A compound comprising a first ligand LA of Formula I,




is disclosed. In the structure of Formula I, ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; Z1-Z4 are each independently C or N; at least two consecutive Z1-Z4 are C, and are fused to a structure of Formula II





or Formula III





Y1; Y1 and Y2 are each independently O, S, Se, CRR′, SiRR′, or GeRR′; each RA, RB, RC, R, and R′ is a hydrogen or a substituent; and any two substituents may be joined or fused together to form a ring. In the compound, LA is complexed to a metal M by the dashed lines in Formula I to form a five-membered chelate ring, and M has an atomic weight greater than 40. Organic light emitting devices and consumer products containing the compounds are also disclosed.