Tetradentate platinum(II) coordination compound of the O^C^N^N type, its manufacturing process and application

Abstract

O^C^N^N-tetradentate platinum(II) coordination compound, having the structure shown in the following formula (II): wherein R1'- R5' are independently selected from the group consisting of hydrogen, halogen, silyl, saturated alkyl with 1-10 C atoms, aryl with 5-20 C atoms, which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, heteroaryl with 5-20 C atoms, which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, and wherein the halogen is F, Cl or Br.

Description

Technical area

[0001] The present invention relates to a novel organometallic material made of O^C^N^N-tetradentate platinum(II) coordination compound, in particular a phosphorescent dopant used in the light-emitting layer of the OLED luminescent device to emit the photons of red light. State of the art

[0002] OLED (organic light-emitting diode) display technology is the latest display technology with broad development prospects. OLED display technology emerged after CRT and LCD. It has self-luminous properties, requires no backlight, offers high visibility and brightness, a wide viewing angle, and fast response. The material is lightweight and thin, offering superior performance for flexible display applications. At the same time, compared with LCD, OLED has low voltage requirements, few component requirements, and low cost. OLED has superior performance and will be widely used in smartphones, televisions, wearable devices, and VR in the future, and has broad development prospects.

[0003] The phenomenon of organic electroluminescence was discovered by Pope's research group in 1963. They used two organic materials, an Ag / anthracene single-crystal / Ag device and a NaCl / anthracene single-crystal doped tetracene / NaCl device, respectively. However, since the thickness of a single anthracene wafer is in the micrometer range (10-20 µm) and a DC voltage of up to 400 V is required to fabricate a single-layer light-emitting device, a faint blue light is observed when a voltage of 400 V is applied. The lifetime of the device is also very short, so it has no practical application value. Therefore, it has not attracted widespread attention in the academic field.

[0004] By 1987, C.W.Tang et al. from KODAK Company in the USA used evaporation technology, using ITO as the anode, and diamine (75 nm) was evaporated as a hole-transfer layer on the ITO glass, and then a layer of Alq3 (60 nm) was evaporated as an electron-transfer layer and light-emitting layer. Finally, magnesium and aluminum with low work function were evaporated as cathodes to fabricate the first OLED device with a sandwich structure. At a voltage of about 5 V, a high-brightness green light was observed, and the brightness reached 1000 cd / m2, the efficiency reached 3 cd / A, and the external quantum efficiency reached 1%. This pioneering work is a milestone, creating a new era of organic optoelectronic research and showing the direction for organic electroluminescence research.

[0005] In the field of OLED materials, doping materials for phosphorescent light-emitting OLED layers have developed rapidly and maturely. These doping materials are mainly based on some organic heavy metal coordination compounds such as iridium, platinum, europium, and osmium. In these heavy coordination compounds, the presence of heavy metal atoms can generate a strong spin-orbital coupling (SOC) effect, causing the hindered spin triplet excitons to transition from the lowest triplet state (T1) to the radiative ground state (S0) to generate phosphorescence. This method simultaneously traps the triplet and singlet excitons, effectively utilizing the triplet excitons that cannot emit light, thus breaking through the bottleneck of the internal quantum efficiency of 25%, so that its quantum efficiency can theoretically reach 100%.This makes the performance of organic electrophosphorescent devices superior, so phosphorescent materials are being more extensively developed and investigated in OLEDs. When dispersed in host materials, phosphorescent metal coordination compounds exhibit very high external quantum efficiencies (EQEs); the external quantum efficiency in recently reported doped phosphorescent OLEDs exceeds 30%.

[0006] OLED technology has undergone more than 30 years of development since its inception. In particular, it has achieved breakthroughs in the efficiency of phosphorescent OLEDs, and OLED technology has shown great promise in commercial applications. In recent years, platinum(II)-based phosphorescent OLED materials have been gradually developed and achieved good research results. Due to the planar structure of platinum(II) coordination compounds, it also leads to easy stacking between molecules and easy formation of excimers, which affects the performance of OLED devices. Generally, large steric groups such as tert-butyl are added to the molecule to improve the three-dimensional structure of the molecule and weaken the interaction between molecules.

[0007] The development of OLED display technology is a laborious and significant research effort. It has excellent properties, but also drawbacks such as short lifetime, poor color purity, and easy aging, which limit the large-scale application of OLED technology. Therefore, the development of new OLED materials with excellent performance, especially doping materials for the light-emitting layer, is the focus and challenge of OLED research.

[0008] In the prior art, O^C^N^N-tetradentate platinum(II) coordination compounds are disclosed, for example, in US 2019 / 0 135 844 A1. Content of the invention

[0009] In the present invention, a novel Pt(II) coordination compound with an O^C^N^N coordination structure based on a carbazole framework is developed that emits red light. Furthermore, its application in organic light-emitting diodes is investigated. Carbazole is a type of electron-rich nitrogen-containing heterocyclic compound with a large π-conjugated rigid planar structure, and this unique structure enables its derivatives to exhibit many excellent optoelectronic performances.

[0010] The novel O^C^N^N-tetradentate platinum(II) coordination compound organometallic material according to the present invention has the structural formula shown in the following formula (II): wherein R1'- R5' are independently selected from the group consisting of hydrogen, halogen, silyl, saturated alkyl having 1-10 C atoms, aryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, heteroaryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, and wherein the halogen is F, Cl or Br.

[0011] Preferably, 0-3 groups among the 5 groups of R1'-R5' are independently represented as aryl having 5-10 C atoms, which is substituted or unsubstituted by halogen or 1-3 C1-C4 alkyl, heteroaryl having 5-10 C atoms, which is substituted or unsubstituted by halogen or 1-3 C1-C4 alkyl; with other groups independently represented as hydrogen, halogen or saturated alkyl having 1-8 C atoms, wherein the halogen is F or Cl.

[0012] Preferably, 0-3 groups among the 5 groups of R1'-R5' are independently represented as phenyl substituted or unsubstituted by C1-C4 alkyl, pyridyl and carbazolyl, with other groups independently represented as hydrogen, fluorine and saturated alkyl having 1-4 C atoms.

[0013] The precursor of the above-mentioned compound, namely the ligand, has the structural formula shown in formula (IV):wherein R1'-R5' are independently selected from the group consisting of hydrogen, halogen, silyl, saturated alkyl having 1-10 C atoms, aryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, heteroaryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, and wherein the halogen is F, Cl or Br.

[0014] For the purposes of this application, the terms halogen, alkyl, aryl, and heterocyclic aromatic groups, unless otherwise specified, may have the following meanings: the above halogen or halo includes fluorine, chlorine, bromine and iodine, preferably F, Cl, Br, more preferably F or Cl, most preferably F.

[0015] A suitable aryl is, for example, phenyl, naphthyl, acenaphthenyl, dihydrogenacenaphthenyl, anthracenyl, fluorenyl, or phenalenyl. The aryl can be substituted (i.e., all carbon atoms capable of substitution carry hydrogen atoms) or substituted at one, more than one, or all substitutable positions of the aryl. Suitable substituents are halogen, preferably F, Br, or Cl, and alkyl with 1-4 carbon atoms, particularly preferably methyl, ethyl, isopropyl, or tert-butyl.

[0016] The above-mentioned alkyl includes alkyl having 1-10 carbon atoms, preferably 1-4 carbon atoms. The alkyl may be branched, straight-chain, or cyclic and may be interrupted by one or more heteroatoms, preferably N, O, or S. Furthermore, the alkyl may be substituted by one or more halogens or the substituents described above with respect to the aryl. The alkyl is particularly preferably selected from a group consisting of methyl, ethyl, isopropyl, n-propyl, isobutyl, n-butyl, tert-butyl, sec-butyl, isopentyl, cyclopropyl, cyclopentyl, and cyclohexyl.

[0017] The above-mentioned heteroaryl groups should be understood as being related to aromatic series and C3-C8 ring groups and containing one oxygen or sulfur atom or 1-4 nitrogen atoms or a combination of one oxygen or sulfur atom and up to two nitrogen atoms, as well as their substituted and benzo- and pyrido-condensed derivatives, for example, by linking via one of the ring-forming carbon atoms, the heteroaryl group may be substituted by one or more of the substituents mentioned for the aryl.

[0018] In certain embodiments, a heteroaryl may be a heterocyclic system bearing the above independent five- or six-membered aromatic series with 0, 1 or 2 substituents. Typical examples of the heteroaryl include, but are not limited to: unsubstituted furans, benzofuran, thiophene, benzothiophene, pyrrole, pyridine, indole, azole, benzoxazole, isoxazole, benzisoxazole, thiazole, benzothiazole, isothiazole, imidazole, benzimidazole, pyrazole, indazole, tetrazole, quinoline, isoquinoline, pyridazine, pyrimidine, purine and pyrazine, furan, 1,2,3-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, triazole, benzotriazole, pteridine, benzoxazole, diazole, benzopyrazole, quinazine, cinnoline, phthalazine, quinazoles and quinoxalines and their mono- or disubstituted derivatives.

[0019] Specific examples are shown below, including but not limited to the following structures:

[0020] An application of the above coordination compound in the organic OLED luminescent devices.

[0021] Using platinum(II) coordination compounds with the above structures, thermally deposited and solution-processed OLED devices can be fabricated.

[0022] An organic luminescent device containing one or more of the above-mentioned coordination compounds.

[0023] The coordination compound is deposited in the form of a layer in the device by thermal deposition.

[0024] The coordination compound is applied in the form of a layer in the device by spin coating.

[0025] The coordination compound is applied in the form of a layer in the device by inkjet printing.

[0026] The above organic luminescent device emits orange-red light when a current is applied.

[0027] The organic metal coordination compound in the present invention has high fluorescence quantum efficiency, good thermal stability and low quenching constant, and can fabricate red light OLED devices with high luminous efficiency and low waste. Short description of the drawing Fig. 1 shows a schematic structural view of the organic electroluminescent device of the present invention. Detailed embodiments

[0028] The present invention is explained in more detail below in connection with exemplary embodiments.

[0029] A process for preparing the above coordination compound, comprising the following steps: As shown below, carbazole derivatives S1 and S2 are reacted according to a Suzuki reaction to obtain a substrate S3, S3 and S4 are reacted according to a Buchwald reaction to obtain S5, S5 is demethylated under the action of pyridine hydrochloride to obtain a ligand S6, and S6 is reacted with K2PtCl4, then the target product P is obtained.

[0030] The present invention is explained in more detail below in connection with exemplary embodiments.

[0031] The initial substrates and solvents involved in the synthesis of the compounds in the present invention can be obtained from suppliers known to those skilled in the art, such as Energy Chemical, J&K and Aladdin. Example 1 Synthesis route:

[0032] Synthesizing compound 3:Take 9.84 g (40.0 mmol) of compound 1, 6.69 g of compound 2 (1.1 eq., 44.0 mmol), potassium carbonate 11.04 g (2.0 eq., 80 mmol) and Pd(PPh3)4 924 mg (0.02 eq., 0.8 mmol) and add to a three-necked flask, vacuum, introduce nitrogen and replace with nitrogen several times, then inject 120 mL of dioxane and 40 mL of water and heat to 105°C. After reaction for 12 h under nitrogen protection, the mixture is cooled to room temperature, then an appropriate amount of water and ethyl acetate are added for extraction, the organic phase is collected, the mixture is dried by anhydrous magnesium sulfate and the solvent is removed by rotary evaporation, using column chromatography of the n-hexane / ethyl acetate system (n-hexane / ethyl acetate of the liquid phase = 10:1), 10.0 g of white solid is obtained with a yield of 92% and a purity of 99.5%.Mass spectrum (ESI+) ([MH]-) C19H14NO, theoretical value: 272.11, actual value: 272.13.

[0033] Synthesizing Compound 5:Take 5.47 g (20 mmol) of Compound 3, 5.17 g (1.1 eq., 22 mmol) of Compound 4, 225 mg (0.02 eq., 1 mmol) of palladium acetate, 0.20 g of tri-tert-butylphosphine (0.04 eq., 2 mmol), 4.5 g (2.0 eq., 0.04 mol) of potassium tert-butoxide and add them to a flask, 100 ml of toluene is added, and the mixture is heated under nitrogen protection and reacted under reflux for 8 hours. After the reaction, the mixture was cooled to room temperature, the solvent was removed by rotary evaporation, an appropriate amount of water and ethyl acetate was added for extraction, and the organic phase was collected and dried. After the solvent was removed by rotary evaporation, a flash silica gel column (n-hexane / liquid phase ethyl acetate = 10:1) was used for separation to obtain 7.3 g of the target product 5 with a yield of 85% and a purity of 99.9%. Mass spectrum (ESI+) ([MH]-) C.29 H 21 N3O, theoretical value: 426.16, actual value: 426.13.

[0034] Synthesizing Compound 6: Take 4.27 g (10 mmol) of Compound 5 and 50 g of pyridine hydrochloride, heat under nitrogen to 200°C, and react for 8 hours. After the reaction, an appropriate amount of water and ethyl acetate are added for extraction. The organic phase is collected and dried. After removing the solvent by rotary evaporation, a flash silica gel column (n-hexane / liquid phase ethyl acetate = 15:1) is used for separation. The mixture is then recrystallized with methanol to obtain 3.3 g of the target product, Compound 6, with a yield of 80% and a purity of 99.9%. Mass spectrum (ESI-) ([MH]-) C 28 H 18 N3O, theoretical value: 412.15, actual value: 412.10.

[0035] Synthesize Compound TM-1:Take 2.06 g (5.0 mmol) of Compound 6, 400 mg of tetrabutylammonium bromide (0.25 eq., 1.25 mmol) and potassium tetrachloroplatinate 2.49 mg (1.2 eq., 6 mmol) and dissolve them in 150 mL of acetic acid, vacuum, introduce nitrogen and replace with nitrogen several times, stir and heat to 130°C and react for 12 hours. After the reaction is complete, the solvent is removed by cooling and rotary evaporation. Then, an appropriate amount of water and ethyl acetate are added for extraction. The organic phase is collected. The mixture is dried over anhydrous magnesium sulfate. The solvent is removed by rotary evaporation. Using column chromatography in the n-hexane / ethyl acetate system, the crude product is vacuum sublimed to obtain 1.67 g of red solid with an overall yield of 55% and a purity of 99.9%. Mass spectrum (ESI+) ([M+H]+) C 28 H 18N3OPt, theoretical value: 607.10, actual value: 607.15. Example 2

[0036] The preparation method of TM-3 is the same as the synthesis route of TM-1, the only difference being that compound 7 is used instead of compound 1. The molecular formula of compound 7 is shown below: Example 3

[0037] The preparation method of TM-5 is the same as the synthesis route of TM-1, the only difference being that compound 7 is used instead of compound 1 and compound 8 is used instead of compound 4. The molecular formula of compound 8 is shown below:

[0038] Below are application examples of the compounds of the present invention.

[0039] ITO / TAPC (60nm) / TCTA:Pt(II) (40nm) / TmPyPb (30nm) / LiF (1nm) / Al (80nm) Device manufacturing process: The transparent anodized indium tin oxide (ITO, 20) (10 Ω / sq) glass substrate 10 is ultrasonically cleaned using acetone, ethanol, and distilled water sequentially and then treated with oxygen plasma for 5 min.

[0040] The ITO substrate is then mounted on the substrate holder of a vacuum gas phase evaporation device. In the evaporation device, the system pressure is set to 10 -6 Torr regulated.

[0041] Then, the hole transfer layer (30) material TAPC is evaporated onto the ITO substrate with a thickness of 60 nm.

[0042] Subsequently, the material of the light-emitting layer (40) TCTA is evaporated with a thickness of 40 nm, which is doped with the platinum(II) coordination compound with a mass fraction of 10%.

[0043] Then the electron transfer layer (50) material TmPyPb is evaporated with a thickness of 30 nm.

[0044] Then, LiF is evaporated to a thickness of 1 nm to form the electron injection layer (60).

[0045] Finally, Al is evaporated to a thickness of 80 nm as the cathode (70) to complete the encapsulation of the device, as shown below.

[0046] The structure and fabrication process of the devices are exactly the same, with the difference that the organic metal coordination compounds P0, P1, P2, P3, and P4 are used sequentially as dopants and doping concentrations in the light-emitting layer. Among them are the O^N^N^O-type red light material of STD.

[0047] Device STD, Device 1, Device 2, and Device 3 are fabricated sequentially. The structure and fabrication process of the devices are exactly the same, with the difference that the platinum(II) coordination compounds STD, TM-1, TM-3, and TM-5 are used sequentially as dopants in the light-emitting layer. The reference material STD is a classic red-light material with an ONCN coordination structure.

[0048] The device comparison results are shown in Table 1 and are based on the performance of the STD device; - means that the data is flat, - means that the relative benchmark performance deteriorates by more than 5%, + means that the relative benchmark performance improves by 5%, and ++ means that the relative benchmark performance improves by 10%. Device 1 Device 2 Device 3 Maximum external quantum efficiency - + ++ External quantum efficiency at 100nit + + ++ Starting voltage - - - Power efficiency at 100nit + + ++

[0049] The maximum external quantum efficiency and start-up voltage of the TM-1-based device 1 are basically the same as those of the STD-based reference device, and the external quantum efficiency and current efficiency at 100 nits are improved by about 5%. From the perspective of molecular structure, TM-1 and STD both have the same planar structure, but TM-1 has a larger conjugated structure, which improves TM-1 to some extent in terms of device performance compared to STD. Compared with the reference device, the TM-3-based device 2 has basically the same start-up voltage, but the maximum external quantum efficiency and the external quantum efficiency and current efficiency at 100 nits are all improved by about 5%.In terms of molecular structure, the introduction of two tert-butyl groups into the molecular structure of TM-3 reduces molecular aggregation and stacking to a certain extent, which is conducive to improving device performance. Compared with the reference device, the TM-5-based device 3 has basically the same start-up voltage, but the maximum external quantum efficiency and the external quantum efficiency and current efficiency at 100 nit are all improved by about 10%. From the perspective of molecular structure, the introduction of four tert-butyl groups into the molecular structure of TM-3 greatly improves the three-dimensionality of the molecule, greatly reduces intermolecular interaction, and at the same time maintains the rigid structure and macroconjugation properties of the molecular skeleton, thus greatly improving device efficiency and achieving optimal performance.In summary, the performance of the organic electroluminescent device fabricated by the present invention exhibits a greater performance improvement compared to the reference device, and the external quantum efficiency or current efficiency is obviously improved. The novel O^C^N^N tetradentate platinum(II) coordination compound concerned has great application value. The tetradentate platinum(II) coordination compound concerned by the present invention is based on a carbazole skeleton, has a large π-conjugated rigid planar structure, can greatly reduce non-radiative energy dissipation such as intramolecular rotation and vibration, and is conducive to improving the luminous efficiency and performance of the platinum(II) coordination compound.The O^C^N^N-tetradentate platinum(II) coordination compound metal-organic material prepared by the present invention has great application value in organic light-emitting diodes and can be used as a phosphorescent dopant for fabricating red-light OLED devices with high luminous efficiency.

Claims

[1] O^C^N^N-tetradentate platinum(II) coordination compound having the structure shown in the following formula (II):wherein R1'- R5' are independently selected from the group consisting of hydrogen, halogen, silyl, saturated alkyl having 1-10 C atoms, aryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, heteroaryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, and wherein the halogen is F, Cl or Br. [2] A coordination compound according to claim 1, wherein 0-3 groups among the 5 groups of R1'-R5' are independently represented as aryl having 5-10 C atoms which is substituted or unsubstituted by halogen or 1-3 C1-C4 alkyl, heteroaryl having 5-10 C atoms which is substituted or unsubstituted by halogen or 1-3 C1-C4 alkyl; wherein other groups are independently represented as hydrogen, halogen or saturated alkyl having 1-8 C atoms, wherein the halogen is F or Cl. [3] A coordination compound according to claim 2, wherein 0-3 groups among the 5 groups of R1'-R5' are independently represented as phenyl substituted or unsubstituted by C1-C4 alkyl, pyridyl and carbazolyl, and wherein other groups are independently represented as hydrogen, fluorine and saturated alkyl having 1-4 C atoms. [4] Coordination compound according to claim 1, having one of the following structures: [5] Precursor of the coordination compound according to any one of claims 1 to 4, namely ligand having a structural formula represented in the following formula (IV):wherein R1'- R5' are independently selected from the group consisting of hydrogen, halogen, silyl, saturated alkyl having 1-10 C atoms, aryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, heteroaryl having 5-20 C atoms which is substituted or unsubstituted by halogen or one or more C1-C4 alkyl, and wherein the halogen is F, Cl or Br. [6] A process for producing a coordination compound according to claim 1, wherein the process comprises the following steps: carbazole derivatives S1 and S2 are reacted according to a Suzuki reaction to obtain a substrate S3, S3 and S4 are reacted according to a Buchwald reaction to obtain S5, S5 is demethylated under the action of pyridine hydrochloride to obtain a ligand S6, and S6 is reacted with K2PtCl4, then the target product P is obtained; and wherein its reaction formula is as follows: [7] Use of the coordination compound according to any one of claims 1 to 4 in the OLED luminescent device. [8] Use according to claim 7, wherein the coordination compound according to any one of claims 1 to 4 is applied in the form of a layer in the OLED luminescent device by thermal deposition, spin coating and inkjet printing. [9] Use according to claim 7, wherein the coordination compound according to any one of claims 1 to 4 is a phosphorescent dopant used in the light-emitting layer to emit the photons.