Small organic molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization as well as preparation method and application of small organic molecule material

Abstract

The invention relates to the technical field of organic electroluminescence, in particular to an intramolecular cyclization small organic molecule material based on carbonyl / nitrogen resonance core as well as a preparation method and application of the intramolecular cyclization small organic molecule material. The blue MR-TADF material with high color purity, high luminous efficiency and high stability is designed. The material is relatively simple to synthesize, mild in condition, high in yield and excellent in electroluminescent performance. Specifically, the multi-resonance electroluminescent material containing the nitrogen carbonyl group has a rigid planar structure, nitrogen atoms are used as electron donors, carbonyl groups are used as electron acceptors, and charge transfer paths in molecules can be limited in specific regions through a multi-resonance effect, so that mutual coupling of electrons and holes in the molecules is reduced, and the luminescence efficiency is improved. Therefore, under the condition that the emission energy is not obviously reduced, small excited state recombination energy is realized, and the color purity and the luminous efficiency of the material are favorably improved.

Description

Technical Field

[0001] The invention relates to the technical field of organic electroluminescence, and in particular to an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization and a preparation method and application thereof. Background Art

[0002] Organic light-emitting diodes (OLEDs) are widely used in displays of smartphones, televisions, and wearable electronic devices due to their advantages such as high brightness, wide viewing angle, low energy consumption, fast response, and flexible display. In recent years, thermally activated delayed fluorescence (TADF) has attracted much attention because it uses inexpensive organic molecules to achieve 100% exciton utilization through the reverse conversion from triplet state to ground state, and has become an important research direction for the next generation of OLED materials. However, while TADF materials achieve high efficiency, the color purity of the device is poor and cannot meet the requirements of full-color display technology. Therefore, achieving high-efficiency, high-definition, and high-color gamut OLEDs remains a major challenge.

[0003] In 2016, Hatakeyama et al. proposed a narrow spectrum strategy and designed a multi-resonance thermally activated delayed fluorescence (MR-TADF) molecule. By doping boron-nitrogen (or oxygen) atoms in the conjugated system, the multiple resonance effect (MR) of boron and nitrogen atoms was utilized to effectively suppress the stretching vibration of the molecular skeleton and achieve a narrow full-width at half maximum (FWHM). This strategy successfully improved the luminescence purity and efficiency of TADF materials and promoted the development of OLED technology. However, most MR-TADF materials currently face complex synthesis, harsh reaction conditions, and low yields, which limit their large-scale application and commercialization process. In particular, MR-TADF materials used for blue light emission face greater challenges in practical applications due to their higher requirements for chemical and thermal stability.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization and a preparation method and application thereof, aiming to solve the problems of low color purity and poor stability of existing MR-TADF materials in blue luminescence.

[0006] The technical solution of the present invention is as follows: An organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization, wherein the general structural formula of the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization is as shown in formula (1) or formula (2): Formula (1); Formula (2); Wherein, R is an alkyl chain or an aromatic ring.

[0007] The organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization, wherein the R is selected from one of the following substituents: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , .

[0008] The organic small molecule material based on carbonyl / nitrogen resonance core molecule intramolecular cyclization, wherein the organic small molecule material based on carbonyl / nitrogen resonance core molecule intramolecular cyclization includes , , One or more of .

[0009] A method for preparing an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization, comprising the steps of: Will Carrying out ester hydrolysis reaction under alkaline conditions to obtain a first product; wherein R1 and R2 are both hydrogen or di-tert-butyl; The first product is concentrated and acidified, and then reacted with oxalyl chloride ions to obtain a second product; The second product is mixed with tin tetrachloride, and after reaction, an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization is obtained.

[0010] The method for preparing organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization, wherein the The preparation method comprises the steps of: Will and Under catalytic conditions, the reaction is carried out to obtain ; Among them, the With the The molar ratio is (1-2):(1-2).

[0011] The method for preparing organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization, wherein the temperature for the reaction under catalytic conditions is 150°C-180°C, and the time for the reaction under catalytic conditions is 30h-40h.

[0012] The method for preparing organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization is characterized in that The step of performing an ester hydrolysis reaction under alkaline conditions to obtain a first product comprises: Will , sodium hydroxide, tetrahydrofuran and a mixed solvent of water to obtain a first mixed solution; The first mixed solution is heated and refluxed to obtain the first product.

[0013] An application of an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization in an organic electroluminescent device.

[0014] The application described above, wherein the organic electroluminescent device includes a cathode, an anode, and an organic thin film layer arranged between the cathode and the anode; the organic thin film layer includes at least one organic light-emitting layer; the organic light-emitting layer contains the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization.

[0015] In the application, the mass percentage of the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization in the organic light-emitting layer is 3%-5%.

[0016] Beneficial effects: The present invention provides an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization and its preparation method and application. The present invention uses the strategy of intramolecular ring and the multiple resonance effect of carbonyl and nitrogen atoms to design a blue MR-TADF material with high color purity, high luminous efficiency and high stability. The synthesis of this material is relatively simple, the conditions are mild, and the yield is high. At the same time, its electroluminescent performance is excellent, which makes this small molecule material have broad application prospects. Specifically, the multiple resonance electroluminescent material containing nitrogen carbonyl has a rigid planar structure, in which the nitrogen atom acts as an electron donor and the carbonyl acts as an electron acceptor. Through the multiple resonance effect, the charge transfer path within the molecule can be confined to a specific area, reducing the mutual coupling of electrons and holes within the molecule, thereby achieving a small excited state reorganization energy without significantly reducing the emission energy, which is beneficial to improving the color purity and luminous efficiency of the material. In addition, the present invention is based on the carbonyl / nitrogen resonance core intramolecular cyclization of organic small molecule materials through effective external group regulation and skeleton design, which can enable MR-TADF materials to achieve highly sharp luminescence peaks, and the spectral broadband is narrower and more stable, thereby making the material show extremely high color purity in the blue luminescence region. Furthermore, the external groups and their modification sites introduced by the present invention play a key role in the molecular skeleton vibration analysis. By introducing the groups at the designated sites, the non-radiative transitions and structural relaxations of the molecular structure are significantly suppressed, the rigidity of the skeleton and the structural stability of the excited state are improved, thereby narrowing the emission spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the synthetic route of M1 in Example 1; Figure 2 is the synthetic route of P1 in Example 1; Figure 3 is the synthetic route of M2 in Example 2; Figure 4 is the synthetic route of M3 in Example 2; Figure 5 is the synthetic route diagram of P2 in Example 2; Figure 6 is the synthetic route of M4 in Example 3; Figure 7 is the synthetic route of P3 in Example 3; Figure 8 The electroluminescence spectrum and external quantum efficiency diagram of the organic electroluminescent device in Example 4 of the present invention. DETAILED DESCRIPTION

[0018] The present invention provides an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization and a preparation method and application thereof. In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as herein.

[0020] The present invention provides an organic small molecule material based on carbonyl / nitrogen resonance core molecule intramolecular cyclization. The general structural formula of the organic small molecule material based on carbonyl / nitrogen resonance core molecule intramolecular cyclization is as shown in formula (1) or formula (2): Formula (1); Formula (2); Wherein, R is an alkyl chain or an aromatic ring.

[0021] In this embodiment, through the strategy of intramolecular ring, the multiple resonance effect of carbonyl and nitrogen atoms is utilized to design a blue MR-TADF material with high color purity, high luminous efficiency and high stability. The synthesis of this material is relatively simple, the conditions are mild, and the yield is high. At the same time, its electroluminescent performance is excellent, so that this small molecule material has a broad application prospect. Specifically, the multiple resonance electroluminescent material containing nitrogen carbonyl has a rigid planar structure, in which nitrogen atoms act as electron donors and carbonyl acts as electron acceptors. Through the multiple resonance effect, the charge transfer path within the molecule can be confined to a specific region, reducing the mutual coupling of electrons and holes within the molecule, thereby achieving a small excited state reorganization energy without significantly reducing the emission energy, which is conducive to improving the color purity and luminous efficiency of the material. In addition, the present invention is based on the carbonyl / nitrogen resonance core intramolecular cyclization of organic small molecule materials through effective external group regulation and skeleton design, thereby inhibiting non-radiative transitions and structural relaxation between ground state excited states, improving the rigidity of the skeleton and the structural stability of the excited state, so that the MR-TADF material can achieve a highly sharp luminescence peak, and the spectral bandwidth is narrower and more stable, thereby making the material exhibit extremely high color purity in the blue luminescence region.

[0022] Specifically, the advantages of "high color purity, high luminescence efficiency and high stability of blue light" are mainly based on the following five structural and electronic properties of organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization: 1. The multiple resonance electroluminescent material containing nitrogen carbonyl has a rigid planar structure, in which the nitrogen atom acts as an electron donor and the carbonyl acts as an electron acceptor. Through the multiple resonance effect, the charge transfer path within the molecule can be confined to a specific area, reducing the mutual coupling of electrons and holes within the molecule, thereby achieving a small excited state reorganization energy without significantly reducing the emission energy. This structural design plays a decisive role in improving the color purity and luminescence efficiency of the material.

[0023] 2. The multiple resonance effect of organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization originates from the delocalized π electron system in the nitrogen carbonyl skeleton molecule, which makes the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) strictly separated in space. MR-TADF materials containing nitrogen carbonyl have strong localized exciton (LE) characteristics. HOMO is mainly distributed on the electron-rich nitrogen atom and its adjacent aromatic ring, while LUMO is concentrated on the carbonyl. This spatially separated electron cloud distribution reduces the coupling between molecules and improves the excited state stability and luminescence purity of the material. At the same time, due to the presence of localized excitons, the energy difference between the triplet state (T1) and the singlet state (S1) of the material is small, which enhances the efficiency of thermally activated delayed fluorescence.

[0024] 3. Since the HOMO and LUMO electron clouds of MR-TADF materials are highly localized and the charge transfer path is limited, the wide emission spectrum phenomenon usually caused by charge transfer molecules is avoided. Unlike traditional charge transfer luminescent materials, MR-TADF materials can achieve highly sharp luminescence peaks, and the spectral bandwidth is usually narrow (FWHM is about 20-40 nm), which makes the material show extremely high color purity in the blue luminescent region.

[0025] 4. The thermally activated delayed fluorescence mechanism of the framework structure allows triplet excitons to return to the singlet state through reverse intersystem crossing (RISC) and undergo radiative transition, which significantly improves the utilization of excitons. The triplet-singlet energy difference of nitrogen-carbonyl-containing MR-TADF materials is small (usually less than 0.2 eV), which greatly improves the efficiency of the RISC process and thus improves the luminescence efficiency. In addition, the rigid structure of organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization effectively suppresses the non-radiative relaxation process within the molecule, further enhancing its photon emission efficiency.

[0026] 5. Based on the above rigid skeleton design, especially the multiple resonance effect of carbonyl and nitrogen atoms, the structural relaxation and distortion of the molecule in the excited state can be reduced, thereby improving the thermal stability and photostability of the material. Due to the lower triplet excited state energy, this type of material can reduce the device aging problem caused by the accumulation of triplet excitons in electroluminescent devices. Therefore, the nitrogen-carbonyl-containing MR-TADF material not only exhibits a long life at high brightness, but also significantly reduces the efficiency roll-off phenomenon of the device. Therefore, through the optimization of the molecular structure, regulation of electronic properties and utilization of the multiple resonance effect of nitrogen-carbonyl MR-TADF materials, this type of material achieves high color purity, high luminous efficiency and high stability in blue luminescence, and has great beneficial effects: on the one hand, groups such as tert-butyl with a smaller spatial structure are conducive to improving the luminescent color purity on the basis of reducing the intramolecular reorganization energy, and are conducive to improving the solubility of the luminescent subject and the operability of the device preparation process; on the other hand, the electron-donating and electron-withdrawing groups with adjustable electronic properties improve the oscillator strength and luminous efficiency of the radiative transition on the basis of adjusting the overall charge distribution, which is conducive to achieving narrow-band emission with high fluorescence efficiency.

[0027] In some embodiments, the R is selected from one of the following substituents: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Through effective external group regulation and skeleton design, MR-TADF materials can achieve highly sharp emission peaks with narrower and more stable spectral bandwidth, which enables the material to exhibit extremely high color purity in the blue emission region.

[0028] In some embodiments, the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization includes , , One or more of the above-mentioned organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization have the characteristics of high color purity, high luminescence efficiency and high stability and are blue MR-TADF materials. Applying them in organic electroluminescent devices can achieve excellent luminescence effects.

[0029] In addition, the present invention also provides a method for preparing an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization, comprising the steps of: Step S10: Carrying out ester hydrolysis reaction under alkaline conditions to obtain a first product; wherein R1 and R2 are both hydrogen or di-tert-butyl; Step S20: Concentrating and acidifying the first product and reacting it with oxalyl chloride ions to obtain a second product; Step S30: mixing the second product with tin tetrachloride to obtain an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization after reaction.

[0030] In this embodiment, a blue MR-TADF material with high color purity, high luminous efficiency and high stability is designed by using the intramolecular ring strategy and the multiple resonance effect of carbonyl and nitrogen atoms. The synthesis of this material is relatively simple, the conditions are mild, and the yield is high. At the same time, its electroluminescent performance is excellent, which makes this small molecule material have broad application prospects.

[0031] In some embodiments, the The preparation method comprises the steps of: Will and Under catalytic conditions, the reaction is carried out to obtain ; Among them, the With the The molar ratio is (1-2): (1-2). When the molar ratio is controlled within this range, the reaction can be carried out under catalytic conditions to obtain .

[0032] Specifically, , copper, cuprous iodide, and potassium carbonate are mixed to obtain a mixed solution, and then , 1,4,7,10,13,16-hexaoxacyclooctadecane and o-dichlorobenzene are added to the mixed solution, and heated under reflux under the protection of nitrogen atmosphere to obtain a reaction mixture; after the reaction mixture is cooled to room temperature, the reaction mixture is poured into a large amount of water, extracted with dichloromethane, the organic layer is dried over anhydrous sodium sulfate, and concentrated under reduced pressure; finally, a mixed solution of dichloromethane and petroleum ether is used as an eluent, and further purified by silica gel column chromatography to obtain .

[0033] In some embodiments, the temperature for the reaction under catalytic conditions is 150° C.-180° C., and the time for the reaction under catalytic conditions is 30 h-40 h. Such conditions are conducive to the reaction and accelerate the reaction efficiency.

[0034] In some embodiments, in step S10, The step of performing an ester hydrolysis reaction under alkaline conditions to obtain a first product comprises: Step S21: , sodium hydroxide, tetrahydrofuran and a mixed solvent of water to obtain a first mixed solution; Step S22: heating and refluxing the first mixed solution to obtain the first product.

[0035] Specifically, the steps S10-S30 specifically include: defg ] A derivative of acridine-7,11-dione, sodium hydroxide and a mixed solution of THF / H2O are heated to reflux to obtain a first product, and the first product is concentrated after cooling to room temperature, and the residue is poured into water and acidified with dilute hydrochloric acid to obtain a precipitate. The precipitate is vacuum dried and dissolved in dry dichloromethane, and oxalyl chloride and a small amount of DMF are added under a nitrogen atmosphere, and reflux treatment is performed to obtain a second product. After adding tin tetrachloride to the second product and continuing to stir, it is quenched with sodium hydroxide and extracted with dichloromethane. Finally, the corresponding electroluminescent material is obtained by purification by silica gel column chromatography. The preparation method is simple to operate and has a high preparation yield.

[0036] In another embodiment, when R is an aromatic ring, The preparation method can also be: and Under catalytic conditions, the reaction is carried out to obtain ; and then and Reaction to obtain .

[0037] In addition, the present invention also provides an application of an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization in an organic electroluminescent device.

[0038] In some embodiments, the organic electroluminescent device includes a cathode, an anode, and an organic thin film layer disposed between the cathode and the anode; the organic thin film layer includes at least one organic light-emitting layer; the organic light-emitting layer contains the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization.

[0039] In some embodiments, the organic thin film layer further includes, but is not limited to, a hole injection layer, a hole transport layer (HTL), a hole blocking layer, an electron blocking layer, an electron transport layer (ETL), and an electron injection layer.

[0040] In some embodiments, the organic electroluminescent device is provided with the anode, hole injection layer, hole transport layer, electron blocking layer, organic light-emitting layer, exciton blocking layer, electron transport layer, electron injection layer and cathode in sequence from the height direction.

[0041] In some embodiments, the conductive anode includes but is not limited to conductive metals, metal oxides or conductive polymers. The anode can easily inject holes into the hole transport layer or the light-emitting layer. The anode material can be selected but not limited to: Al, Cu, Au, Ag, Mg, Fe, Co, Ni, Mn, Pd, Pt, ITO, aluminum-doped zinc oxide and alloys of the above examples. In addition, the anode material can be deposited by any suitable technique, such as physical vapor deposition, including radio frequency magnetron sputtering, vacuum thermal evaporation, electron beam, etc. In some embodiments, the anode is patterned. Patterned ITO conductive substrates can be purchased from the market and used to prepare the device of the present invention.

[0042] In some embodiments, the cathode comprises a conductive metal or metal oxide. The cathode can easily inject electrons into the electron injection layer or the electron transport layer or the light-emitting layer. The cathode material can be selected from but not limited to: Al, Au, Ag, Ca, Ba, Mg, LiF / Al, BaF2 / Al, Cu, Fe, Co, Ni, Mn, Pd, Pt, ITO, etc. The cathode material can be deposited by any suitable technique, such as physical vapor deposition, including radio frequency magnetron sputtering, vacuum thermal evaporation, electron beam, etc.

[0043] In some embodiments, the hole transport layer (HTL) is a material layer located between the anode and the light-emitting layer, and is used to effectively transport holes injected from the anode. Common hole transport layer (HTL) materials include, but are not limited to: TAPC (4,4'-cyclohexane-1,1-diylbis(N,N-dimethylaniline)), PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)), TCTA (tris(4-(9H-carbazole-9-yl)phenyl)amine), NPB (N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine).

[0044] In some embodiments, the hole blocking layer (HBL) is a material layer located between the light emitting layer and the electron transport layer, which is used to prevent holes from entering the electron transport layer while allowing electrons to pass through. Common hole blocking layer (HBL) materials include, but are not limited to: BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), TPBi (1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene), BAlq (aluminum(III)bis(8-hydroxyquinolin-2-yl)bis(benzo[d]imidazole)), Alq3 (tris(8-hydroxyquinolinol)aluminum).

[0045] In some embodiments, a common electron transport layer includes a small molecule material or a polymer material for effectively transporting electrons to the light-emitting layer and preventing electrons from flowing to the cathode. The electron transport layer material can be selected from but not limited to: TPBi (1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene), Alq3 (tris(8-hydroxyquinoline)aluminum), PPF (dibenzo[b,d]furan-2,8-diylbis(diphenylphosphine oxide)), Bphen (4,7-diphenyl-1,10-phenanthroline). The electron transport layer material can be prepared by any suitable technique, such as vacuum evaporation, solution processing, organic vapor deposition, etc.

[0046] In some embodiments, the electron injection layer is located between the electrode and the electron transport layer, and is mainly used to promote the injection of electrons from the electrode into the electron transport layer and reduce the electron injection impedance. Its common materials include: LiF (lithium fluoride) and the like.

[0047] In some embodiments, the mass percentage of the carbonyl / nitrogen resonance core intramolecular cyclization organic small molecule material in the light-emitting layer is 3%-5%.

[0048] In a preferred embodiment, the mass percentage of the carbonyl / nitrogen resonance core intramolecular cyclization organic small molecule material in the light-emitting layer is 3%.

[0049] The method for forming each structural layer in the organic electroluminescent device of the present invention is not particularly limited, and may include but is not limited to the existing vacuum evaporation method, spin coating method, etc. At the same time, the materials used for each structural layer in the electroluminescent device of the present invention are also not particularly limited, and the device structure in the embodiment is only used to illustrate the device performance and characteristics of the present invention.

[0050] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention.

[0051] Example 1 In this embodiment, the organic small molecule material P1 based on carbonyl / nitrogen resonance core intramolecular cyclization is synthesized, and the steps are as follows: The synthesis of M1 is as follows Figure 1As shown: A mixture of carbazole (1.84 g, 11.0 mmol, 1.1 eq), copper (0.64 g, 1.0 mmol, 0.1 eq), cuprous iodide (0.57 g, 3.0 mmol, 0.3 eq) and potassium carbonate (2.76 g, 20.0 mmol, 2.0 eq) was added to a double-necked round-bottom flask. Then 5-tert-butyl-2-bromoisophthalic acid dimethyl ester (3.29 g, 10.0 mmol, 1.0 eq), 1,4,7,10,13,16-hexaoxacyclooctadecane (0.52 g, 2 mol, 0.2 eq) and o-dichlorobenzene (100 mL) were injected into the flask. The mixture was heated to reflux for 36 hours under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was poured into a large amount of water and extracted three times with dichloromethane. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The product was further purified by silica gel column chromatography using dichloromethane / petroleum ether as eluent to obtain compound M1. The H NMR spectrum of compound M1 is 1 H NMR (500 MHz, CDCl3) δ 8.45 (s, 2H), 8.20 (dd, J = 8.2, 1.1Hz, 2H), 7.63 (dd, J = 6.3, 1.4 Hz, 2H), 7.54 (ddd, J = 7.3, 6.4, 1.1 Hz,1H), 7.36 (ddd, J = 8.2, 7.2, 1.4 Hz, 2H), 7.19 (ddd, J = 7.2, 6.3, 1.1 Hz, 1H), 3.90 (s, 6H), 1.32 (s, 9H). The synthesis of P1 is as follows Figure 2As shown: A round bottom flask contained compound 1 (5.0 mmol, 1.0 eq), sodium hydroxide (50.0 mmol, 10.0 eq) and THF / H2O (80 mL, 1:1). The reaction was heated to reflux for 24 h and then cooled to room temperature. The mixture was concentrated by rotary evaporation. Then, the residue was poured into water and acidified with dilute hydrochloric acid. The precipitate was dried overnight in vacuum. The residue was then dissolved in dry dichloromethane under nitrogen atmosphere. Oxalyl chloride ion (15.0 mmol, 3.0 eq) was injected into the reaction system, and then DMF (0.05 mL) was added dropwise. The reaction mixture was heated to reflux for 3 h and then mixed with tin tetrachloride (15.0 mmol, 3.0 eq) and stirred for another 4 h. The reaction mixture was quenched with sodium hydroxide solvent and extracted with dichloromethane. The organic layer was dried and concentrated in vacuum. The crude product was further purified by silica gel column chromatography using dichloromethane / petroleum ether as eluent to obtain P1. The H NMR spectrum of P1 is 1 H NMR (500 MHz, CDCl3) δ9.05 – 8.99 (m, 1H), 8.50 (dt, J = 7.2, 0.8 Hz, 1H), 8.16 (s, 2H), 7.74 (dd, J = 7.0, 1.2 Hz, 1H), 7.44 (t, J = 7.1 Hz, 1H), 7.23 – 7.18 (m, 1H), 7.12 (t, J = 7.1 Hz, 1H), 1.32 (s, 9H). Example 2 This embodiment synthesizes an organic small molecule material P2 based on carbonyl / nitrogen resonance core intramolecular cyclization, and the steps are as follows: The synthesis of M2 is as follows Figure 3As shown: A mixture of 3,6-di-tert-butylcarbazole (3.06 g, 11.0 mmol, 1.1 eq), copper (0.64 g, 1.0 mmol, 0.1 eq), cuprous iodide (0.57 g, 3.0 mmol, 0.3 eq) and potassium carbonate (2.76 g, 20.0 mmol, 2.0 eq) was added to a double-necked flask. Then 5-tert-butyl-2-bromoisophthalic acid dimethyl ester (3.99 g, 10.0 mmol, 1.0 eq), 1,4,7,10,13,16-hexaoxacyclooctadecane (0.52 g, 2 mol, 0.2 eq) and o-dichlorobenzene (100 mL) were injected into the flask. The mixture was heated to reflux for 36 hours under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was poured into a large amount of water and extracted three times with dichloromethane. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The product was further purified by silica gel column chromatography using dichloromethane / petroleum ether as eluent to obtain compound M2. The H NMR spectrum of compound M2 is 1 H NMR (500 MHz, CDCl3): δ 8.74 (d, J = 2.4 Hz, 1H), 8.60(s, 2H), 8.34 (d, J = 2.4 Hz, 1H), 7.88 (d, J = 7.7 Hz, 1H), 7.63 (dd, J =7.7, 2.4 Hz, 1H), 7.55 (d, J = 7.7 Hz, 1H), 7.42 (dd, J = 7.7, 2.4 Hz, 1H),3.89 (s, 4H) 1.37(s,18H). 1 The synthesis of M3 is as follows Figure 4 As shown: Under nitrogen atmosphere, 5-bromo-2-(3,6-di-tert-butyl-9H-carbazole-9-yl) dimethyl isophthalate (0.55 g, 1 mmol, 1 eq) and phenylboric acid (0.14 g, 1.2 mmol, 1.2 eq) and tetrakistriphenylphosphine palladium (3%-5% mol) were dissolved in 10 mL of tetrahydrofuran, and then 0.6 mL of 2 mol / L potassium carbonate solution was added and the mixture was heated at 90-110 °C. o After reacting at 400 °C for 24-36 hours, methanol was added to precipitate a solid, which was filtered and washed with acetone to obtain a crude product, which was further purified by column chromatography to obtain compound M3. The H NMR spectrum of compound M3 is 1 H NMR (500 MHz, DMSO-d 6) δ 8.74 (d, J = 2.4 Hz, 1H), 8.42 (s, 2H), 8.34 (d, J = 2.4Hz, 1H), 7.87 (d, J = 7.7 Hz, 1H), 7.71 (d, J = 7.6 Hz, 1H), 7.67 – 7.60 (m,3H), 7.54 – 7.46 (m, 2H), 7.44 – 7.35 (m, 2H), 3.89 (s, 6H), 1.42 (s, 18H) The synthesis of P2 is as follows Figure 5 As shown: A round bottom flask contained compound M3 (0.55 g, 1.0 mmol, 1.0 eq), sodium hydroxide (4.0 g, 10.0 mmol, 10.0 eq) and THF / H2O (80 mL, 1:1). The reaction was heated and refluxed for 24 hours and then cooled to room temperature. The mixture was concentrated by rotary evaporation. Then, the residue was poured into water and acidified with dilute hydrochloric acid. The precipitate was dried overnight in vacuum. The residue was then dissolved in dry dichloromethane under nitrogen atmosphere. Oxalyl chloride ion (45.0 mmol, 3.0 eq) was injected into the reaction system and then DMF (0.05 mL) was added dropwise. The reaction mixture was heated to reflux for 3 hours and then tin tetrachloride (45.0 mmol, 3.0 eq) was added and stirred for another 4 hours. The reaction mixture was quenched with sodium hydroxide solvent and extracted with dichloromethane. The organic layer was dried and concentrated in vacuum. The crude product was further purified by silica gel column chromatography using dichloromethane / petroleum ether as eluent to obtain P2. The H NMR spectrum of P2 is 1 H NMR (500 MHz, DMSO- d 6) δ 9.04 (d, J = 2.4 Hz, 1H), 8.64 (d, J = 2.4 Hz, 1H), 8.41 (s, 2H), 8.04 (dd, J = 7.0, 2.2 Hz, 2H), 7.67 – 7.61 (m, 2H), 7.54 – 7.46 (m, 2H), 7.44 – 7.37 (m, 1H), 1.44 (s, 18H). Example 3 This embodiment synthesizes an organic small molecule material P3 based on carbonyl / nitrogen resonance core intramolecular cyclization, and the steps are as follows: The synthesis of M4 is as follows Figure 6 As shown: Under nitrogen atmosphere, 5-bromo-2-(3,6-di-tert-butyl-9H-carbazole-9-yl) dimethyl isophthalate (0.55 g, 1 mmol, 1 eq) and (2,2'',4,4'',6,6''-hexamethyl-[1,1':3',1''-terphenyl]-5'-yl) boronic acid (0.44 g, 1.2 mmol, 1.2 eq) and tetrakistriphenylphosphine palladium (3%-5% mol) were dissolved in 10 mL of tetrahydrofuran, and then 0.6 mL of 2 mol / L potassium carbonate solution was added and the mixture was heated at 90-110 °C. o After reacting at 400 °C for 24-36 hours, methanol was added to precipitate a solid, which was filtered and washed with acetone to obtain a crude product, which was further purified by column chromatography to obtain compound M4. The H NMR spectrum of compound M4 is 1 H NMR (500 MHz, DMSO- d 6) δ 8.74(d, J = 2.4 Hz, 1H), 8.45 (s, 2H), 8.34 (d, J = 2.4 Hz, 1H), 7.87 (d, J = 7.7Hz, 1H), 7.71 (d, J = 7.6 Hz, 1H), 7.62 (dd, J = 7.7, 2.4 Hz, 1H), 7.38 (dd, J = 7.7, 2.4 Hz, 1H), 7.29 (d, J = 2.1 Hz, 2H), 7.25 (t, J = 2.2 Hz, 4H), 6.99 (s, 4H), 3.89 (s, 6H), 2.84 (s, 12H), 2.45 (s, 6H), 1.42 (s, 18H). The synthesis of P3 is as follows Figure 7As shown: A round bottom flask contained compound M4 (0.78 g, 1.0 mmol, 1.0 eq), sodium hydroxide (4.0 g, 10.0 mmol, 10.0 eq) and THF / H2O (80 mL, 1:1). The reaction was heated to reflux for 24 h and then cooled to room temperature. The mixture was concentrated by rotary evaporation. Then, the residue was poured into water and acidified with dilute hydrochloric acid. The precipitate was dried overnight in vacuum. The residue was then dissolved in dry dichloromethane under nitrogen atmosphere. Oxalyl chloride ion (45.0 mmol, 3.0 eq) was injected into the reaction system and then DMF (0.05 mL) was added dropwise. The reaction mixture was heated to reflux for 3 h and then tin tetrachloride (45.0 mmol, 3.0 eq) was added and stirred for another 4 h. The reaction mixture was quenched with sodium hydroxide solvent and extracted with dichloromethane. The organic layer was dried and concentrated in vacuum. The crude product was further purified by silica gel column chromatography using dichloromethane / petroleum ether as eluent to obtain P3. The H NMR spectrum of P3 is 1 H NMR (500 MHz, DMSO- d 6) δ 9.04 (d, J = 2.3 Hz, 1H), 8.64 (d, J = 2.4 Hz, 1H), 8.44 (s, 2H), 8.04 (dd, J = 7.0, 2.2 Hz, 2H), 7.36 (d, J = 2.1 Hz, 2H), 7.25 (t, J = 2.1Hz, 1H), 6.99 (s, 4H), 2.84 (s, 12H), 2.45 (s, 6H), 1.44 (s, 18H). Example 4 This embodiment provides an organic electroluminescent device, and the specific preparation steps are as follows: The glass plate coated with the ITO transparent conductive layer was ultrasonically treated in a commercial cleaning agent, rinsed in deionized water, cleaned three times in acetone and ethanol, baked in a clean environment to completely remove moisture, cleaned with ultraviolet light and ozone, and bombarded with a low-energy cation beam. The ITO conductive glass was placed in a vacuum chamber and evacuated to less than 5×10 -5 Pa, using ITO conductive glass as the anode, and evaporating each layer of material on it in sequence, the specific steps are as follows: 4,4'-(cyclohexane-1,1-diyl)bis(N,N-p-toluidine) (TAPC) of the following chemical formula was used as a hole transport material, and a 45 nm TAPC layer was deposited on the ITO anode by vacuum thermal evaporation.

[0052]

[0053] The following compound tris(4-(9H-carbazol-9-yl)phenyl)amine (TCTA) as a hole blocking material was deposited on the hole transport layer in a thickness of 5 nm to form a hole blocking layer.

[0054]

[0055] Then, the following compound mCP (1,3-diphenylimidazo[2,1-b]quinoxaline) was evaporated on the TCTA layer to a thickness of 5 nm as a host material layer.

[0056]

[0057] The mCP was mixed with the following compound 1 at 3% by weight of a light emitting body, and the mixture was deposited to a thickness of 20 nanometers by a vacuum evaporation process to obtain a light emitting layer.

[0058]

[0059] Then, the following compound dibenzo[b,d]furan-2,8-diylbis(diphenylphosphine oxide) (PPF) was evaporated to a thickness of 5 nanometers on the light-emitting layer as an electron transport layer. And on the PPF layer, the compound 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBi) was evaporated to a thickness of 35 nanometers to enhance the electron transport efficiency.

[0060]

[0061] The compound lithium fluoride (LiF) (1 nm) and metal aluminum (100 nm) were sequentially deposited on the electron transport layer as an electron injection layer and a cathode.

[0062] During the above process, the evaporation rates of each material were maintained as follows: the deposition rates of hole injection layer materials and electron injection layer materials were maintained at 0.4 Å / s to 0.7 Å / s. The deposition rates of organic functional layer materials, including hole transport layer, electron blocking layer, light-emitting layer, and electron transport layer materials, were maintained at 2 Å / s to 4 Å / s. The deposition rate of aluminum, a metal electrode material, was maintained at 6 Å / s to 9 Å / s. During the entire deposition process, the vacuum degree was maintained at 1×10 -6 Torr to 5×10 -6 Torr.

[0063] The electroluminescence spectra were collected by using a photon multichannel analyzer PMA-12 (Hamamatsu C10027-01), which can detect in the spectral region of 200–950 nm. The external quantum efficiency of the device was obtained by measuring the forward light intensity using an integrating sphere (Hamamatsu A10094), as Figure 8 All measurements were performed at room temperature in the atmosphere. The above results prove that the nitrogen carbonyl system can achieve narrow-band blue light emission through effective external group regulation and skeleton design.

[0064] In summary, the present invention provides a kind of organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization and its preparation method and application. The present invention uses the strategy of intramolecular ring and the multiple resonance effect of carbonyl and nitrogen atoms to design a blue MR-TADF material with high color purity, high luminous efficiency and high stability. The synthesis of this material is relatively simple, the conditions are mild, and the yield is high. At the same time, its electroluminescent performance is excellent, so that this small molecule material has a broad application prospect. Specifically, the multiple resonance electroluminescent material containing nitrogen carbonyl has a rigid planar structure, wherein the nitrogen atom acts as an electron donor, and the carbonyl acts as an electron acceptor. Through the multiple resonance effect, the charge transfer path in the molecule can be confined to a specific region, reducing the mutual coupling of electrons and holes in the molecule, thereby achieving a small excited state reorganization energy without significantly reducing the emission energy, which is conducive to improving the color purity and luminous efficiency of the material. In addition, the present invention is based on the carbonyl / nitrogen resonance core intramolecular cyclization of organic small molecule materials through effective external group regulation and skeleton design, which can enable MR-TADF materials to achieve highly sharp luminescence peaks, and the spectral broadband is narrower and more stable, thereby making the material show extremely high color purity in the blue luminescence region. Furthermore, the external groups and their modification sites introduced by the present invention play a key role in the molecular skeleton vibration analysis. By introducing the groups at the designated sites, the non-radiative transitions and structural relaxations of the molecular structure are significantly suppressed, the rigidity of the skeleton and the structural stability of the excited state are improved, thereby narrowing the emission spectrum.

[0065] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization, characterized in that: The general structural formula of the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization is shown in Formula (1) or Formula (2): Formula (1); Formula (2); Wherein, R is an alkyl chain or an aromatic ring.

2. The organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization according to claim 1, characterized in that: The R is selected from one of the following substituents: 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 。 3. The organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization according to claim 1, characterized in that: The organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization includes , , One or more of .

4. A method for preparing an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization as claimed in any one of claims 1 to 3, characterized in that: The steps include: Carrying out ester hydrolysis reaction under alkaline conditions to obtain a first product; wherein R1 and R2 are both hydrogen or di-tert-butyl; The first product is concentrated and acidified, and then reacted with oxalyl chloride ions to obtain a second product; The second product is mixed with tin tetrachloride, and after reaction, an organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization is obtained.

5. The method for preparing organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization according to claim 4, characterized in that: Said The preparation method comprises the steps of: Will and Under catalytic conditions, the reaction is carried out to obtain ; Among them, the With the The molar ratio is (1-2):(1-2).

6. The method for preparing organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization according to claim 4, characterized in that: The temperature for carrying out the reaction under the catalytic condition is 150° C.-180° C., and the time for carrying out the reaction under the catalytic condition is 30 h-40 h.

7. The method for preparing organic small molecule materials based on carbonyl / nitrogen resonance core intramolecular cyclization according to claim 4, characterized in that: Will The step of performing an ester hydrolysis reaction under alkaline conditions to obtain a first product comprises: Will , sodium hydroxide, tetrahydrofuran and a mixed solvent of water to obtain a first mixed solution; The first mixed solution is heated and refluxed to obtain the first product.

8. Use of the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization as claimed in any one of claims 1 to 3 in an organic electroluminescent device.

9. The use according to claim 8, characterized in that: The organic electroluminescent device comprises a cathode, an anode and an organic thin film layer arranged between the cathode and the anode; the organic thin film layer comprises at least one organic light-emitting layer; the organic light-emitting layer contains the organic small molecule material based on carbonyl / nitrogen resonance core intramolecular cyclization.

10. The use according to claim 9, characterized in that: The mass percentage of the carbonyl / nitrogen resonance core intramolecular cyclization organic small molecule material in the organic light-emitting layer is 3%-5%.

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