Blue-light-emitting material based on phenanthroimidazole derivative and preparation method and application of blue-light-emitting material

Abstract

The invention discloses a blue-light-emitting material based on a phenanthroimidazole derivative, and a preparation method and application of the blue-light-emitting material. The invention has the prominent characteristics that phenanthroimidazole is used as a donor, two groups with different acceptor capabilities, namely tert-butylbenzene and cyanophenyl, are selected to construct a novel blue light molecule, in addition, a benzene bridge is connected with an anthracene unit, and a certain LE state component is introduced in the long axis direction, so that the luminescence of a hybrid local charge transfer state can be formed, and the luminescence efficiency is improved. And the color purity and the luminous efficiency of the device are improved. Through the design, molecules inherit high luminous efficiency and wide band gap of anthracene groups, and also inherit the advantages of good thermal stability and bipolar transmission of phenanthroimidazole, devices prepared from the luminescent materials have good carrier transmission characteristics, turn-on voltage is 3.0-3.1 V, brightness is greater than 5000 cd.m <-2 >, and the luminescent materials have wide application prospects. The electroluminescent device is used for preparing a lighting source or a flat panel display.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic electroluminescence, and particularly relates to a class of blue light materials based on phenanthroimidazole derivatives, a preparation method thereof, and applications thereof. Background Art

[0002] Organic light emitting diode (OLED) technology has rapidly emerged in the fields of display and lighting due to its high contrast ratio, wide viewing angle, and fashionable design. In addition to these characteristics, organic light emitting diodes also utilize their luminescence characteristics and flexible design to find important applications in the fields of medicine, fashion, sports, etc. The phenomenon of electroluminescence (EL) was first discovered in inorganic materials and has been successfully commercialized. Inspired by the electroluminescence technology of inorganic materials, in the 1950s, researchers began to attempt the research of organic electroluminescent materials. Bernanose et al. at the University of Nancy in France applied a high voltage alternating current of 2000V to organic compounds such as acridine orange and carbazole in air, deposited or dissolved them on cellulose or cellophane films, and observed the first electroluminescence phenomenon, thus initiating the research process of OLED.

[0003] However, the existing blue light OLED materials still have the following technical bottlenecks: As the cornerstone of full-color displays, the performance of blue light OLEDs directly affects color performance and saturation, so it has attracted much attention from scientific researchers and practitioners. Although OLED technology has many advantages, blue OLEDs still face severe challenges in terms of luminous efficiency, durability, and material stability. In particular, although the existing thermally activated delayed fluorescence (TADF) materials can improve the exciton utilization rate through reverse intersystem crossing, the problems of device efficiency roll-off and color shift have not been solved. In recent years, the OLED industry has faced the phenomenon of a shortage of self-luminous materials and urgently needs to develop a self-owned luminous material system. The proposal of the "thermally activated delayed fluorescence" mechanism can effectively improve the exciton utilization rate of organic light emitting materials by utilizing triplet excitons in high-energy states, and has shown great potential and advantages in constructing highly efficient and stable blue light OLED materials.

[0004] Therefore, through the design of the molecular structure, the composition and properties of the excited state can be reasonably regulated, and a series of deep blue thermally activated delayed fluorescence materials have been constructed, providing new ideas for the development of high-quality blue light materials and the preparation of highly efficient blue light OLED devices. Summary of the Invention

[0005] The object of the present invention is to provide a class of preparation of blue light materials based on phenanthroimidazole derivatives and their applications in electroluminescent devices. Phenanthroimidazole compounds have the advantages of simple synthesis, easy modification, relatively wide band gap, high photoluminescence efficiency, good thermal stability and relatively balanced carrier injection / transport capabilities. The anthracene unit has high luminescence efficiency and good bipolar transport characteristics, and is one of the most commonly used building units for blue light materials, which conforms to the design concept of hot exciton materials. By introducing different acceptor groups in the short axis direction of phenanthroimidazole, the properties of its excited state are adjusted to form hybrid local charge transfer excited state luminescence, which is beneficial to narrow band luminescence and high exciton utilization rate. The constructed organic light emitting material is used to prepare high-efficiency blue organic light emitting diodes.

[0006] The structural general formula of the blue light material of the phenanthroimidazole derivative involved in the present invention is shown in the following formula I:

[0007]

[0008] In the formula, R is CN or tert-butyl.

[0009] For the above-mentioned technical solution, preferably, the structural formula of the blue light material is shown in M1 or M2:

[0010]

[0011] On the other hand, the present invention discloses a preparation method of the blue light material of the phenanthroimidazole derivative, which comprises the following steps:

[0012] Using 9,10-phenanthrenequinone, 4-bromobenzaldehyde, aniline containing R substituent and ammonium acetate as raw materials, the corresponding intermediate is obtained by one-step ring closure; then Suzuki reaction is carried out with 9-anthraceneboronic acid, potassium carbonate and adding a palladium catalyst to obtain the blue light material of the corresponding phenanthroimidazole derivative.

[0013] For the above-mentioned technical solution, preferably, the molar ratio of 9,10-phenanthrenequinone, 4-bromobenzaldehyde, aniline containing R substituent to ammonium acetate is 1:(1~1.5):(4~5):(5~6).

[0014] For the above-mentioned technical solution, preferably, the palladium catalyst is selected from at least one of tetrakis(triphenylphosphine)palladium and palladium acetate.

[0015] For the above-mentioned technical solution, preferably, the molar ratio of the intermediate to 9-anthraceneboronic acid and potassium carbonate is 1:(1~3):(6~8); the molar ratio of the intermediate to the palladium catalyst is 35~20:1.

[0016] The present invention also discloses the application of the blue light material of the phenanthroimidazole derivative in an organic electroluminescent device.

[0017] For the technical solution described above, preferably, the organic electroluminescent device includes a light-emitting diode device.

[0018] For the technical solution described above, preferably, the above-mentioned anthracene- and phenanthroimidazole derivative-containing luminescent small molecule can be used as a light-emitting layer for preparing an organic light-emitting diode device. The device structure of the organic electroluminescent device is anode / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / electron injection layer / cathode, where the organic light-emitting layer is a non-doped luminescent small molecule of the above two compounds. The material of the exciton blocking layer is 4,4',4”-tris(carbazol-9-yl)triphenylamine, and the thickness is 3-10 nm.

[0019] For the technical solution described above, preferably, the electroluminescent device is used for preparing a lighting source, a display device or a wearable electronic device.

[0020] In the present invention, a novel blue-light molecule is constructed by using phenanthroimidazole as a donor and selecting two groups with different acceptor abilities, namely tert-butylbenzene and benzonitrile, respectively. The introduction of tert-butyl can increase the torsion angle between the long and short axes to a certain extent, and the introduction of cyano can appropriately increase the donor-acceptor interaction, both of which introduce CT state components to a certain extent. However, their acceptor strengths are relatively weak among common acceptors, so that strong donor-acceptor interactions within the molecule can be avoided, and it is ensured to the greatest extent that the target compound emits blue light. In addition, by connecting the anthracene unit with a benzene bridge, a certain amount of LE state component is introduced in the long-axis direction, and luminescence of a hybrid local charge transfer state (HLCT) can be formed, improving the color purity and device luminescence efficiency of the device. The effects of modification sites and acceptor group strength on the hybrid properties of the molecule are systematically explored, providing new ideas for further guiding the structural design of blue-light phenanthroimidazole derivatives.

[0021] Advantages and beneficial effects of the present invention:

[0022] 1. In the present invention, phenanthroimidazole is used as a donor, and two groups with different acceptor abilities, namely tert-butylbenzene and benzonitrile, are selected. The introduction of tert-butyl increases the torsion angle between the long and short axes, while the introduction of cyano increases the interaction between the donor and acceptor. By two different connection methods, CT state components are introduced, thereby regulating the properties of the excited state and forming hybrid local charge transfer state luminescence. In particular, the introduction of tert-butyl increases the steric hindrance of the molecule, while cyano enhances the electron cloud density. The two work together to optimize the HLCT state components, thereby improving the color purity and luminescence efficiency of the device.

[0023] 2. The anthracene-containing phenanthroimidazole derivative luminescent small molecules provided by the present invention have the characteristics of high hole mobility and high electron mobility, which are beneficial to the transport and injection of holes and electrons in the electroluminescent device, thereby improving the overall performance of the device. Specifically, the anthracene structure in these materials not only has a wide bandgap and a high fluorescence quantum yield, but also combines with the large conjugated rigid structure of the phenanthroimidazole unit, which can effectively promote charge transport while maintaining a high luminescence efficiency.

[0024] 3. For the phenanthroimidazole derivatives provided by the present invention, wherein anthracene has a wide bandgap, a high fluorescence quantum yield, and the phenanthroimidazole unit has a large conjugated rigid structure, the emission of the blue light HLCT state can be constructed. The presence of anthracene endows the material with the characteristic of a wide bandgap, while the large conjugated rigid structure of the phenanthroimidazole unit helps to stabilize the HLCT state. The combination of the two can achieve efficient and stable blue light emission. In addition, due to the high fluorescence quantum yield of this type of compound, it is expected to achieve a high device efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the 1H NMR spectrum of the target compound M1;

[0026] Figure 2 is the 1H NMR spectrum of the target compound M2;

[0027] Figure 3 is the high-resolution mass spectrum of the target compound M1;

[0028] Figure 4 is the high-resolution mass spectrum of the target compound M2; Figures 1-4 As shown, the characteristic peaks in the 1H NMR spectra (1H NMR) of compounds M1 and M2 are completely matched with the hydrogen atom distribution in the target molecule (for example, the singlet of the tert-butyl protons in M1 is at δ = 1.42 ppm with an integration area of 9H), and the error between the molecular ion peak of the high-resolution mass spectrum (HRMS) and the theoretical value is less than 5 ppm, which proves that the target product with high purity has been successfully synthesized, laying a structural foundation for the stability of the subsequent device performance.

[0029] Figure 5 is a schematic diagram of the structure of the electroluminescent device prepared from the materials of the present invention; by optimizing the device layer structure (such as the introduction of the exciton blocking layer TCTA), the exciton diffusion to the non-emitting area can be effectively restricted. Combining with the high carrier mobility (μh / μe > 10^-4 cm 2 / V·s) of the phenanthroimidazole derivative in the light-emitting layer, the synergistic improvement of the low turn-on voltage (<3.5 V) and the high external quantum efficiency (>3%) of the device is finally achieved.

[0030] Figure 6is the electroluminescence spectrum of the target compound M1 under the non-doped device structure; the full width at half maximum (FWHM) of the electroluminescence spectrum of the M1 device is 42 nm, and the CIE coordinates (0.167, 0.106) meet the definition of deep blue light in the BT.2020 standard, proving its narrow-band emission characteristics; while for the M2 device ( Figure 7 ), the FWHM is 48 nm, still significantly better than traditional fluorescent materials (usually >60 nm), indicating that the phenanthroimidazole-anthracene hybrid structure effectively inhibits the spectral peak broadening caused by molecular vibration.

[0031] Figure 7 is the electroluminescence spectrum of the target compound M2 under the non-doped device structure; Figures 6-7 The electroluminescence spectrum proves that the materials of the present invention can achieve narrow-band blue light emission (FWHM < 50 nm) and high color purity (CIEy < 0.15), meeting the requirements of high-end display applications. Detailed implementation manners

[0032] The following combines the drawings and examples to further describe in detail the specific implementation manners of the present invention. The following examples are used to illustrate the present invention, but do not limit the scope of the present invention.

[0033] In the specific implementation process of the present invention, in addition to the key steps described in detail, a variety of conventional chemical reagents and standard operation procedures are used. For example, all solvents such as dichloromethane, N,N-dimethylformamide, methanol, etc. are purchased from commercial suppliers and their purity is ensured. In addition, common chemical reaction conditions such as TLC monitoring, rotary evaporation under reduced pressure, silica gel column chromatography, etc. are standard operations in the field of organic synthesis. The selection of these conventional steps and reagents is based on their wide applicability and reliability, and does not constitute a key impact on understanding the core technology of the present invention, so no detailed description is made.

[0034] The electroluminescent device structure prepared using the product of the present invention is as shown in Figure 5 : The names of each component are: transparent glass or other transparent substrate 1, ITO (indium tin oxide) attached to the transparent substrate as the anode 2, HATCN (dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile) as the hole injection layer 3, TAPC (4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline]) as the hole transport layer 4, TCTA (4,4',4'-tris(carbazol-9-yl)triphenylamine) as the exciton blocking layer 5, the material of the present invention as the light-emitting layer 6, TmPyPB (1,3,5-tris[(3-pyridyl)-3-phenyl]benzene) as the electron transport layer 7, LiF as the electron injection layer 8, and metal Al as the cathode 9.

[0035] The chemical structural formulas of HATCN, TAPC, TCTA, and TmPyPb are as follows:

[0036]

[0037] Example 1

[0038] The structural formula of compound M1 is as follows:

[0039]

[0040] The preparation method of the luminescent material M1 has the following preparation process:

[0041]

[0042] The specific preparation steps are as follows:

[0043] (1) Synthesis of Intermediate 1

[0044] Add 9,10-phenanthrenequinone (2.08 g, 10 mmol), 4-tert-butylaniline (6.4 ml, 40 mmol), ammonium acetate (4.01 g, 50 mmol), 4-bromobenzaldehyde (1.85 g, 10 mmol) and glacial acetic acid (80 ml) into a 250 ml two-necked round-bottom flask. Vacuumize the reaction system and introduce nitrogen, repeating three times. Under nitrogen protection, stir and reflux the reaction at 120 °C for 4 hours. During the reaction, perform TLC plate detection every 30 min to determine the reaction progress. After the reaction is completed, slowly cool to room temperature first, pour the mixture into ice water, then filter to obtain a green crude product, wash it once with acetic acid, twice with water, and three times with ethanol, and purify it by column chromatography. The eluent is petroleum ether / dichloromethane with a ratio of 1:2. Finally, Intermediate 1 (3.03 g, yield 60%) is obtained.

[0045] (2) Synthesis of Compound M1

[0046] Intermediate 1 (1.67 g, 3.3 mmol), 9-anthraceneboronic acid (0.734 g, 3.3 mmol), potassium carbonate (2.76 g, 20 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.12 g, 0.10 mmol) were added to a 100 ml two-necked round-bottom flask. Then, 10 ml of distilled water, 15 ml of tetrahydrofuran, and 20 ml of toluene were added in sequence. The system was evacuated to a vacuum environment, and then nitrogen gas was bubbled into the system three times repeatedly. The temperature was raised to 100 °C under a nitrogen atmosphere, and the mixture was stirred and refluxed for 48 hours. During the reaction process, the reaction progress was detected by TLC plate spotting. After the reaction was completed, the mixture was cooled to room temperature, 20 ml of distilled water was added, and it was extracted 5 times with dichloromethane. The organic phases were combined, dried thoroughly with anhydrous sodium sulfate overnight, and then purified by column chromatography. The eluent was petroleum ether / dichloromethane with a ratio of 1:3. Finally, a yellow solid M1 (1.31 g, yield 66%) was obtained. 1H NMR (400 MHz, DMSO-d6) δ 8.96 (d, J = 8.5 Hz, 1H), 8.91 (d, J = 8.4 Hz, 1H), 8.75 (d, J = 7.9 Hz, 1H), 8.70 (s, 1H), 8.16 (d, J = 8.5 Hz, 2H), 7.81 (dd, J = 7.9, 3.3 Hz, 4H), 7.77–7.69 (m, 4H), 7.62–7.46 (m, 5H), 7.45–7.36 (m, 5H), 7.27–7.22 (m, 1H), 1.42 (s, 9H). HRMS ESI: m / z: 603.2795 [M+H]+. The above analysis results indicate that the obtained product is the expected product.

[0047] Example 2

[0048] The structural formula of compound M2 is as follows:

[0049]

[0050] The preparation method of the luminescent material M2 has the following preparation process:

[0051]

[0052] Synthesis of compound M2

[0053] According to the synthesis of compound M1, the same procedure was followed, substituting 4-tert-butylaniline with p-aminobenzonitrile to obtain a white solid M2 (1.21 g, yield 64%). 1H NMR (600 MHz, DMSO-d6) δ 8.99 (d, J = 8.5 Hz, 1H), 8.94 (d, J = 8.4 Hz, 1H), 8.76 (dd, J = 8.0, 1.5 Hz, 1H), 8.71 (s, 1H), 8.29–8.25 (m, 2H), 8.19–8.12 (m, 4H), 7.85–7.71 (m, 4H), 7.64–7.60 (m, 1H), 7.55 (ddd, J = 8.2, 4.4, 3.0 Hz, 2H), 7.49–7.42 (m, 7H), 7.15 (d, J = 8.2 Hz, 1H). APCI: m / z: 572.2 [M+H]+. The above analysis results indicate that the obtained product is the expected product.

[0054] Example 3

[0055] In this example, a non-doped electroluminescent device with compound M1 as the light-emitting layer was fabricated. The device structure was [ITO / HATCN / TAPC / TCTA / Compound M1 / TmPyPB / LiF / Al].

[0056] Using the vacuum evaporation process, a hole injection layer HATCN (with a thickness of 5 nm), a hole transport layer TAPC (20 nm), an exciton blocking layer TCTA (5 nm), a light-emitting layer of compound M1 prepared in Example 1 (20 nm), an electron transport layer TmPyPB (40 nm), an electron injection layer LiF (1 nm), and metal Al as the cathode (200 nm) were sequentially evaporated on a glass substrate coated with an ITO anode. The pressure was maintained at 5×10 -5 Pa during the evaporation process.

[0057] The turn-on voltage of this device is relatively low, only 3.1 V. The maximum current efficiency, maximum power efficiency, and maximum external quantum efficiency are 3.37 cd·A -1 , 2.97 lm·W -1 and 3.20%, respectively. Additionally, the electroluminescent wavelength of this device is 435 nm, and the CIE coordinates are (0.167, 0.106), located in the deep blue light-emitting region, and the brightness can reach 5975 cd·m -2 .

[0058] Example 4

[0059] In this example, a non-doped electroluminescent device with compound M2 as the light-emitting layer was fabricated. The device structure was [ITO / HATCN / TAPC / TCTA / Compound M2 / TmPyPB / LiF / Al].

[0060] Using the vacuum evaporation process, a hole injection layer HATCN (with a thickness of 5 nm), a hole transport layer TAPC (20 nm), an exciton blocking layer TCTA (5 nm), a light-emitting layer which is the compound M2 prepared in Example 1 (20 nm), an electron transport layer TmPyPB (40 nm), an electron injection layer LiF (1 nm), and a metal Al as the cathode (200 nm) are successively evaporated on a glass substrate coated with an ITO anode. During the evaporation process, the pressure is maintained at 5×10 -5 Pa.

[0061] The turn-on voltage of this device is relatively low, only 3.0 V. The maximum current efficiency, maximum power efficiency, and maximum external quantum efficiency are 1.94 cd·A -1 , 2.03 lm·W -1 and 0.87%, respectively. In addition, the electroluminescence wavelength of this device is 435 nm, and the CIE coordinates are (0.205, 0.213), which is located in the blue light-emitting region, and the brightness can reach 5280 cd·m -2 .

[0062] It should be understood that the above embodiments are only for more clearly explaining the technical solutions of the present invention, rather than limiting its protection scope. Those of ordinary skill in the art can make various modifications and variations to the above embodiments without departing from the spirit and basic principles of the present invention, but these modifications and variations still fall within the protection scope of the claims of the present invention and their equivalent replacements. The protection scope of the present invention should be subject to the appended claims, rather than being limited to the specific details of the above embodiments.

Claims

1. A class of blue light materials based on phenanthroimidazole derivatives, and the compound has a structure shown in the following formula I: The R is tert-butyl or CN.

2. The blue light material according to claim 1, characterized in that: Its structural formula is shown as M1 or M2:

3. The preparation method of the blue light material according to claim 1 or 2, characterized in that, It includes the following steps: Using 9,10-phenanthrenequinone, 4-bromobenzaldehyde, aniline containing R substituent and ammonium acetate as raw materials, obtaining the corresponding intermediate through one-step ring closure; then carrying out Suzuki reaction with 9-anthraceneboronic acid, potassium carbonate and adding a palladium catalyst to obtain the blue light material of the corresponding phenanthroimidazole derivative.

4. The preparation method according to claim 3, wherein The molar ratio of 9,10-phenanthrenequinone, 4-bromobenzaldehyde, aniline containing R substituent to ammonium acetate is 1:(1-1.5):(4-5):(5-6).

5. The preparation method according to claim 3, wherein The palladium catalyst is selected from at least one of tetrakis(triphenylphosphine)palladium and palladium acetate.

6. The preparation method according to claim 3, wherein The molar ratio of the intermediate to 9-anthraceneboronic acid and potassium carbonate is 1:(1-3):(6-8); the molar ratio of the intermediate to the palladium catalyst is 35-20:

1.

7. Application of the blue light material of the phenanthroimidazole derivative as described in claim 1 in an organic electroluminescent device.

8. The application according to claim 7, wherein: The organic electroluminescent device includes a light emitting diode device.

9. The application according to claim 7, characterized in that: The device structure of the organic electroluminescence is anode / hole injection layer / hole transport layer / exciton blocking layer / light emitting layer / electron transport layer / electron injection layer / cathode, wherein the light emitting layer contains the phenanthroimidazole derivative as a non-doped light emitting material; the material of the exciton blocking layer is 4,4',4”-tris(carbazol-9-yl)triphenylamine and the thickness is 3-10 nm.

10. The application according to claim 7, wherein: The electroluminescent device is used for preparing an illumination light source, a display device or a wearable electronic device.

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