Tuning the Emission Colour of Triphenylamine-Capped Cyclometallated Platinum(II) Complexes and Their Application in Luminescent Oxygen Sensing and Organic Light-Emitting Diodes

[(Aryl-ppy)Pt(acac)] (ppy = 2-phenylpyridine, acac = acetylacetonato) derivatives with triphenylamine (TPA) substituents on the ppy ligand have been prepared. The TPA fragment is either directly cyclometallated (Pt-1) or attached to the ppy ligand through a C-C single bond (Pt-2) or a novel alpha-diketo group (Pt-3). All the complexes show room-temperature phosphorescence in fluid solution with emission bands in the range of 530-590 nm, which are red-shifted relative to the model complex [ppyPt(acac)] (lambda(em) = 486 nm). This emission colour tuning effect is attributed to either an elevated HOMO energy caused by electron-donating TPA substituents on the ppy ligand or a decreased LUMO energy caused by the electron-trap effect of electron-withdrawing substituents; both result in a smaller HOMO-LUMO energy gap and thus red-shifted emission. The complexes show extended luminescence lifetimes (tau = 3.0-5.5 mu s) relative to the parent complex [ppyPt(acac)] (tau = 2.6 mu s). The luminescent oxygen-sensing properties of the complexes were studied in solution and polymer films. White light emission was observed with an OLED device fabricated with complex Pt-3 with CIE coordinates of (0.32, 0.32).