Ratiometric luminescence thermometry based on crystal-field alternation at the extremely narrow ⁵D₀ → ⁷F₂ transition band of europium(III)

Structure Determination of Europium Complexes in Solution Using Crystal-Field Splitting of the Narrow f-f Emission Lines

Nine nona-coordinated Eu(III) complexes (1-9) studied here have three unsymmetric β-diketonate ligands and one chiral Ph-Pybox ligand, which can produce eight possible coordination isomers, depending on the position of the three unsymmetric β-diketonate ligands. Substituents on the β-diketonate ligands cause a rational structural rearrangement upon crystallization. Substituents with higher polarity, including -CN, -F, -Cl, -Br, -OMe, and -OEt, employ intercomplex hydrogen bonding to generate an association complex through structural rearrangement upon crystallization. Substituents with lower polarity, including -CF3, -SMe, and -Me, cause the most energetically favorable isomer to crystallize directly from solution. These two crystal structures exhibit well-resolved f-f emission lines with characteristic Stark splitting structures. This work revealed that the configuration of the Eu(III) complexes in solution can be determined by systematic comparison of their Stark splitting structures to those obtained from the solid phase using density functional theory (DFT)-based predictions combined with circular dichroism data.

A Europium(III) Complex Embedded in a Polysulfone Host Matrix: A Flexible Film with Temperature-Responsive Ratiometric Behaviour

An emissive europium(III) complex [C₂ mim][Eu(fod)₄ ] (1; C₂ mim=1-ethyl-3-methyl-imidazolium; fod=1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate) was prepared. The complex shows ratiometric thermal behaviour up to 155 °C. These unusual temperature-dependent properties arise from a solid-solid phase transition that promotes increased contact between the anion and the cation, affecting the emission profile of the emissive anion in two different ratiometric relations. A ultrabright and flexible emissive photopolymer film was obtained using polysulfone (PSU) as the host matrix of 10 % (w/w) of 1, that also induced changes on the lanthanide emissive profile with temperature. A temperature-responsive luminescent film 1/PSU is sensitivr to heating between 100 and 155 °C. Also, the emission lifetime of 1 was not affected by confinement in PSU, while its emission quantum yield was reduced from 82 to 59 %.

A Europium(III) Complex with an Unusual Anion-Cation Interaction: A Luminescent Molecular Thermometer for Ratiometric Temperature Sensing

An unusual thermally sensitive anion-cation interaction, which is characteristic of the anion [Eu(FOD)₄ ]^- , occurs in the complex [CHOL][Eu(FOD)₄ ] (1; CHOL=choline; FOD=1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate) and affects both quantum yield and thermochromic behavior. This prompted the design of an Eu³⁺ -based ratiometric thermometer that functions at temperatures up to 95 °C through a thermally excited state absorption of the Eu³⁺ ion. The reusable temperature-sensitive luminescent complex showed a range of relative sensitivity between 0.45 % C^-1 at 25 °C, with an increase to 7.0 % C^-1 at 95 °C. Confinement of compound 1 in a transparent film of polysulfone resulted in a higher thermal stability of 1 while its luminescence showed a strong temperature dependence.

A stable mixed lanthanide metal–organic framework for highly sensitive thermometry

A stable mixed Ln-MOF with a novel (4,8)-connected binodal network was constructed, which could be used as a ratiometric and colorimetric temperature sensor with high relative sensitivity (S_m = 9.42% per K at 310 K).

Floral and lamellar europium(iii)-based metal–organic frameworks as high sensitivity luminescence sensors for acetone

Floral Eu-BDC and lamellar Eu-BTC as high sensitivity luminescence sensor for acetone.

The effect of ligand symmetry on the ratiometric luminescence characteristics of lanthanides

This work demonstrated that the ligand symmetry of europium(iii) complexes controls the ratiometric luminescence characteristics of lanthanides. Nona-coordinated europium(iii) complexes having unsymmetrical β-diketonate ligands (Cs) exhibit distinctive ratiometric spectral variations in the extremely narrow f-f transition bands over the temperature range from 253 to 323 K. In contrast, no such ratiometric change can be observed in a series of nona-coordinated europium(iii) complexes containing symmetrical β-diketonate ligands (C2v). The remarkable difference depending on the ligand symmetry (Csvs. C2v) suggests that the coordination rearrangement of β-diketonate in the complex causes ratiometric spectral variations in extremely narrow f-f transition bands, where two europium(iii) complex isomers exist in the solution equilibrium. A self-calibration method using dual iso-emissive points is reported, where self-calibration using the two emission intensities at the iso-emissive points reduces the coefficient of variation in luminescence thermometry.

Photoactivatable europium luminescence turn-on by photo-oxygenation of β-diketone having pyrrole rings

This work demonstrates a novel photoactivatable turn-on-type lanthanide(iii) luminescence. A β-diketone substrate having redox-active pyrrole moieties (LH₂) undergoes efficient photo-oxygenation to afford the corresponding α-alkoxy diketone (LHOH) in the presence of lanthanide(iii) ions, which trigger bright europium(iii) red luminescence (PA-Eu^III) turn-on, as well as activating the near-infrared luminescence (λ_em = 976 nm) of ytterbium(iii). A photo-patterning process for security imaging is successfully demonstrated.

Ligand-to-Ligand Interactions That Direct Formation of D2-Symmetrical Alternating Circular Helicate

This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis(4-phenyl-2-oxazolinyl)pyridine [( R)- or ( S)-Ph-Pybox] are successfully directed to the fabrication of a D₂-symmetrical alternating circular helicate with the general formula [( R)- or ( S)-Ph-Pybox]₄(Ln^III)₄(BTP)₆. The lanthanide(III) Ln^III assemblies (Ln^III₄- RRRR and Ln^III₄- SSSS) have a nanometer-size squarelike grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate Ln^III₂L₂ units, where both show ( M)-helicity for Ln^III₄- RRRR and ( P)-helicity for Ln^III₄- SSSS, where π-π stacking interaction is present between the side arm of ( R)-Ph-Pybox (Ph₁) and the adjacent BTP ligand around the Eu^III metal center ( d_ππ = 3.636 Å: the diketonate plane···Ph₁ distance). The newly obtained circular lanthanide(III) helicate exists as single and homochiral diastereomers in solution (Ln^III₄- RRRR and Ln^III₄- SSSS), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (i.e., Ln^III₄- RRRR/Ln^III₄- SSSS).

Chiral supramolecular polymerization leading to eye differentiable circular polarization in luminescence

This work demonstrates a simple methodology to tune the chiroptical properties of chiral europium(iii) complexes by supramolecular polymerization. Helical aggregation of the cesium derivative has updated the highest luminescence dissymmetry factor to date leading to naked eye visualization of circular polarized luminescence using circularly polarized filters.

From 2D → 3D interpenetration to packing: N coligand-driven structural assembly and tuning of luminescent sensing activities towards Fe3+ and Cr2O72− ions

Three complexes were hydrothermally synthesized and exhibited excellent selectivity towards Fe³⁺ and Cr₂O₇²⁻.

Carbon Dot Nanothermometry: Intracellular Photoluminescence Lifetime Thermal Sensing

Nanoscale biocompatible photoluminescence (PL) thermometers that can be used to accurately and reliably monitor intracellular temperatures have many potential applications in biology and medicine. Ideally, such nanothermometers should be functional at physiological pH across a wide range of ionic strengths, probe concentrations, and local environments. Here, we show that water-soluble N,S-co-doped carbon dots (CDs) exhibit temperature-dependent photoluminescence lifetimes and can serve as highly sensitive and reliable intracellular nanothermometers. PL intensity measurements indicate that these CDs have many advantages over alternative semiconductor- and CD-based nanoscale temperature sensors. Importantly, their PL lifetimes remain constant over wide ranges of pH values (5-12), CD concentrations (1.5 × 10^-5 to 0.5 mg/mL), and environmental ionic strengths (up to 0.7 mol·L^-1 NaCl). Moreover, they are biocompatible and nontoxic, as demonstrated by cell viability and flow cytometry analyses using NIH/3T3 and HeLa cell lines. N,S-CD thermal sensors also exhibit good water dispersibility, superior photo- and thermostability, extraordinary environment and concentration independence, high storage stability, and reusability-their PL decay curves at temperatures between 15 and 45 °C remained unchanged over seven sequential experiments. In vitro PL lifetime-based temperature sensing performed with human cervical cancer HeLa cells demonstrated the great potential of these nanosensors in biomedicine. Overall, N,S-doped CDs exhibit excitation-independent emission with strongly temperature-dependent monoexponential decay, making them suitable for both in vitro and in vivo luminescence lifetime thermometry.

Water-stable Eu-MOF fluorescent sensors for trivalent metal ions and nitrobenzene

We have synthesized two functionalized Eu-MOFs and found that the MOFs are promising luminescent probes for selectively sensing metal ions (Fe³⁺and Cr³⁺) and nitrobenzene.

OFF-ON-OFF Dual Emission at Visible and UV Wavelengths from Carbazole Functionalized β-Diketonate Europium(III) Complex

This work demonstrates dual emission "OFF-ON-OFF" switching at visible and UV wavelengths of a carbazole functionalized β-diketone (LH) by a simple change of a europium(III) ion (Eu(3+)) concentration in the submicromolar concentration range. In the presence of 0.25 equiv of Eu(3+) (5 μM), LH forms a luminescent 4:1 complex ([Eu(3+)(L(-))4](-)) exhibiting dual emission at 357 and 613 nm resulting from the local excitation of the carbazole ring and ligand-sensitized luminescence from the Eu(3+)-β-diketonate unit, respectively. The 4:1 complex begins to convert into a 2:1 complex ([Eu(3+)(L(-))2](+)) via a 3:1 complex [Eu(3+)(L(-))3] above a molar ratio ([Eu(3+)]/[LH]) of 0.25, which provides the opportunity for binding of solvent methanol molecules to the vacant site of the Eu(3+) ion in the complex ([Eu(3+)(L(-))2(MeOH)n](+)). The OH oscillators of coordinated methanol molecules facilitate the nonradiative pathway of the Eu(3+) emission; hence the emission at 613 nm almost disappears above the 0.50 equivalent of Eu(3+) (11 μM), while the UV emission at 357 nm remains mostly constant over the whole concentration range.

K+-Induced in situ self-assembly of near-infrared luminescent membrane material armored with bigger Yb(iii) complex crystallites

A semi-rigid ligand could capture effectively Yb³⁺ ions to form a stable Yb³⁺ complex and provide a potential cavity to accommodate alkali metal ions.

A europium(iii)-based metal–organic framework as a naked-eye and fast response luminescence sensor for acetone and ferric iron

A europium(iii)-based MOF as an efficient dual sensor for acetone and Fe³⁺ detection, and the sensing mechanism of both is discussed.

Europium(III)-β-diketonate complex-containing nanohybrid luminescent pH detector

In this work, by loading an Eu(3+)-β-diketonate complex into LAPONITE®, we report an organic-inorganic hybrid pH detection system Eu(3+)(TTA)n@Lap that is valid under acid conditions, which can serve as highly robust, reliable, rapid responsive and sensitive fluorescent pH detector. In addition, this hybrid pH detector can be easily recovered and reused by simply treating with Et3N vapor.