Organic light-emitting devices

Disclosed are electrophosphorescent organic metal complexes with formula (I), (H), (III) or (IV), of either geometrical isomers, comprising two bidentate NN-type ligands, or two NO-type ligands, or a tetradentate NNNN-type ligand or a tetradentate NOON-type ligand, and a transition metal. These electrophosphorescent materials are valuable to the application in organic light-emitting devices (OLEDs), including red-, orange-, or yellow-light OLEDs.published_or_final_versio