High color purity near-ultraviolet hot exciton compound with circular polarization property and application in preparing circular polarization organic electroluminescent device

Abstract

The application relates to a high-color-purity near-ultraviolet hot exciton compound with circular polarization properties and application in preparation of circular polarization organic electroluminescent devices, and belongs to the technical field of organic photoelectric materials. The electroluminescent material is a high-color-purity near-ultraviolet hot exciton compound with circular polarization properties. Two pairs of near-ultraviolet enantiomers are successfully designed and synthesized by combining a chiral group binaphthol, a weak donor dithiophene and a weak donor dibenzofuran, and an acceptor benzonitrile. The two pairs of near-ultraviolet enantiomers all show obvious circular polarization luminescence properties and high fluorescence quantum yields. Electroluminescent devices prepared based on the enantiomers all show near-ultraviolet emission, and the CIE coordinates are (0.168, 0.040) and (0.166, 0.040) respectively, and the external quantum efficiencies are 4.3% and 3.4% respectively. The application provides a new perspective for developing near-ultraviolet hot exciton materials with circular polarization luminescence and high color purity, and is favorable for directly realizing 3D and wide color gamut display in the future.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic photoelectric materials, and in particular relates to a high-color-purity near-ultraviolet thermoexciton compound with circular polarization properties and an application thereof in preparing a circularly polarized organic electroluminescent device. Background Art

[0002] Circularly polarized organic light-emitting diodes (CP-OLEDs) have broad application prospects in 3D displays, circularly polarized light detection field-effect transistor devices (FETs), and personalized diagnosis and treatment. Currently reported materials that can be used to prepare CP-OLEDs devices include polymers, metal complexes, and organic small molecules. Among them, polymer materials and metal complex materials can exhibit obvious circularly polarized electroluminescence signals (CPEL), but have problems such as low device efficiency, high manufacturing cost, and serious environmental pollution. In contrast, chiral organic small molecules have the advantages of low synthesis cost, adjustable luminescence properties, and low toxicity. Therefore, constructing a variety of chiral organic small molecules will be the most direct and effective way to achieve CP-OLEDs with high device efficiency, high circularly polarized luminescence properties, and low efficiency roll-off.

[0003] After decades of development, CP-OLEDs materials have achieved breakthroughs in efficiency and color purity in the red, green, blue and infrared regions. However, research on near-ultraviolet emitting CP-OLEDs materials is still in its infancy. In order to broaden the color gamut and promote technological innovation of near-ultraviolet light sources, it is of great significance to develop high-efficiency, high-color-purity near-ultraviolet emitting CP-OLEDs materials. Traditional fluorescent materials are limited to an exciton utilization rate of 25%, and the external quantum efficiency is usually difficult to break through the theoretical upper limit of 5%. Therefore, improving the utilization rate of triplet excitons has become the key to improving the efficiency of near-ultraviolet devices. To date, the mechanisms for organic fluorescent devices to utilize triplet excitons mainly include: triplet-triplet annihilation (TTA), thermally activated delayed fluorescence (TADF) and hot exciton mechanism. Among them, the upper limit of the exciton utilization rate of TTA materials is 62.5%, and the device efficiency is still not ideal; although TADF materials can theoretically achieve 100% exciton utilization, it requires the separation of HOMO and LUMO orbitals to achieve a smaller single-triplet energy difference (△E ST ), the S1 energy level is usually a strong charge transfer (CT) excited state, which is not conducive to the construction of near-ultraviolet materials.

[0004] Hot exciton materials can be generated by high-energy triplet states (T m , m≥2) to the singlet state (S n, n≥1) utilizes triplet excitons to achieve the separation of triplet exciton conversion and radiative transition channels. Therefore, the properties of the S1 excited state of the hot exciton material will not have a significant impact on the hRISC process. In addition, due to the short lifetime of high-energy excited state excitons, the hRISC process rate is fast enough to effectively alleviate the problem of exciton annihilation of triplet excitons at high current density, which is conducive to obtaining near-ultraviolet emitting circularly polarized materials with high efficiency and low efficiency roll-off. The present application proposes to develop new circularly polarized luminescent hot exciton near-ultraviolet materials and devices by combining molecular design with chemical synthesis, taking into account the dual advantages of circularly polarized luminescence and high color purity, which is conducive to the direct realization of 3D and wide color gamut displays in the future. Summary of the Invention

[0005] The present invention aims to provide a high-color-purity near-ultraviolet thermoexciton compound with circular polarization properties and its use in the preparation of circularly polarized organic electroluminescent devices. The present invention uses a high-color-purity near-ultraviolet thermoexciton compound as the light-emitting layer to produce a high-efficiency, high-color-purity, deep-blue circularly polarized OLED device, which has the potential for practical application.

[0006] The present invention discloses a high color purity near-ultraviolet thermoexciton compound with circular polarization properties, the general structural formula of which is shown as (1):

[0007]

[0008] X is cyano (CN);

[0009] L m for Where * represents the connection position with R and the benzene ring; m is 0 or 1;

[0010] R is * indicates that L m Or the attachment position of the benzene ring.

[0011] Furthermore, the present invention provides a near-ultraviolet thermoexciton compound with high color purity and circular polarization properties, and its structural formula is shown as one of the following:

[0012]

[0013] The circularly polarized near-ultraviolet thermoexciton material provided by the present invention combines high solid-state luminescence efficiency, significant circular polarization properties, and excellent electroluminescent performance. It can be used as a dopant material to prepare the light-emitting layer of a circularly polarized organic electroluminescent device. The host material is CBP, and the mass doping concentration of the near-ultraviolet thermoexciton compound is 5 to 20 wt%. In addition to the light-emitting layer, the organic functional layers of this circularly polarized organic electroluminescent device are one or more of a hole injection layer, a hole transport layer, an exciton blocking layer, an electron transport layer, and an electron injection layer. This circularly polarized organic electroluminescent device can be used to prepare near-ultraviolet circularly polarized organic electroluminescent displays or organic electroluminescent lighting sources.

[0014] The principle of the present invention is to use dibenzothiophene and dibenzofuran as weak donors and benzonitrile as acceptors to construct luminescent molecules. The ortho-linked cyano group helps to reduce the lowest unoccupied orbital (LUMO) and the carrier injection barrier, thereby reducing the charge transfer within the molecule. At the same time, binaphthol is directly combined with the luminescent molecule as a chiral group, which helps to obtain near-ultraviolet emitting CP-OLEDs materials. Based on this, two pairs of near-ultraviolet emitting enantiomers, namely R / S-OBN-CN-DBF and R / S-OBN-CN-DBT, were successfully designed and synthesized. They have high solid-state luminescence efficiency and obvious circularly polarized luminescence properties, and the asymmetry factors in the non-doped thin film are +7.27×10 -4 / -8.37×10 -4 and +4.68×10 -4 / -5.65×10 -4 Electroluminescent devices based on the enantiomers R / S-OBN-CN-DBF and R / S-OBN-CN-DBT exhibit near-UV emission, with CIE coordinates of (0.168, 0.040) and (0.166, 0.040), respectively, and external quantum efficiencies of 4.3% and 3.4%, respectively. This work provides a new perspective for the development of near-UV thermoexciton materials with both circularly polarized luminescence and high color purity, which will facilitate the direct realization of 3D and wide color gamut displays in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 : Schematic diagram of the structure of the organic electroluminescent device prepared by the present invention, in which 1 is a transparent glass substrate, 2 is an ITO conductive film anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is an exciton blocking layer, 6 is an organic light-emitting layer, 7 is an electron transport layer, and 8 is a cathode;

[0016] Figure 2The absorption and emission spectra of R-OBN-CN-DBF in doped thin films are shown in Figure 2. The main absorption peaks are located at 300nm and 329nm respectively; the main emission peak is located at 381nm, which is near-ultraviolet emission. It can be used as an organic near-ultraviolet material to prepare electroluminescent devices.

[0017] Figure 3 The absorption and emission spectra of R-OBN-CN-DBT in doped thin films are shown in Figure 2. The main absorption peaks are located at 299nm and 330nm, respectively; the main emission peak is located at 381nm, which is near-ultraviolet emission. It can be used as an organic near-ultraviolet material to prepare electroluminescent devices.

[0018] Figure 4 The circularly polarized photoluminescence spectrum of R / S-OBN-CN-DBF in the undoped thin film state is shown in Figure 2. The photoluminescence asymmetry factor is +7.27×10 -4 / -8.37×10 -4 .

[0019] Figure 5 The circularly polarized photoluminescence spectrum of R / S-OBN-CN-DBT in the undoped thin film state is shown in Figure 2. The photoluminescence asymmetry factor is +4.68×10 -4 / -5.65×10 -4 .

[0020] Figure 6 This is the external quantum efficiency curve of the R / S-OBN-CN-DBF circularly polarized electroluminescent device prepared in Example 3, with a maximum external quantum efficiency of 4.3%; the inset is the electroluminescence spectrum, with the main peak of the spectrum located at 396 nm.

[0021] Figure 7 This is the external quantum efficiency curve of the R / S-OBN-CN-DBT circularly polarized electroluminescent device prepared in Example 4, with a maximum external quantum efficiency of 3.4%; the inset is the electroluminescence spectrum, with the main peak of the spectrum located at 400 nm. DETAILED DESCRIPTION

[0022] Example 1: The preparation of R / S-OBN-CN-DMF in this example is as follows:

[0023] Synthesis of R / S-OBN-CN: 2-Bromo-4,5-difluorobenzonitrile (305.2 mg, 1.4 mmol), R / S- BINOL (400.4 mg, 1.4 mmol) and K2CO3(483 mg, 3.5 mmol) were mixed, added to a 20 mL dry DMF, heated to 120 °C and stirred for 12 h. After cooling to room temperature, the reaction mixture was poured into water (100 mL), the reaction mixture was extracted three times with dichloromethane and water, and the combined organic layers were condensed in vacuum and purified by column chromatography with a mixture of dichloromethane / petroleum ether (1 :4, v / v) as eluent to give a white solid (422 mg) with a yield of 65%. Mass spectrum MALDI-TOF (m / z): found 464.12 [M + ] : calculated 464.01.

[0024]

[0025] Synthesis of R / S-OBN-CN-DBF: R / S-OBN-CN (464 mg, 1 mmol), DBF Bin (276 mg, 1.3 mmol), K2CO3(1.11 g, 5 mmol), Pd(PPh3)4(70 mg, 0.06 mmol) were mixed added to a 100 mL flask, added to 20 mL toluene and 10 mL water, heated to 90 °C and stirred for 24 h. After cooling to room temperature, the reaction mixture was poured into water (50 mL), the reaction mixture was extracted three times with dichloromethane and water, and the combined organic layers were condensed in vacuum and purified by column chromatography with a mixture of dichloromethane / petroleum ether (1 :4, v / v) as eluent to give a white solid (436 mg) with a yield of 79%. R-OBN-CN-DBF: 1 H NMR (500 MHz, CD2Cl2) δ 8.17 - 8.12 (m, 2H), 8.12 - 8.07 (m, 2H), 8.05 (d, J = 8.1 Hz, 2H), 7.83 (d, J = 6.1 Hz, 2H), 7.68 (s, 1H), 7.66 (s, 1H), 7.63 - 7.60 (m, 2H), 7.59 - 7.53 (m, 6H), 7.48 - 7.43 (m, 3H). Mass spectrum MALDI-TOF (m / z): Calcd for C 39 H 21 NO3, 551.60; Found: 551.51 [M + ]. S-OBN-CN-DBF: 1H NMR(500MHz,DMSO)δ8.33(d,J=8.1Hz,1H),8.24(d,J=9.9Hz,3H),8.15(s,2H),8.14 (s,1H),8.06(s,1H),7.79(d,J=6.4Hz,2H),7.77(d,J=3.7Hz,1H),7.75(s,1H),7.71 (d,J=7.9Hz,1H),7.61(t,J=5.8Hz,2H),7.59(d,J=6.9Hz,1H),7.52(d,J=8.3Hz,1H ),7.50(s,1H),7.47(d,J=7.8Hz,1H),7.44–7.38(m,2H).MALDI-TOF(m / z):Calcdfor C 39 H 21 NO3:551.60;Found:551.15[M + ].

[0026]

[0027] Example 2: The preparation of R / S-OBN-CN-DBT in this example is as follows:

[0028] Synthesis of R / S-OBN-CN-DBT: R / S-OBN-CN (464 mg, 1 mmol), DBTBin (296 mg, 1.3 mmol), K2CO3 (1.11 g, 5 mmol), and Pd(PPh3)4 (70 mg, 0.06 mmol) were mixed and added to a 100 mL flask. 20 mL of toluene and 10 mL of water were added, and the mixture was heated to 90°C and stirred for 24 hours. After cooling to room temperature, the reaction mixture was poured into water (50 mL) and extracted three times with dichloromethane and water. The combined organic layers were condensed in vacuo and purified by column chromatography using a mixed eluent of dichloromethane / petroleum ether (volume ratio 1:4) to obtain a white solid (403 mg) with a yield of 71%. R-OBN-CN-DBT: 1 H NMR (500MHz, CD2Cl2) δ8.35(d,J=8.2Hz,1H),8.31–8.26(m,1H),8.13(s,1H),8.11(d,J=7.1Hz,2H),8.05(d,J=8.4Hz,2H),7.98–7. 93(m,1H),7.82(s,1H),7.73(d,J=8.2Hz,1H),7.59(d,J=8.3Hz,3H),7.58–7.52(m,6H),7.48–7.43(m,2H).MALDI-TOF(m / z):Calcd for C 39H 21 NO2S:567.66;Found:567.44[M + ].S-OBN-CN-DBF: 1 H NMR (500MHz, DMSO) δ8.55(d,J=8.3Hz,1H),8.48(d,J=8.5Hz,1H),8.36(s,1H),8.25(d ,J=2.9Hz,1H),8.23(d,J=2.9Hz,1H),8.18–8.13(m,3H),8.10(d,J=8.7Hz,1H),7.82(d ,J=4.4Hz,1H),7.81–7.78(m,2H),7.77(d,J=6.2Hz,1H),7.75(s,1H),7.62(d,J=7.4Hz ,1H),7.60–7.57(m,2H),7.54–7.49(m,2H),7.43–7.38(m,2H).MALDI-TOF(m / z):Calcd for C 39 H 21 NO2S:567.66;Found:567.32[M + ].

[0029]

[0030] Example 3

[0031] A circularly polarized organic electroluminescent device uses an organic blue light-emitting small molecule with a molecular structure of R-OBN-CN-DBF as a light-emitting layer material (emitters). The structure of the organic electroluminescent device R-OBN-CN-DBF is as follows: ITO / HATCN (6nm) / TAPC (25nm) / TCTA (15nm) / 5wt% emitters: CBP (20nm) / TmPyPB / LiF (1nm) / Al (120nm).

[0032] The device fabrication process is as follows: Preparation of the indium tin oxide (ITO) conductive glass substrate: The substrate was cleaned in an ultrasonic bath with deionized water, isopropyl alcohol, acetone, toluene, acetone, and isopropyl alcohol for 20 minutes each, and then dried in an oven. After treating the ITO conductive glass surface in a UV-ozone cleaner for 40 minutes, it was transferred to a vacuum evaporation device (chamber pressure < 2×10 -4Pa); on the anode ITO conductive glass, the hole injection layer HATCN is vacuum-deposited with a thickness of 5 nm; on HATCN, the hole transport layer TAPC is vacuum-deposited with a thickness of 25 nm: on TAPC, the exciton blocking layer TCTA is evaporated with a thickness of 15 nm; on TCTA, the light-emitting layer CBP:R-OBN-CN-DBF (mass doping concentration is 5 wt%) is evaporated with a thickness of 20 nm; on the light-emitting layer, the electron transport layer TmPyPB is evaporated with a thickness of 40 nm; on TmPyPB, the electron transport layer LiF is evaporated with a thickness of 1 nm; on LiF, the cathode Al is evaporated with a thickness of 100 nm.

[0033] In this example, CBP:R-OBN-CN-DBF (doping concentration of 5 wt%) is used as the light-emitting layer material, and the external quantum efficiency curve of the circularly polarized organic electroluminescent device is as follows: Figure 6 The detailed electroluminescence performance data of the device are listed in Table 1, which shows that the prepared device has high color purity and significant circularly polarized electroluminescence signal.

[0034] Table 1: Relevant data parameters of the device prepared in Example 3

[0035]

[0036] Example 4

[0037] A circularly polarized organic electroluminescent device, using an organic blue light-emitting small molecule with a molecular structure of R-OBN-CN-DBT as a light-emitting layer material (emitters), wherein the structure of the organic electroluminescent device R-OBN-CN-DBT is as follows: ITO / HATCN (6nm) / TAPC (25nm) / TCTA (15nm) / 5wt% emitters: CBP (20nm) / TmPyPB / LiF (1nm) / Al (120nm). The preparation process of the device is similar to that of Example 3. Among them, the external quantum efficiency curve of the circularly polarized organic electroluminescent device prepared with CBP:R-OBN-CN-DBT (mass doping concentration of 5wt%) as the light-emitting layer material is as shown in FIG. Figure 7 The detailed electroluminescence performance data of the device are listed in Table 2, which shows that the prepared device has high color purity and significant circularly polarized electroluminescence signal.

[0038] Table 2: Relevant data parameters of the device prepared in Example 4

[0039]

[0040] The structural formulas of the materials used in the organic electroluminescent devices of Examples 3-4 are as follows, and all of them are commercially available:

[0041]

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high color purity near-ultraviolet exciton compound with circular polarization properties, the structural formula of which is shown as one of the following: 。 2. Use of a high color purity near-ultraviolet thermoexciton compound with circular polarization properties according to claim 1 in the preparation of a circularly polarized organic electroluminescent device, characterized in that: The near-ultraviolet thermoexciton compound is used as a doping material for preparing a light-emitting layer of a circularly polarized organic electroluminescent device. The main material is CBP, and the mass doping concentration of the near-ultraviolet thermoexciton compound is 5-20 wt%.

3. Use of a high color purity near-ultraviolet thermoexciton compound with circular polarization properties in the preparation of a circularly polarized organic electroluminescent device according to claim 2, characterized in that: The organic functional layer of the circularly polarized organic electroluminescent device other than the light-emitting layer is one or more of a hole injection layer, a hole transport layer, an exciton blocking layer, an electron transport layer, and an electron injection layer.

4. Use of a high color purity near-ultraviolet thermoexciton compound with circular polarization properties in the preparation of a circularly polarized organic electroluminescent device according to claim 3, characterized in that: The circularly polarized organic electroluminescent device is used for preparing a near-ultraviolet circularly polarized organic electroluminescent display or an organic electroluminescent lighting source.

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