anhydrous toluene was added, stirred for 16 hours at 110 °C under N2 protection. It was cooled to room temperature, concentrated to remove the organic solvent, 1 L of dichloromethane and 1 L of water were added to the residue, stirred and layered, the organic phase was washed successively with H₂O (500 mL * 3) and saturated aqueous sodium chloride solution (500 mL * 3), and the sodium sulfate was dried and filtered. The filtrate was concentrated and the organic solvent was removed. The grayish-white solid was obtained and purified with EtOH to obtain compound 2.

[0019] (24.33 g, yield: 78.7%). Mass spectrometry: 310.12 (M+H), 1HNMR: 8.42(d,1H), 7.92(dd,1H), 7.87(dd,1H), 7.71(dd,1H), 7.50-7.57(m,3H), 7.30(dd,1H), 6.99-7.20(m,4H), 2.35(S,3H). Synthesis of compound 3:

[0020] Compound 2 (18.5 g, 0.06 mol, 3.0 eq) and IrCl3 3H2O (7.04 g, 0.02 mol, 1.0 eq) were placed in a flask, 2-ethoxyethanol (133.4 mL) and deionized water (66.7 mL) were added, and the mixture was stirred for 16 hours at 110 °C under nitrogen protection. After cooling to room temperature, it was successively filtered with methanol (100 mL * 3) and n-hexane (100 mL * 3) and dried to obtain compound 3 (9.38 g, 55.4%). The obtained compound was used directly in the next step without purification.

[0021] Compound 3 (5.08 g, 3 mmol, 1.0 eq) was dissolved in ethylene glycol monoethyl ether (30 mL), followed by anhydrous sodium carbonate (6.36 g, 60 mmol, 20.0 eq) and acetylacetone (3 g, 30 mmol, 10.0 eq). After addition, the mixture was stirred under nitrogen at 40 °C and cooled to room temperature for 16 hours. 2 g of diatomaceous earth and 300 mL of dichloromethane were added to the reaction solution, and the mixture was then filtered through diatomaceous earth and silica gel to remove the dichloromethane. 40 mL of isopropanol was added to the residue to precipitate and filter the red solids. The solid was treated with ethyl acetate to obtain the target compound CPD 1 (2.56 g, 46.8%). The crude product of 2.56 g of CPD 1 was sublimed and purified to obtain sublimed pure CPD 1 (2 g, 78.1%). Mass spectrometry: 909.23 (M+H)

[0022] Compound 3 (5.08 g, 3 mmol, 1.0 eq) was dissolved in ethylene glycol monoethyl ether (30 mL), followed by anhydrous sodium carbonate (6.36 g, 60 mmol, 20.0 eq) and 3,7-diethyl-4,6-nonidione (6.36 g, 30 mmol, 10.0 eq). After addition, the mixture was stirred under nitrogen at 40 °C and cooled to room temperature for 16 hours. 2 g of diatomaceous earth and 300 mL of dichloromethane were added to the reaction solution, and then the mixture was filtered through diatomaceous earth and silica gel to remove the dichloromethane. 40 mL of isopropanol was added to the residue to precipitate and filter the red solids. The solid was treated with ethyl acetate to obtain the target compound CPD 3 (2.69 g, 43.9%). The crude product of 2.69 g of CPD 3 was sublimed and purified to obtain sublimed pure CPD 3 (1.78 g, 66.2%). Mass spectrometry: 1021.36 (M+H) Design 2

[0023] Synthesis of common intermediates: Synthesis of compound 5:

[0024] Compound 4 (28.92 g, 0.12 mol, 1.2 eq), 1-chloro-6-isopropylisoquinoline (20.5 g, 0.1 mol, 1.0 eq) and Cs2CO3 (97.5 g, 0.3 mol, 3.0 eq) and Pd (dppf) Cl2 (3.655 g, 0.05 mol, 0.05 eq) were placed in a flask and 1 L of anhydrous toluene was added, stirred for 16 hours at 110 °C under N2 protection. The mixture was cooled to room temperature, concentrated to remove the organic solvent, and 1 L of dichloromethane and 1 L of water were added to the residue. The mixture was stirred and layered. The organic phase was washed successively with H₂O (500 mL * 3) and saturated aqueous sodium chloride solution (500 mL * 3). The sodium sulfate was dried and filtered. The filtrate was concentrated, and the organic solvent was removed. A gray-white solid was obtained, and the solid was purified by column chromatography with ethyl acetate / petroleum ether to obtain compound 5 (28.12 g, yield: 76.8%).Mass spectrometry: 367.18 (M+H), 1HNMR:8.4(d,1H), 7.81(dd,1H), 7.74(dd,1H), 7.71(s,1H), 7.50(s,1H), 7.27-7.36(m,3H), 7.1(d,1H), 3.12(q,1H), 2.55(s,3H), 2.35(s,3H), 1.29(d,6H). Synthesis of compound 6:

[0025] Compound 5 (22 g, 0.06 mol, 3.0 eq) and IrCl3 3H2O (7.04 g, 0.02 mol, 1.0 eq) were placed in a flask, 2-ethoxyethanol (133.4 mL) and deionized water (66.7 mL) were added, and the mixture was stirred for 16 hours at 110 °C under nitrogen protection. After cooling to room temperature, it was successively filtered with methanol (100 mL * 3) and n-hexane (100 mL * 3) and dried to obtain compound 6 (9.86 g, 51.3%). The obtained compound was used directly in the next step without purification. Synthesis of CPD 13 (not according to the invention)

[0026] Compound 6 (5.76 g, 3 mmol, 1.0 eq) was dissolved in ethylene glycol monoethyl ether (30 mL), followed by anhydrous sodium carbonate (6.36 g, 60 mmol, 20.0 eq) and acetylacetone (3 g, 30 mmol, 10.0 eq). After addition, the mixture was stirred under nitrogen protection at 40 °C and cooled to room temperature for 16 hours. 2 g of diatomaceous earth and 300 mL of dichloromethane were added to the reaction solution, and the mixture was then filtered through diatomaceous earth and silica gel to remove the dichloromethane. 40 mL of isopropanol was added to the residue to precipitate and filter the red solids. The solid was treated with ethyl acetate to obtain the target compound CPD 13 (2.33 g, 38%). The crude product of 2.33 g of CPD 13 was sublimed and purified to obtain sublimated pure CPD 13 (1.72 g, 73.8%). Mass spectrometry: 1023.34 (M + H) Synthesis of CPD 16 (not according to the invention)

[0027] Compound 6 (5.76 g, 3 mmol, 1.0 eq) was dissolved in ethylene glycol monoethyl ether (30 mL), followed by anhydrous sodium carbonate (6.36 g, 60 mmol, 20.0 eq) and 2,8-dimethyl-4,6-nonidione (6.36 g, 30 mmol, 10.0 eq). After addition, the mixture was stirred under nitrogen at 40 °C and cooled to room temperature for 16 hours. 2 g of diatomaceous earth and 300 mL of dichloromethane were added to the reaction solution, and then the mixture was filtered through diatomaceous earth and silica gel to remove the dichloromethane. 40 mL of isopropanol was added to the residue to precipitate and filter the red solids. The solid was treated with ethyl acetate to obtain the target compound CPD 16 (2.12 g, 32%). The crude product of 2.12 g of CPD 16 was sublimed and purified to obtain sublimed pure CPD 16 (1.65 g, 77.8%). Mass spectrometry: 1107.43 (M + H) Synthesis of CPD 17 (not according to the invention)

[0028] Compound 6 (5.76 g, 3 mmol, 1.0 eq) was dissolved in ethylene glycol monoethyl ether (30 mL), followed by anhydrous sodium carbonate (6.36 g, 60 mmol, 20.0 eq) and 2-acetylphenol (4.08 g, 30 mmol, 10.0 eq). After addition, the mixture was stirred under nitrogen at 40 °C and cooled to room temperature for 16 hours. 2 g of diatomaceous earth and 300 mL of dichloromethane were added to the reaction solution, and the mixture was then filtered through diatomaceous earth and silica gel to remove the dichloromethane. 40 mL of isopropanol was added to the residue to precipitate and filter the red solids. The solids were separated by column chromatography to obtain the target compound CPD 17 (2.58 g, 41%). The crude product of 2.58 g of CPD 17 was sublimed and purified to obtain sublimed pure CPD 17 (1.88 g, 73.1%). Mass spectrometry: 1059.34 (M + H) Synthesis of CPD 18 (not according to the invention) Synthesis of compound 7:

[0029] Compound 6 (19.2 g, 0.01 mol, 1.0 eq) was dissolved in DCM (500 ml), and silver trifluoromethylsulfonate (5.25 g, 0.02 mol, 2.0 eq) and methanol (50 ml) were added successively to the reaction solution. After addition, the mixture was stirred for 16 hours at 30 °C under nitrogen protection. The insoluble solids were removed from the reaction solution using silica gel and diatomaceous earth, and the filtrate was dried by rotation to obtain compound 7 (22 g). The product obtained was used directly for the next reaction. Synthesis of CPD 18:

[0030] Compound 7 (3.41 g, 3 mmol, 1.0 eq) and 2-phenylpyridine (1.4 g, 9 mmol, 3.0 eq) were dissolved in anhydrous ethanol (100 ml), and after addition, the mixture was stirred for 16 hours at 80 °C under nitrogen protection. After filtration, the filtration residue was washed three times with methanol and n-hexane. The target compound CPD 18 (1.68 g, 52%) was obtained by drying. The crude product of 1.68 g of CPD 18 was sublimed and purified to obtain sublimed pure CPD 18 (1.24 g, 73.8%). Mass spectrometry: 1078.36 (M + H). Synthesis of CPD 24 (not according to the invention):

[0031] Compound CPD 18 (2.15 g, 2 mmol, 1.0 eq) and fully deuterated ethanol (100 ml) were dissolved in anhydrous THF (50 ml), and after addition, the mixture was stirred for 16 hours at 80 °C under nitrogen protection. After filtration, the filtration residue was washed three times with methanol and n-hexane. The target compound CPD 24 (2.15 g, 99%) was obtained by drying. The crude product of 2.15 g of CPD 24 was sublimed and purified to obtain sublimed pure CPD 24 (1.54 g, 71.6%). Mass spectrometry: 1078.36 (M + H). Synthesis of CPD 19 (not according to the invention):

[0032] The target compound CPD 19 (1.88 g, 99%) was obtained using the synthesis method of CPD 24. The crude product of 1.88 g of CPD 19 was sublimed and purified to obtain sublimed pure CPD 19 (1.42 g, 75.5%). Mass spectrometry: 1028.38 (M + H) Synthesis of CPD 22 (not according to the invention):

[0033] The target compound CPD 22 (2.35 g, 99%) was obtained using the synthesis method of CPD 24. The crude product of 2.35 g of CPD 22 was sublimed and purified to obtain sublimed pure CPD 22 (1.64 g, 69.9%). Mass spectrometry: 1113.47 (M + H) Synthesis of CPD 23 (not according to the invention):

[0034] The target compound CPD 23 (2.52 g, 99%) was obtained using the synthesis method of CPD 24. The crude product of 2.52 g of CPD 23 was sublimed and purified to obtain sublimed pure CPD 23 (1.92 g, 76.2%). Mass spectrometry: 1065.38 (M + H) embodiment 3 Synthesis of CPD 79: Synthesis of compound 9:

[0035] Compound 8 (29.1 g, 0.12 mol, 1.2 eq), 1-chloroisoquinoline (16.3 g, 0.1 mol, 1.0 eq) and Cs2CO3 (97.5 g, 0.3 mol, 3.0 eq) and Pd (dppf) Cl2 (3.655 g, 0.05 mol, 0.05 eq) were placed in a flask and 1 L of anhydrous toluene was added, stirred for 16 hours at 110 °C under N2 protection. The mixture was cooled to room temperature, concentrated to remove the organic solvent, and 1 L of dichloromethane and 1 L of water were added to the residue. The mixture was stirred and layered. The organic phase was washed successively with H₂O (500 mL * 3) and saturated aqueous sodium chloride solution (500 mL * 3). The sodium sulfate was dried and filtered. The filtrate was concentrated, and the organic solvent was removed. A gray-white solid was obtained, and the solid was separated by column chromatography to obtain compound 9 (23.41 g, yield: 72.1%). Mass spectrometry: 326.1 (M + H), 1HNMR:

[0036] 8.51(d,1H), 7.71-7.82(m,5H), 7.50-7.60(m,3H),7.30-7.4(m,2H), 7.10(d,1H), 2.21(s,3H). Synthesis of compound 10: Compound 9 (19.5 g, 0.06 mol, 3.0 eq) and IrCl3 3H2O (7.04 g, 0.02 mol, 1.0 eq) were placed in a flask, 2-ethoxyethanol (133.4 mL) and deionized water (66.7 mL) were added, and the mixture was stirred for 16 hours at 110 °C under nitrogen protection. After cooling to room temperature, it was successively filtered with methanol (100 mL * 3) and n-hexane (100 mL * 3) and dried to obtain compound 3 (8.54 g, 48.6%). The obtained compound was used directly in the next step without purification. Synthesis of CPD 79:

[0037] The target compound CPD 79 (3.26 g, 46.8%) was obtained using the synthesis and purification procedures of CPD 1. The crude product of 3.26 g of CPD 79 was sublimed and purified to obtain sublimed pure CPD 79 (2.33 g, 71.6%). Mass spectrometry: 941.18 (M+H) Design 4

[0038] Synthesis of CPD 80: Synthesis of compound 12:

[0039] Compound 11 (30.3 g, 0.12 mol, 1.2 eq), 1-chloroisoquinoline (16.3 g, 0.1 mol, 1.0 eq) and Cs2CO3 (97.5 g, 0.3 mol, 3.0 eq) and Pd (dppf) Cl2 (3.655 g, 0.05 mol, 0.05 eq) were placed in a flask and 1 L of anhydrous toluene was added, stirred for 16 hours at 110 °C under N2 protection. The mixture was cooled to room temperature, concentrated to remove the organic solvent, and 1 L of dichloromethane and 1 L of water were added to the residue. The mixture was stirred and layered. The organic phase was washed successively with H₂O (500 mL * 3) and saturated aqueous sodium chloride solution (500 mL * 3). The sodium sulfate was dried and filtered. The filtrate was concentrated, and the organic solvent was removed. A gray-white solid was obtained, and the solid was separated by column chromatography to obtain compound 12 (21.34 g, yield: 63.7%).Mass spectrometry: 336.17 (M+H), 1HNMR: 8.51(d,1H), 7.71-7.82(m,5H), 7.50-7.60(m,3H), 7.30-7.4(m,2H), 7.10(d,1H), 2.32(s,3H),1.67(s,6H). Synthesis of compound 13:

[0040] Compound 12 (20.1 g, 0.06 mol, 3.0 eq) and IrCl3 3H2O (7.04 g, 0.02 mol, 1.0 eq) were placed in a flask, 2-ethoxyethanol (133.4 ml) and deionized water (66.7 ml) were added, and the mixture was stirred for 16 hours at 110 °C under nitrogen protection. After cooling to room temperature, it was successively filtered with methanol (100 ml * 3) and n-hexane (100 ml * 3) and dried to obtain compound 13 (8.96 g, 49.9%). The obtained compound was used directly in the next step without purification. Synthesis of CPD 80:

[0041] The synthesis and purification procedures for CPD 1 yielded the target compound CPD 80 (3.54 g, 47.9%). The crude product of 3.54 g of CPD 80 was sublimed and purified to obtain sublimed pure CPD 80 (2.45 g, 69.2%). Mass spectrometry: 961.33 (M+H)

[0042] The appropriate material is selected and can be used to synthesize and sublimate other compounds through a similar process.

[0043] Application Example: Fabrication of Organic Electroluminescence Devices. A glass substrate with a transparent ITO (100 nm) electrode measuring 50 mm × 50 mm × 1.0 mm was ultrasonically cleaned in ethanol for 10 minutes and treated with N₂ plasma 30 minutes after drying at 150 °C. The washed glass substrate was mounted on the substrate holder of the vacuum evaporation device. First, the compound HATCN was evaporated on one side with a transparent electrode lead in a manner that covered the transparent electrode to form a film with a thickness of 5 nm. Then, a layer of HTM1 was evaporated to form a film with a thickness of 60 nm. Finally, a layer of HTM2 was evaporated onto the HTM1 film to form a film with a thickness of 10 nm.Then, the main material CBP and the doped compound (reference compound X, CPD X) were evaporated onto the HTM2 film layer by co-evaporation. The film thickness is 30 nm, and the ratio of main material to doped material is 90%:10%. The AlQ3 film layer (25 nm) and the LiF film layer (1 nm) were sequentially evaporated onto the light-emitting layer, and finally, a metal layer Al (100 nm) was evaporated as an electrode.

[0044] Evaluation: The above devices were tested for performance. In each embodiment and comparison example, the luminescence spectrum was tested using a constant current supply (Keithley 2400) and a fixed current density through the luminescent element and a spectroradiometer (CS 2000). The voltage value and the time it took for the test brightness to reach 90% of the initial brightness (LT90) were measured simultaneously. The results are as follows: Doped material Starting voltageV Energy efficiency Cd / A Energy efficiency lm / W Peak wavelengths LT90@3000nits Design 1 CPD 1 4,21 24 17,90 614 162 Design 2 CPD 3 4,12 28 21,34 615 178 Design 3 (comparative example) CPD 13 4,05 31 24,03 620 211 Design 4 (comparative example) CPD 16 3,99 33 25,97 626 232 (Comparative example) CPD 17 3,97 30 23,73 623 235 Design 6 (comparative example) CPD 18 3,96 32 25,37 622 264 Design 7 (comparative example) CPD 19 3,88 32 25,90 622 268 Design 8 (comparative example) CPD 22 3,86 34 27,66 628 312 Design 9 (comparative example) CPD 23 3,79 32 26,51 625 295 Design 10 (comparative example) CPD 24 3,82 31 25,48 624 281 Design 11 CPD 79 3,98 26 20,51 616 168 Design 12 CPD 80 4,11 28 21,39 615 176 Comparative example 1 Comparison connection 1 4,56 21 14,46 610 102 Comparative example 2 Comparison connection 2 4,41 20 14,24 612 116 Comparative example 3 Comparison connection 3 4,64 21 14,21 611 94 Comparative example 4 Comparison connection 4 4,88 18 11,58 608 82

[0045] The data comparison in the table above shows that the organic electroluminescent device using the compound of the present invention as a dopant exhibits superior performance in drive voltage, luminescence efficiency, and device lifetime compared to the reference compound. Sublimation temperature comparison: The sublimation temperature is defined as the temperature at which the evaporation rate reaches 1 angstrom per second at a vacuum of 10 degrees. -7 Torr is correct. The test results are as follows: Doped material Sublimation temperature CPD 1 263 CPD 3 262 CPD 13 (Comparison connection) 252 CPD 16 (Comparison connection) 258 CPD 17 (Comparison connection) 260 CPD 18 (Comparison connection) 262 CPD 19 (Comparison connection) 254 CPD 22 (Comparison connection) 259 CPD 23 (Comparison connection) 260 CPD 24 (Comparison connection) 261 CPD 79 262 CPD 80 261 Comparison connection 1 280 Comparison connection 2 288 Comparison connection 3 286 Comparison connection 4 276

[0046] The data comparison in the table above shows that the compound of the present invention has a lower sublimation temperature, which is advantageous for industrial applications.

[0047] The above results show that the compounds of the present invention have the advantages of a low sublimation temperature, high light and electrochemical stability, high color saturation, high luminescence efficiency, and a long device lifetime, and can be used in organic electroluminescent devices. In particular, it can be used as a red luminescent dopant in the OLED industry.

Claims

[1] Organometallic compound with the structural formula as shown in Formula III: where XY is a monoanionic bidentate ligand of type OO or CN that is not identical to the ligand on the left-hand side; wherein R1-R4 are independently selected from hydrogen, deuterium, substituted or unsubstituted C1-C8 alkyl, or substituted or unsubstituted C3-C20 cycloalkyl, wherein the substitution can be by deuterium, F, Cl, Br or C1-C4 alkyl, and wherein at least one of R3 and R4 is not hydrogen; where Z is selected from O, S, C(R)2, where R is independently selected from substituted or unsubstituted C1-C10 alkyl groups. [2] Organometallic compound according to claim 1, wherein R is independently selected from substituted or unsubstituted C1-C8 alkyl groups. [3] Organometallic compound according to any of the preceding claims, wherein XY is a 1,3-diketone compound. [4] Organometallic compound according to any one of the preceding claims, wherein R1-R4 are independently selected from hydrogen, deuterium, substituted or unsubstituted C1-C4 alkyl, or substituted or unsubstituted C3-C20 cycloalkyl. [5] Organometallic compound according to any of the preceding claims having one of the following structural formulas: [6] Use of one of the compounds described in claims 1 to 5 in organic electroluminescent devices. [7] Application according to claim 6, wherein the compound according to claims 1 to 5 is a doping material of phosphorescent host material in the luminescence layer.