N-heterocyclic carbene free radical with efficient green light emission characteristic and preparation method and application thereof

Abstract

The invention belongs to the technical field of N-heterocyclic compounds, and particularly relates to an N-heterocyclic carbene free radical with an efficient green light emission characteristic and a preparation method and application of the N-heterocyclic carbene free radical. The preparation method of the N-heterocyclic carbene free radical comprises the following steps: (1) in an inert atmosphere, adding free carbene I and a bromide solution into a container, then adding a catalyst Ni (COD) 2, carrying out a heating reaction, and carrying out concentration, precipitation and suction filtration on a reaction solution to obtain a compound II; and (2) in an inert atmosphere, dissolving the compound II in THF, cooling the solution to a temperature lower than-35 DEG C, adding KC8, carrying out a stirring reaction, washing the reaction liquid, and carrying out suction filtration to obtain the target product N-heterocyclic carbene free radical. The target product disclosed by the invention has a relatively high phi value and a nanosecond-level light-emitting service life, can promote an OLED device to have relatively high external quantum efficiency, low energy loss and long practical service life, and can be applied to organic light-emitting diode devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of nitrogen heterocyclic compounds, and in particular relates to a nitrogen heterocyclic carbene free radical with high-efficiency green light emission characteristics, and a preparation method and application thereof. Background Art

[0002] Organic light-emitting diodes (OLEDs) have become a promising candidate for next-generation visible light communication (VLC) emitters due to their environmentally friendly properties and potential cost savings. However, emitters derived from fluorescence, phosphorescence, and thermally activated delayed fluorescence are not suitable for OLED-based VLC applications due to their low internal quantum efficiency or long exciton decay lifetime. Based on these challenges, organic luminescent radicals with unique electronic and optical properties have attracted widespread attention as efficient doublet emitters because they can effectively solve the transition problem associated with triplet excitons, thereby achieving fast response (lifetime of several to tens of nanoseconds) and high efficiency (up to 100% internal quantum efficiency upper limit). However, the natural narrow band gap of organic radicals causes their fluorescence emission to mainly emit in the red and near-infrared regions and lack green and blue luminescence, which will be detrimental to the application of OLED-based VLC in multiple fields. Although carbon-centered radicals derived from N-heterocyclic carbenes (NHCs) have successfully obtained green light emission due to their compliance with the anti-Kasha rule, these radicals generally exhibit lower photoluminescence quantum yields (Φ) compared with non-radical organic molecules.

[0003] Therefore, developing free radicals with efficient green-light emitting properties remains a valuable but challenging task. Summary of the invention

[0004] The purpose of the present invention is to provide a nitrogen heterocyclic carbene free radical with efficient green light emission characteristics and a preparation method and application thereof, so as to solve the problem of low quantum yield of existing green light open shell doublet fluorescence.

[0005] The implementation process of the present invention is as follows:

[0006] A nitrogen heterocyclic carbene free radical with high-efficiency green light emission characteristics, the general structural formula of the nitrogen heterocyclic carbene free radical is as follows:

[0007] Wherein, R is a polycyclic aromatic hydrocarbon group.

[0008] Furthermore, the polycyclic aromatic hydrocarbon group is selected from a biphenyl type aromatic hydrocarbon group or a condensed ring aromatic hydrocarbon group.

[0009] Further, the biphenyl type aromatic hydrocarbon group is selected from 4'-N,N-diphenyl biphenyl or 4'-N,N-dihalogenated phenyl biphenyl; the condensed ring aromatic hydrocarbon group is selected from

[0010] Wherein, R1, R2, R3, R4 and R5 are all selected from halogen group, alkyl group having 1-6 carbon atoms, alkoxy group having 1-6 carbon atoms, cyano group or trifluoroalkyl group having 1-6 carbon atoms.

[0011] The method for preparing the above-mentioned nitrogen heterocyclic carbene free radical with high-efficiency green light emission characteristics comprises the following steps:

[0012] (1) under an inert atmosphere, free carbene I and a bromide solution are added to a container, and then a catalyst Ni(COD)2 is added for heating reaction, and the reaction solution is concentrated, precipitated, and filtered to obtain compound II, wherein R in the bromide is a polycyclic aromatic hydrocarbon group;

[0013] (2) Under an inert atmosphere, compound II is dissolved in THF, the solution is cooled to below -35°C, KC8 is added for stirring reaction, and the reaction solution is washed and filtered to obtain the target product, a nitrogen heterocyclic carbene free radical, wherein R in the target product is a polycyclic aromatic hydrocarbon group;

[0014]

[0015] Furthermore, in step (1), the solvent of the bromide solution is dioxane or o-xylene, the inert atmosphere is nitrogen or argon atmosphere, the molar ratio of the carbene I to the bromide is 1:(1-1.1), and the molar ratio of the carbene I to the catalyst Ni(COD)2 is 1:(0.1-0.12); the temperature of the heating reaction is 110-160°C, and the reaction time is 12-24h; in step (2), the inert atmosphere is nitrogen or argon atmosphere, the molar ratio of the compound II to KC8 is 1:(1.2-1.4); the temperature of the stirring reaction is room temperature, and the reaction time is 3-5h.

[0016] Furthermore, R in the bromide and the target product is the same and is selected from a biphenyl type aromatic hydrocarbon group or a condensed ring aromatic hydrocarbon group.

[0017] Furthermore, the biphenyl type aromatic hydrocarbon group is selected from 4'-N,N-diphenyl biphenyl or 4'-N,N-dihalogenated phenyl biphenyl; the condensed ring aromatic hydrocarbon group is selected from

[0018]

[0019] Wherein, R1, R2, R3, R4 and R5 are all selected from halogen group, alkyl group having 1-6 carbon atoms, alkoxy group having 1-6 carbon atoms, cyano group or trifluoroalkyl group having 1-6 carbon atoms.

[0020] Furthermore, in step (1), the preparation process of the carbene I is to add IPr·HCl, then add dioxane or o-xylene solvent, and then add potassium tert-butoxide to react with stirring in a container under an inert atmosphere, and the reaction solution is centrifuged to obtain the supernatant, which is the free carbene I solution, and the free carbene I solution is stored in an inert atmosphere;

[0021]

[0022] Furthermore, the inert atmosphere is nitrogen or argon atmosphere; the molar ratio of IPr·HCl to potassium tert-butoxide is 1:(1.5-2); the stirring reaction temperature is room temperature, and the reaction time is 8-10 hours.

[0023] Application of the above nitrogen heterocyclic carbene radical in organic light emitting diode devices.

[0024] Positive effects of the present invention:

[0025] (1) The method of the present invention is simple, easy to operate, and suitable for wide promotion and application.

[0026] (2) The nitrogen heterocyclic carbene radical of the present invention promotes a large spatial overlap between the carbon center group of the free radical and the connecting segment due to the high conjugation between them, forming a local excited state and aggravating the non-radiative electron-electron exchange relaxation pathway. Therefore, the introduction of a donor group in the connecting segment has a positive effect on the construction of a mixed local and charge transfer state, which not only reduces the negative impact of the spatial overlap between the carbon center group of the free radical and the substituent, but also exhibits a charge transfer characteristic to promote effective luminescence.

[0027] (3) The nitrogen heterocyclic carbene radical of the present invention has a high Φ value and a luminescence lifetime of nanoseconds, which will promote OLED devices to have high external quantum efficiency, small energy loss, and long practical lifetime, and can be applied to organic light-emitting diode devices. In addition, high luminescence efficiency and short lifetime also have potential application value in the preparation of transmitters for fast optical communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the UV absorption spectrum of nitrogen heterocyclic carbene radicals 3b-5b in tetrahydrofuran;

[0029] Figure 2 Fluorescence emission spectra of nitrogen heterocyclic carbene radicals 3b-5b in tetrahydrofuran;

[0030] Figure 3 The fluorescence decay lifetime spectra of nitrogen heterocyclic carbene radicals 3b-5b in tetrahydrofuran;

[0031] Figure 4are the ultraviolet absorption spectra of nitrogen heterocyclic carbene radicals 3b-5b in different polar solvents, wherein a) is nitrogen heterocyclic carbene radical 3b, b) is nitrogen heterocyclic carbene radical 4b, and c) is nitrogen heterocyclic carbene radical 5b;

[0032] Figure 5 are the fluorescence emission spectra of nitrogen heterocyclic carbene radicals 3b-5b in solvents of different polarities, wherein a) is nitrogen heterocyclic carbene radical 3b, b) is nitrogen heterocyclic carbene radical 4b, and c) is nitrogen heterocyclic carbene radical 5b;

[0033] Figure 6 The orientation polarization Δf and Stokes shift (ν a -ν f ) is a linear correlation diagram, wherein a) is nitrogen heterocyclic carbene radical 3b, b) is nitrogen heterocyclic carbene radical 4b, and c) is nitrogen heterocyclic carbene radical 5b;

[0034] Figure 7 is the thermal decomposition temperature (T) of the nitrogen heterocyclic carbene radicals 3b-5b obtained by thermogravimetric analysis. d ) and photostability half-life (t 1 / 2 )picture;

[0035] Figure 8 Simulation diagram of the organic electroluminescent device of nitrogen heterocyclic carbene radicals 4b and 5b. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the embodiments.

[0037] The key to making the free radical molecule itself have high luminescence efficiency is to suppress the non-radiative channel and enhance the radiative channel. Most of the reported carbon-centered free radicals themselves show high Φ values ​​in the red and near-infrared regions, which is mainly due to the charge transfer state formed by the donor-acceptor (DA) chemical structure. This charge transfer state involves strong electron transfer from the electron-donating group to the free radical center, resulting in a high radiation rate constant k r . However, the carbon-centered radicals derived from N-heterocyclic carbenes (NHCs) promote a large spatial overlap between the carbon-centered group of the radical and the connecting fragment due to the high conjugation between them. This results in the formation of local excitations that intensify the non-radiative electron-electron exchange relaxation pathway. Therefore, the introduction of donor groups in the connecting fragment has a positive effect on the construction of mixed local and charge transfer states (HLCT), which not only reduces the negative impact of the spatial overlap between the carbon-centered group of the radical and the substituent, but also exhibits charge transfer properties to promote efficient luminescence.

[0038] In a first aspect, the present invention provides a nitrogen heterocyclic carbene free radical having efficient green light emission characteristics, the general structural formula of the nitrogen heterocyclic carbene free radical is as follows:

[0039]

[0040] Wherein, R is a polycyclic aromatic hydrocarbon group. The polycyclic aromatic hydrocarbon group is selected from a biphenyl type aromatic hydrocarbon group or a condensed ring aromatic hydrocarbon group. The biphenyl type aromatic hydrocarbon group is selected from 4'-N,N-diphenyl biphenyl or 4'-N,N-dihalogenated phenyl biphenyl; the condensed ring aromatic hydrocarbon group is selected from

[0041]

[0042] Wherein, R1, R2, R3, R4 and R5 are all selected from halogen group, alkyl group having 1-6 carbon atoms, alkoxy group having 1-6 carbon atoms, cyano group or trifluoroalkyl group having 1-6 carbon atoms.

[0043] In a second aspect, the present invention provides a method for preparing a nitrogen heterocyclic carbene free radical having efficient green light emission characteristics, comprising the following steps:

[0044] (1) In a nitrogen or argon atmosphere, free carbene I and a bromide solution (the solvent is dioxane or o-xylene) are added to a container, and then a catalyst Ni(COD)2 is added to carry out a heating reaction at 110-160°C for 12-24 hours. The reaction solution is concentrated, precipitated, and filtered to obtain a compound II, wherein R in the bromide is a polycyclic aromatic hydrocarbon group; the molar ratio of the carbene I to the bromide is 1:(1-1.1), and the molar ratio of the carbene I to the catalyst Ni(COD)2 is 1:(0.1-0.12); the amount of the solvent is not limited, as long as the bromide solution can be prepared;

[0045] (2) Under nitrogen or argon atmosphere, compound II is dissolved in THF, the solution is cooled to below -35°C, KC8 is added for stirring reaction, and the reaction solution is washed and filtered to obtain the target product nitrogen heterocyclic carbene free radical, wherein R in the target product is a polycyclic aromatic hydrocarbon group; the molar ratio of compound II to KC8 is 1:(1.2-1.4); the stirring reaction temperature is room temperature, and the reaction time is 3-5h; the amount of solvent THF is not limited, as long as compound II can be dissolved.

[0046]

[0047] Wherein, R in the bromide and the target product is the same and is selected from a biphenyl type aromatic hydrocarbon group or a condensed ring aromatic hydrocarbon group. The biphenyl type aromatic hydrocarbon group is selected from 4'-N,N-diphenyl biphenyl or 4'-N,N-dihalogenated phenyl biphenyl; the condensed ring aromatic hydrocarbon group is selected from

[0048] Wherein, R1, R2, R3, R4 and R5 are all selected from halogen group, alkyl group having 1-6 carbon atoms, alkoxy group having 1-6 carbon atoms, cyano group or trifluoroalkyl group having 1-6 carbon atoms.

[0049] In the above preparation method, the carbene I can be prepared by the existing literature method. The present invention provides a preparation process of carbene I, which is to add IPr·HCl in a container under an inert atmosphere, then add dioxane or o-xylene solvent, and then add potassium tert-butoxide to stir and react, and the reaction solution is centrifuged to take the supernatant, which is the free carbene I solution, and the free carbene I solution is stored in an inert atmosphere;

[0050]

[0051] The inert atmosphere is nitrogen or argon; the molar ratio of IPr·HCl to potassium tert-butoxide is 1:(1.5-2); the stirring reaction temperature is room temperature, and the reaction time is 8-10 hours. The amount of solvent in the preparation process of carbene I of the present invention is not limited, as long as the uniform dispersion of IPr·HCl powder can be achieved.

[0052] In a third aspect, the present invention provides the use of nitrogen heterocyclic carbene radicals in organic light emitting diode devices.

[0053] Example 1

[0054]

[0055] A method for preparing a nitrogen heterocyclic carbene free radical 1b with high-efficiency green light emission characteristics comprises the following steps:

[0056] (1) Under argon atmosphere, a free carbene I solution (carbene I is 1.0 mmol) is placed in a 50 ml Schlenk tube, and then bromide 1 (1.1 mmol) and catalyst Ni(COD)2 (0.12 mmol) are added and stirred at room temperature for 6 minutes to obtain a yellow solution, which is then sealed and reacted at 110°C for 24 hours. After the reaction is complete, a turquoise solution is obtained. The solution is concentrated to 1-3 ml, and then 80 ml of n-hexane is added in small amounts several times to precipitate a solid, which is then washed with the remaining n-hexane until the filtrate has no fluorescence (when irradiated with a 365 nm fluorescent lamp), and then filtered to obtain a light yellow powder 1a (751.6 mg, 83%).

[0057] (2) Under argon atmosphere, 1a (1.0 mmol) was placed in a 50 ml Schlenk tube, and then 15 ml of THF solution was added and stirred until 1a was dissolved into a light yellow solution, and then the above solution was placed in a refrigerator to cool to below -35 ° C and refrigerated for 40 minutes. After the refrigeration, the weighed KC8 (1.4 mmol) was immediately added to the solution to immediately obtain a dark green solution, and then stirred at room temperature for 5 hours. After the reaction was completed, the reaction solution was filtered, and then 80 ml of n-hexane was added and stirred for 20 minutes, and then filtered through a sand core funnel until the filtrate was colorless, and then filtered to obtain a dark green powder nitrogen heterocyclic carbene free radical 1b, with a yield of 603.0 mg, 81%.

[0058] 1a: 1 H-NMR (400MHz, CD3CN): δ7.99-7.98(m,2H),7.61(t,J=7.6Hz,2H),7.54(d,J =8.4Hz,2H),7.42(d,J=7.6Hz,4H),7.37(d,J=8.8Hz,2H),7.08-7.06(m,8H), 7.00(d,J=8.8Hz,2H), 6.88(d,J=8.4Hz,2H), 2.50(sept,J=6.8Hz,4H,CH(CH3)), 1.25(d,J=6.8Hz,12H,CH(CH3)2), 1.07(d,J=6.8Hz,12H,CH(CH3)2)ppm. 13 C{ 1 H}-NMR (100MHz, CD3CN): δ161.3(d,1JC-F=240.6Hz), 158.9(d,1JC-F=240.6Hz), 149.7,146.4, 145.9,144.9,144.0(2)(d,4JC-F=2.3Hz),144.0(0)(d,4JC-F=2.3Hz),133.1,131.0,130.9,13 0.7,128.5,128.0(d,3JC-F=8.2Hz),127.9(d,3JC-F=8.2Hz),127.3,127.1,126.1,121.8,118. 9,117.3(d,2JC-F=22.7Hz),117.0(d,2JC-F=22.7Hz),30.0,25.5,22.7ppm.HRMS(ESI,positive ions):m / z=744.4160[M] + .

[0059] Example 2

[0060]

[0061] A method for preparing a nitrogen heterocyclic carbene free radical 2b with efficient green light emission characteristics comprises the following steps:

[0062] (1) Under nitrogen atmosphere, a free carbene I solution (carbene I is 1.0 mmol) is placed in a 50 ml Schlenk tube, and then bromide 2 (1 mmol) and catalyst Ni(COD)2 (0.1 mmol) are added and stirred at room temperature for 2 minutes to obtain a yellow solution, which is then sealed and reacted at 120°C for 12 hours. After the reaction is complete, a turquoise solution is obtained. The solution is concentrated to 1-3 ml, and then 50 ml of n-hexane is added in small amounts several times to precipitate a solid, which is then washed with the remaining n-hexane until the filtrate has no fluorescence (when irradiated with a 365 nm fluorescent lamp), and then filtered to obtain a light yellow powder 2a (529.4 mg, 80%).

[0063] (2) Under nitrogen atmosphere, 2a (1.0 mmol) was placed in a 50 ml Schlenk tube, and then 15 ml of THF solution was added and stirred until 2a was dissolved into a light yellow solution, and then the above solution was placed in a refrigerator to cool to below -35 ° C and refrigerated for 30 minutes. After the refrigeration, the weighed KC8 (162.1 mg, 1.2 mmol) was immediately added to the solution to immediately obtain a dark green solution, and then stirred at room temperature for 3 hours. After the reaction was completed, the reaction solution was filtered, and then 50 ml of n-hexane was added and stirred for 5 minutes, and then filtered through a sand core funnel until the filtrate was colorless, and then filtered to obtain a dark green powder nitrogen heterocyclic carbene free radical 2b, with a yield of 534.9 mg, 92%.

[0064] 2a: 1 H-NMR (400MHz, CD3CN): δ=7.99 (s, 2H), 7.70 (dd, J=10.0, 7.2Hz, 2H), 7.61 (t, J=7. 6Hz, 2H), 7.46-7.45 (m, 1H), 7.43 (d, J=7.6Hz, 4H), 7.38 (t, J=6.4Hz, 1H), 7.33 (t, J=6.4Hz, 1H), 6.95-6.93(m, 2H), 2.53(sept, J=6.8Hz, 4H, CH(CH3)2), 1.26(d, J=6 .4Hz, 12H, CH(CH3)2), 1.09(s, 6H, C(CH3)2), 1.03(d, J=6.4Hz, 12H, CH(CH3)2)ppm. 13 C{ 1H}-NMR (100 MHz, CD3CN): δ = 155.1, 154.9, 146.7, 145.9, 144.2, 137.4, 133.1, 131.1, 130.4, 129.6, 128.5, 126.9, 126.3, 124.7, 123.9, 122.4, 121.8, 119.1, 47.6, 30.0, 26.8, 25.5, 22.8 ppm, mass spectrum: m / z = 581.3872 [M] + .

[0065] Example 3

[0066]

[0067] A method for preparing a nitrogen heterocyclic carbene radical 3b with efficient green light emission characteristics is the same as the preparation method and parameters of Example 2, except that: compound 2 is replaced by compound 3, and 3a is obtained by reaction (yield is 692.9 mg, 88%), 1 H-NMR (400MHz, CD3CN): δ=7.99 (s, 2H), 7.62 (t, J=7.6Hz, 2H), 7.55 (d, J=8. 4Hz, 2H), 7.42 (d, J=7.6Hz, 4H), 7.38 (d, J=8.4Hz, 2H), 7.29 (t, J=7.6Hz, 4H) , 7.11-7.00 (m, 8H), 6.95 (d, J = 8.4Hz, 2H), 2.51 (sept, J = 6.8Hz, 4H, CH (CH3)), 1.26 (d, J = 6.8Hz, 12H, CH (CH3)2), 1.08 (d, J = 6.8Hz, 12H, CH (CH3)2) ppm. 13 C{ 1 H}-NMR (100 MHz, CD3CN): δ = 149.4, 147.8, 146.3, 145.8, 144.8, 133.0, 131.3, 130.8, 130.6, 130.3, 128.4, 127.2, 126.9, 126.1, 125.7, 124.6, 123.0, 118.8, 29.9, 25.5, 22.6 ppm. Mass spectrum: m / z = 708.4306 [M] + The yield of the final target product, nitrogen heterocyclic carbene radical 3b, was 615.2 mg, 87%.

[0068] Example 4

[0069]

[0070] A method for preparing a nitrogen heterocyclic carbene radical 4b with efficient green light emission characteristics is the same as the preparation method and parameters of Example 2, except that: Compound 2 is replaced by Compound 4, and the reaction yields 4a (yield 670.2 mg, 81%), 1 H-NMR (400MHz, CD2Cl2): δ=8.15 (s, 2H), 7.61 (t, J=7.6Hz, 2H), 7.46-7.42 (m, 2H), 7.37 (d, J=7.6Hz, 4H), 7.26 (t, J=7.2Hz, 4H), 7.07-7.05 (m, 7H), 6. 91 (d, J=8.0Hz, 1H), 6.85-6.83 (m, 2H), 2.50 (sept, J=6.8Hz, 4H, CH(CH3)2), 1.31 (d, J=6.4Hz, 12H, CH(CH3)2)), 1.00 (m, 18H, CH(CH3)2, C(CH3)2)ppm. 13 C{ 1 H}-NMR (100 MHz, CD2Cl2): δ = 155.9, 154.4, 149.8, 147.6, 146.1, 145.1, 143.9, 132.5, 130.6, 129.6, 128.8, 126.5, 125.7, 125.1, 123.8, 123.7, 122.5, 122.2, 119.9, 116.9, 46.9, 29.6, 26.4, 25.4, 22.6 ppm, mass spectrum: m / z = 748.4664 [M] + The yield of the final target product, nitrogen heterocyclic carbene radical 4b, was 666.2 mg, 89%.

[0071] Example 5

[0072]

[0073] A method for preparing a nitrogen heterocyclic carbene radical 5b with efficient green light emission characteristics is the same as the preparation method and parameters of Example 2, except that: Compound 2 is replaced by Compound 5, and the reaction gives 5a (yield is 640.1 mg, 84%), 1H-NMR (400MHz, CD2Cl2): δ=8.18 (s, 2H), 7.61 (t, J=7.6Hz, 2H), 7.45-7.42 (m, 2H), 7.38 (d, J=7.6, 4H), 7.06-6.94 (m, 9H), 6.86-6.84 (m, 3H), 2.52 (sept, J=6.8Hz, 4H, CH(CH3)2), 1.34 (d, J=6.8Hz, 12H, CH(CH3)2), 1.02 (s, 6H, C(CH3)2), 1.00 (d, J=6.8Hz, 12H, CH(CH3)2)ppm. 13 C{ 1 H}-NMR (100MHz, CD2Cl2): δ=160.5(d, 1 J C-F =241.5Hz), 158.1(d, 1 J C-F =241.5Hz), 155.9, 154.1, 149.8, 145.9, 144.9, 143.6 (d, 3 J C-F =11.2Hz), 143.5(d, 3 J C-F =11.2Hz), 132.3, 130.5, 130.2, 128.7, 126.7(d, 4 J C-F =7.4Hz), 126.6(d, 4 J C-F =7.4Hz), 125.5, 123.5, 122.2, 121.1, 119.8, 116.9, 116.4(d, 2 J C-F =22.5Hz), 116.2(d, 2 J C-F =22.5Hz), 115.6, 46.8, 29.4, 26.3, 25.8, 22.5ppm. Mass spectrum: m / z=784.4409[M] + The yield of the final target product, nitrogen heterocyclic carbene radical 5b, was 635.4 mg, 81%.

[0074] Example 6-19

[0075] The preparation method of the nitrogen heterocyclic carbene free radical 6b-19b in Example 6-19 is the same as the preparation method and parameters of Example 1, except that: Compound 1 is replaced by Compound 6-19 in the "Bromide" column in the following table, and the reaction obtains 6a-19a in the "Step (1) Product" column in the following table, and then obtains the nitrogen heterocyclic carbene free radical 6b-19b in the "Step (2) Target Product" column in the following table.

[0076]

[0077]

[0078]

[0079] The present invention provides two methods for preparing carbene I, as follows:

[0080] Embodiment 20

[0081] A method for preparing carbene I, comprising the following steps:

[0082] Under nitrogen atmosphere, the purchased IPr·HCl (424.3 mg, 1 mmol) was placed in a 100 ml eggplant-shaped bottle, and then 20 ml of dioxane solution was added and stirred for 1 minute to disperse evenly, followed by addition of potassium tert-butoxide (168.3 mg, 1.5 mmol), and stirred at room temperature overnight for 8 h. After the reaction was completed, the reaction solution was poured into a 50 ml centrifuge tube for centrifugation, and the supernatant was stored under nitrogen atmosphere. The supernatant was the free carbene I solution.

[0083]

[0084] Embodiment 21

[0085] A method for preparing carbene I, comprising the following steps:

[0086] Under argon atmosphere, the purchased IPr·HCl (424.3 mg, 1 mmol) was placed in a 100 ml eggplant-shaped bottle, and then 25 ml of o-xylene solution was added and stirred for 2 minutes to disperse evenly, followed by addition of potassium tert-butoxide (224.4 mg, 2 mmol), and stirred at room temperature overnight for 10 h. After the reaction was completed, the reaction solution was poured into a 50 ml centrifuge tube for centrifugation, and the supernatant after centrifugation was stored under argon atmosphere. The supernatant was the free carbene I solution.

[0087]

[0088] The optical performance test is as follows:

[0089] (1) Fluorescence test

[0090] The absorption spectra of 3a-5a and free radicals 3b-5b were measured in THF. Figure 1 By comparative analysis, 3b-5b has a new band at 550-900nm that is not found in 3a-5a. The new absorption band is the electronic transition of free radicals. The absorption spectrum of 3b-5b in THF has two similar bands at 330-407nm and 425-550nm, among which 425-550nm corresponds to the fluorescence emission peak.

[0091] Table 1 Fluorescence test results of free radicals 3b-5b in THF solution.

[0092]

[0093] like Figure 2 As shown, in the spectra of 3b-5b, due to the introduction of donor groups, the emission peak appears at about 530 nm.

[0094] like Figure 3 As shown in Table 1, the fluorescence lifetimes of free radicals 3b-5b are between 3.49-5.29ns. The Φ value of 5b is the highest at 70.1%, followed by 4b at 54.2%, and 3b at 50.7%, indicating that the nitrogen heterocyclic carbene free radicals of the present invention all have high Φ values ​​and nanosecond-level luminescence lifetimes, which will promote OLED devices to have high external quantum efficiency, low energy loss, and long practical life.

[0095] like Figure 4 , using the solvation effect to analyze the emission state characteristics. As the solvent polarity increases, the absorption band of 3b-5b slightly red-shifts. The emission peaks of 3b-5b gradually broaden and red-shift as the solvent polarity increases. Figure 5 As shown in Figure 2, 5b has two Lippert-Mataga curves with different slopes. The dipole moment μ of 5b in low polarity solvents e The emission state of 3b-5b is HLCT, which is 1.15D, belonging to the LE state emission range, while in highly polar solvents it is 17.90D, belonging to the CT state emission range. Similar results were observed in 3b and 4b. The experimental results show that the emission state of 3b-5b has HLCT characteristics.

[0096] (2) Application of nitrogen heterocyclic carbene radicals in OLED devices

[0097] High thermal and photostability are very important for the application of nitrogen heterocyclic carbene radicals in OLED devices. Therefore, the thermal and photostability of nitrogen heterocyclic carbene radicals 3b-5b were tested in a nitrogen atmosphere. Figure 6 ).like Figure 7Thermogravimetric analysis (TGA) showed that with the increase of linker stiffness and the introduction of diphenylamine and its derivative groups, the thermal decomposition temperature (T d , corresponding to 5% weight loss) increased, and a similar trend was observed in the photostability of THF by measuring the decay of fluorescence intensity under continuous light irradiation (365 nm excitation wavelength). The nitrogen heterocyclic carbene radicals 3b-5b have higher T d (over 140°C) and light stability (t 1 / 2 >1.87×10 3 s), among which 5b has the highest thermal stability (217℃) and photostability (1.04×10 5 s). In addition, the multi-cycle cyclic voltammogram (50 cycles) of the nitrogen heterocyclic carbene radical is consistent with a reversible one-electron reduction process, indicating that the radical has good stability during oxidation and reduction.

[0098] like Figure 8 , a method for manufacturing an organic light-emitting device, comprising the following steps:

[0099] (1) ultrasonically cleaning a transparent electrode indium tin oxide (ITO) film on a glass substrate for an organic light emitting diode (OLED) device (Geomatec) with acetone, ethanol and distilled water in sequence, and drying the film; then mounting the cleaned anode substrate on a substrate holder of a vacuum vapor deposition device;

[0100] (2) vacuum depositing a hole layer compound PEDOT:PSS (30 nm) onto an ITO electrode, and then co-depositing PVK (10 nm) and the main light-emitting material 4b or 5b obtained in Embodiment 1 of the present invention and a TPBi dopant onto the hole region at a mass ratio of 96.5:3.5 to form a light-emitting layer EML with a thickness of about 50 nm;

[0101] (3) Finally, an electron transport layer B3PYMPM with a thickness of about 60 nm, a cathode LiF with a thickness of about 1 nm, and aluminum with a thickness of about 50 nm are sequentially deposited to complete the manufacture of the organic light-emitting device.

[0102] Table 2 Performance test results of organic electroluminescent devices of nitrogen heterocyclic carbene radicals 4b and 5b

[0103]

[0104] As can be seen from Table 2, the nitrogen heterocyclic carbene radical of the present invention can be successfully applied to organic light-emitting diode devices, with high luminous efficiency, external quantum efficiency and luminous brightness, small energy loss, and long practical life, solving the problem of low quantum yield of existing green light open shell doublet fluorescence. The high luminous efficiency and short life of the nitrogen heterocyclic carbene radical of the present invention also have potential application value in the preparation of transmitters for fast optical communication.

[0105] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and the specific implementation of the present invention cannot be limited to these descriptions. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A nitrogen heterocyclic carbene free radical with efficient green light emission characteristics, characterized in that: The general structural formula of the nitrogen heterocyclic carbene free radical is shown below: Wherein, R is a polycyclic aromatic hydrocarbon group.

2. The nitrogen heterocyclic carbene free radical with efficient green light emission characteristics according to claim 1, characterized in that: The polycyclic aromatic hydrocarbon is selected from biphenyl type aromatic hydrocarbon group or condensed ring aromatic hydrocarbon group.

3. The nitrogen heterocyclic carbene free radical with efficient green light emission characteristics according to claim 2, characterized in that: The biphenyl type aromatic hydrocarbon group is selected from 4'-N,N-diphenyl biphenyl or 4'-N,N-dihalogenated phenyl biphenyl; the condensed ring aromatic hydrocarbon group is selected from Wherein, R1, R2, R3, R4 and R5 are all selected from halogen group, alkyl group having 1-6 carbon atoms, alkoxy group having 1-6 carbon atoms, cyano group or trifluoroalkyl group having 1-6 carbon atoms.

4. The method for preparing the nitrogen heterocyclic carbene free radical with efficient green light emission characteristics according to claim 1, characterized in that: The steps include: (1) under an inert atmosphere, free carbene I and a bromide solution are added to a container, and then a catalyst Ni(COD)2 is added for heating reaction, and the reaction solution is concentrated, precipitated, and filtered to obtain compound II, wherein R in the bromide is a polycyclic aromatic hydrocarbon group; (2) Under an inert atmosphere, compound II is dissolved in THF, the solution is cooled to below -35°C, KC8 is added for stirring reaction, and the reaction solution is washed and filtered to obtain the target product, a nitrogen heterocyclic carbene free radical, wherein R in the target product is a polycyclic aromatic hydrocarbon group; 5. The preparation method according to claim 4, characterized in that: In step (1), the solvent of the bromide solution is dioxane or o-xylene, the inert atmosphere is nitrogen or argon atmosphere, the molar ratio of the carbene I to the bromide is 1:(1-1.1), and the molar ratio of the carbene I to the catalyst Ni(COD)2 is 1:(0.1-0.12); the temperature of the heating reaction is 110-160°C, and the reaction time is 12-24h; in step (2), the inert atmosphere is nitrogen or argon atmosphere, the molar ratio of the compound II to KC8 is 1:(1.2-1.4); the temperature of the stirring reaction is room temperature, and the reaction time is 3-5h.

6. The preparation method according to claim 4, characterized in that: The R in the bromide and the target product is the same and is selected from a biphenyl type aromatic hydrocarbon group or a condensed ring aromatic hydrocarbon group.

7. The preparation method according to claim 6, characterized in that: The biphenyl type aromatic hydrocarbon group is selected from 4'-N,N-diphenyl biphenyl or 4'-N,N-dihalogenated phenyl biphenyl; the condensed ring aromatic hydrocarbon group is selected from Wherein, R1, R2, R3, R4 and R5 are all selected from halogen group, alkyl group having 1-6 carbon atoms, alkoxy group having 1-6 carbon atoms, cyano group or trifluoroalkyl group having 1-6 carbon atoms.

8. The preparation method according to claim 4, characterized in that: In step (1), the preparation process of carbene I is to add IPr·HCl, then add dioxane or o-xylene solvent, and then add potassium tert-butoxide to react with stirring in a container under an inert atmosphere, and the reaction solution is centrifuged to obtain the supernatant, which is the free carbene I solution, and the free carbene I solution is stored in an inert atmosphere; 9. The preparation method according to claim 8, characterized in that: The inert atmosphere is nitrogen or argon atmosphere; the molar ratio of IPr·HCl to potassium tert-butoxide is 1:(1.5-2); the temperature of the stirring reaction is room temperature, and the reaction time is 8-10 hours.

10. Use of the nitrogen heterocyclic carbene radical according to claim 1 in an organic light emitting diode device.

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