High-brightness phosphorescent binuclear Pd (II) complex as well as preparation method and application thereof

Abstract

The invention discloses a high-brightness phosphorescent binuclear Pd (II) complex as well as a preparation method and application thereof, and belongs to the technical field of organic photoelectric materials. The complex has a specific binuclear structural general formula, takes palladium as a metal center, adopts a carbene ligand of a strong sigma donor as a cyclometalated ligand, and selects 4-methyl oxazolidine-2-thioketone and a derivative thereof as bridging ligands. According to the preparation method, a first intermediate and a second intermediate are sequentially synthesized in a nitrogen atmosphere by adopting a one-pot method and finally react with a bridging ligand to obtain a target product, the process is simple and convenient, and intermediate separation is not needed. According to the present invention, through the synergistic effect of the carbene ligand and the bridging ligand, the metal-ligand and metal-metal-ligand charge transfer process is effectively enhanced, the phosphorescence efficiency is significantly improved, and the organic electroluminescent material has excellent thermal stability, and has wide application prospects in organic electroluminescent devices, particularly OLED light emitting layer materials.

Description

Technical Field

[0001] This invention belongs to the field of metal complex luminescent materials technology, and particularly relates to a high-brightness phosphorescent binuclear Pd(II) complex, its preparation method and application. Background Technology

[0002] Third-row transition metal complexes, represented by platinum (Pt) and iridium (Ir), have been widely developed and used as emissive layer materials for organic light-emitting diodes (OLEDs). These complexes benefit from their high phosphorescence quantum yield and easily tunable spectral properties, enabling the successful commercialization of high-performance phosphorescent Pt(II) and Ir(III) complexes, which has greatly promoted the development of OLED technology.

[0003] However, palladium (Pd), a second-row transition metal in the same group as Pt and Ir, rarely uses its corresponding Pd(II) complexes as luminescent centers in OLEDs. The key scientific issue behind this is that the ligand field splitting energy (Δ) of the Pd(II) ion is significantly lower than that of its third-row homologues, and its spin-orbit coupling constant is also smaller. These electronic structure characteristics cause Pd(II) complexes to typically exhibit ligand-centric excited-state properties, often accompanied by long excited-state lifetimes. More importantly, in Pd(II) complexes, the dd state at the metal center is always thermodynamically accessible at room temperature, providing an effective channel for the dissipation of excited-state energy through non-radiative transitions, thus severely impairing its phosphorescent quantum yield and resulting in low luminescence efficiency.

[0004] While theoretically, introducing strong-field ligands, such as cyclometalated C^N ligands (e.g., 2-phenylpyridine) or C^N^N ligands (e.g., 6-phenyl-2,2'-bipyridine), could suppress the deactivation process caused by the dd state, these strategies have yielded limited success in designing highly efficient phosphorescent Pd(II) complexes. Although the research community has made considerable efforts in developing phosphorescent Pd(II) complexes through meticulous ligand design, successfully designing and synthesizing phosphorescent Pd(II) complexes that combine high quantum efficiency with short excited-state lifetimes remains a major challenge in this field, limiting the potential application of Pd(II) complexes in optoelectronics.

[0005] Therefore, there is an urgent need in this field for a novel molecular design strategy and synthesis method that can fundamentally solve the problem of low phosphorescence efficiency of Pd(II) complexes and develop novel Pd(II) luminescent materials with high phosphorescence quantum yield, so as to broaden the selection range of OLED luminescent materials and reduce potential costs. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a high-brightness phosphorescent binuclear Pd(II) complex, its preparation method, and its application, thereby solving the problem that existing Pd(II) complexes cannot simultaneously achieve high quantum efficiency and high brightness luminescence.

[0007] To achieve the above objectives, the present invention provides a high-brightness phosphorescent binuclear Pd(II) complex having the structure shown in the following general formula: or ; Where X is selected from O or S.

[0008] Furthermore, the complex is selected from one of the following structures: , , or .

[0009] This invention effectively coordinates two Pd(II) metal centers simultaneously by introducing specific bridging ligands (i.e., 4-methyloxazolidine-2-thione and its derivatives), forming a stable binuclear structure. These bridging ligands not only act as spatial connectors, but more importantly, their specific electronic structure and coordination ability shorten the distance between the two Pd atoms, promoting metal-metal interactions and initiating a metal-metal-ligand charge transfer process. This process synergizes with the traditional metal-ligand charge transfer process, greatly enhancing intersystem crossing and radiative transition rates, and achieving high phosphorus photon yield.

[0010] The present invention also provides a method for preparing the above-mentioned high-brightness phosphorescent dinuclear Pd(II) complex, comprising the following steps: Provides 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide; The 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide was reacted with silver oxide in a first solvent and an inert atmosphere to obtain a first intermediate reaction solution. The first intermediate reaction solution was reacted with (1,5-cyclooctadiene)palladium dichloride in a second reaction to obtain the second intermediate reaction solution; The second intermediate reaction solution, the second reactant, and the base were subjected to a third reaction in a second solvent and an inert atmosphere to obtain the high-brightness phosphorescent binuclear Pd(II) complex. Wherein, the first intermediate structure is The second intermediate is The second reactant is , , or .

[0011] Furthermore, the conditions for the first reaction include: the first solvent is ultra-dry N,N-dimethylformamide, the reaction temperature is 45-55°C, the reaction time is 20-28 hours, and the reaction is carried out under light-protected conditions.

[0012] Furthermore, the conditions for the second reaction include: the reaction is first carried out at 45-55°C for 1-3 hours, then the temperature is raised to 120-130°C and the reaction continues for 20-28 hours, and the reaction is carried out under light-protected conditions.

[0013] Further, the conditions for the third reaction include: the second solvent is ultra-dry N,N-dimethylformamide, the base is sodium tert-butoxide, the reaction temperature is 60-70°C, the reaction time is 44-52 hours, and the reaction is carried out under light-protected conditions; and / or, After the third reaction is completed, the solvent is removed by rotary evaporation, and the residue is purified by column chromatography using a mixed solvent of petroleum ether and dichloromethane as the eluent.

[0014] Further, the molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to silver oxide is 1:0.5-0.7; and / or, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to (1,5-cyclooctadiene)palladium dichloride is 1:0.9-1.1; and / or, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to the second reactant is 1:3.5-4.5; and / or, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to the base is 1:3.5-4.5.

[0015] The present invention also provides the application of the high-brightness phosphorescent dinuclear Pd(II) complex as described above in the preparation of organic electroluminescent devices, wherein the high-brightness phosphorescent dinuclear Pd(II) complex is used as the light-emitting layer material of the organic electroluminescent device.

[0016] The present invention also provides an organic electroluminescent device comprising a light-emitting layer, wherein the light-emitting layer comprises the above-described high-brightness phosphorescent dinuclear Pd(II) complex.

[0017] Furthermore, the device is an organic light-emitting diode (OLED).

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: This invention discloses a method for synthesizing high-brightness phosphorescent binuclear Pd(II) complexes. On the one hand, by using a carbene ligand with a strong σ donor as a cyclic metal ligand, the spin-orbit coupling between the metal and the ligand is enhanced, promoting the metal-ligand charge transfer process, weakening the dd thermal deactivation process, and improving the quantum yield of the phosphorescent Pd(II) complex. On the other hand, 4-methyloxazolidine-2-thione and its derivatives are introduced as bridging ligands, shortening the distance of the Pd-Pd bond and forming an effective metal-metal-ligand charge transfer process, further improving the quantum yield of the phosphorescent Pd(II) complex. This provides an effective model for the development of high-brightness phosphorescent palladium complexes. Attached Figure Description

[0019] Figure 1 The image shows the molecular stereostructure of the S-configuration complex in Example 1-1 of this invention, obtained by X-ray single-crystal diffraction.

[0020] Figure 2 The molecular stereoscopic structures of the R-configuration complexes in Examples 1-2 of this invention were obtained by X-ray single-crystal diffraction. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0023] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0024] This invention provides a high-brightness phosphorescent dinuclear Pd(II) complex, the structure of which is shown in the following formula: Specifically, this invention provides a method for preparing high-brightness phosphorescent binuclear Pd(II) complexes. A carbene ligand with a strong σ donor is used as a cyclic metal ligand, enhancing the spin-orbit coupling between the metal and the ligand, promoting the metal-ligand charge transfer process, weakening the dd thermal deactivation process, and improving the quantum yield of the phosphorescent Pd(II) complex. Furthermore, 4-methyloxazolidine-2-thione and its derivatives are introduced as bridging ligands, shortening the Pd-Pd bond distance and forming an effective metal-metal-ligand charge transfer process, further improving the quantum yield of the phosphorescent Pd(II) complex. This provides an effective model for the development of subsequent high-brightness phosphorescent Pd(II) complexes.

[0025] In the high-brightness phosphorescent binuclear Pd(II) complex of the present invention, the term (II) represents the valence state of metallic palladium, which has zero, divalent and tetravalent valences, and (II) indicates that its valence state is divalent.

[0026] In this invention, the 4-methyloxazolidine-2-thione and its derivatives are chiral or achiral. In some embodiments, they may be selected from one of the following structures: .

[0027] In some implementations, the carbene ligand may be selected from one of the following structures: .

[0028] In some embodiments, the high-brightness phosphorescent Pd(II) complex may be selected from one of the following structures: .

[0029] In this invention, a method for preparing a high-brightness phosphorescent Pd(II) complex includes the following steps: 1-Methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide is provided; The 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide was reacted with silver oxide to give the first intermediate; The first intermediate was reacted with (1,5-cyclooctadiene)palladium dichloride to obtain the second intermediate; The second intermediate is reacted with the second reactant to obtain the high-brightness phosphorescent Pd(II) complex.

[0030] Wherein, the first intermediate structure is The second intermediate is The second reactant is , , or .

[0031] Specifically, the preparation method of this high-brightness phosphorescent Pd(II) complex includes the following steps: Provides 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide.

[0032] 1-Methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide (1 equivalent) and silver oxide (0.6 equivalent) were added to ultra-dry DMF (10 ml / equivalent) and reacted in the dark at 50 °C under N2 atmosphere for 24 h. The first intermediate was obtained, which required no further processing.

[0033] Add (1,5-cyclooctadiene)palladium dichloride (1 equivalent) to the untreated first intermediate reaction solution, react in the dark at 50°C under N2 atmosphere for 2 hours, then raise the temperature to 125°C and continue the reaction for 24 hours to obtain the second intermediate. Cool to room temperature and no further treatment is required.

[0034] The second reactant (4 equivalents) and sodium tert-butoxide (4 equivalents) were added to the untreated second intermediate reaction solution and reacted in the dark under a N2 atmosphere at 65°C for 48 h. After cooling to room temperature, the solvent was removed by rotary evaporation under vacuum. The residue was purified by column chromatography (petroleum ether / dichloromethane) to obtain the high-brightness phosphorescent binuclear Pd(II) complex.

[0035] This invention provides a high-brightness phosphorescent binuclear Pd(II) complex as described in this invention that achieves high-brightness phosphorescence emission under solid powder conditions.

[0036] The technical solution of the present invention will be described in detail below through specific embodiments.

[0037] Example 1-1: Preparation of complex OMePdC^C In this embodiment, 4-methyl-2-oxazolidinylthione was used as a bridging ligand to prepare the target complex OMePdC^C. The synthetic route is as follows: The specific preparation steps are as follows: (1) Synthesis of the first intermediate 0.39 g (1 mmol) of 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide and 0.14 g (0.6 mmol) of silver oxide were placed in a 100 mL double-necked round-bottom flask. The reaction system was evacuated and purged with nitrogen, and this cycle was repeated three times to completely displace the air in the system. Subsequently, 10 mL of ultra-dry DMF was added to the flask as a solvent under nitrogen protection. The reaction system was placed in an oil bath at 50 °C and stirred in the dark for 24 hours. After the reaction was completed, the resulting reaction solution was a mixture containing the first intermediate, which did not require further processing and could be used directly for the next reaction.

[0038] (2) Synthesis of the second intermediate Under a nitrogen atmosphere and at room temperature, 0.285 g (1 mmol) of (1,5-cyclooctadiene)palladium dichloride (Pd(cod)Cl2) was added to the untreated first intermediate reaction solution. The reaction system was heated to 50 °C and stirred in the dark for 2 hours. Subsequently, the reaction temperature was further increased to 125 °C, and the reaction was continued in the dark with stirring for 24 hours. After the reaction was completed, the reaction system was cooled to room temperature. The resulting reaction solution was a mixture containing the second intermediate, which required no further treatment and could be used directly in the next reaction.

[0039] (3) Synthesis of the target complex OMePdC^C To the untreated second intermediate reaction solution from the previous step, 0.47 g (4 mmol) of 4-methyl-2-oxazolidinyl thione and 0.38 g (4 mmol) of sodium tert-butoxide were added sequentially. The reaction was carried out under nitrogen protection and at 65 °C with stirring in the dark for 48 hours. After the reaction was complete, the reaction solution was cooled to room temperature, and the solvent DMF was removed by rotary evaporation under vacuum. The crude product residue was purified by column chromatography using a petroleum ether / dichloromethane mixed solvent as eluent to obtain the pure target complex OMePdC^C (yield: 23%).

[0040] The characterization data of the product OMePdC^C are as follows: 1 H NMR (600 MHz, CDCl3) δ 8.39 – 8.38 (m, 2H), 7.58 –7.57 (m, 2H), 7.39 – 7.35 (m, 4H), 4.64 – 4.57 (m, 4H), 4.01 (s, 6H), 3.99 (m, 2H), 1.51(d, J = 6.0 Hz, 6H). 13C NMR (151 MHz, CDCl3) δ 180.23 (s), 176.87 (s), 144.98 (s), 142.97(s), 127.28 (s), 119.28 (s), 118.04 (s), 99.55 – 99.23 (m), 74.85 (s), 61.81(s), 34.79(s), 19.40(s). 19 F NMR (565 MHz, CDCl3) δ -119.67 (s), -119.72 (s), -121.27 (s), -121.31 (s), -125.22 (d, J = 26.9 Hz), -132.13 (dd, J = 21.2, 7.8 Hz), -138.60(s), -139.35 (s), -139.73 – -139.86 (m), -159.09 (s), -163.48 (s), -164.19 –-164.37 (m), -164.52 (s). ESI-MS (m / z): Calcd. for C 34 H 26 F6N8O2Pd2S2, 969.9598; Found,970.9598 (M+H + ).

[0041] Examples 1-2: Preparation of complex SMePdC^C In this embodiment, 4-methyl-2-thiazolidinthione was used as a bridging ligand to prepare the target complex SMePdC^C. The synthetic route is as follows: The specific preparation steps are basically the same as those in Example 1-1, except that in step (3): the second reactant added to the second intermediate reaction solution is replaced with 0.63 g (4 mmol) of 4-methyl-2-thiazolidinthione.

[0042] Yield: 21%.

[0043] The product characterization data are as follows: 1 H NMR (600 MHz, CDCl3) δ 8.11 (dd, J = 4.8, 1.3 Hz, 2H), 7.67 – 7.60(m, 2H), 7.50 (dd,J = 8.1, 1.3 Hz, 2H), 7.30 (dd, J = 8.1, 4.8 Hz, 2H), 4.83 –4.77 (m, 2H), 3.64 (s, 6H), 3.41 – 3.33 (m, 4H), 1.78 (s, 3H), 1.77 (s, 3H). 13 C NMR (151 MHz, CDCl3) δ 180.16 (s), 179.95 (s), 145.00 (s), 142.78(s), 126.65 (s), 119.21 (s), 118.34 (s), 99.74 (s), 99.59 (s), 71.93 (s), 41.20 (s), 34.34 (s), 20.34 (s). 19 F NMR (565 MHz, CDCl3) δ -119.86 – -119.91 (m), -124.10 – -124.13(m), -139.43 – -139.53 (m), -140.20 – -140.36 (m), -163.22 – -163.41 (m), -164.30 – -164.36 (m). ESI-MS (m / z): Calcd. for C 34 H 26 F6N8Pd2S4, 1001.9141; Found, 1002.9145 (M+H + ).

[0044] Examples 1-3: Preparation of complex OCyPdC^C In this embodiment, the target complex OCyPdC^C was prepared using hexahydro-2(3H)-benzoxazole as a bridging ligand. The synthetic route is as follows: The specific preparation steps are basically the same as in Example 1-1, except for the third step: the second reactant added to the second intermediate reaction solution is replaced with 0.63 g (4 mmol) of hexahydro-2(3H)-benzoxazole.

[0045] Yield: 23%.

[0046] The product characterization data are as follows: 1H NMR (600 MHz, CDCl3) δ 8.41 – 8.40 (m, 2H), 7.56 – 7.55(m, 2H), 7.39 – 7.34 (m, 4H), 4.10 – 4.06 (m, 8H), 3.74 – 3.69 (m, 2H), 2.46 –2.44 (m,2H), 2.28 – 2.26 (m, 2H), 1.90 – 1.88 (m, 2H), 1.81 – 1.71 (m, 4H), 1.42 –1.35 (m, 4H). 13 C NMR (151 MHz, CDCl3) δ 180.11 (s), 178.12 (s), 144.99 (s), 142.96(s), 127.30 (s), 119.23 (s), 117.97 (s), 99.69 – 99.17 (m), 86.60 (s), 70.37(s), 34.84(s), 30.04(s), 29.27(s), 24.38(s). 19 F NMR (565 MHz, CDCl3) δ -119.66 – -119.71(m), -139.53 – -139.64(m), -164.51 – -164.72 (m). ESI-MS (m / z): Calcd. for C 42 H 42 F6N8O2Pd2S2, 1050.0224; Found1051.0222 (M+H + ).

[0047] Examples 1-4: Preparation of complex SCyPdC^C In this embodiment, the target complex SCyPdC^C was prepared using hexahydro-2(3H)-benzothiazole as a bridging ligand.

[0048] Its synthetic route is as follows: The preparation steps are basically the same as those in Examples 1-3, except for the third step: the second reactant added to the second intermediate reaction solution is replaced with hexahydro-2(3H)-benzothiazole (4 mmol).

[0049] The yield was 18%.

[0050] The product characterization data are as follows: 1 H NMR (600 MHz, CDCl3) δ 8.32 – 8.31 (m, 2H), 7.44 – 7.43(m, 2H), 7.21 – 7.16 (m, 4H), 4.30 – 4.25 (m, 8H), 3.84 – 3.79 (m, 2H), 2.38 –2.36 (m,2H), 2.25 – 2.23 (m, 2H), 1.85 – 1.83 (m, 2H), 1.77 – 1.67 (m, 4H), 1.38 –1.31 (m, 4H). 13 C NMR (151 MHz, CDCl3) δ 180.20 (s), 179.23 (s), 145.04 (s), 141.86(s), 128.39 (s), 120.07 (s), 118.32 (s), 98.66 – 98.15 (m), 85.34 (s), 71.35(s), 34.22(s), 31.24(s), 28.17(s), 24.20(s). 19 F NMR (565 MHz, CDCl3) δ -119.41 – -119.46(m), -139.33 – -139.45(m), -164.32 – -164.54 (m). ESI-MS (m / z): Calcd. for C 42 H 42 F6N8Pd2S4, 1081.9767; Found1082.9785 (M+H + ).

[0051] Test Implementation Examples and Effect Verification: The ultraviolet absorption spectra, photoluminescence spectra, phosphorescence quantum yield, circular dichroism and phosphorescence lifetime of the complexes of Examples 1 to 4 were determined, as well as the thermogravimetric analysis curves of Examples 1 to 3 and the crystal structures of Examples 1 and 2. Example 2-1: Testing the UV absorption spectra of Examples 1-1 to 1-4 The concentration measured using ultraviolet absorption spectroscopy in this invention is 3.0 × 10⁻⁶. -5 mol / dm 3The test solvent was dichloromethane, and the absorption wavelengths of the OMePdC^C complexes were 390 nm, 392 nm, 391 nm, and 394 nm, respectively.

[0052] Example 2-2: Testing the photoluminescence spectra of Examples 1-1 to 1-4 The photoluminescence spectroscopy test samples used in this invention are solid powders from Examples 1-1 to 1-4, wherein the emission wavelength of the OMePdC^C complex is 590 nm; the emission wavelength of the SMePdC^C complex is 593 nm; the emission wavelength of the OCyPdC^C complex is 591 nm; and the emission wavelength of the SCyPdC^C complex is 594 nm. All phosphorescent high-brightness Pd(II) complexes in this invention emit yellow light.

[0053] Examples 2-3: Testing the phosphorescence quantum yield of Examples 1-1 to 1-4 The phosphorescence quantum yields of Examples 1-1 to 1-4 of this invention were measured. The phosphorescence quantum yields of the OMePdC^C complex were 98.5%; those of the SMePdC^C complex were 97.7%; those of the OCyPdC^C complex were 83.6%; and those of the SCyPdC^C complex were 77.3%. These data demonstrate that we have successfully synthesized high-brightness phosphorescent binuclear Pd(II) complexes.

[0054] Examples 2-4: Testing the phosphorescence lifetime of Examples 1-1 to 1-4 Furthermore, we measured the phosphorescence lifetimes of Examples 1-1 to 1-4 of this invention. The phosphorescence lifetime of the OMePdC^C complex was 89.5 μs; the phosphorescence lifetime of the SMePdC^C complex was 90.6 μs; the phosphorescence lifetime of the OCyPdC^C complex was 86.4 μs; and the phosphorescence lifetime of the SCyPdC^C complex was 90.1 μs.

[0055] Examples 2-5: Thermogravimetric analysis curves of Examples 1-1 to 1-3 Thermogravimetric analysis was used to analyze the thermal stability of Examples 1-1 to 1-3. The decomposition temperature of the OMePdC^C complex was 300℃; the decomposition temperature of the SMePdC^C complex was 290℃; and the decomposition temperature of the OCyPdC^C complex was 325℃. This indicates that these high-brightness phosphorescent dinuclear palladium complexes have good thermal stability, are fully capable of vapor deposition of devices, and have good application prospects in the field of organic light-emitting diodes.

[0056] Examples 2-6: Testing the single-crystal structures of Examples 1-1 to 1-2 The binuclear palladium complex in this invention has a pair of enantiomers. The crystal structures of the S-configuration complex in Example 1-1 and the R-configuration complex in Example 1-2 were obtained by X-ray single-crystal diffraction. Figure 1 and Figure 2 As shown, chiral self-sorting was successfully achieved by using a bridging ligand with a single chiral configuration. Specifically, the chiral configuration of the bridging ligand was consistent with the planar chiral configuration of the dinuclear Pd(II) complex. Therefore, its absolute configuration was obtained using a single-crystal diffractometer, verifying its chiral self-sorting capability. This lays a solid foundation for the synthesis of such high-brightness phosphorescent dinuclear planar chiral Pd(II) complexes.

[0057] Examples 2-7: Circular dichroism chromatograms of Examples 1-1 to 1-4 were tested. This invention uses a circular dichroism chromatograph to determine the concentration of samples from Examples 1-1 to 1-4 using circular dichroism chromatograms. -5 mol / dm 3 The test solvent was dichloromethane. Examples 1-1 to 1-4 all showed strong chiral signals at 250-450 nm, and the curves had good ellipticity. The enantiomers in these examples had good spectral symmetry.

[0058] In summary, this invention discloses a method for preparing high-brightness phosphorescent binuclear Pd(II) complexes. On the one hand, by using a carbene ligand with a strong σ donor as a cyclic metal ligand, the spin-orbit coupling between the metal and the ligand is enhanced, promoting the metal-ligand charge transfer process, weakening the dd thermal deactivation process, and improving the quantum yield of the phosphorescent Pd(II) complex. On the other hand, 4-methyloxazolidine-2-thione and its derivatives are introduced as bridging ligands, shortening the distance of the Pd-Pd bond and forming an effective metal-metal-ligand charge transfer process, further improving the quantum yield of the phosphorescent Pd(II) complex. This provides an effective model for the development of high-brightness phosphorescent palladium complexes.

[0059] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-brightness phosphorescent binuclear Pd(II) complex, characterized in that, The complex has the structure shown in the following general formula: or ; Where X is selected from O or S.

2. The high-brightness phosphorescent binuclear Pd(II) complex according to claim 1, characterized in that, The complex is selected from one of the following structures: , , or .

3. A method for preparing a high-brightness phosphorescent binuclear Pd(II) complex according to any one of claims 1 or 2, characterized in that, Includes the following steps: Provides 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide; The 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide was reacted with silver oxide in a first solvent and an inert atmosphere to obtain a first intermediate reaction solution. The first intermediate reaction solution was reacted with (1,5-cyclooctadiene)palladium dichloride in a second reaction to obtain the second intermediate reaction solution; The second intermediate reaction solution, the second reactant, and the base were subjected to a third reaction in a second solvent and an inert atmosphere to obtain the high-brightness phosphorescent binuclear Pd(II) complex. Wherein, the first intermediate structure is The second intermediate is The second reactant is , , or .

4. The preparation method according to claim 3, characterized in that, The conditions for the first reaction include: the first solvent is ultra-dry N,N-dimethylformamide, the reaction temperature is 45-55℃, the reaction time is 20-28 hours, and the reaction is carried out under light-protected conditions.

5. The preparation method according to claim 3, characterized in that, The conditions for the second reaction include: the reaction is first carried out at 45-55°C for 1-3 hours, and then the temperature is raised to 120-130°C to continue the reaction for 20-28 hours, and the reaction is carried out under light-protected conditions.

6. The preparation method according to claim 3, characterized in that, The conditions for the third reaction include: the second solvent is ultra-dry N,N-dimethylformamide, the base is sodium tert-butoxide, the reaction temperature is 60-70°C, the reaction time is 44-52 hours, and the reaction is carried out under light-protected conditions; and / or, After the third reaction is completed, the solvent is removed by rotary evaporation, and the residue is purified by column chromatography using a mixed solvent of petroleum ether and dichloromethane as the eluent.

7. The preparation method according to claim 3, characterized in that, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to silver oxide is 1:0.5-0.7; and / or, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to (1,5-cyclooctadiene)palladium dichloride is 1:0.9-1.1; and / or, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to the second reactant is 1:3.5-4.5; and / or, The molar equivalent ratio of the 1-methyl-3-(3,4,5-trifluorophenyl)-3H-imidazo[4,5-b]pyridine-1-iodide to the base is 1:3.5-4.

5.

8. The use of a high-brightness phosphorescent dinuclear Pd(II) complex as described in any one of claims 1 or 2 in the preparation of an organic electroluminescent device, wherein the high-brightness phosphorescent dinuclear Pd(II) complex is used as the light-emitting layer material of the organic electroluminescent device.

9. An organic electroluminescent device comprising a light-emitting layer, characterized in that, The luminescent layer comprises the high-brightness phosphorescent dinuclear Pd(II) complex as described in any one of claims 1 or 2.

10. The organic electroluminescent device according to claim 9, characterized in that, The device is an organic light-emitting diode.

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