A compound having a formula M(L A) x (L B) y (L C) z: wherein the ligand L A is wherein the ligand L B is wherein the ligand L C is wherein M is a metal having an atomic number greater than 40; wherein x is 1, or 2; wherein y is 1, or 2; wherein z is 0, 1, or 2; wherein x+y+z is the oxidation state of the metal M; wherein X 1, X 2, X 3, and X 4 are C or N; wherein R 1, R 2, R 3, and R 4 are independently selected from group consisting of alkyl, cycloalkyl, aryl, and heteroaryl; wherein at least one of R 1, R 2, R 3, and R 4 has at least two C atoms; wherein R 5 is selected from group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein rings A, C, and D are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; wherein R A, R C, and R D each independently represent mono, di, tri, or tetra-substitution, or no substitution; wherein R B represents di, tri, or tetra-substitution; wherein two adjacent R B form a six-member carbocyclic or heterocyclic ring E fused to ring B; wherein, when ring E is heterocyclic, the only heteroatom is nitrogen; and wherein ring E can be further substituted; wherein (a) at least one of X 1, X 2, X 3, and X 4 is N, (b) ring E is heterocylic, or (c) both; wherein each of R A, R B, R C, and R D are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any adjacent substitutents of R A, R B, R C, and R D are optionally joined to form a fused ring. wherein the ligand L C is wherein M is a metal having an atomic number greater than 40; wherein x is 1, or 2; wherein y is 1, or 2; wherein z is 0, 1, or 2; wherein x+y+z is the oxidation state of the metal M; wherein X 1, X 2, X 3, and X 4 are C or N; wherein R 1, R 2, R 3, and R 4 are independently selected from group consisting of alkyl, cycloalkyl, aryl, and heteroaryl; wherein at least one of R 1, R 2, R 3, and R 4 has at least two C atoms; wherein R 5 is selected from group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein rings A, C, and D are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; wherein R A, R C, and R D each independently represent mono, di, tri, or tetra-substitution, or no substitution; wherein R B represents di, tri, or tetra-substitution; wherein two adjacent R B form a six-member carbocyclic or heterocyclic ring E fused to ring B; wherein, when ring E is heterocyclic, the only heteroatom is nitrogen; and wherein ring E can be further substituted; wherein (a) at least one of X 1, X 2, X 3, and X 4 is N, (b) ring E is heterocylic, or (c) both; (a) at least one of X 1, X 2, X 3, and X 4 is N, (b) ring E is heterocylic, or (c) both; wherein each of R A, R B, R C, and R D are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any adjacent substitutents of R A, R B, R C, and R D are optionally joined to form a fused ring.