Chiral d-f transition rare earth complex and application of polarization electroluminescent material

Abstract

The invention relates to an electroluminescent material, which comprises a complex (R / S)-RN8-EuI2 having the following structure: a complex EuX2-N4 having the following structure: a complex EuX2-cycloN4 having the following structure: wherein X is a negative monovalent ion such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4 or PF6, and X is a negative monovalent ion such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4 or PF6. R is independently selected from H, C1-C18 alkyl, halogen substituted alkyl, halogen atoms, aryl, halogen substituted aryl, alkyl substituted aryl, O, N, S heteroaryl and alkyl containing O, N and S coordination sites, M is Eu (II), Ce (III), Yb (II), Sm (II) and other metal ions with d-f transition luminescence, and at least one chiral site exists at '*'.

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 202211256155.2, filed on October 13, 2022, entitled "Chiral d-f transition rare earth complex and its application as electroluminescent material". TECHNICAL FIELD

[0002] The present application belongs to the field of electroluminescent materials. Specifically, it relates to a chiral d-f transition rare earth complex and the application of polarized electroluminescent material. BACKGROUND

[0003] As a natural phenomenon, polarized light exists widely in nature. Among them, the circularly polarized light manipulation technology has wide application prospects in the fields of 3D display, optical sensing, spintronic devices, optical communication, information storage, etc.

[0004] At present, circularly polarized luminescent materials are mostly obtained by the synthesis of chiral raw materials. The luminescence polarization intensity is measured by g factor, the greater the absolute value, the greater the intensity of polarized light, and the theoretical limit is 2. By increasing the number of chiral groups, designing spatial stacking mode, shortening the distance between chiral groups and luminescent center, changing the morphology of luminescent material, etc., the g factor of chiral luminescent material can be improved to a certain extent.

[0005] The commonly used luminescent materials in the research of organic light-emitting diodes (OLED) at present include fluorescent materials, phosphorescent materials, thermally activated delayed fluorescence materials (TADF), rare earth f-f transition luminescent materials, etc. By introducing chirality into the luminescent molecules, circularly polarized luminescence of different intensities can be obtained. The commonly seen circularly polarized light OLED (CP-OLED) luminescent materials in the literature can be divided into chiral thermally activated delayed fluorescence (TADF) materials with maximum external quantum efficiency EQE max = 32.6%, corresponding to g = 2.0 × 10 -3 ; g max = 6.0 × 10 -2 , corresponding to external quantum efficiency EQE = 3.5%, chiral conjugated polymers (g max = -0.8, corresponding to EQE not reported), chiral phosphorescent transition metal complexes (EQE max = 23.2%, corresponding to g = -3.0 × 10 -4 ; g max = -0.38, corresponding to EQE not reported), chiral f-f transition luminescent lanthanide (III) rare earth complexes (EQE max = 0.05%, corresponding to g = -0.88; EQE = 5.0 × 10 -3 , corresponding to g max= -1.0) and the like. It can be seen that the current CP-OLED light-emitting materials generally have the problem that high efficiency and high optical rotation cannot be achieved simultaneously. SUMMARY

[0006] Compared with these materials, the d-f transition light-emitting materials have the advantages of high exciton utilization, short excited state lifetime and easy adjustment of luminescence, and are expected to prepare high-efficiency and stable OLEDs. So far, the EQE of d-f transition Eu(II) complex OLEDs can reach 17.7%, and the maximum brightness can reach 25470 cd m max -2 ; the EQE of Ce(III) complex can reach 20.8%, and the maximum brightness can reach 31160 cd m max -2 .

[0007] The inventors of the present application hope to take advantage of the high efficiency of d-f transition light-emitting materials to explore the possibility of combining chiral light-emitting materials with d-f transition light-emitting materials, so as to break the problem that chiral light-emitting materials cannot have high efficiency and high g-factor simultaneously. So far, there is no research on d-f transition rare earth complex CP-OLED. With the experience of high g-factor chiral light-emitting materials, the inventors of the present application selected N8-EuI2 with excellent electroluminescent properties as a template, and introduced as many chiral atoms as possible into the N8 skeleton as close as possible to the luminescent center Eu(II), so as to obtain high g-factor electroluminescent materials on the basis of high efficiency.

[0008] Although the above-mentioned advantages exist, there is currently no related report on chiral Eu(II) complexes, and therefore the structure-activity relationship of the luminescent asymmetry factor is not clear. Therefore, more efforts must be made to rationally design Eu(II) complexes and deeply understand the circularly polarized luminescence mechanism to improve the chiral performance of the materials and corresponding devices. The inventors of the present application believe that the multi-dentate N ligand can effectively synthesize Eu(II) complexes with point chirality, axial chirality and plane chirality while maintaining the high efficiency of Eu(II) complexes. Therefore, in the specific embodiments of the present application, the inventors of the present application selected ligands (R / S)-MeN8 and (R / S)- i -PrN8 for designing four complexes named (R / S)-MeN8-EuI2 and (R / S)- i ​​- Eu(II)-containing azamacrocyclic complexes of PrN8-EuI2. A series of crystallographic, spectroscopic, chiral, and theoretical studies were carried out to reveal the photophysical and circularly polarized luminescence properties of these Eu(II) complexes. Then, due to the high efficiency, high luminescence asymmetry factor, and good thermal / air stability of this class of complexes, they were exemplarily selected as the emissive layer materials for CP-OLEDs. The optimized devices have outstanding performance with a maximum EQE of 15.6%, a maximum brightness of 23000 cd·m -2 , and a maximum electroluminescence asymmetry factor of 3.9 × 10 −3 , which are comparable to the state-of-the-art CP-OLED devices with phosphorescent metal complexes or TADF molecules as the emissive materials.

[0009] Embodiments of the present invention provide an electroluminescent material, comprising a complex (R / S)-RN8-EuI2, having a structure as shown below: wherein X is a negative ion such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, each R is independently selected from H, C1-C 18 alkyl, halogen-substituted alkyl, halogen atom, aryl, halogen-substituted aryl, alkyl-substituted aryl, O, N, S heteroaryl, alkyl with O, N, S coordination sites, M is Eu(II), Ce(III), Yb(II), Sm(II), etc. metal ions with d-f transition luminescence, and at least one chiral site at “*”; preferably, all “*” are chiral sites; Alternatively, the electroluminescent material comprises a complex EuX2-N4, having a structure as shown below: wherein X is a negative ion such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, each R is independently selected from H, C1-C 18 alkyl, halogen-substituted alkyl, halogen atom, aryl, halogen-substituted aryl, alkyl-substituted aryl, O, N, S heteroaryl, alkyl with O, N, S coordination sites, M is Eu(II), Ce(III), Yb(II), Sm(II), etc. metal ions with d-f transition luminescence, and at least one chiral site at “*”; preferably, all “*” are chiral sites; Alternatively, the electroluminescent material comprises a complex EuX2-cycloN4, having a structure as shown below: wherein X is a negative ion such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, and each R is independently selected from H, C1-C 18 wherein X is a negative ion such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, and each R is independently selected from H, C1-C

[0010] According to an embodiment of the present application, for example, the light-emitting material comprises (a) (R / S)-MeN8-EuI2, (b) (R / S)-PrN8-EuI2, (c) (R / S)-MeN8-Ce(OTf)3, (d) (R / S)-N4Me4-EuI2, (e) (R / S)-N4Me6-EuI2, (f) (R / S)-N4Me2Et4-EuI2, (g) (R / S)-cycloMeN4-EuI2, (h) (R / S)-hexcycloN4-EuI2. i -PrN8-EuI2, (c) (R / S)-MeN8-Ce(OTf)3, (d) (R / S)-N4Me4-EuI2, (e) (R / S)-N4Me6-EuI2, (f) (R / S)-N4Me2Et4-EuI2, (g) (R / S)-cycloMeN4-EuI2, (h) (R / S)-hexcycloN4-EuI2. An embodiment of the present application also provides an electroluminescent device, comprising a cathode, an anode, and a light-emitting layer between the cathode and the anode, wherein the light-emitting layer comprises the electroluminescent material as described above.

[0011] According to an embodiment of the present application, for example, the light-emitting layer is a mixture of a guest material and a host material, wherein the guest material comprises the electroluminescent material as described above, and the host material comprises m-MTDATA, mCP, mCBP, CzSi, DCPPO, PCzAc, CBP, TCTA, TAPC, DPEPO, mCPCN, BCPO, etc., and the doping concentration is 1wt%-99wt%, preferably 7wt%-10wt%, and most preferably 10wt%, the doping concentration being the percentage of the mass of the guest material in the total mass of the guest material and the host material.

[0012] According to an embodiment of the present application, for example, the electroluminescent device further comprises an electron transport layer between the cathode and the light-emitting layer, and the electron transport layer comprises TmPyPB, DPEPO, TSPO1, Bphen, and / or TPBi.

[0013] According to an embodiment of the present application, for example, the electroluminescent device further comprises a hole transport layer between the anode and the light-emitting layer; preferably, the hole transport layer comprises PCzAc, mCP, m-MTDATA, NPB, PEDOT:PSS, TCTA and / or TAPC.

[0014] According to an embodiment of the present application, for example, the electroluminescent device further comprises an electron transport layer between the cathode and the light-emitting layer and a hole transport layer between the anode and the light-emitting layer.

[0015] Preferably, the hole transport layer comprises TAPC and the electron transport layer comprises Bphen.

[0016] According to an embodiment of the present application, for example, the thickness of the light-emitting layer is 10-40 nm, preferably 15-30 nm, preferably 20-25 nm, most preferably 25 nm.

[0017] According to an embodiment of the present application, for example, the electroluminescent device further comprises a hole blocking layer between the light-emitting layer and the electron transport layer; preferably, the material of the hole blocking layer is TSPOl.

[0018] Preferably, the electroluminescent device further comprises a second hole transport layer between the anode and the hole transport layer; preferably, the material of the second hole transport layer is NPB.

[0019] According to an embodiment of the present application, for example, the structure of the electroluminescent device is: ITO / MoO3(2 nm) / cyclohexylidenebis[N,N'-bis(p-tolyl)aniline] (TAPC, 50 nm) / (R / S)-MeN8-EuI2: 4,4',4"-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA, 10 wt%, 20 nm) / 1,3,5-tris[(3-pyridyl)-3-phenyl]benzene (TmPyPB, 50 nm) / LiF (1 nm) / Al (100 nm). BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the chemical structure of the complex, wherein (a) (R / S)-MeN8-EuI2, (b) (R / S)- i- PrN8-EuI2, (c) (R / S)-MeN8-Ce(OTf)3, (d) (R / S)-N4Me4-EuI2, (e) (R / S)-N4Me6-EuI2, (f) (R / S)-N4Me2Et4-EuI2, (g) (R / S)-MeN4-EuI2, (h) (R / S)-cyclohexN4-EuI2 Figure 2 is a schematic diagram of the crystal structure of the complex in the embodiments of the present application, wherein (a) (R / S)-MeN8-EuI2, (b) (R / S)-N4Me4-EuI2, (c) (R / S)-N4Me6-EuI2, (d) (R / S)-N4Me2Et4-EuI2, (e) (R / S)-MeN4-EuI2, (f) (R / S)-cyclohexN4-EuI2 i - PrN8-EuI2, (c) (S)-MeN8-Ce(OTf)3, (d) (R)-N4Me4-EuI2, (e) (S)-N4Me6-EuI2, (f) (S)-N4Me2Et4-EuI2. DETAILED DESCRIPTION

[0021] The chiral d-f transition rare earth complex and its application as electroluminescent material of the present application will be further described below in conjunction with specific examples. It should be understood that the following examples are only illustratively and explain the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above content of the present application is covered in the scope of the present application intended to be protected. The corresponding full name of the compound is as follows: m-MTDATA 4,4',4''-tris[phenyl(m-methylphenyl)amino]triphenylamine mCP N,N'-dicyclohexyl-3,5-benzene mCBP 3,3-bis(9H-carbazol-9-yl)biphenyl CzSi 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole DCPPO Bis(9H-carbazol-9-yl)(phenyl)phosphine oxide PCzAc 9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine CBP 4,4'-Bis(9-carbazolyl)-1,10-biphenyl TCTA Tris(4-(9-carbazolyl)phenyl)amine TAPC 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)phenylamine] DPEPO Bis[2-((oxo)diphenylphosphoryl)phenyl] ether mCPCN 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazole-3-carbonitrile BCPO Bis-4-(N-carbazolyl)phenyl)phenylphosphine oxide TmPyPB 1,3,5-tris[(3-pyridyl)-3-phenyl]benzene Bphen 4,7-diphenyl-1,10-phenanthroline TPBi 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene TSPO1 diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide NPB N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine PEDOT:PSS poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) Preparation methods and test methods.

[0022] Unless otherwise stated, all chemicals used in the synthesis procedures were commercially available and used as received. 1 H-NMR was measured on a Bruker-400 MHz NMR. Tetramethylsilane (TMS) was used as internal reference for chemical shift correction, where δ TMS Elemental analysis was performed on a VARIO EL analyzer. Eu 2+ All syntheses of complexes were carried out in a glovebox. Solid Eu 2+ All spectroscopic tests of complexes were carried out after encapsulation in paraffin wax between two quartz plates, solutions were tested in a cuvette with a stopcock under N2atmosphere. Commercial paraffin wax was purified by oxidation using KMnO4and column chromatography to remove the fluorescent whitening agent.

[0023] Synthesis of N-p-toluenesulfonyl-2-methylaziridine (Me-Azi): In a 1 L three-necked flask was added 700 mL dichloromethane (DCM), followed by 2-aminopropanol (0.133 mol, 10.00 g), p-toluenesulfonyl chloride (TsCl) (0.277 mol, 52.80 g) and a catalyst 4-dimethylaminopyridine (DMAP) (0.013 mol, 1.58 g) and stirred. To the reaction solution was slowly added triethylamine (TEA) (0.40 mol, 40.49 g) at 0 °C under nitrogen atmosphere, which took about 1 h to complete. After the addition was completed, it was allowed to return to room temperature naturally and the reaction was left overnight. The next day, the reaction solution was washed with 260 mL saturated NH4Cl solution and the organic phase was separated, the aqueous phase was washed with 100 mL DCM for 3 times. The organic phases were combined, dried over anhydrous Na2SO4and the solvent was evaporated to give the crude product as an orange-yellow oil. After column chromatography (eluent: 1 :8 ethyl acetate / petroleum ether mixture), colorless needle-like crystals were obtained, which were supercooled easily, in 56.9% yield. 1H NMR (400 MHz, CDCl3): δ 1.15 (d, 3H, J =5.6 Hz); 1.93 (d, 1H, J =4.6 Hz); 2.34 (s, 3H); 2.50 (d, 1H, J =7.0 Hz); 2.72 (m,1H); 7.24 (d, 2H, J =8.0 Hz); 7.73 (d, 2H, J =8.0 Hz). N-p-Toluenesulfonyl-2-isopropylazacyclopropane ( i Synthesis of 2-aminopropanol (-Pr-Azi): 13.72 g valine (0.133 mol) was used instead of 2-aminopropanol as the amino alcohol raw material. The reaction conditions and post-treatment were the same as those for Me-Azi. The yellow viscous solid obtained by rotary evaporation was recrystallized from petroleum ether (PE). The supernatant was separated by decantation, and upon cooling, fluffy colorless needle-like crystals precipitated. The yield was 50.3%. 1 H NMR (400 MHz, CDCl3): δ 0.80 (d, J = 6.8 Hz, 3H), 0.90 (d, J =6.8 Hz, 3H), 1.41 (m, 1H), 2.10 (d, J = 4.4Hz, 1H), 2.45 (s, 3H), 2.51 (m,1H), 2.62 (d, J = 6.8 Hz, 1H), 7.33 (d, J = 8.0 Hz, 2H), 7.83 (d, J = 8.0 Hz,2H). Synthesis of tris(N-p-toluenesulfonyl-2-aminopropyl)amine (Me-Ts-NTEA): Me-Azi (33.51 mmol, 7.094 g) was added to a 100 mL pressure-resistant reaction flask at room temperature, followed by the sequential addition of 1.55 mL of 7 M ammonia-methanol solution and 3.87 mL of ultra-dry methanol. The flask was sealed and heated to 45 °C in an oil bath for 4 days. After the reaction was completed, 40 mL of methanol (MeOH) was added and refluxed for 2 h. The solvent was evaporated to dryness, and the mixture was separated by column chromatography (eluent: a 1:4 mixture of ethyl acetate, petroleum ether, and anhydrous methanol) to obtain a white solid in 64.3% yield. 1H NMR (400 MHz, CDCl3): δ 0.96 (d, J=6.4 Hz, 9H),2.13 (dd, J=13.0 and 3.8 Hz, 3H), 2.38 (s, 9H), 2.51 (dd, J=12.9 and 11.1 Hz,3H), 3.64-3.67 (m, 3H), 5.74 (br d, J=5.6 Hz, 3H), 7.23 (d, J=7.9 Hz, 6H),7.83 (d, J=8.2 Hz, 6H). Tri(N-p-tolylsulfonyl-2-amino-3-methylbutyl)amine (Me-Ts-NTEA) i Synthesis of Et-Ts-NTEA: The synthesis method is similar to Me-Ts-NTEA. White powder solid was precipitated after reaction at 50 °C for 4 days. The product was obtained by filtration and washed with methanol. The yield was 69.5%. 1 H NMR (400 MHz, CDCl3):δ 0.78 (d, J = 6.9 Hz, 9H), 0.80(d, J = 6.9 Hz, 10H),. 1.70 (pd, J = 6.9, 4.2 Hz, 3H), 2.13 (td, J = 12.0, 11.3,4.6 Hz, 3H), 2.38 (s, 9H), 2.96 (t, J = 12.1 Hz, 3H), 3.82 (ddt, J = 11.5, 8.6,4.5 Hz, 3H), 6.20 (d, J = 7.0 Hz, 3H), 7.23 (d, J = 8.1 Hz, 6H), 7.80 – 7.87 (m,7H). Synthesis of tris(2-aminopropyl)amine (Me-NTEA): Me-Ts-NTEA (7.682 mmol, 5.018 g) and phenol (74.13 mmol, 6.976 g) were added to a 250 mL single-necked flask, followed by the addition of 100 mL of 48% hydrobromic acid. The mixture was refluxed under a nitrogen atmosphere for 2 days, during which the solution changed from colorless to orange-red and then to dark red. After the reaction was complete, the reaction solution was allowed to cool naturally to room temperature, where the system was observed to separate into a black oil phase and a dark orange-red aqueous phase. The aqueous phase was separated, and the pH was adjusted to approximately 1 with 4 M sodium hydroxide (NaOH) solution, followed by washing with ethyl acetate (EA) until pale yellow to colorless. Then, NaOH solution was added again to adjust the pH of the aqueous phase to greater than 13, and the product was extracted with DCM. The organic phase was dried with anhydrous Na2SO4 and filtered. The filtrate was evaporated to dryness to obtain a light yellow oily liquid. The fraction distilled under reduced pressure at 104-107℃ was collected to obtain a colorless and transparent oily liquid. When left to stand, it solidified to form transparent feather-like crystals, with a yield of 50.5%. 1 H NMR (400 MHz, CDCl3): δ 0.95 –1.05 (m, 3H), 1.71 (s, 6H), 2.13 – 2.29 (m, 6H), 3.10 (dqd, J = 9.7, 6.3, 3.3Hz, 3H). Tris(2-amino-3-methylbutyl)amine i Synthesis of -Pr-NTEA: Add to a 250 mL single-necked flask i Pr-Ts-NTEA (6.167 mmol, 4.533 g) and phenol (59.51 mmol, 5.601 g) were reacted, followed by the addition of 100 mL of 40% hydrobromic acid. The mixture was refluxed under a nitrogen atmosphere for 2 days. The post-reaction treatment was similar to that for Me-NTEA, but the pale yellow oily liquid obtained by rotary evaporation of the DCM phase was pure and did not require distillation, with a yield of 87.6%. 1 H NMR (400 MHz, CDCl3): δ 0.90 (d, J =6.7 Hz, 9 H), 0.91 (d, J = 6.7 Hz, 9 H), 1.50 (octet, J = 6.6 Hz, 3 H), 1.89 (br.s, 6 H), 2.26–2.29 (m, 6 H), 2.67–2.72 (m, 3 H). Synthesis of 3,8,12,17,20,25-hexamethyl-1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane (MeN8): 1 g Me-NTEA (5.310 mmol), 38 mL isopropanol, and 1.52 mL TEA were added to a 100 mL three-necked flask under a -78 °C dry ice-acetone bath, and mechanical stirring was started to ensure homogeneity. 1.14 g of 40% glyoxal aqueous solution diluted with 7.6 mL isopropanol was added to a dropping funnel, and then the glyoxal solution was slowly added dropwise to the flask under a nitrogen atmosphere, with a dropping rate controlled at 2 s / drop. After the addition was complete, the reaction system was gradually brought to room temperature and transferred to a 250 mL flask. 1.52 g of sodium borohydride (40.10 mmol, excess) was added in batches, followed by 20 mL of methanol. The mixture was stirred overnight under a nitrogen atmosphere. After overnight, the solvent in the reaction system was evaporated to dryness. The resulting solid was soaked in DCM under a nitrogen atmosphere for 20 min and then filtered. The filtrate was evaporated to dryness to obtain a pale yellow solid. The crude product was dried overnight in a vacuum drying oven at 100 °C, and then sublimated in a sublimation apparatus at 185 °C and 0.1 Pa for 24 h to obtain colorless, flaky, transparent crystals with a yield of 18.3%. 1 H NMR (400 MHz, CDCl3): δ 1.02 (q, J = 3.9, 3.5 Hz, 18H), 1.21 (d, J = 6.1 Hz, 6H), 1.84 (d, J =12.8 Hz, 6H), 2.37– 2.71 (m, 6H), 2.69 – 3.05 (m, 12H). 3,8,12,17,20,25-Hexaisopropyl-1,4,7,10,13,16,21,24-Octazabicyclo[8.8.8]hexacosane ( i Synthesis of -PrN8): The synthesis method is similar to that of N8Me6, for 1 g i -Pr-NTEA (3.670 mmol) was transferred to a single-necked flask, and 2 g of sodium borohydride (52.76 mmol) was added in batches, followed by 13 mL of methanol and stirring for 2 days. The post-treatment was the same as for N8Me6; the crude product, after vacuum drying, was placed in a sublimation apparatus and sublimated at 160 °C and 0.1 Pa for 24 h to obtain colorless granular transparent crystals, with a yield of 8.7%. 1 H NMR (400 MHz, CDCl3): δ 0.86 (d, J = 6.8 Hz, 18H), 0.91 (d, J= 6.9Hz, 18H), 1.71 (pd, J = 7.0, 4.4 Hz, 6H), 2.18 (dd, J = 13.1, 10.1 Hz, 6H), 2.26(dd, J = 13.0, 7.3 Hz, 12H), 2.52 – 2.69 (m, 6H), 2.92 (q, J = 8.5, 6.4 Hz, 6H). Synthesis of (R / S)-MeN8-EuI2: At room temperature, under a nitrogen atmosphere, a tetrahydrofuran solution containing 59 mg (R / S)-MeN8 (0.128 mmol) was added dropwise to a tetrahydrofuran solution containing 52 mg EuI2 (0.128 mmol). The solution changed from nearly colorless to yellow, and an orange-red powder precipitated. The product was obtained by filtration and drying. Elemental analysis calculated C. 24 H 54 EuI2N8(860.52): C, 33.50; H, 6.33; N, 13.02; Elemental analysis results: C, 33.55; H, 6.39; N, 12.77.

[0024] (R / S)- i Synthesis of -PrN8-EuI2: At room temperature, under a nitrogen atmosphere, 80 mg (R / S) of -PrN8-EuI2 was added dropwise to a solution containing 52 mg EuI2 (0.128 mmol) tetrahydrofuran. i A solution of -PrN8 (0.128 mmol) in tetrahydrofuran initially changed from nearly colorless to pale green, exhibiting a bright green glow under UV excitation. With stirring, the solution deepened in color, and a pale green powder precipitated. The product was obtained by filtration and drying. The complex can be purified by vacuum sublimation at 280 °C. Elemental analysis calculated C... 36 H 78 EuI2N8(1028.85): C, 42.03; H, 7.64; N, 10.89; Elemental analysis results: C, 41.57; H, 7.41; N, 10.63.

[0025] Synthesis of (S)-MeN8-Ce(OTf)3: At room temperature, under a nitrogen atmosphere, 45 mg (R / S)-Ce(OTf)3 was added dropwise to a methanol solution containing 59 mg Ce(OTf)3 (0.1 mmol). iA 0.1 mmol PrN8 methanol solution remained colorless until it emitted a bright blue light upon UV excitation. With stirring, the solution turned slightly brown. After drying, recrystallization from DCM / n-hexane yielded the pure product. Elemental analysis calculated C. 27 H 54 CeF9N8O9S3: C, 31.12; H, 5.22; N, 10.75; Elemental analysis results: C, 31.48; H, 5.67; N, 10.43.

[0026] ( R / S )-N,N'-1,2-cyclohexanebis(2-chloroacetamide) (( R / S Synthesis of ()-N2O2Cl2): ( R / S Cyclohexanediamine (3.42 g, 30.0 mmol) and potassium carbonate (10.3 g, 75.0 mmol) were added to a solvent consisting of 23 mL of dichloromethane (DCM) and 18 mL of water. Chloroacetyl chloride (6.72 g, 60.0 mmol) was slowly added dropwise under an ice-water bath. After the addition was complete, the mixture was allowed to return to room temperature and stirred for 12 h, at which point a white solid precipitated. The DCM was removed by rotary evaporation, and the mixture was filtered. The resulting white solid was then dried under vacuum at 60 °C for 12 h to obtain the product. The yield was 9.42 g, with a yield of 93%. 1 H NMR (CDCl3): δ 1.36 (m, 4H, -NH-(CH-CH2-(C H 2)2-CH2-CH)-NH-), 1.82–2.10 (m, 4H, -NH-(CH-C H 2-(CH2)2-C H 2-CH)-NH-),3.77 (m, 2H, -NH-(C H -CH2-(CH2)2-CH2-C H )-NH-), 4.01 (br s, 4H, -C H 2-Cl), 6.82(br s, 2H, N H -CO).

[0027] ( R / S )-N,N'-1,2-cyclohexanebis(2-(dimethylamino)acetamide) (( R / S Synthesis of ()-N4O2Me4): ( R / S4.33 g (16.5 mmol) of N₂O₂Cl₂ was added to an ethanolic solution of dimethylamine (33 wt%, 160 mL, 0.860 mol), and the mixture was stirred at room temperature for 2 days. After the reaction was complete, the solvent was removed under vacuum, the solid was dissolved in 100 mL of DCM, washed three times with water (3 × 100 mL), dried with potassium carbonate, filtered, and the solvent was removed under vacuum to obtain the product. Yield: 1.50 g, yield: 32%. 1 H NMR (CDCl3): δ 1.22-1.38 (m, 4H, -NH-(CH-CH2-(C H 2)2-CH2-CH)-NH-), 1.72–2.05 (m, 4H, NH-(CH-C H 2-(CH2)2-C H 2-CH)-NH-), 2.24 (s, 12H, -N-(C H 3)2), 2.84-2.94 (m, 4H, NH-CO-C H 2-), 3.75 (m, 2H, NH-(C H -CH2-(CH2)2-CH2-C H )-NH-).

[0028] ( R / S )-N 1 N 1 '-Dimethyl-1,2-cyclohexanebis(N 2 N 2 -dimethylethane-1,2-diamine) (( R / S Synthesis of )-N4Me4: In a glove box, LiAlH4 (810 mg, 21.3 mmol) was slowly dispersed in 20 mL of tetrahydrofuran (THF), and then slowly added dropwise to a solution containing ( R / S The mixture was placed in a 100 mL round-bottom flask containing 20 mL of THF solution of 1.50 g (5.28 mmol) of N₂O₂Me₄. After sealing, the flask was refluxed under N₂ protection for 24 h. After the reaction was complete, excess LiAlH₄ was quenched with 2 mL of water, filtered, and the filtrate was evaporated to dryness to obtain a yellow, oily crude product. Sublimation at 90 °C yielded a colorless, oily product. Yield: 528 mg, 39%. 1 H NMR (400 MHz, CDCl3): δ 1.03 (m, 2H, NH-(CH-C H2-(CH2)2-CH2-CH)-NH-), 1.23(m, 2H, -NH-(CH-CH2-(C H 2)2-CH2-CH)-NH-), 1.73 (m, 2H, -NH-(CH-CH2-(C H 2)2-CH2-CH)-NH-), 2.05 (m, 2H, NH-(CH-C H 2-(CH2)2-CH2-CH)-NH-), 2.16 (m, 2H, -NH-(C H -CH2-(CH2)2-CH2-C H )-NH-), 2.23 (s, 12H, -N-(C H 3)2), 2.25 (br s, 2H, -N H ), 2.40(m, 4H, -C H 2-N-(CH3)2), 2.53 (dt, -C H 2-CH2-N-(CH3)2), 2.82 (dt, C H 2-CH2-N-(CH3)2).

[0029] ( R / S Synthesis of )-N4Me4-EuI2: In the glove box, take ( R / S N₄Me₄ (66.0 mg, 0.250 mmol) and EuI₂ (101 mg, 0.250 mmol) were each dissolved in 20 mL of THF. The EuI₂ THF solution was then slowly added dropwise to the N₄Me₄ THF solution, yielding a clear green solution that emitted blue-green light upon excitation at 365 nm. The mixture was stirred at room temperature for 24 h. After the reaction was complete, 20 mL of n-hexane was added to the solution, precipitating a green solid. The product was obtained by filtration. The yield was 90 mg, with a yield of 54%. Elemental analysis calculated C₂. 14 H 32 EuI₂N₄·0.5THF: C, 27.54; H, 5.13; N, 8.03; Elemental analysis results: C, 27.69; H, 5.51; N, 7.84.

[0030] ( R / S )-N,N'-dimethyl-1,2-cyclohexanebis(2-chloro-N-methylacetamide) (( R / S Synthesis of ()-N2O2Me2Cl2): ( R / S 8.52 g (60.0 mmol) of 1,2-dimethyl-1,2-cyclohexanediamine and 20.7 g (150 mmol) of potassium carbonate were added to a solvent consisting of 46 mL of DCM and 36 mL of water. Chloroacetyl chloride (13.4 g, 120 mmol) was slowly added dropwise under an ice-water bath. After the addition was complete, the mixture was allowed to return to room temperature and stirred for 12 h, at which point a white solid precipitated. The DCM was removed by rotary evaporation, and the mixture was filtered. The resulting white solid was then dried under vacuum at 60 °C for 12 h to obtain the product, with a yield of 14.5 g and a yield of 91%. 1 HNMR (400 MHz, CDCl3): δ 1.35 (m, 4H, -N-(CH-CH2-(C H 2)2-CH2-CH)-N-), 1.72–1.87 (m,4H, N-(CH-C H 2-(CH2)2-C H 2-CH)-N-), 2.90 (s, 6H, CO-NC H 3), 4.00-4.08 (m, 4H, -N-CO-C H 2-), 4.56-4.64 (m, 2H, -N-(C H -CH2-(CH2)2-CH2-C H )-N-).

[0031] ( R / S )-N,N'-dimethyl-1,2-cyclohexanebis(2-(dimethylamino)-N-methylacetamide) (( R / S Synthesis of ()-N4Me6O2): ( R / S 2.56 g (8.72 mmol) of N₂O₂Me₂Cl₂ was added to an ethanolic solution of dimethylamine (33 wt%, 86 mL, 0.460 mol), and stirred at room temperature for 2 days. After the reaction was complete, the solvent was removed under vacuum, the solid was dissolved in 100 mL of DCM, washed three times with water (3 × 100 mL), dried with potassium carbonate, filtered, and the solvent was removed under vacuum to obtain the product. Yield: 1.40 g, yield: 51%. 1 H NMR (400 MHz, CDCl3): δ 1.35 (m, 4H, -N-(CH-CH2-(C H 2)2-CH2-CH)-N-), 1.48–1.80 (m, 4H, N-(CH-C H2-(CH2)2-C H 2-CH)-N-), 2.28 (s, 12H, -N-(C H 3)2), 2.85 (s,6H, CO-NC H 3), 2.96-3.12 (m, 4H, -N-CO-C H 2-), 4.62 (m, 2H, -N-(C H -CH2-(CH2)2-CH2-C H )-N-).

[0032] ( R / S )-N 1 N 1 '-Dimethyl-1,2-cyclohexanebis(N 1 N 2 N 2 -trimethylethane-1,2-diamine (( R / S Synthesis of )-N4Me6: In a glove box, LiAlH4 (855 mg, 22.5 mmol) was slowly dispersed in 20 mL of tetrahydrofuran (THF), and then slowly added dropwise to a solution containing ( R / S The mixture was placed in a 100 mL round-bottom flask containing 20 mL of THF solution of 1.40 g (4.50 mmol) of N₄Me₆O₂. After sealing, the flask was refluxed under N₂ protection for 24 h. After the reaction was complete, excess LiAlH₄ was quenched with 2 mL of water, filtered, and the filtrate was evaporated to dryness to obtain a yellow, oily crude product. Sublimation at 90 °C yielded a colorless, oily product. Yield: 630 mg, 55%. 1 H NMR (400 MHz, CDCl3): δ 1.06-1.26 (m, 4H, -N-(CH-CH2-(C H 2)2-CH2-CH)-N-),1.65–1.86 (m, 4H, N-(CH-C H 2-(CH2)2-C H 2-CH)-N-), 2.24 (s, 12H, -N-(C H 3)2), 2.25(s, 6H, CH2-NC H 3), 2.32-2.45 (m, 8H, -NC H 2-C H 2-N-), 2.61-2.65 (m, 2H, -N-(C H-CH2-(CH2)2-CH2-C H )-N-).

[0033] ( R / S Synthesis of )-N4Me6-EuI2: In a glove box, ( R / S )-N4Me6 (71.0 mg, 0.250 mmol) and EuI2 (101 mg, 0.250 mmol) were each dissolved in 20 mL of THF, and then the EuI2 THF solution was slowly added dropwise to ( R / S A pale green, clear solution was obtained by stirring in a THF solution of 1-N4Me6. Upon further stirring, a pale green solid precipitated, emitting blue light upon excitation at 365 nm. The mixture was stirred at room temperature for 24 h. After the reaction was complete, the product was obtained by filtration. The yield was 120 mg, with a yield of 70%. Elemental analysis calculated C... 16 H 36 EuI2N4: C, 27.84; H, 5.26; N, 8.12; Elemental analysis results: C, 27.97; H, 5.30; N, 8.10.

[0034] ( R / S )-N,N'-dimethyl-1,2-cyclohexanebis(2-(diethylamino)-N-methylacetamide) (( R / S Synthesis of ()-N4Me2Et4O2): ( R / S 2.56 g (8.72 mmol) of N₂O₂Me₂Cl₂ was added to an ethanolic solution of diethylamine (33 wt%, 86 mL, 0.460 mol), and the mixture was stirred at room temperature for 2 days. After the reaction was complete, the solvent was removed under vacuum, the solid was dissolved in 100 mL of DCM, washed three times with water (3 × 100 mL), dried with potassium carbonate, filtered, and the solvent was removed under vacuum to obtain the product. Yield: 1.88 g, yield: 59%. 1 H NMR (400 MHz, DMSO): δ 1.08 (t, 12H, -N-(CH2-C H 3)2), 1.10-1.21 (m, 4H,-N-(CH-CH2-(C H 2)2-CH2-CH)-N-), 1.48–1.80 (m, 4H, N-(CH-C H 2-(CH2)2-C H2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C 2-CH3)2), 3.25 (s, 4H, -N-CO-C

[0035] 2-CH3)2), 3.25 (s, 4H, -N-CO-C R 2-CH3)2), 3.25 (s, 4H, -N-CO-C S 2-CH3)2), 3.25 (s, 4H, -N-CO-C 1 2-CH3)2), 3.25 (s, 4H, -N-CO-C 1 2-CH3)2), 3.25 (s, 4H, -N-CO-C 2 2-CH3)2), 3.25 (s, 4H, -N-CO-C 2 2-CH3)2), 3.25 (s, 4H, -N-CO-C 1 2-CH3)2), 3.25 (s, 4H, -N-CO-C R 2-CH3)2), 3.25 (s, 4H, -N-CO-C S 2-CH3)2), 3.25 (s, 4H, -N-CO-C R 2-CH3)2), 3.25 (s, 4H, -N-CO-C S 2-CH3)2), 3.25 (s, 4H, -N-CO-C 1 2-CH3)2), 3.25 (s, 4H, -N-CO-C δ 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H 2-CH3)2), 3.25 (s, 4H, -N-CO-C H-CH2-(CH2)2-CH2-C H )-N-).

[0036] ( R / S Synthesis of )-N4Me2Et4-EuI2: In a glove box, take ( R / S )-N4Me2Et4 (85.0 mg, 0.250 mmol) and EuI2 (101 mg, 0.250 mmol) were each dissolved in 20 mL of THF, and then the EuI2 THF solution was slowly added dropwise to ( R / S In a THF solution of N₄Me₂Et₄, a pale green clear solution was obtained. Upon continued stirring, a pale green solid precipitated, emitting blue light upon excitation at 365 nm. The mixture was stirred at room temperature for 24 h. After the reaction was complete, the product was obtained by filtration. The yield was 115 mg, with a yield of 62%. Elemental analysis calculated C... 16 H 36 EuI2N4: C, 32.18; H, 5.94; N, 7.51; Elemental analysis results: C, 32.00; H, 5.77; N, 7.26.

[0037] Photophysical measurements: Ultraviolet-visible absorption spectra were obtained using a Shimadzu UV-3100 spectrometer. Steady-state / transient PL spectra were recorded on an Edinburgh FLS980 spectrophotometer equipped with a pulsed laser (Edinburgh Ltd). The photoluminescence quantum yield (PLQY) of the crystalline powder was measured using an absolute PLQY measurement system on a Hamamatsu C9920-02.

[0038] Thermal stability analysis: Thermogravimetric analysis was performed using a Q600SDT instrument at a constant N2 flow rate, with heating from room temperature to 700 °C at a heating rate of 15 ° / min.

[0039] OLED fabrication and testing: Indium tin oxide (ITO) anodes were commercially available, with a thin-film resistivity of 14 Ω / Ω squared. -1 The thickness was 80 nm. Prior to preparation, the ITO substrate was cleaned with deionized water, acetone, and ethanol. The organic and metal layers were deposited in separate vacuum chambers at pressures below 1 × 10⁻⁶. -4 Pa. The thickness of each layer and the evaporation rate of all materials were monitored using a quartz crystal monitoring system. For organic materials, the deposition rate was maintained at 0.5–1 Å·s⁻¹. -1 For the cathode, the deposition rate remains at 2–3 Å·s. -1 The effective area of ​​each device is 4 mm. 2All electrical tests and optical measurements were performed under atmospheric conditions, with the devices packaged in a glove box. EL spectra, current density-voltage-luminance (JVL), and EQE data were measured using a computer-controlled Keithley 2400 source meter, an absolute EQE measurement system (C9920-12), and a photon multichannel analyzer (PMA-12, Hamamatsu Photonics).

[0040] Example 1: Structure of the coordination compound Four complexes, (R / S)-MeN8-EuI2 and (R / S)-, were synthesized in a glove box by mixing EuI2 with the corresponding ligands in methanol or tetrahydrofuran. i -PrN8-EuI2 was identified as a product by elemental analysis. The coordination geometry was investigated using single-crystal X-ray diffraction (SCXRD) (see attached manual). Figure 2 Compared to () R )-MeN8-EuI2,(R / S)- i The introduction of the isopropyl group in -PrN8-EuI2 increases steric hindrance, resulting in an increase in the average bond length of the Eu-N bond. R The average bond length of )-MeN8-EuI2 is 2.712 Å. R )- i The average bond length of -PrN8-EuI2 is 2.771 Å. The increased bond length reduces the interaction force between the ligand and the central metal, i.e., weakens the ligand field. This results in smaller splitting of the 5d orbital in Eu(II), while the 4f orbital, located in the inner shell, is unaffected by the external ligand field. The energy difference required for electrons to transition from the lowest energy level (LUMO) of the 5d orbital back to the 4f orbital (HOMO) increases, leading to a blue shift in the emission spectrum.

[0041] Example 2: Photophysical properties of the coordination compound In order to systematically study chiral Eu 2+ The inventors determined the steady-state, transient, and circularly polarized emission spectra of the complex. A methanol solution of (R / S)-MeN8-EuI2 showed orange-yellow emission at a maximum wavelength of (…). λ max The wavelength is 587 nm. The change from methyl to isopropyl increases the Eu-N bond length due to the steric hindrance of the isopropyl group, resulting in (R / S)- i -PrN8-EuI2 λ max560 nm. The excited state lifetime of these complexes is more than one thousand nanoseconds (Table 1). The full width at half maximum (FWHM) of these complexes in solid powder is relatively narrow (the narrowest is only 51 nm) compared to the luminescent materials characterized by the charge transfer (CT) mechanism. The excitation band of these complexes is featureless, ranging between 230 nm-500 nm (EuX2-N8 and EuX2-N8M6) and 230 nm-600 nm (EuX2-N4). From the above photophysical studies, and considering that the ligands in the complex system are saturated organic compounds with very high energy levels, the possibility of ligand-metal charge transfer (LMCT) is excluded. Therefore, the excitation and emission processes can be seen as Eu 2+ electron transitions in the ion, where the ground state is 4f 7 [ 8 S 7 / 2 ], the excited state is 4f 6 [ 7 F0]5s 1 .

[0042] UV-Vis spectra show that (R / S)-MeN8-EuI2 and (R / S)- i -PrN8-EuI2 have high energy absorption (ε > 1000 L·mol -1 ·cm -1 ) at 250 nm, low energy absorption peaks (ε = 747 L mol −1 cm −1 , (R / S-MeN8-EuI2) and ε = 771 L mol −1 cm −1 , (R / S)- i -PrN8-EuI2) at 413 and 404 nm, consistent with their excitation bands. The molar absorption will be greater due to the Laporte and spin-allowed f-d transition.

[0043] Table 1. Summary of the photophysical properties of the four europium sub-complexes 1 1 R / S are two chiral different materials, their luminescence properties are exactly the same except for the chiral direction.

[0044] The inventors tested the luminescence properties of the four complex doped films using circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The four complexes were all doped in m-MTDATA (doping concentration 10 wt%). Their CD spectra show clear mirror symmetry. This strong Cotton effect, which can be attributed to the d-f transition, indicates that the chiral groups introduced successfully introduced chirality into the Eu(II) center. Almost symmetrical emission spectra were also observed from the CPL spectra. The luminescence asymmetry factors of the four complexes are: 4.6 × 10 -3 ((R)-MeN8-EuI2), -5.7 × 10 -3 ((S)-MeN8-EuI2), 6.4 × 10 -3 ((R)- i -PrN8-EuI2) and -5.6 × 10 -3 ((S)- i -PrN8-EuI2), further confirming the chiral nature of the excited state.

[0045] The crystalline powder of (R / S)-N4Me4-EuI2 emits bright sky blue light under 365 nm UV light excitation with a maximum emission wavelength at 488 nm; in contrast, the emission spectrum of (R / S)-N4Me6-EuI2 under UV light excitation is blue-shifted with a maximum emission wavelength of 481 nm; the emission spectrum of (R / S)-N4Me2Et4-EuI2 is further blue-shifted with a maximum peak at 465 nm, presenting a deep blue light emission with CIE of (0.13, 0.08). The excited state lifetimes of the three complex powders corresponding to (R / S)-N4Me4-EuI2, (R / S)-N4Me6-EuI2, (R / S)-N4Me2Et4-EuI2 are 584 ns, 665 ns, 724 ns, respectively, which are consistent with the excited state lifetimes of Eu(II) complexes reported in the literature for d-f transitions, with PLQYs of 46%, 93%, 97%, respectively. The experimentally measured emission peak width (32 ~ 35 nm) and excited state lifetime as short as a few hundred nanoseconds suggest that the emission process is likely to be a Laporte-allowed 5 d-f -4 f 6 5 d 1 transition between the excited state (4 f 7 ) and the ground state (4 d -4 f ) of the central Eu(II).

[0046] The emission spectra of the complexes from (R / S)-N4Me4-EuI2, (R / S)-N4Me6-EuI2to (R / S)-N4Me2Et4-EuI2blue-shifted in turn. This is consistent with the Eu(II) complex 5 d The orbitals are susceptible to the ligand field. Referring to the crystal structure, from N4Me4-EuI2to N4Me6-EuI2, the introduction of methyl groups increases the steric hindrance, making the space around Eu(II) smaller, which can no longer accommodate a molecule of THF coordination, making the coordination number decrease from 7 to 6, and finally making the ligand field weaken, 5 d The orbital splitting becomes smaller, so 5 d The orbital lowest unoccupied molecular orbital (LUMO) of the complex increases, and finally the electron is transferred from 5 d The energy gap (E g ) of the orbital lowest unoccupied molecular orbital (LUMO) to the ground state (HOMO) becomes larger, so the emission blue-shifts. From N4Me6-EuI2to N4Me2Et4-EuI2, the increase of the alkyl chain makes the Eu-N bond, Eu-I bond length increase, the ligand 5 d The orbital force decreases, making the ligand field weaken, also making 5 d The orbital splitting becomes smaller, and the emission blue-shifts.

[0047] Example 3 Thermal and air stability of the complexes The thermal stability of the four compounds was studied by thermogravimetric analysis (TGA). (R / S)-MeN8-EuI2and (R / S)- i -PrN8-EuI2(T d corresponding to 5% weight loss) were 410 °C, 410 °C, 415 °C and 415 °C, respectively. At 550 °C, the residual weight percentages of these compounds were unchanged, which should theoretically be the mass percentage of the metal halide with respect to the total mass, since the decomposition process is temporarily attributed to the breaking of coordination bonds and the volatilization of organic ligands.

[0048] Then the sublimation properties of these compounds were tested under a high vacuum of 10 -5 Pa and gradient heating. It was found that (R / S)-MeN8-EuI2and (R / S)- i -PrN8-EuI2could completely sublime in a small range of 50 mg around 300 °C and 320 °C (test tube temperature, which is different from the sample temperature). It is worth noting that in a large amount of sublimation, there will be obvious decomposition, which may be due to the uneven heating in the sublimation boat.

[0049] Example 4 Electroluminescent device Based on the photophysical and stability studies of Example 2 and Example 3, EuX2-N8 complexes are good candidate light-emitting materials for OLEDs. Due to the lack of experience with Eu(II) complex devices for OLEDs, efforts are needed to optimize the device structure. (R / S)-MeN8-EuI2 was first chosen for device optimization, and subsequent examples include screening host materials, finding the best combination of hole transport layer (HTL) and electron transport layer (ETL), adjusting the emission layer thickness, and then further following the optimization conditions, adjusting the doping concentration and the thickness of the emission layer of (R / S)-MeN8-EuI2 devices, and the materials used.

[0050] The final optimized OLED structure is ITO / MoO3(2 nm) / 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)aniline] (TAPC, 50 nm) / (R / S)-MeN8-EuI2 or (R / S)- i -PrN8-EuI2: 4,4',4''-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA) (10 wt%, 20 nm) / 1,3,5-tris[(3-pyridyl)-3-phenyl]benzene (TmPyPB, 50 nm) / LiF (1 nm) / Al (100 nm). The best (R / S)-MeN8-EuI2 device has an excellent performance with a turn-on voltage (V on ) of 4.7 V, a maximum luminance (L -2 ) of 23000 cd·m max , a maximum current efficiency (CE -1 ) of 56.9 cd·A max , and a highest EQE of 15.6%. The (R / S)- i -PrN8-EuI2 device as a light-emitting material shows a V on , L max , CE max , and EQE of 4.5 V, 19000 cd·m -2 , 41.0 cd·A -1 , and 10.0%, respectively. The device results of the present examples are comparable to most mainstream OLEDs (phosphorescent metal complexes or TADF molecules as light-emitting materials).

[0051] By testing the circularly polarized electroluminescence spectra of the four complex devices, their electroluminescence asymmetry factors are: 3.9 × 10 -3 ((R)-MeN8-EuI2), -3.7 × 10 -3 ((S)-MeN8-EuI2), 3.1 × 10 -3((R)- i -PrN8-EuI2) and -2.6 x 10 -3 ((S)- i -PrN8-EuI2). Due to the higher asymmetric factor, the device is expected to replace the traditional physical filter method in the field of 3D display light source, and to achieve the purpose of simplifying the device structure and increasing the device brightness while obtaining circularly polarized light.

[0052] Example 5 Electroluminescent device - OLED prepared by solution method In view of the poor thermal stability of EuX2-N4and EuX2-N8M6sub-europium complexes, OLED devices using the above-mentioned compounds as the light-emitting layer were prepared by the solution method in this embodiment, and the device structure was ITO / PEDOT:PSS (20 nm) / EuX2-N4or EuX2-N8M6(20 nm) / TPBi (60 nm) / LiF (0.7 nm) / Al (100 nm). The device performance results are shown in Table 2. Although the performance of these devices is not very good at present, it can be predicted that when the film forming process is improved, and the appropriate charge transport material and host material are selected, the performance of the device is expected to be significantly improved.

[0053] Table 2. Device parameters of EuX2-N4and EuX2-N8M6based OLED prepared by solution method n and EuX2-N8M6light-emitting OLED The above has described the embodiments of the present application in detail. However, the present application is not limited to the above-mentioned embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An electroluminescent material, characterized in that, The electroluminescent material comprises a complex (R / S)-RN8-EuI2, which has the following structure: Where X is a monovalent negative ion, such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, and R is independently selected from H, Cl-C 18 Alkyl groups, halogen-substituted alkyl groups, halogen atoms, aryl groups, halogen-substituted aryl groups, alkyl-substituted aryl groups, O, N, S heteroaryl groups, alkyl groups containing O, N, S coordination sites, M being metal ions with df transition luminescence such as Eu(II), Ce(III), Yb(II), Sm(II), etc., and at least one chiral site at the "*" position; preferably, all "*" positions are chiral sites; Alternatively, the electroluminescent material comprises the complex EuX2-N4, which has the following structure: Where X is a monovalent negative ion, such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, and R is independently selected from H, Cl-C. 18 Alkyl groups, halogen-substituted alkyl groups, halogen atoms, aryl groups, halogen-substituted aryl groups, alkyl-substituted aryl groups, O, N, S heteroaryl groups, alkyl groups containing O, N, S coordination sites, M being metal ions with df transition luminescence such as Eu(II), Ce(III), Yb(II), Sm(II), etc., and at least one chiral site at the "*" position; preferably, all "*" positions are chiral sites; Alternatively, the electroluminescent material comprises a complex EuX2-cycloN4 having the following structure: Where X is a monovalent negative ion, such as F, Cl, Br, I, OCN, SCN, CN, CF3SO3, BF4, or PF6, and R is independently selected from H, Cl-C. 18 Alkyl groups, halogen-substituted alkyl groups, halogen atoms, aryl groups, halogen-substituted aryl groups, alkyl-substituted aryl groups, O, N, S heteroaryl groups, alkyl groups containing O, N, S coordination sites, M being metal ions with df transition luminescence such as Eu(II), Ce(III), Yb(II), Sm(II), etc., and at least one chiral site at the "*" position; preferably, all "*" positions are chiral sites.

2. The electroluminescent material according to claim 1, characterized in that, The luminescent material includes (a) (R / S)-MeN8-EuI2, (b) (R / S)- i The structural formulas of the above complexes are as follows: (c) (R / S)-MeN8-Ce(OTf)3, (d) (R / S)-N4Me4-EuI2, (e) (R / S)-N4Me6-EuI2, (f) (R / S)-N4Me2Et4-EuI2, (g) (R / S)-MeN4-EuI2, (h) (R / S)-cyclohexN4-EuI2. 。 3. An electroluminescent device, characterized in that, The electroluminescent device includes a cathode, an anode, and a light-emitting layer located between the cathode and the anode, wherein the light-emitting layer includes the electroluminescent material as described in claim 1 or 2.

4. The electroluminescent device according to claim 3, characterized in that, The light-emitting layer is a mixture of a guest material and a host material, wherein the guest material includes the electroluminescent material as described in claim 1 or 2, and the host material includes m-MTDATA, mCP, mCBP, CzSi, DCPPO, PCzAc, CBP, TCTA, TAPC, DPEPO, mCPCN, BCPO, with a doping concentration of 1wt%-99wt%, preferably 7wt%-10wt%, and most preferably 10wt%, wherein the doping concentration is the percentage of the mass of the guest material to the total mass of the guest material and the host material.

5. The electroluminescent device according to claim 3 or 4, characterized in that, The electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer, the electron transport layer comprising TmPyPB, DPEPO, TSPO1, Bphen and / or TPBi.

6. The electroluminescent device according to claim 3 or 4, characterized in that, The electroluminescent device further includes a hole transport layer located between the anode and the light-emitting layer; preferably, the hole transport layer includes PCzAc, mCP, m-MTDATA, NPB, PEDOT:PSS, TCTA and / or TAPC.

7. The electroluminescent device according to claim 5 or 6, characterized in that, The electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer, and a hole transport layer located between the anode and the light-emitting layer; Preferably, the hole transport layer includes TAPC, and the electron transport layer includes Bphen.

8. The electroluminescent device according to any one of claims 3-7, characterized in that, The thickness of the light-emitting layer is 10-40nm, preferably 15-30nm, more preferably 20-25nm, and most preferably 25nm.

9. The electroluminescent device according to claim 5, characterized in that, The electroluminescent device further includes a hole blocking layer located between the light-emitting layer and the electron transport layer; preferably, the hole blocking layer is made of TSPO1. Preferably, the electroluminescent device further includes a second hole transport layer located between the anode and the hole transport layer; preferably, the material of the second hole transport layer is NPB.

10. The electroluminescent device according to claim 3, characterized in that, The structure of the electroluminescent device is: ITO / MoO3 (2 nm) / 4,4′-cyclohexylbis[N,N-di(4-methylphenyl)aniline](TAPC, 50 nm) / (R / S)-MeN8-EuI2 or (R / S)- i -PrN8-EuI2: 4,4',4''-Tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA) (10 wt%, 20 nm) / 1,3,5-Tris[(3-pyridyl)-3-phenyl]benzene (TmPyPB, 50 nm) / LiF (1 nm) / Al (100 nm).

Images