Phosphorescent platinum(II) complexes containing different β-diketonate ligands: Synthesis, tunable excited-state properties, and their application in bioimaging

A series of square-planar Pt(II) complexes [Pt(C^N)(O^O)] (1-5) (C^N = 2-phenylpyridine, O^O denotes a series of β-diketonate ligands) is reported. Detailed studies of theoretical calculations, electrochemical and photophysical properties have shown that their excited states can be attributed to the mixing of ³MLCT, ³LLCT and ³LC/ ³ILCT transitions. For 1, the excited state is dominated by the C^N ligand. The excited states of complexes 2-5, however, are dominated by O^O ligands. Through variation of the β-diketonate ligands, the emission colors of 1-5 can be tuned from blue-green to yellow. Further investigations have revealed that the emission of 4 in the solid state can be attributed to the ³MLCT and ³LLL'CT transitions, which has been confirmed by X-ray diffraction studies as well as theoretical calculations. Moreover, exclusive staining of cytoplasm and low cytotoxicity have been observed for 1-4, which makes them promising candidates as phosphorescent probes for bioimaging.