Luminescent Eu(II) complexes with characteristic d–f transitions have potential applications in many fields, especially organic light‐emitting diodes (OLEDs), due to their satisfactory advantages including short excited‐state lifetimes, 100% theoretical exciton utilization efficiency and tunable emission colors. Up to now, most light‐emitting layers in OLEDs are typically fabricated through high‐vacuum thermal evaporation process, which is uneconomical for large‐area and multi‐dopant devices. In this work, eight Eu(II) complexes with substituted tris(2‐aminoethyl)amine or triethanolamine ligands are designed and synthesized, and their structural and photophysical properties are studied. These complexes exhibit tunable maximum emission wavelengths in the range of 437–553 nm and high photoluminescence quantum yields up to 75%. Furthermore, this work demonstrates the application of Eu(II) complex in solution‐processed OLEDs with high efficiency and luminance for the first time. The optimized device show a maximum external quantum efficiency of 9.2% and a maximum luminance of 1780 cd m−2 with an emission peak at 485 nm.
A new heteronuclear EuII–MnII complex with high photoluminescence quantum yield is designed and synthesized, which represents the first example of f → d molecular sensitization.
Rare earth europium(II) complexes based on d-f transition luminescence have characteristics of broad emission spectra, tunable emission colors and short excited state lifetimes, showing great potential in display, lighting and other fields. In this work, four complexes of Eu(II) and bis(pyrazolyl)borate ligands, where pyrazolyl stands for pyrazolyl, 3-methylpyrazolyl, 3,5-dimethylpyrazolyl or 3-trifluoromethylpyrazole, were designed and synthesized. Due to the varied steric hindrance of the ligands, different numbers of solvent molecules (tetrahydrofuran) are participated to saturate the coordination structure. These complexes showed blue-green to yellow emissions with maximum wavelength in the range of 490–560 nm, and short excited state lifetimes of 30–540 ns. Among them, the highest photoluminescence quantum yield can reach 100%. In addition, when the complexes were heated under vacuum or nitrogen atmosphere, they finally transformed into the complexes of Eu(II) and corresponding tri(pyrazolyl)borate ligands and sublimated away.
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