Ring metal palladium tetramer as well as preparation method and application thereof

Abstract

The invention provides a cyclometalated palladium tetramer as well as a preparation method and application thereof, and belongs to the technical field of photoelectric materials. The cyclometalated palladium tetramer provided by the invention can be used as a novel phosphorescent luminescent material for an organic light-emitting diode, and a new thought is provided for application of Pd metal in the design of a phosphorescent luminescent material structure.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic materials, and in particular to a cyclometallated palladium tetramer and a preparation method and application thereof. Background Art

[0002] Organic light-emitting diodes (OLEDs) use organic compounds as the light-emitting layer and have attracted much attention due to their fast response speed, thin and light devices, flexibility, and excellent optical properties. To further improve the electroluminescent efficiency of OLEDs, researchers have successively developed a variety of emission materials based on fluorescence and phosphorescence. Phosphorescent materials can simultaneously capture singlet and triplet excitons, converting triplet energy into luminescent singlet states through spin-orbit coupling, theoretically increasing the internal quantum efficiency of the device to 100%, while traditional fluorescent materials can only utilize about 25% of singlet excitons for luminescence; in addition, through targeted molecular design, the emission peak of phosphorescent materials can cover the entire visible light band, achieving multi-color regulation. Summary of the Invention

[0003] The purpose of the present invention is to provide a cyclometallated palladium tetramer and its preparation method and application. The cyclometallated palladium tetramer provided by the present invention can be used as a new type of phosphorescent material for organic light-emitting diodes, solving the problem of insufficient existing phosphorescent materials and proposing a new idea for the application of Pd metal in the design of phosphorescent material structures.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a cyclometallated palladium tetramer having a structure shown in any one of (I) to (II):

[0006]

[0007] Wherein, the dinitrogen ligand includes any one of the following structures:

[0008] R1 is H, methyl, trifluoromethyl, cyano, tert-butyl or phenyl;

[0009] The R2 is H, alkyl or phenyl.

[0010] Preferably, it has the structure shown in any one of (I-1), (I-2), (I-3), (II-1), (II-2), and (II-3):

[0011]

[0012] Preferably, it has the structure shown in any one of C1 to C9:

[0013]

[0014] The present invention provides a method for preparing the cyclometalated palladium tetramer described in the above scheme, comprising the following steps: mixing a bispalladium chloride-bridged dimer, a dinitrogen ligand, a first polar solvent, and an alkaline reagent to perform a displacement reaction to obtain the cyclometalated palladium tetramer;

[0015] The bis-palladium chloride bridge dimer has a structure shown in any one of the following: a structure shown in any one of (III) to (IV):

[0016]

[0017] The dinitrogen ligand includes any one of the following structures:

[0018] Preferably, the molar ratio of the bispalladium chloride bridge dimer to is 1:(1.1-2).

[0019] Preferably, the molar ratio of the bis-palladium chloride bridge dimer to the alkaline reagent is 1:(4-6).

[0020] Preferably, the alkaline agent is potassium carbonate.

[0021] The polar organic solvent includes 1,2-dichloroethane or chloroform.

[0022] The temperature of the replacement reaction is 70-120° C., and the time is 24 hours; the replacement reaction is carried out in a light-proof and protective atmosphere.

[0023] The present invention provides the use of the cyclometallated palladium tetramer described in the above scheme or the cyclometallated palladium tetramer prepared by the preparation method described in the above scheme in the emission layer of an organic light-emitting diode.

[0024] The invention provides a cyclometal palladium tetramer, which has excellent luminous efficiency and long luminous life and can be used as a luminous center in an emission layer of an organic light-emitting diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figures 1 to 3 The molecular structures of cyclometallated palladium tetramers C1, C4, and C7 are shown;

[0026] Figure 4 The UV-visible absorption spectra of cyclometallated palladium tetramers C1, C4, and C7 in solution at 25°C.

[0027] Figure 5 is the normalized emission spectra of cyclometallated palladium tetramers C1, C4, and C7 in solution at 25°C;

[0028] Figure 6Normalized emission spectra of cyclometallated palladium tetramers C1, C4, and C7 in solid powder state at 25°C. DETAILED DESCRIPTION

[0029] The present invention provides a cyclometallated palladium tetramer having a structure shown in any one of (I) to (II):

[0030]

[0031] Wherein, the dinitrogen ligand includes any one of the following structures:

[0032] R1 is H, methyl, trifluoromethyl, cyano, tert-butyl or phenyl;

[0033] The R2 is H, alkyl or phenyl.

[0034] In the present invention, the alkyl group is preferably a cyano group, a methyl group, a trifluoromethyl group, a tert-butyl group, an ethyl group or an isopropyl group.

[0035] The cyclometallated palladium tetramer of the present invention is a palladium complex, and N, C and Pd are connected through a coordination bond.

[0036] In the present invention, the cyclometallated palladium tetramer preferably has a structure represented by any one of (I-1), (I-2), (I-3), (II-1), (II-2), and (II-3); more preferably has a structure represented by any one of C1 to C9 (as listed above and will not be repeated here).

[0037] The present invention provides a method for preparing the cyclometalated palladium tetramer described in the above scheme, comprising the following steps: mixing a bispalladium chloride-bridged dimer, a dinitrogen ligand, a first polar solvent, and an alkaline reagent to perform a displacement reaction to obtain the cyclometalated palladium tetramer;

[0038] The bis-palladium chloride bridge dimer has a structure shown in any one of formulas (III) to (IV):

[0039]

[0040] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known in the art or are prepared by methods well known in the art.

[0041] In the present invention, the bis-palladium chloro-bridged dimer is preferably prepared by itself, and the preparation method of the bis-palladium chloro-bridged dimer preferably comprises the following steps:

[0042] The ligand is dissolved in a second polar solvent, and sodium tetrachloropalladate is added to the resulting solution to carry out an addition reaction to obtain a bispalladium chlorobridge dimer; the ligand has a structure shown in any one of (V) to (V1):

[0043]

[0044] In the present invention, the molar ratio of the ligand to sodium tetrachloropalladate is preferably 1:(2-2.1).

[0045] In the present invention, the second polar solvent is preferably glacial acetic acid. The present invention has no special requirements on the amount of the second polar solvent, as long as it can completely dissolve the ligand.

[0046] In the present invention, the addition reaction time is 24 hours; the addition reaction is preferably carried out under stirring conditions. In the present invention, the addition reaction temperature is preferably 100-120° C. and is carried out under reflux conditions.

[0047] In the present invention, the equation of the addition reaction is as follows:

[0048]

[0049] After the addition reaction is completed, the present invention preferably filters the obtained reaction mixture, washes it with water, methanol, and diethyl ether, and then purifies it by recrystallization to obtain a bis-palladium chloride-bridged dimer.

[0050] After obtaining the bis-palladium chloro-bridged dimer, the present invention mixes the bis-palladium chloro-bridged dimer, a dinitrogen ligand, a first polar solvent and an alkaline reagent to carry out a replacement reaction to obtain the cyclometallated palladium tetramer.

[0051] In the present invention, the molar ratio of the bis-palladium chloride bridge dimer to the dinitrogen ligand is 1:(1.1-2).

[0052] In the present invention, the alkaline agent is preferably potassium carbonate. In the present invention, the molar ratio of the bis-palladium chloride bridge dimer to the alkaline agent is preferably 1:(4-6), more preferably 1:5.

[0053] In the present invention, the type of the first polar solvent is 1,2-dichloroethane or chloroform; the replacement reaction is preferably carried out under light-proof conditions; the temperature of the replacement reaction is preferably 70-90° C.; and the replacement reaction time is 24 hours.

[0054] After the replacement reaction is completed, the present invention preferably filters the obtained reaction mixture, washes it with water, methanol, and diethyl ether, and then purifies it by recrystallization to obtain the cyclometalated palladium tetramer.

[0055] The present invention provides the use of the cyclometallated palladium tetramer described in the above scheme or the cyclometallated palladium tetramer prepared by the preparation method described in the above scheme in the emission layer of an organic light-emitting diode.

[0056] The cyclometallated palladium tetramer and its preparation method provided by the present invention are described in detail below with reference to the following examples, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] The synthetic route of cyclometallated palladium tetramer C1 is as follows:

[0059]

[0060] The specific preparation steps are as follows:

[0061] (i) Compound V-1 (232 mg, 1 mmol), sodium tetrachloropalladate (542 mg, 2 mmol), and tetramethylammonium chloride (2.18 g, 10 mmol) were placed in a Schlenk flask and pumped for 10 min. After the flask was filled with N2, 100 ml of degassed acetic acid was added to the flask. The flask was purged with N2 for 20 min and stirred at 120°C for 48 h. The solid product was filtered and washed three times with acetic acid, water, methanol, and ether to obtain a bis-palladium chloride-bridged dimer.

[0062] (ii) Bis-palladium chloride-bridged dimer III-1 (549 mg, 1 mmol), XX-1 (294 mg, 1.5 mmol), and potassium carbonate (829 mg, 6 mmol) were placed in a Schlenk flask and pumped for 10 min. After the flask was filled with N2, 100 ml of degassed 1,2-dichloroethane was added to the flask. The flask was purged with N2 for 20 min and stirred at 90°C for 24 h. The solid product was filtered and washed three times with water, methanol, and ether to obtain cyclometallated palladium tetramer C1.

[0063] Example 2

[0064] The synthetic route of cyclometallated palladium tetramer C2 is as follows:

[0065]

[0066] The specific preparation steps are similar to those in Example 1, with the only difference being that the dinitrogen ligand VII-1 is replaced by compound VIII-1.

[0067] Example 3

[0068] The synthetic route of cyclometallated palladium tetramer C3 is as follows:

[0069]

[0070] The specific preparation steps are similar to those in Example 1, except that the dinitrogen ligand VII-1 is replaced by compound Ix-1.

[0071] Example 4

[0072] The synthetic route of cyclometallated palladium tetramer C4 is as follows:

[0073]

[0074] The specific preparation steps are as described in Example 1, with the only difference being that compound V-1 is replaced by compound V-2.

[0075] Example 5

[0076] The synthetic route of cyclometallated palladium tetramer C5 is as follows:

[0077]

[0078] The specific preparation steps are as described in Example 1, with the only difference being that compound V-1 is replaced by compound V-2, and the dinitrogen ligand VII-1 is replaced by compound VIII-1.

[0079] Example 6

[0080] The synthetic route of cyclometallated palladium tetramer C6 is as follows:

[0081]

[0082] The specific preparation steps are as described in Example 1, with the only difference being that compound V-1 is replaced by compound V-2, and the dinitrogen ligand VII-1 is replaced by compound IX-1.

[0083] Example 7

[0084] The synthetic route of cyclometallated palladium tetramer C7 is as follows:

[0085]

[0086] The specific preparation steps are as follows:

[0087] (i) The specific preparation steps are as shown in Example 1(i).

[0088] (ii) A Schlenk flask was charged with bis-palladium chloride-bridged dimer IV-1 (577 mg, 1 mmol), XX-1 (294 mg, 1.5 mmol), and potassium carbonate (829 mg, 6 mmol). The mixture was pumped for 10 min. After the flask was filled with N2, 100 ml of degassed chloroform was added to the flask. The mixture was purged with N2 for 20 min and stirred at 70°C in the dark for 24 h. After completion of the reaction, the residue was rotary evaporated, extracted with dichloromethane, and then purified by column chromatography to obtain cyclometallated palladium tetramer C7.

[0089] Example 8

[0090] The synthetic route of cyclometallated palladium tetramer C8 is as follows:

[0091]

[0092] The specific preparation steps are as described in Example 7, with the only difference being that the dinitrogen ligand VII-1 is replaced by compound VIII-1.

[0093] Example 9

[0094] The synthetic route of cyclometallated palladium tetramer C9 is as follows:

[0095]

[0096] The specific preparation steps are as described in Example 7, with the only difference being that the dinitrogen ligand VII-1 is replaced by compound IX-1.

[0097] Structure and performance characterization:

[0098] The molecular structures of C1, C4 and C7 were analyzed by single crystal X-ray diffraction. The results are shown in the table below. Figures 1 to 3 . Figures 1 to 3 The thermal ellipsoid is drawn at a probability level of 30%. Hydrogen atoms are omitted for clarity. Figures 1 to 3 It can be seen that the target structure of the cyclometallated palladium tetramer was obtained.

[0099] The cyclometallated palladium tetramers C1, C4 and C7 were dissolved in dichloromethane and their UV-visible absorption spectra were measured at 25°C. Figure 4 .

[0100] The cyclometallated palladium tetramers C1, C4 and C7 were dissolved in dichloromethane and their normalized emission spectra at 25°C were measured. Figure 5 .

[0101] The normalized emission spectra of the cyclometallated palladium tetramers C1, C4, and C7 were measured at 25°C in the solid powder state. Figure 6 .

[0102] The luminescence properties of the cyclometallated palladium tetramer prepared in the present invention under the above-mentioned different states are summarized below, as shown in Table 1.

[0103] Table 1 Photophysical properties of cyclometallated palladium tetramers C1, C4, and C7.

[0104] Note: In Table 1, "a" represents measurements of the compound in dichloromethane at room temperature, and "b" represents measurements in N2-degassed CH2Cl2. "Em" stands for "emission wavelength," "Φ" stands for "phosphorescence quantum yield," "τ" stands for "phosphorescence lifetime," "Solid" stands for "solid state," and "CH2Cl2" stands for "liquid state." Phosphorescence quantum yields were measured using an integrating sphere. The radiative rate constant (Kr) and nonradiative rate constant (Knr) were estimated using the following equations: Kr = Φ / τ, Knr = (1-Φ) / τ.

[0105] As shown in Table 1, the cyclometallated palladium tetramer provided by the present invention has an excellent quantum yield and a phosphorescence lifetime at the micrometer level, indicating a long luminescence lifetime, which meets the preparation requirements of OLEDs devices.

Claims

1. A cyclometallated palladium tetramer, characterized in that Having the structure shown in any one of (I) to (II): Among them, the Include any of the following structures: R1 is H, methyl, trifluoromethyl, cyano, tert-butyl or phenyl; The R2 is H, alkyl or phenyl.

2. The cyclometallated palladium tetramer according to claim 1, characterized in that Having the structure represented by any one of (I-1), (I-2), (I-3), (II-1), (II-2), and (II-3):

3. The cyclometallated palladium tetramer according to claim 1 or 2, characterized in that Having the structure shown in any one of C1 to C9:

4. The method for preparing the cyclometallated palladium tetramer according to claims 1 to 3, comprising the following steps: A bispalladium chloride bridge dimer, a dinitrogen ligand, a first polar solvent and an alkaline reagent are mixed to carry out a displacement reaction to obtain the cyclometallated palladium tetramer; the bispalladium chloride bridge dimer has a structure shown in any one of the following: having a structure shown in any one of (III) to (IV): The dinitrogen ligand includes any one of the following structures:

5. The preparation method according to claim 4, characterized in that The molar ratio of the double palladium chloride bridge dimer to the double nitrogen ligand is 1:(1.1-2).

6. The preparation method according to claim 4, characterized in that The molar ratio of the double palladium chloride bridge dimer to the alkaline reagent is 1: (4-6).

7. The preparation method according to claim 4 or 6, characterized in that: The alkaline reagent is potassium carbonate.

8. The preparation method according to claim 4, characterized in that The polar organic solvent includes 1,2-dichloroethane or chloroform.

9. The preparation method according to claim 4, characterized in that The temperature of the replacement reaction is 70-120° C., and the time is 24 hours. The replacement reaction is carried out in a light-proof and protective atmosphere.

10. Use of the cyclometallated palladium tetramer according to any one of claims 1 to 3 or the cyclometallated palladium tetramer prepared by the preparation method according to any one of claims 4 to 9 in an emission layer of an organic light-emitting diode.

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