T-type phenanthroimidazole heat exciton blue fluorescent material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of organic electroluminescent materials, and discloses a T-type phenanthroimidazole heat exciton blue fluorescent material as well as a preparation method and application thereof. According to the invention, p-cyanophenyl with electron withdrawing capability is introduced to 5-position and 10-position carbon atoms of a phenanthroimidazole core skeleton as an acceptor part, and triphenylamine and 4-carbazolyl phenyl with electron donating capability are introduced to 2-position carbon atoms as donor parts, so that the excited state property of the T-type phenanthroimidazole derivative is effectively regulated and controlled. The molecular design endows the organic semiconductor material with the characteristic of emitting blue fluorescence in both a solution state and a solid state, and shows a heat exciton fluorescence behavior.

Description

Technical Field

[0001] The invention relates to the technical field of organic electroluminescent materials, and in particular discloses a novel T-type phenanthroimidazole thermoexciton blue fluorescent material and a preparation method and application thereof. Background Art

[0002] In the field of organic electroluminescence (OLEDs), the evolution of luminescent materials has encompassed multiple stages, from traditional fluorescent materials to phosphorescent materials, and finally to pure organic luminescent materials with high exciton utilization efficiency. In traditional fluorescent OLEDs, spin statistics limit the utilization efficiency of singlet excitons to approximately 25%, while 75% of triplet excitons undergo non-radiative transitions, resulting in significant energy loss. Although phosphorescent materials containing noble metals can achieve theoretical exciton utilization efficiencies as high as 100%, their high cost remains a significant limiting factor. For TTA materials, their exciton utilization efficiency (EUE) can reach as high as 62.5%, relying on the fusion of two triplet excitons to form a singlet exciton. Achieving the maximum efficiency of TTA materials requires precisely tailoring the molecular structure to meet specific energy requirements. TADF materials effectively utilize triplet excitons through a process called reverse intersystem crossing (RISC) from the lowest triplet excited state (T1) to the lowest singlet excited state (S1). However, TADF materials face many challenges, including strong charge transfer (CT) effects that lead to broadening of the emission spectrum, red shift, and degradation of light color, as well as significant efficiency drops at high brightness due to long luminescence lifetimes in the millisecond range. Against this backdrop, Professor Ma Yuguang and his team proposed a hot exciton material with high-energy triplet antisystem crossing properties. This type of material mainly achieves high-energy triplet intersystem crossing from higher triplet states (T n , where n ≥ 2) to higher singlet states (S m , where m ≥ 1) to capture triplet excited states through a high-energy reverse intersystem crossing (hRISC) process, achieving exciton utilization of up to 100%. This process also shortens the triplet exciton lifetime to nanoseconds, significantly reducing triplet exciton accumulation and thus minimizing efficiency roll-off. This research has achieved significant breakthroughs in luminescence efficiency and quickly attracted widespread attention from both academia and industry. Hot excitonic material systems primarily utilize heteroatom-containing donor and acceptor structures to tailor their excited-state properties to meet the requirements of hot excitonic processes. Although significant progress has been made in developing hot excitonic materials based on donor-acceptor structures, the number of high-performance hot excitonic materials remains limited. In particular, the development of efficient and stable hot excitonic blue fluorescent materials remains challenging. Therefore, in-depth research on organic electroluminescent devices based on hot excitonic materials is of great scientific and practical significance for advancing OLED technology.

[0003] In current research on thermoexciton materials, phenanthren[9,10-d]-imidazole, a group with bipolar transport properties, is often used to construct blue fluorescent materials by introducing donors at the 2-carbon position of its imidazole group. However, the range of materials modified at other positions (particularly the 5- and 10-carbon positions) is relatively limited. This current situation indicates that much work remains to be done to expand the range of thermoexciton materials and further optimize their electroluminescent properties, particularly in developing efficient and stable thermoexciton blue fluorescent materials. Summary of the Invention

[0004] This invention uses phenanthroimidazole as the core skeleton, introduces p-cyanophenyl groups as acceptors at the 5- and 10-positions of the phenanthroimidazole, and introduces triphenylamine and 4-carbazolylphenyl groups as donors at the imidazole carbon atom at the 2-position. This results in a T-shaped phenanthroimidazole thermoexciton blue fluorescent material. By combining the donor-like triphenylamine or carbazole group with the acceptor-like p-cyanophenyl group in a T-shaped configuration, the charge transfer (CT) transition between the donor and the acceptor is effectively promoted. This structural design provides a favorable channel for the formation of thermoexcitons, significantly improving the luminescence efficiency of the material. Furthermore, the invention utilizes phenanthroimidazole, a core skeleton motif with bipolar transport properties. Its rigid structure effectively suppresses nonradiative molecular transitions, thereby improving the luminescence efficiency of the thermoexciton blue fluorescent material. Furthermore, the invention also thoroughly investigates the effects of triphenylamine and carbazole as donors on the photophysical properties of the luminescent material, providing important theoretical basis and experimental guidance for the exploration of high-performance thermoexciton blue fluorescent materials. This has significant scientific significance and application value.

[0005] In order to achieve the above technical objectives, the present invention synthesized a type of T-type phenanthroimidazole thermoexciton blue fluorescent material with phenanthroimidazole as the core skeleton, p-cyanophenyl as the acceptor, triphenylamine and 4-carbazolylphenyl as the donor. The material has the following structures: The present invention synthesizes a type of thermoexciton material with a triphenylamine derivative as a donor and tris(triazole)triazine as an acceptor. The material has the following structure: The preparation method of the T-type phenanthroimidazole thermoexciton blue fluorescent material comprises the following steps: (1) 4-Diphenylaminobenzaldehyde or 4-(9H-carbazole-9-yl)benzaldehyde, 2,7-dibromophenanthrenequinone, aniline, ammonium acetate and acetic acid were placed in a two-necked flask and refluxed at 120°C for 3 hours under argon protection. The mixture was cooled to room temperature and filtered. The filter cake was washed with acetic acid, a 1:1 acetic acid aqueous solution and deionized water in sequence, purified by column chromatography and recrystallized from dichloromethane / n-hexane to obtain the intermediate 2BrDPAPPI or 2BrCzPPI. (2) 2BrDPAPPI or 2BrCzPPI, 4-cyanophenylboronic acid, anhydrous potassium carbonate, tetrakis(triphenylphosphine)palladium, deionized water, toluene and tetrahydrofuran were placed in a double-necked flask and refluxed at 90°C for 72 hours under argon protection. The crude product was filtered and purified by column chromatography and recrystallized from dichloromethane / n-hexane to obtain a T-type phenanthroimidazole thermoexciton blue fluorescent material.

[0006] Synthesis of intermediate 2BrDPAPPI: (1) The molar ratio of raw materials: 4-diphenylaminobenzaldehyde: 2,7-dibromophenanthrenequinone: aniline: ammonium acetate = 1: 0.8~1.2: 3~5: 4~6; (2) Temperature: 100~130℃; (3) Reaction time: 2 to 6 hours; (4) Eluent (volume ratio): dichloromethane: petroleum ether = 1:2~8.

[0007] Synthesis of intermediate 2BrCzPPI: (1) The molar ratio of raw materials: 4-diphenylaminobenzaldehyde: 2,7-dibromophenanthrenequinone: aniline: ammonium acetate = 1: 0.8~1.2: 3~5: 4~6; (2) Temperature: 100~130℃; (3) Reaction time: 2 to 6 hours; (4) Eluent (volume ratio): dichloromethane: petroleum ether = 1:2~8.

[0008] Synthesis of compound 1: (1) Molar ratio of raw materials: 2BrDPAPPI (0.75 mmol, 0.52 g), 4-cyanophenylboronic acid (2.5 mmol, 0.38 g), anhydrous potassium carbonate (10 mmol, 1.05 g), tetrakis(triphenylphosphine)palladium (0.05 g, 0.044 mmol) = 1:2~4:5~15:0.05~0.08; (2) Temperature: 80~110℃; (3) Reaction time: 60~80 hours; (4) Eluent (volume ratio): ethyl acetate: petroleum ether = 1:2.5~7.5.

[0009] Synthesis of compound 2: (1) Molar ratio of raw materials: 2BrCzPPI (0.75 mmol, 0.52 g), 4-cyanophenylboronic acid (2.5 mmol, 0.38 g), anhydrous potassium carbonate (10 mmol, 1.05 g), tetrakis(triphenylphosphine)palladium (0.05 g, 0.044 mmol) = 1:2~4:5~15:0.05~0.08; (2) Temperature: 80~110℃; (3) Reaction time: 60~80 hours; Eluent (volume ratio): ethyl acetate: petroleum ether = 1:2.5~7.5.

[0010] Another object of the present invention is to provide an application of a thermoexciton blue fluorescent material as a luminescent material for an organic electroluminescent diode to obtain an organic electroluminescent device with excellent luminescent performance.

[0011] The organic light-emitting diode structure is: ITO / TAPC: MoO3(30 nm) / TAPC (10 nm) / ADN: compound 1 or 2 (5wt%, 10wt%, 15wt%, 20wt%) (20 nm) / TPBi (20 nm) / TPBi: 20% Liq (30 nm) / Al(150 nm).

[0012] Using the above-mentioned T-type phenanthroimidazole thermoexciton blue fluorescent material constructed based on phenanthroimidazole as the core skeleton, p-cyanophenyl as the acceptor, triphenylamine and 4-carbazolylphenyl as the donors as the dopant of the light-emitting layer, an electroluminescent device was prepared. The color coordinates of the bluest device were (0.15, 0.11), the highest external quantum efficiency reached 4.22%, and it showed very low efficiency roll-off.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The present invention uses phenanthroimidazole as the core skeleton, p-cyanophenyl as the acceptor, triphenylamine and 4-carbazolylphenyl as the donor. By precisely controlling the structure of the donor molecule, the characteristics of the simultaneous existence of hybrid localized states and charge transfer states in the molecule are successfully constructed, thereby forming a thermal exciton channel. A new T-type phenanthroimidazole thermal exciton blue fluorescent material has been developed. Its luminescence mechanism is significantly different from the luminescence principles of currently reported traditional fluorescent materials, TTA materials, noble metal phosphorescent materials and thermally activated delayed fluorescent materials. (2) The electroluminescent device using this type of T-type phenanthroimidazole thermoexciton blue fluorescent material as the dopant of the light-emitting layer obtained the color coordinates of the bluest device to be (0.15, 0.11), the highest external quantum efficiency reached 4.22%, and showed very low efficiency roll-off phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a photoluminescence spectrum of Compound 1 prepared in Example 1 of the present invention in n-hexane, triethylamine, dibutyl ether, isopropyl ether, ethyl acetate, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, acetone and acetonitrile solutions; Figure 2 This is a photoluminescence spectrum of compound 2 prepared in Example 1 of the present invention in n-hexane, triethylamine, dibutyl ether, isopropyl ether, ethyl acetate, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, acetone and acetonitrile solutions; Figure 3 This is a graph showing the instantaneous lifespan of Compound 1 in a solid powder state, as prepared in Example 1 of the present invention; Figure 4 This is a graph showing the instantaneous lifespan of compound 2 prepared in Example 1 of the present invention in a solid powder state; Figure 5 The electroluminescence spectra of an electroluminescent device prepared using Compound 1 obtained in Example 1 of the present invention as a luminescent material at different doping concentrations are shown below: Figure 6 The brightness-voltage-current density curves of an electroluminescent device prepared using Compound 1 obtained in Example 1 of the present invention as a luminescent material at different doping concentrations; Figure 7 The external quantum efficiency-brightness-current efficiency curves of an electroluminescent device prepared using Compound 1 obtained in Example 1 of the present invention as a luminescent material at different doping concentrations; Figure 8 The electroluminescence spectra of an electroluminescent device prepared using compound 2 obtained in Example 1 of the present invention as a luminescent material at different doping concentrations are shown below: Figure 9 Brightness-voltage-current density curves of an electroluminescent device prepared using Compound 2 prepared in Example 1 of the present invention as a luminescent material at different doping concentrations; Figure 10 The external quantum efficiency-brightness-current efficiency curves of an electroluminescent device prepared using compound 2 obtained in Example 1 of the present invention as a luminescent material at different doping concentrations. DETAILED DESCRIPTION

[0015] The following specific implementation cases are intended to further illustrate the present invention, but these specific implementation cases do not limit the scope of protection of the present invention in any way.

[0016] Example 1 The synthesis scheme of the T-type phenanthroimidazole thermoexciton blue fluorescent material based on the present invention is as follows: Synthesis of intermediate 2BrDPAPPI 4-Dianilinobenzaldehyde (4.0 mmol, 1.09 g), 2,7-dibromophenanthrenequinone (4.0 mmol, 1.44 g), aniline (16.0 mmol, 14.6 mL), ammonium acetate (20 mmol, 1.48 g), and acetic acid (20 mL) were placed in a two-necked flask and refluxed at 120°C for 3 hours under argon protection. The mixture was cooled to room temperature and filtered. The filter cake was washed with acetic acid, a 1:1 aqueous acetic acid solution, and deionized water in sequence. The product was purified by column chromatography (eluent: dichloromethane: petroleum ether = 1:5) and recrystallized from dichloromethane / n-hexane to obtain 2BrDPAPPI as a white solid. 1 H NMR (400 MHz, DMSO- d 6) δ 8.84 (dd, J = 12.5,9.0 Hz, 2H), 8.75 (d, J = 2.3 Hz, 1H), 7.82 (dd, J = 8.9, 2.3 Hz, 1H), 7.78 –7.73 (m, 5H), 7.69 (dd, J = 8.9, 2.1 Hz, 1H), 7.52 – 7.46 (m, 2H), 7.38 – 7.32(m, 4H), 7.15 – 7.09 (m, 2H), 7.08 – 7.04(m, 4H), 7.03 (d, J = 2.1 Hz, 1H),6.85 – 6.79 (m, 2H). Synthesis of intermediate 2BrCzPPI 4-(9H-carbazol-9-yl)benzaldehyde (4.0 mmol, 1.08 g), 2,7-dibromophenanthrenequinone (4.0 mmol, 1.44 g), aniline (16.0 mmol, 14.6 mL), ammonium acetate (20 mmol, 1.48 g), and acetic acid (20 mL) were placed in a two-necked flask and refluxed at 120°C for 3 hours under argon protection. The mixture was cooled to room temperature and filtered. The filter cake was washed with acetic acid, a 1:1 aqueous acetic acid solution, and deionized water in sequence. The product was purified by column chromatography (eluent: dichloromethane:petroleum ether = 1:5) and recrystallized from dichloromethane / n-hexane to obtain 2BrCzPPI as a white solid. 1 H NMR (400 MHz, Chloroform- d ) δ 9.07(s, 1H), 8.51(dd, J= 25.8, 8.0 Hz, 2H), 8.13 (d, J = 7.4 Hz, 2H), 7.74 (d, J =9.6 Hz, 6H), 7.61 (d, J = 8.6 Hz, 4H), 7.41 (s, 4H), 7.30 (s, 2H), 7.23 (s, 2H). Synthesis of compound 1 2BrDPAPPI (0.75 mmol, 0.52 g), 4-cyanophenylboronic acid (2.5 mmol, 0.38 g), anhydrous potassium carbonate (10 mmol, 1.05 g), tetrakis(triphenylphosphine)palladium (0.05 g, 0.044 mmol), deionized water (8.0 mL), toluene (10.0 mL), and tetrahydrofuran (5.0 mL) were placed in a two-necked flask and refluxed at 90°C under argon for 72 hours. The reaction was then filtered and the crude product was purified by column chromatography (eluent: ethyl acetate:petroleum ether = 1:5) and recrystallized from dichloromethane / n-hexane to give 0.45 g of a white solid with a yield of 81%. 1 H NMR (400 MHz, Chloroform- d ) δ9.16 (s, 1H), 8.81 (dd, J = 19.9, 8.7 Hz, 2H), 8.02 (d, J = 5.6 Hz, 2H), 7.91 (d, J = 8.6 Hz, 1H), 7.79 (dd, J = 12.2, 7.9 Hz, 3H), 7.69 (d, J = 6.6 Hz, 3H), 7.66 –7.58 (m, 4H), 7.57 – 7.45 (m, 2H), 7.38 (d, J = 8.3 Hz, 3H), 7.28 (d, J = 7.7 Hz,4H), 7.08 (dd, J = 13.5, 7.4 Hz, 6H), 6.96 (d, J = 8.2 Hz, 2H). Synthesis of compound 2 2BrCzPPI (0.75 mmol, 0.52 g), 4-cyanophenylboronic acid (2.5 mmol, 0.38 g), anhydrous potassium carbonate (10 mmol, 1.05 g), tetrakis(triphenylphosphine)palladium (0.05 g, 0.044 mmol), deionized water (8.0 mL), toluene (10.0 mL), and tetrahydrofuran (5.0 mL) were placed in a two-necked flask and refluxed at 90°C under argon for 72 hours. The reaction was then filtered and the crude product was purified by column chromatography (eluent: ethyl acetate:petroleum ether = 1:5) and recrystallized from dichloromethane / n-hexane to give 0.29 g of a white solid with a yield of 53%. 1 H NMR (400 MHz, Chloroform- d ) δ 9.07 –8.82 (m, 3H), 8.14 (t, J = 9.4 Hz, 3H), 8.05 (d, J = 8.7 Hz, 1H), 7.93 (dd, J =33.7, 8.4 Hz, 11H), 7.77 (t, J = 6.8 Hz, 4H), 7.45 (dd, J = 10.6, 7.3 Hz, 7H),7.34 (t, J = 7.1 Hz, 2H). Example 2 The photoluminescence properties of compounds 1 and 2 in Example 1 were tested in different solutions. Compounds 1 and 2 were dissolved in n-hexane, triethylamine, dibutyl ether, isopropyl ether, ethyl acetate, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, acetone and acetonitrile solutions, and their photoluminescence spectra in different solutions were tested. Figure 1 and 2 As shown in the figure, both compounds exhibit distinct solvatochromic changes with increasing solvent polarity, a typical hallmark of CT characteristics within the corresponding excited-state molecules. Furthermore, compared to the n-hexane solution, the maximum red shift for compound 1 in acetonitrile solution is 80 nm, and for compound 2, 32 nm.

[0017] Example 3 The fluorescence lifetimes of compounds 1 and 2 in Example 1 were tested in solid powder state. Figure 3 and 4 As shown in Figure 3, the fluorescence lifetimes of the two compounds were fitted to be 10.03 ns and 1.61 ns, respectively, both of which are short lifetimes.

[0018] Example 4 The application of compounds 1 and 2 in Example 1 in organic electroluminescent devices. An organic electroluminescent diode having a structure of ITO / TAPC: MoO3 (30 nm) / TAPC (10 nm) / ADN: compound 1 or 2 (5wt%, 10wt%, 15wt%, 20wt%) (20 nm) / TPBi (20 nm) / TPBi: 20% Liq (30 nm) / Al (150 nm) was prepared using the compound as a dopant in the device light-emitting layer. Among them, ITO was used as the anode, TAPC:MoO3 was used as the hole injection layer, TAPC was used as the hole transport layer, TPBi was used as the electron transport and exciton blocking layer, TPBi: 20% Liq was used as the electron injection layer, Al was used as the cathode, and ADN was used as the main material. The electroluminescence spectrum of compound 1 in Example 1 in the organic electroluminescent device is as follows: Figure 5 As shown, in the devices with 5wt%, 10wt%, 15wt%, and 20wt% doping, blue light emission is exhibited, and the maximum emission peaks are 472 nm, 480 nm, 480 nm, and 480 nm, respectively, and the corresponding color coordinates are (0.15, 0.25), (0.17, 0.32), (0.17, 0.33), and (0.18, 0.34), respectively. The brightness-voltage-current density curve of compound 1 in Example 1 in the organic electroluminescent device is shown in FIG. Figure 6 As shown in Figure 2, the maximum luminance of the devices with 5wt%, 10wt%, 15wt%, and 20wt% doping is 25032 cd m -2 、25260cd m -2 、21024 cd m -2 、18720 cd m -2 The external quantum efficiency-brightness-current efficiency curve of compound 1 in Example 1 in an organic electroluminescent device is as follows: Figure 7 As shown in FIG, the maximum external quantum efficiency in the devices with 5wt%, 10wt%, 15wt% and 20wt% doping is 4.15%, 3.71%, 4.22% and 3.47% respectively. The electroluminescence spectrum of compound 2 in Example 1 in the organic electroluminescent device is as shown in FIG. Figure 8 As shown in Figure 2, the devices with 5wt%, 10wt%, 15wt% and 20wt% doping all showed blue light emission, with maximum emission peaks of 448 nm, 452 nm, 456 nm and 458 nm, respectively, and corresponding color coordinates of (0.16, 0.10), (0.15, 0.11), (0.15, 0.15) and (0.15, 0.13), respectively. The brightness-voltage-current density curve of compound 2 in Example 1 in the organic electroluminescent device is shown in Figure 2. Figure 9As shown in Figure 2, the maximum luminance of the devices with 5wt%, 10wt%, 15wt%, and 20wt% doping is 50861 cd m -2 、5826 cd m -2 、6466 cd m -2 、7872 cd m -2 The external quantum efficiency-brightness-current efficiency curve of compound 2 in Example 1 in an organic electroluminescent device is as follows: Figure 10 As shown, the maximum external quantum efficiency in the devices with 5wt%, 10wt%, 15wt% and 20wt% doping are 2.40%, 2.98%, 2.45% and 2.80%, respectively.

Claims

1. A T-type phenanthroimidazole thermoexciton blue fluorescent material, characterized by: The fluorescent material is based on phenanthroimidazole as the core skeleton, with p-cyanobenzene introduced as an acceptor on the 5- and 10-carbon atoms, and triphenylamine introduced on the 2-carbon atom. Its molecular structure is shown in Formula 1; 4-carbazolylphenyl is introduced as a donor on the 2-carbon atom. Its molecular structure is shown in Formula 2.

2. The method for preparing the T-type phenanthroimidazole thermoexciton blue fluorescent material according to claim 1, wherein: Here are the steps: (1) 4-Diphenylaminobenzaldehyde or 4-(9H-carbazole-9-yl)benzaldehyde, 2,7-dibromophenanthrenequinone, aniline, ammonium acetate and acetic acid were placed in a two-necked flask and refluxed at 120°C for 3 hours under argon protection. The mixture was cooled to room temperature and filtered. The filter cake was washed with acetic acid, a 1:1 acetic acid aqueous solution and deionized water in sequence, purified by column chromatography and recrystallized from dichloromethane / n-hexane to obtain the intermediate 2BrDPAPPI or 2BrCzPPI. (2) 2BrDPAPPI or 2BrCzPPI, 4-cyanophenylboronic acid, anhydrous potassium carbonate, tetrakis(triphenylphosphine)palladium, deionized water, toluene and tetrahydrofuran were placed in a double-necked flask and refluxed at 90°C for 72 hours under argon protection. The crude product was filtered and purified by column chromatography and recrystallized from dichloromethane / n-hexane to obtain a T-type phenanthroimidazole thermoexciton blue fluorescent material.

3. The use of the T-type phenanthroimidazole thermoexciton blue fluorescent material according to claim 1, characterized in that: The T-type phenanthroimidazole thermoexciton blue fluorescent material is used as the light-emitting layer of the organic light-emitting diode.

4. The use of the T-type phenanthroimidazole thermoexciton blue fluorescent material according to claim 3, characterized in that: The organic light-emitting diode structure is: ITO / TAPC: MoO3 (30 nm) / TAPC (10 nm) / ADN: compound 1 or 2 (5wt%, 10wt%, 15wt%, 20wt%) (20 nm) / TPBi (20 nm) / TPBi: 20% Liq (30 nm) / Al (150 nm).

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