Organic electroluminescent materials and devices

An organic light emitting device (OLED) comprising:

• an anode;
• a cathode;
• and
• an organic layer disposed between the anode and the cathode, wherein the organic layer comprises a compound comprising 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 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 X8 are each independently C or N;
• each of X9 to X12 is C;
• 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 an aromatic 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.