Synthesis, Structure, Photoluminescence, and Electroluminescence of Four Europium Complexes: Fabrication of Pure Red Organic Light‐Emitting Diodes from Europium Complexes

Four new europium complexes were prepared by treating europium(III) trifluoro(thenoyl)acetonate trihydrate with new tridentate ligands, based on dipyrazolyltriazine and utilized as emitting materials in electroluminescent devices. The complexes were characterized by elemental analysis, FTIR spectroscopy, UV/Vis spectrophotometry, and 1 H NMR spectroscopy. The coordinated ligands serve as light‐harvesting chromophores in the complexes, with absorption maxima in the range 334–402 nm [ ε = (8.9–81.4) × 10 3 m –1 cm –1 ]. The ligands efficiently sensitize europium luminescence, with maximum quantum‐yield ( Q L Eu ) and observed lifetime ( τ obs ) values of 34 % and 600 µs in the solid state and 35 % and 528 µs in toluene, respectively. The radiative lifetimes of Eu ( 5 D 0 ) are in the range 1170–1281 µs and the ligand‐to‐metal energy‐transfer efficiency ( η sens ) is in the range 71–92 % for those complexes in the solid state and in the range 68–97 % for those in solution. Additionally, organic light‐emitting diodes (OLEDs), which exhibited pure red emission, were fabricated with europium(III) complexes. It is shown that by modifying the [Eu(tta) 3 · 3H 2 O] molecule with ancillary ligands, one can tune and control its electroluminescence spectra, along with its electrical properties, such as the current/voltage characteristics of OLED devices based on [Eu(tta) 3 ( L )]. The best OLED presented a maximum luminance of 3156 cd/m 2 and a maximum efficiency of 0.7 cd/A at an applied voltage of 8 V.