Patent Publication Number: US-2023144101-A1

Title: Light-emitting material with a polycyclic ligand

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation-in-part of U.S. application Ser. No. 17/241,836, filed Apr. 27, 2021 and entitled “LIGHT-EMITTING MATERIAL WITH A POLYCYCLIC LIGAND” which claims priority to Chinese Patent Application No. CN 202010362117.X filed on Apr. 30, 2020, Chinese Patent Application No. CN 202011219604.7 filed on Nov. 9, 2020, and Chinese Patent Application No. CN 202110348602.6 filed on Apr. 1, 2021, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to compounds used in organic electronic devices such as organic light-emitting devices. More particularly, the present disclosure relates to a metal complex with a polycyclic ligand and an electroluminescent device and a compound composition including the metal complex. 
     BACKGROUND 
     Organic electronic devices include, but are not limited to, the following types: organic light-emitting diodes (OLEDs), organic field-effect transistors (O-FETs), organic light-emitting transistors (OLETs), organic photovoltaic devices (OPVs), dye-sensitized solar cells (DSSCs), organic optical detectors, organic photoreceptors, organic field-quench devices (OFQDs), light-emitting electrochemical cells (LECs), organic laser diodes and organic plasmon emitting devices. 
     In 1987, Tang and Van Slyke of Eastman Kodak reported a bilayer organic electroluminescent device, which comprises an arylamine hole transporting layer and a tris-8-hydroxyquinolato-aluminum layer as the electron and emitting layer (Applied Physics Letters, 1987, 51 (12): 913-915). Once a bias is applied to the device, green light was emitted from the device. This device laid the foundation for the development of modern organic light-emitting diodes (OLEDs). State-of-the-art OLEDs may comprise multiple layers such as charge injection and transporting layers, charge and exciton blocking layers, and one or multiple emissive layers between the cathode and anode. Since the OLED is a self-emitting solid state device, it offers tremendous potential for display and lighting applications. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on flexible substrates. 
     The OLED can be categorized as three different types according to its emitting mechanism. The OLED invented by Tang and van Slyke is a fluorescent OLED. It only utilizes singlet emission. The triplets generated in the device are wasted through nonradiative decay channels. Therefore, the internal quantum efficiency (IQE) of the fluorescent OLED is only 25%. This limitation hindered the commercialization of OLED. In 1997. Forrest and Thompson reported phosphorescent OLED, which uses triplet emission from heavy metal containing complexes as the emitter. As a result, both singlet and triplets can be harvested, achieving 100% IQE. The discovery and development of phosphorescent OLED contributed directly to the commercialization of active-matrix OLED (AMOLED) due to its high efficiency. Recently, Adachi achieved high efficiency through thermally activated delayed fluorescence (TADF) of organic compounds. These emitters have small singlet-triplet gap that makes the transition from triplet back to singlet possible. In the TADF device, the triplet excitons can go through reverse intersystem crossing to generate singlet excitons, resulting in high IQE. 
     OLEDs can also be classified as small molecule and polymer OLEDs according to the forms of the materials used. A small molecule refers to any organic or organometallic material that is not a polymer. The molecular weight of the small molecule can be large as long as it has well defined structure. Dendrimers with well-defined structures are considered as small molecules. Polymer OLEDs include conjugated polymers and non-conjugated polymers with pendant emitting groups. Small molecule OLED can become the polymer OLED if post polymerization occurred during the fabrication process. 
     There are various methods for OLED fabrication. Small molecule OLEDs are generally fabricated by vacuum thermal evaporation. Polymer OLEDs are fabricated by solution process such as spin-coating, inkjet printing, and slit printing. If the material can be dissolved or dispersed in a solvent, the small molecule OLED can also be produced by solution process. 
     The emitting color of the OLED can be achieved by emitter structural design. An OLED may comprise one emitting layer or a plurality of emitting layers to achieve desired spectrum. In the case of green, yellow, and red OLEDs, phosphorescent emitters have successfully reached commercialization. Blue phosphorescent device still suffers from non-saturated blue color, short device lifetime, and high operating voltage. Commercial full-color OLED displays normally adopt a hybrid strategy, using fluorescent blue and phosphorescent yellow, or red and green. At present, efficiency roll-off of phosphorescent OLEDs at high brightness remains a problem. In addition, it is desirable to have more saturated emitting color, higher efficiency, and longer device lifetime. 
     Phosphorescent metal complexes can be used as phosphorescent doping materials of light-emitting layers and applied to the field of organic electroluminescence lighting or display. 
     CN110698518A discloses a metal complex with a structure of 
     
       
         
         
             
             
         
       
     
     wherein X is N or P. One of many structures disclosed is 
     
       
         
         
             
             
         
       
     
     This disclosure has discussed the improvement in performance of materials due to bridge connection via an N or P atom. However, it does not notice the performance improvement brought by the further introduction of a fused ring system at a specific position of a specific ring. 
     CN110790797A discloses a metal complex with a structure of 
     
       
         
         
             
             
         
       
     
     One of many structures disclosed is 
     
       
         
         
             
             
         
       
     
     This disclosure has discussed the improvement in performance of materials due to bridge connection via an O or S atom. However, it does not notice the performance improvement brought by the further introduction of a fused ring system at a specific position of a specific ring. 
     Phosphorescent metal complexes can be used as phosphorescent doping materials of light-emitting layers and applied to the field of organic electroluminescence lighting or display. The currently developed metal complexes still have various deficiencies in performance when used in electroluminescent devices. To meet the increasing requirements of the industry such as lower voltage, higher device efficiency, light-emitting color within a particular wavelength range, more saturated light-emitting color, and longer device lifetime, the research and development related to metal complexes still needs to be deepened. 
     SUMMARY 
     The present disclosure aims to provide a series of metal complexes having a polycyclic ligand(s) to solve at least part of the above-mentioned problems. The metal complexes can be used as light-emitting materials in organic electroluminescent devices. While maintaining a very narrow full width at half maximum (FWHM), these novel metal complexes can better adjust the light-emitting colors of the devices, reduce the driving voltages of the devices or maintain the driving voltages of the devices at low voltage levels, improve the efficiency of the devices, and greatly increase the lifetimes of the devices. These novel metal complexes can provide better device performance. 
     According to an embodiment of the present disclosure, disclosed is a metal complex including a ligand L a  having a structure represented by Formula 1: 
     
       
         
         
             
             
         
       
         
         
           
             wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 30 carbon atoms, or a heteroaromatic ring having 3 to 30 carbon atoms; 
             R i  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; and R ii  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
             Y is selected from SiR y R y , GeR y R y , NR y , PR y , O, S or Se; 
             when two R y  are present at the same time, the two R y  may be the same or different; 
             X 1  and X 2  are, at each occurrence identically or differently, selected from CR x  or N; 
             R, R i , R ii , R x , and R y  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             adjacent substituents R i , R x , R y , R and R ii  can be optionally joined to form a ring; 
             the metal is selected from a metal with a relative atomic mass greater than 40. 
           
         
       
    
     According to another embodiment of the present disclosure, further disclosed is an electroluminescent device including an anode, a cathode and an organic layer disposed between the anode and the cathode, wherein the organic layer includes a metal complex including a ligand L a , having a structure represented by Formula 1: 
     
       
         
         
             
             
         
       
         
         
           
             wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 30 carbon atoms, or a heteroaromatic ring having 3 to 30 carbon atoms; 
             R i  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; and R ii  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
             Y is selected from SiR y R y , GeR y R y , NR y , PR y , O, S or Se; 
             when two R y  are present at the same time, the two R y  may be the same or different; 
             X 1  and X 2  are, at each occurrence identically or differently, selected from CR x  or N; 
             R, R i , R ii , R x , and R y , are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             adjacent substituents R i , R x , R y , R and R ii  can be optionally joined to form a ring; 
             the metal is selected from a metal with a relative atomic mass greater than 40. 
           
         
       
    
     According to another embodiment of the present disclosure, further disclosed is a compound composition including the metal complex described in the preceding embodiments. 
     The novel metal complexes having a polycyclic ligand(s), as disclosed by the present disclosure, may be used as light-emitting materials in electroluminescent devices. While maintaining a very narrow FWHM, these novel metal complexes can better adjust the light-emitting colors of the devices, reduce the driving voltages of the devices or maintain the driving voltages of the devices at low voltage levels, improve the efficiency of the devices, and greatly increase the lifetimes of the devices. These novel metal complexes can provide better device performance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram of an organic light-emitting apparatus that may include a metal complex and a compound composition disclosed herein. 
         FIG.  2    is a schematic diagram of another organic light-emitting apparatus that may include a metal complex and a compound composition disclosed herein. 
         FIG.  3    is a diagram illustrating Formula 1 of the ligand L a , of a metal complex disclosed herein. 
         FIG.  4    is a structure diagram of a typical top-emitting OLED device that may include a metal complex and a compound combination disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     OLEDs can be fabricated on various types of substrates such as glass, plastic, and metal foil.  FIG.  1    schematically shows an organic light emitting device  100  without limitation. The figures are not necessarily drawn to scale. Some of the layers in the figures can also be omitted as needed. Device  100  may include a substrate  101 , an anode  110 , a hole injection layer  120 , a hole transport layer  130 , an electron blocking layer  140 , an emissive layer  150 , a hole blocking layer  160 , an electron transport layer  170 , an electron injection layer  180  and a cathode  190 . Device  100  may be fabricated by depositing the layers described in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, the contents of which are incorporated by reference herein in its entirety. 
     More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference herein in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F 4 -TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference herein in its entirety. Examples of host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference herein in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference herein in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference herein in their entireties, disclose examples of cathodes including composite cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers are described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference herein in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference herein in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference herein in its entirety. 
     A structure of a typical top-emitting OLED device is shown in  FIG.  4   . An OLED device  300  comprises an anode layer  301 , a hole injection layer (HIL0)  302 , a first hole transport layer (HTL1)  303 , a second hole transport layer (HTL2)  304  (also referred to as a prime layer), an emissive layer (EML)  305 , a hole blocking layer (HBL)  306  (as an optional layer), an electron transport layer (ETL)  307 , an electron injection layer (EIL)  308 , a cathode layer  309  and a capping layer  310 . The anode layer  301  is a material or a combination of materials having a high reflectivity, including but not limited to Ag, Al, Ti, Cr, Pt, Ni, TiN and a combination of the above materials with ITO and/or MoOx (molybdenum oxide). Generally, the reflectivity of the anode is greater than 50%; preferably, the reflectivity of the anode is greater than 70%; more preferably, the reflectivity of the anode is greater than 80%. The cathode layer  309  should be a translucent or transparent conductive material, including but not limited to a MgAg alloy. MoOx, Yb, Ca, ITO, IZO or a combination thereof and having an average transmittance of greater than 15% for light having a wavelength in a visible region; preferably, the average transmittance for the light having the wavelength in the visible region is greater than 20%; more preferably, the average transmittance for the light having the wavelength in the visible region is greater than 25%. 
     The layered structure described above is provided by way of non-limiting examples. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely. It may also include other layers not specifically described. Within each layer, a single material or a mixture of multiple materials can be used to achieve optimum performance. Any functional layer may include several sublayers. For example, the emissive layer may have two layers of different emitting materials to achieve desired emission spectrum. 
     In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer or multiple layers. 
     An OLED can be encapsulated by a barrier layer.  FIG.  2    schematically shows an organic light emitting device  200  without limitation.  FIG.  2    differs from  FIG.  1    in that the organic light emitting device include a barrier layer  102 , which is above the cathode  190 , to protect it from harmful species from the environment such as moisture and oxygen. Any material that can provide the barrier function can be used as the barrier layer such as glass or organic-inorganic hybrid layers. The barrier layer should be placed directly or indirectly outside of the OLED device. Multilayer thin film encapsulation was described in U.S. Pat. No. 7,968,146, which is incorporated by reference herein in its entirety. 
     Devices fabricated in accordance with embodiments of the present disclosure can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. Some examples of such consumer products include flat panel displays, monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, smart phones, tablets, phablets, wearable devices, smart watches, laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles displays, and vehicle tail lights. 
     The materials and structures described herein may be used in other organic electronic devices listed above. 
     As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from the substrate. There may be other layers between the first and second layers, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between. 
     As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form. 
     A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand. 
     It is believed that the internal quantum efficiency (IQE) of fluorescent OLEDs can exceed the 25% spin statistics limit through delayed fluorescence. As used herein, there are two types of delayed fluorescence, i.e. P-type delayed fluorescence and E-type delayed fluorescence. P-type delayed fluorescence is generated from triplet-triplet annihilation (TTA). 
     On the other hand, E-type delayed fluorescence does not rely on the collision of two triplets, but rather on the transition between the triplet states and the singlet excited states. Compounds that are capable of generating E-type delayed fluorescence are required to have very small singlet-triplet gaps to convert between energy states. Thermal energy can activate the transition from the triplet state back to the singlet state. This type of delayed fluorescence is also known as thermally activated delayed fluorescence (TADF). A distinctive feature of TADF is that the delayed component increases as temperature rises. If the reverse intersystem crossing rate is fast enough to minimize the non-radiative decay from the triplet state, the fraction of back populated singlet excited states can potentially reach 75%. The total singlet fraction can be 100%, far exceeding 25% of the spin statistics limit for electrically generated excitons. 
     E-type delayed fluorescence characteristics can be found in an exciplex system or in a single compound. Without being bound by theory, it is believed that E-type delayed fluorescence requires the luminescent material to have a small singlet-triplet energy gap (ΔE S-T ). Organic, non-metal containing, donor-acceptor luminescent materials may be able to achieve this. The emission in these materials is generally characterized as a donor-acceptor charge-transfer (CT) type emission. The spatial separation of the HOMO and LUMO in these donor-acceptor type compounds generally results in small ΔE S-T . These states may involve CT states. Generally, donor-acceptor luminescent materials are constructed by connecting an electron donor moiety such as amino- or carbazole-derivatives and an electron acceptor moiety such as N-containing six-membered aromatic rings. 
     Definition of Terms of Substituents 
     Halogen or halide—as used herein includes fluorine, chlorine, bromine, and iodine. 
     Alkyl—contemplates both straight and branched chain alkyl groups. The alkyl group may be an alkyl group having 1 to 20 carbon atoms, preferably an alkyl group having 1 to 12 carbon atoms, and more preferably an alkyl group having 1 to 6 carbon atoms. Examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, neopentyl group, 1-methylpentyl group, 2-methylpentyl group, 1-pentylhexyl group, l-butylpentyl group, 1-heptyloctyl group, and 3-methylpentyl group. Additionally, the alkyl group may be optionally substituted. The carbons in the alkyl chain can be replaced by other hetero atoms. Of the above, preferred are methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, n-pentyl group, and neopentyl group. 
     Cycloalkyl—as used herein contemplates cyclic alkyl groups. Preferred cycloalkyl groups are those containing 4 to 10 ring carbon atoms and include cyclobutyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, 4,4-dimethylcylcohexyl, 1-adamantyl, 2-adamantyl, 1-norbornyl, 2-norbornyl and the like. Additionally, the cycloalkyl group may be optionally substituted. The carbons in the ring can be replaced by other hetero atoms. 
     Heteroalkyl—as used herein, includes a group formed by replacing one or more carbons in an alkyl chain with a hetero-atom(s) selected from the group consisting of a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a phosphorus atom, a silicon atom, a germanium atom, and a boron atom. Heteroalkyl may be those having 1 to 20 carbon atoms, preferably those having 1 to 10 carbon atoms, and more preferably those having 1 to 6 carbon atoms. Examples of heteroalkyl include methoxymethyl, ethoxymethyl, ethoxyethyl, methylthiomethyl, ethylthiomethyl, ethylthioethyl, methoxymethoxymethyl, ethoxymethoxymethyl, ethoxyethoxyethyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, mercaptomethyl, mercaptoethyl, mercaptopropyl, aminomethyl, aminoethyl, aminopropyl, dimethylaminomethyl, trimethylgermanylmethyl, trimethylgermanylethyl, trimethylgermanylisopropyl, dimethylethylgermanylmethyl, dimethylisopropylgermanylmethyl, tert-butyldimethylgermanylmethyl, triethylgermanylmethyl, triethylgermanylethyl, triisopropylgermanylmethyl, triisopropylgermanylethyl, trimethylsilylmethyl, trimethylsilylethyl, trimethylsilylisopropyl, triisopropylsilylmethyl, and triisopropylsilylethyl. Additionally, the heteroalkyl group may be optionally substituted. Additionally, the heteroalkyl group may be optionally substituted. 
     Alkenyl—as used herein contemplates both straight and branched chain alkene groups. Preferred alkenyl groups are those containing 2 to 15 carbon atoms. Examples of the alkenyl group include vinyl group, allyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1,3-butandienyl group, 1-methylvinyl group, styryl group, 2,2-diphenylvinyl group, 1,2-diphenylvinyl group, I-methylallyl group, 1,1-dimethylallyl group, 2-methylallyl group, 1-phenylallyl group, 2-phenylallyl group, 3-phenylallyl group, 3,3-diphenylallyl group, 1,2-dimethylallyl group, I-phenyll-butenyl group, and 3-phenyl-1-butenyl group. Additionally, the alkenyl group may be optionally substituted. 
     Alkynyl—as used herein contemplates both straight and branched chain alkyne groups. Preferred alkynyl groups are those containing 2 to 15 carbon atoms. Additionally, the alkynyl group may be optionally substituted. 
     Aryl or aromatic group—as used herein includes noncondensed and condensed systems. Preferred aryl groups are those containing six to sixty carbon atoms, preferably six to twenty carbon atoms, more preferably six to twelve carbon atoms. Examples of the aryl group include phenyl, biphenyl, terphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl, biphenyl, terphenyl, triphenylene, fluorene, and naphthalene. Additionally, the aryl group may be optionally substituted. Examples of the non-condensed aryl group include phenyl group, biphenyl-2-yl group, biphenyl-3-yl group, biphenyl-4-yl group, p-terphenyl-4-yl group, p-terphenyl-3-yl group, p-terphenyl-2-yl group, m-terphenyl-4-yl group, m-terphenyl-3-yl group, m-terphenyl-2-yl group, o-tolyl group, m-tolyl group, p-tolyl group, p-t-butylphenyl group, p-(2-phenylpropyl)phenyl group, 4′-methylbiphenylyl group, 4″-t-butyl p-terphenyl-4-yl group, o-cumenyl group, m-cumenyl group, p-cumenyl group, 2,3-xylyl group, 3,4-xylyl group, 2,5-xylyl group, mesityl group, and m-quarterphenyl group. 
     Heterocyclic group or heterocycle—as used herein includes aromatic and non-aromatic cyclic groups. Hetero-aromatic also means heteroaryl. Preferred non-aromatic heterocyclic groups are those containing 3 to 7 ring atoms which include at least one hetero atom such as nitrogen, oxygen, and sulfur. The heterocyclic group can also be an aromatic heterocyclic group having at least one heteroatom selected from nitrogen atom, oxygen atom, sulfur atom, and selenium atom. 
     Heteroaryl—as used herein includes noncondensed and condensed hetero-aromatic groups that may include from one to five heteroatoms. Preferred heteroaryl groups are those containing three to thirty carbon atoms, preferably three to twenty carbon atoms, more preferably three to twelve carbon atoms. Suitable heteroaryl groups include dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine, preferably dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, triazine, benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogs thereof. Additionally, the heteroaryl group may be optionally substituted. 
     Alkoxy—it is represented by —O-Alkyl. Examples and preferred examples thereof are the same as those described above. Examples of the alkoxy group having 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms include methoxy group, ethoxy group, propoxy group, butoxy group, pentyloxy group, and hexyloxy group. The alkoxy group having 3 or more carbon atoms may be linear, cyclic or branched. 
     Aryloxy—it is represented by —O-Aryl or —O-heteroaryl. Examples and preferred examples thereof are the same as those described above. Examples of the aryloxy group having 6 to 40 carbon atoms include phenoxy group and biphenyloxy group. 
     Arylalkyl—as used herein contemplates an alkyl group that has an aryl substituent. Additionally, the arylalkyl group may be optionally substituted. Examples of the arylalkyl group include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 1-phenylisopropyl group, 2-phenylisopropyl group, phenyl-t-butyl group, alpha.-naphthylmethyl group, 1-alpha-naphthylethyl group, 2-alpha-naphthylethyl group, 1-alpha-naphthylisopropyl group, 2-alpha-naphthylisopropyl group, beta-naphthylmethyl group, 1-beta-naphthylethyl group, 2-beta-naphthylethyl group, l-beta-naphthylisopropyl group, 2-beta-naphthylisopropyl group, p-methylbenzyl group, m-methylbenzyl group, o-methylbenzyl group, p-chlorobenzyl group, m-chlorobenzyl group, o-chlorobenzyl group, p-bromobenzyl group, m-bromobenzyl group, o-bromobenzyl group, p-iodobenzyl group, m-iodobenzyl group, o-iodobenzyl group, p-hydroxybenzyl group, m-hydroxybenzyl group, o-hydroxybenzyl group, p-aminobenzyl group, m-aminobenzyl group, o-aminobenzyl group, p-nitrobenzyl group, m-nitrobenzyl group, o-nitrobenzyl group, p-cyanobenzyl group, m-cyanobenzyl group, o-cyanobenzyl group, I-hydroxy-2-phenylisopropyl group, and 1-chloro-2-phenylisopropyl group. Of the above, preferred are benzyl group, p-cyanobenzyl group, m-cyanobenzyl group, o-cyanobenzyl group, I-phenylethyl group, 2-phenylethyl group, l-phenylisopropyl group, and 2-phenylisopropyl group. 
     Alkylgermanyl—as used herein contemplates a germanyl substituted with an alkyl group. The alkylgermanyl may be those having 3 to 20 carbon atoms, preferably those having 3 to 10 carbon atoms. Examples of alkylgermanyl include trimethylgermanyl, triethylgermanyl, methyldiethylgermanyl, ethyldimethylgermanyl, tripropylgermanyl, tributylgermanyl, triisopropylgermanyl, methyldiisopropylgermanyl, dimethylisopropylgermanyl, tri-t-butylgermanyl, triisobutylgermanyl, dimethyl-t-butylgermanyl, and methyldi-t-butylgermanyl. Additionally, the alkylgermanyl may be optionally substituted. 
     Arylgermanyl—as used herein contemplates a germanyl substituted with at least one aryl group or heteroaryl group. Arylgermanyl may be those having 6 to 30 carbon atoms, preferably those having 8 to 20 carbon atoms. Examples of arylgermanyl include triphenylgermanyl, phenyldibiphenylylgermanyl, diphenylbiphenylgermanyl, phenyldiethylgermanyl, diphenylethylgermanyl, phenyldimethylgermanyl, diphenylmethylgermanyl, phenyldiisopropylgermanyl, diphenylisopropylgemianyl, diphenylbutylgermanyl, diphenylisobutylgermanyl, and diphenyl-t-butylgermanyl. Additionally, the arylgermanyl may be optionally substituted. 
     The term “aza” in azadibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective aromatic fragment are replaced by a nitrogen atom. For example, azatriphenylene encompasses dibenzo[f,h]quinoxaline, dibenzo[f,h]quinoline and other analogues with two or more nitrogens in the ring system. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein. 
     In the present disclosure, unless otherwise defined, when any term of the group consisting of substituted alkyl, substituted cycloalkyl, substituted heteroalkyl, substituted arylalkyl, substituted alkoxy, substituted aryloxy, substituted alkenyl, substituted aryl, substituted heteroaryl, substituted alkylsilyl, substituted arylsilyl, substituted amino, substituted acyl, substituted carbonyl, substituted carboxylic acid group, substituted ester group, substituted sulfinyl, substituted sulfonyl and substituted phosphino is used, it means that any group of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, alkenyl, aryl, heteroaryl, alkylsilyl, arylsilyl, amino, acyl, carbonyl, carboxylic acid group, ester group, sulfinyl, sulfonyl and phosphino may be substituted with one or more groups selected from the group consisting of deuterium, a halogen, an unsubstituted alkyl group having 1 to 20 carbon atoms, an unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, an unsubstituted heteroalkyl group having 1 to 20 carbon atoms, an unsubstituted arylalkyl group having 7 to 30 carbon atoms, an unsubstituted alkoxy group having 1 to 20 carbon atoms, an unsubstituted aryloxy group having 6 to 30 carbon atoms, an unsubstituted alkenyl group having 2 to 20 carbon atoms, an unsubstituted aryl group having 6 to 30 carbon atoms, an unsubstituted heteroaryl group having 3 to 30 carbon atoms, an unsubstituted alkylsilyl group having 3 to 20 carbon atoms, an unsubstituted arylsilyl group having 6 to 20 carbon atoms, an unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group and a phosphino group, and combinations thereof. 
     It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent. 
     In the compounds mentioned in the present disclosure, the hydrogen atoms can be partially or fully replaced by deuterium. Other atoms such as carbon and nitrogen can also be replaced by their other stable isotopes. The replacement by other stable isotopes in the compounds may be preferred due to its enhancements of device efficiency and stability. 
     In the compounds mentioned in the present disclosure, multiple substitutions refer to a range that includes a double substitution, up to the maximum available substitutions. When a substitution in the compounds mentioned in the present disclosure represents multiple substitutions (including di, tri, tetra substitutions etc.), that means the substituent may exist at a plurality of available substitution positions on its linking structure, the substituents present at a plurality of available substitution positions may be the same structure or different structures. 
     In the compounds mentioned in the present disclosure, adjacent substituents in the compounds cannot connect to form a ring unless otherwise explicitly defined, for example, adjacent substituents can be optionally joined to form a ring. In the compounds mentioned in the present disclosure, adjacent substituents can be optionally joined to form a ring, including both the case where adjacent substituents can be joined to form a ring, and the case where adjacent substituents are not joined to form a ring. When adjacent substituents can be optionally joined to form a ring, the ring formed may be monocyclic or polycyclic, as well as alicyclic, heteroalicyclic, aromatic or heteroaromatic. In such expression, adjacent substituents may refer to substituents bonded to the same atom, substituents bonded to carbon atoms which are directly bonded to each other, or substituents bonded to carbon atoms which are more distant from each other. Preferably, adjacent substituents refer to substituents bonded to the same carbon atom and substituents bonded to carbon atoms which are directly bonded to each other. 
     The expression that adjacent substituents can be optionally joined to form a ring is also intended to mean that two substituents bonded to the same carbon atom are joined to each other via a chemical bond to form a ring, which can be exemplified by the following formula: 
     
       
         
         
             
             
         
       
     
     The expression that adjacent substituents can be optionally joined to form a ring is also intended to mean that two substituents bonded to carbon atoms which are directly bonded to each other are joined to each other via a chemical bond to form a ring, which can be exemplified by the following formula: 
     
       
         
         
             
             
         
       
     
     Furthermore, the expression that adjacent substituents can be optionally joined to form a ring is also intended to mean that, in the case where one of the two substituents bonded to carbon atoms which are directly bonded to each other represents hydrogen, the second substituent is bonded at a position at which the hydrogen atom is bonded, thereby forming a ring. This is exemplified by the following formula: 
     
       
         
         
             
             
         
       
     
     According to an embodiment of the present disclosure, disclosed is a metal complex including a ligand L a  having a structure represented by Formula 1: 
     
       
         
         
             
             
         
       
         
         
           
             wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 30 carbon atoms, or a heteroaromatic ring having 3 to 30 carbon atoms; 
             R i  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; and R ii  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
             Y is selected from SiR y R y , GeR y R y , NR y , PR y , O, S or Se; 
             when two R y  are present at the same time, the two R y  may be the same or different; for example, when Y is selected from SiR y R y , the two R y  may be the same or different; in another example, when Y is selected from GeR y R y , the two R y  may be the same or different; 
             X 1  and X 2  are, at each occurrence identically or differently, selected from CR x  or N; 
             R, R i , R ii , R x , and R y  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             adjacent substituents R i , R x , R y , R and R ii  can be optionally joined to form a ring; 
             the metal is selected from a metal with a relative atomic mass greater than 40. 
           
         
       
    
     In the present disclosure, the expression that adjacent substituents R i , R x , R y , R and R; can be optionally joined to form a ring is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R i , two substituents R ii , two substituents R y , two substituents R x , substituents R i  and R x , substituents R and R y , and substituents R ii  and R, can be joined to form a ring. Obviously, these substituents may not be joined to form a ring. 
     According to an embodiment of the present disclosure, wherein the metal complex optionally contains other ligand(s) which is(are) optionally joined to the L a  to form a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand. 
     According to an embodiment of the present disclosure, wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 18 carbon atoms, or a heteroaromatic ring having 3 to 18 carbon atoms. 
     According to an embodiment of the present disclosure, wherein the ring A or the ring B is each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 18 carbon atoms, or a heteroaromatic ring having 3 to 18 carbon atoms. 
     According to an embodiment of the present disclosure, wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 10 carbon atoms, or a heteroaromatic ring having 3 to 10 carbon atoms. 
     According to an embodiment of the present disclosure, wherein the ring A or the ring B is each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 10 carbon atoms, or a heteroaromatic ring having 3 to 10 carbon atoms. 
     According to an embodiment of the present disclosure, wherein the L a  is selected from a structure represented by any one of Formula 2 to Formula 19 and Formula 22 to Formula 23: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
         
         
           
             wherein 
             in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  and X 2  are each independently selected from CR x  or N; X 3  to X 7  are each independently selected from CR i  or N; and A 1  to A 6  are each independently selected from CR ii  or N; 
             Z is, at each occurrence identically or differently, selected from CR iii R iii , SiR iii , R iii , PR iii , O, S or NR m ; when two R m  are present at the same time, the two R m  are the same or different; for example, when Z is selected from CR iii R iii , the two R iii , are the same or different; in another example, when Z is selected from SiR iii R iii , the two R iii  are the same or different; 
             Y is selected from SiR y R y , NR y , PR y , O, S or Se; when two R y  are present at the same time, the two R y  may be the same or different; for example, when Y is selected from SiR y R y , the two R y  may be the same or different; 
             R, R i , R ii , R x , R y  and R iii  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             adjacent substituents R, R x , R y , R i , R ii  and R iii  can be optionally joined to form a ring. 
           
         
       
    
     In the present disclosure, the expression that adjacent substituents R, R x , R y , R i , R ii  and R iii , can be optionally joined to form a ring is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R i , two substituents R ii , two substituents R x , two substituents R y , two substituents R iii , substituents R i  and R x , substituents R ii  and R iii , substituents R and R y , substituents R y  and R iii , and substituents R and R iii , can be joined to form a ring. Obviously, these substituents may not be joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, L a  is selected from a structure represented by Formula 2, Formula 9, Formula 11 or Formula 12. 
     According to an embodiment of the present disclosure, wherein, L a  is selected from a structure represented by Formula 2. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, at least one of X 1  to X n  and/or A 1  to A m  is selected from N, wherein the X n  corresponds to one with the largest number of X 1  to X 7  in any one of Formula 2 to Formula 19 and Formula 22 to Formula 23, and the A m  corresponds to one with the largest number of A 1  to A 6  in any one of Formula 2 to Formula 19 and Formula 22 to Formula 23. For example, in the case of Formula 2, the X n  corresponds to one with the largest number of X 1  to X 7  in Formula 2, that is X 5 ; and the A m , corresponds to one with the largest number of A 1  to A 6  in Formula 2, that is A 4 . That is, in Formula 2, at least one of X 1  to X 5  and/or A 1  to A 4  is selected from N. In another example, in the case of Formula 12, the X n  corresponds to one with the largest number of X 1  to X 7  in Formula 12, that is X 3 ; and the A m  corresponds to one with the largest number of A 1  to A 6  in Formula 12, that is A 4 . That is, in Formula 12, at least one of X 1  to X 3  and/or A 1  to A 4  is selected from N. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, at least one of X 1  to X n  is selected from N, wherein the X n  corresponds to one with the largest number of X 1  to X 7  in any one of Formula 2 to Formula 19 and Formula 22 to Formula 23. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 2  is N. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  and X 2  are each independently selected from CR x ; X 3  to X 7  are each independently selected from CR i ; A 1  to A 6  are each independently selected from CR ii ; and adjacent substituents R x , R i , R ii  can be optionally joined to form a ring. 
     In this embodiment, the expression that adjacent substituents R x , R i , R ii  can be optionally joined to form a ring is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R i , two substituents R ii , two substituents R x , and substituents R i  and R x , can be joined to form a ring. Obviously, these substituents may not be joined to form a ring. 
     According to an embodiment of the present disclosure, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  and X 2  are each independently selected from CR x ; X 3  to X 7  are each independently selected from CR i ; and A 1  to A 6  are each independently selected from CR ii ; and the R x , R i  and R ii  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group and combinations thereof; and adjacent substituents R x , R i , R ii  can be optionally joined to form a ring. 
     According to an embodiment of the present disclosure, in Formula 2 to Formula 19 and Formula 22 to Formula 23. X 1  and X 2  are each independently selected from CR x ; X 3  to X 7  are each independently selected from CR i ; and A 1  to A 6  are each independently selected from CR ii ; and at least two of the R x , R i  and R ii  are, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group and combinations thereof; and adjacent substituents R x , R i , R ii  can be optionally joined to form a ring. 
     In this embodiment, the expression that at least two of the R x , R i  and R ii  are, at each occurrence identically or differently, selected from the group of substituents is intended to mean that at least two substituents in the group consisting of two substituents R x , all substituents R; and all substituents R ii  are, at each occurrence identically or differently, selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  and X 2  are each independently selected from CR x ; X 3  to X 7  are each independently selected from CR i ; and A 1  to A 6  are each independently selected from CR ii ; and at least three of the R x , R i  and R ii  are, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group and combinations thereof; and adjacent substituents R x , R i , R ii  can be optionally joined to form a ring. 
     In this embodiment, the expression that at least three of the R x , R i  and R ii  are, at each occurrence identically or differently, selected from the group of substituents is intended to mean that at least three substituents in the group consisting of two substituents R x  all substituents R i  and all substituents R ii  are, at each occurrence identically or differently, selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 11 and Formula 22 to Formula 23, X 4  and X 5  are each independently selected from CR i , and in Formula 12 to Formula 19, X 3  is selected from CR i . 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 11 and Formula 22 to Formula 23, X 4  or X 5  is selected from CR i ; and in Formula 12 to Formula 19, X 3  is selected from CR i . 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 11 and Formula 22 to Formula 23, X 4  and X 5  are each independently selected from CR i ; and in Formula 12 to Formula 19, X 3  is selected from CR i ; and the R i  is, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 11 and Formula 22 to Formula 23, X 4  or X 5  is selected from CR i , and in Formula 12 to Formula 19, X 3  is selected from CR i ; and the R i  is, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 11 and Formula 22 to Formula 23, X 4  and X 5  are each independently selected from CR i ; and in Formula 12 to Formula 19, X 3  is selected from CR i ; and the R i  is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, t-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, norbornyl, adamantyl, trimethylsilyl, isopropyldimethylsilyl, phenyldimethylsilyl, trifluoromethyl, cyano, phenyl and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 11 and Formula 22 to Formula 23, X 4  or X 5  is selected from CR i ; and in Formula 12 to Formula 19, X 3  is selected from CR i ; and the R i  is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, t-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, norbornyl, adamantyl, trimethylsilyl, isopropyldimethylsilyl, phenyldimethylsilyl, trifluoromethyl, cyano, phenyl and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, R is selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, R is selected from hydrogen, deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, t-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, deuterated methyl, deuterated ethyl, deuterated isopropyl, deuterated t-butyl, deuterated neopentyl, deuterated cyclopentyl, deuterated cyclopentylmethyl, deuterated cyclohexyl, trimethylsilyl or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, Y is selected from O or S. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, Y is selected from O. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  and X 2  are each independently selected from CR x . 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  and X 2  are each independently selected from CR x ; and the R x  is, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  is selected from CR x  and X 2  is N. 
     According to an embodiment of the present disclosure, wherein, in Formula 2 to Formula 19 and Formula 22 to Formula 23, X 1  is selected from CR x  and X 2  is N; and the R x  is, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 20 or Formula 21: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 20 and Formula 21, 
             Y is selected from O or S; 
             R x1 , R x2 , R i1 , R i2 , R i3 , R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; 
             R is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, the ligand L a  has a structure represented by Formula 20 or Formula 21: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 20 and Formula 21, 
             Y is selected from O or S; 
             at least one or two of R x1 , R x2 , R i1 , R i2  and R i3  and/or of R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof; R is selected from halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 20 or Formula 21: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 20 and Formula 21, 
             Y is selected from O or S; 
             at least one or two of R x1 , R x2 , R i1 , R i2  and R i3  and/or of R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; R is selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 20 or Formula 21: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 20 and Formula 21, 
             Y is selected from O or S; 
             R i2  is selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; and 
             R is selected from the group consisting of: halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; and at least one or two of R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 20 or Formula 21: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 20 and Formula 21, 
             Y is selected from O or S; 
             R i2  is selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atones, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; and 
             R is selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; and at least one or two of R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, in Formula 20 and Formula 21, one (for example R ii1  or R ii2  or R ii3 ) or two (for example, R ii1  and R ii2 , or R ii2  and R ii3 , or R ii1  and R ii3 ) of R ii1 , R ii2  and R ii3  are, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 20 and Formula 21, at least one of R x1 , R x2 . R i1 , R i2 , R i3 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 3 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms and combinations thereof. 
     In this embodiment, the expression that at least one of R x1 , R x2 , R i1 , R i2 , R i3 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group of substituents is intended to mean that: at least one of R x1  and R x2  is, at each occurrence identically or differently, selected from the group of substituents, and/or at least one of R i1 , R i2  and R i3  is, at each occurrence identically or differently, selected from the group of substituents, and/or at least one of R ii1 , R ii2 , R ii3  and R ii4  is, at each occurrence identically or differently, selected from the group of substituents, and/or R is selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 20 and Formula 21, at least one of R i2 , R i3 , R ii1 , R ii2 , R ii3  and R is, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 3 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms and combinations thereof. 
     In this embodiment, the expression that at least one of R i2 , R i3 , R ii1 , R ii2 , R ii3  and R is, at each occurrence identically or differently, selected from the group of substituents is intended to mean that: at least one of R i2  and R i3  is, at each occurrence identically or differently, selected from the group of substituents, and/or at least one of R ii1 , R ii2  and R ii3  is, at each occurrence identically or differently, selected from the group of substituents, and/or R is selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 20 and Formula 21, at least one of R x1 , R x2 , R i1 , R i2 , R i3 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 ring carbon atoms and combinations thereof. 
     In this embodiment, the expression that at least one of R x1 , R x2 , R i1 , R i2 , R i3 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group of substituents is intended to mean that: at least one of R x1  and R x2  is, at each occurrence identically or differently, selected from the group of substituents, and/or at least one of R i1 , R i2  and R i3  is, at each occurrence identically or differently, selected from the group of substituents, and/or at least one of R ii1 , R ii2 , R ii3  and R ii4  is, at each occurrence identically or differently, selected from the group of substituents, and/or R is selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, L a  is, at each occurrence identically or differently, selected from the group consisting of L a1  to L a1706 , wherein the specific structures of the L a1  to L a1706  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, L a  is, at each occurrence identically or differently, selected from the group consisting of L a1  to L a1803 , wherein the specific structures of the L a1  to L a1706  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, L a  is, at each occurrence identically or differently, selected from the group consisting of L a1  to L a1931 , wherein the specific structures of the L a1  to L a1931  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, hydrogens in structures of the L a1  to L a1931  may be partially or fully substituted by deuterium, the specific structures of the L a1  to L a1931  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, in the Formula 1, two substituents R i  are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 1′: 
     
       
         
         
             
             
         
       
         
         
           
             wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 30 carbon atoms or a heteroaromatic ring having 3 to 30 carbon atoms; and the ring C is selected from an aromatic ring having 6 to 30 carbon atoms or a heteroaromatic ring having 6 to 30 ring atoms; 
             R i  and R ii  represent, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; and R iii  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
             Y is selected from SiR y R y , GeR y R y , NR y , PR y , O, S or Se; 
             when two R y  are present at the same time, the two R y  may be identical or different; 
             X 1  and X 2  are, at each occurrence identically or differently, selected from CR x  or N; 
             R, R i , R ii , R x  and R y  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             R iii  is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and adjacent substituents R i , R x , R y , R, R ii  and R iii  can be optionally joined to form a ring. 
           
         
       
    
     In the present disclosure, the expression that adjacent substituents R i , R x , R y , R, R ii  and R iii  can be optionally joined to form a ring is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R i , two substituents R ii , two substituents R iii , two substituents R y , two substituents R x , substituents R i  and R x , substituents R i  and R iii , substituents R and R y , and substituents R iii  and R, can be joined to form a ring. Obviously, it is possible that none of these substituents are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein R iii  represents, at each occurrence identically or differently, mono-substitution or multiple substitutions; and
         R iii  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof.       

     According to an embodiment of the present disclosure, wherein the metal complex optionally comprises other ligand(s) which may be optionally joined to the L a  to form a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand. 
     According to an embodiment of the present disclosure, wherein the ring A and/or the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 18 carbon atoms or a heteroaromatic ring having 3 to 18 carbon atoms; and the ring C is selected from an aromatic ring having 6 to 18 carbon atoms or a heteroaromatic ring having 6 to 18 ring atoms. 
     According to an embodiment of the present disclosure, wherein the ring A and/or the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 10 carbon atoms or a heteroaromatic ring having 3 to 10 carbon atoms; and the ring C is selected from an aromatic ring having 6 to 10 carbon atoms or a heteroaromatic ring having 6 to 10 ring atoms. 
     According to an embodiment of the present disclosure, wherein the L a  is selected from a structure represented by any one of Formula 2-2 to Formula 2-17: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
         
         
           
             wherein 
             in Formula 2-2 to Formula 2-17, X 1  and X 2  are, at each occurrence identically or differently, selected from CR x , or N; X 3  is selected from CR i  or N; A 1  to A 6  are, at each occurrence identically or differently, selected from CR ii  or N; X 4  to X 7  are, at each occurrence identically or differently, selected from CH, CR iii  or N, and at least one of X 4  to X 7  is selected from CR iii ; 
             Z is, at each occurrence identically or differently, selected from CR iv , R iv , SiR iv R iv , PR iv , O, S or NR iv ; when two R iv  are present at the same time, the two R iv , are identical or different; for example, when Z is selected from CR iv R iv , the two R iv  are identical or different; in another example, when Z is selected from SiR iv R iv , the two R iv  are identical or different; 
             Y is selected from SiR y R y , NR y , PR y , O, S or Se; when two R y  are present at the same time, the two R y  may be identical or different; for example, when Y is selected from SiR y R y , the two R y  are identical or different; 
             R, R x , R y , R i , R ii  and R iv  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             R iii  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and adjacent substituents R i , R x , R y , R, R ii , R iii  and R iv  can be optionally joined to form a ring. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein Lu is selected from a structure represented by Formula 2-2 or Formula 2-3. 
     According to an embodiment of the present disclosure, wherein L a  is selected from a structure represented by Formula 2-3. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, at least one of X 1  to X n  and/or A 1  to A m  is selected from N, wherein X n  corresponds to one with the largest serial number among X 1  to X 7  in any one of Formula 2-2 to Formula 2-17, and A m  corresponds to one with the largest serial number among A 1  to A 6  in any one of Formula 2-2 to Formula 2-17. For example, in Formula 2-3, X n  corresponds to X 7  whose serial number is the largest among X 1  to X 7  in Formula 2-3, and A m  corresponds to A 4  whose serial number is the largest among A 1  to A 6  in Formula 2-3, that is, in Formula 2-3, at least one of X 1  to X 7  and/or A 1  to A 4  is selected from N. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, at least one of X 1  to X n  is selected from N, wherein X n  corresponds to one with the largest serial number among X 1  to X 7  in any one of Formula 2-2 to Formula 2-17. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 2  is N. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 1  and X 2  are each independently selected from CR x ; X 3  is selected from CR i ; A 1  to A 6  are each independently selected from CR ii ; X 4  to X 7  are, at each occurrence identically or differently, selected from CH or CR iii , and at least one of X 4  to X 7  is selected from CR iii ; adjacent substituents R x , R i , R ii  and R iii  can be optionally joined to form a ring. 
     In the present disclosure, the expression that adjacent substituents R x , R i , R ii  and R iii  can be optionally joined to form a ring is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R ii , two substituents R iii , two substituents R x , substituents R i  and R iii , and substituents R i  and R x , can be joined to form a ring. Obviously, it is possible that none of these substituents are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 1  and X 2  are each independently selected from CR x ; X 3  is selected from CR i ; A 1  to A 6  are each independently selected from CR ii ; X 4  to X 7  are, at each occurrence identically or differently, selected from CH or CR iii , and at least one of X 4  to X 7  is selected from CR iii ; and the R x , R i  and R ii  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group and combinations thereof;
         R iii  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group and combinations thereof; and   adjacent substituents R x , R i , R ii  and R iii  can be optionally joined to form a ring.       

     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 1  and X 2  are each independently selected from CR x ; X 3  is selected from CR i ; A 1  to A 4  are each independently selected from CR ii ; X 4  to X 7  are, at each occurrence identically or differently, selected from CH or CR iii , and at least one of X 4  to X 7  is selected from CR iii ; and at least one or two of the R x , R i  and R ii  is(are), at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group and combinations thereof;
         R iii  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, t-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, norbornyl, adamantyl, trimethylsilyl, isopropyldimethylsilyl, phenyldimethylsilyl, trifluoromethyl, a cyano group, phenyl and combinations thereof; and adjacent substituents R x , R i , R ii  and R iii  can be optionally joined to form a ring.       

     In this embodiment, the expression that at least one or two of the R x , R i  and R ii  is(are), at each occurrence identically or differently, selected from the group of substituents is intended to mean that at least one or two substituents in the group consisting of two substituents R x , all substituents R i  and all substituents R ii  is(are), at each occurrence identically or differently, selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, at least one or two of A 1  to A 6  is(are) selected from CR ii ; X 3  is selected from CR i . 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, at least one or two of A 1  to A 6  is(are) selected from CR ii , and the R ii  is, at each occurrence identically or differently, selected from deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group or a combination thereof; and
         X 3  is selected from CR i , and the R i  is, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, a cyano group or a combination thereof.       

     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, at least one or two of A 1  to A 6  is selected from CR ii , and the R ii  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, 1-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, norbornyl, adamantyl, trimethylsilyl, isopropyldimethylsilyl, phenyldimethylsilyl, trifluoromethyl, a cyano group, phenyl and combinations thereof; and
         X 3  is selected from CR i , wherein the R i  is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, 1-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, norbornyl, adamantyl, trimethylsilyl, isopropyldimethylsilyl, phenyldimethylsilyl, trifluoromethyl, a cyano group, phenyl and combinations thereof.       

     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, R is selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, R is selected from hydrogen, deuterium, fluorine, methyl, ethyl, isopropyl, isobutyl, t-butyl, neopentyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, deuterated methyl, deuterated ethyl, deuterated isopropyl, deuterated isobutyl, deuterated t-butyl, deuterated neopentyl, deuterated cyclopentyl, deuterated cyclopentylmethyl, deuterated cyclohexyl, trimethylsilyl or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17. Y is selected from O or S. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, Y is selected from O. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 1  and X 2  are each independently selected from CR x . 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 1  is selected from CR x , and X 2  is selected from CR x  or N. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-2 to Formula 2-17, X 1  is selected from CR x , and X 2  is selected from CR x  or N; and the R x  is, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 2-18: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 2-18, 
             Y is selected from O or S; 
             R x1 , R x2 , R i , R ii1 , R ii2 , R ii3 , R ii4 , R, R iii1 , R iii2 , R iii3  and R iii4  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
             at least one of R iii1 , R iii2 , R iii3  and R iii4  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, the ligand L has a structure represented by Formula 2-18: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 2-18, 
             Y is selected from O or S; 
             one or two of R x1  and R x2  and/or at least one or two of R ii1 , R ii2 , R ii3  and R ii4  is(are), at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; R is selected from halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof; and 
             at least one or two of R iii1 , R iii2 , R ii3  and R iii4  is(are), at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, the ligand L a  has a structure represented by Formula 2-18: 
     
       
         
         
             
             
         
       
         
         
           
             wherein in Formula 2-18, 
             Y is selected from O or S; 
             one or two of R x1  and R x2  and/or at least one or two of R ii1 . R ii2 , R ii3  and R ii4  is(are), at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; R is selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms or a combination thereof; 
             at least one or two of R iii1 , R iii2 , R iii3  and R iii4  is(are), at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, in Formula 2-18,
         Y is selected from O or S;   at least one or two of R iii1 , R iii2 , R iii3  and R iii4 , and at least one or two of R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; and   R is selected from the group consisting of: halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof.       

     According to an embodiment of the present disclosure, wherein, in Formula 2-18, Y is selected from O or S;
         at least one or two of R ii1 , R ii2 , R iii3  and R iii4  and at least one or two of R ii1 , R ii2 , R ii3  and R ii4  are, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof; and   R is selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof.       

     According to an embodiment of the present disclosure, wherein, in Formula 2-18, one (for example, R ii1  or R ii2  or R ii3 ) or two (for example, R ii1  and R ii2 , R ii2  and R ii3 , or R ii1  and R ii3 ) of R ii1 , R ii2  and R ii3  is(are), at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-18, at least one of R x1 , R x2 , R iii1 , R iii2 , R iii3 , R iii4 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 3 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms and combinations thereof. 
     In this embodiment, the expression that at least one of R x1 , R x2 , R iii1 , R iii2 , R iii3 , R iii4 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group of substituents is intended to mean that at least one of R x1  and R x2  is, at each occurrence identically or differently, selected from the group of substituents, and/or that at least one of R iii2 . R iii3  and R iii4  is, at each occurrence identically or differently, selected from the group of substituents, and/or that at least one of R ii1 , R ii2 , R ii3  and R ii4  is, at each occurrence identically or differently, selected from the group of substituents, and/or that R is selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-18, at least one of R iii2 . R iii3 , R ii1 , R ii2 , R ii3  and R is, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 3 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms and combinations thereof. 
     In this embodiment, the expression that at least one of R iii2 , R iii3 , R ii1 , R ii2 , R ii3  and R is, at each occurrence identically or differently, selected from the group of substituents is intended to mean that at least one of R iii2  and R iii3  is, at each occurrence identically or differently, selected from the group of substituents, and/or that at least one of R ii1 , R ii2  and R ii3  is, at each occurrence identically or differently, selected from the group of substituents, and/or that R is selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, in Formula 2-18, at least one of R x1 , R x2 , R iii1 , R iii2 , R iii3 , R iii4 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group consisting of: substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 ring carbon atoms and combinations thereof. 
     In this embodiment, the expression that at least one of R x1 , R x2 , R iii1 , R iii2 , R iii3 , R iii4 , R ii1 , R ii2 , R ii3 , R ii4  and R is, at each occurrence identically or differently, selected from the group of substituents is intended to mean that at least one of R x1 , and R x2  is, at each occurrence identically or differently, selected from the group of substituents, and/or that at least one of R iii1 , R iii2 , R iii3  and R iii4  is, at each occurrence identically or differently, selected from the group of substituents, and/or that at least one of R ii1 , R ii2 , R ii3  and R ii4  is, at each occurrence identically or differently, selected from the group of substituents, and/or that R is selected from the group of substituents. 
     According to an embodiment of the present disclosure, wherein, L a  is, at each occurrence identically or differently, selected from the group consisting of L a1  to L a1906 , wherein the specific structures of L a1  to L a1906 , are referred to claim  14 . 
     According to an embodiment of the present disclosure, wherein, hydrogens in the structures of the L a1  to L a1906  can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, the metal complex has a structure of M(L a ) m (L b ) n (L c ) q ;
         wherein, the metal M is selected from a metal with a relative atomic mass greater than 40; L a , L b  and L c  are a first ligand, a second ligand and a third ligand of the metal complex, respectively; m is 1, 2 or 3, n is 0, 1 or 2, q is 0, 1 or 2, and m+n+q is equal to the oxidation state of the metal M; when m is greater than 1, the multiple L a  are the same or different; when n is 2, the two L b  are the same or different; when q is 2, the two L c  are the same or different;   L a , L b  and L c  can be optionally joined to form a multi-dentate ligand; for example, L a , L b  and L c  can be optionally joined to form a tetradentate ligand or a hexadentate ligand; it is possible that L a , L b  and L c  are not joined, so that no multi-dentate ligand is formed;   L b  and L c  are, at each occurrence identically or differently, selected from the group consisting of the following structures:       

     
       
         
         
             
             
         
       
         
         
           
             wherein R a , R b  and R c  represent, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
             X b  is, at each occurrence identically or differently, selected from the group consisting of: O, S, Se, NR N1  and CR C1 R C2 ; 
             X c  and X d  are, at each occurrence identically or differently, selected from the group consisting of: O. S, Se and NR N2 ; 
             R a , R b , R c , R N1 , R N2 , R C1  and R C2  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             wherein adjacent substituents R a , R b , R c , R N1 , R N2 , R C1  and R C2  can be optionally joined to form a ring. 
           
         
       
    
     In this embodiment, the expression that adjacent substituents R a , R b , R c , R N1 , R N2 , R C1  and R C2  can be optionally joined to form a ring is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R a , two substituents R b , two substituents R c , substituents R a  and R b , substituents R a  and R c , substituents R b  and R c , substituents R a  and R N1 , substituents R b  and R N1 , substituents R a  and R C1 , substituents R a  and R C2 , substituents R b  and R C1 , substituents R b  and R C2 , substituents R a  and R N2 , substituents R b  and R N2 , and substituents R C1  and R C2 , may be joined to form a ring. Obviously, these substituents may not be joined to form a ring. 
     In this embodiment, the expression that L a , L b  and L c  can be optionally joined to form a multi-dentate ligand is intended to mean that any two or three of L a , L b  and L c  can be joined to form a tetradentate ligand or a hexadentate ligand. Obviously, it is possible that L a , L b  and L c  are not joined, so that no multi-dentate ligand is formed. 
     According to an embodiment of the present disclosure, wherein, the metal M is selected from Ir, Rh, Re, Os, Pt, Au or Cu. 
     According to an embodiment of the present disclosure, wherein, the metal M is selected from Ir, Pt or Os. 
     According to an embodiment of the present disclosure, wherein, the metal M is Ir. 
     According to an embodiment of the present disclosure, wherein, L b  is, at each occurrence identically or differently, selected from the following structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 1  to R 7  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, Li, is, at each occurrence identically or differently, selected from the following structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein at least one of R 1  to R 3  is selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof; and/or at least one of R 4  to R 6  is substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, L b  is, at each occurrence identically or differently, selected from the following structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein at least two of R 1  to R 3  are selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof; and/or at least one of R 4  to R 6  is substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, L b  is, at each occurrence identically or differently, selected from the following structure: 
     
       
         
         
             
             
         
       
         
         
           
             wherein at least two of R 1  to R 3  are selected from substituted or unsubstituted alkyl having 2 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 2 to 20 carbon atoms or a combination thereof; and/or at least two of R 4  to R 6  are selected from substituted or unsubstituted alkyl having 2 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 2 to 20 carbon atoms or a combination thereof. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, the metal complex has a general formula of Ir(L a ) m (L b ) 3-m  and a structure represented by Formula 1-1 or Formula 1-2: 
     
       
         
         
             
             
         
       
         
         
           
             wherein 
             m is 1 or 2; 
             X 1  and X 2  are, at each occurrence identically or differently, selected from CR x  or N; X 3  is, at each occurrence identically or differently, selected from CR i  or N; A 1  to A 4  are, at each occurrence identically or differently, selected from CR ii  or N; X 4  to X 7  are, at each occurrence identically or differently, selected from CH, CR iii  or N, and at least one of X 4  to X 7  is selected from CR iii ; 
             Y is selected from SiR y R y , NR y , PR y , O, S or Se; when two R y  are present at the same time, the two R y  are identical or different; 
             R, R x , R y , R i , R i1 , R 1 , R 2 . R 3 , R 4 , R 5 , R 6  and R 7  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             R iii  is, at each occurrence identically or differently, selected from the group consisting of: deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted alkylgermanyl having 3 to 20 carbon atoms, substituted or unsubstituted arylgermanyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
             adjacent substituents R, R x , R y , R i . R ii  and R iii  can be optionally joined to form a ring; and 
             adjacent substituents R 1 , R 2 , R 3 , R 4 , R 5 , R 6  and R 7  can be optionally joined to form a ring. 
           
         
       
    
     According to an embodiment of the present disclosure, wherein, at least one or two of R 1  to R 3  is(are), at each occurrence identically or differently, selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof; and/or at least one or two of R 4  to R 6  is(are), at each occurrence identically or differently, selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, at least two of R 1  to R 3  are, at each occurrence identically or differently, selected from substituted or unsubstituted alkyl having 2 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 2 to 20 carbon atoms or a combination thereof; and/or at least two of R 4  to R 6  are, at each occurrence identically or differently, selected from substituted or unsubstituted alkyl having 2 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 2 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, L b  is, at each occurrence identically or differently, selected from the group consisting of L b1  to L b322 , and L c  is, at each occurrence identically or differently, selected from the group consisting of L c1  to L c231 . The specific structures of the L b1  to L b322  and the L c1  to L c231  are referred to claim  19 . 
     According to an embodiment of the present disclosure, wherein, the metal complex has a structure of Ir(L a ) 2 (L b ) or Ir(L a ) 2 (L c ) or Ir(L a )(L c ) 2 ;
         wherein, when the metal complex has a structure of Ir(L a ) 2 (L b ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1706  and L b  is selected from any one of the group consisting of L b1  to L b322 ; when the metal complex has a structure of Ir(L a ) 2 (L c ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1706  and L c  is selected from any one of the group consisting of L c1  to L c231 ; and when the metal complex has a structure of Ir(L a )(L c ) 2 , L a  is selected from any one of the group consisting of L a1  to L a1706  and L c  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L c1  to L c231 . In the present embodiment, the specific structures of the L a1  to L a1706  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836.       

     According to an embodiment of the present disclosure, wherein, the metal complex has a structure of Ir(L a ) 2 (L b ) or Ir(L a ) 2 (L c ) or Ir(L a )(L c ) 2 ;
         wherein, when the metal complex has a structure of Ir(L a ) 2 (L b ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1803  and L b  is selected from any one of the group consisting of L b1  to L b322 ; when the metal complex has a structure of Ir(L a ) 2 (L c ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1803  and L c  is selected from any one of the group consisting of L c1  to L c231 ; and when the metal complex has a structure of Ir(L a )(L c ) 2 , L a  is selected from any one of the group consisting of L a1  to L a1803  and L c  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L c1  to L c231 . In the present embodiment, the specific structures of the L a1  to L a1803  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836.       

     According to an embodiment of the present disclosure, wherein, the metal complex has a structure of Ir(L a ) 2 (L b ) or Ir(L a ) 2 (L c ) or Ir(L a )(L) 2 ;
         wherein, when the metal complex has a structure of Ir(L a ) 2 (L c ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1931  and L b  is selected from any one of the group consisting of L b1  to L b322 ; when the metal complex has a structure of Ir(L a ) 2 (L c ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1931  and L c  is selected from any one of the group consisting of L c1  to L c231 ; and when the metal complex has a structure of Ir(L a )(L c ) 2 . L a  is selected from any one of the group consisting of L a1  to L a1931  and is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L c1  to L c231 . In the present embodiment, the specific structures of the L a1  to L a1931  are referred to claim 38 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836.       

     According to an embodiment of the present disclosure, wherein, the metal complex is selected from the group consisting of Compound 1 to Compound 260, wherein the specific structures of the Compound 1 to Compound 260 are referred to claim 43 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, the metal complex is selected from the group consisting of Compound 1 to Compound 290, wherein the specific structures of the Compound 1 to Compound 290 are referred to claim 43 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, the metal complex is selected from the group consisting of Compound 1 to compound 312, wherein the specific structures of the Compound 1 to Compound 312 are referred to claim 43 in US 2022/0109118 A1 published at Apr. 7, 2022, of U.S. application Ser. No. 17/241,836. 
     According to an embodiment of the present disclosure, wherein, the metal complex has a structure of Ir(L a ) 2 (L b ) or Ir(L a ) 2 (L c ) or Ir(L a )(L c ) 2  or Ir(L a )(L b )(L c ); wherein when the metal complex has a structure of Ir(L a ) 2 (L b ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1906 , and L b  is selected from any one of the group consisting of L b1  to L b322 ; when the metal complex has a structure of Ir(L a ) 2 (L c ), L a  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L a1  to L a1906  and L is selected from any one of the group consisting of L c1  to L c231 ; when the metal complex has a structure of Ir(L a )(L c ) 2 , L a  is selected from any one of the group consisting of L a1  to L a1906  and L c  is, at each occurrence identically or differently, selected from any one or any two of the group consisting of L c1  to L c231 ; when the metal complex has a structure of Ir(L a )(L b )(L c ), L a  is selected from any one of the group consisting of L a1  to L a1906 , L b  is selected from any one of the group consisting of L b1  to L b322 , and L c  is selected from any one of the group consisting of L c1  to L c231 . 
     According to an embodiment of the present disclosure, wherein, the metal complex is selected from the group consisting of Compound 2-1 to Compound 2-1028, wherein the specific structures of the Compound 2-1 to Compound 2-1028 are referred to claim  20 . 
     According to an embodiment of the present disclosure, an electroluminescent device is further disclosed, comprising:
         an anode,   a cathode, and   an organic layer disposed between the anode and the cathode, wherein the organic layer includes a metal complex including a ligand L a  having a structure represented by Formula 1:       

     
       
         
         
             
             
         
       
         
         
           
             wherein the ring A and the ring B are each independently selected from a five-membered unsaturated carbocyclic ring, an aromatic ring having 6 to 30 carbon atoms, or a heteroaromatic ring having 3 to 30 carbon atoms; 
             R i  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; and R ii  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
             Y is selected from SiR y R y , GeR y R y , NR y , PR y , O, S or Se; 
             when two R y  are present at the same time, the two R y  may be the same or different; 
             X 1  and X 2  are, at each occurrence identically or differently, selected from CR x  or N; 
             R, R i , R ii , R x  and R y  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
             adjacent substituents R i , R x , R y , R and R ii  can be optionally joined to form a ring; the metal is selected from a metal with a relative atomic mass greater than 40. 
           
         
       
    
     According to an embodiment of the present disclosure, in the electroluminescent device, the organic layer is a light-emitting layer and the metal complex is a light-emitting material. 
     According to an embodiment of the present disclosure, the electroluminescent device emits red light. 
     According to an embodiment of the present disclosure, the electroluminescent device emits white light. 
     According to an embodiment of the present disclosure, in the electroluminescent device, the organic layer is a light-emitting layer, wherein the light-emitting layer further includes at least one host material. 
     According to an embodiment of the present disclosure, in the electroluminescent device, the at least one host material includes at least one chemical group selected from the group consisting of: benzene, pyridine, pyrimidine, triazine, carbazole, azacarbazole, indolocarbazole, dibenzothiophene, aza-dibenzothiophene, dibenzofuran, azadibenzofuran, dibenzoselenophene, triphenylene, azatriphenylene, fluorene, silafluorene, naphthalene, quinoline, isoquinoline, quinazoline, quinoxaline, phenanthrene, azaphenanthrene and combinations thereof. 
     According to another embodiment of the present disclosure, further disclosed is a compound composition which includes a metal complex whose specific structure is as shown in any one of the embodiments described above. 
     According to another embodiment of the present disclosure, further disclosed is a compound combination, which comprises a metal complex whose specific structure is as shown in any one of the preceding embodiments. 
     Combination with Other Materials 
     The materials described in the present disclosure for a particular layer in an organic light emitting device can be used in combination with various other materials present in the device. The combinations of these materials are described in more detail in U.S. Pat. App. No. 20160359122 at paragraphs 0132-0161, which is incorporated by reference herein in its entirety. The materials described or referred to the disclosure are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination. 
     The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in combination with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The combination of these materials is described in detail in paragraphs 0080-0101 of U.S. Pat. App. No. 20150349273, which is incorporated by reference herein in its entirety. The materials described or referred to the disclosure are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination. 
     In the embodiments of material synthesis, all reactions were performed under nitrogen protection unless otherwise stated. All reaction solvents were anhydrous and used as received from commercial sources. Synthetic products were structurally confirmed and tested for properties using one or more conventional equipment in the art (including, but not limited to, nuclear magnetic resonance instrument produced by BRUKER, liquid chromatograph produced by SHIMADZU, liquid chromatograph-mass spectrometry produced by SHIMADZU, gas chromatograph-mass spectrometry produced by SHIMADZU, differential Scanning calorimeters produced by SHIMADZU, fluorescence spectrophotometer produced by SHANGHAI LENGGUANG TECH., electrochemical workstation produced by WUHAN CORRTEST, and sublimation apparatus produced by ANHUI BEQ, etc.) by methods well known to the persons skilled in the art. In the embodiments of the device, the characteristics of the device were also tested using conventional equipment in the art (including, but not limited to, evaporator produced by ANGSTROM ENGINEERING, optical testing system produced by SUZHOU FATAR, life testing system produced by SUZHOU FATAR, and ellipsometer produced by BEIJING ELLITOP, etc.) by methods well known to the persons skilled in the art. As the persons skilled in the art are aware of the above-mentioned equipment use, test methods and other related contents, the inherent data of the sample can be obtained with certainty and without influence, so the above related contents are not further described in this present disclosure. 
     Material Synthesis Example 
     The method for preparing a compound in the present disclosure is not limited herein. Typically, the following compounds are used as examples without limitations, and synthesis routes and preparation methods thereof are described below. 
     Synthesis Example 1: Synthesis of Compound 81 
     Step 1: Synthesis of Intermediate 2 
     
       
         
         
             
             
         
       
     
     5 g (24.03 mmol) of Raw material 1 was dissolved in 50 mL of DCM, and 5.39 g (1.3 eq, 31.24 mmol) of meta-chloroperoxybenzoic acid (m-CPBA) was added at room temperature and stirred for 24 h. After TLC showed that the raw material disappeared, the solvents were removed in vacuo to obtain crude Intermediate 2 which was directly used in the next step. 
     Step 2: Synthesis of Intermediate 3 
     
       
         
         
             
             
         
       
     
     Intermediate 2 obtained in step 1 was dissolved in 24 mL of phosphorus oxychloride, warmed to 100° C., stirred for 3 h, and cooled to 0° C. An aqueous solution of NaOH was slowly added dropwise until the pH was 9 and the system was extracted three times with DCM (50 mL*3). The organic phases were combined, washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate, and the solvents were removed in vacuo. The residue was purified through column chromatography (PE:EA=30:1) to obtain 1.98 g of Intermediate 3 with a yield of 34% over two steps. 
     Step 3: Synthesis of Intermediate 5 
     
       
         
         
             
             
         
       
     
     3 g (18.96 mmol) of Intermediate 4 was dissolved in 30 mL of anhydrous tetrahydrofuran and cooled to −78° C. n-BuLi (1 M, 22.75 mL) (1.2 eq, 22.75 mmol) was slowly added dropwise under a nitrogen atmosphere. After addition, the system was warmed to room temperature and stirred for 1 h. The system was cooled to −78° C. and 4.63 g (1.3 eq, 24.65 mmol) of 1,2-dibromoethane was slowly added dropwise. After addition, the system was warmed to room temperature and stirred overnight. The reaction was quenched with saturated ammonium chloride and extracted three times with EA (40 mL*3). The organic phases were combined, washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate, and the solvents were removed in vacuo. The residue was purified through column chromatography (PE:EA=100:1) to obtain 3.82 g of Intermediate 5 with a yield of 85%. 
     Step 4: Synthesis of Intermediate 6 
     
       
         
         
             
             
         
       
     
     2.5 g (10.57 mmol) of Intermediate 5, 0.387 g (0.05 eq, 0.53 mmol) of PdCl 2 (dppf). 1.56 g (1.5 eq, 15.85 mmol) of AcOK, 3.22 g (1.2 eq, 12.68 mmol) of bis(pinacolato)diboron (B 2 Pin 2 ) were dissolved in 30 mL of 1,4-dioxane, heated to 80° C., and stirred overnight. The system was cooled to room temperature, the solvents were removed in vacuo, and the residue was purified through column chromatography (PE:EA=20:1) to obtain 2.21 g of Intermediate 6 as a white solid with a yield of 74%. 
     Step 5: Synthesis of Intermediate 7 
     
       
         
         
             
             
         
       
     
     3.93 g (1.2 eq, 13.85 mmol) of Intermediate 6, 2.78 g (1 eq, 11.54 mmol) of Intermediate 3, 0.387 g (0.05 eq, 0.58 mmol) of Pd(PPh 3 ) 4 , 1.83 g (1.5 eq, 17.31 mmol) of Na 2 CO 3  were dissolved in 30 mL of 1,4-dioxane and 10 mL of water, heated to 90° C., and stirred overnight. The system was cooled to room temperature, the solvents were removed in vacuo, and the residue was purified through column chromatography (PE:EA=50:1) to obtain 3 g of Intermediate 7 as a white solid with a yield of 72%. 
     Step 6: Synthesis of Intermediate 8 
     
       
         
         
             
             
         
       
     
     3.03 g (8.32 mmol) of Intermediate 7 was dissolved in 30 mL of DCM and cooled to 0° C. BBr 3  was slowly added dropwise under a nitrogen atmosphere and stirred for 2 h. The reaction was quenched with an aqueous solution of NaHCO 3  and extracted with DCM (60 mL* 3 ). The organic phases were combined, washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate, and the solvents were removed in vacuo. The residue was purified through column chromatography (PE:EA=4:1) to obtain 1.17 g of Intermediate 8 with a yield of 40%. 
     Step 7: Synthesis of Intermediate 9 
     
       
         
         
             
             
         
       
     
     1.2 g (I eq, 3.33 mmol) of Intermediate 8, 24 mg (0.05 eq, 0.17 mmol) of CuBr, and 2.82 g (4 eq, 13.3 mmol) of K 3 PO 4  were dissolved in 15 mL of DMF, heat to 90° C., and stirred overnight. The system was cooled to room temperature and diluted with water to precipitate out a product. The product was filtered through Celite and washed with 1 L of DCM to obtain 0.81 g of Intermediate 9 with a yield of 90%. The obtained yellow solid Intermediate 9 was recrystallized from toluene. The obtained solid Intermediate 9 had a purity of 99.7%. 
     Step 8: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     1.2 g (3 eq, 4.45 mmol) of Intermediate 9 was dissolved in 24 mL of 2-ethoxyethanol and 8 mL of water at room temperature, 523 mg (I eq, 1.48 mmol) of IrCl 3 .3H 2 O were added, and the system was purged with nitrogen three times at room temperature, heated to 130° C., refluxed for 24 h at 130° C., and cooled to room temperature. The system was filtered to obtain solids, and the solids were washed with ethanol until the washing liquid was colorless and suction-filtered for about 15 min until ethanol on the solids completely disappeared, to obtain 1.13 g of an iridium dimer as a red solid with a yield of 99%. The iridium dimer was directly used in the next step without further purification. 
     Step 9: Synthesis of Compound 81 
     
       
         
         
             
             
         
       
     
     1.13 g (1 eq, 0.74 mmol) of the iridium dimer obtained in step 8 was added to a 100 mL round-bottom flask, 510 mg (5 eq, 3.7 mmol) of K 2 CO 3  and 0.74 g (4 eq, 2.96 mmol) of 3,7-diethyl-3-methyl-4,6-nonanedione were added, and the system was purged with nitrogen three times at room temperature, stirred under nitrogen protection for 24 h, and filtered through Celite. The solids were washed with ethanol until the washing liquid was colorless and suction-filtered for about 15 min to remove ethanol adsorbed to the solids. Under vacuum filtration, the red solids on the Celite were dissolved in 200 mL of dichloromethane. 20 mL of ethanol was added to the flask, and dichloromethane was removed in vacuo. A product was precipitated from the remaining ethanol and filtered, and ethanol adsorbed to the solids was removed completely through suction filtration. The solids were purified through silica gel column chromatography (PE:DCM=10:1). The obtained crude solids were dissolved in 200 mL of dichloromethane. 20 mL of ethanol was added, and dichloromethane was removed in vacuo. A product was precipitated from the remaining ethanol and filtered, and ethanol adsorbed to the solids was removed completely through suction filtration to obtain Compound 81 as a red solid (with a mass of 1.13 g and a yield of 80%). The purity of Compound 81 was 99.6%. The product was confirmed as the target product with a molecular weight of 954.3. 
     Synthesis Example 2: Synthesis of Compound 83 
     Step 1: Synthesis of Intermediate 11 
     
       
         
         
             
             
         
       
     
     Intermediate 10 (7.6 g, 35.1 mmol) was dissolved in 70 mL of ultra-thy tetrahydrofuran, the reaction solution was cooled to 0° C., and a solution of n-butyl lithium (15.5 mL, 38.7 mmol) was added dropwise thereto under nitrogen protection. After the dropwise addition, the reaction was maintained at this temperature for 1 h, isopropyl pinacol borate (iPrOBpin) (8.49 g, 45.6 mmol) was added thereto, and after addition, the reaction was warmed to room temperature for 2 h. Then, the reaction was quenched with a saturated solution of ammonium chloride. Ethyl acetate was added to the reaction, liquids were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried, and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (using an eluent of ethyl acetate:petroleum ether=1:50, v/v) to obtain the target product Intermediate 11 as a colorless oily liquid (4.7 g, with a yield of 39.1%). 
     Step 2: Synthesis of Intermediate 13 
     
       
         
         
             
             
         
       
     
     Intermediate 12 (3.19 g, 13.7 mmol), Intermediate 11 (4.7 g, 13.7 mmol), tetrakis(triphenylphosphine)palladium (0.8 g. 0.69 mmol), sodium carbonate (2.18 g, 20.55 mmol), 1,4-dioxane (60 mL), and water (15 mL) were added to a 250 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, liquids were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried, and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (using an eluent of ethyl acetate:petroleum ether=1:10, v/v) to obtain the target product Intermediate 13 as a white solid (3.5 g. with a yield of 73.0%). 
     Step 3: Synthesis of Intermediate 14 
     
       
         
         
             
             
         
       
     
     Intermediate 13 (4.1 g, 10 mmol) was dissolved in 20 mL of ethanol, and then 20 mL of 2 M HCl were added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutrality. A large amount of yellow solids were precipitated front the solution. The solids were filtered, washed with water several times, and suction-filtered to obtain the target product Intermediate 14 as a yellow solid (3.3 g, with a yield of 93.2%). 
     Step 4: Synthesis of Intermediate 15 
     
       
         
         
             
             
         
       
     
     Intermediate 14 (3.3 g, 9.3 mmol), cuprous bromide (133 mg, 0.9 mmol), 2,2,6,6-tetramethylheptanedione (1.37 g, 7.44 mmol), cesium carbonate (7.6 g, 23.25 mmol), and DMF (90 mL) were heated to 135° C. and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. 200 mL of water were added to the solution until a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times, and suction-filtered to obtain the target product Intermediate 15 as a yellow solid (3.10 g, with a yield of 96%). 
     Step 5: Synthesis of Intermediate 16 
     
       
         
         
             
             
         
       
     
     Intermediate 15 (3.42 g, 10.8 mmol), isobutylboronic acid (2.2 g, 21.6 mmol), palladium acetate (I 21 mg, 0.54 mmol), Sphos (443 mg, 1.08 mmol), potassium phosphate trihydrate (8.63 g, 32.4 mmol), and toluene (80 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (using an eluent of ethyl acetate:petroleum ether=1:30, v/v) to obtain the target product Intermediate 16 as a yellow solid (1.8 g, with a yield of 49.4%). 
     Step 6: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 16 (1.8 g, 5.3 mmol), iridium trichloride trihydrate (628 mg, 1.78 mmol), 2-ethoxyethanol (21 mL), and water (7 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution, so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 7: Synthesis of Compound 83 
     
       
         
         
             
             
         
       
     
     The solution of iridium dimer, 3,7-diethyl-3-methylnonane-4,6-dione (663 mg, 2.67 mmol), and potassium carbonate (1.23 g, 8.9 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the solution was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 1.1 g of Compound 83 with a yield of 57%. The product was further purified through column chromatography. The structure of the compound was confirmed through NMR and LC-MS as the target product with a molecular weight of 1094.5. 
     Synthesis Example 3: Synthesis of Compound 64 
     Step 1: Synthesis of Intermediate 18 
     
       
         
         
             
             
         
       
     
     Intermediate 17 (2.93 g, 12.54 mmol), Intermediate 11 (3.9 g, 11.4 mmol), Pd(dppf)Cl 2  (439 mg, 0.6 mmol), and K 2 CO 3  (4.73 g, 34.2 mmol) were mixed in dioxane/water (42 mL/14 mL), purged with nitrogen, and reacted overnight at room temperature. The solution was filtered through Celite and extracted with EA three times. The organic phases were combined, concentrated, and subjected to column chromatography to obtain Intermediate 18 (3 g with a yield of 63.7%). 
     Step 2: Synthesis of Intermediate 20 
     
       
         
         
             
             
         
       
     
     Intermediate 18 (3.8 g, 9.2 mmol) was added to a mixed solution of 12 N HCl (7.6 mL) and MeOH (20 mL) and reacted at 54° C. for 2 h. After TLC detected that the reaction was completed, the system was cooled to room temperature, added with a saturated solution of NaHCO 3  to adjust the pH to about 7-8, and extracted with EA three times. The organic phases were combined, washed with a saturated aqueous solution of sodium chloride, and concentrated to obtain a crude product of Intermediate 19, which was directly used in the next step without further purification. The crude product of Intermediate 19 (2.6 g. 7.2 mmol), CuBr (103 mg, 0.72 mmol), 2,2,6,6-tetratmethyl-3,5-heptanedione (1.06 g, 5.76 mmol), and Cs 2 CO 3  (5.87 g, 18 mmol) were mixed in DMF (72 mL), purged with nitrogen, reacted overnight, and cooled to room temperature. The product was filtered out. The filter cake was washed with an appropriate amount of DMF, washed with EtOH and PE, and dried to obtain Intermediate 20 (1.85 g with a yield of 63% over two steps). 
     Step 3: Synthesis of Intermediate 21 
     
       
         
         
             
             
         
       
     
     Intermediate 20 (1.85 g, 5.82 mmol), isobutylboronic acid (1.19 g, 11.64 mmol), Pd(OAc) 2  (65 mg, 0.29 mmol), Sphos (238 mg, 0.58 mmol), and K 3 PO 4 .3H 2 O (4.66 g, 17.5 mmol) were mixed in toluene (58 mL) and refluxed at 120° C. under nitrogen protection. After HPLC detected that Intermediate 21 was converted completely, the reaction solution was cooled to room temperature, filtered through Celite, concentrated, and subjected to column chromatography to obtain Intermediate 21 (1.3 g of yellow solids with a yield of 66%). 
     Step 4: Synthesis of Compound 64 
     
       
         
         
             
             
         
       
     
     Intermediate 21 (825 mg, 2.42 mmol), IrCl 3 .3H 2 O (286 mg, 0.81 mmol), ethoxyethanol (11.5 mL), and water (3.5 mL) were added to a 100 mL single-necked flask, purged with nitrogen, and refluxed at 130° C. for 24 h. After the reaction was cooled to room temperature, the resulting precipitate was filtered out and the filter cake was washed with ethanol and dried. The resulting iridium dimer, 3,7-diethyl-1,1,1-trifluorononane-4,6-dione (319 mg, 1.2 mmol), K 2 CO 3  (560 mg, 4.05 mmol), and ethoxyethanol (13 mL) were mixed in a 100 mL single-necked flask, purged with nitrogen, and reacted overnight at room temperature. After TLC detected that the reaction was completed, stirring was stopped. The reaction solution was filtered through Celite. The filter cake was washed with an appropriate amount of EtOH. The crude product was washed with DCM into a 250 mL eggplant-shaped flask. EtOH (about 5 mL) was added to the crude product, and DCM was removed through rotary evaporation at room temperature until solids were precipitated. The solids were filtered and washed with an appropriate amount of EtOH to obtain Compound 64 (80 mg with a yield of 8.7%). The product was confirmed as the target product with a molecular weight of 1136.4. 
     Synthesis Example 4: Synthesis of Compound 93 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 22 (0.76 g, 1.92 mmol), iridium trichloride trihydrate (226 mg, 0.64 mmol), 2-ethoxyethanol (7.5 mL), and water (2.5 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution, so that a solution of an iridium dimer in ethoxyethanol was obtained, which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 93 
     
       
         
         
             
             
         
       
     
     The solution of iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3-methylnonane-4,6-dione (450 mg, 1.84 mmol), and potassium carbonate (0.64 g, 4.45 mmol) were added to a 25 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the solution was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 550 mg of Compound 93 with a yield of 71%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1206.6. 
     Synthesis Example 5: Synthesis of Compound 117 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     Intermediate 23 (2.1 g, 5.56 mmol), iridium trichloride trihydrate (494 mg, 1.4 mmol), ethoxyethanol (I 8 mL), and water (6 mL) were added to a 250 mL single-necked flask, purged with nitrogen, and refluxed at 130° C. for 24 h. After the reaction was cooled to room temperature, the resulting precipitate was filtered out and the filter cake was washed with ethanol and dried to obtain an iridium dimer which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 117 
     
       
         
         
             
             
         
       
     
     The obtained iridium dimer, 3,7-diethyl-3,7-dimethyl-4,6-nonanedione (421 mg, 1.75 mmol), potassium carbonate (1.94 mg, 14 mmol), and ethoxyethanol (24 mL) were mixed in a 100 mL single-necked flask, purged with nitrogen, and reacted overnight at 55° C. After TLC detected that the reaction was completed, stirring was stopped. The reaction solution was filtered through Celite, the filter cake was washed with an appropriate amount of ethanol, and the crude product was washed with dichloromethane into a 250 mL eggplant-shaped flask. Ethanol (about 5 mL) was added, and dichloromethane was removed through rotary evaporation at room temperature until solids were precipitated. The solids were filtered out, washed with an appropriate amount of ethanol, dried, dissolved in dichloromethane, concentrated, and subjected to column chromatography to obtain Compound 117 as a red solid (1 g with a yield of 60%). The purity of the compound was 99.4%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1192.6. 
     Synthesis Example 6: Synthesis of Compound 116 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 24 (1.37 g, 3.73 mmol), iridium trichloride trihydrate (329 mg, 0.93 mmol), 2-ethoxyethanol (12 mL), and water (4 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 116 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (430 mg, 1.79 mmol), and potassium carbonate (0.62 g, 4.48 mmol) were added to a 50 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 810 mg of Compound 116 with a yield of 82.2%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1164.5. 
     Synthesis Example 7: Synthesis of Compound 261 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 25 (0.76 g, 1.92 mmol), iridium trichloride trihydrate (226 mg, 0.64 mmol), 2-ethoxyethanol (7.5 mL), and water (2.5 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution, so that a solution of an iridium dimer in ethoxyethanol was obtained, which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 261 
     
       
         
         
             
             
         
       
     
     The solution of iridium dimer in ethoxyethanol obtained in the previous step. 3,7-diethyl-3,7-dimethylnonane-4,6-dione (450 mg, 1.84 mmol), and potassium carbonate (0.64 g, 4.45 mmol) were added to a 25 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated, but not to dryness. The solution was filtered to obtain 1.75 g of Compound 261 with a yield of 96%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1220.6. 
     Synthesis Example 8: Synthesis of Compound 262 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of intermediate 26 (0.76 g, 1.92 mmol), iridium trichloride trihydrate (226 mg, 0.64 mmol), 2-ethoxyethanol (7.5 mL), and water (2.5 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution, so that a solution of an iridium dimer in ethoxyethanol was obtained, which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 262 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-1,1,1-trifluorononane-4,6-dione (450 mg, 1.84 mmol), and potassium carbonate (0.64 g, 4.45 mmol) were added to a 25 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 1.35 g of Compound 262 with a purity of 98.86% and a yield of 92%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1246.5. 
     Synthesis Example 9: Synthesis of Compound 264 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     Intermediate 27 (800 mg, 2.1 mmol), iridium trichloride trihydrate (250 mg, 0.7 mmol), ethoxyethanol (7.5 mL), and water (2.5 mL) were added to a 100 mL single-necked flask, purged with nitrogen, and refluxed at 130° C. for 24 h. After the reaction was cooled, the solution was concentrated and the solvents were removed through rotary evaporation to obtain an iridium dieter which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 264 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step was added with 3,7-diethyl-3,7-dimethylnonane-4,6-dione (337 mg, 1.4 mmol), potassium carbonate (967 mg, 7 mmol), and ethoxyethanol (14 mL), purged with nitrogen, and reacted at room temperature for 48 h. The reaction solution was filtered through Celite. The filter cake was washed with an appropriate amount of ethanol. The crude product was washed with dichloromethane into a 250 mL eggplant-shaped flask. Ethanol (about 5 mL) was added to the crude product, and dichloromethane was removed through rotary evaporation at room temperature until solids were precipitated. The solids were filtered out, washed with an appropriate amount of ethanol, dried, dissolved in dichloromethane, concentrated, and purified through column chromatography to obtain Compound 264 (570 mg). The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1192.6. 
     Synthesis Example 10: Synthesis of Compound 263 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 28 (0.46 g, 1.28 mmol), iridium trichloride trihydrate (130 mg, 0.37 mmol), 2-ethoxyethanol (4.5 mL), and water (1.5 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 263 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (133 mg, 0.55 mmol), and potassium carbonate (0.25 g, 1.84 mmol) were added to a 50 mL round-bottom flask and reacted at 40° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 300 mg of Compound 263 with a yield of 73.7%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1164.5. 
     Synthesis Example 11: Synthesis of Compound 266 
     Step 1: Synthesis of an Iridium Dither 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 29 (1.45 g, 3.42 mmol), iridium trichloride trihydrate (346 mg, 0.98 mmol). 2-ethoxyethanol (12 mL), and water (4 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 266 
     
       
         
         
             
             
         
       
     
     The iridium dimer (0.67 g, 0.31 mmol) obtained in the previous step, 3,7-diethyl-3-methylnonane-4,6-dione (0.21 g, 0.94 mmol), and potassium carbonate (0.43 g, 3.1 mmol) were dissolved in 9 mL of ethoxyethanol and reacted at 40° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 370 mg of Compound 266 with a yield of 47.3%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1262.6. 
     Synthesis Example 12: Synthesis of Compound 265 
     Step 1: Synthesis of Compound 265 
     
       
         
         
             
             
         
       
     
     The iridium dimer (0.67 g, 0.31 mmol), Intermediate 30 (0.21 g, 0.94 mmol), and potassium carbonate (0.43 g, 31 mmol) were dissolved in 9 mL of ethoxyethanol and reacted at 40° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 370 mg of Compound 265 with a yield of 47.3%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1302.6. 
     Synthesis Example 13: Synthesis of Compound 267 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 31 (0.6 g, 1.68 mmol), iridium trichloride trihydrate (198 mg, 0.56 mmol), 2-ethoxyethanol (7.5 mL), and water (2.5 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 267 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (270 mg, 1.12 mmol), and potassium carbonate (0.77 g, 5.6 mmol) were added to a 25 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain a crude product with a purity of 91.6% (0.4 g). The product was further purified through column chromatography to obtain the final product Compound 267 (0.3 g) with a yield of 47%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1136.5. 
     Synthesis Example 14: Synthesis of Compound 269 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 32 (1.5 g, 4.2 mmol), iridium trichloride trihydrate (427 mg, 1.2 mmol). 2-ethoxyethanol (12 mL), and water (4 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dither as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 269 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (580 mg, 2.4 mmol), and potassium carbonate (0.83 g, 6.04 mmol) were dissolved in 16 mL of ethoxyethanol and reacted at 40° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 940 mg of Compound 269 with a yield of 66%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1166.5. 
     Synthesis Example 15: Synthesis of Compound 288 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 33 (1.2 g, 2.93 mmol), iridium trichloride trihydrate (427 mg, 1.2 mmol). 2-ethoxyethanol (12 mL), and water (4 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 288 
     
       
         
         
             
             
         
       
     
     The iridium dimer (0.67 g, 0.31 mmol) obtained in the previous step, Intermediate 34 (414 mg, 1.76 mmol), and sodium hydroxide (176 mg, 4.4 mmol) were dissolved in 16 mL of ethoxyethanol and reacted at 40° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 410 mg of Compound 288 with a yield of 27.4%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1248.6. 
     Synthesis Example 16: Synthesis of Compound 273 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 35 (1.3 g, 3.54 mmol), iridium trichloride trihydrate (204 mg, 0.58 mmol), 2-ethoxyethanol (18 mL), and water (6 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 273 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (0.21 g. 0.87 mmol), and potassium carbonate (0.40 g, 2.9 mmol) were added to a 100 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain a crude product (0.7 g). The crude product was further purified through column chromatography to obtain Compound 273 (0.6 g) with a yield of 91%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1136.5. 
     Synthesis Example 17: Synthesis of Compound 282 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of intermediate 36 (1.77 g, 3.87 mmol), iridium trichloride trihydrate (390 mg, 1.11 mmol), 2-ethoxyethanol (24 mL), and water (8 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 282 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (0.4 g, 1.66 mmol), and potassium carbonate (0.77 mg. 5.6 mmol) were added to a 100 mL round-bottom flask and reacted at 50° C. for 48 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain a crude product (0.7 g). The crude product was further purified through column chromatography to obtain Compound 282 (0.25 g) with a yield of 17%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1344.6. 
     Synthesis Example 18: Synthesis of Compound 287 
     Step 1: Synthesis of Compound 287 
     
       
         
         
             
             
         
       
     
     The iridium dimer (0.94 g. 0.45 mmol). 3,7-diethyl-3,7-dimethylnonane-4,6-dione (0.32 g, 1.34 mmol), and potassium carbonate (0.62 mg, 4.45 mmol) were dissolved in 25 mL of ethoxyethanol and reacted at 40° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 0.87 g of Compound 287 with a yield of 78%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1248.6. 
     Synthesis Example 19: Synthesis of Compound 291 
     Step 1: Synthesis of Intermediate 38 
     
       
         
         
             
             
         
       
     
     Intermediate 37 (2.68 g, 8.69 mmol) and TMEDA (1.31 g, 11.3 mmol) were dissolved in 80 mL of ultra-dry THF. The reaction system was cooled to 0° C. and then n-butyl lithium (4.2 mL, 10.43 mmol, 2.5 M) was slowly added. After reacting for 1 h at this temperature, isopropyl pinacol borate (2.102 g, 11.3 mmol) was added and reacted overnight. After TLC showed that the reaction was completed, saturated ammonium chloride was added to quench the reaction. The solution was extracted with EA, dried, and filtered, and the solvent was removed through rotary evaporation to obtain a crude product. The crude product was purified through silica gel column chromatography to obtain Intermediate 38 (3.86 g. 82%). 
     Step 2: Synthesis of Intermediate 39 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 12 (1.95 g, 8.4 mmol), Intermediate 38 (3.85 g, 8.4 mmol), Pd(PPh 3 ) 4  (0.48 g, 0.42 mmol), sodium carbonate (1.34 g, 12.6 mmol), and 1,4-dioxane/water (32 mL/8 mL) was heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. Water was added to the reaction system. The organic phase was extracted with EA, dried, and filtered, and the solvent was removed through rotary evaporation to obtain Intermediate 39 (3.1 g with a yield of 70%). 
     Step 3: Synthesis of Intermediate 40 
     
       
         
         
             
             
         
       
     
     Intermediate 39 (3.1 g. 5.91 mmol) was dissolved in 15 mL of ethanol. Then, the reaction system was slowly added with 15 mL of HCl (2N), heated to reflux, and reacted for 2 h. After TLC showed that the reaction was completed, the reaction system was cooled to room temperature, neutralized to be neutral by adding a solution of sodium bicarbonate, and filtered to obtain a crude solid product. The crude solid product was purified through column chromatography to obtain Intermediate 40 (2.75 g with a yield of 99.78%). 
     Step 4: Synthesis of Intermediate 41 
     
       
         
         
             
             
         
       
     
     Intermediate 40 (2.75 g, 5.9 mmol), cuprous bromide (86 mg, 0.6 mmol), 2,2,6,6-tetramethylheptanedione (0.88 g, 4.8 mmol), cesium carbonate (4.89 g, 15 mmol), and DMF (60 mL) were heated to 135° C. and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. Water was added thereto until a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times, and suction-filtered to obtain Intermediate 41 as a yellow solid (2.54 g with a yield of 99.8%). 
     Step 5: Synthesis of Intermediate 42 
     
       
         
         
             
             
         
       
     
     Intermediate 41 (2.54 g, 5.91 mmol), neopentylboronic acid (1.37 g, 11.83 mmol), Pd 2 (dba) 3  (135 mg, 0.15 mmol), Sphos (243 mg, 0.59 mmol). K 3 PO 4 .3H 2 O (4.72 g, 17.7 mmol) and toluene (30 mL) were mixed. The system was purged with nitrogen three times, heated to reflux, and reacted overnight. After TLC detected that the reaction was completed, the system was cooled to room temperature, and the solvent was removed through rotary evaporation to obtain a crude product. The crude product was purified through column chromatography to obtain Intermediate 42 (1.8 g with a yield of 65%). 
     Step 6: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 42 (1.4 g. 3.0 mmol), iridium trichloride trihydrate (0.35 g, 1.0 mmol), 2-ethoxyethanol (12 mL), and water (4 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 7: Synthesis of Compound 291 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-1,1,1-trifluorononane-4,6-dione (0.39 g, 1.5 mmol), and potassium carbonate (0.69 g, 5.00 mmol) were dissolved in 16 mL of ethoxyethanol and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 0.71 g of Compound 291 with a yield of 41.2%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1386.7. 
     Synthesis Example 20: Synthesis of Compound 292 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 43 (1.4 g, 2.92 mmol), iridium trichloride trihydrate (0.34 g, 0.97 mmol), 2-ethoxyethanol (12 mL), and water (4 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 292 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-1,1,1-trifluorononane-4,6-dione (0.38 g, 1.5 mmol), and potassium carbonate (0.67 g, 4.85 mmol) were dissolved in 16 mL of ethoxyethanol and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 0.67 g of Compound 292 with a yield of 49%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1414.7. 
     Synthesis Example 21: Synthesis of Compound 293 
     Step 1: Synthesis of Compound 293 
     
       
         
         
             
             
         
       
     
     The iridium dimer (1.01 g, 0.97 mmol), 3,3,7-triethylnonane-4,6-dione (0.4 g, 1.5 mmol), and potassium carbonate (0.72 g, 4.85 mmol) were dissolved in 16 mL of ethoxyethanol and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 0.62 g of Compound 293 with a yield of 45%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1388.8. 
     Synthesis Example 22: Synthesis of Compound 294 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 44 (0.68 g, 1.60 mmol), iridium trichloride trihydrate (0.16 g, 0.45 mmol), 2-ethoxyethanol (6 mL), and water (2 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 294 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step. 3,7-diethyl-3,7-dimethylnonane-4,6-dione (0.22 g, 0.9 mmol), and potassium carbonate (0.62 g. 4.5 mmol) were dissolved in 16 mL of ethoxyethanol and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The resulting solid was added with dichloromethane and the filtrate was collected. Then ethanol was added and the resulting solution was concentrated but not to dryness. The solution was filtered to obtain 0.42 g of Compound 294 with a yield of 73%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1276.7. 
     Synthesis Example 23: Synthesis of Compound 295 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 45 (2.03 g, 4.93 mmol), iridium trichloride trihydrate (0.48 g. 1.37 mmol), 2-ethoxyethanol (33 mL), and water (11 mL) was refluxed under a nitrogen atmosphere for 24 h. The solution was cooled to room temperature and filtered to obtain an iridium dimer as a red solid which was directly used in the next step without further purification. 
     Step 2: Synthesis of Compound 295 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-1,1,1-trifluorononane-4,6-dione (0.53 g, 2 mmol), and potassium carbonate (0.95 g, 6.85 mmol) were mixed in ethoxyethanol (23 mL), purged with nitrogen, and reacted at room temperature for 48 h. The reaction solution was filtered through Celite. The filter cake was washed with an appropriate amount of EtOH. The crude product was washed with DCM into a 250 mL eggplant-shaped flask. EtOH (about 10 mL) was added thereto, and DCM was removed through rotary evaporation at room temperature until solids were precipitated. The solids were filtered and washed with an appropriate amount of EtOH to obtain a crude product. The crude product was purified through column chromatography to obtain 0.1 g of Compound 295 with a yield of 5.7%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1278.5. 
     Synthesis Example 24: Synthesis of Compound 280 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     Intermediate 46 (0.15 g, 0.526 mmol) was dissolved in 9 mL of 2-ethoxyethanol and 3 mL of water at room temperature, IrCl 3 .3H 2 O (62 mg, 0.175 mmol) was added, and the system was heated to 160° C. in an autoclave, refluxed for 24 h at this temperature, and cooled to room temperature. The solution was filtered. The solids were washed with ethanol until the washing liquid was colorless and then suction-filtered to obtain an iridium dimer as a red solid which was directly used in the next step without being purified. 
     Step 2: Synthesis of Compound 280 
     
       
         
         
             
             
         
       
     
     The iridium dimer (0.25 g. 0.157 mmol) obtained in the previous step was added to a 100 mL round-bottom flask, K 2 CO 3  (217 mg, 1.57 mmol) and 3,7-diethyl-3-methylnonane-4,6-dione (142 mg, 0.629 mmol) were added, and 5 mL of 2-ethoxyethanol and 5 mL of DCM were added. The system was purged three times at room temperature, heated to 40° C., and stirred for 24 h under nitrogen protection. DCM was removed in vacuo. The system was filtered through Celite. The solids were washed with ethanol until the washing liquid was colorless and then suction-filtered to remove ethanol. Under vacuum filtration, the red solids on the Celite were dissolved in 200 mL of dichloromethane. 20 mL of ethanol was added, and dichloromethane was removed in vacuo to precipitate out a solid which was tittered to obtain Compound 280 as a red solid (195 mg, 0.20 mmol, with a yield of 63.7%). The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 986.3. 
     Synthesis Example 25: Synthesis of a Compound Comprising Ligand L a1931    
     Step 1: Synthesis of Intermediate 48 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 12 (1.63 g, 7.0 mmol), Intermediate 47 (3.9 g, 7.4 mmol), Pd(PPh 3 ) 4  (0.4 g, 0.35 mmol), sodium carbonate (1.11 g, 10.5 mmol) and 1,4-dioxane/water (28 mL/7 mL) was heated under nitrogen protection to reflux overnight. After TLC showed that the reaction was complete, the system was cooled to room temperature. Water was added to the reaction system. The organic phase was extracted with EA, dried and filtered. The solvent was removed via rotary-evaporation to obtain Intermediate 48 (3.2 g, 76% yield). 
     Step 2: Synthesis of Intermediate 49 
     
       
         
         
             
             
         
       
     
     Intermediate 48 (3.2 g, 5.33 mmol) was dissolved in 15 mL of ethanol. 15 mL of HCl (2N) was then slowly added to the reaction system, followed by heating to reflux and reacting for 2 h. After TLC showed that the reaction was complete, the system was cooled to room temperature, neutralized by adding sodium bicarbonate solution to neutral, filtered to obtain a solid crude which was purified by column chromatography to obtain Intermediate 49 (2.65 g, 94.5% yield). 
     Step 3: Synthesis of Intermediate 50 
     
       
         
         
             
             
         
       
     
     Intermediate 49 (2.65 g, 5.0 mmol), cuprous bromide (72 mg, 0.5 mmol), 2,2,6,6-tetramethylheptanedione (0.74 g, 4.0 mmol), cesium carbonate (4.07 g, 12.5 mmol) and DMF (50 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was complete, the system was cooled to room temperature. Water was added to the system to precipitate out a large amount of yellow solids which was filtered, washed with water several times and suction-filtered to obtain Intermediate 50 as a yellow solid (2.26 g, 92.4% yield). 
     Step 4: Synthesis of Intermediate 51 
     
       
         
         
             
             
         
       
     
     Intermediate 50 (2.26 g, 4.62 mmol), neopentylboronic acid (1.07 g, 9.23 mmol), Pd 2 (dba) 3  (106 mg, 0.12 mmol), Sphos (190 mg, 0.46 mmol), K 3 PO 4 .3H 2 O (3.69 g, 13.9 mmol) and toluene (30 mL) were mixed. The system was purged with nitrogen three times, heated to reflux, and reacted overnight. After TLC showed that the reaction was complete, the system was cooled to room temperature. The solvent was removed through rotary-evaporation to obtain a crude product, which was purified by column chromatography to obtain Intermediate 51 (1.8 g, 74% yield). The structure of this intermediate was confirmed as the target structure by LC-MS with the molecular weight of 525.3. 
     Starting from Intermediate 51, a compound of the present disclosure comprising the ligand L a1931  can be obtained by the person skilled in the art by referring to the methods in the prior art or by following the methods of Synthesis Examples 1 to 24. 
     Synthesis Example 25: Synthesis of Compound Ir(L a1805 ) 2 L b122    
     Step 1: Synthesis of Compound Ir(L a1805 ) 2 L b122   
     
       
         
         
             
             
         
       
     
     The iridium dimer (1.01 g, 0.97 mmol), 3,7-diethyl-3-methylnonane-4,6-dione (0.34 g, 1.5 mmol) and K 2 CO 3  (0.72 g, 4.85 mmol) were dissolved in 20 mL of 2-ethoxyethanol. The system was protected under nitrogen and reacted at 50° C. for 24 h. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.68 g of Compound Ir(L a1805 ) 2 L b122  with a yield of 51%. The structure of the compound was confirmed through LC-MS as the target product with a molecular weight of 1374.8. 
     Those skilled in the art will appreciate that the above preparation methods are merely illustrative. Those skilled in the art can obtain other compound structures of the present disclosure through the modifications of the preparation methods. 
     Device Example 
     Device Example 1 
     First, a glass substrate having an Indium Tin Oxide (ITO) anode with a thickness of 120 nm was cleaned and then treated with oxygen plasma and UV ozone. After the treatment, the substrate was dried in a glovebox to remove moisture. Next, the substrate was mounted on a substrate holder and placed in a vacuum chamber. Organic layers specified below were sequentially deposited through vacuum thermal evaporation on the ITO anode at a rate of 0.2 to 2 Angstroms per second at a vacuum degree of about 10 −8  torr. Compound HI was used as a hole injection layer (HIL) with a thickness of 100 Å. Compound HT was used as a hole transporting layer (HTL) with a thickness of 400 Å. Compound EB1 was used as an electron blocking layer (EBL) with a thickness of 50 Å. Compound 81 of the present disclosure was doped in a host compound RH to be used as an emissive layer (EML, 2:98) with a thickness of 400 Å. Compound HB was used as a hole blocking layer (HBL) with a thickness of 50 Å. On the HBL, Compound ET and 8-hydroxyquinolinolato-lithium (Liq) were co-deposited as an electron transporting layer (ETL) with a thickness of 350 Å. Finally, Liq with a thickness of 1 nm was deposited as an electron injection layer, and A1 with a thickness of 120 nm was deposited as a cathode. The device was transferred back to the glovebox and encapsulated with a glass lid and a moisture getter to complete the device. 
     Device Example 2 
     The preparation method in Device Example 2 was the same as that in Device Example 1, except that Compound 81 of the present disclosure was replaced with Compound 83 of the present disclosure in the emissive layer (EML). 
     Device Example 3 
     The preparation method in Device Example 3 was the same as that in Device Example 1, except that Compound 81 of the present disclosure was replaced with Compound 64 of the present disclosure in the emissive layer (EML), and Compound 64 of the present disclosure was doped with Compound RH at a ratio of 3:97, and Compound EB1 was replaced with Compound EB2 in the electron blocking layer (EBL). 
     Device Example 4 
     The preparation method in Device Example 4 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 93 of the present disclosure in the emissive layer (EML). 
     Device Example 5 
     The preparation method in Device Example 5 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 117 of the present disclosure in the emissive layer (EML). 
     Device Example 6 
     The preparation method in Device Example 6 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 116 of the present disclosure in the emissive layer (EML). 
     Device Example 7 
     The preparation method in Device Example 7 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 261 of the present disclosure in the emissive layer (EML). 
     Device Example 8 
     The preparation method in Device Example 8 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 262 of the present disclosure in the emissive layer (EML). 
     Device Example 9 
     The preparation method in Device Example 9 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 264 of the present disclosure in the emissive layer (EML). 
     Device Example 10 
     The preparation method in Device Example 10 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 263 of the present disclosure in the emissive layer (EML). 
     Device Example 11 
     The preparation method in Device Example 11 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 266 of the present disclosure in the emissive layer (EML). 
     Device Example 12 
     The preparation method in Device Example 12 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 265 of the present disclosure in the emissive layer (EML). 
     Device Example 13 
     The preparation method in Device Example 13 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 267 of the present disclosure in the emissive layer (EML). 
     Device Example 14 
     The preparation method in Device Example 14 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 282 of the present disclosure in the emissive layer (EML). 
     Device Example 15 
     The preparation method in Device Example 15 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 273 of the present disclosure in the emissive layer (EML). 
     Device Example 16 
     The preparation method in Device Example 16 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 294 of the present disclosure in the emissive laver (EML). 
     Device Example 17 
     The preparation method in Device Example 17 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 287 of the present disclosure in the emissive layer (EML). 
     Device Example 18 
     The preparation method in Device Example 18 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 291 of the present disclosure in the emissive layer (EML). 
     Device Example 19 
     The preparation method in Device Example 19 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 292 of the present disclosure in the emissive layer (EML). 
     Device Example 20 
     The preparation method in Device Example 20 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 293 of the present disclosure in the emissive layer (EML). 
     Device Example 21 
     The preparation method in Device Example 21 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound 295 of the present disclosure in the emissive layer (EML). 
     Device Comparative Example 1 
     The preparation method in Device Comparative Example 1 was the same as that in Device Example 1, except that Compound 81 of the present disclosure was replaced with Compound RD in the emissive layer (EML). 
     Device Comparative Example 2 
     The preparation method in Device Comparative Example 2 was the same as that in Device Example 3, except that Compound 64 of the present disclosure was replaced with Compound RD in the emissive layer (EML). 
     The structures and thicknesses of partial layers of the devices are shown in the following table. The layers using more than one material were obtained by doping different compounds at weight ratios as recorded. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Partial device structures in device examples and comparative examples 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Device No. 
                 HIL 
                 HTL 
                 EBL 
                 EML 
                 HBL 
                 ETL 
               
               
                   
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                 Example 1 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB1 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 RD (98:2) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 1 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB1 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 81 (98:2) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB1 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 83 (98:2) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 3 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 64 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                 Example 2 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 RD (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 4 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 93 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 5 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 117 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 6 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 116 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 7 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 261 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 8 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 262 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 9 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 264 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 10 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 263 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 11 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 266 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 12 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 265 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 13 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 267 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 14 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 282 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 15 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 273 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 16 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 294 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 17 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 287 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 18 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 291 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 19 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 292 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 20 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 293 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 21 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB2 (50 Å) 
                 RH:Compound 
                 HB (50 Å) 
                 ET:Liq 
               
               
                   
                   
                   
                   
                 295 (97:3) 
                   
                 (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                   
               
            
           
         
       
     
     The structures of the materials used in the devices are shown as follows: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Current-voltage-luminance (IVL) and lifetime characteristics of the devices were measured at different current densities and voltages. Table 2 shows the CIE data, driving voltage (V), maximum emission wavelength (λ max ), full width at half maximum (FWHM), and external quantum efficiency (EQE) of Device Example 1, Device Example 2, and Device Comparative Example 1 measured at a constant current of 15 mA/cm 2  and the lifetime (LT97) measured at a constant current of 80 mA/cm 2   
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Device data 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 λ max   
                 FWHM 
                 Voltage 
                 EQE 
                 LT97 
               
               
                 Device No. 
                 CIE (x, y) 
                 (nm) 
                 (nm) 
                 (V) 
                 (%) 
                 (h) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 (0.525, 0.472) 
                 566 
                 28.3 
                 3.79 
                 17.5 
                 2 
               
               
                 Example 1 
               
               
                 Example 1 
                 (0.645, 0.351) 
                 606 
                 28.7 
                 3.24 
                 18.4 
                 30 
               
               
                 Example 2 
                 (0.674, 0.324) 
                 618 
                 31 
                 3.55 
                 23.8 
                 105 
               
               
                   
               
            
           
         
       
     
     Discussion 
     From the data shown in Table 2, it can be seen that the FWHMs of Comparative Example 1 and Examples 1 and 2 were all around 30 nm, which are very remarkable. But, Comparative Example 1 had a maximum emission wavelength of 566 nm. Examples 1 and 2, however, achieved a large red shift of the maximum emission wavelength by designing the molecular structure of a light-emitting dopant, so that the emission wavelengths were between 606 urn and 620 nm, which satisfies the requirement on different red emission wavelength hands. At a constant current of IS mA/cm 2 , Examples 1 and 2 were superior to Comparative Example 1 in terms of the voltage and the external quantum efficiency. Especially, the external quantum efficiency of Example 2 was 36% higher than that of Comparative Example 1. According to the data on the lifetime LT97 of Comparative Example 1 and Examples 1 and 2 at a constant current of 80 mA/cm 2 , the lifetime of Comparative Example 1 under this condition was 2 hours, the lifetime of Example 1 was 30 hours, and the lifetime of Example 2 was 105 hours. Therefore, it can be seen that the compounds disclosed by the present disclosure can greatly improve the lifetime of an electroluminescent device. From the preceding data analysis, it can be seen that while maintaining a very narrow FWHM, the Examples can effectively adjust the emission wavelength to meet the requirement on red light emission, reduce the voltage, improve the EQE, and most importantly, greatly improve the lifetime, thereby providing excellent performance. 
     Table 3 shows the CIE data, driving voltage (V), maximum emission wavelength (λ max ), full width at half maximum (FWHM), and lifetime (LT97) of Device Example 3 measured at a constant current of 15 mA/cm 2 . 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Device data 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 CIE 
                 λ max   
                 FWHM 
                 Voltage 
                 LT97 
               
               
                 Device No. 
                 (x, y) 
                 (nm) 
                 (nm) 
                 (V) 
                 (h) 
               
               
                   
               
               
                 Example 3 
                 (0.683, 0.313) 
                 633 
                 39 
                 3.78 
                 180 
               
               
                   
               
            
           
         
       
     
     Discussion 
     From the data shown in Table 3, it can be seen that Example 3 achieved an emission wavelength of 633 not by adjusting the molecular structure, which is in a deep red region. At a constant current of 15 mA/cm 2 , Example 3 had a very narrow FWHM of 39 nm and a relatively low driving voltage of 3.78 V. 
     Table 4 shows the CIE data, driving voltage (V), maximum emission wavelength (λ max ), full width at half maximum (FWHM), and external quantum efficiency (EQE) of Device Comparative Example 2, and Device Examples 4 to 21 measured at a constant current of 15 mA/cm 2  and the lifetime (LT97) at a constant current of 80 mA/cm 2 . 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Device data 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 λ max   
                 FWHM 
                 Voltage 
                 EQE 
                 LT97 
               
               
                 Device No. 
                 CIE (x, y) 
                 (nm) 
                 (nm) 
                 (V) 
                 (%) 
                 (h) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 (0.529, 0.469) 
                 566 
                 29.3 
                 4.21 
                 21.83 
                 3 
               
               
                 Example 2 
               
               
                 Example 4 
                 (0.671, 0.328) 
                 616 
                 32.3 
                 4.37 
                 22.28 
                 81 
               
               
                 Example 5 
                 (0.672, 0.326) 
                 617 
                 31.6 
                 4.12 
                 23.38 
                 84 
               
               
                 Example 6 
                 (0.667, 0.331) 
                 614 
                 31.0 
                 4.27 
                 21.91 
                 61 
               
               
                 Example 7 
                 (0.671, 0.328) 
                 616 
                 32.5 
                 4.32 
                 22.84 
                 63 
               
               
                 Example 8 
                 (0.683, 0.315) 
                 623 
                 32.9 
                 4.25 
                 21.96 
                 139 
               
               
                 Example 9 
                 (0.671, 0.328) 
                 616 
                 32.3 
                 4.32 
                 23.65 
                 119 
               
               
                 Example 10 
                 (0.673, 0.326) 
                 617 
                 31.4 
                 4.30 
                 22.85 
                 108 
               
               
                 Example 11 
                 (0.686, 0.316) 
                 623 
                 34.1 
                 4.33 
                 23.63 
                 149 
               
               
                 Example 12 
                 (0.679, 0.320) 
                 622 
                 34.3 
                 4.20 
                 22.95 
                 148 
               
               
                 Example 13 
                 (0.684, 0.315) 
                 623 
                 35.7 
                 4.69 
                 23.08 
                 80 
               
               
                 Example 14 
                 (0.687, 0.312) 
                 625 
                 33.5 
                 4.23 
                 25.88 
                 41 
               
               
                 Example 15 
                 (0.650, 0.349) 
                 607 
                 31.4 
                 4.15 
                 23.34 
                 31 
               
               
                 Example 16 
                 (0.677, 0.322) 
                 618 
                 31.0 
                 4.33 
                 21.88 
                 149 
               
               
                 Example 17 
                 (0.670, 0.328) 
                 616 
                 32.1 
                 4.31 
                 21.94 
                 54 
               
               
                 Example 18 
                 (0.676, 0.321) 
                 621 
                 32.9 
                 4.33 
                 22.25 
                 63 
               
               
                 Example 19 
                 (0.673, 0.325) 
                 619 
                 31.8 
                 4.30 
                 21.70 
                 51 
               
               
                 Example 20 
                 (0.678, 0.320) 
                 621 
                 31.6 
                 4.53 
                 22.95 
                 106 
               
               
                 Example 21 
                 (0.683, 0.314) 
                 625 
                 32.8 
                 4.00 
                 21.25 
                 46 
               
               
                   
               
            
           
         
       
     
     Discussion 
     From the device data in Table 4, it can also be seen that Examples 4 to 13, where the compounds of the present disclosure were used as a dopant in the light-emitting layer, all achieved a large red shift of the maximum emission wavelength of the devices. The emission wavelengths of Examples 4 to 13 were between 614 nm and 623 nm and can meet the requirement on different red emission wavelength hands. While the maximum emission wavelength of Comparative Example 2 where Comparative Compound RD was used was only 566 nm and cannot meet the requirement on the light-emitting colors of red light-emitting devices at all. In addition, though the FWHMs and voltages of Examples 4 to 13 were basically the same as or slightly worse than those of Comparative Example 2 at a constant current of 15 mA/cm 2 , it should be noted that the FWHMs of Examples 4 to 13, that were less than 36 nm, are still at high levels in the industry and the voltages of Examples 4 to 13 are also still relatively low in the industry. On the other hand, the external quantum efficiency of all Examples 4 to 13 was further improved compared to the very high external quantum efficiency of Comparative Example 2. Most importantly, the lifetimes LT97 of Examples 4 to 13 at a constant current of 80 mA/cm 2  were all greatly improved (at least about 20 fold and up to about 50 fold) relative to the lifetime of Comparative Example 2 (which was only 3 hours under this condition and cannot meet the requirement at all). All the above comparisons prove again that the compounds disclosed by the present disclosure have very excellent performance. 
     From the device data in Table 4, it can also be seen that Examples 14 to 21, where the compounds of the present disclosure were used as a dopant in the light-emitting layer, all achieved a large red shift of the maximum emission wavelength of the devices. The emission wavelengths of Examples 14 to 21 were between 607 nm and 625 nm and can meet the requirement on different red emission wavelength hands. While the maximum emission wavelength of Comparative Example 2 where Comparative Compound RD was used was only 566 nm and cannot meet the requirement on the light-emitting colors of red light-emitting devices at all. In addition, though the FWHMs and voltages of Examples 14 to 21 were basically the same as or slightly worse than those of Comparative Example 2 at a constant current of 15 mA/cm 2 , it should be noted that the FWHMs of Examples 14 to 21, that were less than 34 nm, are still at high levels in the industry and the voltages of Examples 14 to 21 are also still relatively low in the industry. On the other hand, the external quantum efficiency of all Examples 14 to 21 was further improved compared to the very high external quantum efficiency of Comparative Example 2. Most importantly, the lifetimes LT97 of Examples 14 to 21 at a constant current of 80 mA/cm 2  were all greatly improved (at least about 9 fold and up to about 50 fold) relative to the lifetime of Comparative Example 2 (which was only 3 hours under this condition and cannot meet the requirement at all). All the above comparisons prove again that the compounds disclosed by the present disclosure have very excellent performance. 
     Additional Synthesis Example 
     Synthesis Example 2-1: Synthesis of Compound 2-341 
     Step 1: Synthesis of Intermediate 2-3 
     
       
         
         
             
             
         
       
     
     Intermediate 2-1 (2.1 g, 5.2 mmol), Intermediate 2-2 (2.43 g, 5.2 mmol), tetrakis(triphenylphosphine)palladium (0.295 g, 0.26 mmol), sodium carbonate (0.818 g, 7.7 mmol), 1,4-dioxane (20 mL) and water (5 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:3, v/v) to obtain Intermediate 2-3 as a white solid (2.9 g, with a yield of 78.5%). 
     Step 2: Synthesis of Intermediate 2-4 
     
       
         
         
             
             
         
       
     
     Intermediate 2-3 (2.9 g, 4.1 mmol) was dissolved in 10 mL of ethanol, and then 10 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain Intermediate 2-4 as a yellow solid (2.6 g, with a yield of 97.2%). 
     Step 3: Synthesis of Intermediate 2-5 
     
       
         
         
             
             
         
       
     
     Intermediate 2-4 (2.6 g, 4.0 mmol), cesium carbonate (2.6 g, 8 mmol) and DMF (40 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain Intermediate 2-5 as a yellow solid (2 g, with a yield of 99.9%). 
     Step 4: Synthesis of Intermediate 2-6 
     
       
         
         
             
             
         
       
     
     Intermediate 2-5 (2 g, 4 mmol), neopentylboronic acid (935 mg, 8 mmol), palladium acetate (90 mg, 0.4 mmol), Sphos (328 mg, 0.8 mmol), potassium phosphate trihydrate (3.2 g, 12 mmol) and toluene (30 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:20, v/v) to obtain Intermediate 2-6 as a yellow solid (2 g, with a yield of 94.4%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-6 (1.1 g, 2.08 mmol), iridium trichloride trihydrate (293 mg, 0.83 mmol), 2-ethoxyethanol (18 mL) and water (6 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-341 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3-methylnonane-4,6-dione (271 mg, 12 mmol) and potassium carbonate (0.57 g, 4.15 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.27 g of Compound 2-341 with a yield of 22%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1474.8. 
     Synthesis Example 2-2: Synthesis of Compound 2-441 
     Step 1: Synthesis of Compound 2-441 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in step 5 of Synthesis Example 2-1,3,7-diethyl-3,7-dimethylnonane-4,6-dione (58 mg, 0.24 mmol) and potassium carbonate (0.11 g, 0.8 mmol) were added to a 50 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.05 g of Compound 2-441 with a yield of 21%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1488.8. 
     Synthesis Example 2-3: Synthesis of Compound 2-442 
     Step 1: Synthesis of Intermediate 2-8 
     
       
         
         
             
             
         
       
     
     Intermediate 2-7 (1.6 g, 4.1 mmol), Intermediate 2-2 (1.93 g, 4.1 mmol), tetrakis(triphenylphosphine)palladium (0.237 g, 0.2 mmol), sodium carbonate (0.652 g. 6.2 mmol), 1,4-dioxane (16 mL) and water (4 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:3, v/v) to obtain Intermediate 2-8 as a white solid (2.46 g, with a yield of 86.5%). 
     Step 2: Synthesis of Intermediate 2-9 
     
       
         
         
             
             
         
       
     
     Intermediate 2-8 (2.46 g, 3.5 mmol) was dissolved in 10 mL of ethanol, and then 10 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain Intermediate 2-9 as a yellow solid (2.32 g, with a yield of 99.9%). 
     Step 3: Synthesis of Intermediate 2-10 
     
       
         
         
             
             
         
       
     
     Intermediate 2-9 (2.32 g, 3.65 mmol), cesium carbonate (3.56 g. 10.9 mmol) and DMF (35 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain Intermediate 2-10 as a yellow solid (1.4 g, with a yield of 80.3%). 
     Step 4: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-10 (1.4 g, 2.93 mmol), iridium trichloride trihydrate (344 mg, 0.98 mmol), 2-ethoxyethanol (21 mL) and water (7 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 5: Synthesis of Compound 2-442 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (353 mg, 1.47 mmol) and potassium carbonate (0.67 g, 4.9 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.88 g of Compound 2-442 with a yield of 64.8%. The product was further purified through column chromatography. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1384.6. 
     Synthesis Example 2-4: Synthesis of Compound 2-438 
     Step 1: Synthesis of Intermediate 2-12 
     
       
         
         
             
             
         
       
     
     Intermediate 2-1 (1.45 g, 3.59 mmol), Intermediate 2-11 (1.43 g, 3.59 mmol), tetrakis(triphenylphosphine)palladium (0.27 g, 0.18 mmol), sodium carbonate (0.57 g, 5.4 mmol), 1,4-dioxane (16 mL) and water (4 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction solution, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:2, v/v) to obtain Intermediate 2-12 as a white solid (2.2 g, with a yield of 95.7%). 
     Step 2: Synthesis of Intermediate 2-13 
     
       
         
         
             
             
         
       
     
     Intermediate 2-12 (2.2 g, 3.4 mmol) was dissolved in 10 mL of ethanol, and then 10 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain Intermediate 2-13 as a yellow solid (1.8 g, with a yield of 99.8%). 
     Step 3: Synthesis of Intermediate 2-14 
     
       
         
         
             
             
         
       
     
     Intermediate 2-13 (1.8 g, 3.4 mmol), cesium carbonate (2.2 g, 6.8 mmol) and DMF (30 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain Intermediate 2-14 as a yellow solid (1.2 g, with a yield of 83.2%). 
     Step 4: Synthesis of Intermediate 2-15 
     
       
         
         
             
             
         
       
     
     Intermediate 2-14 (1.2 g, 2.83 mmol), neopentylboronic acid (656 mg, 5.66 mmol), palladium acetate (32 mg, 0.14 mmol), Sphos (116 mg, 0.28 mmol), potassium phosphate trihydrate (2.26 g, 8.49 mmol) and toluene (20 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:20, v/v) to obtain Intermediate 2-15 as a yellow solid (0.88 g, with a yield of 67.5%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-15 (0.88 g, 1.91 mmol), iridium trichloride trihydrate (193 mg, 0.55 mmol), 2-ethoxyethanol (I 8 mL) and water (6 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-438 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (200 mg. 0.83 mmol) and potassium carbonate (0.38 g, 2.75 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.41 g of Compound 2-438 with a yield of 55.3%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1348.7. 
     Synthesis Example 2-5: Synthesis of Compound 2-446 
     Step 1: Synthesis of Intermediate 2-17 
     
       
         
         
             
             
         
       
     
     Intermediate 2-16 (1.45 g, 3.59 mmol), Intermediate 2-11 (1.43 g, 3.59 mmol), tetrakis(triphenylphosphine)palladium (0.27 g, 0.18 mmol), sodium carbonate (0.57 g, 5.4 mmol), 1,4-dioxane (16 mL) and water (4 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:2, v/v) to obtain Intermediate 2-17 as a white solid (2.0 g, with a yield of 90%). 
     Step 2: Synthesis of Intermediate 2-18 
     
       
         
         
             
             
         
       
     
     Intermediate 2-17 (2.2 g. 3.4 mmol) was dissolved in 10 mL of ethanol, and then 10 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain Intermediate 2-18 as a yellow solid (1.8 g, with a yield of 99.8%). 
     Step 3: Synthesis of Intermediate 2-19 
     
       
         
         
             
             
         
       
     
     Intermediate 2-18 (1.8 g, 3.4 mmol), cesium carbonate (2.2 g, 6.8 mmol) and DMF (35 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain intermediate 2-19 as a yellow solid (1.2 g, with a yield of 83.2%). 
     Step 4: Synthesis of Intermediate 2-20 
     
       
         
         
             
             
         
       
     
     Intermediate 2-19 (1.2 g, 2.83 mmol), neopentylboronic acid (656 mg, 5.66 mmol), palladium acetate (32 mg, 0.14 mmol), Sphos (116 mg, 0.28 mmol), potassium phosphate trihydrate (2.26 g, 8.49 mmol) and toluene (20 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:50, v/v) to obtain Intermediate 2-20 as a yellow solid (0.88 g, with a yield of 67.5%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-20 (0.51 g, 1.1 mmol), iridium trichloride trihydrate (130 mg, 0.37 mmol), 2-ethoxyethanol (27 mL) and water (9 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-446 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (130 mg, 0.55 mmol) and potassium carbonate (0.26 g, 1.85 mmol) were added to a 100 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.24 g of Compound 2-446 with a yield of 48%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1348.7. 
     Synthesis Example 2-6: Synthesis of Compound 2-1021 
     Step 1: Synthesis of Intermediate 2-21 
     
       
         
         
             
             
         
       
     
     Intermediate 2-16 (1.89 g, 4.68 mmol), Intermediate 2-2 (2.18 g, 4.67 mmol), tetrakis(triphenylphosphine)palladium (0.27 g, 0.23 mmol), sodium carbonate (0.74 g, 7 mmol), 1,4-dioxane (28 mL) and water (7 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:2, v/v) to obtain Intermediate 2-21 as a white solid (2.3 g, with a yield of 70%). 
     Step 2: Synthesis of Intermediate 2-22 
     
       
         
         
             
             
         
       
     
     Intermediate 2-21 (4.5 g, 6.34 mmol) was dissolved in 30 mL of ethanol, and then 30 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain Intermediate 2-22 as a yellow solid (3.1 g, with a yield of 99.8%). 
     Step 3: Synthesis of Intermediate 2-23 
     
       
         
         
             
             
         
       
     
     Intermediate 2-22 (3.1 g, 6.34 mmol), cesium carbonate (5.16 g, 15.8 mmol) and DMF (50 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain Intermediate 2-23 as a yellow solid (5.5 g, with a yield of 88%). 
     Step 4: Synthesis of Intermediate 2-24 
     
       
         
         
             
             
         
       
     
     Intermediate 2-23 (3.13 g, 6.3 mmol), neopentylboronic acid (2.21 g, 19 mmol), palladium acetate (144 mg, 0.64 mmol), Sphos (525 mg, 1.28 mmol), potassium phosphate trihydrate (5.1 g, 19.02 mmol) and toluene (30 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:20, v/v) to obtain Intermediate 2-24 as a yellow solid (2.6 g, with a yield of 75%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-24 (1.6 g, 3 mmol), iridium trichloride trihydrate (356 mg, 1 mmol), 2-ethoxyethanol (36 mL) and water (12 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and filtered. The solids were washed with methanol and dried under a vacuum condition so that an iridium dimer was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-1021 
     
       
         
         
             
             
         
       
     
     The iridium dieter obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (360 mg, 1.5 mmol), potassium carbonate (0.69 g, 5 mmol) and 2-ethoxyethanol (35 mL) were added to a 100 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.1 g of Compound 2-1021 with a yield of 6%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1488.8. 
     Synthesis Example 2-7: Synthesis of Compound 2-405 
     Step 1: Synthesis of Intermediate 2-26 
     
       
         
         
             
             
         
       
     
     Intermediate 2-25 (1.45 g. 3.59 mmol), Intermediate 2-11 (1.43 g, 3.59 mmol), tetrakis(triphenylphosphine)palladium (0.27 g, 0.18 mmol), sodium carbonate (0.57 g, 5.4 mmol), 1,4-dioxane (16 mL) and water (4 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:2, v/v) to obtain Intermediate 2-26 as a white solid (2.2 g, with a yield of 95.7%). 
     Step 2: Synthesis of Intermediate 2-27 
     
       
         
         
             
             
         
       
     
     Intermediate 2-26 (2.2 g. 3.4 mmol) was dissolved in 10 mL of ethanol, and then 10 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain Intermediate 2-27 as a yellow solid (1.8 g, with a yield of 99.8%). 
     Step 3: Synthesis of Intermediate 2-28 
     
       
         
         
             
             
         
       
     
     Intermediate 2-27 (1.8 g, 3.4 mmol), cesium carbonate (2.2 g, 6.8 mmol) and DMF (35 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain Intermediate 2-28 as a yellow solid (1.2 g, with a yield of 83.2%). 
     Step 4: Synthesis of Intermediate 2-29 
     
       
         
         
             
             
         
       
     
     Intermediate 2-28 (1.2 g, 2.83 mmol), neopentylboronic acid (656 mg, 5.66 mmol), palladium acetate (32 mg, 0.14 mmol), Sphos (116 mg, 0.28 mmol), potassium phosphate trihydrate (2.26 g, 8.49 mmol) and toluene (20 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:50, v/v) to obtain Intermediate 2-29 as a yellow solid (0.88 g, with a yield of 67.5%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-29 (0.88 g, 1.91 mmol), iridium trichloride trihydrate (193 mg. 0.55 mmol), 2-ethoxyethanol (I 8 mL) and water (6 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and filtered so that 210 mg of iridium dimer was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-405 
     
       
         
         
             
             
         
       
     
     The iridium dimer (210 mg, 0.114 mmol) obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (165 mg, 0.69 mmol), potassium carbonate (0.1 g, 1.35 mmol) and ethoxyethanol (10 mL) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.1 g of Compound 2-405 with a yield of 13.5%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1348.7. 
     Synthesis Example 2-8: Synthesis of Compound 2-205 
     Step 1: Synthesis of Compound 2-205 
     
       
         
         
             
             
         
       
     
     The iridium dimer (210 mg, 0.114 mmol) obtained in step 5 of Synthesis Example 2-7, 3,7-diethyl-1,1,1-trifluorononane-4,6-dione (184 mg, 0.69 mmol), potassium carbonate (0.1 g, 1.35 mmol) and ethoxyethanol (10 mL) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.1 g of Compound 2-205 with a yield of 13.2%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1374.6. 
     Synthesis Example 2-9: Synthesis of Compound 2-1019 
     Step 1: Synthesis of Intermediate 2-31 
     
       
         
         
             
             
         
       
     
     Intermediate 2-30 (2.2 g, 5.2 mmol), Intermediate 2-11 (2.43 g, 5.2 mmol), tetrakis(triphenylphosphine)palladium (0.295 g, 0.26 mmol), sodium carbonate (0.818 g, 7.7 mmol), 1,4-dioxane (20 mL) and water (5 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:3, v/v) to obtain Intermediate 2-31 as a white solid (2.9 g, with a yield of 76.5%). 
     Step 2: Synthesis of Intermediate 2-32 
     
       
         
         
             
             
         
       
     
     Intermediate 2-31 (2.9 g, 4.1 mmol) was dissolved in 10 mL of ethanol, and then 10 mL of 2 M HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times, and pumped to obtain Intermediate 2-32 as a yellow solid (2.7 g, with a yield of 97.2%). 
     Step 3: Synthesis of Intermediate 2-33 
     
       
         
         
             
             
         
       
     
     Intermediate 2-32 (2.7 g, 4.0 mmol), cesium carbonate (2.6 g, 8 mmol) and DMF (40 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. 100 mL of water was added thereto, and a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and dried to obtain Intermediate 2-33 as a yellow solid (2 g, with a yield of 98.4%). 
     Step 4: Synthesis of Intermediate 2-34 
     
       
         
         
             
             
         
       
     
     Intermediate 2-33 (2 g, 3.94 mmol), neopentylboronic acid (914 mg, 7.88 mmol), palladium acetate (90 mg, 0.4 mmol), Sphos (328 mg. 0.8 mmol), potassium phosphate trihydrate (3.2 g, 12 mmol) and toluene (30 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:20, v/v) to obtain Intermediate 2-34 as a yellow solid (1.1 g, with a yield of 50.6%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-34 (1.1 g, 2.02 mmol), iridium trichloride trihydrate (293 mg, 0.83 mmol). 2-ethoxyethanol (18 mL) and water (6 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-1019 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (271 mg, 1.2 mmol) and potassium carbonate (0.57 g, 4.15 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.22 g of Compound 2-1019 with a yield of 17.5%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1376.7. 
     Synthesis Example 2-10: Synthesis of Compound 2-447 
     Step 1: Synthesis of Intermediate 2-36 
     
       
         
         
             
             
         
       
     
     Intermediate 2-16 (2.61 g, 6.47 mmol), Intermediate 2-35 (2.67 g, 6.47 mmol), tetrakis(triphenylphosphine)palladium (0.37 g, 0.32 mmol), sodium carbonate (1.03 g, 9.7 mmol), 1,4-dioxane (52 mL) and water (13 mL) were added to a round-bottom flask. Then, the reaction was heated to 90° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:2, v/v) to obtain the target product Intermediate 2-36 as a white solid (3.1 g, 72%). 
     Step 2: Synthesis of Intermediate 2-37 
     
       
         
         
             
             
         
       
     
     Intermediate 2-36 (3.12 g, 4.77 mmol) was dissolved in 20 mL of ethanol, and then 20 mL of 2 N HCl was added thereto, and then the reaction was heated to reflux and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Then, a saturated solution of sodium carbonate was added to adjust the pH to neutral. A large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times, and pumped to dryness to obtain the target product Intermediate 2-37 as a yellow solid (2.74 g, 96%). 
     Step 3: Synthesis of Intermediate 2-38 
     
       
         
         
             
             
         
       
     
     Intermediate 2-37 (2.74 g, 4.6 mmol), cesium carbonate (3.89 g, 11.93 mmol) and DMF (40 mL) were heated to 135° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Water was added to the solution until a large amount of yellow solids were precipitated from the solution. The solids were filtered, washed with water several times and pumped to dryness to obtain the target product Intermediate 2-38 as a yellow solid (1.84 g, 91%). 
     Step 4: Synthesis of Intermediate 2-39 
     
       
         
         
             
             
         
       
     
     Intermediate 2-38 (0.56 g, 1.27 mmol), neopentylboronic acid (0.42 g, 3.81 mmol), Pd 2 (dba) 3  (0.058 g, 0.06 mmol), Sphos (0.052 g, 0.127 mmol), potassium phosphate trihydrate (1.02 g, 3.81 mmol) and toluene (15 mL) were heated to reflux and reacted overnight under nitrogen protection. After TLC showed that the reaction was completed, the system was cooled to room temperature. The solution was poured into a funnel filled with Celite and filtered. The filtrate was collected and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:100, v/v) to obtain the target product intermediate 2-39 as a yellow solid (0.58 g, 95%). 
     Step 5: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-39 (0.58 g, 1.23 mmol), iridium trichloride trihydrate (0.12 g, 0.35 mmol), 2-ethoxyethanol (36 mL) and water (12 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 6: Synthesis of Compound 2-447 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (0.13 g, 0.53 mmol), potassium carbonate (0.69 g, 5 mmol) and 2-ethoxyethanol (35 mL) were added to a round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.18 g of Compound 2-447 with a yield of 37%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1376.7. 
     Synthesis Example 2-11: Synthesis of Compound 2-1020 
     Step 1: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-40 (1 g. 2.17 mmol), iridium trichloride trihydrate (293 mg, 0.83 mmol), 2-ethoxyethanol (18 mL) and water (6 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 2: Synthesis of Compound 2-1020 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (271 mg, 1.2 mmol) and potassium carbonate (0.57 g, 4.15 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.45 g of Compound 2-1020 with a yield of 40.1%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1350.7. 
     Synthesis Example 2-12: Synthesis of Compound 2-1018 
     Step 1: Synthesis of Intermediate 2-41 
     
       
         
         
             
             
         
       
     
     Intermediate 2-19 (344 mg, 0.81 mmol) and [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium dichloride (28 mg, 0.04 mmol) were dissolved in THE (5 mL). 2 mol/L of 3,3,3-trifluoro-2,2-dimethylpropylmagnesium bromide in THE (4 mL) was added thereto under nitrogen protection and reacted at 45° C. The reaction was monitored through LC-MS and stopped until Intermediate 2-19 disappeared. An aqueous solution of ammonium chloride was added to quench the reaction, and the solution was extracted with EA. The organic phases were collected, dried, subjected to rotary evaporation to remove the solvent and isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:100, v/v) to obtain Intermediate 2-41 (248 mg, with a yield of 60%). 
     Step 2: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-41 (0.28 g, 0.54 mmol), iridium trichloride trihydrate (50 mg, 0.14 mmol), 2-ethoxyethanol (15 mL) and water (5 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and filtered. The solids were collected and washed with methanol three times. The solvent was removed under a vacuum condition, and an iridium dimer as a red solid was collected, which was used in the next step without further purification. 
     Step 3: Synthesis of Compound 2-1018 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (51 mg, 0.21 mmol), potassium carbonate (98 mg, 0.71 mmol) and ethoxyethanol (15 mL) were added to a 100 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.1 g of Compound 2-1018 with a yield of 49%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1456.6. 
     Synthesis Example 2-13: Synthesis of Compound 2-452 
     Step 1: Synthesis of Intermediate 2-44 
     
       
         
         
             
             
         
       
     
     Intermediate 2-42 (418 mg, 0.95 mmol), Intermediate 2-43 (370 mg, 1 mmol), tetrakis(triphenylphosphine)palladium (55 mg, 0.048 mmol), sodium carbonate (151 mg, 1.43 mmol), 1,4-dioxane (8 mL) and water (2 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:3, v/v) to obtain Intermediate 2-44 as a white solid (500 mg, with a yield of 81.3%). 
     Step 2: Synthesis of Intermediate 2-45 
     
       
         
         
             
             
         
       
     
     Intermediate 2-44 (500 mg, 0.77 mmol) and diphenyl ether (4 mL) were heated to 180° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:20, v/v) to obtain Intermediate 2-45 as a yellow solid (110 mg, with a yield of 30%). 
     Step 3: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-45 (110 mg, 0.23 mmol), iridium trichloride trihydrate (25 mg, 0.077 mmol), 2-ethoxyethanol (6 mL) and water (2 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution, so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 4: Synthesis of Compound 2-452 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (111 mg, 0.46 mmol) and potassium carbonate (159 mg, 1.15 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.04 g of Compound 2-452 with a yield of 37.6%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1380.6. 
     Synthesis Example 2-14: Synthesis of Compound 2-1017 
     Step 1: Synthesis of Intermediate 2-47 
     
       
         
         
             
             
         
       
     
     Intermediate 2-19 (0.5 g, 1.18 mmol), Intermediate 2-46 (346 mg, 2.36 mmol), Pd 2 (dba) 3  (12 mg, 0.012 mmol), tBuDavephos (21 mg. 0.06 mmol), lithium acetate (0.39 g, 5.9 mmol), water (43 mg, 2.36 mmol) and DMF (30 mL) were added to a reaction tube, sealed under nitrogen protection, heated to 150° C. and reacted overnight. After the reaction was completed, the system was cooled to room temperature and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography to obtain Intermediate 2-47 as a yellow solid (0.4 g, 73.5%). 
     Step 2: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-47 (0.7 g, 1.52 mmol), iridium trichloride trihydrate (0.18 g, 0.5 mmol), 2-ethoxyethanol (27 mL) and water (9 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and filtered. The solids were washed with methanol and dried so that an iridium dimer was obtained, which was used in the next step without further purification. 
     Step 3: Synthesis of Compound 2-1017 
     
       
         
         
             
             
         
       
     
     The iridium dimer obtained in the previous step. 3,7-diethyl-3,7-dimethylnonane-4,6-dione (0.18 g. 0.76 mmol), potassium carbonate (0.35 g, 2.53 mmol) and 2-ethoxyethanol (10 mL) were added to a 100 mL round-bottom flask and reacted at 50° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.37 g of Compound 2-1017 with a yield of 54%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1352.6. 
     Synthesis Example 2-15: Synthesis of Compound 2-1022 
     Step 1: Synthesis of Intermediate 2-49 
     
       
         
         
             
             
         
       
     
     Intermediate 2-42 (600 mg, 1.37 mmol), Intermediate 2-48 (546 mg, 1.43 mmol), tetrakis(triphenylphosphine)palladium (79 mg. 0.069 mmol), sodium carbonate (218 mg, 2.06 mmol), 1,4-dioxane (8 mL) and water (2 mL) were added to a 100 mL round-bottom flask. Then, the reaction was heated to 80° C. under nitrogen protection and stirred overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. Ethyl acetate was added to the reaction, layers were separated, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried and subjected to rotary evaporation to dryness to obtain a crude product. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:3, v/v) to obtain Intermediate 2-49 as a white solid (620 mg, with a yield of 68.4%). 
     Step 2: Synthesis of Intermediate 2-50 
     
       
         
         
             
             
         
       
     
     Intermediate 2-49 (620 mg, 0.94 mmol) and diphenyl ether (5 mL) were heated to 140° C. under nitrogen protection and reacted overnight. After TLC showed that the reaction was completed, the system was cooled to room temperature. The crude product was isolated through silica gel column chromatography (eluent: ethyl acetate:petroleum ether=1:20, v/v) to obtain Intermediate 2-50 as a yellow solid (260 mg, with a yield of 56.5%). 
     Step 3: Synthesis of an Iridium Dimer 
     
       
         
         
             
             
         
       
     
     A mixture of Intermediate 2-50 (260 mg, 0.53 mmol), iridium trichloride trihydrate (62 mg, 0.18 mmol), 2-ethoxyethanol (9 mL) and water (3 mL) was refluxed under a nitrogen atmosphere for 24 h. The system was cooled to room temperature and subjected to rotary evaporation to carefully remove water in the solution so that a solution of an iridium dimer in ethoxyethanol was obtained, which was used in the next step without further purification. 
     Step 4: Synthesis of Compound 2-1022 
     
       
         
         
             
             
         
       
     
     The solution of the iridium dimer in ethoxyethanol obtained in the previous step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (86 mg, 0.36 mmol) and potassium carbonate (124 mg, 0.9 mmol) were added to a 100 mL round-bottom flask and reacted at 60° C. for 24 h under nitrogen protection. Then, the system was poured into a funnel filled with Celite to be filtered and washed with ethanol. The obtained solids were added with dichloromethane and the filtrate was collected. Ethanol was added and the resulting solution was concentrated, but not to dryness. The residue was filtered to obtain 0.08 g of Compound 2-1022 with a yield of 31.5%. The structure of the Compound was confirmed through LC-MS as the target product with a molecular weight of 1408.6. 
     Those skilled in the art will appreciate that the above preparation methods are merely exemplary. Those skilled in the art can obtain other compound structures of the present disclosure through the modifications of the preparation methods. 
     With a special design of a ligand structure, the metal complexes of the present disclosure achieve a deeper red light emission. The following photoluminescence (PL) spectroscopy data further proves that this deeper red light emission is an unexpected superior effect. 
     Photoluminescence Spectrum Data 
     The photoluminescence (PL) spectroscopy data of the compounds of the present disclosure and the comparative compounds was measured using a fluorescence spectrophotometer LENGGUANG F98 produced by SHANGHAI LENGGUANG TECHNOLOGY CO., LTD. Samples of the compounds of the present disclosure or the comparative compounds were prepared into solutions each with a concentration of 3×10 −5  mol/L by using HPLC-grade toluene and then excited at room temperature (298 K) using light with a wavelength of 500 nm, and their emission spectrums were measured. Measurement results are shown in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Photoluminescence spectrum data 
               
            
           
           
               
               
               
            
               
                   
                   
                 Maximum Emission 
               
               
                 No. 
                 Sample No. 
                 Wavelength λ max  (nm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 Compound RD-A 
                 623 
               
               
                 2 
                 Compound RD-B 
                 619 
               
               
                 3 
                 Compound Ir(L a1805 ) 2 L b122   
                 619 
               
               
                 4 
                 Compound 2-442 
                 631 
               
               
                 5 
                 Compound 2-341 
                 622 
               
               
                 6 
                 Compound 2-441 
                 622 
               
               
                   
               
            
           
         
       
     
     The structures of the related compounds of the present disclosure and comparative compounds are shown as follows: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A phenylisoquinoline ligand is a type of ligand structure that is widely studied and applied in the related art, especially in the field of red phosphorescent metal complexes. In the researches, it has been found that introduction of an additional fused ring structure on the isoquinoline ring of this type of ligand leads to a significant blue-shifted emission wavelength, as can be seen, for example, from the data in Table 5, that the maximum emission wavelength of Compound RD-B comprising a phenyl benzoisoquinoline ligand is blue-shifted by 4 nm over that of Compound RD-A. In the present disclosure, a fused ring structure is also introduced into the ligand structures of Compound 2-442, Compound 2-341 and Compound 2-441 of the present disclosure at the same position of the isoquinoline ring. However, the maximum emission wavelengths of Compound 2-442. Compound 2-341 and Compound 2-441 each have a significant red shift over that of Compound Ir(L a1805 ) 2 L b122 . This effect of red shift is quite opposite to the change trend found in the related art. These comparisons show the uniqueness of the metal complex structure of the present disclosure. The present disclosure provides a metal complex which has a completely new structure and can achieve an unexpected deeper red light emission. 
     Additional Device Example 
     Device Example 2-1 
     First, a glass substrate having an indium tin oxide (ITO) anode with a thickness of 120 nm was cleaned and then treated with oxygen plasma and UV ozone. After the treatment, the substrate was dried in a glovebox to remove moisture. Then, the substrate was mounted on a substrate holder and placed in a vacuum chamber. Organic layers specified below were sequentially deposited through vacuum thermal evaporation on the ITO anode at a rate of 0.2 to 2 Angstroms per second and a vacuum degree of about 10 −8  torr. Compound HI-1 was doped in Compound HT for use as a hole injection layer (HIL, 3:97) with a thickness of 100 Å. Compound HT was used as a hole transporting layer (HTL) with a thickness of 400 Å. Compound EB2 was used as an electron blocking layer (EBL) with a thickness of 50 Å. Compound 2-341 of the present disclosure was doped in a host compound RH1 for use as an emissive layer (EML, 5:95) with a thickness of 400 Å. Compound HB was used as a hole blocking layer (HBL) with a thickness of 50 Å. On the HBL, Compound ET and 8-hydroxyquinolinolato-lithium (Liq) were co-deposited as an electron transporting layer (ETL) with a thickness of 350 Å. Finally, Liq was deposited as an electron injection layer with a thickness of 1 nm, and Al was deposited as a cathode with a thickness of 120 nm. The device was transferred back to the glovebox and encapsulated with a glass lid and a moisture getter to complete the device. 
     Device Example 2-3 
     The preparation method in Device Example 2-3 was the same as that in Device Example 2-1, except that in the emissive layer (EML), Compound 2-341 of the present disclosure was replaced with Compound 2-438 of the present disclosure and the weight ratio of Compound 2-438 and Compound RH1 was 3:97. 
     Device Example 2-4 
     The preparation method in Device Example 2-4 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-446 of the present disclosure. 
     Device Example 2-5 
     The preparation method in Device Example 2-5 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-1021 of the present disclosure. 
     Device Example 2-6 
     The preparation method in Device Example 2-6 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-405 of the present disclosure. 
     Device Example 2-7 
     The preparation method in Device Example 2-7 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-1019 of the present disclosure. 
     Device Example 2-8 
     The preparation method in Device Example 2-8 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-447 of the present disclosure. 
     Device Example 2-9 
     The preparation method in Device Example 2-9 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-1020 of the present disclosure. 
     Device Example 2-10 
     The preparation method in Device Example 2-10 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-1018 of the present disclosure. 
     Device Example 2-11 
     The preparation method in Device Example 2-11 was the same as that in Device Example 2-3, except that in the emissive layer (EML), Compound 2-438 of the present disclosure was replaced with Compound 2-1017 of the present disclosure. 
     Structures and thicknesses of part of layers of the devices are shown in the following table. A layer using more than one material is obtained by doping different compounds at their weight ratio as recorded. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Part of device structures in device examples 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Device No. 
                 HIL 
                 HTL 
                 EBL 
                 EML 
                 HBL 
                 ETL 
               
               
                   
               
               
                 Example 2-1 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-341 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-3 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-438 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-4 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-446 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-5 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-1021 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-6 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-405 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-7 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-1019 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-8 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-447 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-9 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-1020 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-10 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-1018 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2-11 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 HT:Compound 
                 HT 
                 EB2 
                 RH1:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 HI-1 (97:3) 
                 (400 Å) 
                 (50 Å) 
                 2-1017 (97:3) 
                 (50 Å) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                   
               
            
           
         
       
     
     The structures of the materials used in the devices are shown as follows: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     IVL characteristics of the devices were measured. Table 7 shows the CIE data, driving voltage (Voltage), maximum emission wavelength (λ max ), full width at half maximum (FWHM) and external quantum efficiency (EQE) of the device examples and the device comparative examples measured at a constant current of 15 mA/cm 2 . 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Device data 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 CIE 
                 λ max   
                 FWHM 
                 Voltage 
                 EQE 
               
               
                 Device No. 
                 (x, y) 
                 (nm) 
                 (nm) 
                 (V) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 2-1 
                 (0.688, 0.311) 
                 625 
                 32.7 
                 3.81 
                 25.86 
               
               
                 Example 2-3 
                 (0.678, 0.321) 
                 618 
                 32.4 
                 3.32 
                 26.44 
               
               
                 Example 2-4 
                 (0.675, 0.324) 
                 617 
                 32.2 
                 3.35 
                 27.05 
               
               
                 Example 2-5 
                 (0.684, 0.315) 
                 623 
                 32.5 
                 3.71 
                 25.62 
               
               
                 Example 2-6 
                 (0.679, 0.320) 
                 620 
                 32.7 
                 3.37 
                 24.59 
               
               
                 Example 2-7 
                 (0.678, 0.321) 
                 619 
                 32.1 
                 3.43 
                 24.57 
               
               
                 Example 2-8 
                 (0.688, 0.311) 
                 625 
                 34.1 
                 3.58 
                 26.47 
               
               
                 Example 2-9 
                 (0.677, 0.322) 
                 619 
                 32.4 
                 3.39 
                 26.67 
               
               
                 Example 2-10 
                 (0.679, 0.320) 
                 620 
                 32.6 
                 3.41 
                 25.76 
               
               
                 Example 2-11 
                 (0.684, 0.315) 
                 623 
                 33.2 
                 3.42 
                 25.01 
               
               
                   
               
            
           
         
       
     
     Discussion 
     As can be seen from the data shown in Table 7, Example 2-1 has a significant red shift in color while a very narrow full width at half maximum and a relatively low voltage are maintained, with the CIEx being shifted to 0.688, and the maximum emission wavelength being red-shifted to 625 nm, achieving a deeper red light emission. Moreover, the external quantum efficiency in Example 2-1 also has a further significant improvement. It proves that the present disclosure provides deep red phosphorescent materials with a narrow peak width, a low voltage and high efficiency and fully proves that the compounds of the present disclosure have broad application prospect. 
     The maximum emission wavelengths in Examples 2-3 to 2-11 each has a red shift while a very narrow full width at half maximum and a low voltage level are maintained, achieving a deeper red light emission. Moreover, the device efficiency in Examples 2-3 to 2-11 has a further significant improvement. In particular, Examples 2-3, 2-4, 2-8 and 2-9 all achieve ultra-high device efficiency of more than 26%. Again, it proves that the present disclosure provides deep red phosphorescent materials with a narrow peak width, a low voltage and high efficiency and fully proves that the compounds of the present disclosure have broad application prospect. 
     Further, since a top-emitting device structure is a device structure widely applied to commercial devices, the excellent effect of the metal complexes of the present disclosure in the top-emitting device is further verified in the present disclosure. 
     Device Example 2-2 
     Firstly, a 0.7 mm thick glass substrate was provided. On the glass substrate, indium tin oxide (ITO) 75 Å/Ag 1500 Å/ITO 150 Å were pre-patterned for use as an anode. Then, the substrate was dried in a glovebox to remove moisture, mounted on a holder and transferred into a vacuum chamber. Organic layers specified below were sequentially deposited through vacuum thermal evaporation on the anode at a rate of 0.01 to 10 Å/s and a vacuum degree of about 10 −6  torr. Firstly, Compound HT1 and Compound HI-1 were simultaneously deposited as a hole injection layer (HIL, 97:3, 100 Å). On the HIL, Compound HT1 was deposited for use as a hole transporting layer (HTL, 2200 Å). The HTL was also used as a microcavity adjustment layer. Then, on the hole transporting layer, Compound EB3 was deposited for use as an electron blocking layer (EBL, 50 Å). Then, Compound 2-341 of the present disclosure and Compound RH1 were co-deposited as an emissive layer (EML, 3:97, 400 Å). On the EML, Compound ET1 and Liq were co-deposited as an electron transporting layer (ETL, 40:60, 350 Å). A metal Yb (10 Å) was deposited as an electron injection layer (EIL), and the metals Ag and Mg were co-deposited as a cathode (140 Å) at a ratio of 9:1. Finally, Compound CPL54 was deposited as a cathode capping layer (CPL, 650 Å). Compound CPL54 was purchased from JIANGSU SUNERA TECHNOLOGY CO., LTD. The device was transferred back to the glovebox and encapsulated with a glass lid and a moisture getter in a nitrogen atmosphere to complete the device. 
     Device Example 2-12 
     The preparation method in Device Example 2-12 was the same as that in Device Example 2-2, except that in the emissive layer (EML), Compound 2-341 of the present disclosure was replaced with Compound 2-447 of the present disclosure. 
     Structures and thicknesses of part of layers of the devices are shown in the following table. A layer using more than one material is obtained by doping different compounds at their weight ratio as recorded. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Part of device structures in Examples 2-2 and 2-12 
               
            
           
           
               
               
               
               
               
               
            
               
                 Device No. 
                 HI-1L 
                 HTL 
                 EBL 
                 EML 
                 ETL 
               
               
                   
               
               
                 Example 2-2 
                 Compound HI- 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 1:Compound 
                 HT1 
                 EB3 
                 RH1:Compound 
                 ET1:Liq 
               
               
                   
                 HT1 (3:97) 
                 (2200 Å) 
                 (50 Å) 
                 2-341 (97:3) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                 (350 Å) 
               
               
                 Example 2-12 
                 Compound HI- 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                   
                 1:Compound 
                 HT1 
                 EB3 
                 RH1:Compound 
                 ET1:Liq 
               
               
                   
                 HTI (3:97) 
                 (2200 Å) 
                 (50 Å) 
                 2-447 (97:3) 
                 (40:60) 
               
               
                   
                 (100 Å) 
                   
                   
                 (400 Å) 
                 (350 Å) 
               
               
                   
               
            
           
         
       
     
     The structures of the new materials used in the devices are shown as follows: 
     
       
         
         
             
             
         
       
     
     IVL characteristics of the devices were measured. At 10 mA/cm 2 . CIE data, maximum emission wavelength λ max , voltage (V), full width at half maximum (FWHM) and external quantum efficiency (EQE) of the devices were measured. The data was recorded and shown in Table 9. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Device data in Examples 2-2 and 2-12 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 CIE 
                 λ max   
                 FWHM 
                 Voltage 
                 EQE 
               
               
                 Device ID 
                 (x, y) 
                 (nm) 
                 (nm) 
                 (V) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 2-2 
                 (0.690, 0.310) 
                 623 
                 25.0 
                 3.23 
                 55.33 
               
               
                 Example 2-12 
                 (0.691, 0.308) 
                 624 
                 24.4 
                 3.23 
                 53.21 
               
               
                   
               
            
           
         
       
     
     As can be seen from Table 9, the top-emitting device in Example 2-2 using the compound of the present disclosure at the emissive layer also has very excellent performance. In Example 2-2, a very narrow full width at half maximum is maintained, and a relatively low voltage level is maintained. Further, the emitted color in Example 2-2 also has a significant red shift, with the CIEx being shifted to 0.690 and the maximum emission wavelength being red-shifted to 623 nm. Moreover, in Example 2-2, in the case where the voltage is maintained, the EQE has a significant improvement and achieves ultra high efficiency up to 55.33%. Example 2-12 exhibits an extremely narrow full width at half maximum level quid a relatively low voltage level is maintained. More importantly, the maximum emission wavelength in Example 2-12 has a significant red shift. Moreover, the EQE also has a significant improvement, and also achieves an extremely high efficiency more than 50%. Example 2-12 has very excellent device performance similar to that in Example 2-2. Again, it proves that the metal complexes of the present disclosure have excellent characteristics and a great application potential in the top-emitting device. 
     In summary, while maintaining a very narrow FWHM, the compounds disclosed by the present disclosure can effectively adjust the emission wavelength to meet the requirement on red light emission, reduce the voltage or maintain the voltage at a low level, improve the EQE, and most importantly, greatly improve the lifetime, thereby providing excellent performance. 
     According to our researches on OLED red light-emitting materials, when the substituent R in the structure of Formula I is not a hydrogen atom, the emission spectrum of the materials can be well adjusted and the external quantum efficiency of the materials can be improved: 
     
       
         
         
             
             
         
       
     
     However, according to our repeated researches, a ligand with the structure of Formula II cannot be successfully coordinated with a metal to form a metal complex: 
     
       
         
         
             
             
         
       
     
     Surprisingly, if the substituent R in Formula I is designed, through structural design, as a part of a fused ring, then (1) a ligand with a corresponding structure, such as Formula I disclosed by the present disclosure, can be successfully coordinated with a metal to form a metal complex; (2) as shown by the results of researches on devices using the related compounds, metal complexes having such structure disclosed by the present disclosure, when used as light-emitting materials in electroluminescent devices, all exhibit excellent device performance, and they can effectively adjust the emission wavelength to meet the requirement on red light emission, obtain a very narrow FWHM, reduce the voltage or maintain a low voltage, improve the EQE, and most importantly, greatly increase the lifetime. These results further highlight the uniqueness and importance of the present disclosure. 
     It should be understood that various embodiments described herein are merely embodiments and not intended to limit the scope of the present disclosure. Therefore, it is apparent to those skilled in the art that the present disclosure as claimed may include variations of specific embodiments and preferred embodiments described herein. Many of the materials and structures described herein may be replaced with other materials and structures without departing from the spirit of the present disclosure. It should be understood that various theories as to why the present disclosure works are not intended to be imitative.