A method for preparing green light host material

Abstract

The present invention provides a method for preparing a green light host material, which relates to the field of organic electroluminescent devices. The method comprises mixing 2,6-dibromo-4-cyanopyridine, 9-phenyl-9H-carbazole-2-boric acid, etc. to obtain a mixed solution; refluxing the mixed solution to obtain a reactant; separating the reactant, concentrating the organic phase, obtaining a crude product, and subjecting the crude product to column chromatography. When the green light host material prepared by the present invention is used as the host of a green light device, the maximum brightness (L max ) is 62080cdm ‑2 , maximum current efficiency (η c,max ) is 44.05cdA ‑1 , maximum power efficiency (η p,max ) is 35.86lmW ‑1 , maximum external quantum efficiency (EQE max ) is 12.46%, the efficiency roll-off of the device is very low, 1000 and 10000cdA ‑1 The roll-off is only 0.3% and 8.3% respectively.

Description

Technical Field

[0001] The present invention relates to the technical field of organic electroluminescent devices, and in particular to a method for preparing a green light host material. Background Art

[0002] Phosphorescent organic light-emitting diodes (PhOLEDs) have a dominant position in practical applications because they can utilize the spin-orbit coupling (SOC) effect of heavy metals and can effectively utilize triplet and singlet excitons at the same time to achieve a theoretical internal quantum efficiency of 100%. However, phosphorescent luminescent materials usually encounter triplet-triplet annihilation (TTA) or triplet-polaron annihilation problems at high concentrations. Fortunately, the application of host-guest doping, which uniformly disperses heavy metal complex luminescent materials in a suitable host, effectively alleviates the concentration-induced quenching problem. Therefore, compared with the luminescent material, the host material is equally important in achieving high-performance electroluminescent performance.

[0003] Generally speaking, qualified host materials should meet the following requirements: 1) triplet energy level (E T ) is higher than the guest luminescent material so as to confine the triplet excitons within the emitting layer (EML); 2) good thermal stability, which can withstand the high temperature during device preparation and the Joule heat generated during operation while maintaining morphological stability; 3) energy level matching with the adjacent layer material to facilitate the transport of carriers, thereby reducing the driving voltage. In addition, maintaining charge transport balance is crucial to improving the performance of PhOLEDs, and bipolar host materials composed of electron-rich donors (D) and electron-deficient acceptors (A) have been shown to meet this requirement. By simultaneously reducing the charge injection barrier for holes and electrons, bipolar host materials can balance carrier transport and expand the carrier recombination area, thereby effectively improving EL performance. In order to suppress the E caused by the intramolecular charge transfer (ICT) effect between the D and A groups, the E T To reduce the 3 Hybrid atoms or through meta-bonding. To date, many bipolar host materials have been designed and synthesized using the above strategies.

[0004] Carbazole has excellent thermal stability, good hole transport ability and high E T It is widely used in the construction of bipolar host materials. Dong et al. connected 1,3,5-triazine and phenylcarbazole through the meta position to obtain two bipolar host materials H1 and H2. The green light device with these two materials as the main body obtained more than 100,000 cd m -2The brightness and external quantum efficiency of 13.0% and 15.0% were achieved. Park et al. designed and synthesized the host material Cz-Trz by connecting 1,3,5-triazine and phenylcarbazole through sp3 carbon atoms. The green light device based on Cz-Trz achieved an external quantum efficiency of 21.4% (Park IS, SeoH, Tachibana H, Kim JU, Zhang JB, Son SM, Yasuda T. Cyclohexane-Coupled Bipolar Host Materials with High Triplet Energies for Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence. ACS Appl. Mater. Interfaces 2017, 9, 2693-2700). Guo et al. synthesized the host material DPDDC by connecting an indenocarboxylate and 1,3,5-triazine via a meta-phenyl group. The external quantum efficiency of a green light-emitting device based on this material reached 23.6% (Guo KP, Wang HD, Wang ZX, Si CF, Peng CY, Chen G, Zhang JH, Wang GF, Wei B. Stable green phosphorescence organic light-emitting diodes with low efficiency roll-off using a novel bipolar thermally activated delayed fluorescence material as host. Chem. Sci., 2017, 8, 1259-1268.). 4-Cyanopyridine is a very promising electron donor due to the excellent electron transport ability of the cyano and pyridine groups. Li et al. introduced 4-cyanopyridine into mCP to synthesize a bipolar host 3-PyCNmCP. The external quantum efficiency of the green light device based on it reached 24.7% (Li W, Li JY, Liu D, Li DL, Wang F. Cyanopyridine Based Bipolar Host Materials for Green Electrophosphorescence with Extremely Low Turn-On Voltages and High Power Efficiencies. ACS Appl. Mater. Interfaces, 2016, 8, 21497-21504.).In 2018, Li et al. introduced phenylcarbazole into the 3,5 positions of 4-cyanopyridine to synthesize a green light-emitting host 3-DCzPyCN, and the device achieved an external quantum efficiency of 24.2% (Li DL, Liu D, Wang M, Dong RZ, Li W. Cyanopyridine-based bipolar host materials for phosphorescent light-emitting diodes with low efficiency roll-off: Importance of charge balance. Dyes Pigm., 2018, 159, 230-237.). There are no reports in the prior art on the preparation of green light-emitting host materials by introducing phenylcarbazole into other positions of 4-cyanopyridine. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a green light host material. The green light host material prepared by the preparation method provided by the present invention has good thermal stability and excellent bipolar transmission properties.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a green light host material, comprising the following steps:

[0008] 1) mixing 2,6-dibromo-4-cyanopyridine, 9-phenyl-9H-carbazole-2-boronic acid, potassium carbonate, toluene, ethanol, water and ditriphenylphosphine palladium dichloride to obtain a mixed solution;

[0009] 2) refluxing the mixed solution obtained in step 1) to obtain a reactant;

[0010] 3) The reactant obtained in step 2) is separated and the organic phase is concentrated to obtain a crude product, and the crude product is separated by column chromatography to obtain a green light host material.

[0011] Preferably, the structure of the green light host material is as shown in Formula I:

[0012]

[0013] Preferably, in step 1), the mass ratio of the mass of 2,6-dibromo-4-cyanopyridine, the mass of 9-phenyl-9H-carbazole-2-boronic acid, the mass of potassium carbonate, the volume of toluene, the volume of ethanol, the volume of water and the mass ratio of ditriphenylphosphine palladium dichloride is 1 g:2.41 g:2.11 g:20 mL:10 mL:10 mL:0.03 g.

[0014] Preferably, the conditions for the reflux reaction in step 2) include: reflux reaction for 6 hours under nitrogen protection and a temperature of 60-75°C.

[0015] Preferably, the eluent used in the column chromatography separation in step 3) includes ethyl acetate and petroleum ether.

[0016] Preferably, the volume ratio of ethyl acetate to petroleum ether is 1:3.

[0017] Preferably, the conditions for column chromatography separation in step 3) include: performance indicators of silica gel column (1) shape: spherical and broken gel; (2) particle size: 2-5 μm.

[0018] The beneficial effects of the present invention are:

[0019] The present invention introduces the phenylcarbazole group with excellent electroluminescent performance into the 2,6 positions of 4-cyanopyridine through the 2-position of carbazole to synthesize a new green light host material 2,6-bis(9-phenyl-9H-carbazole-2-yl)-4-cyanopyridine (hereinafter referred to as BPh2CzCN). The meta-position connection mode weakens the intramolecular charge transfer effect of the material, making E T Maintained at 2.54eV. When used as the main body of a green light device, the maximum brightness of the device (L max ) is 62080cd m -2 , maximum current efficiency (η c,max ) is 44.05cdA -1 , maximum power efficiency (η p,max ) is 35.86lmW -1 , maximum external quantum efficiency (EQE max ) is 12.46%, and the efficiency roll-off of the device is very low, 1000 and 10000cdA -1 The roll-off is only 0.3% and 8.3% respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below.

[0021] Figure 1 This is the synthetic route of the compound BPh2CzCN;

[0022] Figure 2 TGA (a) and DSC (b) curves of BPh2CzCN;

[0023] Figure 3 UV-visible absorption (a), fluorescence and low-temperature phosphorescence spectra of BPh2CzCN in DCM (concentration 10 - 5M);

[0024] Figure 4 UV-visible absorption (a) and fluorescence spectra of BPh2CzCN in different solvents (concentration 10 -5 M);

[0025] Figure 5 The optimized configuration and HOMO / LUMO distribution of BPh2CzCN;

[0026] Figure 6 BPh2CzCN in DMF (10 -3 M) cyclic voltammetry curve;

[0027] Figure 7 JV curve of the single carrier device of BPh2CzCN;

[0028] Figure 8 Schematic diagram of the energy levels of device G and the structure of the materials used;

[0029] Figure 9 (a) Current density-voltage-luminance curve of device G; (b) Current efficiency-luminance-external quantum efficiency curve of device G; (c) Power efficiency-luminance curve of device G; (d) Electroluminescence spectrum of device G at 4-8V voltage. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a green light host material, comprising the following steps:

[0031] 1) mixing 2,6-dibromo-4-cyanopyridine, 9-phenyl-9H-carbazole-2-boronic acid, potassium carbonate, toluene, ethanol, water and ditriphenylphosphine palladium dichloride to obtain a mixed solution;

[0032] 2) refluxing the mixed solution obtained in step 1) to obtain a reactant;

[0033] 3) The reactant obtained in step 2) is separated and the organic phase is concentrated to obtain a crude product, and the crude product is separated by column chromatography to obtain a green light host material.

[0034] In the present invention, the structure of the green light host material is shown in Formula I:

[0035]

[0036] The present invention mixes 2,6-dibromo-4-cyanopyridine, 9-phenyl-9H-carbazole-2-boronic acid, potassium carbonate, toluene, ethanol, water, and ditriphenylphosphine palladium dichloride to obtain a mixed solution. In the present invention, the mass ratio of the 2,6-dibromo-4-cyanopyridine, the mass of the 9-phenyl-9H-carbazole-2-boronic acid, the mass of the potassium carbonate, the volume of the toluene, the volume of the ethanol, the volume of the water, and the mass ratio of the ditriphenylphosphine palladium dichloride is preferably 1g:2.41g:2.11g:20mL:10mL:10mL:0.03g. The 2,6-dibromo-4-cyanopyridine, 9-phenyl-9H-carbazole-2-boronic acid, and potassium carbonate are the reactants; the toluene, ethanol, and water constitute the solvent system; and the ditriphenylphosphine palladium dichloride is the catalyst.

[0037] The present invention refluxes the obtained mixed solution to obtain a reactant. In the present invention, the reflux reaction conditions preferably include: refluxing for 6 hours under nitrogen protection at a temperature of 60-75°C.

[0038] The present invention separates the obtained reactants and concentrates the organic phase to obtain a crude product, which is then subjected to column chromatography to obtain a green light-emitting main material. In the present invention, the eluent used for the column chromatography separation preferably includes ethyl acetate and petroleum ether. In the present invention, the volume ratio of ethyl acetate to petroleum ether is preferably 1:3. In the present invention, the conditions for the column chromatography separation preferably include: performance indicators of the silica gel column (1) shape: spherical and broken gel; (2) particle size: about 2-5 μm.

[0039] In order to further illustrate the present invention, the present invention is described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] Compound synthesis:

[0042] Figure 1 This is a synthetic route for the green light host material (abbreviated as BPh2CzCN). The material is synthesized in one step by Suzuki coupling reaction of 2,6-dibromo-4-cyanopyridine and phenylcarbazole boronic acid, and purified by column chromatography to a purity of 99.55%. The product is used 1 H& 13 The product was fully characterized by C nuclear magnetic resonance (NMR) (H spectrum, deuterated reagent, standard substance TMS, sample size 5 mg, scanning cycle 8-32) and high-resolution mass spectrometry (HRMS) (400.0125 MW, accuracy 5 ppm).

[0043] Synthesis of 2,6-bis(9-phenyl-9H-carbazole-2-yl)-4-cyanopyridine (BPh2CzCN): Add 2,6-dibromo-4-cyanopyridine (1.0 g, 3.82 mmol), 9-phenyl-9H-carbazole-2-boronic acid (2.41 g, 8.39 mmol) and K2CO3 (2.11 g, 15.27 mmol) into a three-necked flask, and then add toluene (20 mL), ethanol (10 mL), deionized water (10 mL) and ditriphenylphosphine palladium dichloride (0.03 g, 0.043 mmol), and reflux at 60-75 ° C under nitrogen protection for 6 h. After the reaction, the liquids were separated and the organic phase was concentrated. The crude product was separated by column chromatography using ethyl acetate / petroleum ether (volume ratio 1:3) as the eluent (performance indicators of silica gel column: (1) shape: spherical and broken gel; (2) particle size: approximately 2-5 μm). 1.28 g of light green product, BPh2CzCN, was obtained with a yield of 57.1% and a purity of 99.55%. The melting point was >280°C. 1 H NMR(400MHz, CDCl3)δ:8.25(d,J=8.0Hz,2H),8.20(d,J=8.0Hz,2H),8.06-8.10(m,4H), 7.85(s,2H),7.60-7.68(m,8H),7.50-7.55(m,2H),7.43-49(m,4H),7.31-7.36(m,2H). 13 C NMR(101MHz, CDCl3)δ:158.72,141.93,141.25,137.36,135.50,130.10,127.83,127.15,126.72,124.96 ,122.84,121.69,120.77,120.76,120.34,119.80,119.20,117.32,110.04,108.47.HRMS(ESI,m / z):[M] + calculated for C 42 H 26 N4,586.2157,found 586.2160.

[0044] Example 2

[0045] Thermal properties of the green light host material prepared in Example 1

[0046] In order to withstand the high temperature during vacuum evaporation for a long time and increase the service life of OLEDs, good thermal stability is a necessary property for qualified OLEDs materials. Therefore, the thermal stability of BPh2CzCN was evaluated by thermogravimetric analysis (TGA uses N2 before 400℃ and switches to air after 400℃. A small amount of weight loss before 350℃; 400-500℃: main weight loss step) and differential scanning calorimetry (DSC ordinate: heat flow rate; abscissa: temperature T (or time t) peak). Figure 2 It can be seen from a and Table 1 that the thermal decomposition temperature of the material (T d The temperature at which 5 wt% weight loss is generated is 448 ° C, showing good thermal stability. In the DSC test, a sharp endothermic peak appeared at 295 ° C in the first round of temperature scanning, which corresponds to the melting point of BPh2CzCN; in the second round of scanning, the glass transition temperature (T g ) is 133°C. Higher T d and T g This makes BPh2CzCN promising for application in high-performance and long-life OLED devices.

[0047] Table 1 Photophysical, electrochemical and thermal properties of BPh2CzCN

[0048]

[0049] a Maximum absorption wavelength tested in dilute DCM solution; b Obtained by cyclic voltammetry test; c Obtained by the onset peak of low-temperature phosphorescence spectrum (77K); d obtained by DSC and TGA; f Obtained by the onset peak of fluorescence spectrum and low-temperature phosphorescence spectrum.

[0050] Example 3

[0051] Photophysical properties of the green light host material prepared in Example 1

[0052] The photophysical properties of BPh2CzCN were studied using ultraviolet-visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy (FL) in dilute dichloromethane solution. Figure 3 As shown in the figure, the maximum absorption wavelength of BPh2CzCN is 361nm, and the initial absorption wavelength is 398nm. Based on this, it can be inferred that its optical band gap (E g ) is 3.12eV. The maximum emission wavelength of BPh2CzCN's room temperature fluorescence is 452nm, and it emits sky blue. In order to better understand the excited state properties of BPh2CzCN, its solvation effect in solvents of different polarities was studied. Figure 4As shown, with increasing solvent polarity, its absorption spectrum remains essentially unchanged (within 5 nm), while its emission spectrum exhibits a significant solvent-induced red shift (83 nm), indicating that BPh2CzCN has a strong CT feature in its excited state. Furthermore, its triplet energy level, estimated from the onset peak of its low-temperature (77 K) phosphorescence spectrum in 2-methyltetrahydrofuran, is 2.54 eV, which is higher than the triplet energy level of commonly used green phosphorescent materials, indicating that this compound can serve as a host material for green light-emitting materials.

[0053] Example 4

[0054] Theoretical calculation and electrochemical properties of the green light host material prepared in Example 1

[0055] In order to further study the electronic properties of BPh2CzCN, BAIKE BIOTECH (SHANGHAI) CO., LTD performed density functional theory (DFT) calculations using Gaussian 09 with the B3LYP / 6-31G* basis set.

[0056] (Lu T, Chen FW. Multiwfn: A multifunctional wavefunction analyzer. J. Comput. Chem., 2012, 33, 580-592.). like Figure 5 As shown, the LUMO energy level of BPh2CzCN is primarily distributed on the 4-cyanopyridine unit, with slight diffusion to the carbazole. Its HOMO energy level is primarily dispersed across the two carbazole groups, with a small amount diffusing to the 9-phenyl group of the carbazole. The well-separated HOMO and LUMO energy levels of BPh2CzCN give it bipolar transport properties, enabling the simultaneous transport of both electrons and holes, making it suitable as a bipolar host material.

[0057] The transport of charge carriers in OLEDs involves repeated oxidation and reduction of materials, so the electrochemical properties of BPh2CzCN were evaluated using cyclic voltammetry (CV). Figure 6 As shown in Table 1, the oxidation and reduction starting potentials of BPh2CzCN are 1.31 and -1.91 eV, respectively. HOMO =-(4.4+E onset ox ) and E LUMO =-(4.4+E onset red ), the HOMO / LUMO energy levels of BPh2CzCN were determined to be -5.71 and -2.49 eV, respectively.

[0058] Example 5

[0059] Preparation of single-carrier devices using the green light host material prepared in Example 1

[0060] Achieving balanced carrier transport is a key factor in achieving high-performance OLEDs. Therefore, single-carrier devices with the structures of [ITO / TPBi (10 nm) / BPh2CzCN (50 nm) / TPBi (10 nm) / LiF (1 nm) / Al (100 nm)] and [ITO / MoO3 (3 nm) / TAPC (10 nm) / BPh2CzCN (50 nm) / TAPC (10 nm) / Al (100 nm)] were prepared by layer-by-layer spin coating to evaluate the charge transport capability of the BPh2CzCN prepared in Example 1. 1,3,5-Tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBi) and 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-toluidine) (TAPC) served as electron and hole transport layers, respectively, and MoO3 and LiF served as hole and electron injection layers, respectively.

[0061] from Figure 7 It can be seen that in the low voltage range, both single-carrier devices have very high current density, indicating that BPh2CzCN has good bipolar properties and can maintain good carrier balance when used as the main material of PhOLEDs.

[0062] Example 6

[0063] Electroluminescent properties

[0064] In order to evaluate the electronic luminescence performance of BPh2CzCN prepared in Example 1, a layer-by-layer spin-coating green light device G was prepared using 2-tris(2-phenylpyridine)iridium(III) (Ir(ppy)3) as the luminescent material. The structure was [ITO / MoO3(3nm) / TAPC(40nm) / TCTA(10nm) / BPh2CzCN:Ir(ppy)3(20nm; 6wt%) / TmPyPB(50nm) / LiF(1nm) / Al(100nm)], wherein tris(4-(9H-carbazol-9-yl)phenyl)amine (TCTA) and 3,3'-(5'-(3-(pyridin-3-yl)phenyl)-[1,1':3',1"-triphenyl]-3,3"-diyl)dipyridine (TmPyPB) were used as the exciton blocking layer and electron transport layer, respectively. The energy level diagram of the device and the structures of the materials used in the device are shown in Figure 2. Figure 8[ITO anode / MoO3 (3nm) hole injection layer / TAPC (40nm) hole transport layer / TCTA (10nm) exciton blocking layer / BPh2CzCN:Ir(ppy)3 (20nm; 6wt%) light-emitting layer / TmPyPB (50nm) electron transport layer / LiF (1nm) / Al (100nm) cathode].

[0065] from Figure 9 From the data in Table 2, we can see that the startup voltage of device G (V on ) is as low as 3V, thanks to the appropriate energy level of BPh2CzCN and the energy level matching of adjacent layer materials. The wavelength of the device's luminescence spectrum is at 519nm (CIE coordinates are (0.333, 0.610)), which is a standard green light emission, that is, the emission of Ir(ppy)3. The L of device G is max 62080cd m -2 , η c,max 44.05 cdA -1 , η p,max 35.86lmW -1 ,EQE max It is worth noting that the efficiency roll-off of the device is very low, with brightness of 1000 and 10000 cdA. -1 The roll-off is only 0.3% and 8.3%. Figure 9 As shown in Figure d, the luminescence spectrum of device G hardly changes when the voltage increases from 4 V to 8 V, indicating that the device has good stability. These all indicate that BPh2CzCN can be used as the main material of high-performance green PhOLEDs.

[0066] Table 2 Electroluminescence performance parameters of device G

[0067]

[0068] a Brightness is 1cdm -2 The voltage at b Maximum brightness; c Maximum value; d Color coordinates when the voltage is 6V.

[0069] From the above examples, it can be concluded that the green light host material BPh2CzCN designed and synthesized by the present invention has good thermal stability, suitable HOMO / LUMO energy levels and triplet energy levels. Single carrier device tests and simulation calculations show that the material has bipolar transport characteristics. Device tests show that the green light device with BPh2CzCN as the main body starts at 3.0V, L max 62080cdm -2 , ηc,max 44.05 cdA -1 , η p,max 35.86lmW -1 ,EQE max The device has good stability and low efficiency roll-off, with a power consumption of 1000 and 10000 cdA. -1 The roll-off is only 0.3% and 8.3% when the BPh2CzCN is 0.5% and 1.3% respectively. The above results show that BPh2CzCN has excellent bipolar transmission properties and is suitable as a green light host material.

[0070] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a green light host material, characterized in that: The following steps are involved: 1) mixing 2,6-dibromo-4-cyanopyridine, 9-phenyl-9H-carbazole-2-boronic acid, potassium carbonate, toluene, ethanol, water and ditriphenylphosphine palladium dichloride to obtain a mixed solution; 2) refluxing the mixed solution obtained in step 1) to obtain a reactant; 3) separating the reactant obtained in step 2) and concentrating the organic phase to obtain a crude product, and subjecting the crude product to column chromatography to obtain a green light host material; The structure of the green light host material is shown in Formula I: In the step 1), the mass ratio of 2,6-dibromo-4-cyanopyridine, the mass of 9-phenyl-9H-carbazole-2-boronic acid, the mass of potassium carbonate, the volume of toluene, the volume of ethanol, the volume of water, and ditriphenylphosphine palladium dichloride is 1 g:2.41 g:2.11 g:20 mL:10 mL:10 mL:0.03 g; The conditions for the reflux reaction in step 2) include: reflux reaction for 6 hours under nitrogen protection and a temperature of 60-75°C.

2. The preparation method according to claim 1, characterized in that The eluents used in the column chromatography separation in step 3) include ethyl acetate and petroleum ether.

3. The preparation method according to claim 2, characterized in that The volume ratio of the ethyl acetate to petroleum ether is 1:

3.

4. The preparation method according to claim 1, characterized in that The conditions for column chromatography separation in step 3) include: performance indicators of silica gel column: (1) shape: spherical and broken gel; (2) particle size: 2-5 μm.

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