Luminescent material and its preparation method and application

Abstract

The present invention discloses a luminescent material, its preparation method, and application. The structure of the luminescent material is shown in formula (I); in formula (I), R1 and R2 represent substituents at any position on the benzene ring; R1 and R2 are independently selected from hydrogen, C1-C10 linear alkyl, or C3-C8 cycloalkyl; Host is a main unit with adjustable photophysical properties; m, a, b, c, and d are molar percentages, independently selected from 1% to 99%, and m+a+b+c+d=100%. The luminescent material of the present invention can be used as a red-emitting thermally excited delayed fluorescence material to prepare organic electroluminescent devices, and the device has a low turn-on voltage. #imgabs0#

Description

Technical Field

[0001] The invention relates to a luminescent material and a preparation method and application thereof. Background Art

[0002] Polymer light-emitting diodes (PLEDs) have shown potential in commercial flat-panel display and solid-state lighting applications with high contrast, wide color gamut, low latency, low cost, and low energy consumption. Conjugated polymers with thermally activated delayed fluorescence (TADF) properties have attracted great interest due to their ease of fabrication and excellent device performance, especially non-doped PLEDs.

[0003] CN106117524A discloses a thermally activated delayed fluorescence conjugated polymer luminescent material containing a sulfone group in the side chain, and its preparation method and application. CN108864416A discloses a polymer luminescent material, its preparation method and application. In this patent document, a suitable thermally excited delayed fluorescence unit alkyl-substituted phenothiazine-dibenzothiophene sulfone is copolymerized with a main unit. CN111574431A discloses a multifunctional organic luminescent material based on carbazole and benzophenone derivatives. CN113493564A discloses an organic polymer luminescent material, in which the electron donor and the electron acceptor are alternately connected through a σ connection with sufficient space to interrupt the conjugation, that is, oxygen atoms or sulfur atoms. CN114409840A discloses a polymer luminescent material, its preparation method and application. The polymer material is a polymer luminescent material based on spatial charge transfer, in which the donor and the acceptor are not directly connected, and the charge transfer between the donor and the acceptor is achieved only through the form of spatial charge transfer.

[0004] To date, optimization of chemical modification and device architecture has led to improvements in the maximum external quantum efficiency (EQE) of non-doped solution-processed PLEDs. However, the development of red-emitting materials with TADF properties is still lagging. For example, the turn-on voltage still needs to be reduced. Summary of the Invention

[0005] In view of this, one object of the present invention is to provide a luminescent material. This luminescent material is a red-emitting material exhibiting thermally excited delayed fluorescence, and a device in which this material is used as a luminescent layer has a low turn-on voltage. Another object of the present invention is to provide a method for preparing the luminescent material. A further object of the present invention is to provide applications of the luminescent material. The present invention achieves the above-mentioned objects through the following technical solutions.

[0006] In one aspect, the present invention provides a luminescent material having a structure as shown in formula (I):

[0007]

[0008] In formula (I), R1 and R2 represent substituents at any position on the benzene ring; R1 and R2 are independently selected from hydrogen, C1-C10 straight-chain alkyl or C3-C8 cycloalkyl;

[0009] Host is a main unit with adjustable photophysical properties; m, a, b, c, d are mole percentages, independently selected from 1% to 99%, and m+a+b+c+d=100%.

[0010] According to the luminescent material of the present invention, preferably, the host unit Host is selected from one of the following structures:

[0011]

[0012] Wherein, R is selected from C5-C15 alkyl.

[0013] According to the luminescent material of the present invention, preferably, R1 and R2 are independently selected from hydrogen or a C1-C6 straight-chain alkyl group.

[0014] According to the luminescent material of the present invention, preferably, R1 and R2 are independently selected from hydrogen or C1-C3 straight-chain alkyl.

[0015] According to the luminescent material of the present invention, preferably, its structure is as shown in formula (II):

[0016]

[0017] Wherein, m, a, b, c, and d are mole percentages, independently selected from 1% to 99%, and m+a+b+c+d=100%.

[0018] According to the luminescent material of the present invention, preferably, the weight average molecular weight of the luminescent material is 5000 to 30000 Daltons, and the polydispersity coefficient is 1.5 to 2.5.

[0019] On the other hand, the present invention also provides a method for preparing the luminescent material as described above, comprising the following steps:

[0020] (1) subjecting the compound represented by formula (A) to a substitution reaction to obtain a first intermediate represented by formula (B);

[0021]

[0022] In formula (A) and formula (B), R1 and R2 represent substituents at any position on the benzene ring; R1 and R2 are independently selected from hydrogen, C1-C10 linear alkyl or C3-C8 cycloalkyl; in formula (B), X is chlorine, bromine or iodine;

[0023] (2) reacting the first intermediate with a halide of Host to obtain a luminescent material represented by formula (I);

[0024] Among them, Host is the main unit with controllable photophysical properties.

[0025] According to the preparation method of the present invention, preferably:

[0026] In step (1), N-halosuccinimide is reacted with the compound represented by formula (A) at a molar ratio of 4.5 to 5.5:1 to obtain a first intermediate;

[0027] In step (2), a coupling reaction is carried out between the first intermediate and the halogenated compound of Host at a molar ratio of 1:8.9 to 9.5 in the presence of an organic nickel catalyst to obtain a polymer material represented by formula (I).

[0028] In another aspect, the present invention also provides use of the luminescent material described above in preparing an organic electroluminescent device.

[0029] In yet another aspect, the present invention further provides an organic electroluminescent device comprising the light-emitting material as described above.

[0030] The luminescent material of the present invention is a red-emitting material with thermally excited delayed fluorescence properties. The organic electroluminescent device formed with the luminescent material as a light-emitting layer has a low turn-on voltage and high brightness. Furthermore, the efficiency roll-off of the device is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The luminescent material obtained in the embodiment of the present invention 1 H NMR spectrum. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0033] <Luminescent Materials>

[0034] The luminescent material of the present invention is a material having D n -A type TADF characteristics of the hyperbranched conjugated polymer (HCP), can be used for high-performance red light-emitting PLED. The structure of the luminescent material of the present invention is shown in formula (I):

[0035]

[0036] Devices formed from such luminescent materials as light-emitting layers have a relatively low turn-on voltage and still exhibit high brightness. This is likely due to the multiple intramolecular charge transfer (ICT) channels induced by the quasi-equivalent donors of the TADF core, which greatly promotes the reverse intersystem crossing (RISC) process and singlet exciton radiative transitions of the HCP of the present invention. Based on the rapid energy transfer process of the HCP, the strongly electron-withdrawing oxygen atoms located on the TADF core donor fragments further accelerate the transfer of holes from the side chains to the core.

[0037] In formula (I), R1 and R2 represent substituents at any position on the benzene ring, that is, they are substituents at any position on the benzene ring where they are located.

[0038] R1 is independently selected from hydrogen, C1-C10 straight chain alkyl or C3-C8 cycloalkyl; preferably, R1 is independently selected from hydrogen or C1-C6 straight chain alkyl. More preferably, R1 is independently selected from hydrogen or C1-C3 straight chain alkyl.

[0039] R2 is independently selected from hydrogen, C1-C10 straight chain alkyl or C3-C8 cycloalkyl; preferably, R2 is independently selected from hydrogen or C1-C6 straight chain alkyl. More preferably, R2 is independently selected from hydrogen or C1-C3 straight chain alkyl.

[0040] Examples of C1-C10 alkyl groups include, but are not limited to, methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl. Examples of C3-C8 cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. According to a specific embodiment of the present invention, R1 is hydrogen and R2 is hydrogen.

[0041] In the present invention, Host is a main unit with controllable photophysical properties.

[0042] Preferably, the host unit Host is selected from one of the following structures:

[0043]

[0044]

[0045] wherein R is selected from a C5-C15 alkyl group, preferably a C5-C15 straight-chain alkyl group, and more preferably a C6-C10 straight-chain alkyl group.

[0046] In the present invention, m, a, b, c, and d are mole percentages. m, a, b, c, and d are independently selected from 1% to 99%, preferably 5% to 80%, and more preferably 10% to 60%. m + a + b + c + d = 100%. The ratio of m:(a + b + c + d) can be 1:1 to 100, preferably 1:5 to 60, and more preferably 1:6 to 10.

[0047] According to a preferred embodiment of the present invention, the structure of the luminescent material of the present invention is shown in formula (II):

[0048]

[0049]

[0050] In formula (II), m, a, b, c, and d are mole percentages. m, a, b, c, and d are independently selected from 1% to 99%, preferably 5% to 80%, and more preferably 10% to 60%. m + a + b + c + d = 100%. The ratio of m:(a + b + c + d) can be 1:1 to 100, preferably 1:5 to 60, and more preferably 1:6 to 10.

[0051] In the present invention, the weight average molecular weight Mw of the luminescent material is 5000 to 30000 Daltons, and the polydispersity index PDI is 1.5 to 2.5.

[0052] <Preparation method>

[0053] The method for preparing the luminescent material of the present invention comprises: (1) synthesizing a first intermediate; and (2) synthesizing a target luminescent material. Detailed description is given below.

[0054] Synthesis of the first intermediate

[0055] The compound represented by formula (A) is subjected to a substitution reaction to obtain a first intermediate represented by formula (B).

[0056]

[0057] The structure of the first intermediate is shown below:

[0058]

[0059] In formula (A) and formula (B), R1 and R2 represent substituents at any position on the benzene ring; R1 and R2 are independently selected from hydrogen, C1-C10 straight-chain alkyl or C3-C8 cycloalkyl.

[0060] R1 can be independently selected from hydrogen, C1-C10 straight chain alkyl or C3-C8 cycloalkyl; preferably, R1 is independently selected from hydrogen or C1-C6 straight chain alkyl. More preferably, R1 is independently selected from hydrogen or C1-C3 straight chain alkyl.

[0061] R2 is independently selected from hydrogen, C1-C10 straight chain alkyl or C3-C8 cycloalkyl; preferably, R2 is independently selected from hydrogen or C1-C6 straight chain alkyl. More preferably, R2 is independently selected from hydrogen or C1-C3 straight chain alkyl.

[0062] Examples of C1-C10 alkyl groups include, but are not limited to, methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl. Examples of C3-C8 cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. According to a specific embodiment of the present invention, R1 is hydrogen and R2 is hydrogen.

[0063] In formula (B), X is chlorine, bromine or iodine, preferably bromine or iodine, more preferably bromine.

[0064] In step (1), an N-halogenated succinimide at a molar ratio of 4.5 to 5.5:1 is reacted with the compound represented by formula (A) to obtain a first intermediate. The N-halogenated succinimide may be N-chlorosuccinimide, N-bromosuccinimide, or N-iodosuccinimide.

[0065] The molar ratio of N-halosuccinimide to the compound represented by formula (A) can be 4.5 to 5.5:1, preferably 4.7 to 5.2:1, and more preferably 5.0 to 5.1:1. This is conducive to improving the reaction yield and having a higher purity.

[0066] The reaction solvent may be a halogenated alkane, for example, dichloromethane or chloroform, preferably dichloromethane. The reaction temperature may be -5 to 5°C, preferably 0 to 5°C, more preferably 0 to 5°C. The reaction time may be 10 to 20 hours, preferably 10 to 16 hours, more preferably 12 to 16 hours.

[0067] According to one embodiment of the present invention, the compound represented by formula (A) is dissolved in dichloromethane to obtain a first solution; N-bromosuccinimide is dissolved in anhydrous dichloromethane to obtain a second solution. The second solution is dropwise added to the first solution in the dark at 0-5°C to react, and stirred for 10-16 hours.

[0068] After the reaction is complete, the reaction can be quenched with water and then extracted with a halogenated alkane. The extract is dried over anhydrous sodium sulfate, filtered, and concentrated to obtain a crude product. The crude product is purified by silica gel column, and the eluent can be a mixture of petroleum ether and dichloromethane. The volume ratio of petroleum ether to dichloromethane can be 1:8.5 to 9.5, preferably 1:9.

[0069] Synthesize target luminescent materials

[0070] The first intermediate reacts with a halide of Host to obtain a luminescent material represented by formula (I); wherein Host is a main unit having adjustable photophysical properties.

[0071] Preferably, the host unit Host is selected from one of the following structures:

[0072]

[0073]

[0074] wherein R is selected from a C5-C15 alkyl group, preferably a C5-C15 straight-chain alkyl group, and more preferably a C6-C10 straight-chain alkyl group.

[0075] The halide of Host may be a chloride of Host, a bromide of Host or an iodide of Host, preferably a bromide of Host.

[0076] According to a specific embodiment of the present invention, the halide of Host has a structure as shown in formula (III):

[0077]

[0078] According to one embodiment of the present invention, a first intermediate with a molar ratio of 1:8.9-9.5 is subjected to a coupling reaction with a halide of Host in the presence of an organic nickel catalyst to obtain a luminescent material represented by formula (I).

[0079] The molar ratio of the first intermediate to the halide of Host may be 1:8.9-9.5, preferably 1:8.95-9.2, and more preferably 1:9.0-9.1.

[0080] The organic nickel catalyst is bis(1,5-cyclooctadiene) nickel (Ni(COD)2), and the mass ratio of the organic nickel catalyst to the first intermediate is 5.5-6.5:1, preferably 5.6-6.3:1, and more preferably 5.7-6.2:1. The auxiliary agent is a mixture of 2,2-bipyridine and 1,5-cyclooctadiene.

[0081] The reaction temperature may be 75 to 90° C., preferably 80 to 90° C., more preferably 80 to 85° C. The reaction time may be 36 to 56 h, preferably 40 to 56 h, more preferably 48 to 52 h.

[0082] According to a specific embodiment of the present invention, under argon protection, the first intermediate, the bromide of Host, bis(1,5-cyclooctadiene)nickel (referred to as Ni(COD)2), 2,2-bipyridine, and 1,5-cyclooctadiene are dissolved in anhydrous tetrahydrofuran (THF), stirred and reacted at 80-90°C for 48-52h, and then bromobenzene is added as a capping group, and the reaction is continued at 75-90°C for 20-36h.

[0083] After the reaction is complete, the reaction is terminated with 5-10 wt% dilute hydrochloric acid to wash away the catalyst and 2,2-bipyridine, followed by extraction with a halogenated alkane (e.g., dichloromethane or chloroform). The extracted organic layer is washed with water, dried over magnesium sulfate pentahydrate, filtered, and concentrated to obtain a crude product.

[0084] In the present invention, the crude product can be completely dissolved in tetrahydrofuran and then dropped into methanol for precipitation and purification. After sedimentation and separation, the solid is further purified by Soxhlet extraction (the solvent can be ethanol) to obtain the luminescent material.

[0085] <Application>

[0086] The present invention also provides use of the luminescent material described above in preparing an organic electroluminescent device.

[0087] The luminescent material can be used as the light-emitting layer of an organic electroluminescent device. The turn-on voltage of the organic electroluminescent device formed is low and the brightness is high. In addition, the efficiency roll-off of the formed device is small. In the single-layer non-doped organic electroluminescent device formed (the single-layer non-doped organic electroluminescent device is composed of an anode layer / hole injection layer / light-emitting layer / electron injection layer / cathode layer), the turn-on voltage can be as low as 2.5V. And the efficiency roll-off is small, for example, when the brightness is less than 100cd / m 2 No roll-off at 500cd / m 2 The device's maximum brightness can reach 4036cd / m 2 , 500cd / m 2 The external quantum efficiency is 8.11%.

[0088] <Organic electroluminescent device>

[0089] The present invention also provides an organic electroluminescent device, which comprises the luminescent material described above.

[0090] The instruments used in the examples are described below:

[0091] The nuclear magnetic resonance (NMR) and mass spectrometry (MS) data were acquired using a Bruker Ascend 400 MHz and 700 MHz NMR spectrometer (Bruker, Germany) and a Waters Xevo-G2-SQ-TOFMS mass spectrometer (Waters, USA).

[0092] Fluorescence data were obtained using a Hitachi F-7000 fluorescence spectrometer (Hitachi, Japan) and a FLS-980 transient fluorescence spectrometer (Edinburgh, UK). Brightness data were obtained using a PR670 spectroradiometer (Pioneer Technology, Taiwan, China).

[0093] Example

[0094] The intermediate reaction equation is as follows:

[0095]

[0096] The compound represented by formula (A) (816.3 mg, 1.5 mmol) was dissolved in 20 ml of anhydrous dichloromethane at 0° C. to obtain a first solution. N-bromosuccinimide NBS (1.34 g, 7.5 mmol) was dissolved in 80 ml of anhydrous dichloromethane DCM to obtain a second solution.

[0097] Under dark conditions and at 0°C, the second solution was added dropwise to the first solution to react and stirred for 12 hours. After the reaction was completed, the reaction was quenched with water, washed three times with water and extracted with dichloromethane. The extract was dried over anhydrous sodium sulfate, filtered and concentrated to obtain a crude product. The crude product was purified by silica gel column using a mixture of petroleum ether and dichloromethane (volume ratio of 1:9) as eluent to obtain the first intermediate (i.e., the compound shown in formula (B)). The structure of the first intermediate was identified, and the results are as follows:

[0098] 1 H NMR (400MHz, Chloroform-d) δ 8.10 (d, J = 8.4 Hz, 1H), 7.50 ( d, J = 8.5 Hz, 1H), 6.87 ( d, J = 2.2 Hz, 1H), 6.75 ( dd, J = 8.6, 2.2 Hz, 1H), 5.85 ( d, J = 8.6 Hz, 1H).

[0099] 13 C NMR (101MHz, Chloroform-d) δ191.63,144.32,142.69,137.40,133.11,132.68,130.87,126.52,119.19,114.57,113.75.

[0100] LC-MS m / z[M+H] calculated value is C 37 H 20 Br4N2O3+H 859.82; measured value is 859.82.

[0101] The reaction equation of the luminescent material is as follows:

[0102]

[0103] wherein m, a, b, c, and d are independently selected from 1% to 99%, m+a+b+c+d=100%, and m:(a+b+c+d) is 1:6 to 10.

[0104] Under argon, the first intermediate (0.1 mmol), 1-hexylcarbazole bromine (0.9 mmol), bis(1,5-cyclooctadiene) nickel (Ni(COD)2, 500 mg), 2,2-bipyridine (BPY, 300 mg), and 1,5-cyclooctadiene (COD, 0.5 ml) were dissolved in 10 ml of anhydrous tetrahydrofuran (THF) and stirred at 80°C for 48 hours. Subsequently, 0.5 ml of bromobenzene was added as a capping group, and the reaction was continued for 24 hours. The temperature was lowered, and the reaction system was terminated by adding dilute hydrochloric acid to the reaction system. The catalyst and 2,2-bipyridine were washed away, and the reaction was then extracted with dichloromethane. The organic layer was washed with water and dried over anhydrous magnesium sulfate. Filtered and concentrated to obtain the crude product. The crude product was dissolved in 10 ml of tetrahydrofuran (THF) and added dropwise to cooled methanol for precipitation. After sedimentation and separation, the obtained solid is further purified using a Soxhlet extraction apparatus (ethanol as an extractant) to obtain a luminescent material.

[0105] After testing, the obtained luminescent material has Mw=21514, PDI=1.44, 1 H NMR spectra can be found in Figure 1 The photophysical characterization data are shown in Table 1.

[0106] Table 1

[0107]

[0108] Note: 7.5% means m is 7.5%, which is calculated based on the characteristic peaks of NMR.

[0109] The above-mentioned luminescent materials were used as the luminescent layer to form a device: the luminescent material of the present invention (7.5%, i.e., m = 7.5%) was used as the undoped luminescent layer, indium tin oxide (ITO) and aluminum (Al) were used as the anode and cathode, respectively, PSS:PEDOT (poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid) and TMPYPB (1,3,5-tris(3-pyridyl-3-phenyl)benzene) were used as the hole and electron injection materials, respectively, and the substrate was glass. The device performance data is shown in Tables 2 and 3.

[0110] Table 2

[0111]

[0112] It can be seen from the table that the turn-on voltage is low.

[0113] Table 3

[0114]

[0115] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A luminescent material, characterized in that: Its structure is shown in formula (I): In formula (I), R1 and R2 represent substituents at any position on the benzene ring; R1 and R2 are independently selected from hydrogen, C1-C10 straight-chain alkyl or C3-C8 cycloalkyl; Host is a main unit with adjustable photophysical properties; m, a, b, c, d are mole percentages, independently selected from 1% to 99%, and m + a + b + c + d = 100%; The host unit Host is selected from one of the following structures: Wherein, R is selected from C5-C15 alkyl.

2. The luminescent material according to claim 1, characterized in that R1 and R2 are each independently selected from hydrogen or a C1-C6 straight chain alkyl group.

3. The luminescent material according to claim 1, characterized in that R1 and R2 are each independently selected from hydrogen or a C1-C3 straight chain alkyl group.

4. The luminescent material according to claim 1, characterized in that Its structure is shown in formula (II): Wherein, m, a, b, c, and d are mole percentages, independently selected from 1% to 99%, and m+a+b+c+d=100%.

5. The luminescent material according to any one of claims 1 to 4, characterized in that The weight average molecular weight of the luminescent material is 5000 to 30000 Daltons, and the polydispersity coefficient is 1.5 to 2.

5.

6. The method for preparing a luminescent material according to claim 1, wherein: The steps include: (1) subjecting the compound represented by formula (A) to a substitution reaction to obtain a first intermediate represented by formula (B); In formula (A) and formula (B), R1 and R2 represent substituents at any position on the benzene ring; R1 and R2 are independently selected from hydrogen, C1-C10 linear alkyl or C3-C8 cycloalkyl; in formula (B), X is chlorine, bromine or iodine; (2) reacting the first intermediate with a halide of Host to obtain a luminescent material represented by formula (I); Among them, Host is the main unit with controllable photophysical properties.

7. The preparation method according to claim 6, characterized in that: In step (1), N-halosuccinimide is reacted with the compound represented by formula (A) at a molar ratio of 4.5 to 5.5:1 to obtain a first intermediate; In step (2), a coupling reaction is carried out between the first intermediate and the halogenated compound of Host at a molar ratio of 1:8.9 to 9.5 in the presence of an organic nickel catalyst to obtain a polymer material represented by formula (I).

8. Use of the luminescent material according to any one of claims 1 to 5 in the preparation of an organic electroluminescent device.

9. An organic electroluminescent device, characterized in that: The light-emitting material comprises the light-emitting material according to any one of claims 1 to 5.

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