Efficient Visible‐Light‐Excitable Eu³⁺ Complexes for Red Organic Light‐Emitting Diodes

Abstract

Visible-light-excited Eu 3+ complexes have received much attention in the last years due to the rapidly increasing demand for less-harmful biomarkers and low-voltage driven emitters in optoelectronics. Nevertheless, these complexes usually exhibit poor emission quantum yields, contrarily to the ones excited in the ultraviolet spectral region. To address this challenge, a series of complexes based on trivalent lanthanide ions, [Eu(bpyO2)(2), Gd (5)} and Ln(tta) 3 (bpyO2) {Ln = Eu (3), Gd (6)}, were synthesized using 2-thenoyltrifluoroacetone (Htta) as primary ligand and 2,2′-dipyridyl N,N′-dioxide (bpyO2) as neutral donor, and characterized, with special emphasis on their crystal struc-[a] Phantom-g, CICECO -was achieved through chemical modifications of the ligand structure with an expanded π-conjugated system [40] and using either neutral tris-(Q Ln L = 0.75 at 415 nm [49] and 0.40 at 400 nm [46] ) or anionic tetrakis-Eu 3+ --diketonates (Q Ln L = 0.80 at 410 nm [40] and Q Ln L = 0.45 at 400 nm [48] ).In this work, we followed a rational design to synthesize three Eu 3+ --diketonate complexes, 1, 2 and 3, using 2-thenoyltrifluoroacetone (Htta) and 2,2′-dipyridyl N,N′-dioxide (bpyO2) as the primary and ancillary ligands, respectively. The excitation window of 3 unprecedently extends into the visible region (up to 480 nm), well-above what was reported previously for analogous visible-light-excitable Eu 3+ -based complexes (up to 440-450 nm). [40,46,48] Detailed theoretical calculations performed with both time-dependent density functional theory (TD-DFT) and LUMPAC software [51] are also presented showing an excellent accord with the experimental intensity parameters, radiative and non-radiative decay rates, and intrinsic and absolute emission quantum yields. Moreover, 3 displayed excellent colour purity, with Commission Internationale d'Éclairage (CIE) chromaticity coordinates (0.66, 0.33), and was successfully employed for the fabrication of organic light-emitting diodes (OLEDs). Results and DiscussionScheme 1 summarizes the adopted synthesis procedure. Complexes 1-3 were characterized using ATR/FT-IR spectroscopy, mass spectrometry, and elemental analyses. In the FT-IR spectra, the stretching and bending vibrations of N-O group of bpyO2 ligand are observed in 1 (1260, 853 and 837 cm -1 ) and 3 (1255, 856 and 836 cm -1 ) ( Figure S1). The carbonyl stretching frequency of Htta has been shifted from 1645 cm -1 to 1600 and 1, 2, 3, 4, and 6 were analysed by singlecrystal XRD. The most relevant structural features of 1-3 are depicted in Figure 1 and those of 4 and 6 are given in Figure S3 and S4, respectively. Selected bond lengths and bond angles Eur. Single-Crystal X-ray Structures Suitable crystals of

A Hybrid Materials Approach for Fabricating Efficient WLEDs Based on Di‐Ureasils Doped with Carbon Dots and a Europium Complex

“…This is exactly the conclusion of the single‐crystal data of Eu(tta) 3 (bpyO 2 ). [ 59 ] Nevertheless, comparison of the energy, full‐width‐at‐half‐maximum (fwhm), and relative intensity of the 5 D 0 → 7 F 0‐4 transitions in the pristine complex with those in the hybrids, evidences significant changes (Figure 2c,d, and Figure S1d, Supporting Information). Such differences induced by the Eu(tta) 3 (bpyO 2 ) incorporation into the d‐U(600) matrix are well illustrated by the blue‐shift (from 17245 ± 1 to 17265 ± 1 cm −1 ) and the broadening (from 20 ± 1 to 56 ± 1 cm −1 ) of the 5 D 0 → 7 F 0 transition observed in dU6‐Eu and dU6‐aCDs/Eu relatively to the values observed in the pristine complex.…”

“…[58] Characteristic absorption bands are found at ~240, 290 and 340 nm for Htta and at 268 and 340 nm for Eu(tta)3(bpyO2) in the UV−visible absorption spectra of 1.010 −5 M methanol solutions. [59] The corresponding UV-visible absorption spectrum of solid-state Eu(tta)3(bpyO2) reveals a maximum absorbance centered at 398 nm, ascribed to the π→π* transitions of the tta − ligand, with bathochromic shift compared to that of Eu(tta)3(bpyO2) in methanol solution (Figure S1b, Supporting Information). The relatively weak absorption peaks discerned at 464, 525, and 535 nm are attributed to 7 F0→ 5 D2, 7 F0→ 5 D1 and 7 F1→ 5 D0 transitions of Eu 3+ , respectively.…”

“…The Eu(tta)3(bpyO2) complex responsible for the red emission component of WLEDs was synthesized and characterized in a previous work. [59] Synthesis of d-U(600) doped with Eu(tta)3(bpyO2): Typically, 0.5 g of d-UPTES(600) was mixed with 1 mL of EtOH under stirring for 20 min, followed by the addition of 11.0 mg of Eu(tta)3(bpyO2) in a solution composed of 1.0 mL of EtOH and 49.4 μL of the 0.01 M HCl solution. The resulting solution was stirred at room temperature and then transferred to an oven at 50 ℃.…”

Recent Developments in Lanthanide-Doped Alkaline Earth Aluminate Phosphors with Enhanced and Long-Persistent Luminescence

“…Particularly, the development of codoped SrAl 2 O 4 :Eu 2+ ,Dy 3+ (Dy: dysprosium) phosphors by Matsuzawa et al has received considerable attention for the replacement of traditional ZnS-based phosphors, owing to their improved afterglow intensities, lifetimes, and chemical stabilities compared to those of the previously synthesized phosphors [ 5 ]. The intense emission of rare-earth-based phosphor has led to extensive applications in light-emitting diode (LED) devices, thin-film electroluminescent (TFEL) devices, optoelectronic or cathodoluminescent devices, safety marks, radiation dosimetry, X-ray imaging, bioimaging, and photodynamic therapy [ 14 , 15 , 16 , 17 , 18 , 19 ]. In particular, their applications as LED devices can help in replacing argon-mercury discharge fluorescent lamps, which are extensively used for general lighting purposes.…”

Complex formation of REEs with polydentate organic ligands

“…Фотофизические свойства ионов лантанидов нашли широкое применение в различных технологических и научно-исследовательских областях -от разработки передовых оптических и светопреобразующих устройств [7,10] до получения биоизображений [8,20] и лечения онкологических заболеваний методом фотодинамической терапии [4,19].…”