Light-emitting element, light-emitting device, electronic device, and lighting device

Abstract

A novel organometallic complex with high reliability is provided. A light-emitting element includes an EL layer between a pair of electrodes. The EL layer includes at least a light-emitting layer. The light-emitting layer contains an organometallic complex. The organometallic complex includes a first ligand and a second ligand which are coordinated to a central metal. The HOMO is distributed over the first ligand, and the LUMO is distributed over the second ligand. The first ligand and the second ligand are cyclometalated ligands.

1 . A light-emitting element comprising an EL layer between a pair of electrodes,
 wherein the EL layer includes at least a light-emitting layer,   wherein the light-emitting layer includes an organometallic complex,   wherein the organometallic complex includes a first ligand and a second ligand coordinated to a central metal,   wherein the first ligand has a HOMO and the second ligand has a LUMO, and   wherein the first ligand and the second ligand are cyclometalated ligands.   
     
     
         2 . The light-emitting element according to  claim 1 ,
 wherein a first heteroaromatic ring coordinated to the central metal and included in the first ligand is different from a second heteroaromatic ring coordinated to the central metal and included in the second ligand.   
     
     
         3 . The light-emitting element according to  claim 2 ,
 wherein the first heteroaromatic ring includes a first monocyclic ring containing a nitrogen atom coordinated to the central metal,   wherein the second heteroaromatic ring includes a second monocyclic ring containing a nitrogen atom coordinated to the central metal, and   wherein the first monocyclic ring is different from the second monocyclic ring.   
     
     
         4 . The light-emitting element according to  claim 3 , wherein the number of members in each of the first monocyclic ring and the second monocyclic ring is 5 or 6. 
     
     
         5 . The light-emitting element according to  claim 3 , wherein the number of the nitrogen atom in the first monocyclic ring is 1 and the number of the nitrogen atom in the second monocyclic ring is 2 or 3. 
     
     
         6 . The light-emitting element according to  claim 3 ,
 wherein the first monocyclic ring is a pyridine ring, and   wherein the second monocyclic ring is a pyrimidine ring or a triazine ring.   
     
     
         7 . The light-emitting element according to  claim 3 ,
 wherein the first heteroaromatic ring is a pyridine ring, and   wherein the second heteroaromatic ring is a pyrimidine ring or a triazine ring.   
     
     
         8 . The light-emitting element according to  claim 1 , wherein the central metal is iridium. 
     
     
         9 . A light-emitting device comprising a transistor or a substrate, and the light-emitting element according to  claim 1 . 
     
     
         10 . An electronic device comprising a microphone, a camera, an operation button, an external connection portion or a speaker, and the light-emitting device according to  claim 9 . 
     
     
         11 . An electronic device comprising a housing or a touch sensor, and the light-emitting device according to  claim 9 . 
     
     
         12 . A lighting device comprising a transistor or a substrate, and the light-emitting element according to  claim 1 . 
     
     
         13 . A light-emitting element comprising an EL layer between a pair of electrodes,
 wherein the EL layer includes at least a light-emitting layer,   wherein the light-emitting layer includes an organometallic complex,   wherein the organometallic complex includes a first ligand and a second ligand coordinated to a central metal,   wherein a HOMO is distributed over the first ligand and a LUMO is distributed over the second ligand, and   wherein the first ligand and the second ligand are cyclometalated ligands.   
     
     
         14 . The light-emitting element according to  claim 13 ,
 wherein a first heteroaromatic ring coordinated to the central metal and included in the first ligand is different from a second heteroaromatic ring coordinated to the central metal and included in the second ligand.   
     
     
         15 . The light-emitting element according to  claim 14 ,
 wherein the first heteroaromatic ring includes a first monocyclic ring containing a nitrogen atom coordinated to the central metal,   wherein the second heteroaromatic ring includes a second monocyclic ring containing a nitrogen atom coordinated to the central metal, and   wherein the first monocyclic ring is different from the second monocyclic ring.   
     
     
         16 . The light-emitting element according to  claim 15 , wherein the number of members in each of the first monocyclic ring and the second monocyclic ring is 5 or 6. 
     
     
         17 . The light-emitting element according to  claim 15 , wherein the number of the nitrogen atom in the first monocyclic ring is 1 and the number of the nitrogen atom in the second monocyclic ring is 2 or 3. 
     
     
         18 . The light-emitting element according to  claim 15 ,
 wherein the first monocyclic ring is a pyridine ring, and   wherein the second monocyclic ring is a pyrimidine ring or a triazine ring.   
     
     
         19 . The light-emitting element according to  claim 15 ,
 wherein the first heteroaromatic ring is a pyridine ring, and   wherein the second heteroaromatic ring is a pyrimidine ring or a triazine ring.   
     
     
         20 . The light-emitting element according to  claim 13 , wherein the central metal is iridium. 
     
     
         21 . A light-emitting device comprising a transistor or a substrate, and the light-emitting element according to  claim 13 . 
     
     
         22 . An electronic device comprising a microphone, a camera, an operation button, an external connection portion or a speaker, and the light-emitting device according to  claim 21 . 
     
     
         23 . An electronic device comprising a housing or a touch sensor, and the light-emitting device according to  claim 21 . 
     
     
         24 . A lighting device comprising a transistor or a substrate, and the light-emitting element according to  claim 13 . 
     
     
         25 . An organometallic complex having a structure represented by General Formula (G1): 
       
         
           
           
               
               
           
         
         where R 1  to R 15  separately represent hydrogen, a halogen group, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, or a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
       
     
     
         26 . An organometallic complex having a structure represented by General Formula (G2): 
       
         
           
           
               
               
           
         
         where n is 1 or 2, and R 1  to R 15  separately represent hydrogen, a halogen group, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, or a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms.