Mixed pyrazole boron coordination Ce (III) complex and application of mixed pyrazole boron coordination Ce (III) complex as luminescent material

Abstract

The invention relates to a mixed Ce (III) complex, which has the following structure as shown in the specification, or has the following structure; or has the following structure.

Description

Technical Field

[0001] This invention belongs to the field of organic electroluminescent materials. In particular, this invention relates to a mixed-type pyrazole boron-coated Ce(III) complex and its application as an electroluminescent material. Background Technology

[0002] Rare earth complexes are an important class of luminescent materials. Based on their mechanism, the luminescence of rare earth complexes can be mainly classified into three types: ligand-involved luminescence, luminescence from the central ion's 4f-4f transition, and luminescence from the central ion's 5d-4f transition. Sc(III), Y(III), Gd(III), La(III), and Lu(III) exhibit luminescence due to their 4f-4f transition. 0 4f 7 or 4f 14 The fully empty, half-filled, or fully filled electron structures of lanthanide complexes result in ligand-mediated luminescence. Most rare-earth complexes exhibit luminescence via 4f-4f transitions, such as Eu(III) and Tb(III) complexes. Because the 4f- electrons are located in the inner shell and shielded by the outer 5s and 5p electrons, their emission is less affected by the external ligand field, resulting in a narrow emission spectrum and a relatively fixed maximum emission peak position. Furthermore, since the ff transition is a parity-forbidden transition, the excited-state lifetime of these complexes is typically on the order of hundreds of microseconds. Although lanthanide complexes based on ff transition luminescence offer advantages such as narrow emission peaks and high theoretical efficiency when applied to organic light-emitting diodes (OLEDs), their long excited-state lifetimes often lead to problems such as low maximum brightness, severe efficiency roll-off, and the inability to achieve deep blue light, limiting their further application in OLEDs.

[0003] Compared to rare-earth complexes that emit light via ff transitions, the luminescence of Ce(III), Eu(II), Yb(II), and Sm(II) complexes primarily originates from electric dipole-allowed 5d-4f transitions. Since the 5d-4f transition is parity-allowed, it exhibits a relatively short excited-state lifetime (on the order of nanoseconds). Furthermore, because the 5d orbital is susceptible to ligand field influence, the emission wavelength and luminescence efficiency of the complexes can be tuned and optimized by altering the coordination environment around the central ion. Among the four ions mentioned above, Ce(III) exhibits the highest luminescence due to the electric dipole-allowed 5d-4f transition. 4+ / Ce 3+ The redox couple has the highest standard electrode potential, therefore Ce(III) complexes are the most difficult to oxidize and have the best stability. Their application prospects are significantly better than other rare-earth complexes that exhibit df transition luminescence. Meanwhile, Ce... 3+Ions have higher vacuum energy levels, making it easier to achieve deep blue light emission. Furthermore, Ce(III) complexes have been shown to exhibit 100% exciton utilization in OLEDs. However, OLEDs using deep blue Ce(III) complexes are currently scarce, and their device performance needs further improvement. Therefore, constructing deep blue Ce(III) complexes suitable for high-performance OLEDs is crucial, especially obtaining Ce(III) complexes with different luminescent properties by adjusting ligand structures and using this to study the relationship between structure, photophysical properties, and electroluminescence performance, thereby guiding the design and synthesis of Ce(III) complexes. Summary of the Invention

[0004] Embodiments of the present invention provide a Ce(III) complex having a structure shown in any of the following structural formulas: Among them, R, R 1 R 2 It is independently selected from any one of hydrogen, unsubstituted alkyl, substituted alkyl, alkoxy, halogen atom, unsubstituted alkenyl, halogen-substituted alkenyl, unsubstituted alkynyl, unsubstituted phenyl, substituted phenyl, unsubstituted aryl, substituted aryl, alkyl or heterocyclic containing O, N, or S coordination sites; X is a monovalent ion, independently selected from any one of trifluoromethanesulfonate, pyrazolium anion, halogen, or pseudohalogen. Preferably, R, R 1 R 2 It is independently selected from any one of hydrogen, unsubstituted C1-C18 alkyl, unsubstituted C1-C18 alkoxy, halogen atom, C2-C18 unsubstituted alkenyl, C2-C18 halogen-substituted alkenyl, C2-C18 unsubstituted alkynyl, phenyl, substituted phenyl, C6-C18 unsubstituted aryl, and heterocycles containing O, N, or S coordination sites; Preferably, R, R 1 R 2 It is independently selected from any one of hydrogen, methyl, ethyl, tert-butyl, phenyl, and iodine atoms; In a further preferred embodiment, R is hydrogen; Further preferred, R 1 Independently selected from hydrogen and methyl; Further preferred, R 2 It is independently selected from hydrogen, methyl, tert-butyl, and iodine atoms.

[0005] According to one embodiment of the present invention, for example, the Ce(III) complex includes: Ce(Tp)2(Bp), Ce(Tp)(Bp)2, Ce(Tp)2(B ... 2Me (Bp)2Me )2, its structure is as follows: Preferably, the Ce(III) complex is Ce(Tp)2(Bp) or Ce(Tp)(Bp)2; more preferably, the Ce(III) complex is Ce(Tp)2(Bp).

[0006] An embodiment of the present invention provides an electroluminescent device, the electroluminescent device comprising a cathode, an anode, and a light-emitting layer located between the cathode and the anode, wherein the light-emitting layer comprises the Ce(III) complex as described above.

[0007] According to one embodiment of the present invention, for example, 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 above, and the host material is selected from the triplet energy level E to prevent energy back-transfer quenching from the guest material to the host material. T Main materials with a voltage higher than 2.6 eV; Preferably, the host material is selected from any one or a mixture of any two of the following: mCP, CzSi, TSPO1, DPEPO, and DPPOC. Preferably, the doping concentration is 1-50 wt%, more preferably 5-20 wt%, and most preferably 12 wt%, 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.

[0008] According to one embodiment of the present invention, for example, the electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer; Preferably, to prevent exciton energy in the host material layer from diffusing to the electron transport layer, the electron transport layer is an electron transport material with a triplet energy level greater than or equal to 2.3 eV; Preferably, the electron transport layer includes TmPyPB, TSPO1, DPEPO, BPhen and / or TpBi; More preferably, the electron transport layer includes TSPO1 and / or BPhen.

[0009] According to one embodiment of the present invention, for example, the electroluminescent device further includes a hole transport layer located between the anode and the light-emitting layer; Preferably, the hole transport layer is a hole transport material with a triplet energy level greater than or equal to 2.3 eV; Preferably, the hole transport layer includes mCP, CzSi, m-MTDATA and / or TAPC; More preferably, the hole transport layer includes mCP and / or CzSi.

[0010] According to one embodiment of the present invention, for example, 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 comprises mCP and / or CzSi, and the electron transport layer comprises TSPO1 and / or BPhen; Preferably, the electroluminescent device further includes an electron injection layer located between the cathode and the electron transport layer, and the electroluminescent device further includes a hole injection layer located between the anode and the hole transport layer; More preferably, the electron injection layer comprises LiF, and the hole injection layer comprises MoO3.

[0011] According to one embodiment of the present invention, for example, the thickness of the light-emitting layer is 1-50 nm, preferably 10-40 nm, preferably 15-30 nm, preferably 20-25 nm, and most preferably 20 nm.

[0012] According to one embodiment of the present invention, for example, the structure of the electroluminescent device is: ITO / MoO3 (2nm) / CzSi:MoO3 (30 nm) / CzSi (10 nm) / CzSi:Ce(Tp)2(Bp) (20 nm) / TSPO1 (10 nm) / BPhen (40 nm) / LiF / Al. Attached Figure Description

[0013] Figure 1 These are the Ce(III) complexes Ce(Tp)2(Bp), Ce(Tp)(Bp)2, and Ce(Tp) prepared in the embodiments of the present invention. 2Me (Bp) 2Me )2 Emission spectrum in solid state (excitation wavelength 280 nm).

[0014] Figure 2 These are the Ce(III) complexes Ce(Tp)2(Bp), Ce(Tp)(Bp)2, and Ce(Tp) prepared in the embodiments of the present invention. 2Me (Bp) 2Me )2 Excitation spectra in solid state (monitoring wavelengths are their respective maximum emission wavelengths: 438 nm, 434 nm and 480 nm).

[0015] Figure 3 This is a current density-voltage-brightness curve of the electroluminescent device D1 in an embodiment of the present invention.

[0016] Figure 4 This is a power efficiency-brightness-EQE curve of the electroluminescent device D1 in this embodiment of the invention. Detailed Implementation

[0017] The following will further illustrate the mixed Ce(III) complexes of the present invention and their applications as electroluminescent materials with specific examples. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0018] The full name of the compound corresponding to the abbreviation: mCP: 1,3-Bis(9H-carbazol-9-yl)benzene CzSi: 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole TSPO1: Diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide DPEPO: Di[2-((oxo)diphenylphosphino)phenyl] ether DPPOC: 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphoxy)carbazole TmPyPB: 1,3,5-Tris[(3-pyridyl)-3-phenyl]benzene BPhen: 4,7-Diphenyl-1,10-Phenanthroline TpBi: 1,3,5-Tris(N-phenylbenzimidazol-2-yl)benzene m-MTDATA:4,4',4''-Tris[phenyl(m-tolyl)amino]triphenylamine TAPC: 4,4'-cyclohexylbis[N,N-di(4-methylphenyl)aniline] Given that Ce(III) complexes are theoretically excellent electroluminescent materials, and given the scarcity of reports on OLEDs based on deep blue Ce(III) complexes, the inventors of this invention synthesized three Ce(III) complex structures: Ce(Tp)2(Bp), Ce(Tp)(Bp)2, and Ce(Tp)2(Bp). 2Me (Bp) 2Me (The structures and synthetic routes of the three complexes are shown below), and their photoluminescence and electroluminescence properties were investigated accordingly. The luminescence of all four complexes originates from the central Ce group. 3+ The df transition of the ion alters Ce by changing the ligand structure. 3+The ligand field surrounding the ion yielded Ce(III) complexes with different emission colors: Ce(Tp)₂(Bp)₂ and Ce(Tp)(Bp)₂ emitting deep blue light, and Ce(Tp)₂ emitting sky blue light. 2Me (Bp) 2Me Ce(Tp)2 exhibits a photoluminescence quantum yield (PLQY) close to 100% in its solid powder state, making it a promising candidate for photoluminescence applications. Furthermore, the inventors of this invention have also fabricated OLED devices based on Ce(Tp)2(Bp). Through device structure optimization, they discovered that the optimal device achieves a maximum external quantum efficiency (EQE) of 19.7%, breaking the current efficiency record (14.0%) for deep blue Ce(III) complex OLED devices in the literature, demonstrating the enormous application potential of this type of material in OLEDs.

[0019] Example 1: Synthesis and Characterization of Coordination Compounds In this embodiment, we synthesized three tripyrazole boron ligands and three dipyrazole boron ligands, and based on these, we synthesized nine mixed Ce(III) complexes. The synthesis of the complexes was carried out in a nitrogen glove box with an oxygen content of less than 0.1 ppm.

[0020] Synthesis of potassium dipyrazole borohydride (KBp): 34.04 g of pyrazole (500.0 mmol) and 10.78 g of potassium borohydride (200.0 mmol) were added to a 250 mL round-bottom flask. The system was evacuated and purged with nitrogen three times. The temperature was raised to 120 °C and the reaction was stirred. The generated hydrogen gas was collected using a water displacement gas collector. Heating was stopped when approximately 8.96 L of hydrogen gas (400 mmol) was collected. For post-treatment, 100 mL of toluene was added to the system and the mixture was refluxed and stirred for 30 min. The mixture was filtered while hot, and the filter cake was washed with toluene. The filter cake was collected to obtain 20.01 g of white powder, with a yield of 53.8%. 1 H NMR (400 MHz, DMSO- d 6) δ 7.33 (d, J = 1.3 Hz, 2H), 7.22 (d, J = 1.6 Hz, 2H), 5.93 (t, J = 1.8 Hz, 2H). Synthesis of potassium tripyrazole borohydride (KTp): 23.15 g of pyrazole (350.0 mmol) and 5.394 g of potassium borohydride (100.0 mmol) were added to a 250 mL round-bottom flask. The system was evacuated and purged with nitrogen three times. The temperature was raised to 180 °C and the reaction was stirred. The generated hydrogen gas was collected using a water displacement collecting device. Heating was stopped when approximately 6.72 L (300 mmol) of hydrogen gas was collected. For post-treatment, 60 mL of toluene was added to the system and refluxed with stirring for 30 min. The mixture was filtered while hot, and the filter cake was washed with toluene. The filter cake was collected to obtain 20.43 g of white powder, with a yield of 81.0%. 1 H NMR (400 MHz, DMSO- d 6) δ 7.34 (dd, J = 3.1, 1.8Hz, 6H), 6.02 (t, J = 1.8 Hz, 3H). Potassium di(3,5-dimethylpyrazole)borohydride (KBp) 2Me Synthesis of 3,5-dimethylpyrazole (250.0 mmol) and potassium borohydride (100.0 mmol) were added to a 250 mL round-bottom flask. The system was evacuated and purged with nitrogen three times. The temperature was raised to 120 °C and the reaction was stirred. The generated hydrogen gas was collected using a water displacement collecting device. Heating was stopped when approximately 4.48 L (200 mmol) of hydrogen gas was collected. For post-treatment, 60 mL of toluene was added to the system and the mixture was refluxed and stirred for 30 min. The mixture was filtered while hot, and the filter cake was washed with toluene. The filter cake was collected to obtain 18.41 g of white powder, with a yield of 76.0%. 1 H NMR (400 MHz, DMSO- d 6): δ 5.46 (s, 2H), 2.17 (s, 6H), 2.02 (s, 6H). Potassium tris(3,5-dimethylpyrazole)borohydride (KTp) 2Me Synthesis of 3,5-dimethylpyrazole (400.0 mmol) and potassium borohydride (100.0 mmol) were added to a 250 mL round-bottom flask. The system was evacuated and purged with nitrogen three times. The mixture was heated to 180 °C with stirring, and the generated hydrogen gas was collected using a water displacement collector. Heating was stopped when approximately 6.72 L (300 mmol) of hydrogen gas was collected. For post-treatment, the system was collected directly, and 3,5-dimethylpyrazole was removed by sublimation at 120 °C. Sublimation at 280 °C yielded 15.37 g of white powder, with a yield of 45.7%. 1 H NMR (400 MHz, DMSO- d6) δ 5.53 (s,3H), 2.04 (s, 9H), 2.02 (s, 9H). Potassium di(4-methylpyrazole)borohydride (KBp) Me Synthesis of 4-methylpyrazole (250.0 mmol) and potassium borohydride (100.0 mmol) were added to a 250 mL round-bottom flask. The system was evacuated and purged with nitrogen three times, heated to 120 °C, stirred, and the generated hydrogen gas was collected using a water displacement collector. Heating was stopped when approximately 4.48 L (200 mmol) of hydrogen gas was collected. For post-treatment, 60 mL of toluene was added to the system and refluxed for 30 min. The mixture was filtered while hot, and the filter cake was washed with toluene. The filter cake was collected to obtain 16.70 g of white powder, with a yield of 78.0%. 1 H NMR (400 MHz, DMSO- d 6): δ 6.04(s, 2H), 5.72 (s, 2H), 2.11 (s, 2H), 2.04 (s, 6H). Potassium tris(4-methylpyrazole)borohydride (KTp) Me Synthesis of 4-methylpyrazole: 32.84 g of 4-methylpyrazole (400.0 mmol) and 5.394 g of potassium borohydride (100.0 mmol) were added to a 250 mL round-bottom flask. The system was evacuated and purged with nitrogen three times. The temperature was raised to 160 °C and the reaction was stirred. The generated hydrogen gas was collected using a water displacement collecting device. Heating was stopped when approximately 6.72 L (300 mmol) of hydrogen gas was collected. For post-treatment, the system was collected directly, and 4-methylpyrazole was removed by sublimation at 120 °C. Sublimation at 260 °C yielded 19.12 g of white powder, with a yield of 65.0%. 1 H NMR (400 MHz, Methanol- d 4) δ 7.26 (s, 3H), 6.88 (s, 3H), 2.01 (s, 9H). Synthesis of Ce(Tp)₂(Bp): 1.861 g KBp (10.00 mmol), 5.043 g KTp (20.00 mmol), and 100 mL tetrahydrofuran were placed in a 250 mL round-bottom flask in a glove box. After thorough mixing, 5.873 g cerium trifluoromethanesulfonate (10.00 mmol) was added, and the mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 200 °C to give 3.172 g of the expected white crystals, yield 44.5%. Elemental analysis calculations: C 24 H 28 B3CeN 16Measured values: C, 40.42; N, 31.43; H, 3.96. Actual values: C, 40.63; N, 31.52; H, 4.13.

[0021] Synthesis of Ce(Tp)(Bp)₂: 3.722 g KBp (20.00 mmol), 2.521 g KTp (10.00 mmol), and 100 mL tetrahydrofuran were placed in a 250 mL round-bottom flask in a glove box. After thorough mixing, 5.873 g cerium trifluoromethanesulfonate (10.00 mmol) was added, and the mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 180 °C to give 2.184 g of the expected white crystals, with a yield of 33.7%. 21 H 26 B3CeN 14 Measured values: C, 38.98; N, 30.30; H, 4.05. Actual values: C, 39.14; N, 30.62; H, 4.35.

[0022] Synthesis of Ce(Tp)(Bp)(OTf): 1.861 g KBp (10.00 mmol), 2.521 g KTp (20.00 mmol), and 100 mL tetrahydrofuran were placed in a 250 mL round-bottom flask in a glove box. After thorough mixing, 5.873 g cerium trifluoromethanesulfonate (10.00 mmol) was added, and the mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 180 °C to give 1.654 g of the expected white crystals, yield 25.40%. Elemental analysis calculations: C 16 H 18 B2CeN 10 F3SO3: C, 29.60; N, 21.58; H, 2.79. Measured values: C, 29.63; N, 21.05; H, 2.49.

[0023] Ce(Tp 2Me (Bp) 2Me Synthesis of 2: 3.363 g KTp was taken from the glove box. 2Me (10.00 mmol), 4.843 gKBp 2Me (20.00 mmol) 100 mL of tetrahydrofuran was added to a 250 mL round-bottom flask, stirred thoroughly, and then 5.873 g of cerium trifluoromethanesulfonate (10.00 mmol) was added. The mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 220 °C to give 3.426 g of the expected pale yellow crystals, with a yield of 43.4%. C31 H 46 B3CeN 14 Measured values: C, 47.29; N, 24.91; H, 5.89. Actual values: C, 47.64; N, 24.62; H, 5.95.

[0024] Ce(Tp 2Me )2(Bp 2Me Synthesis of KTp: 6.726 g of KTp was taken from a glove box. 2Me (20.00 mmol), 2.422 gKBp 2Me 10.00 mmol of tetrahydrofuran was added to a 250 mL round-bottom flask, stirred thoroughly, and then 5.873 g of cerium trifluoromethanesulfonate (10.00 mmol) was added. The mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 240 °C to give 3.426 g of the expected pale yellow crystals, with a yield of 43.4%. 40 H 56 B3CeN 16 Measured values: C, 51.46; N, 24.01; H, 6.05. Actual values: C, 51.35; N, 23.98; H, 6.12.

[0025] Ce(Tp 2Me (Bp) 2Me Synthesis of )(OTf): 3.363 g KBp was taken from the glove box. 2Me (10.00 mmol), 2.422 gKTp 2Me 10.00 mmol of cerium trifluoromethanesulfonate and 100 mL of tetrahydrofuran were added to a 250 mL round-bottom flask and stirred until homogeneous. Then, 5.873 g of cerium trifluoromethanesulfonate (10.00 mmol) was added and the mixture was stirred overnight at room temperature. For post-treatment, the system was filtered directly, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 180 °C to give 0.832 g of the expected white crystals, with a yield of 10.70%. Elemental analysis calculation: C 25 H 38 B2CeN 10 F3SO3: C, 38.62; N, 18.02; H, 4.93. Measured values: C, 38.69; N, 17.82; H, 4.49.

[0026] Ce(Tp Me (Bp) Me Synthesis of 2: 2.941 g KTp was taken from the glove box. Me (10.00 mmol), 4.282 g KBp2Me (20.00 mmol) 100 mL of tetrahydrofuran was added to a 250 mL round-bottom flask, stirred thoroughly, and then 5.873 g of cerium trifluoromethanesulfonate (10.00 mmol) was added. The mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 220 °C to give 3.426 g of the expected pale yellow crystals, with a yield of 43.4%. C 28 H 40 B3CeN 14 Measured values: C, 45.12; N, 26.32; H, 5.41. Actual values: C, 45.22; N, 26.65; H, 5.87.

[0027] Ce(Tp Me )2(Bp Me Synthesis of KTp: 5.882 g of KTp was taken from the glove box. 2Me (20.00 mmol), 2.142 g KBp 2Me 10.00 mmol of tetrahydrofuran was added to a 250 mL round-bottom flask, stirred thoroughly, and then 5.873 g of cerium trifluoromethanesulfonate (10.00 mmol) was added. The mixture was stirred overnight at room temperature. For post-treatment, the system was directly filtered, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 240 °C to give 3.426 g of the expected pale yellow crystals, with a yield of 43.4%. 32 H 44 B3CeN 16 Measured values: C, 46.56; N, 27.16; H, 5.37. Actual values: C, 51.35; N, 23.98; H, 6.12.

[0028] Ce(Tp Me (Bp) Me Synthesis of (OTf): 2.941 g KBp was taken from the glove box. Me (10.00 mmol), 2.142 gKTp Me 10.00 mmol of cerium trifluoromethanesulfonate and 100 mL of tetrahydrofuran were added to a 250 mL round-bottom flask and stirred until homogeneous. Then, 5.873 g of cerium trifluoromethanesulfonate (10.00 mmol) was added and the mixture was stirred overnight at room temperature. For post-treatment, the system was filtered directly, the filtrate was collected, the solvent was removed under reduced pressure, and the remaining solid was sublimated at 180 °C to give 1.507 g of the expected white crystals, with a yield of 21.30%. Elemental analysis calculation: C 20 H 28 B2CeN 10F3SO3: C, 33.96; N, 19.80; H, 3.99. Measured values: C, 33.51; N, 19.54; H, 3.64.

[0029] Example 2: Crystal structure of the coordination compound All of the above complexes emitted bright blue light under 365 nm ultraviolet flashlight illumination. We selected three complexes, Ce(Tp)₂(Bp), Ce(Tp)(Bp)₂, and Ce(Tp)₂, that continued to emit blue light even after the glove box was removed. 2Me (Bp) 2Me 2) Further characterization was performed. Single crystals of all three complexes were obtained by sublimation, and the single crystals were characterized by X-ray diffraction. The crystal structure data are listed in Table 1.

[0030] Complex Ce(Tp)(Bp)2, Ce(Tp) 2Me (Bp) 2Me The central Ce(III) group has seven N atoms coordinated to it and exhibits a similar coordination polyhedral structure. However, due to the complex Ce(Tp) 2Me (Bp) 2Me The introduction of the methyl group in )2 increases the steric hindrance between pyrazoles, significantly lengthening the distance between the coordinating atom and the central atom in the complex Ce(Tp) 2Me (Bp) 2Me The average coordination bond length of Ce(Tp)(Bp)2 is 2.640 Å, while that of Ce(Tp)(Bp)2 is 2.577 Å. Compared to Ce(Tp)(Bp)2, Ce(Tp)2(Bp)2 has an additional pyrazole providing N coordination, resulting in increased steric hindrance in the coordination layer; its average Ce-N bond length is 2.612 Å. Table 1. Complexes Ce(Tp)2(Bp), Ce(Tp)(Bp)2 and Ce(Tp) 2Me (Bp) 2Me Summary of crystallographic data for 2) Example 3: Photophysical properties of the coordination compound Complexes Ce(Tp)2(Bp), Ce(Tp)(Bp)2 and Ce(Tp) 2Me (Bp) 2Me In their solid states, all three complexes emit bright blue light under UV excitation (365 nm). The emission and excitation spectra of the three complexes in their solid states are as follows: Figure 1 and Figure 2 As shown, the emission spectra of these compounds are all typical bimodal emission of Ce(III) complexes, Ce(Tp)2(Bp), Ce(Tp)(Bp)2, and Ce(Tp)2(Bp). 2Me (Bp)2Me The maximum emission wavelengths of Ce(Tp)2(Bp) and Ce(Tp)(Bp)2 are located at 438 nm, 434 nm, and 480 nm, respectively. The CIE coordinates of the emission spectra of the three complex crystals are (0.14, 0.10), (0.14, 0.09), and (0.18, 0.34), respectively. The CIE coordinates of Ce(Tp)2(Bp) and Ce(Tp)(Bp)2 are located near the NTSC standard blue light point (0.14, 0.08), indicating that the synthesized new complexes have high-purity deep blue light emission. Compared with the solid-state emission spectra of complexes Ce(Tp)2(Bp) and Ce(Tp)(Bp)2, Ce(Tp)2(B ... 2Me (Bp) 2Me The solid-state emission spectrum of Ce(Tp)2 showed a significant red shift, which may be because the methyl group introduced onto the pyrazole has a certain electron-donating effect, increasing the intensity of the ligand field, leading to a greater degree of 5d orbital splitting, a lower energy level of the lowest excited state, and ultimately resulting in a red shift in the spectrum. Complexes Ce(Tp)2(Bp), Ce(Tp)(Bp)2, and Ce(Tp) 2Me (Bp) 2Me The solid-state quantum yields of Ce(Tp)2 were 100%, 85%, and 80%, respectively. The high quantum yields stemmed from the excellent encapsulation of the Ce(III) center by the ligands, with Ce(Tp)2(Bp) possessing the highest coordination number and exhibiting the strongest protection of the central ion, thus conferring the highest quantum yield. The complexes Ce(Tp)2(Bp), Ce(Tp)(Bp)2, and Ce(Tp) 2Me (Bp) 2Me The excited state lifetimes in the solid state are 47 ns, 43 ns and 50 ns, respectively. The shorter excited state lifetimes are consistent with the parity-allowed and spin-allowed characteristics of Ce(III) complex df transitions, and are typical excited state lifetimes of Ce(III) complex df transitions.

[0031] Comparing the overall performance of the three complexes, it can be found that the complex Ce(Tp)2(Bp) has higher luminous efficiency and higher color purity. In addition, Ce(Tp)2(Bp) also has excellent stability in air, exhibiting the best overall performance and best meeting the requirements for deep blue Ce(III) complexes.

[0032] Example 4: Electroluminescence Research All three complexes exhibit near-100% PLQY, nanosecond-level excited-state lifetimes, and blue light emission, making them promising electroluminescent materials. Considering that Ce(Tp)₂(Bp) possesses the best luminous efficiency and stability, the inventors of this invention investigated the application of this type of complex as a luminescent material in OLEDs, using Ce(Tp)₂(Bp) as an example. To study its electroluminescent performance, it was first doped into five host materials with high triplet energy levels (doping concentration of 10 wt%), and the PLQY of these films was tested. As shown in Table 2, the film exhibited the highest PLQY (96%) when Ce(Tp)₂(Bp) was doped into CzSi. High PLQYs (92%) and 90%) were also obtained when doped into DPEPO and DPPOC host materials, respectively.

[0033] Table 2. PLQY of the complex Ce(Tp)2(Bp) in different host materials Given that high PLQY is a prerequisite for high electroluminescence efficiency, the inventors of this invention first fabricated OLED devices D1-D3 using CzSi, DPEPO, and DPPOC as the main materials and Ce(Tp)2(Bp) as the luminescent material. The device structures are as follows: D1: ITO / MoO3(2 nm) / CzSi:MoO3(30 nm) / CzSi (10 nm) / CzSi:Ce(Tp)2(Bp) (20nm) / TSPO1 (10 nm) / BPhen (40 nm) / LiF / Al D2: ITO / MoO3(2 nm) / CzSi:MoO3(30 nm) / CzSi (10 nm) / DPEPO:Ce(Tp)2(Bp) (20nm) / TSPO1 (10 nm) / BPhen (40 nm) / LiF / Al D3: ITO / MoO3(2 nm) / CzSi:MoO3(30 nm) / CzSi (10 nm) / DPPOC:Ce(Tp)2(Bp) (20nm) / TSPO1 (10 nm) / BPhen (40 nm) / LiF / Al The main performance parameters of devices D1-D3 are listed in Table 3. As can be seen from the table, device D1 has the best overall performance, with a turn-on voltage (V... on The voltage is 5.2V, and the maximum EQE is (EQE). max The percentage was 19.7%, and the maximum brightness (L) was [missing information]. max The value is 24.4 cd m. -2 , at 10 cd m -2The CIE coordinates during operation are (0.14, 0.12). It is worth noting that this device achieves the highest CIE coordinates among all reported deep blue OLEDs based on Ce(III) complexes. y Among those less than 0.15, the highest maximum EQE is achieved. The current density-voltage-luminance curves and power-luminance-EQE curves for devices D1-D3 are listed below. Figure 3 and Figure 4 .

[0034] Table 3 Main parameters of devices D1-D3 The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Ce(III) complex, characterized in that, The Ce(III) complex has any of the following structures: Among them, R, R 1 R 2 It is independently selected from any one of hydrogen, unsubstituted alkyl, substituted alkyl, alkoxy, halogen atom, unsubstituted alkenyl, halogen-substituted alkenyl, unsubstituted alkynyl, unsubstituted phenyl, substituted phenyl, unsubstituted aryl, substituted aryl, and heterocycles containing O, N, or S coordination sites; X is a monovalent ion, independently selected from any one of trifluoromethanesulfonate, pyrazolium anion, halogen, and pseudohalogen. Preferably, R, R 1 R 2 It is independently selected from any one of hydrogen, unsubstituted C1-C18 alkyl, unsubstituted C1-C18 alkoxy, halogen atom, C2-C18 unsubstituted alkenyl, C2-C18 halogen-substituted alkenyl, C2-C18 unsubstituted alkynyl, phenyl, substituted phenyl, C6-C18 unsubstituted aryl, and heterocycles containing O, N, or S coordination sites; Preferably, R, R 1 R 2 It is independently selected from any one of hydrogen, methyl, ethyl, tert-butyl, phenyl, and iodine atoms; In a further preferred embodiment, R is hydrogen; Further preferred, R 1 Independently selected from hydrogen and methyl; Further preferred, R 2 It is independently selected from hydrogen, methyl, tert-butyl, and iodine atoms.

2. The Ce(III) complex according to claim 1, characterized in that, The R, R 1 and R 2 All are hydrogen atoms.

3. The Ce(III) complex according to claim 1, characterized in that, The Ce(III) complexes include Ce(Tp)2(Bp), Ce(Tp)(Bp)2, Ce(Tp)2, and Ce(Tp)2(B ... 2Me (Bp) 2Me )2, its structure is as follows: 。 4. 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 Ce(III) complex according to any one of claims 1-3.

5. The electroluminescent device according to claim 4, characterized in that, The luminescent layer is a mixture of a guest material and a host material, wherein the guest material includes the Ce(III) complex as described in any one of claims 1-3, and the host material is selected from the triplet energy level E. T Main materials with a voltage higher than 2.6 eV; Preferably, the host material is selected from any one or a mixture of any two of the following: mCP, CzSi, TSPO1, DPEPO, and DPPOC. Preferably, the doping concentration is 1-50 wt%, more preferably 5-20 wt%, and most preferably 12 wt%, 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.

6. The electroluminescent device according to claim 4 or 5, characterized in that, The electroluminescent device further includes an electron transport layer located between the cathode and the light-emitting layer; Preferably, the electron transport layer is an electron transport material with a triplet energy level greater than or equal to 2.3 eV; Preferably, the electron transport layer includes TmPyPB, TSPO1, DPEPO, BPhen and / or TpBi; More preferably, the electron transport layer includes TSPO1 and / or BPhen.

7. The electroluminescent device according to claim 4 or 5, 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 is a hole transport material with a triplet energy level greater than or equal to 2.3 eV; Preferably, the hole transport layer includes mCP, CzSi, m-MTDATA and / or TAPC; More preferably, the hole transport layer includes mCP and / or CzSi.

8. The electroluminescent device according to claim 6 or 7, 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 comprises mCP and / or CzSi, and the electron transport layer comprises TSPO1 and / or BPhen; Preferably, the electroluminescent device further includes an electron injection layer located between the cathode and the electron transport layer, and the electroluminescent device further includes a hole injection layer located between the anode and the hole transport layer; More preferably, the electron injection layer comprises LiF, and the hole injection layer comprises MoO3.

9. The electroluminescent device according to any one of claims 4-8, characterized in that, The thickness of the light-emitting layer is 1-50 nm, preferably 10-40 nm, more preferably 15-30 nm, more preferably 20-25 nm, and most preferably 20 nm.

10. The electroluminescent device according to claim 4, characterized in that, The structure of the electroluminescent device is: ITO / MoO3 (2 nm) / CzSi:MoO3 (30 nm) / CzSi (10 nm) / CzSi:Ce(Tp)2(Bp) (20 nm) / TSPO1 (10 nm) / BPhen (40 nm) / LiF / Al.

Images