A multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution and its application in organic electroluminescent devices

Abstract

A multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution and its application in organic electroluminescent devices belong to the technical field of organic electroluminescent devices. The multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution described in the present invention introduces heavy atoms on the periphery of the multi-resonance skeleton to increase the spin-orbit coupling of the system, improve the reverse intersystem crossing rate from the triplet state to the singlet state, and suppress the efficiency roll-off; at the same time, it does not increase the structural relaxation of the molecule, affect the multi-resonance characteristics of the entire system, and maintain the narrow half-width and high luminous efficiency of the system. The organic electroluminescent device prepared in this way overcomes the shortcomings of MR-TADF materials such as serious efficiency attenuation at high brightness, and realizes an organic electroluminescent device with high efficiency, high color purity and low efficiency roll-off, which has an important role in promoting the further popularization of organic electroluminescent technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic electroluminescent devices, and in particular relates to a multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution and its application in organic electroluminescent devices. Background Art

[0002] Organic light-emitting diodes (OLEDs) are a new display technology with advantages such as high brightness, fast response, wide viewing angle, simple processing, and flexibility. They have made significant progress in full-color display and lighting applications, becoming a hot trend in current industrialization. In recent years, third-generation luminescent materials—thermally activated delayed fluorescence (TADF) materials—have been widely developed and applied in electronic devices due to their ability to effectively utilize triplet excitons, becoming a cutting-edge research hotspot in the field of luminescent materials. However, most current TADF materials utilize donor-acceptor structures. Vibrational coupling between the ground and excited states and structural relaxation of the excited state result in a wide full-width at half maximum (FWHM) of their emission spectra (>70nm), which cannot meet the high color purity requirements of full-color display technology. Although device structures using filters or optical microcavities can meet the color purity requirements of displays, this not only complicates the device structure but also results in significant energy loss, which is not conducive to energy conservation and environmental protection.

[0003] In recent years, new TADF materials with boron / nitrogen multiple resonance (MR) effects have been reported one after another. They can maximally suppress the bonding / antibonding characteristics, structural relaxation, and vibration coupling of the excited state, thereby achieving narrow-band emission characteristics. At the same time, they have a large oscillator strength (f) and the resulting high fluorescence quantum yield (PLQY), which is conducive to achieving high color purity and high luminescence efficiency. However, the reverse intersystem crossing (RISC) rate (k RISC is 10 3 -10 4 s -1 ) is slow, usually leading to the accumulation of triplet excitons and subsequent exciton annihilation, resulting in severe efficiency roll-off at high brightness. -2When the EQE is too low, the efficiency even drops to less than half of the maximum EQE, hindering their commercial application potential. Furthermore, the boron / nitrogen multiple resonance system compound has a relatively rigid planar structure, with strong molecular interactions and easy aggregation. This easily leads to aggregation-induced quenching when preparing electroluminescent devices, further deteriorating the luminescence performance of the material and the color purity of the device. Therefore, the development of new organic light-emitting materials and electroluminescent devices with high efficiency, high color purity, and high efficiency at high brightness is of great significance for practical applications and will play an important role in promoting the further popularization of OLED technology. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that k RISC The slow quenching effect of triplet exciton annihilation and the aggregation-induced quenching effect between molecules leads to the serious efficiency roll-off problem of electroluminescent devices at high brightness. According to the Fermi level rule, k RISC The energy level difference between the single triplet state and the ST ) is related to spin-orbit coupling (SOC), and the ΔE of MR-TADF molecules ST Between 0.1eV and 0.2eV. Therefore, if we want to increase k RISC , it is necessary to increase the SOC of the system. It is generally believed that the greater the nuclear charge number of the atomic nuclei contained in the system, the higher the SOC intensity, and the higher the possibility of electron spin flipping, which is the "heavy atom effect". However, the introduction of heavy atoms (sulfur or selenium atoms) on the multi-resonance skeleton will increase the structural relaxation of the molecule, so that the half-width of the MR-TADF molecule increases (FWHM>50nm), affecting the color purity of the molecule. In response to the existing problems, the present invention provides a simple and effective strategy to improve the RISC rate of MR-TADF materials without affecting the color purity, that is, by introducing heavy atoms on the periphery of the multi-resonance skeleton to increase the SOC of the system, while not increasing the structural relaxation of the molecule, affecting the multi-resonance characteristics of the system, maintaining the narrow half-width of the system, and overcoming the shortcomings of the serious attenuation of device efficiency and the widening of the half-width under high brightness of MR-TADF materials.

[0005] The structural formula of the multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution described in the present invention is as follows:

[0006]

[0007] Wherein R is sulfur (S) or selenium (Se);

[0008] Furthermore, the multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution of the present invention has a structural formula as shown in one of the following:

[0009]

[0010] An organic electroluminescent device prepared using the product of the present invention comprises a cathode, an anode, and one or more organic layers between the two electrodes, at least one of which is an organic light-emitting layer. The organic light-emitting layer is composed of a peripheral heavy atom-substituted multi-resonance thermally activated delayed fluorescent material prepared by the present invention as a guest material and PhCzBCz as a host material, with the guest material doping ratio being 2-5% by weight. The electroluminescent device can be used to prepare an organic electroluminescent display or an organic electroluminescent lighting source.

[0011] Furthermore, an embodiment of the present invention provides an organic electroluminescent device, which is composed of a transparent substrate, an ITO conductive film (anode), a hole injection layer (HATCN), a hole transport layer (TAPC), an exciton blocking layer (TCTA and mCP), a light-emitting layer, an electron transport layer (TmPyPB), an electron injection layer (LiF) and a cathode layer (Al) from bottom to top. All functional layers can be prepared by a vacuum evaporation film-forming process.

[0012] Preferably, some organic compounds used in the device are commercially available or prepared according to known literature or patents, and the molecular structure is shown below:

[0013]

[0014] The beneficial effects of the present invention are:

[0015] The multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution of the present invention has high luminescence efficiency, high reverse intersystem crossing rate and narrow half-peak width. RISCThe quenching of triplet excitons is relatively slow, resulting in the accumulation of triplet excitons and subsequent exciton annihilation, including the quenching of triplet excitons and triplet excitons (TTA), the quenching of triplet excitons and singlet excitons (TSA), and the quenching between triplet excitons and polarons (TPA). These quenching processes are the main reason for the efficiency roll-off of MR-TADF devices. If you want to achieve a device with low efficiency roll-off, you must find a way to reduce the accumulation of triplet excitons, avoid the quenching of triplet excitons, increase the movement rate of triplet excitons, and convert them into singlet excitons to produce delayed fluorescence. The present invention provides a simple and effective strategy to improve the RISC of MR-TADF materials without affecting the color purity, that is, by introducing heavy atoms on the periphery of the multi-resonance skeleton to increase the SOC of the system, while not affecting the multi-resonance characteristics of the system and maintaining the narrow half-width of the system. The organic electroluminescent device prepared in this way overcomes the shortcomings of MR-TADF materials such as severe efficiency attenuation at high brightness, and realizes an organic electroluminescent device with high efficiency, high color purity and low efficiency roll-off, which plays an important role in promoting the further popularization of organic electroluminescent technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : Schematic diagram of the structure of the organic electroluminescent device prepared by the present invention, in which 1 is a transparent substrate, 2 is an ITO 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, 8 is an electron injection layer, and 9 is a cathode.

[0017] Figure 2 : Ultraviolet (Abs.), fluorescence (FL.) and low-temperature phosphorescence (Phos.) spectra of compound BN-1; the maximum absorption peak is 468nm, the main emission peak is at 483nm, which is blue-green emission, with a half-peak width of 22nm; the energies of S1 and T1 calculated from the main peak positions of fluorescence and low-temperature phosphorescence are 2.57eV and 2.40eV, respectively, and the ΔE of the two molecules can be calculated. ST It is 0.17eV.

[0018] Figure 3 : UV, fluorescence and low-temperature phosphorescence spectra of compound BN-2; the maximum absorption peak is 468nm, the main emission peak is at 485nm, which is blue-green emission, with a half-peak width of 22nm; the energies of S1 and T1 calculated from the main peak positions of fluorescence and low-temperature phosphorescence are 2.56eV and 2.42eV respectively, and the ΔE of the two molecules can be calculated ST It is 0.14eV.

[0019] Figure 4 : External quantum efficiency curve of electroluminescent device prepared by compound BN-1, the maximum external quantum efficiency is 43.1% (the brightness at this time is 20.7 cd m -2); at a brightness of 1000 cd m -2 When the external quantum efficiency is 24.8%, the inset is the electroluminescence spectrum under a driving voltage of 6V. The main peak of electroluminescence is located at 492nm, which is the emission of blue-green light. It has high color purity and a half-peak width of 27nm.

[0020] Figure 5 : External quantum efficiency curve of electroluminescent device prepared by compound BN-2, the maximum external quantum efficiency is 36.9% (the brightness at this time is 186.0 cd m -2 ); at a brightness of 1000 cd m -2 When , the external quantum efficiency is 31.8%; the inset is the electroluminescence spectrum under a driving voltage of 6V. The main peak of electroluminescence is located at 492nm, which is the emission of blue-green light. It has high color purity and a half-peak width of 28nm. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings to facilitate understanding of the present invention by those skilled in the art. Obviously, the embodiments described are only a part of the present experiment and are not complete embodiments. Non-essential modifications, equivalent substitutions and improvements made to the present invention based on the above invention by those skilled in the art should all be included in the scope of protection of the present invention. The raw materials mentioned below are all commercially available or prepared according to known literature or patents. The process steps and preparation methods not mentioned are all process steps and preparation methods well known to those skilled in the art.

[0022] Example 1: The preparation of BN-1 in this example is as follows:

[0023]

[0024] Synthesis of M1: Under nitrogen protection, a solution of 3,6-di-tert-butylcarbazole (9.8 g, 35.2 mmol) in 60 mL of anhydrous DMF (N,N-dimethylformamide) was slowly added dropwise to a mixture of cesium carbonate (13.0 g, 40.0 mmol) and 50 mL of anhydrous DMF over 20 minutes. After the reaction system was stirred at room temperature for 2 hours, a solution of 1-bromo-2,6-difluorobenzene (3.1 g, 16.0 mmol) in 20 mL of anhydrous DMF was added dropwise over 15 minutes. The mixture was heated to 140°C and stirred for 24 hours, then cooled to room temperature. The reaction system was poured into ice water (2000 g), the white solid was filtered and dried in a vacuum oven, and then further purified by column chromatography using a mixed eluent of dichloromethane / petroleum ether (volume ratio 1:3) to obtain M1 (9.1 g) as a white solid with a yield of 80%. 1H NMR (500MHz, CDCl3) δ (ppm): 8.16 (d, J = 1.9 Hz, 4H), 7.67 (dd, J = 8.8, 6.6 Hz, 1H), 7.6 1(d,J=8.4Hz,2H),7.51(dd,J=8.6,1.9Hz,4H),7.12(d,J=8.6Hz,4H),1.47(s,36H). 13 C NMR (151 MHz, CDCl3) δ (ppm): 143.03, 139.66, 139.27, 130.86, 129.30, 125.83, 123.81, 123.38, 116.47, 109.40, 34.81, 32.07; Mass spectrum MALDI-TOF (m / z) [M + ]: The measured value is 711.5 and the theoretical value is 711.8.

[0025]

[0026] Synthesis of M2: Under nitrogen protection and an ice-water bath, a solution of tert-butyllithium (1.3 M tert-butyllithium in n-pentane, 19.4 mL, 25.2 mmol) in tert-butylbenzene (100 mL) was heated to 60°C and stirred for 2 hours. Boron tribromide (2.4 mL, 25.2 mmol) was then added at -30°C, and the reaction system was stirred at room temperature for another hour. Finally, N,N-diisopropylethylamine (3.5 mL, 25.2 mmol) was added at 0°C. The reaction system was stirred at 130°C for 6 hours and then cooled to room temperature. 5 mL of methanol was added to the reaction system to quench any residual boron tribromide. The mixture was extracted with 200 mL of water and 200 mL of dichloromethane. The organic layers were combined and concentrated in vacuo. The product was then purified by column chromatography using a mixture of dichloromethane and petroleum ether (1:20, by volume) as the eluent to afford M2 (2.1 g) as a yellow solid in a 26% yield. 1 H NMR (500MHz, CDCl3) δ (ppm): 9.12 (d, J = 1.8Hz, 2H), 8.46 (d, J = 1.7Hz, 2H), 8.38 (d, J = 8.8Hz, 2H), 8.3 3–8.24(m,4H),7.99(td,J=8.3,1.3Hz,1H),7.65(dd,J=8.7,2.1Hz,2H),1.67(s,18H),1.53(s,18H). 13C NMR (151 MHz, CDCl3) δ (ppm): 145.24, 144.58, 144.25, 141.54, 138.36, 132.99, 129.79, 127.05, 124.32, 123.65, 123.19, 121.56, 120.62, 117.22, 114.12, 107.93, 35.18, 34.81, 32.21, 31.88; Mass Spectrometry MALDI-TOF (m / z) [M + ]: The measured value is 640.5 and the theoretical value is 640.7.

[0027]

[0028] Synthesis of M3: Under nitrogen, the catalyst methoxy(cyclooctadiene)iridium(I) dimer (43.1 mg, 0.065 mmol) and 4,4'-di-tert-butyl-2,2'-bipyridine (34.9 mg, 0.13 mmol) were added to a solution of M2 (4.20 g, 6.5 mmol) and pinacol diboron (1.68 g, 6.6 mmol) in ultra-dry tetrahydrofuran (60 mL). The mixture was then sparged with nitrogen for 5 minutes, heated to reflux, and stirred for 24 hours. After cooling to room temperature, the reaction mixture was concentrated under reduced pressure and further purified by column chromatography using a mixture of dichloromethane and petroleum ether (1:20 by volume) to afford a yellow solid (4.50 g) in 90% yield. 1 H NMR (500MHz, CDCl3) δ (ppm): 9.14 (d, J = 1.9 Hz, 2H), 8.79 (s, 2H), 8.53 (d, J = 8.8 Hz, 2H), 8.48 (d, J = 1.8 Hz,2H),8.27(d,J=2.0Hz,2H),7.74(dd,J=8.8,2.1Hz,2H),1.67(s,18H),1.54(s,18H),1.49(s,12H). 13 C NMR (151 MHz, CDCl3) δ (ppm): 145.17, 144.55, 143.68, 141.64, 138.48, 129.77, 126.93, 124.59, 123.75, 121.65, 120.75, 117.10, 114.44, 113.77, 84.34, 35.18, 34.82, 32.21, 31.87, 25.09; Mass Spectrometry MALDI-TOF (m / z) [M + ]: The measured value is 766.8 and the theoretical value is 766.7.

[0029]

[0030] Synthesis of BN-1: Under nitrogen, 3-bromobenzothiophene (213 mg, 1 mmol), M3 (766 mg, 1 mmol), K2CO3 (2.76 g, 20 mmol), and Pd(PPh3)4 (23 mg, 0.02 mmol) were 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 12 hours. After cooling to room temperature, the reaction mixture was poured into water (100 mL) and extracted with dichloromethane and water. The organic layers were combined, concentrated in vacuo, and purified by column chromatography using a mixed eluent of dichloromethane / petroleum ether (volume ratio 1:10) to obtain BN-1 (500 mg) as a pale yellow solid in a 65% yield. 1 H NMR (500MHz, CDCl3) δ (ppm): 9.13 (s, 2H), 8.51 (d, J = 13.6Hz, 4H), 8.43 (s, 1H), 8.39 (d, J = 8.8Hz, 2H), 8.30 (d, J = 1.7Hz, 2H), 8.27–8.21(m,3H),8.08(s,1H),7.74–7.66(m,4H),7.58(t,J=7.3Hz,2H),7.44(t,J=7.4Hz,2H),1.69(s,18H),1.56(s,18H). 13 C NMR (126 MHz, CDCl3) δ (ppm): 145.61, 144.80, 141.87, 141.60, 140.12, 139.46, 138.05, 130.12, 129.68, 129.17, 128.89, 127.20, 126.56, 124.78, 124.05, 123.70, 121.56, 121.02, 120.79, 118.19, 117.45, 114.86, 114.14, 109.41, 106.25, 35.17, 34.84, 32.14, 31.81; Mass Spectrometry MALDI-TOF (m / z) [M + ]: The measured value is 907.1 and the theoretical value is 907.0.

[0031] Example 2: The preparation of BN-2 in this example is as follows:

[0032]

[0033] Synthesis of M4: SeO2 (11.0 g, 0.099 mol) was dissolved in 48% hydrobromic acid (43.0 mL, 0.4 mol) and stirred for 15 minutes. Phenylacetylene (5 g, 0.05 mol) and 2-cyclohexene-1-one (4.7 mL) were dissolved in 300 mL of dioxane and slowly added to the mixed solution of SeO2 and hydrobromic acid. The mixture was allowed to react overnight and quenched with water. The liquid was extracted with dichloromethane and concentrated to obtain a crude product, which was separated and purified by column chromatography using petroleum ether:dichloromethane (volume ratio 20:1) as the developing solvent to obtain M4 (6.60 g, yield: 70%) as a white solid. Mass spectrum MALDI-TOF (m / z) [M + ]: The measured value is 260.1 and the theoretical value is 260.0.

[0034]

[0035] Synthesis of BN-2: Under nitrogen protection, M4 (260 mg, 1 mmol), M3 (766 mg, 1 mmol), K2CO3 (2.76 g, 20 mmol), Pd(PPh3)4 (23 mg, 0.02 mmol) were mixed and added to a 100 mL flask. 20 mL of toluene and 10 mL of water were added, heated to 90 ° C and stirred for 12 hours. After cooling to room temperature, the reaction mixture was poured into water (100 mL) and extracted with dichloromethane and water. The organic layers were combined, concentrated in vacuo, and purified by column chromatography with a mixed eluent of dichloromethane / petroleum ether (volume ratio 1:10) to obtain BN-2 (450 mg) as a light yellow solid with a yield of 55%. 1 H NMR (500MHz, CDCl3) δ (ppm): 9.19 (s, 2H), 8.53 (t, J = 8.0Hz, 4H), 8.37 (d, J = 8.7Hz, 2H), 8.28 (dd, J = 14.1, 7.0Hz, 4H) ,8.14(d,J=7.9Hz,1H),7.62(d,J=8.7Hz,2H),7.55(t,J=7.5Hz,1H),7.52–7.46(m,1H),1.72(s,18H),1.54(s,18H); 13C NMR (126 MHz, CDCl3) δ (ppm): 145.42, 144.76, 144.53, 142.27, 141.74, 140.58, 138.32, 129.86, 127.52, 127.13, 126.36, 125.78, 124.85, 124.54, 123.70, 122.45, 121.72, 120.73, 117.29, 114.18, 108.61, 35.22, 34.81, 32.23, 31.83; Mass Spectrometry MALDI-TOF (m / z) [M + ]: The measured value is 819.7 and the theoretical value is 819.8.

[0036] The technical effects and advantages of the present invention are demonstrated and verified by applying the compound of the present invention to an organic electroluminescent device to test its actual performance.

[0037] Effect Example 1: Preparation of organic electroluminescent device BN-1

[0038] The following demonstrates and verifies the technical effects and advantages of the present invention by applying the compounds of the present invention to organic electroluminescent devices and testing their actual performance. The specific device preparation process and device performance testing experimental procedures are as follows: The device preparation process is as follows: Preparation of an indium tin oxide (ITO) conductive glass substrate: The substrate is 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 surface of the ITO conductive glass in a UV ozone cleaner for 40 minutes, it is transferred to a vacuum evaporation device (with a chamber pressure of <2×10 -4 Pa); on the anode ITO conductive glass, the hole injection layer HATCN is vacuum-deposited with a thickness of 6 nm; on the HATCN, the hole transport layer TAPC is vacuum-deposited with a thickness of 30 nm; on the TAPC, the exciton blocking layer TCTA is evaporated with a thickness of 5 nm; on the TCTA, the exciton blocking layer mCP is evaporated with a thickness of 5 nm; on the mCP, the organic light-emitting layer EML is evaporated with a thickness of 20 nm; on the organic light-emitting layer, the electron transport layer TmPyPB is evaporated with a thickness of 40 nm; on the TmPyPB, the electron injection layer LiF is evaporated with a thickness of 1 nm; on the LiF, the cathode Al is evaporated with a thickness of 100 nm.

[0039] The structure of the organic electroluminescent device BN-1 is as follows: ITO / HATCN (6nm) / TAPC (30nm) / TCTA (5nm) / mCP (5nm) / EML (20nm) / TmPyPB (40nm) / LiF (1nm) / Al (100nm), where EML represents the light-emitting layer, and the light-emitting layer is composed of a host material PhCzBCz with a mass percentage of 97% and a guest light-emitting material BN-1 with a mass percentage of 3%.

[0040] A DC voltage was applied to the organic electroluminescent device BN-1 prepared in this example, and the luminescence performance was evaluated using a Spectrascan PR655 luminance meter. The current-voltage characteristics were measured using a computer-controlled Keithley 2400 digital source meter. As luminescence characteristics, the electroluminescent spectrum, half-peak width, CIE color coordinates, external quantum efficiency (%), power efficiency (lm / W), and maximum brightness (cd / m2) were measured as a function of the applied DC voltage. 2 The detailed electroluminescent performance data of the device are listed in Table 1. The measured values ​​of the device are as follows: the spectral peak is 492nm, the half-peak width is 27nm, the CIE color coordinates are (0.09, 0.42), the maximum power efficiency is 81.1lm / W and the maximum brightness is 33123cd / m 2 , the maximum external quantum efficiency is 43.1%. When the brightness reaches 100cd / m 2 and 1000cd / m 2 When , the external quantum efficiency can still be maintained at 40.2% and 24.8%.

[0041] Effect Example 2: Preparation of organic electroluminescent device BN-2

[0042] The preparation method is the same as that of Example 1, except that the guest luminescent material BN-1 used in the luminescent layer is replaced by BN-2. The specific device structure is as follows: ITO / HATCN (6nm) / TAPC (30nm) / TCTA (5nm) / mCP (5nm) / EML (20nm) / TmPyPB (40nm) / LiF (1nm) / Al (100nm), where EML represents the luminescent layer, and the luminescent layer is composed of 97% by mass of the main material PhCzBCz and 3% by mass of the guest luminescent material BN-2.

[0043] A DC voltage was applied to the organic electroluminescent device BN-2 prepared in this example, and the luminescence performance was evaluated using a Spectrascan PR655 luminance meter. The current-voltage characteristics were measured using a computer-controlled Keithley 2400 digital source meter. As luminescence characteristics, the electroluminescent spectrum, half-peak width, CIE color coordinates, external quantum efficiency (%), power efficiency (lm / W), and maximum brightness (cd / m2) were measured as a function of the applied DC voltage. 2 The detailed electroluminescent performance data of the device are listed in Table 1. The measured values ​​of the device are as follows: the spectral peak is 492nm, the half-peak width is 28nm, the CIE color coordinates are (0.09, 0.43), the maximum power efficiency is 60.7lm / W and the maximum brightness is 61814cd / m 2 , the maximum external quantum efficiency is 36.9%. When the brightness reaches 100cd / m 2 and 1000cd / m 2 When the external quantum efficiency is 36.7% and 31.8%, the

[0044] Table 1: Data parameters of electroluminescent devices provided by the effect embodiment

[0045]

[0046] 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 multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution, the structural formula of which is shown below: ； Wherein R is S or Se.

2. Use of the multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution according to claim 1 in the preparation of an organic electroluminescent device.

3. Use of a multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution in the preparation of an organic electroluminescent device as claimed in claim 2, characterized in that: The organic electroluminescent device is composed of a cathode, an anode, and one or more organic layers between the two electrodes, at least one of the organic layers is an organic light-emitting layer, and the organic light-emitting layer is composed of a multi-resonance thermally activated delayed fluorescent material based on peripheral heavy atom substitution prepared according to claim 1 as a doping guest material and PhCzBCz as a doping host material, and the mass doping ratio of the guest material is 2-5%.

4. Use of a multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution in the preparation of an organic electroluminescent device as claimed in claim 3, characterized in that: The organic electroluminescent device consists of a transparent substrate, an ITO conductive film anode, a hole injection layer, a hole transport layer, an exciton blocking layer, an organic light-emitting layer, an electron transport layer, an electron injection layer and a cathode layer from bottom to top.

5. Use of a multi-resonance thermally activated delayed fluorescence material based on peripheral heavy atom substitution in the preparation of an organic electroluminescent device as claimed in claim 3 or 4, characterized in that: The electroluminescent device is used for preparing an organic electroluminescent display or an organic electroluminescent lighting source.

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