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

Abstract

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.