Bipolar-transporting dinuclear europium(III) complexes involving carbazole and oxadiazole units: Synthesis, photophysical and electroluminescent properties

A class of bipolar-transporting dinuclear europium (III) complexes involving a carbazole and a oxadizaole fragments was synthesized and characterized by elemental analysis, infrared spectro-scopy and thermal analyses. Compared to the mononuclear europium (III) tris(dibenzoylmethane) (1,10-phenanthroline), these dinuclear europium (III) complexes presented better thermal stability, and similar UV-vis absorption and photoluminescence spectra in dichloromethane. Two intense UV-vis absorption bands at around 282 nm and 352 nm, and a characteris-tical red emission peak at 614 nm from the 5D0 → 7F2 transition of the central Eu3+ ions were observed under photo-excitation, respectively. Using the Eu2(DBM)6(FPhOXD6CzPhen2) as emitters and a blend of poly (vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as a host matrix, the single emitting-layer polymer light-emitting devices exhibited saturated red electrolumine- scent emission from Eu3+ ion at dopant concentrations from 1 wt % to 8 wt %.

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► Four novel bipolar-transporting dinuclear europium (III) complexes were designed and synthesized.
► All dinuclear complexes exhibited better thermal stability.
► An electron-donoring substituent group is more efficient to improve the thermal stability of its europium complexes.
► These complexes showed higher quantum yield than unfunctionalized mononuclear europium ternary complex.