Narrow-band green delayed fluorescence carbon quantum framework with high quantum yield as well as preparation method and application of narrow-band green delayed fluorescence carbon quantum framework

Abstract

The invention relates to the field of fluorescent carbon nanomaterials, in particular to a high-quantum-yield narrow-band green delayed fluorescence carbon quantum framework and a preparation method and application thereof. The method comprises the following steps: by taking 1-bromo-3-fluorobenzene and boron tribromide as carbon source precursors, adding a reaction catalyst into a carbon source precursor solution, heating a mixed solution, and reacting at 120-150 DEG C for 18-24 hours to obtain a carbon quantum framework solution. The narrow-band delayed fluorescence carbon quantum framework prepared by the invention is formed by bonding four dibenzo [fg, op] tetraene units through a symmetric boron bridge, and has a rigid non-planar conjugated framework structure. The narrow-band delayed fluorescence carbon quantum framework with the quantum yield of 98% prepared by the invention has a wide application prospect in the field of electroluminescence. The compound is applied to an electroluminescent diode, has the advantages of high external quantum efficiency, low efficiency roll-off and the like, and is expected to be used as a low-cost and environment-friendly novel luminescent material to be applied to the field of next-generation display.

Description

Technical Field

[0001] The invention relates to the field of fluorescent carbon nanomaterials, and in particular to a high quantum yield narrow-band green delayed fluorescent carbon quantum framework and a preparation method and application thereof. Background Art

[0002] The continuous maturity of 5G communication technology has promoted the development of display technology from high-definition to ultra-high-definition display. The ideal green light material must meet the conditions of maximum emission peak at 532nm and sufficiently narrow half-peak width. In fact, green light is located in the middle of the visible spectrum. Slight spectral broadening or shoulder peaks will lead to its CIE y The decrease in the value of green light will damage the color purity of green light. Therefore, compared with blue light and red light, the development of green light materials with extremely narrow half-width for ultra-high color purity display devices faces great challenges.

[0003] At present, inorganic semiconductor quantum dots light-emitting diodes (QLEDs) have become a research hotspot in the field of new generation ultra-high-definition displays due to their advantages such as narrow half-width, adjustable luminescence, and solution processing. In particular, the core-shell structure LEDs based on CdSe / CdZnSe / ZnS have achieved a FWHM of less than 30nm in the green light region (537nm), and the device external quantum efficiency is close to the theoretical limit. However, the inherent heavy metal elements (Cd, Pb, etc.) have potential safety issues for the natural environment and human health, as well as poor photothermal stability, which limit their large-scale development and application. Therefore, it is particularly important to develop environmentally friendly, highly stable, and low-cost luminescent materials for the new generation of display technology.

[0004] Carbon quantum dots (CQDs) are a new type of fluorescent carbon nanomaterials with a size less than 10 nm and a significant quantum confinement effect, which have attracted widespread attention. More importantly, compared with traditional inorganic semiconductor QDs, CQDs have multiple advantages such as almost no toxicity, low cost, stable fluorescence, and solution processing, and may become an ideal candidate material for realizing the next generation of high-performance display devices. In recent years, the directional design of CQDs optical properties has been achieved by regulating size, shape, surface functional groups, etc., and fluorescent CQDs emitting from deep ultraviolet to near-infrared have been successfully prepared. However, due to the lack of precise structural regulation strategies, the application of CQDs materials in high-performance electroluminescent LEDs still faces the following key challenges: (1) The half-width is wide (FWHM>80nm), showing poor color purity; (2) There is spin confinement between singlet and triplet states, and triplet excitons cannot be used. The device external quantum efficiency (EQE<5%) is low and cannot meet practical needs. Summary of the invention

[0005] The purpose of the present invention is to provide a narrow-band delayed fluorescence carbon quantum framework with a quantum yield of 98%.

[0006] Another object of the present invention is to provide a method for preparing the above carbon quantum framework material.

[0007] Another object of the present invention is to provide applications of the carbon quantum framework material.

[0008] The narrow-band delayed fluorescent carbon quantum framework with high quantum yield according to the present invention is prepared by a method comprising the following steps:

[0009] 1-bromo-3-fluorobenzene and boron tribromide are used as precursors, dissolved in an organic solvent, a reaction catalyst is added to the carbon source precursor solution, the mixed solution is heated, and the reaction is carried out at 120-150° C. for 18-24 hours to obtain a carbon quantum framework solution, wherein the reaction catalyst includes cesium carbonate or potassium tert-butoxide;

[0010] The obtained carbon quantum framework solution is eluted and dried to obtain carbon quantum framework solid powder.

[0011] According to the high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, 1-bromo-3-fluorobenzene and boron tribromide are dissolved in an organic solvent, N,N-dimethylformamide.

[0012] According to the high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, a mixed solvent of dichloromethane and petroleum ether is used as an eluent, purified by basic alumina column chromatography, and dried to obtain a carbon quantum framework solid powder.

[0013] According to the high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, the mass ratio of the catalyst to the carbon source precursor is 1:10 to 1:100. According to the technical solution of the present application, the catalyst cesium carbonate or potassium tert-butoxide is very important for preparing a high quantum yield narrow-band green delayed fluorescent carbon quantum framework. If a strong base is not added as a catalyst, only changing other reaction conditions such as temperature, time, etc. cannot synthesize a high quantum yield narrow-band green delayed fluorescent carbon quantum framework.

[0014] According to the high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, the molar ratio of 1-bromo-3-fluorobenzene to boron tribromide is in the range of 1:2, 1:3 or 1:5.

[0015] According to the method for preparing a high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, the method comprises the following steps:

[0016] 1-bromo-3-fluorobenzene and boron tribromide are used as precursors, dissolved in an organic solvent, a reaction catalyst is added to the carbon source precursor solution, the mixed solution is heated, and the reaction is carried out at 120-150° C. for 18-24 hours to obtain a carbon quantum framework solution, wherein the reaction catalyst includes cesium carbonate or potassium tert-butoxide;

[0017] The obtained carbon quantum framework solution is eluted and dried to obtain carbon quantum framework solid powder.

[0018] According to the method for preparing the high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, 1-bromo-3-fluorobenzene and boron tribromide are dissolved in an organic solvent N,N-dimethylformamide.

[0019] According to the method for preparing a high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, a mixed solvent of dichloromethane and petroleum ether is used as an eluent, purified by alkaline alumina column chromatography, and dried to obtain a carbon quantum framework solid powder.

[0020] According to the method for preparing a high quantum yield narrow-band green delayed fluorescent carbon quantum framework of the present invention, the mass ratio of the catalyst to the carbon source precursor is 1:10 to 1:100 in milligrams.

[0021] Another object of the present invention is to apply the prepared narrow-band delayed fluorescence carbon quantum framework material with a quantum yield of 98% to an electroluminescent diode device.

[0022] The present invention prepares a non-planar carbon quantum framework structure formed by four dibenzo[fg,op]tetraene units bonded by symmetrical boron bridges, with a half-peak width of only 38nm and high color purity; at the same time, the carbon quantum framework structure effectively reduces the single-triplet energy level difference (0.07eV), and the anti-intersystem crossing efficiency is as high as 1.1×10 6 s -1 , achieving efficient delayed fluorescence characteristics, the EQE of the corresponding device max More than 20% and shows a small efficiency roll-off (brightness of 1000cd m -2 This study is expected to promote the rapid development of CQDs-based electroluminescent devices in the potential field of display technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The fluorescence spectra of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1 under excitation at different wavelengths;

[0024] Figure 2 The normalized ultraviolet absorption and fluorescence spectra of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0025] Figure 3 This is a time-resolved fluorescence spectrum of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0026] Figure 4 The time-resolved fluorescence spectra of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1 at different temperatures;

[0027] Figure 5 The fluorescence and low-temperature phosphorescence spectra of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0028] Figure 6 This is a transmission electron microscope image of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0029] Figure 7 This is a scanning tunneling microscope image of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0030] Figure 8 is the X-ray photoelectron spectrum of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0031] Fig. 9 This is the infrared spectrum of the narrow-band delayed fluorescence carbon quantum framework prepared in Example 1;

[0032] Fig.10 The electroluminescent diode device structure prepared in Example 2;

[0033] Fig.11 This is a graph showing the emission spectrum of the narrow-band delayed fluorescence carbon quantum frame light-emitting diode prepared in Example 2 as the voltage changes.

[0034] Fig.12 The current density-voltage-brightness characteristic curve of the carbon quantum frame light-emitting diode with delayed fluorescence prepared in Example 2;

[0035] Fig.13 This is a graph showing the external quantum efficiency-brightness characteristic curve of the spectral delayed fluorescence carbon quantum frame light-emitting diode prepared in Example 2;

[0036] Fig.14 This is a current efficiency-brightness-power efficiency characteristic curve of the spectral delayed fluorescence carbon quantum frame light-emitting diode prepared in Example 2. DETAILED DESCRIPTION

[0037] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0038] According to the technical solution of the present invention, 1-bromo-3-fluorobenzene and boron tribromide are selected as carbon source precursors to synthesize a narrow-band green delayed fluorescent carbon quantum framework with a quantum yield of 98%.

[0039] The high quantum yield narrow-band green delayed fluorescent carbon quantum framework according to the present invention is prepared by a method comprising the following steps:

[0040] (1) 1-Bromo-3-fluorobenzene and boron tribromide are used as carbon source precursors and stirred to dissolve in an organic solvent, N,N-dimethylformamide. The catalyst is cesium carbonate or potassium tert-butoxide. The above solution is then heated in a three-necked round-bottom flask and reacted at 120-150° C. for 18-24 hours to obtain a green narrow-band delayed fluorescent carbon quantum framework solution.

[0041] (2) Collect the solution after the above reaction, use a mixed solvent of dichloromethane and petroleum ether as an eluent, purify it by alkaline alumina column chromatography, and finally freeze-dry to obtain a carbon quantum framework solid powder. The carbon quantum framework solid powder prepared by the present invention has good solubility in common organic solvents such as dichloromethane, toluene, tetrahydrofuran, n-hexane, 1,4-dioxane, N,N-dimethylformamide, etc.

[0042] Example 1. Preparation of a narrow-band green delayed fluorescent carbon quantum framework with a quantum yield of 98%

[0043] 0.17g 1-bromo-3-fluorobenzene and 0.25g boron tribromide were dissolved in N,N-dimethylformamide solution (50mL), and 0.33g cesium carbonate was added as a catalyst (wherein the molar ratio of 1-bromo-3-fluorobenzene, boron tribromide and cesium carbonate was 1:1:1), and then reacted at 120-150°C for 18-24 hours to obtain a carbon quantum framework solution. During the reaction, as the reaction time increased, the appearance color of the solution gradually changed to light yellow. After the reaction was completed, it was naturally cooled to room temperature, the solution was concentrated, and then purified by alkaline alumina column chromatography using a mixed solvent of dichloromethane and petroleum ether as an eluent.

[0044] As an alternative technical solution of this embodiment, the molar ratio of 1-bromo-3-fluorobenzene to boron tribromide is in the range of 1:1 to 1:5.

[0045] As an alternative technical solution of the present embodiment, the volume mass ratio of the catalyst to the carbon source precursor in milliliters: milligrams is 10:1, 1:1, 1:10, or 1:100.

[0046] As an alternative technical solution of this embodiment, potassium tert-butoxide is used instead of cesium carbonate as a catalyst, wherein the mass ratio of the catalyst cesium carbonate or potassium tert-butoxide to the carbon source precursor is 10:1 and 1:1, respectively.

[0047] As an alternative technical solution of this embodiment, the reaction temperature is 120°C, 130°C, or 150°C.

[0048] The prepared carbon quantum framework dilute solution emits bright green fluorescence under a portable ultraviolet lamp (365nm), showing excitation-independent intrinsic state fluorescence characteristics ( Figure 1 ), the half-peak width is only 38nm, indicating that the carbon quantum dot framework has a narrow spectrum band property; the emission peak is at 521nm, and the characteristic exciton absorption peak is at 480nm ( Figure 2 ), which is close to the maximum fluorescence excitation wavelength, further indicating that the fluorescence of the carbon quantum framework comes from energy band transition. The time-resolved fluorescence spectrum shows that the green light carbon quantum framework decays in a double exponential manner, with lifetimes of 8.4ns and 735ns ( Figure 3 ); By testing the variable temperature time-resolved fluorescence spectrum, the proportion of the delayed component increases with increasing temperature, indicating that there is a thermal activation energy for delayed fluorescence ( Figure 4 ). By testing the low-temperature phosphorescence spectrum, the energy level difference between the singlet and triplet states of the carbon quantum framework was calculated to be 0.07 eV ( Figure 5 ), the absolute fluorescence quantum yield was measured to be as high as 98%.

[0049] Transmission electron microscopy observed that the narrow-band green delayed fluorescence carbon quantum framework has a uniform size distribution, with an average particle size of 3.4nm ( Figure 6 Scanning tunneling microscopy clearly observed that the carbon quantum framework is composed of four dibenzo[fg,op]tetraene units bonded by symmetrical boron bridges and has a rigid non-planar conjugated framework structure ( Figure 7 ). X-ray photoelectron spectroscopy results show that the carbon quantum framework is mainly composed of four elements: C, B, O, and N, with atomic percentages of 88.38%, 4.91%, 2.42%, and 5.11%, respectively. Figure 8 ). The infrared spectrum of the carbon quantum frame solid proves the existence of NH, CN, CB, CO and C=C functional groups ( Fig. 9 ).

[0050] Comparative Example 1

[0051] Except that cesium carbonate or potassium tert-butoxide is used instead of the strong base catalyst in Example 1, other reaction conditions are the same as those in Example 1, but the half-peak width of the prepared carbon quantum frame is greater than 50 nm, and the single-three state energy level difference is larger (greater than 0.2 eV), resulting in weaker delayed fluorescence characteristics, and the corresponding device efficiency is less than 5%.

[0052] Example 2: Preparation of electroluminescent diode

[0053] The narrow-band green delayed fluorescent carbon quantum framework with a quantum yield of 98% prepared in Example 1 is used as an active light-emitting layer in a monochromatic electroluminescent diode. Fig.10 As shown, the light-emitting diode device structure includes a transparent glass substrate (glass), an anode layer (ITO), a hole injection layer poly 3,4-ethylenedioxythiophene: polystyrene sulfonate (PEDOT:PSS), an active light-emitting layer (narrow-band green delayed fluorescence carbon quantum framework), an electron transport layer 12,4,6-tris[3-(diphenylphosphinoyl)phenyl]-1,3,5-triazole (POT2T), and a cathode layer (Cs2CO3 / Al) from bottom to top. The electroluminescent diode device structure is described as: ITO / PEDOT:PSS / CDs / POT2T / Cs2CO3 / Al.

[0054] The preparation method of the electroluminescent diode device is as follows:

[0055] (1) Using acetone solution, isopropanol solution and deionized water, the transparent conductive substrate ITO glass was ultrasonically cleaned, and then dried with dry nitrogen. Then, it was baked in an oven at 150°C for 10 minutes. The ITO film on the glass substrate was used as the anode layer of the device;

[0056] (2) The dried substrate was moved into a vacuum chamber and the ITO glass was subjected to UV-ozone pretreatment for 15 min in an oxygen pressure environment;

[0057] (3) Spin coating PEDOT:PSS on the treated ITO at a speed of 4000 rpm, a spin coating time of 30 s, and a thickness of 40 nm. Then anneal in an oven at 150 °C for 15 min;

[0058] (4) Spin-coat a narrow-band green delayed fluorescent carbon quantum framework solution on the PEDOT:PSS layer at a speed of 3000 rpm, a spin-coating time of 30 s, and a thickness of 10 nm. Then anneal in an oven at 80 °C for 30 min;

[0059] (5) Then ITO was transferred to a nitrogen glove box. 40 nm POT2T was vacuum deposited at a pressure of 3×10 -4 Pa, the evaporation rate is 0.1 nm / s, and the evaporation rate and thickness are monitored by a film thickness meter;

[0060] (6) Then vacuum evaporate 1nm Cs2CO3, 100nm Al, and the pressure is 3×10 -4 Pa, the evaporation rate is 0.1 and 0.3 nm / s, and the evaporation rate and thickness are monitored by a film thickness meter;

[0061] (7) The device is not packaged, and the current-voltage-brightness characteristics of the device are directly tested, and the luminous spectrum parameters of the device are tested at the same time;

[0062] The peak value of the device's electroluminescence is 522nm, and the emission peak position does not change with voltage, which is very stable ( Fig.11 ). The current density-voltage-brightness characteristic curve is as follows Fig.12 The narrow-band green delayed fluorescence carbon quantum framework light-emitting diode can achieve a maximum brightness of 19130cd / m 2 ; The maximum external quantum efficiency is 20.4% ( Fig.13 ), and lower efficiency roll-off (at a brightness of 1000cd / m 2 When the external quantum efficiency is 18.0%), the maximum current efficiency and power efficiency are 65.3cdA respectively. -1 and 59.5lm W -1 ( Fig.14 ).

[0063] The above embodiments are only used to explain the technical solution of the present application and do not limit the protection scope of the present application.

Claims

1. A high quantum yield narrow-band green delayed fluorescence carbon quantum framework, characterized in that: The carbon quantum framework is prepared by a method comprising the following steps: 1-bromo-3-fluorobenzene and boron tribromide are used as precursors, dissolved in an organic solvent, a reaction catalyst is added to the carbon source precursor solution, the mixed solution is heated, and the reaction is carried out at 120-150° C. for 18-24 hours to obtain a carbon quantum framework solution, wherein the reaction catalyst is cesium carbonate or potassium tert-butoxide; The obtained carbon quantum framework solution is eluted and dried to obtain carbon dot solid powder.

2. The high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 1, characterized in that: The organic solvent is N,N-dimethylformamide.

3. The high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 1, characterized in that: The mixture of dichloromethane and petroleum ether is used as an eluent, purified by alkaline alumina column chromatography, and dried to obtain a carbon quantum framework solid powder.

4. The high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 1, characterized in that: The mass ratio of the catalyst to the carbon source precursor is 1:10 to 1:

100.

5. A method for preparing a high quantum yield narrow-band green delayed fluorescence carbon quantum framework, characterized in that: The method comprises the following steps: 1-bromo-3-fluorobenzene and boron tribromide are used as precursors, dissolved in an organic solvent, a reaction catalyst is added to the carbon source precursor solution, the mixed solution is heated, and the reaction is carried out at 120-150° C. for 18-24 hours to obtain a carbon quantum framework solution, wherein the reaction catalyst is cesium carbonate or potassium tert-butoxide; The obtained carbon quantum framework solution is eluted and dried to obtain carbon quantum framework solid powder.

6. The method for preparing the high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 5, characterized in that: The organic solvent is N,N-dimethylformamide.

7. The method for preparing a high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 5, characterized in that: The mixture of dichloromethane and petroleum ether is used as an eluent, purified by alkaline alumina column chromatography, and dried to obtain a carbon quantum framework solid powder.

8. The method for preparing a high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 5, characterized in that: The mass ratio of the catalyst to the carbon source precursor is 1:10 to 1:

100.

9. Application of the high quantum yield narrow-band green delayed fluorescence carbon quantum framework according to claim 1.

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