2-Phenylquinoline-Based Cyclometalated Platinum(II) Complexes: Synthesis and Structure-Photoelectric Properties Relationship in Oxygen Sensing

Novel 2-phenylquinoline-based cyclometalated Pt-II complexes are synthesized and fully characterized. 2-Phenylquinoline derivatives with a functional group at the 4-position of the phenyl ring are prepared through an efficient Pd-catalyzed ligand-free and aerobic Suzuki reaction of 2-bromoquinoline with arylboronic acids. The photophysical properties of the complexes demonstrate that the introduction of a diphenylamino group at the 4-position of the phenyl ring affects the HOMO level of the Pt-II complex significantly, resulting in a marked decrease in energy gap. The emission or energy gap is not influenced clearly by other substituents (methyl, cyano, fluoro, trifluoromethyl, methoxyl, carbazol-9-yl) at the 4-position of the phenyl ring. All the complexes show redshifted room-temperature phosphorescence emission (at 578-599nm) relative to the model complex Pt(ppy)acac (at 486nm). The oxygen sensitivity of the complexes is evaluated quantitatively in a polymer film. The films containing the Pt-II complexes are sensitive to O-2, and the luminescence changes gradually and reversibly with O-2 concentration. The Pt-II complex with a triphenylamino moiety exhibits the highest sensitivity (K-SV(app)=0.020Torr(-1)). The 2-phenylquinoline-based Pt-II complexes are potential candidates for efficient luminescent oxygen sensing. The present results provide a systematic study on the structure-property relationship between the 2-phenylquinoline-based Pt-II complexes and oxygen sensing.