A compound including a first ligand LA having the structure of Formula I, is disclosed. In Formula I, rings A and B are each a 6-membered rings; Z1 and Z2 are each carbon or nitrogen; each RA and RB is independently hydrogen or a variety of substituents; any two substituents are optionally joined or fused into a ring; at least one RA or RB comprises an aromatic group substituted by a bridge structure, and this RA or RB joins with an adjacent substituent and fuses to ring A or B; the bridge structure comprises a backbone structure that forms a fused first ring; the backbone structure is saturated, comprises at least one heteroatom, and is optionally further substituted; and the ligand LA is coordinated to a metal M that can be coordinated to other ligands.