Polyaryl Ether Dendrimer with a 4-Phenylacetyl-5-pyrazolone-based Terbium(III) Complex as Core: Synthesis and Photopysical Properties

Influence of Ligand Environment Stoichiometry on NIR-Luminescence Efficiency of Sm3+, Pr3+ and Nd3+ Ions Coordination Compounds

Six new complexes of the ligand HQcy (-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) and Ln3+ ions with emission in the near-infrared (Nd3+) or visible and near-infrared (Sm3+, Pr3+) spectral regions were synthesized and characterized using various methods, including single crystal X-ray diffraction. The study demonstrated that both tris complexes [LnQcy3(H2O)(EtOH)] and tetrakis-acids [H3O][LnQcy4] can be synthesized by varying the synthetic conditions. The photochemical properties of the complexes were investigated experimentally and theoretically using various molecular spectroscopy techniques and Judd-Ofelt theory. The objective was to quantitatively and qualitatively disclose the influence of complex stoichiometry on its luminescence properties. The study showed that the addition of an extra ligand molecule (in the tetrakis species) increased molar extinction by up to 2 times, affected the shape of photoluminescence spectra, especially of the Pr3+ complex, and increased the quantum yield of the Sm3+ complex by up to 2 times. The results obtained from this study provide insights into the luminescent properties of lanthanide coordination compounds, which are crucial for the design and development of novel photonic materials with tailored photophysical properties.

Dynamics of the Ligand Excited States Relaxation in Novel β-Diketonates of Non-Luminescent Trivalent Metal Ions

Complexes emitting in the blue spectral region are attractive materials for developing white-colored light sources. Here, we report the luminescence properties of novel coordination compounds based on the trivalent group 3, 13 metals, and the 1-phenyl-3-methyl-4-cyclohexylcarbonyl-pyrazol-5-onate (Q^CH) ligand. [M(Q^CH)₃] (M = Al, Ga, and In), [M(Q^CH)₃(H₂O)] (M = Sc, Gd, and Lu), [Lu(Q^CH)₃(DMSO)], and [La(Q^CH)₃(H₂O)(EtOH)] complexes were synthesized and structurally characterized by a single-crystal X-ray diffraction study. It has been found that the luminescence quantum yields of the ligand increase by one order of magnitude upon metal coordination. A significant correspondence between the energies of the ligand's excited states and the luminescence quantum yields to the metal ion's atomic numbers was found using molecular spectroscopy techniques. The replacement of the central ion with the heavier one leads to a monotonic increase in singlet state energy, while the energy of the triplet state is similar for all the complexes. Time-resolved measurements allowed us to estimate the intersystem crossing (ISC) rate constants. It was shown that replacing the Al³⁺ ion with the heavier diamagnetic Ga³⁺ and In³⁺ ions decreased the ISC rate, while the replacement with the paramagnetic Gd³⁺ ion increased the ISC rate, which resulted in a remarkably bright and room-temperature phosphorescence of [Gd(Q^CH)₃(H₂O)].

Self-Assembly of a Two-Dimensional Coordination Polymer Based on Silver and Lanthanide Tetrakis-Acylpyrazolonates: An Efficient New Strategy for Suppressing Ligand-to-Metal Charge Transfer Quenching of Europium Luminescence

A new strategy for the easy polymerization of anionic [Ln(Q^cy)₄]^- (HQ^cy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Q^cy)₄]_n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Q^cy)₄]^- to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Q^cy)₄]_n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Q^cy)₄]^- is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Q^cy)₄]_n polymer. Sensibilization coefficients for H₃O[Eu(Q^cy)₄], [AgEu(Q^cy)₄]_n, and H₃O[Sm(Q^cy)₄] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm³⁺) and PLQY measurements.

Dual-sensitized Eu(III)/Tb(III) complexes exhibiting tunable luminescence emission and their application in cellular-imaging

Two novel dual-photosensitized stable complexes, namely [Eu(dpq)(BTFA)₃] (1) and [Tb(dpq)(BTFA)₃] (2), have been successfully assembled via a mixed ligand approach using dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) and 3-benzoyl-1,1,1-trifluoroacetone (BTFA). The crystallographic data reveal mononuclear lanthanide cores in both 1 and 2, in which each eight-coordinated Ln(III) ion is located in a slightly distorted dodecahedron (D_2d). The room-temperature photoluminescence spectra of complexes 1 and 2 indicate that both BTFA and dpq can effectively sensitize Eu(III) and Tb(III) characteristic luminescence. Moreover, heterometallic Ln-complexes can be synthesized, leading to a new series of differently doped EuxTb1-x complexes. Luminescence experiments on them reveal dual-emission peaks of Eu³⁺ and Tb³⁺, which lead to a gradual change in the luminous colour between yellow-green, yellow, orange, orange-red and red upon increasing the Eu³⁺ content. On the basis of the intrinsic strong emission properties and nontoxic nature of complexes 1 and 2, we explore their potential application as cellular imaging agents. Fluorescence microscopy data suggest the cytosolic and nuclear localization of 1 and 2 in HeLa and MCF-7 cells.

Preparation of polymer–rare earth complexes based on Schiff-base-containing salicylic aldehyde groups attached to the polymer and their fluorescence emission properties

In this study, the salicylaldehyde hydrazone was bonded onto the side chains of poly (styrene-co-butyl acrylate), firstly obtaining a series of novel Schiff base-functionalized polymers. and using the base-containing polymers as macromolecular ligands through further reaction with EuCl3/YbCl3·6H2O, a series of polymer-rare earth complexes based on Eu(III)/Yb(III) ion were successfully prepared. The structures of the schiff base-containing polymers and their corresponding complexes were characterized by means of infrared spectra and UV spectra. The thermal properties of the functionalized polymers and complexes were investigated by TGA, and the fluorescence properties of the complexes were also researched by fluorescence spectrum. The experimental results show that the complexes have fine thermal stability likely because of the bidentate chelate effect of base-containing polymer and the conjugative effect of salicylaldehyde hydrazone group on the side chain of poly (styrene-co-butyl acrylate). More important, the salicylaldehyde hydrazone group on the side chains of poly(styrene-co-butyl acrylate) can efficaciously sensitize the fluorescence emission of the center ion due to effective intramolecular energy transfer. All the Eu(III)/Yb(III) complexes exhibit characteristic photoluminescence peaks in the visible region. The fluorescence excitation spectra of the complexes were obtained by monitoring the emission of Eu3+/Yb3+ ion at 497 nm, and the peak at 433 nm was found to be the optimal excitation peak. The concentration of salicylaldehyde hydrazone group was changed gradually with the variation of the molar ratio between the butyl acrylate and styrene (1:0.5; 1:1; 1:1.5; 1:2; 1:2.5), and the differences in their fluorescent intensity were followed, and the fluorescence intensity was very weak when the molar ratio of the butyl acrylate to styrene is equal to 1:2.5, while the fluorescence intensity reached a maximum value in the molar ratio of 1:1.

An intense luminescent Dy(iii) single-ion magnet with the acylpyrazolonate ligand showing two slow magnetic relaxation processes

A new Dy(iii)-acylpyrazolonate complex displays both intense yellow-light emission and single-ion magnet behavior with two slow magnetic relaxation processes, acting as a potential bifunctional material.

The synthesis, structure and physical properties of lanthanide(III) complexes with nicotinic acid

This article reports the synthesis of novel, rare-earth coordination complexes with nicotinic acid. Three compounds with the general formula Ln2[(C5H4NCOO)6(H2O)4] (Ln = Yb, 1; Ln = Gd, 2; Ln = Nd, 3) were prepared from relatively cheap and readily available reactants. Their compositions and structure were characterized by IR spectroscopy and single-crystal X-ray diffraction. The magnetic and thermogravimetric properties were also studied. The complexes consist of centrosymetric, dimeric molecules having all six nicotinato ligands coordinated with the central atom in the bidentate mode. The coordination environment of the Ln3+ for all three compounds is 8. Here we describe the crystal structure of Yb and Gd complexes with nicotinic acid.

A new europium(III) complex containing a neutral ligand of 2-(pyridin-2-yl)-1H-benzo[d]imidazole: thermal, electrochemical, luminescent properties

A new europium(III) complex i.e. Eu(ECTFBD)3PBI was synthesized, where ECTFBD and PBI are 4-(9-ethyl-9H-carbazol-3-yl)-1,1,1-trifluoro-4-oxobutan-2-olate anion and 2-(pyridin-2-yl)-1H-benzo[d]imidazole, respectively. Its IR, UV-Vis spectra, electrochemical, thermal properties as well as photoluminescent performances in solid state and in CH2Cl2 were investigated. Eu(ECTFBD)3PBI exhibited strong red emission without any emission from ECTFBD and PBI in solid state, but with a very weak emission from ECTFBD in CH2Cl2. We explored this difference of the luminesecences of Eu(ECTFBD)3PBI in solid state and in CH2Cl2 based on the excited triplet energy levels of ECTFBD and PBI.