WO2020220414A1 - Thermally activated delayed fluorescence material and preparation method therefor, and display device - Google Patents

Abstract

Provided are a thermally activated delayed fluorescence material and a preparation method therefor, and a display device. The thermally activated delayed fluorescence material comprises an electron donor and an electron acceptor, wherein the electron donor comprises at least two benzene rings and a seven-membered ring connected between the two benzene rings. The preparation method involves simple processes, easy purification and produces a high yield. A luminescent layer in the display device contains the thermally activated delayed fluorescence material.

Description

Thermally activated delayed fluorescent material, preparation method thereof and display device Technical field

The invention relates to the technical field of organic electroluminescent materials, in particular to a thermally activated delayed fluorescent material, a preparation method thereof, and a display device.

Background technique

Organic electroluminescence is a kind of luminescence phenomenon realized by the use of organic materials under the excitation of external electric field and current.

In 1963, Pope et al. of New York University in the United States first observed organic electroluminescence with single crystal anthracene as the light-emitting layer under a driving voltage of 100V. However, due to defects such as low luminous efficiency and excessive driving voltage, it did not cause widespread attention. Until 1987, CWTang and others of Kodak Company of the United States used vacuum evaporation technology to use aromatic diamine as the hole transport layer, 8-hydroxyquinoline aluminum (Alq3) as the electron transport layer and the new type of light-emitting layer. The layered OLED (Organic Light-Emitting Diode, organic light-emitting diode) structure has achieved higher brightness, higher external quantum efficiency and lower driving voltage, which has stimulated great interest in the research of OLED by scientific researchers. It is possible to realize commercialization.

In recent years, due to its active light emission, large viewing angle, fast corresponding speed, wide temperature adaptation range, low driving voltage, low power consumption, high brightness, simple production process, light and thin, and flexible display, OLED displays And the lighting field shows great application prospects, attracting the attention of scientific researchers and companies. In OLED, the pros and cons of light-emitting layer materials are decisive for the industrialization of OLED. The usual luminescent layer material consists of host and guest luminescent materials, and the luminous efficiency and lifetime of luminescent materials are two important indicators of the quality of luminescent materials. Early OLED light-emitting materials were traditional fluorescent materials. Since the ratio of singlet and triplet excitons in OLED is 1:3, while traditional fluorescent materials can only use singlet excitons to emit light, the OLED theory of traditional fluorescent materials The internal quantum efficiency is 25%. Due to the spin-orbit coupling effect of heavy atoms, metal complex phosphorescent materials can achieve 100% utilization of singlet excitons and triplet excitons, and are now also used in red and green OLED displays. However, phosphorescent materials usually use heavy metals such as iridium (Ir), platinum (Pt), osmium (Os) and other precious metals, which are not only costly, but also more toxic. In addition, efficient and long-life phosphorescent metal complex materials are still a great challenge.

In 2012, Adachi et al. proposed a pure organic light-emitting molecule with a "Thermally Activated Delayed Fluorescence" (TADF) mechanism. Through reasonable DA structure molecular design, the molecule has a smaller minimum singlet state and triplet energy. Level difference (ΔEST), so that the triplet excitons can return to the singlet state through RISC, and then radiate to the ground state to emit light, so that single and triplet excitons can be used at the same time to realize excitons The utilization rate of 100%, without the participation of heavy metals. In addition, the TADF material has a rich structure design, and most of its physical properties are easily adjusted to obtain high-efficiency and long-life organic light-emitting materials that meet the requirements.

For TADF materials, especially red light materials, due to the large plane acceptor structure, the π-π stacking between molecules is serious, and the π-π stacking easily causes the material to aggregate, leading to luminescence quenching. The usual solution is to suppress the aggregation of materials to quench the luminescence phenomenon by doping. However, the phenomenon of aggregation and quenching still exists after the general molecular doping, and the doping ratio of the luminescent material is small, which will reduce the efficiency of the device. .

technical problem

The purpose of the present invention is to provide a thermally activated delayed fluorescent material, a preparation method thereof, and a display device to solve the problem of serious accumulation of π-π between molecules in the thermally activated delayed fluorescent material in the prior art, and electron acceptor and electron donor The highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) between the two have a high degree of overlap, and the difference between the lowest singlet and triplet energy levels is too large, resulting in luminescence quenching Phenomenon, the low working efficiency of the display device.

Technical solutions

To achieve the above objective, the present invention provides a thermally activated delayed fluorescent material, which includes an electron donor and an electron acceptor. Wherein, the electron donor includes at least two benzene rings and a seven-membered ring connected between the two benzene rings.

Further, the molecular structure of the electron donor includes one of the following structures:

Further, the molecular structure of the electron acceptor includes one of the following structures:

The present invention also provides a method for preparing thermally activated delayed fluorescent material, which includes the following steps:

Synthesis of the first target: placing the electron donor, the electron acceptor, and the catalyst in a reaction vessel to obtain a reaction solution, fully reacting in an argon atmosphere to obtain a mixed solution, and the mixed solution contains the target produced by the reaction.

Extracting the first target: cooling the mixed solution to room temperature, and extracting the target in the mixed solution.

Purifying the first target: purifying the target to obtain the near-infrared photothermal activated delayed fluorescent material.

Further, in the step of synthesizing the first target, the catalyst is toluene, potassium carbonate and palladium tetrakistriphenylphosphine. The electron acceptor, the electron donor, the toluene and the potassium carbonate are placed together in the reaction vessel, and then the reaction vessel is placed in an argon atmosphere, and the reaction vessel is added The palladium tetrakistriphenylphosphorus is used to obtain a reaction solution.

Further, the step of extracting the target substance includes adding dichloromethane to the reaction solution for extraction, and drying after multiple extractions to obtain the target substance.

Further, the step of purifying and treating the target substance includes using an eluent to purify the target substance for the first time by a silica gel column chromatography method to obtain the thermally activated delayed fluorescence material. Wherein, the eluent in the silica gel column chromatography method is petroleum ether and dichloromethane, and the volume ratio of the petroleum ether and the dichloromethane is 1:1.

Further, before the step of synthesizing the first target, it further includes a step of forming an electron donor. The step of forming an electron donor includes the following steps:

Synthesis of the second target: placing the first compound, the second compound and the catalyst in a reaction vessel to obtain a reaction solution, and fully react in an argon atmosphere to obtain a mixed solution, and the mixed solution contains the target produced by the reaction.

Extracting the second target: cooling the mixed solution to room temperature, and extracting the target in the mixed solution.

Purifying the second target: purifying the target to obtain a third compound having the electron donor structure.

Wherein, the structure of the first compound has at least two benzene rings and a seven-membered ring connected between the two benzene rings. The second compound has at least one benzene ring in its structure.

Further, the catalyst is tris(dibenzylideneacetone) dipalladium, tri-tert-butylphosphine·tetrafluoroborate, sodium tert-butoxide and toluene.

The present invention also provides a display device, which includes a substrate, a first electrode layer, an injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a second electrode layer. The first electrode layer is provided on the substrate. The injection layer is provided on the first electrode layer. The hole transport layer is provided on the injection layer. The light-emitting layer is provided on the hole transport layer. The electron transport layer is provided on the light-emitting layer. The second electrode layer is provided on the electron transport layer. Wherein, the light-emitting layer includes the thermally activated delayed fluorescent material as described above.

Further, the material of the injection layer is 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene. The material of the hole transport layer is 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline]. Therefore, the material of the electron transport layer is 1,3,5-tris(3-(3-pyridyl)phenyl)benzene.

Beneficial effect

The advantages of the present invention are: a thermally activated delayed fluorescent material in the present invention, the two benzene rings in its molecular structure are connected by a saturated seven-membered ring, which can effectively inhibit the π-π stacking between molecules, thereby obtaining high Photoluminescence quantum efficiency (PLQY), and its electron donating ability is between diphenylamine and acridine, which can effectively reduce the overlap of HOMO and LUMO between the electron acceptor and the electron donor, and obtain the lowest singlet and The thermally activated delayed fluorescent material with a small triple energy level difference greatly reduces the phenomenon of luminescence quenching and improves the working efficiency of the display device.

The preparation method of the thermally activated delayed fluorescent material in the present invention has simple process, easy purification and high yield.

In a display device of the present invention, the light-emitting layer contains the thermally activated delayed fluorescent material, so that the fluorescent efficiency of the light-emitting layer is higher and the stability is better, thereby also improving the luminous efficiency and service life of the display device.

Description of the drawings

Fig. 1 is a preparation process of thermally activated delayed fluorescent material in an embodiment of the present invention;

Figure 2 is a preparation process of the step of forming an electron donor in an embodiment of the present invention;

Figure 3 is a fluorescence emission spectrum of a thermally activated delayed fluorescent material in an embodiment of the present invention;

FIG. 4 is a layered structure diagram of a display device in an embodiment of the present invention.

The components in the figure are represented as follows:

Display device 100;

Substrate 101; First electrode layer 102;

Injection layer 103; Hole transport layer 104;

Light emitting layer 105; Electron transport layer 106;

The second electrode layer 107.

Embodiments of the invention

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in the specification, so as to fully introduce the technical content of the present invention to those skilled in the art, so as to demonstrate that the present invention can be implemented by examples, so that the technical content disclosed by the present invention is clearer and the present invention Those skilled in the art can more easily understand how to implement the present invention. However, the present invention can be embodied by many different forms of embodiments. The protection scope of the present invention is not limited to the embodiments mentioned in the text, and the description of the following embodiments is not intended to limit the scope of the present invention.

The terms "first", "second", "third", etc. (if any) in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and not necessarily used to describe a specific order Or precedence. It should be understood that the objects described in this way can be interchanged under appropriate circumstances.

The terms used in the specification of the present invention are only used to describe specific embodiments, and are not intended to show the concept of the present invention. Unless there is a clearly different meaning in the context, the expression used in the singular form encompasses the expression in the plural form. In the specification of the present invention, it should be understood that terms such as "including", "having" and "containing" are intended to indicate the possibility of the features, numbers, steps, actions or combinations thereof disclosed in the specification of the present invention, but not The possibility that one or more other features, numbers, steps, actions or combinations thereof may exist or may be added is excluded.

The context has clear hints to the contrary, otherwise all the steps of the methods described in this article can be executed in any appropriate order. The changes of the present invention are not limited to the described sequence of steps. Unless otherwise claimed, any and all examples or exemplary language (for example, "for example") provided herein are only used to better illustrate the concept of the present invention, and not to limit the scope of the concept of the present invention. Without departing from the spirit and scope, those skilled in the art will easily understand various modifications and adaptations.

The molecular structure of the thermally activated delayed fluorescent material provided in the embodiment of the present invention is a D-A structure formed by the reaction of an electron donor (D) and an electron acceptor (A). Wherein, the molecular structure of the electron donor (D) includes at least two benzene rings and a seven-membered ring connected between the two benzene rings, and its molecular structure includes one of the following structures:

The molecular structure of the electron acceptor (A) includes one of the following structures:

Through the arrangement and combination of the electron donor (D) and the electron acceptor (A) including the above-mentioned structure, a total of 24 kinds of thermally activated delayed fluorescent materials of DA structure can be combined, and the thermally activated delayed fluorescent materials are used as luminescent guests. Applied in organic electroluminescent devices, organic electroluminescent devices with higher efficiency and performance can be prepared.

The embodiment of the present invention also provides a method for preparing the thermally activated delayed fluorescent material. In this embodiment, the compound with the electron donor (D) is 5-(4-bromophenyl)-5H-dibenzo[b,f]cycloheximide, which has the electron acceptor The compound of (A) is 2-(4,4,5,5-tetramethyl-1,3,2-1,3,2-dioxoborolan-2-yl)-anthraquinone, the The molecular structural formula of the target thermally activated delayed fluorescent material prepared by the preparation method is:

The thermally activated delayed fluorescent material of this molecular structure is one of the above 24 kinds of thermally activated delayed fluorescent materials of D-A structure. The preparation process is shown in Figure 1, and the specific preparation steps are as follows:

Step S10) Forming an electron donor (D): The first compound iminodibenzyl and the second compound p-bromoiodobenzene react under the action of a catalyst to synthesize the compound 5-(4-bromo) having an electron donor (D) Phenyl)-5H-dibenzo[b,f]cycloheximine.

Step S20) Synthesis of the first target: in a 250mL three-necked flask, add 5-(4-bromophenyl)-5H-dibenzo[b,f]cyclohexanimine (3.49g, 10mmol), 2 -(4,4,5,5-tetramethyl-1,3,2-1,3,2-dioxoborolan-2-yl)-anthraquinone (3.34g, 10mmol), 50mL of toluene And 20mL of 2.5M potassium carbonate aqueous solution, and use argon for pumping. Then, palladium tetrakistriphenylphosphorus (0.72 g, 0.6 mmol) is added, and the reaction solution is fully reacted in an argon atmosphere to obtain a mixed solution, and the mixed solution contains the first target produced by the reaction.

Step S30) Extract the first target; after the mixed solution is cooled to room temperature, it is extracted three times with dichloromethane and washed three times with water, and then the extract obtained after three extractions is dried and filtered with anhydrous sodium sulfate and spin-dried to obtain The first target.

Step S40) Purify the first target; use 200-300 mesh silica gel column chromatography, and use petroleum ether and dichloromethane (volume ratio of 1:1) as eluents to separate and purify the product, and finally obtain 4.05 g The delayed fluorescent material is thermally activated, and the yield is 85%.

The preparation process is shown in formula 1:

In this embodiment, the compound with the electron donor (D) used is 5-(4-bromophenyl)-5H-dibenzo[b,f]cycloheximine, which has an electron acceptor The compound of body (A) is 2-(4,4,5,5-tetramethyl-1,3,2-1,3,2-dioxoborolan-2-yl)-anthraquinone, but It is not limited to these two compounds. In other embodiments of the present invention, it can also be other compounds, but the preparation methods are basically the same, so they are not listed here.

In the step of forming an electron donor (D), the first compound and the second compound are reacted to synthesize a compound with an electron donor (D) under the action of a catalyst. The preparation process of the step of forming an electron donor is as follows As shown in Figure 2, the specific preparation steps are as follows:

Step S11) Synthesis of the second target: In a 100mL Schlenk bottle, add iminodibenzyl (1.95g, 10mmol), p-bromoiodobenzene (4.24g, 10mmol), tris(dibenzylidene) Acetone) two palladium (0.18g, 0.2mmol), tri-tert-butylphosphine·tetrafluoroborate (0.23g, 0.8mmol) and sodium tert-butoxide (2.40g, 25mmol), then use argon for pumping , And adding 40 mL of anhydrous and oxygen-free toluene, the reaction solution is fully reacted in an argon atmosphere to obtain a mixed solution, and the mixed solution contains the second target produced by the reaction.

Step S12) Extract the second target; after the mixed solution is cooled to room temperature, it is extracted three times with dichloromethane and washed three times with water, and then the extract obtained after three extractions is dried, filtered and concentrated with anhydrous sodium sulfate to obtain the second Two target objects.

Step S13) Purify the second target; use 200-300 mesh silica gel column chromatography, and use petroleum ether and dichloromethane (volume ratio 1:1) as eluents to separate and purify the product to obtain 3.22 g The compound 5-(4-bromophenyl)-5H-dibenzo[b,f]cycloheximine of the electron donor (D) has a yield of 92%.

The preparation process formula is shown in formula 2:

In this embodiment, the first compound is iminodibenzyl, and the second compound is p-bromoiodobenzene, but it is not limited to these two compounds. In other embodiments of the present invention, it can be used as required. Adjusted to other compounds, but the preparation method is basically the same, so I won't list them all here.

The fluorescence emission spectrum of the thermally activated delayed fluorescent material prepared in the embodiment of the present invention is shown in FIG. 3. It is based on the calculated photoluminescence peak (PL Peak), lowest singlet state (S ₁ ), lowest triplet energy level (T ₁ ), lowest singlet and triplet energy level difference (ΔEST), and photoluminescence peak calculated based on the B3LYP theory. Luminous quantum efficiency (PLQY) is shown in Table 1:

Table 1

In the thermally activated delayed fluorescent material provided in the embodiment of the present invention, the two benzene rings in the molecular structure are connected by a saturated seven-membered ring, which can effectively inhibit the π-π stacking between molecules, thereby obtaining high photoinduced Luminous quantum efficiency (PLQY), and its electron donating ability is between diphenylamine and acridine, which can effectively reduce the overlap of HOMO and LUMO between the electron acceptor and the electron donor, and obtain the lowest singlet and triplet energy The thermally activated delayed fluorescent material with a small level difference greatly reduces the phenomenon of luminescence quenching and improves the working efficiency of the display device.

The method for preparing a thermally activated delayed fluorescent material provided in the embodiment of the present invention has a simple process, easy purification and high yield.

An embodiment of the present invention also provides a display device. As shown in FIG. 4, the display device includes a substrate 101, a first electrode layer 102, an injection layer 103, a hole transport layer 104, and a light emitting layer 105. , An electron transport layer 106 and a second electrode layer 107.

The substrate 101 is a glass substrate for protecting the overall structure of the display device 100. The first electrode layer 102 is disposed on the substrate 101, and is made of indium tin oxide transparent conductive glass for transmitting current. The injection layer 103 is disposed on the first electrode layer 102, and its material is 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaaza Triphenylene (HATCH) is used to effectively inject hole energy from the first electrode layer 102 into the device. The hole transport layer 104 is provided on the injection layer 103, and its material is 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC), which is used to The holes injected from the electrode are transported to the light-emitting layer 105. The light-emitting layer 105 is disposed on the hole transport layer 104, and its material includes the thermally activated delayed fluorescent material, which converts electrical energy into light energy, thereby providing a light source for the display device 100. The electron transport layer 106 is provided on the light-emitting layer 105, and its material is 1,3,5-tris(3-(3-pyridyl)phenyl)benzene (Tm3PyPB) for electrons injected from the electrode To the light-emitting layer 105. The second electrode layer 107 is disposed on the electron transport layer 106, and its material is lithium fluoride or aluminum.

When the device is subjected to a forward bias voltage derived from a direct current, the applied voltage energy will drive electrons and holes to be injected into the light-emitting layer 104 from the hole transport layer 103 and the electron transport layer 105 respectively, and in the When the light-emitting layer 104 meets and combines, the so-called electron-hole recombination is formed. When a chemical molecule is excited by external energy, if the electron spin is paired with the ground state electron, it is a singlet state, and the light released is so-called fluorescence. Conversely, if the spins of the excited state electrons and the ground state electrons are not paired and parallel, it is called a triplet state, and the light emitted is so-called phosphorescence.

In order to better illustrate the performance of the thermally activated delayed fluorescent material in the present invention, a performance test was performed on the final product display device 100 containing the thermally activated delayed fluorescent material. This test mainly detects the highest brightness, electroluminescence peak (EL Peak) and the maximum external quantum efficiency. The specific data is shown in Table 2.

Maximum brightness (cd/m2)	EL peak(nm)	Maximum external quantum efficiency (%)
3395	613	twenty two

Table 2

Among them, the current, brightness, and voltage characteristics of the device are completed by the Keithley source measurement system (Keithley 2400 Sourcemeter, Keithley 2000 Currentmeter) with a calibrated silicon photodiode, and the electroluminescence spectrum is measured by the French JY company SPEX CCD3000 spectrometer Yes, all measurements are done in room temperature atmosphere.

It can be seen from Table 2 that the near-infrared photothermally activated delayed fluorescent material of the present invention has excellent light-emitting performance, and the light-emitting layer 105 made of it has higher fluorescent efficiency and better stability, thereby also improving the light-emitting efficiency of the display device 100 and Service life.

In a display device provided in an embodiment of the present invention, the light-emitting layer of the display device contains the thermally activated delayed fluorescent material, so that the fluorescent efficiency of the light-emitting layer is higher, and the stability is better, thereby also improving the display device The luminous efficiency and service life.

Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be devised as long as they do not deviate from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It can also be understood that features described in combination with a single embodiment can be used in other embodiments.

Claims (10)

1. A thermally activated delayed fluorescent material, wherein the thermally activated delayed fluorescent material includes an electron donor and an electron acceptor; wherein, the electron donor includes at least two benzene rings and is connected between the two benzene rings The seven-membered ring.
2. 8. The thermally activated delayed fluorescent material of claim 1, wherein the molecular structure of the electron donor includes one of the following structures:

   
3. 4. The thermally activated delayed fluorescent material of claim 1, wherein the molecular structure of the electron acceptor includes one of the following structures:

   
4. A method for preparing thermally activated delayed fluorescent material includes the following steps:

   Synthesize the first target:

   Placing the electron donor, the electron acceptor, and the catalyst in a reaction vessel to obtain a reaction solution, which is fully reacted in an argon atmosphere to obtain a mixed solution, and the mixed solution contains the target produced by the reaction;

   Extract the first target:

   Cooling the mixed solution to room temperature, adding dichloromethane to the reaction solution for extraction, to obtain the target;

   Purification treatment of the first target:

   The eluent is used to purify the target by a silica gel column chromatography method to obtain the thermally activated delayed fluorescence material.
5. The method for preparing a thermally activated delayed fluorescent material according to claim 4, wherein:

   In the step of synthesizing the first target: the catalyst is toluene, potassium carbonate and palladium tetrakistriphenylphosphine;

   The electron donor, the electron acceptor, the toluene, and the potassium carbonate are placed in the reaction vessel together, and then the reaction vessel is placed in an argon atmosphere, and added to the reaction vessel The palladium tetrakistriphenylphosphorus is used to obtain a reaction solution.
6. The method for preparing a thermally activated delayed fluorescent material according to claim 4, wherein:

   In the step of purifying and treating the target, the eluent in the silica gel column chromatography method is petroleum ether and dichloromethane, and the volume ratio of the petroleum ether and the dichloromethane is 1:1.
7. The method for preparing a thermally activated delayed fluorescent material according to claim 4, wherein:

   Before the step of synthesizing the first target, it further includes a step of forming an electron donor,

   The step of forming an electron donor includes the following steps:

   Synthesis of the second target:

   Placing the first compound, the second compound and the catalyst in a reaction vessel to obtain a reaction solution, and fully react in an argon atmosphere to obtain a mixed solution, and the mixed solution contains the target product produced by the reaction;

   Extract the second target:

   Cooling the mixed solution to room temperature, and extracting the target in the mixed solution;

   Purification of the second target:

   Purifying the target to obtain a third compound having the electron donor structure;

   Wherein, the structure of the first compound has at least two benzene rings and a seven-membered ring connected between the two benzene rings; the structure of the second compound has at least one benzene ring.
8. The method for preparing a thermally activated delayed fluorescent material according to claim 5, wherein:

   The catalyst is tris(dibenzylideneacetone) dipalladium, tri-tert-butylphosphine·tetrafluoroborate, sodium tert-butoxide and toluene.
9. A display device, which includes:

   A substrate;

   A first electrode layer disposed on the substrate;

   An injection layer arranged on the first electrode layer;

   A hole transport layer disposed on the injection layer;

   A light-emitting layer disposed on the hole transport layer;

   An electron transport layer provided on the light-emitting layer;

   A second electrode layer arranged on the electron transport layer;

   Wherein, the light-emitting layer comprises the thermally activated delayed fluorescent material according to claim 1.
10. The display device according to claim 9, wherein:

    The material of the injection layer is 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene;

    The material of the hole transport layer is 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline];

    Therefore, the material of the electron transport layer is 1,3,5-tris(3-(3-pyridyl)phenyl)benzene.

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