Binuclear iridium complex and its preparation method and application

Abstract

The present invention discloses a binuclear iridium complex and its preparation method and application, belonging to the field of optical limiting materials. The present invention prepares four binuclear iridium complexes, and improves the absorption properties of the ground state and excited state of the complex by adjusting the distance between the metal centers, thereby realizing the regulation of the anti-saturation absorption performance of the binuclear iridium complex; and compared with the standard sample fullerene C 60 In comparison, the binuclear iridium complexes prepared in the present invention all have excellent reverse saturation absorption performance, and their optical limiting properties are significantly better than those of the standard sample.

Description

Technical Field

[0001] The present invention belongs to the field of optical limiting materials, and in particular relates to a binuclear iridium complex and a preparation method and application thereof. Background Art

[0002] With the rapid development of laser technology, optoelectronic devices are increasingly exposed to strong laser environments and are extremely vulnerable to laser attacks. On the basis of ensuring the normal operation of these devices, making them resistant to laser attacks is a difficult problem that needs to be solved urgently. The development of high-performance strong laser protection materials is one of the main ways to achieve effective laser protection. Optical limiting materials can have both high transmittance for weak light and low transmittance for strong light at the same wavelength. They have obvious advantages in ultrafast response protection against high-energy, continuous wide-band lasers. They are currently recognized as the most practical laser protection materials. Among many material systems, metal organic complexes are considered to be one of the most effective optical limiting materials. They show good optical limiting performance in the visible light region and even the near-infrared region, with a high damage threshold and a short response time.

[0003] Cyclometallated iridium (Ir) complexes have been widely used as anti-saturable absorbers in the field of optical limiting materials over the past decade due to their high intersystem crossing efficiency, long luminescence lifetime, excellent photostability, and easily modifiable structure. Ir complexes possess long-lived triplet excited states whose excited-state absorption is stronger than their ground-state absorption, resulting in anti-saturable absorption capability. This has led to their extensive research as anti-saturable absorbers in optical limiting materials. Compared to mononuclear complexes, binuclear complexes may exhibit metal-metal interactions, and their photophysical properties can be effectively manipulated by modifying bridging ligands and cyclometallated ligands, achieving red and even near-infrared emission. Adding additional metal atoms to the metal complex can effectively enhance the spin-orbit coupling and thus the intersystem crossing efficiency, thereby enabling the manipulation of the anti-saturable absorption properties of binuclear iridium complexes. However, the interaction between the metal centers is affected by the distance between the metal centers; too close or too far distances can affect the charge transfer pathway and efficiency. Summary of the Invention

[0004] The present invention provides a binuclear iridium complex and its preparation method and application, and four binuclear iridium complexes are prepared; 60 In comparison, the binuclear iridium complexes prepared in the present invention all have excellent reverse saturation absorption performance, and their optical limiting properties are significantly better than those of the standard sample.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] The preparation method of a binuclear iridium complex comprises the following steps:

[0007] Synthesis of C^N ligand L-0: 2-acetylbenzothiophene, 2-aminobenzophenone, and diphenyl phosphate were added to m-cresol via a cycloaddition reaction at 140°C under a nitrogen atmosphere for 24 hours. The C^N ligand was then extracted, dried, and purified by column chromatography.

[0008] Synthesis of N^N ligand L-1: 2,5-Dibromopyrazine and 2-tributylstannylpyridine were catalyzed by tetrakistriphenylphosphine palladium and cuprous iodide in a toluene-based solvent via a Suzuki coupling reaction. The reaction was carried out at 115°C for 12 hours under a nitrogen atmosphere. N^N ligand L-1 was obtained through extraction, drying, and column chromatography purification.

[0009] Synthesis of N^N ligand L-2: Bis(triphenylphosphine)nickel chloride and anhydrous DMF were stirred at room temperature under a nitrogen atmosphere, zinc powder was added, and stirring was continued until the color of the solution changed from green to dark brown. 5-Bromo-2,2'-bipyridine was added, and the reaction type was Suzuki coupling reaction. The mixture was stirred at room temperature under a nitrogen atmosphere until the reaction was complete. The mixture was poured into ammonia / water to form a gray precipitate. The N^N ligand L-2 was obtained through extraction, drying, and column chromatography purification.

[0010] Synthesis of N^N ligand L-3: 5-bromo-2,2`-bipyridine, benzene-1,4-diboronic acid, potassium carbonate, tetrakistriphenylphosphine palladium, tetrahydrofuran / water / ethanol (v / v / v) 6:3:5, reaction type Suzuki coupling reaction, reaction at 80°C under nitrogen atmosphere for 20 hours, the product was extracted, dried, and purified by column chromatography to obtain N^N ligand L-3.

[0011] Synthesis of iridium-chloride dimer;

[0012] IrCl3·H2O and C^N ligand were added to a mixed solution of water and ethylene glycol ethyl ether (1 / 3, v / v). The reaction type was coordination reaction. The mixed system was reacted at 130°C under a nitrogen atmosphere for 24 h. After the reaction, the mixture was filtered under reduced pressure and dried in vacuum to obtain the corresponding iridium chloride dimer.

[0013] Synthesis of complexes Y-1-Di to Y-4-Di;

[0014] Synthesis of complex Y-1-Di: The N^N ligand 2,2'-bipyrimidine and iridium chloride dimer were added to a mixture of dichloromethane and methanol (2 / 1, v / v) for a coordination reaction. The mixture was refluxed under a nitrogen atmosphere for 24 hours. The product was extracted, dried, and purified by column chromatography to obtain complex Y-1-Di.

[0015] Synthesis of complex Y-2-Di: N^N ligand L-1 and iridium chloride dimer were added to a mixture of dichloromethane and methanol (2 / 1, v / v) for a coordination reaction. The mixture was refluxed under a nitrogen atmosphere for 24 hours. The product was extracted, dried, and purified by column chromatography to obtain complex Y-2-Di.

[0016] Synthesis of complex Y-3-Di: N^N ligand L-2 and iridium chloride dimer were added to a mixture of dichloromethane and methanol (2 / 1, v / v) for a coordination reaction. The mixture was refluxed under a nitrogen atmosphere for 24 hours. The product was extracted, dried, and purified by column chromatography to obtain complex Y-3-Di.

[0017] Synthesis of complex Y-4-Di: The N^N ligand L-3 and iridium chloride dimer were added to a mixed solution of dichloromethane and methanol (2 / 1, v / v) in a coordination reaction. The mixture was refluxed under a nitrogen atmosphere for 24 hours. The product was extracted, dried, and purified by column chromatography to obtain complex Y-4-Di.

[0018] The structures of the complexes Y-1-Di to Y-4-Di synthesized by the above-described method are as follows:

[0019]

[0020] The complexes Y-1-Di to Y-4-Di can be used in optical limiting materials and have excellent reverse saturation absorption performance.

[0021] Beneficial effects: The present invention provides a binuclear iridium complex and its preparation method and application. By adjusting the distance between the metal centers to synthesize different iridium complexes, the absorption properties of the complex ground state and excited state can be improved, thereby achieving the regulation of the anti-saturation absorption performance of the binuclear iridium complex. 60 In comparison, the binuclear iridium complexes prepared in the present invention all have excellent reverse saturation absorption performance, and their optical limiting properties are significantly better than those of the standard sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the binuclear iridium complex of the present invention;

[0023] Figure 2 is a synthetic route of the binuclear iridium complex of the present invention;

[0024] Figure 3 The single crystal structures and distances between metals of (a) Y-1-Di, (b) Y-2-Di, and (c) Y-4-Di in the embodiments of the present invention;

[0025] Figure 4are the torsion angles of the two pyridine rings of the Y-1-Di intermediate bridging ligand in the embodiment of the present invention;

[0026] Figure 5 (a) The torsion angle of the pyridines at both ends of the pyrazine in the Y-2-Di molecule bridging ligand, and (b) the torsion angle between the Ir atom of the Y-2-Di molecule and the pyrazine in the embodiment of the present invention;

[0027] Figure 6 is the torsion angle between the bipyridine at both ends and the middle benzene ring of the Y-4-Di molecular bridging ligand in the embodiment of the present invention;

[0028] Figure 7 Crystal stacking diagrams of (a) Y-1-Di, (b) Y-2-Di, and (c) Y-4-Di in embodiments of the present invention;

[0029] Figure 8 Schematic diagram of the intermolecular forces of (a) Y-1-Di, (b) Y-2-Di, and (c) Y-4-Di in the embodiments of the present invention;

[0030] Figure 9 Surface distribution diagrams of (ac)Y-1-Di, (bf)Y-2-Di, and (gi)Y-4-Di mapped by dnorm, shape-index, and curvedness in the embodiment of the present invention;

[0031] Figure 10 Schematic diagram of the proportion of the short-range interaction of (a) Y-1-Di, (b) Y-2-Di, and (c) Y-4-Di on the Hirshfeld surface in an embodiment of the present invention;

[0032] Figure 11 The UV-visible absorption spectra of the complexes Y-1-Di to Y-4-Di in dichloromethane solution in the examples of the present invention are shown in FIG.

[0033] Figure 12 The UV-visible absorption spectra of the complexes Y-1-Di to Y-4-Di in different solvents in the examples of the present invention are shown;

[0034] Figure 13 The complexes Y-1-Di to Y-4-Di in the embodiment of the present invention are in dichloromethane solution (c=1.0×10 - 5 mol / L) (a) Emission spectrum (b) Normalized emission spectrum;

[0035] Figure 14 The phosphorescence emission spectra of the complexes Y-1-Di to Y-4-Di in the examples of the present invention (a) in dichloromethane solution in argon and air atmospheres; (b) at 77K and room temperature;

[0036] Figure 15 The normalized emission spectra of the complexes Y-1-Di to Y-4-Di in different solvents (c=1×10 -5 mol / L);

[0037] Figure 16 The time-dependent transient absorption spectra of the complexes Y-1-Di, Y-3-Di and Y-4-Di in degassed toluene solution (c = 1 × 10 -5 mol / L,λ ex =355nm);

[0038] Figure 17 In the embodiment of the present invention, under 532nm laser irradiation, the complexes Y-1-Di~Y-4-Di and C 60 Incident light-outgoing light energy curve in acetonitrile solution. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0040] like Figure 2 As shown, the preparation method of the binuclear iridium complex comprises the following steps:

[0041] (1) Synthesis of C^N ligand L-0 and N^N ligands L-1 to L-3

[0042] Ligand L-0: 2-Acetylbenzothiophene (5.0 g, 28.37 mmol), 2-aminobenzophenone (5.6 g, 28.37 mmol), and diphenyl phosphate (7.8 g, 31.17 mmol) were added to a 250 mL two-necked flask, followed by 150 mL of m-cresol. The mixture was reacted at 140°C under a nitrogen atmosphere for 24 h. After the reaction, 60 mL of trimethylamine was added to obtain a precipitate, which was then washed with ethanol, filtered, and dried under vacuum to obtain 6.75 g of a white solid powder (70% yield). 1 H NMR(400MHz,DMSO-d6)δ8.51(d,J=0.8Hz,1H),8.24(s,1H),8.12(dt,J=8.3,1.0Hz,1H),8.0 6-8.02(m,1H),7.92-7.87(m,1H),7.88-7.80(m,2H),7.69-7.57(m,6H),7.47-7.39(m,2H).

[0043] Ligand L-1: 2,5-dibromopyrazine (1.00 g, 4.1 mmol), 2-tributylstannylpyridine (3.30 g, 8.7 mmol), tetrakistriphenylphosphine palladium (0.24 g, 0.21 mmol) and cuprous iodide (40 mg, 0.21 mmol) were added to a 250 mL two-necked flask, followed by the addition of 20 mL of toluene. The mixture was reacted at 115 ° C. under a nitrogen atmosphere for 12 h. After extraction and drying, the residue was purified by column chromatography (200-300 mesh silica gel, eluent: n-hexane / ethyl acetate = 10 / 1, v / v) to give 400 mg of a white solid with a yield of 43%. 1 H NMR (400MHz, CDCl3) δ9.68 (s, 2H), 8.77 (dt, J=4.8, 1.8, 0.9Hz, 2H), 8.47 (dt, J= 7.9,1.1Hz,2H),7.90(ddd,J=7.7,1.8Hz,2H),7.40(ddd,J=7.5,4.8,1.2Hz,2H).

[0044] Ligand L-2: Add bis(triphenylphosphine)nickel chloride (2.78 g, 4.25 mmol) and 50 mL of anhydrous DMF to a 250 mL two-necked flask. Stir the mixture under nitrogen atmosphere at room temperature for 10 min, then add zinc powder (0.28 g, 4.25 mmol) and continue stirring for 45 min. At this time, the color of the solution changes from green to dark brown. Add 5-bromo-2,2`-bipyridine (1.00 g, 4.25 mmol) and stir under nitrogen atmosphere at room temperature for 10 h. After the reaction is completed, pour the mixture into a beaker containing 100 ml of ammonia / water (1:9 v / v) to generate a gray precipitate. The post-treatment process is consistent with the steps of ligand L-1 to obtain 593 mg of a yellow solid with a yield of 45%. 1 HNMR(400MHz,DMSO-d6)δ9.19(d,J=2.2Hz,2H),8.75(d,J=4.7Hz,2H),8.54(d,J= 8.3Hz,2H),8.50-8.41(m,4H),8.01(t,J=7.7Hz,2H),7.51(dd,J=7.4,4.9Hz,2H).

[0045] Ligand L-3: 5-bromo-2,2'-bipyridine (0.58 g, 2.46 mmol), benzene-1,4-diboronic acid (0.2 g, 1.21 mmol), potassium carbonate (0.85 g, 6.16 mmol) and tetrakistriphenylphosphine palladium (0.14 g, 0.12 mmol) were added to a 250 mL two-necked flask, followed by the addition of 28 mL of tetrahydrofuran / water / ethanol (6:3:5, v / v / v). The mixture was reacted at 80 ° C under a nitrogen atmosphere for 20 h. The post-treatment process was consistent with the steps of ligand L-1 to obtain 350 mg of a white solid with a yield of 75%. 1 H NMR(400MHz, CDCl3) δ9.02(d,J=2.3Hz,2H),8.77-8.72(m,2H),8.54(d,J=8.3Hz,2H),8.48( d,J=7.9Hz,2H),8.12(dd,J=8.2,2.4Hz,2H),7.92-7.81(m,6H),7.37(dd,J=7.4,4.8Hz,2H).

[0046] (2) Synthesis of iridium-chloride dimer

[0047] C^N ligand L-0 (3.04 g, 9.0 mmol) and IrCl3·H2O (1.58 g, 4.5 mmol) were added to a 250 mL two-necked flask, followed by the addition of a mixed solution of 100 mL of ethylene glycol ethyl ether and water (3 / 1, v / v). The mixed solution was reacted at 130°C under a nitrogen atmosphere for 24 h. The mixed system gradually turned deep red. After the reaction, the mixture was poured into a beaker containing 150 mL of water and stirred for half an hour. The mixture was then filtered under reduced pressure and the obtained solid was dried in a vacuum drying oven to obtain 4.5 g of deep red solid powder with a yield of 87%. No further purification was required, and the iridium chloride dimer could be directly used in the next reaction.

[0048] (3) Synthesis of complexes Y-1-Di to Y-4-Di

[0049] Complex Y-1-Di: 2,2'-bipyrimidine (40 mg, 0.252 mmol), silver trifluoromethanesulfonate (71 mg, 0.277 mmol) and iridium chloride dimer (500 mg, 0.277 mmol) were added to a mixed solvent of 40 mL of dichloromethane and 20 mL of methanol. The mixture was reacted at 60°C under a nitrogen atmosphere for 24 h, followed by the addition of potassium hexafluorophosphate (714 mg, 3.9 mmol) and continued stirring for 1 h. After the reaction, the mixture was washed with water and extracted with dichloromethane to obtain an organic phase, which was then distilled under reduced pressure to remove the solvent. The residue was purified by column chromatography (200-300 silica gel, eluent: dichloromethane / methanol = 100 / 1, v / v) to obtain a red solid. The product was recrystallized from dichloromethane and n-hexane and further purified to obtain a brown solid powder, Y-1-Di: 78 mg, yield: 30%. 1 H NMR (400MHz, DMSO-d6): δ9.19(dd,J=4.8,2.0Hz,3H),8.75(dd,J=5.7,2.1Hz,3H),8.09(s,3H),8.06(d,J=8.1Hz,3H),7.96(dd,J=5.7,4.8Hz,4H),7.7 4-7.65(m,22H),7.36(ddd,J=8.2,6.6,1.4Hz,4H),7.27-7.21(m,4H),7.12 -7.00(m,8H),6.86-6.77(m,4H),6.51(d,J=8.2Hz,4H).HRMS(ESI)(M-2PF6 - ):m / z calcd 823.19574; found:823.19452.

[0050] Complex Y-2-Di: Ligand L-1 (54 mg, 0.231 mmol) and iridium chloride dimer (458 mg, 0.253 mmol) were added to a mixed solution of 60 mL of dichloromethane and methanol (2 / 1, v / v), and the mixture was reacted at 60 ° C under a nitrogen atmosphere for 24 hours. Potassium hexafluorophosphate (714 mg, 3.9 mmol) was then added and stirred for 1 hour. After the reaction, the mixture was washed with water and extracted with dichloromethane to obtain an organic phase. The solvent was then removed by distillation under reduced pressure to obtain a residue, which was purified by column chromatography (200-300 silica gel, eluent: dichloromethane / methanol = 100 / 1, v / v) to obtain a brown solid. The product was recrystallized from dichloromethane and n-hexane and further purified to obtain 99 mg of a brown solid with a yield of 25%. 1H NMR(400MHz, DMSO-d6)δ9.13(s,1H),8.47(d,J=5.5Hz,1H),8.34(dd,J=8.8,7.3Hz,1H),8.21(s,1H),8.10-8.06(m ,1H),8.03(d,J=8.0Hz,1H),8.00-7.96(m,2H),7.91(t,J=6.9Hz,1H),7.83-7.62(m,9H),7.51(t,J=8.4Hz,3H),7. 44(d,J=8.9Hz,1H),7.36-7.32(m,1H),7.22(d,J=7.3Hz,2H),7.14(t,J=7.6Hz,1H),6.75(t,J=7.7Hz,1H),6.71-6 .66(m,2H),6.50(t,J=7.6Hz,1H),6.37(d,J=8.3Hz,1H),6.13(d,J=8.3Hz,1H),5.09(t,J=8.2Hz,1H).HRMS(M-2PF6 - ) 2+ :m / z calcd982.1770; found:982.1727.

[0051] Complex Y-3-Di: Ligand L-2 (78 mg, 0.252 mmol), silver trifluoromethanesulfonate (71 mg, 0.277 mmol) and iridium chloride dimer (500 mg, 0.277 mmol) were added to a mixed solvent of 60 mL of dichloromethane and 30 mL of methanol. The mixed system was reacted at 60 ° C under a nitrogen atmosphere for 24 hours, and then potassium hexafluorophosphate (714 mg, 3.9 mmol) was added and stirred for 1 hour. After the reaction, the mixed system was washed with water and extracted with dichloromethane to obtain an organic phase. The solvent was then distilled off under reduced pressure to obtain a residue, which was purified by column chromatography (200–300 silica gel, eluent: dichloromethane / methanol = 100 / 1, v / v) to obtain a red solid. The product was further purified by recrystallization from dichloromethane and n-hexane to obtain 85 mg of red solid powder, with a yield of 15%. 1H NMR (400MHz, DMSO-d6) δ8.67(d,J=8.2Hz,4H),8.49(d,J=8.2Hz,2H),8.44-8.40(m,2H),8.20(dd,J=8.8,7.3Hz, 2H),8.11(d,J=8.0Hz,4H),8.07-8.02(m,4H),7.93(d,J=8.0Hz,2H),7.85-7.79(m,2H),7.77-7.67(m,12H),7.66 -7.55(m,12H),7.29(t,J=7.6Hz,2H),7.25-7.17(m,6H),7.11(t,J=8.6Hz,4H),7.02-6.97(m,2H),6.86(t,J=7. 8Hz,2H),6.76(t,J=7.7Hz,2H),6.65(t,J=8.0Hz,2H),6.54(d,J=8.3Hz,2H),6.38(d,J=8.2Hz,2H).HRMS(M-2PF6 - ) 2+ :m / z calcd 1020.1927; found:1020.1938.

[0052] Complex Y-4-Di: Ligand L-3 (97 mg, 0.252 mmol), silver trifluoromethanesulfonate (71 mg, 0.277 mmol) and iridium chloride dimer (500 mg, 0.277 mmol) were added to a mixed solvent of 60 mL of dichloromethane and 30 mL of methanol, and the mixture was reacted at 60 ° C under a nitrogen atmosphere for 24 h. Potassium hexafluorophosphate (714 mg, 3.9 mmol) was then added and stirred for 1 h. After the reaction, the mixture was washed with water and extracted with dichloromethane to obtain an organic phase. The solvent was then removed by distillation under reduced pressure to obtain a residue which was purified by column chromatography (200-300 silica gel, eluent: dichloromethane / methanol = 100 / 1, v / v) to obtain a red solid. The product was further purified by recrystallization from dichloromethane and n-hexane to obtain 175 mg of a red solid powder with a yield of 30%. 1H NMR (400MHz, DMSO-d6) δ8.62(d,J=10.0Hz,4H),8.52(d,J=8.8Hz,4H),8.45(d,J=5.8Hz,2H),8.2 0(t,J=8.0Hz,2H),8.16-8.02(m,8H),7.83(d,J=8.6Hz,6H),7.77-7.61(m,15H),7.53(s,4H),7.4 6-7.43(m,4H),7.38-7.32(m,4H),7.27(td,J=11.8,10.3,5.9Hz,6H),7.15(d,J=8.7Hz,2H),7.05 (dt,J=16.5,8.0Hz,4H),6.84(dt,J=12.3,7.6Hz,4H),6.54(dd,J=15.1,8.2Hz,4H).HRMS(M-2PF6 - ) 2+ :m / z calcd 1058.2083; found:1058.2173.

[0053] Test results

[0054] The yields of the target complexes Y-1-Di, Y-2-Di, Y-3-Di and Y-4-Di were 30%, 25%, 15% and 30% respectively. 1 H NMR and HRMS were used to characterize the target molecule and confirmed that its structure was consistent with the expected one.

[0055] Crystal structure analysis

[0056] The solvent evaporation method was used to grow single crystals, with methanol as the good solvent and ether as the poor solvent. The complex was first completely dissolved in a small beaker with the good solvent to form a saturated solution, then sealed with a poor solvent and left to evaporate slowly at room temperature. After a week, rod-shaped crystals of the binuclear complexes Y-1-Di, Y-2-Di, and Y-4-Di were obtained. They all belong to the C2 / c space group and the monoclinic system. Figure 3 It can be observed that the distance between the Y-1-Di metal centers is The distance between the iridium metal centers in Y-2-Di molecules is The iridium metal center of the Y-4-Di molecule is further away. Figure 3(b) shows that the four N on the Y-4-Di molecule bridging N^N ligand are located on the same side, so the two iridium metal centers are also located on the same side. The Y-4-Di molecule as a whole is like a barbell, with the complex Ir molecules at both ends and the benzene ring in the middle of the N^N ligand connecting them. The distance between the metal centers of Y-4-Di is obviously farther, and the two ends are relatively independent, while the structures of Y-1-Di and Y-2-Di molecules are more compact. Although the single crystal data of Y-3-Di have not been directly obtained, it can be reasonably inferred based on the three single crystal data that have been obtained that the distance between the metal centers of Y-3-Di is between This range is between the metal center distances of Y-2-Di and Y-4-Di; as expected during molecular design, the distance between Y-1-Di metals is the shortest, and the distances between Y-2-Di to Y-4-Di metals gradually increase.

[0057] from Figure 4 It can be observed that the two pyridines in the Y-1-Di intermediate bridging ligand have a very small torsion angle of 4.54°, almost in the same plane. Compared with Y-2-Di and Y-4-Di, the Y-1-Di bridging ligand has the smallest torsion angle. The single crystal structure of this molecule resembles the letter "H," with two iridium metal centers coordinated by bipyridines along a central line. The cyclometallated ligands stand vertically at both ends, highly symmetrically centered around the bridging N^N ligand. Y-1-Di has the most regular shape, making it easier to stack.

[0058] from Figure 5 It can be observed that the torsion angles of the pyridines at both ends of the Y-2-Di bridged N^N ligand and the pyrazine in the middle are 14.94° and 4.58°, respectively. This results in different torsion angles between the iridium metal center coordinated to it and the pyrazine, indicating that the molecule has a certain degree of twisting and the two iridium metal centers are not in the same plane. Figure 6 It shows that the torsion angles of the bipyridine at both ends of the Y-4-Di bridged N^N ligand and the middle benzene ring are the same, both 33.15°. The two ends are highly symmetrical with the benzene ring on the bridged ligand as the center, and the two iridium metal centers are in the same plane. Figure 7 The unit cell stacking diagram shows that the stacking mode is completely different from that of Y-1-Di. Y-1-Di belongs to H aggregation, while Y-2-Di and Y-4-Di belong to J aggregation. The Y-2-Di molecules are connected head to tail along the b axis and head to head along the c axis, and are arranged in sequence like an "eight". This makes its stacking relatively loose. The molecules of Y-4-Di are arranged in a zipper-like staggered arrangement with head to tail. This arrangement is more compact, so the molecular stacking density of Y-4-Di is relatively higher, which is also reflected in the crystal data (Table 1). The density of the complex Y-4-Di is 1.356g / cm 3 , and the density of the complex Y-2-Di is 1.290 g / cm3 Combined with the previous analysis of the torsion angles of their bridging ligands, the Y-1-Di bridging ligand has the smallest torsion angle and the most regular shape, so it is easier to stack. In addition, its H-aggregated stacking mode makes it have the highest molecular packing density of 1.556 g / cm 3 .

[0059] Table 1 Crystal structure parameters of complexes Y-1-Di, Y-2-Di and Y-4-Di

[0060]

[0061] Figure 8 This shows that there are multiple forces between Y-2-Di stacking molecules, and there is a CH-π interaction between adjacent molecular cyclometallated ligands. HH effect SS function and SH At the same time, there is a weak π-π stacking interaction between molecules There is a CH-π interaction between the benzene rings of Y-4-Di stacking molecules SH effect and HH interaction

[0062] Hirshfeld and 2D fingerprint analysis

[0063] Crystal-Explorer software is used to generate Hirshfeld surface analysis and 2D fingerprint images, which can be used to visualize the crystal structure. Figure 9 The red spots in (a) and (d) show the strong interaction points between molecules, which are mainly SH / HS interactions, while the white and blue areas represent the intermolecular distances that are greater than or equal to the van der Waals force distance, and the interaction force is weaker. Figure 9 As can be seen in (b) in the Y-2-Di complex, the phenylbiquinoline portion of the cyclometallated C^N ligand has a bow-tie shape consisting of blue and red triangles. Figure 9 (c) shows a smooth surface at the corresponding position, indicating the presence of π-π interactions within the Y-2-Di complex. The shape-index surface distribution of the Y-4-Di complex also reveals a bow-tie shape composed of blue and red triangles on the cyclometallated ligands. The curvedness surface map also shows a smooth surface at the corresponding position, indicating the presence of π-π interactions between the C^N ligands within the Y-4-Di complex.

[0064] HH interactions play a dominant role in the 2D fingerprint map, e.g. Figure 10 As shown, in complex Y-2-Di, the three interactions account for a total of 77.1%, with HH interactions accounting for the highest proportion at 51.6%, followed by CH / HH at 18.2%, and FH / HF at 7.3%. In complex Y-4-Di, the three interactions account for a total of 81.6%, with HH interactions accounting for the highest proportion at 53.9%, followed by CH / HC at 22.2%, and SH / HS at 5.5%. It is noteworthy that only complex Y-1-Di exhibits Ir-C / C-Ir and Ir-N / N-Ir interactions, while complexes Y-2-Di and Y-4-Di lack these two interactions. Y-1-Di has the shortest bridging ligands, the smallest pyridine ring distortion, the most regular molecule, and more compact intermolecular packing, resulting in the highest molecular packing density and a greater likelihood of contact between the iridium metal center and other atoms.

[0065] Ground state absorption

[0066] The UV-visible absorption spectra of the four binuclear iridium complexes Y-1-Di~Y-4-Di are as follows: Figure 11 The detailed photophysical data are summarized in Table 2. The complexes Y-1-Di to Y-4-Di all show strong absorption bands and obvious fine structures between 250-430 nm, which are attributed to the cyclometallated ligand and the bridged N^N ligand. 1 π,π* transition, the moderate intensity absorption peak at 430-550nm comes from 1 MLCT 1 LLCT, the absorption peak after 550nm comes from spin-forbidden 3 MLCT / 3 LLCT. Figure 12 It can be seen that the absorption peaks of this series of complexes before 250-430nm do not change with the change of solvent polarity and can be attributed to 1 π,π* transition, and the broad absorption band after 430-550nm produces a slight blue shift with the increase of solvent polarity. This solvent color effect indicates that the polarity of the excited state of the complex molecule is smaller than that of its ground state, which further confirms the existence of MLCT characteristics in this absorption peak.

[0067] Table 2 Photophysical data of complexes Y-1-Di to Y-4-Di

[0068]

[0069] [a] The molar extinction coefficient corresponding to the maximum absorption peak in dichloromethane solution at room temperature;

[0070] [b] Maximum emission wavelength and absolute quantum yield in dichloromethane solution at room temperature

[0071] [c] Maximum nanosecond transient absorption peak and triplet excited state lifetime in toluene solution;

[0072] [d] The signal is too weak to be detected.

[0073] triplet emission

[0074] In order to observe the photoluminescence process of the complexes Y-1-Di~Y-4-Di, their emission spectra in dichloromethane solution were tested ( Figure 13 ), all four complexes emit phosphorescence, but the emission intensity of complexes Y-1-Di and Y-2-Di is very weak, and the emission of complexes Y-3-Di and Y-4-Di is significantly stronger. Their maximum emission wavelengths are 669nm, 665nm, 662nm and 658nm respectively. After normalizing their emission intensities, it can be seen that as the N^N ligands of complexes Y-1-Di to Y-4-Di gradually increase, the distance between the two iridium metal centers becomes farther and farther, and their maximum emission wavelengths gradually blue-shift, and the emission intensity gradually increases. This shows that as the distance between the binuclear iridium metals increases, the possibility of the two iridium metal centers interacting becomes lower, and their properties become closer to those of mononuclear complexes. This is most obvious in the complex Y-4-Di with the farthest distance between the metal centers. Its emission is significantly enhanced, and its emission state properties are very similar to those of the mononuclear complex Ir. These results are in line with the expected results of molecular design. Figure 14 As shown, the four binuclear complexes all exhibit oxygen-sensitive properties, and compared with room temperature, their maximum emission wavelengths at 77K are significantly blue-shifted, the emission spectra become narrower and the fine structure is more obvious, which indicates that the emission of the complexes Y-1-Di~Y-4-Di here comes from the phosphorescence emission of the triplet excited state.

[0075] like Figure 15 As shown, the solvation effect of complexes Y-2-Di and Y-3-Di is not obvious. With the change of solvent polarity, their emission spectra do not change significantly, while the complex Y-1-Di shows a very obvious solvatochromic effect. From the low-polarity solvent toluene to the high-polarity solvent acetonitrile, the maximum emission wavelength of Y-1-Di blue-shifts by 28nm. Y-4-Di also has a slight negative solvation effect. With the increase of solvent polarity, its maximum emission wavelength also gradually blue-shifts, but the solvation effect is not as obvious as that of Y-1-Di. In summary, the phosphorescence emission of complexes Y-1-Di and Y-4-Di mainly comes from 3 MLCT, while the emission peaks of the complexes Y-2-Di and Y-3-Di come from 3π,π*.

[0076] Transient difference absorption spectroscopy

[0077] The time-dependent transient difference absorption spectrum of the complex in degassed toluene solution is shown in Figure 2. Figure 16 As shown, the TA spectrum of the complex Y-2-Di was too weak to be measured. However, the complex Y-1-Di exhibited broad positive transient difference absorption peaks in the 400-650 nm range, while the complexes Y-3-Di and Y-4-Di exhibited broad positive transient difference absorption peaks in the 400-750 nm range, indicating that the excited-state absorption of the complexes is greater than the ground-state absorption within this wavelength range. The triplet excited-state lifetimes of the complexes Y-1-Di, Y-3-Di, and Y-4-Di were 148 ns, 1.04 μs, and 8.86 μs, respectively, suggesting that these three complexes possess good anti-saturation absorption properties.

[0078] Optical limiting properties

[0079] In order to explore the optical limiting properties of these four complexes, C 60 As a reference material, the nonlinear optical properties of the complexes Y-1-Di~Y-4-Di were studied under 532nm laser. Figure 17 As shown in the figure, all four complexes exhibit nonlinear characteristics. As the incident laser energy gradually increases, the output energy density gradually decreases. Although the complexes Y-2-Di and Y-3-Di have certain anti-saturation absorption capabilities, their optical limiting performance is much worse than that of the complexes Y-1-Di and Y-4-Di, and even weaker than that of the reference material C. 60 The complexes Y-1-Di and Y-4-Di exhibit excellent reverse saturation absorption performance. When the incident light energy density reaches 2.0 J / cm 2 When the output light energy density of the complex Y-4-Di is reduced to 0.40 J / cm 2 The decrease was 80%, and the output light energy density of the complex Y-1-Di was reduced to 0.36J / cm 2 Compared with the complex Y-1-Di, the complex Y-4-Di has a longer triplet excited state lifetime, while the optical limiting performance of the two complexes is similar. This indicates that most of the triplet excited state energy of the complex Y-4-Di is consumed through radiative transitions, which is also supported by its high absolute quantum yield (15.2%).

[0080] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A binuclear iridium complex, characterized in that There are four types of complexes, and their structures are as follows: 。 2. The method for preparing the binuclear iridium complex according to claim 1, wherein The following steps are involved: The C^N ligand L-0 and N^N ligands L-1 to L-3 were synthesized by Suzuki coupling reaction, wherein the structural formula of the C^N ligand L-0 is: ， The structural formulas of the N^N ligands L-1 to L-3 are respectively: 、 、 ； IrCl3·H2O and C^N ligand L-0 were used to carry out coordination reaction to synthesize iridium-chloride dimer; Complexes Y-1-Di~Y-4-Di were synthesized respectively by coordination reaction of N^N ligand 2,2'-bipyrimidine, N^N ligand L-1~L-3 with iridium chloride dimer.

3. The method for preparing a binuclear iridium complex according to claim 2, wherein The synthesis of C^N ligand L-0 includes the following steps: adding 2-acetylbenzothiophene, 2-aminobenzophenone and diphenyl phosphate to m-cresol, reacting at 140°C for 24 hours under a nitrogen atmosphere, and obtaining C^N ligand L-0 through extraction, drying and column chromatography purification.

4. The method for preparing a binuclear iridium complex according to claim 2, wherein The synthesis of N^N ligand L-1 includes the following steps: 2,5-dibromopyrazine and 2-tributylstannylpyridine are reacted under the catalysis of tetrakistriphenylphosphine palladium and cuprous iodide, the solvent used in the reaction is toluene, and the reaction is carried out at 115°C for 12 hours in a nitrogen atmosphere. The N^N ligand L-1 is obtained through extraction, drying, and column chromatography purification.

5. The method for preparing a binuclear iridium complex according to claim 2, wherein The synthesis of N^N ligand L-2 includes the following steps: bis(triphenylphosphine)nickel chloride and anhydrous DMF (N,N-dimethylformamide) are stirred and mixed at room temperature under a nitrogen atmosphere, zinc powder is added, and stirring is continued until the color of the solution changes from green to dark brown, 5-bromo-2,2'-bipyridine is added, and stirring is continued at room temperature under a nitrogen atmosphere until the reaction is complete. The mixture is poured into ammonia / water to form a gray precipitate, which is then extracted, dried, and purified by column chromatography to obtain N^N ligand L-2.

6. The method for preparing a binuclear iridium complex according to claim 2, wherein: The synthesis of N^N ligand L-3 includes the following steps: 5-bromo-2,2'-bipyridine, benzene-1,4-diboronic acid, potassium carbonate, tetrakistriphenylphosphine palladium, and tetrahydrofuran / water / ethanol in a v / v / v ratio of 6:3:5, reacting at 80°C under a nitrogen atmosphere for 20 hours. The product is extracted, dried, and purified by column chromatography to obtain N^N ligand L-3.

7. The method for preparing a binuclear iridium complex according to claim 2 or 3, wherein: The synthesis of iridium chloride dimer includes the following steps: IrCl3·H2O and C^N ligand L-0 are added to a mixed solution of water and ethylene glycol ethyl ether with a v / v ratio of 1 / 3, reacted at 130°C under a nitrogen atmosphere for 24 hours, and then filtered under reduced pressure after the reaction. The corresponding iridium chloride dimer is obtained after vacuum drying.

8. The method for preparing a binuclear iridium complex according to claim 2, wherein: The preparation of complex Y-1-Di includes the following steps: adding N^N ligand 2,2'-bipyrimidine and iridium chloride dimer to a mixed solution of dichloromethane and methanol with a v / v ratio of 2 / 1, refluxing for 24 hours under a nitrogen atmosphere, and extracting, drying, and purifying the product by column chromatography to obtain complex Y-1-Di.

9. The method for preparing a binuclear iridium complex according to claim 2, wherein: The preparation of complexes Y-2-Di~Y-4-Di includes the following steps: N^N ligands L-1~L-3 and iridium chloride dimer are respectively added to a mixed solution of dichloromethane and methanol with a v / v ratio of 2 / 1, and the mixture is refluxed for 24 hours under a nitrogen atmosphere. The products are extracted, dried, and purified by column chromatography to obtain complexes Y-2-Di~Y-4-Di, respectively.

10. The use of the binuclear iridium complex according to claim 1, characterized in that: The binuclear iridium complex is used for optical limiting materials.

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