WO2020211122A1

WO2020211122A1 - Bipolar thermally activated delayed fluorescence material, preparation method therefor, and organic electroluminescent diode device

Info

Publication number: WO2020211122A1
Application number: PCT/CN2019/085613
Authority: WO
Inventors: 罗佳佳; 严舒星
Original assignee: 武汉华星光电半导体显示技术有限公司
Priority date: 2019-04-16
Filing date: 2019-05-06
Publication date: 2020-10-22
Also published as: CN109970642A

Abstract

The present invention relates to a bipolar thermally activated delayed fluorescence material, a preparation method therefor, and an organic electroluminescent diode device. The structure general formula of the bipolar thermally activated delayed fluorescence material is as shown in the following formula I: (I). In formula I above, R₁ represents a chemical group as an electron acceptor, and R₂ represents a chemical group as an electron donor. The present invention uses the 100% internal quantum utilization efficiency of the TADF material, and applies the bipolar thermally activated delayed fluorescence material to an organic electroluminescent diode device as a host material of a conventional fluorescent material, so that the fluorescent device can achieve a device efficiency comparable to that of a phosphorescent device of a phosphorescent heavy metal complex, the utilization rate of excitons is greatly improved, while the problems of poor color gamut and long exciton lifetime caused by using TADF material directly as a material for a light emitting layer are solved.

Description

Bipolar thermally activated delayed fluorescent material and preparation method thereof and organic electroluminescent diode device

Technical field

The invention belongs to the technical field of electroluminescent materials, and particularly relates to a bipolar thermally activated delayed fluorescent material, a preparation method thereof, and an organic electroluminescent diode device.

Background technique

Organic Light-Emitting Diode (OLED) display panels have active light emission without backlight, high luminous efficiency, large viewing angle, fast response speed, large temperature adaptation range, relatively simple production and processing technology, and drive The advantages of low voltage, low energy consumption, lighter and thinner, flexible display and huge application prospects have attracted the attention of many researchers.

The principle of the OLED device is that under the action of an electric field, holes and electrons are injected from the anode and the cathode respectively, through the hole injection layer, the hole transport layer, the electron injection layer, and the electron transport layer, respectively, to form excitons in the light emitting layer. Exciton radiation attenuates luminescence.

As the core component of OLED devices, organic electroluminescent materials have a great impact on the performance of the devices. The light-emitting layer material of an OLED device generally contains a mixed host material and a guest material, among which the light-emitting guest material that plays a leading role is very important. The light-emitting guest materials used in early OLED devices were fluorescent materials. Since the ratio of singlet and triplet excitons in OLED devices is 1:3, the theoretical internal quantum efficiency (IQE) of OLED devices based on fluorescent materials is only It can reach 25%, which greatly limits the application of fluorescent electroluminescent devices. Due to the spin-orbit coupling of heavy atoms, heavy metal complex phosphorescent materials can simultaneously use singlet and triplet excitons to achieve 100% IQE. However, the commonly used heavy metals are precious metals such as iridium (Ir) and platinum (Pt), and the phosphorescent materials of heavy metal complexes still need a breakthrough in blue light materials. The pure organic thermally activated delayed fluorescence (TADF) material has a molecular structure combining electron donor (D) and electron acceptor (A). Through clever molecular design, the molecule has a small minimum single triplet energy difference (ΔE) _ST ), so that the triplet excitons can return to the singlet state through the reverse intersystem crossing (RISC), and then through the radiation transition to the ground state to emit light, so that the singlet and triplet excitons can be used at the same time, and 100% can also be achieved IQE.

For TADF materials, fast reverse intersystem crossing constant (k _RISC ) and high photoluminescence quantum yield (PLQY) are necessary conditions for the preparation of high-efficiency OLED devices. At present, TADF materials with the above conditions are still relatively scarce compared to heavy metal Ir complexes. And because the TADF material has a very broad spectrum and the exciton lifetime in the order of microseconds, it greatly limits its application in mass production device structures.

In addition, an effective host material should have an ideal band gap in order to efficiently transfer energy to the guest, good carrier transport properties to achieve balanced recombination of carriers in the emission layer, and match the energy levels of adjacent layers to achieve effective High charge injection, and sufficient thermal and morphological stability to extend the life of the device, so the development of host materials is extremely important for high-efficiency electroluminescent devices.

Traditional host materials usually only have a single carrier transport property, and this unbalanced carrier transport property has shown disadvantages to the turn-on voltage and lifetime of OLEDs. The development of new host materials requires good bipolar carrier (hole and electron) injection and transport properties to prevent carriers from accumulating between the light-emitting layer and the charge transport layer, causing the exciplex at the interface to emit light , Resulting in low external quantum efficiency, power efficiency, current efficiency and other main parameters of the device, high starting voltage, and unstable spectrum. Therefore, bipolar host materials that can balance carrier transport have attracted considerable attention in recent years.

Summary of the invention

The purpose of the present invention is to provide a bipolar thermally activated delayed fluorescent material, which has ultra-fast reverse inter-system crossing rate and high luminous efficiency, is a blue TADF compound with significant TADF characteristics and high energy level, and can be used as an organic electroluminescent material. The host material of the light-emitting layer of the light-emitting diode.

Another object of the present invention is to provide a method for preparing a bipolar thermally activated delayed fluorescent material, which is easy to operate and has a high yield of the target product.

Another object of the present invention is to provide an organic electroluminescent diode device, which uses the above-mentioned bipolar thermally activated delayed fluorescent material as the main material of the light-emitting layer, which can achieve a device efficiency comparable to that of a phosphorescent device of a phosphorescent heavy metal complex, while simultaneously solving The problem of color gamut difference and long exciton lifetime caused by the direct use of TADF material as the light-emitting layer material, and the bipolar carrier injection and transport properties of the bipolar host material make the carrier transport more balanced, The efficiency and stability of the device can be further improved.

In order to achieve the above-mentioned purpose of the invention, the present invention provides a bipolar thermally activated delayed fluorescent material, which has a chemical structure shown in the following formula 1:

Formula one

In the above formula 1, R ₁ represents a chemical group as an electron acceptor, R ₂ represents a chemical group as an electron donor, and R _{2 is} in the ortho, para or meta position of the sulfur atom in the benzene ring.

The chemical group R _{1 of} the electron acceptor is selected from any one of the following groups:

The chemical group R _{2 of} the electron donor is selected from any one of the following groups:

The bipolar thermally activated delayed fluorescent material is compound 1, compound 2, or compound 3. The structural formulas of compound 1, compound 2 and compound 3 are as follows:

The invention also provides a preparation method of the bipolar thermally activated delayed fluorescent material, the chemical synthesis route is as follows:

Specifically: add halogenated raw materials, electron donor compounds, palladium acetate and tri-tert-butylphosphine tetrafluoroborate with a molar ratio of 1:1-2:0.02-0.1:0.1-0.2 to the reaction flask, and then Under anhydrous and oxygen-free environment, add sodium tert-butoxide at a molar ratio of 1-2:1 to the halogenated raw materials, and inject toluene with dewatering and deoxygenation under argon atmosphere, and react at 110-130℃ for 20- 30 hours; cool to room temperature, pour the reaction solution into ice water, combine the organic phases after extraction, spin into silica gel, separate and purify by column chromatography to obtain the product, calculate the yield;

The general structural formula of the halogenated raw material is

Among them, R ₁ represents a chemical group as an electron acceptor, and Br is in the ortho, para or meta position of the sulfur atom in the benzene ring;

The general structural formula of the electron donor-containing compound is R ₂ -H, where R ₂ represents a chemical group as an electron donor.

The electron-donating compound is 9,10-dihydro-9,9-dimethyl acridine;

The halogenated raw material is raw material 1, raw material 2 or raw material 3, and the structural formulas of raw material 1, raw material 2 and raw material 3 are respectively

The present invention also provides an organic electroluminescent diode device, including a substrate, a first electrode provided on the substrate, an organic functional layer provided on the first electrode, and a second electrode provided on the organic functional layer ；

The organic functional layer includes one or more organic film layers, and at least one of the organic film layers is a light-emitting layer;

The light-emitting layer includes a mixed host material and a guest material;

The host material is selected from one or more of the above-mentioned bipolar thermally activated delayed fluorescent materials.

The light-emitting layer is formed by vacuum evaporation or solution coating.

The guest material is PPA.

The substrate is a glass substrate, the material of the first electrode is indium tin oxide, and the second electrode is a double-layer composite structure composed of a lithium fluoride layer and an aluminum layer;

The organic functional layer includes a multilayer organic film layer, the multilayer organic film layer includes a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer. The material of the hole injection layer is HATCN. The material of the hole transport layer is TCTA, and the material of the electron transport layer is TmPyPB.

Compared with existing materials and technologies, the present invention has the following advantages and beneficial effects:

(1) The bipolar thermally activated delayed fluorescent material of the present invention has an ultra-fast reverse inter-system crossing rate and high luminous efficiency, is a high-energy blue TADF compound with significant TADF characteristics, and the preparation method is easy to operate and obtain The yield of the target product is higher.

(2) The organic electroluminescent diode device of the present invention utilizes the 100% internal quantum utilization efficiency of the TADF material, and uses the bipolar thermally activated delayed fluorescent material as the main material of the traditional fluorescent material to be applied to the organic electroluminescent diode device , Enables the fluorescent device to achieve the device efficiency comparable to the phosphorescent device of the phosphorescent heavy metal complex, greatly improves the exciton utilization rate, and at the same time solves the color gamut difference and exciton lifetime caused by the direct use of TADF material as the light-emitting layer material Problems such as excessive length, and the bipolar carrier injection and transport properties of the bipolar host material make the carrier transport more balanced, which can further improve the efficiency and stability of the device. Based on the bipolar thermal activation of the present invention Organic electroluminescent diode devices with delayed fluorescent materials have achieved very high device efficiency.

Description of the drawings

The technical solutions and other beneficial effects of the present invention will be made obvious by describing in detail the specific embodiments of the present invention in conjunction with the accompanying drawings.

In the attached picture,

Figure 1 is a schematic diagram of the molecular structure of compound 1-3 prepared in specific examples 1-3 of the present invention;

Figure 2 is a photoluminescence spectrum of compound 1-3 prepared in specific examples 1-3 of the present invention in a toluene solution at room temperature;

Fig. 3 is a schematic diagram of the structure of the organic electroluminescent diode device of the present invention.

detailed description

Some unspecified raw materials used in the present invention are all commercially available products. The preparation methods of some compounds will be described in the implementation case. The present invention will be further described in detail below in conjunction with specific examples, but the implementation of the present invention is not limited thereto.

Example 1:

The synthetic route of target compound 1 is as follows:

Add raw material 1 (1.93g, 5mmol), 9,10-dihydro-9,9-dimethylacridine (1.25g, 6mmol), palladium acetate Pb(OAc) (45mg, 0.2mmol) into a 100mL two-neck flask ) And tri-tert-butylphosphine tetrafluoroborate (t-Bu) ₃ HPBF ₄ (0.17g, 0.6mmol), and then add sodium tert-butoxide NaOt-Bu (0.58g, 6mmol) in the glove box. 40 mL of toluene that had been previously dewatered and deoxygenated was injected under an air atmosphere, and reacted at 120°C for 24 hours. Cool to room temperature, pour the reaction solution into 200 mL ice water, extract three times with dichloromethane, combine the organic phases, spin into silica gel, and separate and purify by column chromatography (dichloromethane: n-hexane, v: v, 3:2) to obtain 2.3 g of compound 1 as a white powder with a yield of 89%.

1HNMR (300MHz, CD2Cl2, δ): 7.62 (d, J = 6.3Hz, 2H), 7.35 (d, J = 6.6Hz, 2H), 7.19-7.14 (m, 6H), 6.95-6.90 (m, 2H) ,1.69(s,6H).

MS(EI) m/z: [M] ⁺ calcd for C ₂₇ H ₁₈ F ₅ NO ₂ P, 515.10; found, 515.08.

Example 2:

The synthetic route of target compound 2 is as follows:

Add raw material 2 (1.93g, 5mmol), 9,10-dihydro-9,9-dimethylacridine (1.25g, 6mmol), palladium acetate (45mg, 0.2mmol) and tert Butylphosphine tetrafluoroborate (0.17g, 0.6mmol), and then add sodium tert-butoxide (0.58g, 6mmol) in the glove box, in an argon atmosphere, inject 40mL of toluene that has been dewatered and deoxygenated beforehand. React at 120°C for 24 hours. Cool to room temperature, pour the reaction solution into 200 mL ice water, extract three times with dichloromethane, combine the organic phases, spin into silica gel, and separate and purify by column chromatography (dichloromethane: n-hexane, v: v, 3:2) to obtain 1.7 g of compound 2 as a white powder, with a yield of 66%.

¹ H NMR (300MHz, CD ₂ Cl ₂ , δ): 7.69 (d, J = 6.0Hz, 1H), 7.52-7.44 (m, 3H), 7.19-7.14 (m, 6H), 6.95-6.90 (m, 2H), 1.69(s, 6H).

MS(EI)m/z:[M] ⁺ calcd for C ₂₇ H ₁₈ F ₅ NO ₂ P,515.10; found,515.06.

Example 3:

The synthetic route of target compound 3 is as follows:

To a 100mL two-neck flask was added raw material 3 (1.93g, 5mmol), 9,10-dihydro-9,9-dimethylacridine (1.25g, 6mmol), palladium acetate (45mg, 0.2mmol) and tertiary Butylphosphine tetrafluoroborate (0.17g, 0.6mmol), and then add sodium tert-butoxide (0.58g, 6mmol) in the glove box, in an argon atmosphere, inject 40mL of toluene that has been dewatered and deoxygenated beforehand. React at 120°C for 24 hours. Cool to room temperature, pour the reaction solution into 200 mL ice water, extract three times with dichloromethane, combine the organic phases, spin into silica gel, and separate and purify by column chromatography (dichloromethane: n-hexane, v: v, 3:2) to obtain 1.1 g of compound 3 as a white powder with a yield of 43%.

¹ H NMR (300MHz, CD ₂ Cl ₂ , δ): 7.72 (d, J = 6.3 Hz, 2H), 7.35-7.29 (m, 3H), 7.19-7.14 (m, 6H), 6.95-6.90 (m, 2H), 1.69(s, 6H).

MS (EI) m/z: [M] ⁺ calcd for C ₂₇ H ₁₈ F ₅ NO ₂ P, 515.10; found, 515.07.

Figure 1 shows the orbital arrangement of compound 1-3. It can be clearly seen from Figure 1 that the highest electron occupied orbital (HOMO) and lowest electron unoccupied orbital (LUMO) of compound 1-3 are arranged in In different units, complete separation is achieved, which helps to reduce the energy difference ΔEST between systems, thereby improving the ability of reverse intersystem crossing. Figure 2 shows the photoluminescence spectra of Compound 1-3 in n-hexane solution at room temperature. For compounds 1-3, the lowest singlet energy level S1 and the lowest triplet energy level T1 of the molecule were simulated and calculated.

The relevant data of Examples 1-3 are shown in Table 1. It can be seen from Table 1 that the ΔEst of all the compounds is less than 0.3ev, which achieves a small singlet and triplet energy level difference, and has an obvious delayed fluorescence effect.

Table 1. Results of photophysical properties of compounds 1-3

In Table 1, PL Peak represents the photoluminescence peak, S1 represents the singlet energy level, T1 represents the triplet energy level, and ΔEST represents the difference between the singlet and triplet energy levels.

Example 4:

Preparation of organic electroluminescent diode (OLED) devices:

As shown in Figure 1, the bipolar thermally activated delayed fluorescent material of the present invention is used as the guest material of the light-emitting layer of the organic electroluminescent diode device, which may include a substrate 9, an anode layer 1, and a hole injection layer arranged from bottom to top. 2. Hole transport layer 3, light emitting layer 4, electron transport layer 5, and cathode layer 6. Wherein, the substrate 9 is a glass substrate, the material of the anode 1 is indium tin oxide (ITO), the substrate 9 and the anode 1 together form ITO glass, and the sheet resistance of the ITO glass is 10Ω/cm ² . The material of the hole injection layer 2 is HATCN, the material of the hole transport layer 3 is TCTA, the material of the light-emitting layer is a mixture of the activated delayed fluorescence compound of the present invention and PPA, and the electron transport layer 5 is The material is TmPyPB. The cathode has a double-layer structure composed of a lithium fluoride (LiF) layer and an aluminum (Al) layer.

Among them, HATCN refers to 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene, TCTA refers to 4,4',4”-tri (Carbazol-9-yl) triphenylamine, PPA refers to 9-pyrenyl-(10)-4-triphenylaminoanthracene, TmPyPB refers to 1,3,5-tris(3-(3-pyridyl)phenyl) benzene.

The organic electroluminescent diode device can be manufactured according to methods known in the art, and the specific method is: sequentially vapor-depositing a 2nm thick HATCN film, a 35nm thick TCTA film, and a DPEPO film on the cleaned ITO glass under high vacuum conditions. Activation delayed fluorescence compound, 40nm thick TmPyPB film, 1nm thick LiF film and 100nm thick Al film. The device as shown in Figure 3 is made by this method, and the specific device structures are as follows:

Device 1:

ITO/HATCN(2nm)/TCTA(35nm)/Compound 1: PPA(5%40nm)/TmPyPB(40nm)/LiF(1nm)/Al(100nm)

Device 2:

ITO/HATCN(2nm)/TCTA(35nm)/Compound 2: PPA(5%40nm)/TmPyPB(40nm)/LiF(1nm)/Al(100nm)

Device 3:

ITO/HATCN(2nm)/TCTA(35nm)/Compound 3: PPA(5% 40 nm)/TmPyPB(40nm)/LiF(1nm)/Al(100nm)

The current-brightness-voltage characteristics of devices 1-3 are completed by the Keithley source measurement system (Keithley 2400 Sourcemeter, Keithley 2000 Currentmeter) with a calibrated silicon photodiode, and the electroluminescence spectrum is performed by the French JY company SPEX CCD3000 spectrometer All measurements are done in room temperature atmosphere. The performance data of devices 1-3 are shown in Table 2 below.

Table 2. Performance results of devices based on compounds 1-3 as guest materials for the light-emitting layer

In Table 2, CIEy is the y coordinate value of the standard CIE color space.

In summary, the present invention synthesizes a series of bipolar thermally activated delayed fluorescent materials with low single triplet energy level difference, high luminous efficiency and fast reverse intersystem crossing constant through clever molecular design. A high-energy bipolar blue TADF material with significant TADF characteristics and a reasonable synthesis route design, resulting in a higher yield of the target product. The present invention further utilizes the 100% internal quantum utilization efficiency of the TADF material to reduce the above-mentioned bipolar thermal Activation delayed fluorescent materials are used as the main material of traditional fluorescent materials to be applied to organic electroluminescent diode devices, so that fluorescent devices can achieve device efficiency comparable to phosphorescent devices of phosphorescent heavy metal complexes, greatly improving the exciton utilization rate, and at the same time It solves the problems of color gamut difference and long exciton lifetime caused by directly using TADF material as the light-emitting layer material, and the bipolar carrier injection and transport properties of the bipolar host material make the carrier transport more balanced It can further improve the efficiency and stability of the device. The organic electroluminescent diode devices based on the bipolar thermally activated delayed fluorescent material of the present invention have achieved very high device efficiency.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, etc. made without departing from the spirit and principle of the present invention Simplified, all should be equivalent replacement methods, and they are all included in the protection scope of the present invention.

Claims

A bipolar thermally activated delayed fluorescent material with a chemical structure shown in the following formula 1:

In the above formula 1, R 1 represents a chemical group as an electron acceptor, R 2 represents a chemical group as an electron donor, and R 2 is in the ortho, para or meta position of the sulfur atom in the benzene ring.
The bipolar thermally activated delayed fluorescent material according to claim 1, wherein the chemical group R 1 of the electron acceptor is selected from any one of the following groups:

The chemical group R 2 of the electron donor is selected from any one of the following groups:
The bipolar thermally activated delayed fluorescent material of claim 2 is compound 1, compound 2, or compound 3. The structural formulas of compound 1, compound 2 and compound 3 are as follows:
A method for preparing bipolar thermally activated delayed fluorescent material, the chemical synthesis route is as follows:

Specifically: add halogenated raw materials, electron donor compounds, palladium acetate and tri-tert-butylphosphine tetrafluoroborate with a molar ratio of 1:1-2:0.02-0.1:0.1-0.2 to the reaction flask, and then Under anhydrous and oxygen-free environment, add sodium tert-butoxide at a molar ratio of 1-2:1 to the halogenated raw materials, and inject toluene with dewatering and deoxygenation under argon atmosphere, and react at 110-130℃ for 20- 30 hours; cool to room temperature, pour the reaction solution into ice water, combine the organic phases after extraction, spin into silica gel, separate and purify by column chromatography to obtain the product, calculate the yield;

The general structural formula of the halogenated raw material is
Among them, R 1 represents a chemical group as an electron acceptor, and Br is in the ortho, para or meta position of the sulfur atom in the benzene ring;

The general structural formula of the electron donor-containing compound is R 2 -H, where R 2 represents a chemical group as an electron donor.
The method for preparing a bipolar thermally activated delayed fluorescent material according to claim 4, wherein the chemical group R 1 of the electron acceptor is selected from any one of the following groups:

The chemical group R 2 of the electron donor is selected from any one of the following groups:
The method for preparing a bipolar thermally activated delayed fluorescent material according to claim 5, wherein the electron-donating compound is 9,10-dihydro-9,9-dimethylacridine;

The halogenated raw material is raw material 1, raw material 2 or raw material 3, and the structural formulas of raw material 1, raw material 2 and raw material 3 are respectively
An organic electroluminescent diode device, comprising a substrate, a first electrode provided on the substrate, an organic functional layer provided on the first electrode, and a second electrode provided on the organic functional layer;

The organic functional layer includes one or more organic film layers, and at least one of the organic film layers is a light-emitting layer;

The light-emitting layer includes a mixed host material and a guest material;

The host material is selected from one or more of the bipolar thermally activated delayed fluorescent materials according to claim 1.
8. The organic electroluminescent diode device of claim 7, wherein the light-emitting layer is formed by vacuum evaporation or solution coating.
8. The organic electroluminescent diode device of claim 7, wherein the guest material is PPA.
The organic electroluminescent diode device of claim 7, wherein the substrate is a glass substrate, the material of the first electrode is indium tin oxide, and the second electrode is composed of a lithium fluoride layer and an aluminum layer Double-layer composite structure;

The organic functional layer includes a multilayer organic film layer, the multilayer organic film layer includes a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer. The material of the hole injection layer is HATCN. The material of the hole transport layer is TCTA, and the material of the electron transport layer is TmPyPB.