Alcohol-soluble host material for carbon dot electroluminescent device and preparation method and application thereof

Abstract

The invention relates to the technical field of electroluminescent materials and devices, in particular to an alcohol-soluble host material for a carbon dot electroluminescent device as well as a preparation method and application of the alcohol-soluble host material. The alcohol-soluble host material for the carbon dot electroluminescent device has a structure as shown in a formula I. According to the invention, phosphate ester is introduced into the alcohol-soluble host material as a side chain, so that on one hand, the solubility of the host material in ethanol can be effectively improved, and on the other hand, the film-forming ability of the host material can be effectively improved. Diphenylamine, carbazole and carbazole derivatives are used as donors, triazine is used as an acceptor, and the host material can be endowed with the characteristic of bipolar transmission. Test results show that the alcohol-soluble host material provided by the invention has excellent alcohol solubility and film-forming ability comparable to that of a polymer host material, and also has good hole and electron transport ability, so that carrier transport is effectively balanced, and the luminous efficiency of a host-guest doped electroluminescent device is improved.

Description

Technical Field

[0001] This invention relates to the field of electroluminescent materials and devices, and in particular to an alcohol-soluble host material for carbon dot electroluminescent devices, its preparation method, and its application. Background Technology

[0002] Carbon-based high-efficiency luminescent materials, as a new class of luminescent materials, have demonstrated strong competitiveness in the field of electroluminescence due to their tunable bandgap emission, wide availability of raw materials, good solution processability, low cost, and excellent semiconductor properties. Currently, thermally activated delayed fluorescent carbon dots (CDs), narrow-emission CDs, phosphorescent CDs, and fluorescent CDs with a quantum yield (PLQY) approaching 100% have been successfully developed, and high-performance electroluminescent devices have been fabricated based on these materials. These devices have broad application prospects in the display and lighting fields. However, these CDs generally suffer from severe aggregation quenching effects. To overcome this problem, it is necessary to introduce host materials to suppress the aggregation quenching of carbon dots in order to obtain high-performance electroluminescent devices. Water- and alcohol-soluble CDs, as a class of fluorescent CDs, can exhibit a PLQY approaching 100% and are currently mainly used in life sciences, photoluminescence, laser technology, ion detection, and luminescent solar concentrators. However, few studies have reported the use of water- and alcohol-soluble CDs as guest luminescent materials in the research of electroluminescent devices. This is mainly due to two factors: First, the choice of solvent is crucial to ensuring adequate mixing of CDs with the host material, and the polarity difference limits the range of available solvents. Water- and alcohol-soluble CDs differ significantly in polarity from the host materials commonly used in electroluminescence, making it difficult to achieve good dispersion and processing in the same solvent system. Second, water- and alcohol-soluble CDs themselves have a strong aggregation quenching effect, which further increases the difficulty of applying them to electroluminescent devices.

[0003] Currently, commonly used host materials include poly(9-vinylcarbazole) (PVK), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-n-butyl)phenyl)-diphenylamine)] (TFB), and 4,4'-bis(9-carbazole)biphenyl (CBP). According to the principle of "like dissolves like," the polarity of these materials means that the processing of the luminescent layer solution can only be done using toxic solvents such as halogenated hydrocarbons. Furthermore, these hole-transporting host materials have inherent limitations such as low electron mobility, which severely hinders carrier transport balance, reduces the carrier recombination region, and lowers the device's luminous efficiency. In addition, while polymer hosts such as PVK have good film-forming ability, their synthesis is complex and expensive. Small molecule host materials such as CBP are simpler to synthesize, but they have strong structural rigidity and a high glass transition temperature (T0). gThe lower [aspect ratio] makes it impossible to obtain film morphologies comparable to polymers through solution processing. This limits the development of carbon dot electroluminescence.

[0004] Based on this, we propose the following design principles for alcohol-soluble host materials: 1. Select suitable weak electron-donating and weak electron-withdrawing units to form a donor-acceptor configuration blue host material with a wider band gap to accommodate more carbon dots of various colors. Simultaneously, ensure bipolar transport properties to balance carrier transport, broaden the carrier recombination region, and improve device performance. 2. Introduce large polar functional groups into the electron-donating units. This ensures efficient alcohol solubility of the host material, reduces the π-π stacking degree, and improves film-forming ability without altering its carrier transport properties. Furthermore, the introduction of large polar functional groups allows the host material to have energy levels matching adjacent functional layers, reducing the injection barrier for holes and electrons, thereby lowering the device's driving voltage. 3. The host material should have good carbon dot dispersion to minimize carbon dot aggregation and quenching, reducing exciton quenching caused by carbon dot π-π stacking and improving device luminescence efficiency. 4. The host material should have good thermal stability and a high TL. g It is crucial to ensure both the structural stability of the host material during annealing and to prevent phase transformation at the annealing temperature, thus maintaining a favorable film morphology. Therefore, developing high-performance bipolar transport alcohol-soluble host materials allows for the use of green solution processing for the light-emitting layer of CDs (Diode-Based Light Emitting Diodes), aligning with environmentally friendly and sustainable development principles and reducing environmental harm. Furthermore, solution processing technology offers lower costs and can be used for large-scale fabrication. Simultaneously, it can significantly improve device performance. In conclusion, the development of alcohol-soluble host materials is of great significance for the large-scale fabrication and application of environmentally friendly CDs electroluminescent devices. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide an alcohol-soluble host material for carbon dot electroluminescent devices, its preparation method and application.

[0006] To achieve the above objectives, the present invention provides an alcohol-soluble host material for carbon dot electroluminescent devices, having the structure shown in Formula I:

[0007]

[0008] Among them, R1, R2, and R3 are independently selected from H or one or more electron-donating groups with phosphate ester side chains;

[0009] Furthermore, R1, R2, and R3 are not all H at the same time.

[0010] This invention provides a method for preparing the alcohol-soluble host material of the above-mentioned carbon dot electroluminescent device, comprising:

[0011] S1) Electron-donating units with phosphate ester side chains are prepared by introducing phosphate ester side chains into electron-donating units through palladium-catalyzed carbon-phosphorus (CP) coupling reaction.

[0012] S2) The electron-donating unit with the phosphate ester side chain and the electron-withdrawing unit shown in Formula I-a are subjected to a nucleophilic substitution reaction to obtain the alcohol-soluble host material shown in Formula I for carbon dot electroluminescent devices.

[0013]

[0014] X1, X2, and X3 are independently selected from H or F, and not all of them are H.

[0015] This invention provides the application of the alcohol-soluble host material for carbon dot electroluminescent devices as the light-emitting layer of carbon dot electroluminescent devices.

[0016] This invention provides an electroluminescent device, comprising: a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an anode;

[0017] The light-emitting layer includes the alcohol-soluble host material used in carbon dot electroluminescent devices.

[0018] Compared with the prior art, the alcohol-soluble host material for carbon dot electroluminescent devices provided by the present invention has the structure shown in Formula I.

[0019] The present invention achieves the following beneficial effects:

[0020] (1) This invention is the first to use phosphate ester as a side chain to synthesize alcohol-soluble host material. The synthesis method is simple and efficient, with high product yield and low cost, and can be prepared on a large scale.

[0021] (2) The alcohol-soluble main material prepared by the present invention has excellent solubility and can be dissolved in solvents such as toluene, chlorobenzene, dichloromethane, ethyl acetate, tetrahydrofuran, chloroform, acetone, isopropanol, ethanol, methanol, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. It also has excellent film-forming ability.

[0022] (3) The alcohol-soluble host material prepared by the present invention has a wide range of applications and can be applied to most solution-processable CDs guest luminescent materials.

[0023] (4) The alcohol-soluble host material prepared by the present invention has good electron and hole transport capabilities, which ensures the transport balance of charge carriers in the light-emitting layer based on the host material and is beneficial to improving the light-emitting efficiency of the device.

[0024] (5) The alcohol-soluble host material with phosphate ester as side chain synthesized in this invention is processed with green solvent ethanol solution, and the preparation of water-ethanol soluble CDs electroluminescent devices is realized for the first time. The multicolor carbon dot electroluminescent devices prepared by ethanol solution processing have achieved record-breaking performance. Attached Figure Description

[0025] Figure 1 The 1H NMR spectrum of 3,6-dibromocarbazole (3,6-2BrCz) is shown.

[0026] Figure 2 The 1H NMR spectrum of carbazole diethyl 3,6-bisphosphate (2POCz) is shown.

[0027] Figure 3 The 1H NMR spectrum of 2-(4-fluorophenyl)-4,6-diphenyl-1,3,5-triazine (TRZ-F);

[0028] Figure 4 The 2PCT NMR spectrum is a hydrogen NMR spectrum.

[0029] Figure 5 The image shows the carbon NMR spectrum of 2PCT.

[0030] Figure 6 The phosphorus NMR spectrum of 2PCT;

[0031] Figure 7 The mass spectrum is for 2 PCT.

[0032] Figure 8 The solubility diagram of 2PCT in ethanol;

[0033] Figure 9 Atomic force microscopy (AFM) image of a thin film prepared by spin coating with 2PCT;

[0034] Figure 10 AFM image of a 2PCT-doped 2.5% mass fraction G-CDs spin-coated film;

[0035] Figure 11 The graph shows the brightness (L)-current density (J)-voltage (V) characteristics of an electroluminescent device.

[0036] Figure 12 The current efficiency (η) - current density (J) characteristic curve of the electroluminescent device;

[0037] Figure 13 This is the electroluminescence spectrum of a multicolor electroluminescent device. Detailed Implementation

[0038] This invention provides an alcohol-soluble host material for carbon dot electroluminescent devices, having the structure shown in Formula I:

[0039]

[0040] Among them, R1, R2, and R3 are independently selected from H or one or more electron-donating groups with phosphate ester side chains;

[0041] Furthermore, R1, R2, and R3 cannot all be H simultaneously. Preferably, any one or two of R1, R2, and R3 are not H, or none of them are H.

[0042] The structure of the phosphate ester side chain is as follows:

[0043]

[0044] Wherein, R is preferably a substituted or unsubstituted alkyl, aryl or heteroaryl group.

[0045] The alkyl group is preferably a C1 to C10 alkyl group, more preferably a C1 to C6 alkyl group. In some specific embodiments, the alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

[0046] The aryl group is preferably a C6-C12 aryl group, more preferably a C6-C10 aryl group, and even more preferably a phenyl group or a fused aryl group formed by the fusion of 2 to 4 phenyl groups. In some specific embodiments, the aryl group is selected from phenyl, naphthyl, anthraceneyl, phenanthryl, perylene, pyrene, or benzo[a]phenanthryl.

[0047] The heteroaryl group is preferably a five- to six-membered monocyclic heteroaryl group. The heteroatom of the heteroaryl group includes one or more of N, O, and S. In some specific embodiments, the heteroaryl group is selected from pyrroleyl, furanyl, thiophenyl, pyridyl, pyrimidinyl, imidazolyl, pyranyl, triazineyl, etc.

[0048] The aforementioned alkyl, aryl, and heteroaryl groups may be further substituted by one or more of the following substituents: halogen, deuterium, hydroxyl, nitro, cyano, amino, sulfonic acid, and carboxyl.

[0049] The electron-donating group connecting the phosphate ester side chain is preferably a heteroaryl group containing N, O, or S heteroatoms, and more preferably a carbazole group, N,N-diphenylamino group, indole-carbazole group, or indole-fluorenyl group.

[0050] Any one or more hydrogen atoms in the electron-donating group may be further substituted, preferably by any one or more of halogen, deuterium, hydroxyl, nitro, cyano, amino, sulfonic acid, carboxyl, C1-C6 alkyl, aryl, more preferably by any one or more of F, Cl, Br, deuterium, hydroxyl, nitro, cyano, amino, sulfonic acid, carboxyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, phenyl.

[0051] The number of phosphate ester side chains in the aforementioned electron-donating groups is preferably 1, 2, or 3, more preferably 1 or 2.

[0052] Preferably, the electron-donating group with the phosphate ester side chain is selected from any of the following structures:

[0053]

[0054] The range of R is as described above and will not be repeated here.

[0055] Preferably, R is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, or phenyl.

[0056] In some specific embodiments, the alcohol-soluble host material has any of the following structures:

[0057]

[0058]

[0059] The R is as described above.

[0060] In the aforementioned structural formula, single bond Indicates the connection location.

[0061] Compounds 1 to 24 shown above are representative structures that conform to the spirit and principles of this invention. It should be understood that listing the specific structures of the above compounds is only for better explanation of this invention and is not intended to limit this invention.

[0062] In some specific embodiments, the alcohol-soluble host material has the following structure:

[0063]

[0064] This invention introduces phosphate esters in the form of conjugated side chains, endowing the compound with excellent alcohol solubility, with a solubility in ethanol greater than 200 mg / mL. -1Using ethanol as a solvent, the solution-processed film exhibits a very low root-mean-square roughness (RMS < 1 nm), with flatness comparable to common polymer host materials such as PVK. This type of material employs a donor-acceptor structure commonly used in organic optoelectronics, using triphenylamine, carbazole, and carbazole derivatives as donors and 1,3,5-triphenyl-1,3,5-triazine as acceptor to construct a host material with bipolar transport characteristics. This balances carrier transport, reduces exciton quenching, and ultimately improves the electroluminescence efficiency of the device. This invention develops a bipolar transport alcohol-soluble host material with excellent film-forming properties, achieving for the first time water-ethanol-soluble carbon dot electroluminescence. This allows carbon dot electroluminescent devices to be prepared using the green solvent ethanol and can be used to fabricate large-area electroluminescent devices.

[0065] The present invention also provides a method for preparing the above-mentioned alcohol-soluble host material for carbon dot electroluminescent devices, comprising:

[0066] S1) Electron-donating units with phosphate ester side chains are prepared by introducing phosphate ester side chains into electron-donating units through palladium-catalyzed carbon-phosphorus (CP) coupling reaction.

[0067] S2) The electron-donating unit with the phosphate ester side chain and the electron-withdrawing unit shown in Formula I-a are subjected to a nucleophilic substitution reaction to obtain the alcohol-soluble host material shown in Formula I for carbon dot electroluminescent devices.

[0068]

[0069] X1, X2, and X3 are independently selected from H or F, and not all of them are H.

[0070] Preferably, step S1) above includes: contacting an electron-donating unit with a halogen substituent and a phosphite compound to perform a carbon-phosphorus (CP) coupling reaction to obtain an electron-donating unit with a phosphate ester side chain.

[0071] The structure of the phosphite compound is as follows:

[0072]

[0073] The range of R is as described above.

[0074] The catalyst for the reaction preferably includes palladium acetate.

[0075] The solvent for the reaction is preferably tetrahydrofuran.

[0076] The preferred temperature for the reaction is reflux, and the preferred reaction time is 5–20 h.

[0077] In step S2), NaH is preferably used as the acid-binding agent.

[0078] The solvent for the reaction in step S2) is preferably N,N-dimethylformamide (DMF); the reaction temperature is preferably 100-150°C; and the reaction time is preferably 4-10 h.

[0079] The present invention also provides the application of the above-mentioned alcohol-soluble host material for carbon dot electroluminescent devices as the light-emitting layer of carbon dot electroluminescent devices.

[0080] Preferably, the alcohol-soluble host material for the carbon dot electroluminescent device is used as the host material for the light-emitting layer of the carbon dot electroluminescent device.

[0081] The present invention also provides an electroluminescent device, comprising: a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an anode.

[0082] The light-emitting layer includes the alcohol-soluble host material used in carbon dot electroluminescent devices.

[0083] The alcohol-soluble main material can be processed using renewable solvent ethanol. By dissolving it in ethanol solvent, a film can be formed using methods such as spin coating, inkjet printing, or printing to obtain the light-emitting layer.

[0084] Preferably, the alcohol-soluble host material is used as the host material, that is, the light-emitting layer includes a host material and a guest material;

[0085] The host material includes the alcohol-soluble host material used in carbon dot electroluminescent devices.

[0086] Preferably, the guest material includes polychrome alcohol-soluble carbon dots.

[0087] Preferably, the guest material includes one or more of alcohol-soluble green carbon dots, alcohol-soluble yellow carbon dots, and alcohol-soluble red carbon dots.

[0088] The mass of the object material preferably accounts for 2.5% to 20% of the mass of the body material.

[0089] The present invention does not impose any special limitations on the materials of the cathode, electron transport layer, hole transport layer, hole injection layer and anode, and can use materials that are well known to those skilled in the art and suitable for electroluminescent devices.

[0090] In some specific embodiments, the cathode material is indium tin oxide (ITO).

[0091] In some specific implementations, the electron transport layer is magnesium-doped zinc oxide (ZnMgO).

[0092] In some specific embodiments, the hole transport layer is an organic small molecule 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC).

[0093] In some specific implementations, the hole injection layer is molybdenum trioxide (MoO3).

[0094] In some specific implementations, the anode material is preferably aluminum (Al).

[0095] The present invention does not impose any special limitations on the preparation method of the electroluminescent device. Preferably, the electron transport layer and the light-emitting layer are both processed by ethanol spin coating, and the other functional layers are processed by vacuum thermal deposition.

[0096] In some specific implementation schemes, the host material and the guest light-emitting material are dissolved in ethanol solvent, and then a film is formed by spin coating, inkjet printing, printing or other methods to obtain the light-emitting layer of the CDs electroluminescent device.

[0097] The following description of embodiments further illustrates the specific implementation of the present invention in detail, to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the concept and technical solution of the present invention. The given embodiments are merely illustrative of the present invention and are not intended to limit the scope of the invention.

[0098] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0099] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0100] Example 1: Preparation of 3,6-2BrCz

[0101]

[0102] Weigh 6.0 g (35.88 mmol) of carbazole and add it to a 200 mL single-necked round-bottom flask. Add a magnetic stir bar and 60 mL of DMF. Place the flask in an ice-salt bath and stir. Once the solution in the flask has cooled to 0 °C, weigh 12.77 g (71.76 mmol) of N-bromosuccinimide (NBS) and slowly add it to the solution in portions. React overnight in the dark. After the reaction is complete, the reaction solution is extracted with ethyl acetate and saturated brine. The organic phase is dried over anhydrous Na2SO4. The crude product is subjected to column chromatography using petroleum ether and dichloromethane as eluents, finally yielding 10.03 g (30.86 mmol) of 3,6-2BrCz, with a yield of 86%.

[0103] The structural confirmation data for 3,6-2BrCz are as follows:

[0104] 1¹H NMR (400MHz, CDCl₃) δ 8.13 (d, J = 2.0Hz, 2H), 8.08 (s, 1H), 7.52 (dd, J = 8.6, 2.0Hz, 2H), 7.30 (d, J = 8.6Hz, 2H). See the ¹H NMR spectrum. Figure 1 .

[0105] Example 2: Preparation of 2POCz

[0106]

[0107] Weigh 1.37 g (2.47 mmol) of 1,1'-bisphenylphosphine ferrocene (DPPF) and 0.503 g (5.13 mmol) of potassium acetate (KOAc), add them to a 250 mL two-necked flask, add a magnetic stir bar, add 80 mL of tetrahydrofuran (THF) and 10 mL of triethylamine (Et3N), weigh 0.28 g (1.25 mmol) of palladium acetate (Pd(OAc)2) and add it to the two-necked flask, evacuate under nitrogen (N2) protection, reflux for 15 min, stop heating, and after the reaction solution cools to room temperature, accurately weigh 10.0 g (30.77 mmol) of 3,6-2BrCz and 17.0 g (123.1 mmol) of diethyl phosphite, dissolve them in 20 mL of THF to prepare a solution, purge the air from the solution and quickly add it to the reaction system, reflux overnight. After the reaction was completed, the reaction solution was extracted with deionized water and dichloromethane, the organic phase was dried with anhydrous Na2SO4, and the crude product was subjected to column chromatography with dichloromethane and ethanol as eluents. The final product was 12.05 g (27.43 mmol), with a yield of 89%.

[0108] The structural confirmation data for 2POCz are as follows: 1 ¹H NMR (400MHz, CDCl₃) δ 10.82 (s, 1H), 8.62 (d, J = 15.2 Hz, 2H), 7.87 (ddd, J = 12.4, 8.2, 1.4 Hz, 2H), 7.58 (dd, J = 8.3, 3.3 Hz, 2H), 4.27–4.01 (m, 8H), 1.34 (t, J = 7.0 Hz, 12H). See the ¹H NMR spectrum. Figure 2 .

[0109] Example 3: Preparation of TRZ-F

[0110]

[0111] 2.41 g (10.85 mmol) of 4-fluorophenylboronic acid pinacol ester and 4.33 g (16.17 mmol) of 2-chloro-4,6-diphenyl-1,3,5-triazine were accurately weighed and added to a 250 mL two-necked flask. A magnetic stir bar was added, along with 60 mL of o-xylene solvent, 16 mL of 2MK2CO3 aqueous solution, and 0.25 g (0.22 mmol) of tetrakis(triphenylphosphine)palladium (Pd(PPh3)4). The mixture was then evacuated under N2 atmosphere and heated to 125 °C for 24 h. After cooling to room temperature, the reaction mixture was extracted with dichloromethane and deionized water. The organic phase was dried over anhydrous Na2SO4. The crude product was subjected to column chromatography using petroleum ether and dichloromethane as eluents, yielding 3.19 g (9.74 mmol) of the final product, with a yield of 90%.

[0112] The structural confirmation data for TRZ-F are as follows: 1 ¹H NMR (400MHz, CDCl₃) δ 8.85–8.79 (m, 6H), 7.68–7.60 (m, 6H), 7.30–7.28 (m, 2H). See ¹H NMR spectrum. Figure 3 .

[0113] Example 4: Preparation of 2PCT

[0114]

[0115] Accurately weigh 1.0 g (2.28 mmol) of 2POCz and 0.11 g (2.74 mmol) of NaH (60% dispersed in paraffin oil) into a 50 mL two-necked flask. Add 15 mL of ultra-dry DMF, evacuate to N2 protection, and react at room temperature for 0.5 h. Weigh 0.822 g (2.51 mmol) of TRZ-F, dissolve it in 15 mL of ultra-dry DMF, add it to the two-necked flask, and heat to 130 °C for 8 h. After the reaction mixture cools to room temperature, extract the reaction solution with saturated brine and ethyl acetate. Elute the crude product by column chromatography with dichloromethane and ethanol as eluents, finally obtaining 1.1 g (1.48 mmol) of product, with a yield of 65%.

[0116] The structural confirmation data for 2PCT are as follows: 1 H NMR (400MHz, MeOD) δ8.73(d,J=8.6Hz,2H),8.63(d,J=14.0Hz,2H),8.52(d,J=8.3Hz,4H),7.79(dd,J=12.4,8.5Hz,2H) ,7.60(d,J=8.6Hz,2H),7.50(dd,J=7.9,3.8Hz,4H),7.42(t,J=7.4Hz,4H),4.22-4.08(m,8H),1.35(t,J=7.1Hz,12H). 13C NMR (101MHz, MeOD)δ

[0117] 172.81,171.57,144.45,140.86,137.11,136.93,133.81,131.83,131.14,131.02,129.93,129.64,127.73,126.45,126.33,124.37,124.19,121.65,119.71,111.89,111.73,63.81,63.76,16.77,16.71. 31 P NMR(162MHz, CDCl3)δ20.14.UPLC-MS(m / z):[M]+calcd.for C 41 H 40 N4O6P2, 746.24; Found: [M+H]+, 747.22. See the proton spectrum. Figure 4 The carbon spectrum can be found here. Figure 5 Phosphorus spectrum (see) Figure 6 Mass spectrum (see) Figure 7 .

[0118] The solubility of 2PCT in ethanol is as follows Figure 8 As shown, Figure a is the absorbance intensity versus concentration curve of 2PCT. Figure b shows the absorbance intensity versus concentration curve of different concentrations (2-40 μg / mL). -1 The absorption spectrum of the 2PCT standard solution shows a linear relationship between the absorbance at 325 nm and the concentration. A saturated ethanol solution of 2PCT was prepared and diluted to 10,000 times its volume in ethanol; the concentration of the resulting solution was set as x μg / mL. -1 Calculations yielded x = 27.32 μg / mL. -1 That is, the solubility of 2PCT in ethanol is 273.2 mg / mL. -1 .

[0119] Figure 9 The AFM image of the film prepared by spin coating of 2PCT shows that the film has a smooth appearance and the solution-processed film has a very low root mean square roughness (RMS of 0.625 nm), indicating that 2PCT has excellent film-forming properties.

[0120] Example 5: Application of 2PCT in Green CDs (G-CDs) Electroluminescent Devices

[0121] The device structure is ITO / ZnMgO (40nm) / 2PCT:2.5wt% G-CDs (45nm) / TAPC (30nm) / MoO3 (10nm) / Al (100nm). The device is named G-LEDs. The dried ITO glass was treated with ultraviolet ozone (UVO) for 30 min to improve the work function and surface energy of ITO. An ethanol dispersion of ZnMgO was spin-coated and annealed to form an electron transport layer. 2PCT and G-CDs were co-dissolved in ethanol and mixed uniformly at a mass ratio of 40:1, then spin-coated and annealed to form the light-emitting layer. Subsequently, a 30nm TAPC layer was vacuum-deposited as a hole transport layer, a 10nm MoO3 layer as a hole injection layer, and a 100nm metallic Al layer as the anode. The device's turn-on voltage (V) is... on ), maximum electroluminescence (L) max ), maximum current efficiency (η) max Photoelectric data such as electroluminescence (EL) spectroscopy can be found in [link to relevant documentation]. Figure 11 , 12 13 and Table 1.

[0122] The guest luminescent material is water-soluble G-CDs, which are synthesized according to the literature reported by Lu Siyu et al. in 2023 entitled: Carbon Dots with Blue-to-Near-Infrared Lasing for Colorful Speckle-Free Laser Imaging and Dynamical Holographic Display (Adv. Mater. 2023, 35, 2302536).

[0123] Figure 10 The image shows the AFM pattern of the thin film prepared by spin coating of 2PCz-TRZ doped with 2.5% mass fraction G-CDs. It can be seen that the film has a smooth appearance and the solution-processed film has a very low root mean square roughness (RMS of 0.497 nm), indicating that 2PCz-TRZ doped with 2.5% mass fraction G-CDs still has excellent film-forming properties.

[0124] Figure 11 This is a graph showing the brightness (L)-current density (J)-voltage (V) characteristics of an electroluminescent device.

[0125] Figure 12 This is a curve showing the current efficiency (η) versus current density (J) characteristics of an electroluminescent device.

[0126] Figure 13 This is the electroluminescence spectrum of a multicolor electroluminescent device.

[0127] Example 6: Application of 2PCT in yellow CDs electroluminescent devices

[0128] The only difference from Example 5 is that the guest luminescent material is alcohol-soluble yellow light-emitting CDs (RT-CDs), which have excellent solubility in ethanol. The RT-CDs were synthesized according to the literature reported by Tan Zhan'ao et al. in 2023 entitled Gram-Scale Room-Temperature Synthesis of Solid-State Fluorescent Carbon Nanodots for Bright Electroluminescent Light Emitting Diodes (Small 2023,19,2206715).

[0129] The device structure is ITO / ZnMgO (40nm) / 2PCT:20wt% RT-CDs (45nm) / TAPC (30nm) / MoO3 (10nm) / Al (100nm). The device is named Y-LEDs. The device fabrication process is consistent with that of Example 5. The device's V on L max η max Optoelectronic data such as EL spectra can be found Figure 11 , 12 13 and Table 1.

[0130] Example 7: Application of 2PCT in Red CDs Electroluminescent Devices

[0131] The only difference from Example 5 is that the guest luminescent material is alcohol-soluble red light-emitting diodes (R-CDs), which have excellent solubility in ethanol. The R-CDs were synthesized according to the literature reported by Tan Zhan'ao et al. in 2023, entitled "Engineering organic-inorganic perovskite planar heterojunction for efficient carbon dots based light-emitting diodes" (Appl. Phys. Rev. 2022, 9, 021406).

[0132] The device structure is ITO / ZnMgO (40nm) / 2PCT:6wt% R-CDs (45nm) / TAPC (30nm) / MoO3 (10nm) / Al (100nm). The device is named R-LEDs. The device fabrication process is consistent with that of Example 5. The device's V on L max η max Optoelectronic data such as EL spectra can be found Figure 11 , 1213 and Table 1.

[0133] Table 1

[0134]

[0135] Depend on Figure 11 , 12 As shown in Tables 1, 13, and 1, the carbon dot LEDs prepared using the alcohol-soluble host material exhibit low start-up voltage, high brightness, and high current efficiency. This marks the first time in the field of carbon dot electroluminescence that multicolor LEDs have been processed using ethanol as a solvent solution, achieving record-breaking performance. This is attributed to the excellent alcohol solubility, film-forming ability, carrier transport ability, and carbon dot dispersion ability of the alcohol-soluble host material.

[0136] This invention introduces phosphate esters as side chains into an alcohol-soluble host material, which effectively improves the solubility of the host material in ethanol and enhances its film-forming ability. Using diphenylamine, carbazole, and carbazole derivatives as donors and triazine as acceptors imparts bipolar transport properties to the host material. Experimental results show that the alcohol-soluble host material provided by this invention possesses excellent alcohol solubility, film-forming ability comparable to polymer host materials, and good hole and electron transport capabilities, thereby effectively balancing carrier transport and improving the luminous efficiency of host-guest doped electroluminescent devices.

[0137] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An alcohol-soluble host material for carbon dot electroluminescent devices, having the structure shown in Formula I: in, R1, R2, and R3 are independently selected from H or one or more electron-donating groups with phosphate ester side chains; Furthermore, R1, R2, and R3 are not all H at the same time.

2. The alcohol-soluble host material for carbon dot electroluminescent devices according to claim 1, characterized in that, The electron-donating group with the phosphate ester side chain is selected from any of the following structures: Wherein, R is selected from substituted or unsubstituted C1 to C10 alkyl, aryl or heteroaryl groups.

3. The alcohol-soluble host material for carbon dot electroluminescent devices according to claim 2, characterized in that, The R is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, or phenyl.

4. The alcohol-soluble host material for carbon dot electroluminescent devices according to claim 1, characterized in that, The alcohol-soluble host material has any of the following structures: The R is as described in any one of claims 2 to 3.

5. A method for preparing the alcohol-soluble host material for carbon dot electroluminescent devices according to any one of claims 1 to 4, comprising: S1) Electron-donating units with phosphate ester side chains are prepared by introducing phosphate ester side chains into electron-donating units through palladium-catalyzed carbon-phosphorus (CP) coupling reaction. S2) The electron-donating unit with the phosphate ester side chain and the electron-withdrawing unit shown in Formula I-a are subjected to a nucleophilic substitution reaction to obtain the alcohol-soluble host material shown in Formula I for carbon dot electroluminescent devices. X1, X2, and X3 are independently selected from H or F, and not all of them are H.

6. The application of the alcohol-soluble host material for carbon dot electroluminescent devices as described in any one of claims 1 to 4 as the light-emitting layer of carbon dot electroluminescent devices.

7. The application according to claim 6, characterized in that, The alcohol-soluble host material used in carbon dot electroluminescent devices serves as the host material for the light-emitting layer of the carbon dot electroluminescent device.

8. An electroluminescent device, comprising: Cathode, electron transport layer, light-emitting layer, hole transport layer, hole injection layer, and anode; The light-emitting layer comprises the alcohol-soluble host material for carbon dot electroluminescent devices as described in any one of claims 1 to 4.

9. The electroluminescent device according to claim 8, characterized in that, The light-emitting layer comprises a host material and a guest material; The host material includes the alcohol-soluble host material for carbon dot electroluminescent devices as described in any one of claims 1 to 4; The object material includes polychrome alcohol-soluble carbon dots.

10. The electroluminescent device according to claim 9, characterized in that, The guest material includes one or more of alcohol-soluble green carbon dots, alcohol-soluble yellow carbon dots, and alcohol-soluble red carbon dots; The mass of the object material accounts for 2.5% to 20% of the mass of the body material.

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