An aggregation-induced phosphorescence material, a synthesis method thereof and an OLED light-emitting device

Abstract

The application provides an aggregation-induced phosphorescent material, a preparation method and application thereof, and an OLED device containing the same. The structural general formula of the room-temperature phosphorescent material is (1). Wherein R1 and R2 are the same or different, and R1 and R2 are derivatives of carbazole or phenothiazine or phenoxazine or diphenylamine or acridine. The phosphorescent material promotes the ISC from singlet state to triplet state and the phosphorescent emission through aggregation. The synthesis method is simple in process, easy in purification, high in yield, and the luminous performance and thermal performance of the final product can be adjusted by connecting different groups. The OLED device prepared by the solution processing method has a maximum photoluminescence quantum yield (PLQY) close to 53%, and an external quantum efficiency (EQE) of 18.63%, which exceeds the traditional 20% light coupling output efficiency. The application provides a new strategy for constructing a pure organic phosphorescent OLED.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic optoelectronic materials, and particularly relates to a novel aggregation-induced phosphorescent material, a synthesis method thereof and an OLED light-emitting device comprising the same. BACKGROUND

[0002] Organic light-emitting diodes (OLEDs) have great potential applications in developing new generation flat panel displays and energy-saving solid-state lighting. Fluorescent materials are the first generation of light-emitting materials in OLEDs, which greatly limit the application of fluorescent electroluminescent devices due to the exciton utilization rate of only 25%. Thus, they are gradually replaced by heavy metal complex phosphorescent materials, because they can utilize both singlet (25%) and triplet (75%) excitons, resulting in a quantum efficiency of 100%. However, traditional inorganic complex phosphorescent materials contain noble metal elements (Ir, Pt), which greatly increase the cost in industrial production, and heavy metal elements are not environmentally friendly. In recent years, pure organic phosphorescent materials have attracted more and more attention from researchers due to their low cost, environmental friendliness, variety, good processing performance and other advantages.

[0003] The key factor for phosphorescence is the intersystem crossing (ISC) process from the excited singlet state to the excited triplet state, which produces triplet excitons and inhibits the non-radiative decay process of the excited state exciton, realizing room temperature phosphorescence. However, few metal-free RTP materials with high quantum yield (PLQY) have been reported, because of the small SOC of organic compounds and the easy susceptibility of triplet excited states, which are easily deactivated by thermal vibration or surrounding oxygen. It is a challenge to develop excellent pure organic phosphorescent materials. In order to limit thermal vibration and isolate oxygen from phosphorescence, phosphorescent materials are usually embedded in a polymer matrix, including macrocyclic molecules or crystal-induced engineering strategies. At the same time, heavy atoms (Br, I) or heteroatoms (N, O, S) are introduced into the structure of phosphorescent molecules to enhance the intersystem crossing (ISC) process.

[0004] Based on the above strategies, RTP crystalline materials with high PLQY and long lifetime (millisecond, second) have been reported in recent years. However, due to the high crystal structure dependence of phosphorescence, the poor flexibility of these materials limits their application. And the material with a long lifetime of milliseconds will cause the enrichment of triplet excitons in electroluminescent devices, which will bring serious efficiency roll-off. Although amorphous RTP materials are known for their processability, the PLQY of these materials is still low. Therefore, it is particularly important to prepare RTP materials with high PLQY and relatively short long lifetime (microsecond). SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide an aggregation-induced room-temperature phosphorescent material, a preparation method and use thereof, and an OLED device comprising the same. The phosphorescent material can emit sky blue phosphorescence and can be used as a light-emitting guest material of an OLED device. An OLED device prepared by a solution processing method thereof has a maximum photoluminescence quantum yield (PLQY) close to 53%, and an external quantum efficiency (EQE) of 18.63%, which exceeds the conventional 20% light coupling output efficiency. The present application proposes a new strategy for constructing a pure organic phosphorescent OLED.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] The present application provides an aggregation-induced room-temperature phosphorescent material, the structural general formula of which is shown in the following formula:

[0008]

[0009] wherein R1 and R2 are the same or different, and R1 and R2 are derivatives of carbazole or phenothiazine or phenoxazine or diphenylamine or acridine.

[0010] The R1 and R2 are selected from the following structures:

[0011]

[0012] The present application further provides a synthesis method of the aggregation-induced room-temperature phosphorescent material, comprising the following steps:

[0013] The derivatives of carbazole or phenothiazine or phenoxazine or diphenylamine or acridine and malonyl dichloride are stirred in dry THF at room temperature for 30 minutes. Then, the reaction solution is concentrated under reduced pressure, and then washed twice with a NaHCO3 solution. The crude product is purified by column chromatography to obtain the product (1).

[0014]

[0015] The further step is: dissolving the product (1) in anhydrous DCM, and adding BF3·Et2O dropwise to the solution. The solution is stirred in the dark overnight. Then, water (30 mL) is added to the solution, and the organic layer is collected, washed with saturated NaHCO3 and brine, dried with anhydrous Na2SO4, and concentrated under reduced pressure. The crude product is recrystallized from ethanol and DCM to obtain the product.

[0016] The product structural formula is shown in the following formula:

[0017]

[0018] wherein R1 and R2 are the same or different, and R1 and R2 are derivatives of carbazole or phenothiazine or phenoxazine or diphenylamine or acridine.

[0019] R1and R2are selected from the following structures:

[0020]

[0021] THF is the abbreviation of tetrahydrofuran, DCM is the abbreviation of dichloromethane, and the concentration of BF3·Et2O is ~ 46.5% BF3.

[0022] If R1and R2are the same, the molar ratio of R1and R2to malonyl dichloride is 2:1. If R1and R2are not the same, the molar ratio of R1, R2and malonyl dichloride is R1:R2:malonyl dichloride = 1:1:1. The amount of THF is 15-20 ml THF per 1 mmol of malonyl dichloride.

[0023] The developing agent is petroleum ether / DCM = 1:1 (v / v).

[0024] The molar ratio of the product (1) to the BF3·Et2O solution is 1:3, and the amount of BF3·Et2O is 400 μL per 1 mmol.

[0025] The volume ratio of the ethanol / DCM mixture is 10:1.

[0026] The present application also provides an OLED device using an aggregation-induced room-temperature phosphorescent material, comprising: indium tin oxide (ITO) (180 nm) / PEDOT:PSS (45 nm) / EML (30 nm) / TPBi (60 nm) / Liq (1 nm) / aluminum (100 nm). PEDOT:PSS serves as a hole injection layer, TPBi and Liq serve as an electron transport layer and an electron injection layer. The light-emitting layer (EML) comprises a mixture of mCP host and phosphorescent materials at different doping concentrations. The structure of the phosphorescent material is shown as follows:

[0027]

[0028] wherein R1and R2are the same or different, and R1and R2are derivatives of carbazole or phenothiazine or phenoxazine or diphenylamine or acridine.

[0029] Beneficial effects: The pure organic room-temperature phosphorescent material designed and synthesized in the present application promotes ISC from singlet state to triplet state and phosphorescent emission through aggregation. The synthesis method is simple in process, easy in purification, and high in yield, and the light-emitting performance, thermal performance, etc. of the final product can be adjusted by connecting different groups; the EQE of the sky blue organic light-emitting diode device prepared by solution spin coating using the above-mentioned phosphorescent material reaches a record 18.63%, which exceeds the traditional 20% light coupling output efficiency. The present application opens a new door for the development of the next generation of high-performance pure organic phosphorescent OLEDs. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Synthetic route of the phosphorescent material of the present application.

[0031] Figure 2 Single crystal pattern of the compound of Example 1 prepared.

[0032] Figure 3 UV-Vis absorption spectrum and photoluminescence spectrum pattern of the compound of Example 1 prepared in dichloromethane solution.

[0033] Figure 4 Photoluminescence spectrum pattern of the compound of Example 1 in mcp thin film with different doping concentrations.

[0034] Figure 5 Cyclic voltammogram of the compound of Example 1 prepared.

[0035] Figure 6 Thermogravimetric analysis pattern of the compound of Example 1 prepared.

[0036] Figure 7 Structure schematic diagram of the OLED device using the aggregation-induced phosphorescent material of the present application.

[0037] Figure 8 External quantum efficiency pattern of the OLED device using the aggregation-induced phosphorescent material of the present application with different doping concentrations.

[0038] Figure 9 Electroluminescence spectrum pattern of the OLED device using the aggregation-induced phosphorescent material of the present application with different doping concentrations.

[0039] Figure 10 Luminance-voltage pattern of the OLED device using the aggregation-induced phosphorescent material of the present application with different doping concentrations. DETAILED DESCRIPTION

[0040] In order to further clarify the technical means adopted by the present application and its effects, the embodiments of the present application are described in detail below in combination with the preferred embodiments of the present application and the accompanying drawings, but the present application is not limited to the following embodiments. The methods are all conventional methods unless otherwise specified. The raw materials can be obtained from public commercial channels unless otherwise specified. It should be noted that, as long as there is no conflict, each feature in each embodiment of the present application can be combined with each other, and the technical solutions formed thereby are all within the protection scope of the present application.

[0041] The present application provides an aggregation-induced room temperature phosphorescent material, the structure general formula of which is shown in the following formula:

[0042]

[0043] wherein R1and R2may be the same or different, R1and R2are derivatives of carbazole or phenothiazine or phenoxazine or diphenylamine or acridine.

[0044] The R1and R2are selected from the following structures:

[0045]

[0046] Referring to Figure 1 The present application also provides a synthesis method of the aggregation-induced room temperature phosphorescent material.

[0047] The following will be described in conjunction with specific examples.

[0048] Preferred embodiment one

[0049]

[0050] The synthesis route is as shown in Figure 1 :

[0051] Step 1: 3,6-di-tert-butylcarbazole (0.84 g, 3 mmol) was added to a 50 mL two-necked flask, 20 mL of dry THF was added, and 0.15 mL of malonyl dichloride (1.5 mmol) was slowly added under a nitrogen atmosphere. Then the reaction was stirred at room temperature for 30 minutes. After the reaction was completed, the reaction solution was concentrated under reduced pressure, and then washed twice with NaHCO3solution. The crude product was purified by column chromatography (silica gel, petroleum ether / DCM = 1:1, v / v) to obtain a white solid product (0.94 g, 70%).

[0052] Step 2: The product obtained in the previous step (0.63 g, 1 mmol) was dissolved in 20 mL of dry CH2Cl2, and then BF3·Et2O (400 μL, 3 mmol) was added dropwise. The solution was stirred in the dark overnight. After the reaction was completed, water (30 ml) was added to the solution, and the organic layer was collected, washed twice with saturated NaHCO3and brine, respectively, the organic phase was separated, dried with anhydrous Na2SO4, and concentrated under reduced pressure. The crude product was recrystallized from ethanol and DCM to obtain the product of Example one, a white solid (540 mg, 80%).

[0053] The structure confirmation data of the product are as follows:

[0054] Nuclear magnetic hydrogen spectrum: 1 H NMR (400 MHz, Chloroform-d) δ 8.14 (d, J = 8.8 Hz, 4H), 8.02 (d, J = 1.6 Hz, 4H), 7.60 (dd, J = 8.8, 1.7 Hz, 4H), 6.72 (s, 1H), 1.47 (s, 36H).

[0055] Nuclear magnetic carbon spectrum: 13 C NMR (101 MHz, Chloroform-d) δ 167.30, 148.65, 136.46, 127.65, 125.65, 117.01, 115.90, 79.39, 35.29, 32.01.

[0056] Nuclear magnetic fluorine spectrum: 19 F NMR (376 MHz, Chloroform-d) δ -142.98.

[0057] Mass spectrum: HRMS (MALDI-TOF, m / z): C 43 H 49 BF2N2O2, 674.6902.

[0058] The single crystal structure is shown in Figure 2. Figure 2 .

[0059] Preferred embodiment two

[0060]

[0061] Step 1: 4,4'-Dimethoxydiphenylamine (0.34 g, 1.5 mmol), 3,6-di-tert- butylcarbazole (0.42 g, 1.5 mmol) were added to a 50 mL two-necked flask, 20 mL dry THF was added, 0.15 mL malonyl dichloride (1.5 mmol) was added slowly under nitrogen atmosphere. Then the reaction was stirred at room temperature for 1 hour. After the reaction was completed, the reaction solution was concentrated under reduced pressure, then washed with NaHC03solution twice. The crude product was purified by column chromatography (silica gel, petroleum ether / DCM = 1 : 1, v / v) to obtain white solid product (0.48 g, 55%).

[0062] Step 2: The product obtained in the previous step (0.288 g, 0.5 mmol) was dissolved in 20 mL dry CH2Cl2, then BF3·Et20 (400 μL, 3 mmol) was added dropwise. The solution was stirred in the dark overnight. After the reaction was completed, water (30 ml) was added to the solution, and the organic layer was collected, washed with saturated NaHC03and brine twice respectively, the organic phase was separated, dried with anhydrous Na2S04, and concentrated under reduced pressure. The crude product was recrystallized from ethanol and DCM to obtain the product of Example two, white solid (250 mg, 80%).

[0063] The structure confirmation data of the product are as follows:

[0064] Nuclear magnetic hydrogen spectrum: 1H NMR(400MHz,Chloroform-d)δ8.36(d,J=8.8Hz,2H),8.1(d,J=1.6Hz,2H),7.80(dd,J =8.8,1.7Hz,2H),6.98(d,4H),6.71(d,4H),5.75(s,1H),3.82(s,6H),1.45(s,18H).

[0065] Theoretical simulation calculations were performed on the molecules of the phosphorescent material in Example 1. The lowest singlet energy level was 2.94 eV, and the lowest triplet energy level was 2.82 eV. The difference between the two energy levels was very small, enabling effective intersystem crossing to generate phosphorescent emission, thereby achieving a quantum efficiency of 100%.

[0066] The quantum yield of the phosphorescent material in this embodiment is greatly enhanced in the solid state at room temperature compared to that in the toluene solution, indicating that it has the characteristics of aggregation-induced emission. Figure 4 The display shows that the phosphorescent material in this embodiment can be used in the field of sky blue light OLED.

[0067] Therefore, the present invention also provides an OLED device using the above phosphorescent material, see Figure 7 , which includes, from left to right, an anode, a hole injection layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode.

[0068] The components of each layer are as follows: anode: ITO (indium tin oxide), thickness of 180nm; hole transport layer: PEDOT:PSS, thickness of 45nm; light-emitting layer: mCP host material mixed with phosphorescent material with different doping concentrations, 30nm; electron transport layer: TPBi, thickness of 60nm; electron injection layer: 8-hydroxyquinolinic acid lithium (Liq), thickness of 1nm; cathode: Al, thickness of 100nm.

[0069] In the above examples, the structural formula corresponding to the abbreviation of the material is as follows:

[0070]

[0071] The steps for device preparation are:

[0072] After cleaning the patterned ITO glass substrate, a 45 nm thick PEDOT:PSS (8000) layer (hole injection layer, HIL) was spin-coated on the ITO. The PEDOT:PSS layer was then annealed at 180°C for 10 minutes. An emitting layer (EML) of chlorobenzene solution was spin-coated on the surface of the PEDOT:PSS at a speed of 3000 rpm and then annealed at 80°C to remove the residual solvent. The electron transport layer (TPBi) and the electron injection layer (lithium 8-hydroxyquinolinate, Liq) were prepared in a vacuum chamber at 10-4 The Al layer was deposited by thermal evaporation at a rate of about 0.5 A / s. The rate of Liq was about 0.5 A / s. To prevent degradation effects due to oxygen and moisture, the devices were encapsulated in a nitrogen atmosphere glovebox prior to EL measurements.

[0073] The electroluminescent properties of the devices were measured with a Photoresearch SpectraScan PR735 spectrometer and a Keithley 2400 source meter.

[0074] The quantum efficiency-current density characteristics of the device prepared in this example are shown in Fig. 6. Figure 8

[0075] The electroluminescent spectrum of the device prepared in this example is shown in Fig. 7. Figure 9

[0076] The luminance-voltage characteristics of the device prepared in this example are shown in Fig. 8. Figure 10

[0077] When the doping concentration was 30.0 wt%, the maximum external quantum efficiency (EQE max ) of the device was 18.63%, the maximum current efficiency (CE max ) was 47.71 cd / A, and the maximum power efficiency (PE max ) was 37.47 lm / W. The Commission Internationale de L'Eclairage color coordinates were (0.22, 0.42). The PLQY of the 30.0 wt% mixed film we tested was close to 53%. The light coupling output efficiency (ηout) of the device was 35%. This was 20% higher than the conventional light coupling output efficiency (ηout)

[0078] The phosphorescent material, the preparation method thereof, and the OLED device comprising the same of the present application are illustrated by the above examples, but the present application is not limited to the above examples, i.e. it does not mean that the present application must rely on the above examples to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. all fall within the protection scope and disclosure scope of the present application.​​​

Claims

1. An aggregation-induced room temperature phosphorescent material, characterized in that: The molecular structure is shown in (II) or (III): ； （Ⅱ） （Ⅲ）。 2. A method for preparing an aggregation-induced room temperature phosphorescent material, characterized in that: The preparation of the compound of claim 1 with a molecular structure as shown in (II) comprises the following steps: Step 1: 0.84 g, 3 mmol of 3,6-di-tert-butylcarbazole was added to a 50 mL two-necked flask, 20 mL of dry THF was added, and 0.15 mL, 1.5 mmol of malonyl dichloride was slowly added under a nitrogen atmosphere; the reaction was then stirred at room temperature for 30 minutes; after the reaction was completed, the reaction solution was concentrated under reduced pressure and then washed twice with NaHCO3 solution; the crude product was purified by column chromatography using petroleum ether / DCM = 1:1, v / v as the developing solvent to obtain a white solid product; Step 2: Dissolve 0.63 g, 1 mmol of the product obtained in the previous step in 20 mL of dry CH2Cl2, and then add 400 μL, 3 mmol of BF3•Et2O dropwise; stir the solution in the dark overnight; after the reaction is complete, add 30 ml of water to the solution, collect the organic layer, wash it twice with saturated NaHCO3 and brine, respectively, separate the organic phase, dry it over anhydrous Na2SO4, and concentrate it under reduced pressure; the crude product is recrystallized from ethanol and DCM to obtain the compound with the molecular structure shown in (II).

3. A method for preparing an aggregation-induced room temperature phosphorescent material, characterized in that: The preparation of the compound of claim 1 with a molecular structure as shown in (III) comprises the following steps: Step 1: 0.34 g, 1.5 mmol of 4,4 ’ 1,4-dimethoxydiphenylamine, 0.42 g, 1.5 mmol of 3,6-di-tert-butylcarbazole were added to a 50 mL two-necked flask, and 20 mL of dry THF was added. Under a nitrogen atmosphere, 0.15 mL, 1.5 mmol of malonyl dichloride was slowly added; the reaction was then stirred at room temperature for 1 hour; after the reaction was completed, the reaction solution was concentrated under reduced pressure and then washed twice with NaHCO3 solution; the crude product was purified by column chromatography using petroleum ether / DCM = 1:1, v / v as the developing solvent to obtain a white solid product; Step 2: Dissolve 0.288 g, 0.5 mmol of the product obtained in the previous step in 20 mL of dry CH2Cl2, and then add 400 μL, 3 mmol of BF3•Et2O dropwise; stir the solution in the dark overnight; after the reaction is complete, add 30 ml of water to the solution, collect the organic layer, wash it twice with saturated NaHCO3 and brine, respectively, separate the organic phase, dry it over anhydrous Na2SO4, and concentrate it under reduced pressure; recrystallize the crude product from ethanol and DCM to obtain the compound with the molecular structure shown in (III).

4. An OLED device using an aggregation-induced room temperature phosphorescent material, characterized in that: Indium tin oxide ITO / PEDOT: PSS / EML / TPBi / Liq / aluminum; wherein, ITO, thickness is 180nm; PEDOT:PSS, thickness is 45nm; EML, thickness is 30nm; TPBi, thickness is 60nm; Liq, thickness is 1nm; aluminum, thickness is 100nm; PEDOT:PSS acts as a hole injection layer, TPBi and Liq act as electron transport layer and electron injection layer; the light-emitting layer EML comprises a mixture of an mCP main body and phosphorescent materials at different doping concentrations; the phosphorescent material is the aggregation-induced room temperature phosphorescent material as described in claim 1.

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