CN110627789B - Thermal activation delay fluorescent material, preparation method thereof and electroluminescent device - Google Patents

Thermal activation delay fluorescent material, preparation method thereof and electroluminescent device Download PDF

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CN110627789B
CN110627789B CN201910793645.8A CN201910793645A CN110627789B CN 110627789 B CN110627789 B CN 110627789B CN 201910793645 A CN201910793645 A CN 201910793645A CN 110627789 B CN110627789 B CN 110627789B
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activated delayed
thermally activated
delayed fluorescence
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罗佳佳
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Wuhan China Star Optoelectronics Semiconductor Display Technology Co Ltd
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Abstract

The invention discloses a thermal activation delayed fluorescent material, a preparation method thereof and an electroluminescent device. The invention synthesizes the thermal activation delayed fluorescent material with excellent luminous performance by connecting two electron donors on the basis of the pyridone structure, thereby improving the luminous efficiency of the OLED luminous device.

Description

Thermal activation delay fluorescent material, preparation method thereof and electroluminescent device
Technical Field
The invention relates to the technical field of organic light-emitting materials, in particular to a thermal activation delayed fluorescent material, a preparation method thereof and an electroluminescent device.
Background
At present, organic light-emitting diodes (OLEDs) are receiving wide attention due to their advantages of self-luminescence, high luminous efficiency, large viewing angle, fast response speed, low driving voltage, and being lighter and thinner. In an OLED light emitting device, a light emitting guest material playing a leading role is crucial, a light emitting guest material used in an early OLED is a fluorescent material, and since the exciton ratio of a singlet state to a triplet state in the OLED is 1:3, the theoretical Internal Quantum Efficiency (IQE) of the OLED based on the fluorescent material can only reach 25%, which greatly limits the application of the fluorescent electroluminescent device. The heavy metal complex phosphorescent material can simultaneously utilize singlet excitons and triplet excitons due to the spin-orbit coupling effect of heavy atoms, so that the quantum efficiency reaches 100%. However, the commonly used heavy metals are precious metals such as Ir and Pt, and the heavy metal complex phosphorescent materials have yet to be broken through in the aspect of blue light materials.
The Thermal Activation Delayed Fluorescence (TADF) material enables molecules to have smaller minimum single triplet energy level difference through ingenious molecular design, so that triplet excitons can return to a singlet state through reverse intersystem crossing and then jump to a ground state through radiation to emit light, and therefore the material can simultaneously utilize the singlet and triplet excitons and can also enable the quantum efficiency to reach 100%. For TADF materials, a fast reverse intersystem crossing constant and a high photoluminescence quantum yield are essential conditions for the preparation of high efficiency OLEDs. At present, the TADF material with the above conditions is still deficient relative to the heavy metal Ir complex.
In summary, the conventional OLED light-emitting material has low quantum efficiency, which results in low light-emitting efficiency of the OLED, and thus the light-emitting performance of the OLED is not good.
Disclosure of Invention
In view of this, the present invention provides a thermally activated delayed fluorescence material, a method for preparing the same, and an electroluminescent device, so as to solve the problem of poor light emitting performance of the conventional OLED.
In order to solve the above problems, the technical scheme provided by the invention is as follows:
the embodiment of the invention provides a thermal activation delayed fluorescent material, which has a chemical structure shown as the following formula:
Figure BDA0002180229920000021
wherein R is1And R2Are both chemical groups that are electron donors.
In an embodiment of the present invention, R is1And said R2Each selected from one of the following groups:
Figure BDA0002180229920000022
Figure BDA0002180229920000023
and
Figure BDA0002180229920000024
in one embodiment of the present invention, the thermally activated delayed fluorescence material has one selected from the following chemical structures:
Figure BDA0002180229920000031
and
Figure BDA0002180229920000032
the embodiment of the invention provides a preparation method of a thermal activation delayed fluorescent material, which comprises the following steps:
a step of preparing reaction liquid, which is to place a halogenated raw material, a compound containing an electron donor and a catalyst in a reaction vessel to obtain reaction liquid;
performing a target compound synthesis step of reacting the reaction solution at a temperature of 100 to 200 ℃ for 12 to 48 hours to obtain a mixed solution having a target compound therein;
performing an extraction step, cooling the mixed solution to room temperature, and extracting the target compound in the mixed solution; and
and performing a target compound purification treatment step, and separating and purifying the target compound to obtain the thermally activated delayed fluorescence material, wherein the thermally activated delayed fluorescence material has a chemical structure shown as the following formula:
Figure BDA0002180229920000033
wherein R is1And R2Are both chemical groups of the electron donor.
In an embodiment of the present invention, R is1And said R2Each selected from one of the following groups:
Figure BDA0002180229920000034
Figure BDA0002180229920000041
Figure BDA0002180229920000042
and
Figure BDA0002180229920000043
in one embodiment of the present invention, the thermally activated delayed fluorescence material has one selected from the following chemical structures:
Figure BDA0002180229920000044
and
Figure BDA0002180229920000045
in one embodiment of the invention, the catalyst comprises palladium acetate, tri-tert-butylphosphine tetrafluoroborate and sodium tert-butoxide.
In one embodiment of the invention, the molar ratio of halogenated starting material to electron donor-containing compound is between 1:2 to 1:3, or more; the molar ratio of the halogenated raw material to the palladium acetate is 1: 0.02 to 1: between 0.1; the molar ratio of halogenated starting material to tri-tert-butylphosphine tetrafluoroborate is between 1: 0.1 to 1: between 0.3; and the molar ratio of the halogenated raw material to the sodium tert-butoxide is 1:2 to 1:3, or less.
In one embodiment of the present invention, the target compound purification treatment step comprises: purifying the target compound by a silica gel column chromatography method by using a developing agent to obtain the heat-activated delayed fluorescence material.
An embodiment of the present invention provides an electroluminescent device, including:
a substrate layer;
a hole injection layer disposed on the substrate layer;
the hole transport layer is arranged on the hole injection layer;
a light emitting layer disposed on the hole transport layer;
an electron transport layer disposed on the light emitting layer; and
a cathode layer disposed on the electron transport layer,
wherein the material of the light emitting layer comprises the thermally activated delayed fluorescence material of any of the embodiments described above.
The invention has the beneficial effects that: the invention synthesizes the thermal activation delayed fluorescent material with excellent luminous performance by connecting two electron donors on the basis of the pyridone structure, thereby improving the luminous efficiency of the OLED luminous device.
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FIG. 1 is a flowchart of a method for preparing a thermally activated delayed fluorescence material according to an embodiment of the present invention.
Fig. 2 is a schematic cross-sectional view of an electroluminescent device according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments refers to the accompanying drawings for illustrating the specific embodiments in which the invention may be practiced. Furthermore, directional phrases used herein, such as, for example, upper, lower, top, bottom, front, rear, left, right, inner, outer, lateral, peripheral, central, horizontal, lateral, vertical, longitudinal, axial, radial, uppermost or lowermost, etc., refer only to the orientation of the attached drawings. Accordingly, the directional terms used are used for explanation and understanding of the present invention, and are not used for limiting the present invention.
The thermally activated delayed fluorescence material of the embodiment of the invention has a chemical structure shown as the following formula:
Figure BDA0002180229920000051
wherein R is1And R2Are both chemical groups that are electron donors.
In one embodiment, the thermally activated delayed fluorescence material of the embodiments of the present invention is synthesized by linking two electron donors based on a pyridone structure.
In one embodiment, R is1And said R2Each selected from one of the following groups:
Figure BDA0002180229920000061
Figure BDA0002180229920000062
and
Figure BDA0002180229920000063
in one embodiment, the thermally activated delayed fluorescence material has one selected from the following chemical structures:
Figure BDA0002180229920000064
and
Figure BDA0002180229920000065
the thermal activation delayed fluorescent material provided by the embodiment of the invention is synthesized by connecting two electron donors on the basis of a pyridone structure, so that the thermal activation delayed fluorescent material with excellent luminous performance is synthesized, the luminous efficiency of an OLED (organic light emitting diode) luminous device is improved, and specific experimental data are described in the paragraph at the back.
Referring to fig. 1, the present embodiment further provides a method 10 for preparing a thermally activated delayed fluorescence material, including steps 11 to 14: a step of preparing a reaction solution, in which a halogenated raw material, an electron donor-containing compound and a catalyst are placed in a reaction vessel to obtain a reaction solution (step 11); performing a target compound synthesis step of reacting the reaction solution at a temperature of 100 to 200 ℃ for 12 to 48 hours to obtain a mixed solution having the target compound therein (step 12); performing an extraction step of cooling the mixed solution to room temperature to extract the target compound in the mixed solution (step 13); and performing a target compound purification treatment step, separating and purifying the target compound to obtain the thermally activated delayed fluorescence material, wherein the thermally activated delayed fluorescence material has a chemical structure shown in the following formula 1, wherein R is1And R2Are both chemical groups of the electron donor (step 14).
Figure BDA0002180229920000071
Referring to fig. 2, the present embodiment further provides an electroluminescent device 20, including: a substrate layer 21; a hole injection layer 22 disposed on the substrate layer 21; a hole transport layer 23 disposed on the hole injection layer 22; a light-emitting layer 24 provided on the hole transport layer 23; an electron transport layer 25 disposed on the light emitting layer 24; and a cathode layer 26 disposed on the electron transport layer 25, wherein the light emitting layer 24 comprises the thermally activated delayed fluorescence material according to any of the embodiments.
Example 1:
firstly, a reaction solution preparation step is carried out, and a halogenated raw material, an electron donor-containing compound and a catalyst are placed in a reaction vessel to obtain a reaction solution. In one embodiment, the halogen in the halogenated starting material may comprise any one of fluorine, chlorine, bromine, iodine and . In another embodiment, the halogenated starting material comprises a pyridone structure. In one example, the chemical structure of the halogenated starting material, such as bromine, is described by the following formula:
Figure BDA0002180229920000072
in example 1, the electron donor-containing compound was diphenylamine, and the catalyst contained palladium acetate (Pd (OAc)2) Tri-tert-butylphosphine tetrafluoroborate ((t-Bu)3HPBF4) And sodium tert-butoxide (NaOt-Bu). In one example, the molar ratio of halogenated starting material to electron donor-containing compound is between 1:2 to 1:3, or more; the molar ratio of the halogenated raw material to the palladium acetate is 1: 0.02 to 1: between 0.1; the molar ratio of halogenated starting material to tri-tert-butylphosphine tetrafluoroborate is between 1: 0.1 to 1: between 0.3; and the molar ratio of the halogenated raw material to the sodium tert-butoxide is 1:2 to 1:3, or less. In example 1, 5mmol of a halogenated raw material, 12mmol of diphenylamine, 0.4mmol of palladium acetate, and 1.2mmol of tri-tert-butylphosphine tetrafluoroborate were put into a reaction vessel (e.g., a two-necked bottle), followed by adding 12mmol of sodium tert-butoxide to the reaction vessel in a glove box 1 and under an argon atmosphere to obtain a reaction liquid.
Then, a target compound synthesis step is performed, and the reaction solution is reacted at a temperature of 100 to 200 ℃ for 12 to 48 hours to obtain a mixed solution having the target compound therein. In one embodiment, the target compound synthesis step may be performed under an argon atmosphere, and toluene (about 100 ml) from which moisture and oxygen are previously removed may be added to the reaction vessel. In another embodiment, the target compound synthesis step is a reaction carried out at a temperature of about 120 ℃ for about 24 hours.
And then carrying out an extraction step, cooling the mixed solution to room temperature, and extracting the target compound in the mixed solution. Adding the mixed solution to ice water (e.g., 200 ml); it was extracted three more times with dichloromethane to give an organic phase which was spun into silica gel.
And then carrying out a target compound purification treatment step, and separating and purifying the target compound to obtain the thermally activated delayed fluorescent material, wherein the thermally activated delayed fluorescent material has a chemical structure shown as the following formula:
Figure BDA0002180229920000081
in one embodiment, the target compound purification treatment step comprises: purifying the target compound by a silica gel column chromatography method by using a developing agent to obtain the heat-activated delayed fluorescence material. In one example, the target compound purification treatment step includes solid-liquid separation by a silica gel column chromatography method in which a eluent, for example, includes dichloromethane and n-hexane, wherein the volume ratio of dichloromethane to n-hexane is, for example, 1:2, to give 2.1 g of light blue powder with a yield of 62%, and the mass spectrum is characterized by ms (ei) m/z: 680.21.
It is worth mentioning that the synthetic route of example 1 can be illustrated by the following formula.
Figure BDA0002180229920000091
Next, various data analyses were performed on example 1, and the characteristic parameters obtained were as shown in table 1 below. Table 1 shows the measured PL peak (PL peak) and lowest singlet state (S) of example 11) Lowest triplet energy level (T)1) Highest Occupied Molecular Orbital (Highest Occupied Molecular Orbital; HOMO) and the Lowest unoccupied molecular Orbital (Lowest unoccupied molecular Orbital; LUMO), and the like.
TABLE 1
Figure BDA0002180229920000092
Theoretical simulation calculation is performed on the molecules of the thermally activated delayed fluorescent material in this embodiment 1, the energy level of the lowest singlet state is 2.57eV, the energy level of the lowest triplet state is 2.40eV, and the energy level difference between the two is small, so that triplet excitons can return to the singlet state through the cross-over between the reverse systems, and further the quantum efficiency reaches 100%.
The wavelength of photoluminescence of the thermal activation delayed fluorescent material in a toluene solution has a peak value (namely PL peak) around 483 nm at room temperature, which shows that the thermal activation delayed fluorescent material in this embodiment can be used in the field of blue OLEDs.
Next, an electroluminescent device according to an embodiment of the present invention was fabricated, wherein the material of the light-emitting layer of the electroluminescent device was the thermally activated delayed fluorescence material according to embodiment 1. The manufacturing method of the electroluminescent device comprises the following steps: sequentially evaporating a hole injection layer (MoO) on a cleaned conductive glass (ITO) substrate under a high vacuum condition3) A hole transport layer (TCTA), the thermally activated delayed fluorescence material (DPEPO) of example 1, an electron transport layer (1,3, 5-tris (3- (3-pyridyl) phenyl) benzene; tm3PyPB), and a cathode layer (1nm LiF and 100nm Al). The device shown in fig. 2 is manufactured by the method, and the structure of each specific device is as follows:
ITO/MoO3(2nm)/TCTA (35 nm)/example 1 (DPEPO; 10% 20nm)/Tm3PyPB (40nm)/LiF (1nm)/Al (100 nm).
Further, performance measurements were performed on the above electroluminescent device, wherein the current-luminance-voltage characteristics of the device were measured by a Keithley source measurement system (Keithley2400source meter, Keithley 2000Currentmeter) with a calibrated silicon photodiode, and the electroluminescence spectra were measured by a SPEX CCD3000 spectrometer, JY, france, all in a room temperature atmosphere. The performance data for the devices described therein are shown in table 2 below.
TABLE 2
Figure BDA0002180229920000101
As can be seen from table 2 above, the maximum current efficiency of the electroluminescent device using the thermally activated delayed fluorescence material prepared in example 1 as the material of the light emitting layer of the electroluminescent device was 29.3cd/a, and the maximum external quantum efficiency was 24.3%. In addition, the electroluminescent device of example 1 has high luminous efficiency and brightness, high manufacturing efficiency, and long service life.
Example 2:
example 2 was prepared in a manner substantially similar to example 1, except that the electron donor-containing compound used was carbazole. After the purification treatment step of the objective compound was carried out, 2.4 g of pale blue powder was obtained in 71% yield, and the mass spectrum was characterized by MS (EI) m/z: 676.23.
The synthetic route of example 2 can be illustrated by the following formula.
Figure BDA0002180229920000111
Next, various data analyses were performed on example 2, and the characteristic parameters obtained were as shown in table 3 below.
TABLE 3
Figure BDA0002180229920000112
Theoretical simulation calculation is performed on the molecules of the thermally activated delayed fluorescent material in this embodiment 2, the energy level of the lowest singlet state is 2.75eV, the energy level of the lowest triplet state is 2.69eV, and the energy level difference between the two is small, so that triplet excitons can return to the singlet state through the cross between the reverse systems, and further the quantum efficiency reaches 100%.
The wavelength of photoluminescence of the thermally activated delayed fluorescent material in a toluene solution has a peak value (i.e., PL peak) around 452 nm at room temperature, which illustrates that the thermally activated delayed fluorescent material in this embodiment can be used in the field of blue OLEDs.
Next, an electroluminescent device according to an embodiment of the present invention is manufactured, wherein a material of a light-emitting layer of the electroluminescent device is the thermally activated delayed fluorescence material according to embodiment 2. The manufacturing method of the electroluminescent device comprises the following steps: sequentially evaporating air on a cleaned conductive glass (ITO) substrate under a high vacuum conditionHole injection layer (MoO)3) A hole transport layer (TCTA), the thermally activated delayed fluorescence material (DPEPO) of example 2, an electron transport layer (1,3, 5-tris (3- (3-pyridyl) phenyl) benzene; tm3PyPB), and a cathode layer (1nm LiF and 100nm Al). The device shown in fig. 2 is manufactured by the method, and the structure of each specific device is as follows:
ITO/MoO3(2nm)/TCTA (35 nm)/example 2 (DPEPO; 10% 20nm)/Tm3PyPB (40nm)/LiF (1nm)/Al (100 nm).
Further, performance measurements were performed on the above electroluminescent device, wherein the current-luminance-voltage characteristics of the device were measured by a Keithley source measurement system (Keithley2400source meter, Keithley 2000Currentmeter) with a calibrated silicon photodiode, and the electroluminescence spectra were measured by a SPEX CCD3000 spectrometer, JY, france, all in a room temperature atmosphere. The performance data for the devices described therein are shown in table 4 below.
TABLE 4
Figure BDA0002180229920000121
As can be seen from table 4 above, the maximum current efficiency of the electroluminescent device using the thermally activated delayed fluorescence material prepared in example 2 as the material of the light emitting layer of the electroluminescent device was 18.3cd/a, and the maximum external quantum efficiency was 20.6%. In addition, the electroluminescent device of embodiment 2 has high luminous efficiency and brightness, high manufacturing efficiency, and long service life.
Example 3:
example 3 was prepared in a manner substantially similar to example 1, except that the electron donor-containing compound used was 9, 9' -dimethylacridine. After the purification treatment step of the objective compound was carried out, 2.5 g of pale blue powder was obtained in 66% yield, and the mass spectrum was characterized by MS (EI) m/z: 760.22.
The synthetic route of example 3 can be illustrated by the following formula.
Figure BDA0002180229920000122
Next, various data analyses were performed on example 3, and the characteristic parameters obtained were as shown in table 5 below.
TABLE 5
Figure BDA0002180229920000123
Theoretical simulation calculation is performed on the molecules of the thermally activated delayed fluorescent material in this embodiment 3, the energy level of the lowest singlet state is 2.70eV, the energy level of the lowest triplet state is 2.66eV, and the energy level difference between the two is small, so that triplet excitons can return to the singlet state through the cross between the reverse systems, and further the quantum efficiency reaches 100%.
The wavelength of photoluminescence of the thermally activated delayed fluorescent material in a toluene solution has a peak value (i.e., PL peak) around 460 nm at room temperature, which illustrates that the thermally activated delayed fluorescent material in this embodiment can be used in the field of blue OLEDs.
Next, an electroluminescent device according to an embodiment of the present invention is fabricated, wherein a material of a light-emitting layer of the electroluminescent device is the thermally activated delayed fluorescence material according to embodiment 3. The manufacturing method of the electroluminescent device comprises the following steps: sequentially evaporating a hole injection layer (MoO) on a cleaned conductive glass (ITO) substrate under a high vacuum condition3) A hole transport layer (TCTA), the thermally activated delayed fluorescence material (DPEPO) of example 3, an electron transport layer (1,3, 5-tris (3- (3-pyridyl) phenyl) benzene; tm3PyPB), and a cathode layer (1nm LiF and 100nm Al). The device shown in fig. 2 is manufactured by the method, and the structure of each specific device is as follows:
ITO/MoO3(2nm)/TCTA (35 nm)/example 3 (DPEPO; 10% 20nm)/Tm3PyPB (40nm)/LiF (1nm)/Al (100 nm).
Further, performance measurements were performed on the above electroluminescent device, wherein the current-luminance-voltage characteristics of the device were measured by a Keithley source measurement system (Keithley2400source meter, Keithley 2000Currentmeter) with a calibrated silicon photodiode, and the electroluminescence spectra were measured by a SPEX CCD3000 spectrometer, JY, france, all in a room temperature atmosphere. The performance data for the devices described therein are shown in table 6 below.
TABLE 6
Figure BDA0002180229920000131
As can be seen from table 6 above, the maximum current efficiency of the electroluminescent device using the thermally activated delayed fluorescence material prepared in example 3 as the material of the light emitting layer of the electroluminescent device was 25.2cd/a, and the maximum external quantum efficiency was 22.3%. In addition, the electroluminescent device of example 3 has high luminous efficiency and brightness, high manufacturing efficiency, and long service life.
According to the invention, the two electron donors are connected on the basis of the pyridone structure to synthesize the thermal activation delayed fluorescent material with excellent luminescence property, so that the luminescence efficiency of the OLED luminescent device is improved, the quantum efficiency can reach 100%, and the material can be used in the field of blue-light OLEDs. In addition, when the thermally activated delayed fluorescence material of the embodiment of the invention is applied to the light emitting layer of the electroluminescent device, the electroluminescent device has good light emitting performance (for example, the highest current efficiency and the maximum external quantum efficiency). Furthermore, through the matching of different electron donor species, blue TADF materials with significant TADF characteristics can be designed.
The present invention has been described in relation to the above embodiments, which are only exemplary of the implementation of the present invention. It must be noted that the disclosed embodiments do not limit the scope of the invention. Rather, modifications and equivalent arrangements included within the spirit and scope of the claims are included within the scope of the invention.

Claims (8)

1. A thermally activated delayed fluorescence material, characterized in that: the thermally activated delayed fluorescence material has a chemical structure shown as the following formula:
Figure FDA0002641221230000011
wherein R is1And R2Are each selected from the followingOne of the groups:
Figure FDA0002641221230000012
Figure FDA0002641221230000013
and
Figure FDA0002641221230000014
2. the thermally activated delayed fluorescence material of claim 1, wherein: the thermally activated delayed fluorescence material has one selected from the following chemical structures:
Figure FDA0002641221230000015
and
Figure FDA0002641221230000016
3. a preparation method of a thermally activated delayed fluorescent material is characterized by comprising the following steps: the preparation method of the thermal activation delayed fluorescence material comprises the following steps:
a step of preparing reaction liquid, which is to place a halogenated raw material, a compound containing an electron donor and a catalyst in a reaction vessel to obtain reaction liquid;
performing a target compound synthesis step of reacting the reaction solution at a temperature of 100 to 200 ℃ for 12 to 48 hours to obtain a mixed solution having a target compound therein;
performing an extraction step, cooling the mixed solution to room temperature, and extracting the target compound in the mixed solution; and
and performing a target compound purification treatment step, and separating and purifying the target compound to obtain the thermally activated delayed fluorescence material, wherein the thermally activated delayed fluorescence material has a chemical structure shown as the following formula:
Figure FDA0002641221230000021
wherein R is1And R2Each selected from one of the following groups:
Figure FDA0002641221230000022
Figure FDA0002641221230000031
and
Figure FDA0002641221230000032
4. the method for preparing a thermally activated delayed fluorescence material according to claim 3, wherein: the thermally activated delayed fluorescence material has one selected from the following chemical structures:
Figure FDA0002641221230000033
and
Figure FDA0002641221230000034
5. the method for preparing a thermally activated delayed fluorescence material according to claim 3, wherein: the catalyst comprises palladium acetate, tri-tert-butylphosphine tetrafluoroborate and sodium tert-butoxide.
6. The method for preparing a thermally activated delayed fluorescence material according to claim 5, wherein: the molar ratio of halogenated starting material to compound containing electron donor is between 1:2 to 1:3, or more; the molar ratio of the halogenated raw material to the palladium acetate is 1: 0.02 to 1: between 0.1; the molar ratio of halogenated starting material to tri-tert-butylphosphine tetrafluoroborate is between 1: 0.1 to 1: between 0.3; and the molar ratio of the halogenated raw material to the sodium tert-butoxide is 1:2 to 1:3, or less.
7. The method for preparing a thermally activated delayed fluorescence material according to claim 3, wherein: the target compound purification treatment step comprises: purifying the target compound by a silica gel column chromatography method by using a developing agent to obtain the heat-activated delayed fluorescence material.
8. An electroluminescent device, comprising:
a substrate layer;
a hole injection layer disposed on the substrate layer;
the hole transport layer is arranged on the hole injection layer;
a light emitting layer disposed on the hole transport layer;
an electron transport layer disposed on the light emitting layer; and
a cathode layer disposed on the electron transport layer,
wherein the material of the light emitting layer contains the thermally activated delayed fluorescence material according to any one of claims 1 to 2.
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