Composition–Thermometric Properties Correlations in Homodinuclear Eu³⁺ Luminescent Complexes

Abstract

A family of homodinuclear Ln 3+ (Ln 3+ = Gd 3+ , Eu 3+ ) luminescent complexes with the general formula [Ln 2 (β-diketonato) 6 ( N -oxide) y ] has been developed to study the effect of the β-diketonato and N -oxide ligands on their thermometric properties. The investigated complexes are [Ln 2 (tta) 6 (pyrzMO) 2 ] (Ln = Eu ( 1 ·C 7 H 8 ), Gd ( 5 )), [Ln 2 (dbm) 6 (pyrzMO) 2 ] (Ln = Eu ( 2 ), Gd ( 6 )), [Ln 2 (bta) 6 (pyrzMO) 2 ] (Ln = Eu ( 3 ), Gd ( 7 )), [Ln 2 (hfac) 6 (pyrzMO) 3 ] (Ln = Eu ( 4 ), Gd ( 8 )) (pyrzMO = pyrazine N -oxide, Htta = thenoyltrifluoroacetone, Hdbm = dibenzoylmethane, Hbta = benzoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone, C 7 H 8 = toluene), and their 4,4′-bipyridine N -oxide (bipyMO) analogues. Europium complexes emit a bright red light under UV radiation at room temperature, whose intensity displays a strong temperature ( T ) dependence between 223 and 373 K. This remarkable variation is exploited to develop a series of luminescent thermometers by using the integrated intensity of the 5 D 0 → 7 F 2 europium transition as the thermometric parameter (Δ). The effect of different β-diketonato and N -oxide ligands is investigated with particular regard to the shape of thermometer calibration (Δ vs T ) and relative thermal sensitivity curves: i.e.. the change in Δ per degree of temperature variation usually indicated as S r (% K –1 ). The thermometric properties are determined by the presence of two nonradiative deactivation channels, back energy transfer (BEnT) from Eu 3+ to the ligand triplet levels and ligand to metal charge transfer (LMCT). In the complexes bearing tta and dbm ligands, whose triplet energy is ca. 20000 cm –1 , both deactivation channels are active in the same temperature range, and both contribute to determine the thermometric properties. Conversely, with bta and hfac ligands the response of the europium luminescence to temperature variation is ruled by LMCT channels since the high triplet energy (>2...

Circularly polarized luminescence of Eu(III) complexes with chiral 1,1′‐bi‐2‐naphtol‐derived bisphosphate ligands

“…The 5 D 0 → 7 F 2 transitions depict a significant hypersensitivity, which is commonly reported for europium 𝛽‐diketonato complexes (Figure S20a–d). 57 The shape of the 5 D 0 → 7 F 2 transition is similar for the species [( S/R )‐1] and [( S , R )‐3] , or [( S , S , S/R , R , R )‐2] and [( S , S , S/R , R , R )‐4] . Nevertheless the ratio R of the intensities of the transition 5 D 0 → 7 F 2 and 5 D 0 → 7 F 1 (R = I( 5 D 0 → 7 F 2 )/I( 5 D 0 → 7 F 1 )) is found close for all the compounds, that is, 23.0 for [( S/R )‐1] , 21.8 for [( S , S , S/R , R , R )‐2] , 20.6 for [( S , R )‐3] , and 20.2 for [( S , S , S/R , R , R )‐4] , highlighting a similar symmetry of the Eu(III) site in the compound series.…”

“…7 F 2 transitions depict a significant hypersensitivity, which is commonly reported for europium β-diketonato complexes (Figure S20a-d). 57 The shape of the 5 It is worth noticing that a value of R > 10 is commonly observed for Eu(III) β-diketonate complexes. [58][59][60][61][62][63] The emission decay curves can be fitted by monoexponential functions (Figure S21) confirming the presence of single spectroscopic Eu(III) site and thus supporting the existence of single monomeric species in solution.…”

Stoichiometrically Controlled Assembly of Lanthanide Molecular Complexes of the Heteroditopic Divergent Ligand 4′-(4-Pyridyl)-2,2′:6′,2″-terpyridine N-Oxide in Hypodentate or Bridging Coordination Modes. Structural, Magnetic, and Photoluminescence Studies

“…In our previous work, we showed that heterocyclic N -oxide ligands such as pyrazine N -oxide or 4,4′-bipyridine N -oxide (bipyMO) react with neutral lanthanide tris-β-diketonato Eu­(β-diketonate) 3 fragments stabilizing homodinuclear molecular compounds Eu 2 (β-diketonate) 6 ( N -oxide) y (β-diketonate = thenoyltrifluoroacetonate, dibenzoylmethanate, benzoyltrifluoroacetonate, or hexafluoroacetylacetonate; y = 2 or 3). − Heterotopic ligands in these molecular compounds behave as O donor bridging and hypodentate ligands maintaining an uncoordinated nitrogen donor functionality. Luminescence studies have established the effect of the β-diketonato and N -oxide ligands on the thermometric properties of the obtained compounds, which are determined by the presence of two nonradiative deactivation channels, back energy transfer from Eu 3+ to the ligand triplet levels and ligand to metal charge transfer (LMCT), the latter being strongly influenced by the N -oxide ligands.…”

Bright red emission with high color purity from Eu(iii) complexes with π-conjugated polycyclic aromatic ligands and their sensing applications

“…6a ). 107 These dinuclear Eu( iii ) complexes exhibited efficient photosensitized emission properties and effective temperature-dependent emission intensity changes, originating from both ligand-to-metal charge transfer (LMCT) and localized ligand T 1 quenching sites.…”