A compound having a carbene ligand LA of Formula I: is disclosed wherein ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; Z is nitrogen or carbon; R7 represents from mono-substitution to the possible maximum number of substitution, or no substitution; R1, R2, R3, R4, R5, R6, and R7 are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrite, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; any adjacent substituents of R1, R2, R3, R4, R5, R6, and R7 are optionally joined or fused into a ring or a double bond; the ligand LA is coordinated to a metal M through the carbene carbon and Z; and the ligand LA is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.