A compound having a formula M(LA)x(LB)y(LC)z, where ligand LA is ligand LB is and LC is is disclosed. In formula M(LA)x(LB)y(LC)z, M is a metal having an atomic number greater than 40; x is 1 or 2; y is 0, 1, or 2; z is 0, 1, or 2; x+y+z is the oxidation state of the metal M; A1-A8 are carbon or nitrogen; ring B is bonded to ring A through a C—C bond; M is bonded to ring A through a M-C bond; X is O, S, Se, CRR′, or NR1; rings C and D are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; R3 represents mono, or di-substitution, or no substitution; R2, RC, and RD each independently represent mono, di, tri, or tetra-substitution, or no substitution; R4 represents mono, di, tri, or tetra-substitution; at least one R4 is a five-membered or six-membered heterocyclic ring which can be further substituted by RE; where RE represents mono, di, tri, or tetra-substitution, or no substitution; each R substituent is independently selected from a variety of moieties; and any adjacent R substitutents are optionally joined to form a ring.