Efficient Layers of Emitting Ternary Lanthanide Complexes for Fabricating Red, Green, and Yellow OLEDs

Abstract

A series of novel nona- and octacoordinate highly volatile and luminescent complexes, [Eu(hfaa)3(indazole)3] and [Ln(hfaa)3(indazole)2] (Ln = Tb, Dy, and Lu), were synthesized using a monoanionic bidentate hexafluoroacetylacetone (hfaa(-)) and a neutral monodentate indazole ligand. The X-ray diffraction analyses of their single-crystals indicate that the complexes are mononuclear. The Eu complex is nonacoordinate and has a distorted monocapped square antiprismatic structure whereas the terbium and dysprosium complexes are octacoordinate and possess a trigonal bicapped prism geometry. The indazole units are involved in π-π stacking interaction and N-H···F hydrogen bonding with the fluorine atoms of hfaa(-). The photophysical studies of indazole and the complexes show that the triplet states are at the appropriate positions and make ligand-to-metal energy transfer process efficient. A strong protective shield is provided by the coordination of three hfaa(-) moieties (which have low frequency C-F vibrational oscillators), and two/three ancillary indazole ligands around these metal ions ascribe higher quantum yields and longer radiative life times (ΦEu = 69% ± 10, 989 ± 1 μs, ΦTb = 33% ± 10, 546 ± 1 μs, and ΦDy = 2.5% ± 10, 13.6 ± 1 μs) to these novel compounds. The emission from europium, terbium, and dysprosium are, respectively, red, green, and yellow. Finally, these compounds were used, as emitting layers, to fabricate electroluminescent devices of their respective colors. The best devices are found with the following structure: ITO/CuPc (15 nm)/[Eu complex]:CBP or [Tb complex]:CBP or [Dy complex]:CBP (80 nm)/BCP (25 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm), which indicates an improved EL performance for the Eu device over the Eu devices reported in the literature. The ligand, indazole, is a good sensitizer for trivalent europium, terbium, and dysprosium ions. It together with hfaa(-) plays an important role in fabricating OLEDs, especially, processed at low temperature.

Review on the Electroluminescence Study of Lanthanide Complexes

“…In 2015, a new terbium(III) complex Tb‐11 (Scheme ) was synthesized using hexafluoroacetylacetone and indazole as the anionic and neutral ligands, respectively . The PLQY of Tb‐11 reached 33% in the solid state.…”

“…In 2015, Ahmed et al used hexafluoroacetylacetone as the anionic ligand to synthesize Eu‐92 (Scheme ). The PLQY of Eu‐92 reached 67% and 69% in solution and solid state, respectively.…”

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

“…In the past decade, a significant amount of research has been devoted to the investigation of the photophysical properties of lanthanide complexes, owing to their widespread applications in the fields of molecular sensing, optoelectronic devices, disease diagnosis, security inks, and biomedical imaging. [1][2][3][4][5][6][7][8] In particular, the high luminescence efficiencies of lanthanide complexes make them attractive for solid-state lighting and electroluminescent display. Most of the lanthanide complexes 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.…”

A Suitable Functionalization of Nitroindazoles with Triazolyl and Pyrazolyl Moieties via Cycloaddition Reactions

“…The corresponding nitroindazole-pyrazoline derivatives were obtained in good to excellent yields.Molecules 2020, 25, 126 2 of 18 antipyretic, antioxidant, antiparasitic, antimicrobial, antitumoral and anti-inflammatory activities, among others [5][6][7][21][22][23].Indazoles are another important group of N-heterocycles with significant biological activities as nitric oxide synthase (NOS) inhibitors, kinase inhibitors, anti-inflammatory, anticancer, antimicrobial, antifungal, antimalarial, and antileishmanial agents, among others.Some anticancer and anti-inflammatory drugs based in indazole scaffolds are commercially available [24][25][26][27][28][29][30]. Besides the biological properties presented by indazole derivatives, this family of N-heterocycles also showed potential to be used in other fields as corrosion inhibitors, components for OLEDs and battery applications, and as copolymerizing molecules for new materials [31][32][33][34].Following our interest on developing synthetic approaches to functionalize the indazole core [35,36], we decided to follow the 1,3-dipolar cycloaddition methodology to substitute nitroindazoles with triazole or pyrazoline moieties, aiming in such way to obtain new compounds with improved biological features for different applications. In the strategy envisaged it was considered that the alkylation of indazole with 1,2-dibromoethane using liquid-liquid phase transfer catalysis, could afford not only the N-1and N-2-bromoethylindazoles, but also the corresponding N-1and N-2-vinylindazoles [37].…”

“…Some anticancer and anti-inflammatory drugs based in indazole scaffolds are commercially available [24][25][26][27][28][29][30]. Besides the biological properties presented by indazole derivatives, this family of N-heterocycles also showed potential to be used in other fields as corrosion inhibitors, components for OLEDs and battery applications, and as copolymerizing molecules for new materials [31][32][33][34].…”