Conjugated and nonconjugated bipolar-transporting dinuclear europium(III) complexes involving triphenylamine and oxadiazole units: synthesis, photophysical and electroluminescent properties

Two novel bipolar-transporting dinuclear europium(III) complexes incorporating both hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) units into the dual phenanthroline ligands were successfully synthesized and characterized by IR, elemental analysis, electrochemical, photophysical analysis, and thermogravimetric analysis, in which the OXD unit was attached onto TPA unit by conjugated and unconjugated linkages for the europium complex A and B, respectively. Compared with complex B, complex A exhibited higher thermal stability and quantum efficiency. A maximum brightness of 296.3 cd/m2 at voltage of 8.5 V was obtained in the complex A-doped devices with saturated red emission using a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole as a host matrix, which is about two-times higher than that from the complex B-doped devices with the same configuration. To best of our knowledge, this is one of the best results based on the dinuclear europium(III) complexes by spin-casting method.