The synthesis and properties of the europium(III) complexes using trifluorene-phenanthroline derivative as ligand

Two europium(III) complexes of Tfl-PIPEu(TTA)3 and PIPEu(TTA)3 (Tfl = alkyltrifluorene, PIP = phenyl-1H-imidazo[4,5-f] [1,10]phenanthroline, TTA = 2-thenoyltrifluoroacetone) were synthesized, which contain an alkyltrifluorene unit or octyl unit, respectively. Their thermal, optophysical, electrochemical properties and dispersibility were investigated. The electroluminescence (EL) properties of Tfl-PIPEu(TTA)3 and PIPEu(TTA)3 were also examined. It was found that the Tfl-PIPEu(TTA)3-based devices have a better EL performance compared to PIPEu(TTA)3-based devices because Tfl-PIPEu(TTA)3 exhibits a more matched energy levels with the polyvinylcarbazole:2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PVK-PBD) and better dispersibility in the PVK-PBD blend. The Tfl-PIPEu(TTA)3-based devices show a sharp red emission at 616 nm with a full width at half-maximum of 10 nm at the dopant concentrations from 1.0 to 8.0 wt% and a maximum brightness of 229 cd m− 2 is obtained at 4.0 wt% doped concentration. The maximum brightness is 2.52 times higher than that of the PIPEu(TTA)3-based devices. Our work indicates that the introduction of an alkyltrifluorene unit can improve the device performance for its resulting europium(III) complexes.