A novel compound is disclosed which includes a ligand LA of Formula I, Formula II, Formula III, or Formula IV: wherein: ring B is independently a 5-membered or 6-membered carbocyclic or heterocyclic ring; X1 to X4 are each independently selected from the group consisting of C, N, and CR; at least one pair of adjacent X1 to X4 are each C and fused to a structure of Formula V where indicated by “”; X5 to X12 are each independently C or N; the maximum number of N within a ring is two; Z and Y are each independently selected from the group consisting of O, S, Se, NR′, CR′R″, SiR′R″, and GeR′R″; RB and RC each independently represents zero, mono, or up to a maximum allowed substitutions to its associated ring; each of RB, RC, R, R′, and R″ is independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, boryl, and combinations thereof; and two substituents can be joined or fused to form a ring; the ligand LA is complexed to a metal M through the two indicated dash lines of each Formula; and the ligand LA can be joined with other ligands to form a tridentate, tetradentate, pentadentate, or hexadentate ligand.