Organometallic compound and organic light-emitting diode including the same

An organometallic compound of Chemical Formula I is described: wherein R is a fused ring system connected to X1 and X2, comprising one of Chemical Formula II-IV; Y is preferably CR19R20, NR19, O, S or SO2; Ra and R1-R20 are H or substituents as defined herein; (Z1-Z2) is a bidentate ligand; m is 1-3 and n is 0-2 where m+n is an oxidation number of metal M; M is a metal, preferably iridium or platinum. The organometallic compound of formula I acts as a dopant of a light-emitting layer of an organic light-emitting diode (OLED). Preferred compounds of chemical formula I include but are not limited to, those were R forms, with the pyrimidine ring to which it is attached, a naphtho[2',1':4,5]thieno[2,3-d]pyrimidine, benz[4,5]indeno[2,1-d]pyrimidine or 11H-benzo[f]pyrimido[4,5-b]indole as shown herein. Preferred bidentate ligands (Z1-Z2) include 1,3-dicyclohexyl-2-methylpropane-1,3-dione and 3,7-diethylnonane-4,6-dione. An organic light emitting device including the organic light emitting diode can be a display device or a lighting device.