The organic light-emitting diodes (OLEDs) using the iridium complexes of coumarin derivatives as emissive dopants were known to be highly efficient and stable. These coumarin-based Ir(III) complexes were reported to trap and transport electrons effectively in the emissive layer. In this paper, the synthesis and photophysical, electroluminescent properties of platinum (II) complexes cyclometallated with coumarin derivatives are reported. We have prepared a new series of phosphorescent platinum (II) complexes containing 3-(2-pyridinyl)coumarin (pc) as an ancillary ligand. The new heteroleptic platinum complexes, Pt(C^N)(pc) (C^N = 2-(2,4-difluorophenyl)pyridine (F-2-ppy), 2-phenylpyridine (ppy) and 2-phenylquinoline (pq)) were characterized by H-1 NMR and mass spectrometer. As main ligands, F-2-ppy, ppy and pq were employed, which should provide the drastically different ligand molecular orbital energy levels. The platinum complexes synthesized herein showed various luminescence maxima from 551 to 596nm with rather wide emission ranges, depending upon the relative energy levels of their main and ancillary ligands. The photoabsorption, photoluminescence and electroluminescence of the complexes were studied.