Lanthanide Complexes with 2-(Tosylamino)-benzylidene-N-(aryloyl)hydrazones: Universal Luminescent Materials

Abstract

Lanthanide complexes Ln(L 1 )(HL 1 ) (Ln = Lu, Yb, Er, Gd, Eu, Sm) and Ln(L 2 )(HL 2 ) (Ln = Lu, Yb, Gd, Eu) with 2-(tosylamino)-benzylidene-N-(aryloyl)hydrazones (H 2 L 1 , aryloyl = 2-hydroxybenzoyl; H 2 L 2 , aryloyl = isonicotinoyl) were obtained with the aim to explore them as new luminescent materials. They were found to form monomeric species independently on the aryloyl group, and their crystal structures were determined from single-crystal Xray data (Yb(L 2 )(HL 2 )•0.5(C 2 H 5 OH)), as well as from powder X-ray data by Rietveld refinement (Eu(L 1 )(HL 1 )). Ytterbium complexes exhibited intense luminescence, which allowed using them in host-free organic light-emitting diodes, which demonstrated remarkable efficiency of near infrared electroluminescence (50 μW/W) at low voltage (5 V). The special mechanism of europium luminescence quenching allowed using europium complexes as luminescent thermometers, which demonstrated very high sensitivity up to 12%/K. The theory of luminescence thermometry based on a three-level system was proposed, which allowed predicting sensitivity with high accuracy (error within 20%).

Record efficiency of 1000 nm electroluminescence from a solution-processable host-free OLED

“…12 Recently we demonstrated a rather high efficiency of an NIR OLED based on the ytterbium complex Yb(L 3 )(HL 3 ) with 2-tosylaminobenzylidene-piridyloylhydrazone (H 2 L 3 ), which reached 50 μW W −1 . 13 The number of electroluminescent compounds of this class is, however, limited due to their insufficient solubility. To increase solubility, ligand halogenation was recently successfully proposed by some of us, 14,15 and a significant increase in luminescence efficiency was observed due to the possibility to fine tune the OLED heterostructure.…”

“…The same coordination environment of Ln 3+ was earlier observed in K(C 2 H 5 OH) 3 [Yb(L 1 ) 2 ], 16 Yb(HL 1 )(L 1 )(EtOH) 2 (H 2 O), Yb(HL 1 )(L 1 )(H 2 O) 2 Lu(HL 1 ) 2 Cl, and Er(HL 1 )(L 1 ), 21 as well as in Yb(L 3 )(HL 3 )(EtOH) (H 2 L 3 = 2-tosylaminobenzylidene-pyridyloylhydrazone). 13…”

“…S15†). 16,21,26 According to density functional theory (DFT) data, the highest occupied molecular orbitals (HOMOs) are localized on the (L) 2− ligands, while the lowest unoccupied molecular orbitals (LUMOs) are localized on the (HL) − . Since the DFT method, suitable for ground-state calculations, significantly overestimates the energies of virtual orbitals, including the lowest unoccupied molecular orbital (LUMO), a dual-stage approach to determine LUMO energy was used, as in ref.…”

Luminescent Thermometers: From a Library of Europium(III) β‐Diketonates to a General Model for Predicting the Thermometric Behaviour of Europium‐Based Coordination Systems

“…i) Usually, when experimental Δ(T) curves are fitted with the Mott-Seitz equation, the energy terms obtained can differ from the experimental values to a large extent, up to 10-40 %. [17,[25][26][27]29,32] ii) The determination of triplet energies from phosphorescence spectra of gadolinium complexes can give different results depending on the approach used. In particular, the two most frequently adopted methods are: drawing a tangent line in the highest energy edge of the phosphorescence spectra, or locating the phosphorescence zero-zero phonon energy by taking the maximum of the highest energy vibronic band.…”

“…After acknowledging the presence of these correlations, a question arises: is it possible to use Equation (2) (or some derived forms) to predict the thermometric properties of a luminescent molecule or, even better, to guide the design of a new system with a thermometric response determined a priori in a particular temperature range? Only recently, some works [8,17] have started to consider the possibility of using MS equation or "thermally coupled levels" models to predict the behaviour -in the form of Δ(T) and/or S r (T) -of a molecular luminescent thermometer.…”