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

Abstract

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 1H 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) × 103 m–1 cm–1]. The ligands efficiently sensitize europium luminescence, with maximum quantum‐yield (QLEu) and observed lifetime (τobs) values of 34 % and 600 µs in the solid state and 35 % and 528 µs in toluene, respectively. The radiative lifetimes of Eu (5D0) are in the range 1170–1281 µs and the ligand‐to‐metal energy‐transfer efficiency (ηsens) 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)3·3H2O] 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/m2 and a maximum efficiency of 0.7 cd/A at an applied voltage of 8 V.

Review on the Electroluminescence Study of Lanthanide Complexes

“…Based on aforementioned considerations, several tridentate ligands were applied as neutral ligands in europium(III) complex and consequently complexes Eu‐31 to Eu‐46 ( Scheme and ) were designed and synthesized . Among these complexes based OLEDs, the device ITO/TPD/ Eu‐40 :CBP/TPBi/LiF/Al behaved a maximum luminance of 1982.5 cd m −2 , a maximum CE of 9.9 cd A −1 , and an impressive maximum EQE up to 7.4%.…”

Impact of chiral ligands on photophysical and electro‐optical properties of β‐diketonate europium complexes in circularly polarized OLEDs

“…The relative integrated intensity of the 5 D 0 → 7 F 2 transition with respect to that of the 5 D 0 → 7 F 1 (hereafter indicated as A 21 ) in the Eu(III) complex measures the symmetry of the coordination sphere, 31 and the distortion of the symmetry around the Eu(III) ion enhances the probability of the electric‐dipole transition. A 21 values of 16.30 and 15.63, calculated for Eu(TTA) 3 i PrPyBox and Eu(TTA) 3 Phen, respectively (Table S1), are considerably large 32 indicating a reduction of the symmetry around Eu ions with respect to other β‐diketonate Eu(III) complexes 29 …”

Red Fluorescent Eu(TTA)3BIP Complex and Its Application in Blue Light‐Reducing Film

“…where A 1 and A 2 are the pre-exponential factors, and τ 1 and τ 2 are the fast and slow components of the luminescence lifetimes for the exponential components. [24][25][26] And the fluorescence lifetime of the Eu(TTA) 3 BIP complex was calculated to be 0.36 ms.…”