A compound, Ir(L A) m (L B) 3-m, having a structure of Formula I, wherein each of moiety A and moiety C is independently a 5-membered carbocyclic or heterocyclic ring, a 6-membered carbocyclic or heterocyclic ring, or a polycyclic fused ring system comprising 5-membered and/or 6-membered carbocyclic or heterocyclic rings; moiety B is imidazole and Z 1 is N; Z 2 is C or N; m is 1 or 2; R A, R B, and R C each independently represent mono to the maximum allowable substitution, or no substitution; at least one of R 1, R 2, R 3, R 4 has a structure of Formula II, or is a 5-membered heterocyclic ring; X 1 is CR 1a or N, X 2 is CR 2a or N, X 3 is CR 3a or N, X 4 is CR 4a or N, and X 5 is CR 5a or N; each of R 1, R 2, R 3, R 4, R A, R B, R C, R 1a, R 2a, R 3a, R 4a, and R 5a is independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, boryl, arylalkyl, alkoxy, aryloxy, amino, germyl, selenyl, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; at least one of R 1a, R 2a, R 3a, R 4a, R 5a is selected from the group consisting of cycloalkyl, alkyl, silyl, germyl, partially or fully deuterated variants thereof, partially or fully fluorinated variants thereof, and combinations thereof; if R 3 has Formula II, R 3a is alkyl, and each of R 1a, R 2a, R 4a, and R 5a is H, then R 3a is partially or fully deuterated or R 3a comprises at least four carbon atoms; and wherein any two substituents may be joined or fused to form a ring, with the provisos that R 1a, R 2a, R 3a, R 4a, and R 5a do not form a 6-membered ring. each of moiety A and moiety C is independently a 5-membered carbocyclic or heterocyclic ring, a 6-membered carbocyclic or heterocyclic ring, or a polycyclic fused ring system comprising 5-membered and/or 6-membered carbocyclic or heterocyclic rings; moiety B is imidazole and Z 1 is N; Z 2 is C or N; m is 1 or 2; R A, R B, and R C each independently represent mono to the maximum allowable substitution, or no substitution; at least one of R 1, R 2, R 3, R 4 has a structure of Formula II, or is a 5-membered heterocyclic ring; X 1 is CR 1a or N, X 2 is CR 2a or N, X 3 is CR 3a or N, X 4 is CR 4a or N, and X 5 is CR 5a or N; each of R 1, R 2, R 3, R 4, R A, R B, R C, R 1a, R 2a, R 3a, R 4a, and R 5a is independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, boryl, arylalkyl, alkoxy, aryloxy, amino, germyl, selenyl, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; at least one of R 1a, R 2a, R 3a, R 4a, R 5a is selected from the group consisting of cycloalkyl, alkyl, silyl, germyl, partially or fully deuterated variants thereof, partially or fully fluorinated variants thereof, and combinations thereof; if R 3 has Formula II, R 3a is alkyl, and each of R 1a, R 2a, R 4a, and R 5a is H, then R 3a is partially or fully deuterated or R 3a comprises at least four carbon atoms; and wherein any two substituents may be joined or fused to form a ring, with the provisos that R 1a, R 2a, R 3a, R 4a, and R 5a do not form a 6-membered ring.