Optical spectroscopy of europium 3,5-dinitrosalicylates—Intense red luminophores

It was found, that alkali metal-europium dinitrosalicylates of composition M₃Eu(3,5-NO₂-Sal)₃·nH₂O (M = Li, Na, K, Cs) are intense red luminophores with wide excitation band. Using methods of optical spectroscopy we studied the influence of nitrogroups and alkali metal counterions on Eu³⁺ luminescence efficiency and on processes of excitation energy transfer to Eu³⁺ ion in compounds synthesized. The Eu³⁺ luminescence and Eu³⁺ luminescence excitation spectra, as well as vibrational IR and Raman spectra were investigated. Details of the structure of compounds were discussed. The network of hydrogen bonds in lanthanide dinitrosalicylates is weakening at introduction of large alkali metal ions in compounds and at the increase of the temperature. As a consequence, the long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu³⁺ excitation spectra arises at inclusion of Cs⁺ cations instead of Li⁺ in the crystal lattice of europium dinitrosalicylates and at heating of these compounds. To obtain the energy of the lowest excited triplet state the phosphorescence spectra of alkali metal-gadolinium compounds M₃Gd(3,5-NO₂-Sal)₃·nH₂O, of alkali metal dinitrosalicylate and salicylate salts were measured with time delay. Change of the energies of ligand electronic states and ligand–metal charge transfer state (LM CTS) can give a two-three orders of magnitude enhancement of the Eu³⁺ luminescence efficiency in dinitrosalicylates in comparison with salicylates and ten-fold enhancement at the substitution of Li⁺ and Na⁺ for Cs⁺ in dinitrosalicylates.     

Photodecomposition of Eu3+ complexes with macromolecular ligands based on acrylic acid

The spectroluminescent and photochemical properties of Eu³⁺ complexes with copolymers of acrylic acid and alkyl methacrylates were studied. It was found that the photochemical behavior of the macromolecular complexes differs significantly from that of the lowmolecular analogs: in the course of photodecomposition the luminescence intensity of Eu³⁺ noticeably increases rather than diminishes. The efficiency of the luminescence build up of Eu³⁺ depends on the composition and the structure of the initial macromolecular complexes. A low concentration of the metal, low content of acrylic acid, and increase in the length of the alkyl radical of methacrylate favor the enhancement of the efficiency of luminescence build up of the rare-earth ion.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1559–1562, September, 1993.     

Some recent developments in pressure tuning spectroscopy

Pressure tuning spectroscopy has proved to be a powerful tool for studying a wide variety of electronic phenomena. In this review we present two recent examples of the application of high pressure luminescence: (1) a test of the validity of a kinetic model for the emission characteristics of molecules that emit from excited states with different degrees of charge transfer and different geometries (molecules with twisted intramolecular charge transfer (TICT)); (2) an elucidation of the mechanism for the large difference observed between the luminescence efficiencies of [Ru(bpy)₃]²⁺ and [Ru(bpy)₂(py)₂]²⁺ in solid media.In 1994, Prof. H. G. Drickamer was awarded theHonoris causa degree by the Russian Academy of Sciences.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1195–1202, July, 1995.     

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente LXI. Welche Oxidationszahl hat Cer im tiefvioletten 1,1′,4,4′-Tetrakis(trimethylsilyl)cerocen?

Using the original and not a newly suggested synthesic route, Ce[C₈H₆(1,4-SiMe₃)₂]₂ (1) was resynthesized as an oil of deep purple color. The absorption, MCD and luminescence spectra of this compound were measured at room temperature as well as at low temperatures. Especially, the low-temperature spectra are more consistent with a Ce^III compound.     

New 2,2′-Bipyridine Derivatives and Their Luminescence Properties with Europium(III) and Terbium(III) Ions

Twenty differently substituted 2,2′,2″,2? -[(2,2′-bipyridine-6,6′-diyl)bis(methylenenitrilo)]tetrakis(acetc acids) 75–94 were synthesized with the purpose of developing new markers to be used in bioaffinity assays based on the unique luminescence properties of Eu^III and Tb^III ions. The relative luminescence yields, excitation maxima, and emission decay constants were determined for the corresponding Eu^III and Tb^III chelates. The substituents at the bipyridine moiety had a significant effect on the luminescence properties: the best relative luminescence yields R were obtained for ligands with electron-donating substituents (e.g. Me, Ph), electron-withdrawing substituents (e.g. NO₂, COOH) had a reverse effect. However, no clear correlation between the relative luminescence yields and the substituent parameters was found.     

增强掺Tb凝胶玻璃荧光性能的有机螯合体的选择

采用原位合成技术, 用溶胶凝胶法制备了稀土离子(Tb^3＋), β-二酮及协同体共掺的二氧化硅玻璃, 测量了它们发射光谱和红外光谱, 并进行了XRD, SEM和TG-DSC测试. 探讨各不同成分原位合成稀土有机配合物在二氧化硅玻璃中的发光性能及热处理温度对发光性能的影响. 结果表明, 在凝胶玻璃中掺入能级较匹配的β-二酮, 可以使稀土离子的荧光增强; 合适的协同体的引用也能使稀土离子的荧光增强. 这些结果为今后制备荧光较强的含Tb离子的SiO₂凝胶玻璃提供了一定的依据.     

Influence of Chelating Groups on the Luminescence Properties of Europium(III) and Terbium(III) chelates in the 2,2′-bipyridine series

Eight different 2,2′-bipyridine derivatives, i.e. 2, 5, 8, 10, 12, 13, 15 , and 19 (Schemes 1 and 2), were prepared to study the influence of the chelating groups on the luminescence properties of their Eu^III and Tb^III chelates. According to our luminescence results, 2,2′-(methylenenitrilo)bis(acetic acid) as well as (methylenenitrilo)bis-(methylphosphonic acid) in 6- and 6′-position of 2,2′-bipyridine is a suitable group when developing luminescent markers for bioaffinity assays based on time-resolved luminescence measurement.     

Synthesis and Optical Properties of 2,13‐Dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6

A new crown ether of 2,13‐dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6 was synthesized from 2,13‐diformyl‐ dibenzo[b,k]‐18‐crown‐6 with 2‐aminothiophenol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na⁺, K⁺, Rb⁺ and Cs⁺ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied.     

Excitation Energy-Transfer Processes in the Sensitization Luminescence of Europium in a Highly Luminescent Complex

The excitation energy transfer (EET) pathways in the sensitization luminescence of Eu^III and the excitation energy migration between the different ligands in [Eu(fod)₃dpbt] [where fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and dpbt=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine], exhibiting well-separated fluorescence excitation and phosphorescence bands of the different ligands, were investigated by using time-resolved luminescence spectroscopy for the first time. The data clearly revealed that upon the excitation of dpbt, the sensitization luminescence of Eu^III in [Eu(fod)₃dpbt] was dominated by the singlet EET pathway, whereas the triplet EET pathway involving T₁(dpbt) was inefficient. The energy migration from T₁(dpbt) to T₁(fod) in [Eu(fod)₃dpbt] was not observed. Moreover, upon the excitation of fod, a singlet EET pathway for the sensitization of Eu^III luminescence, including the energy migration from S₁(fod) to S₁(dpbt) was revealed, in addition to the triplet EET pathway involving T₁(fod). Under the excitation of dpbt at 410 nm, [Eu(fod)₃dpbt] exhibited an absolute quantum yield for Eu^III luminescence of 0.59 at 298 K. This work provides a solid and elegant example for the concept that singlet EET pathway could dominate the sensitization luminescence of Eu^III in some complexes.     

Isotopic effects on the time-dependences of 420 nm ice luminescence excited by UV light

The kinetics of the 420 nm luminescence emitted from H₂O and D₂O polycrystalline Ih ices have been studied over the 77 to 162 K temperature range. In the case of both H₂O and D₂O ices, it was found that the luminescence rise and decay curves consisted of two luminescence components, and superimposing two first-order curves with different rate constants gave the best fit to the decay and rise curves. The mean lifetimes of the two luminescence components were 1.08 ± 0.03 s and 2.47 ± 0.03 s. The rate constants were found to have negligible temperature dependences, which led to activation energies well below those obtained for either activation-limited processes or even diffusion-limited processes. Furthermore, it was found that the luminescence kinetics were not affected by isotopic substitution of D for H in the ice lattice. These observations suggest that the rate-determining step in the mechanism for the production of the luminescence is a slow (probably spinforbidden) electronic transition that can occur at two different rates due to the presence of two different types of trapping sites in the ice lattice. A possible candidate for the electronic transition is the ⁴Σ → X ²Π transition of excited OH^. radicals and not the previously suggested and ubiquitous A ²Σ⁺ → X ²Π transition of this species. Published in Russian in Kinetika i Kataliz 2006, Vol. 47, No. 5, pp. 709–721. This text was submitted by the authors in English.     

Preparation and Characterization of GdTaO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> Sol-Gel Luminescence Thin Films

High quality GdTaO₄:Eu³⁺ luminescence films have been successfully prepared through a modified sol-gel process. The films were prepared using inorganic materials as raw materials, and the thermal decomposition and UV assisted technique were introduced to improve the quality of the film and reduce the period for forming the thick film. Results of structural studies by atomic force microscopy (AFM) and X-ray diffraction (XRD) showed that the surface was smooth and the structure was monoclinic with the average grain size of about 55 nm. The emission and excitation spectra of the film were investigated. Related to the transition ⁵ D₀ →⁷ F₁ and ⁵ D₀→⁷ F₂ of Eu³⁺ ions, the main luminescence peaks were observed at 591 and 611 nm respectively, and the luminescence peak at 345 nm was detected simultaneously related to the TaO₄³⁻ emission. Transmission spectrum and decay curve of the luminescence are also presented in this paper.     

Chemical and electrochemical synthesis,structure, photoluminescent properties,and biological activity of 4-methyl-N-[2-[(Z)-2-(2-pyridyl)alkyliminomethyl]phenyl]benzenesulfamide zinc(II) complexes

A series of Zn(II) complexes of the tridentate azomethine ligands, condensation products of 2-(N-tosylamino)benzaldehyde and 2-aminoalkylpyridines, were synthesized by chemical and electrochemical methods. All compounds were characterized on the basis of C, H, N elemental analysis, Fourier-transform infrared, ¹H nuclear magnetic resonance, UV–Vis, and photoluminescence studies. The local atomic structures of complexes were determined from analysis of extended X-ray absorption fine structure and X-ray absorption near-edge structure of Zn K-edges. The molecular structure of chloro-{4-methyl-N-[2-[(Z)-2-pyridyl)ethyliminomethyl]phenyl]benzenesulfamide}zinc(II) was determined by X-ray single-crystal diffraction. The fluorescence spectra show that these complexes in dimethyl sulfoxide solutions at room temperature emit bright blue luminescence at 435–461 nm with fluorescence quantum yields in the range of 0.20–0.31. The assignment and the nature of the bands in experimental UV–Vis spectra of complexes were analyzed using time-dependent density functional theory calculations B3LYP/6-31G(d). The azomethines and complexes of zinc have been screened for their antibacterial, protistocidal, and fungistatic activities against Penicillium italicum, Colpoda steinii, Escherichia coli 078, and Staphylococcus aureus P-209, and the results are compared with the activity of furazolidone, chloroquine, and Fundazol.     

Synthesis,Structure, and Luminescent Properties of Antimony(III) Complexes with N,N"-Diphenylguanidine

Complexes of antimony(III) halides with N,N"-diphenylguanidine were synthesized for the first time and studied using X-ray diffraction analysis and luminescence spectroscopy. The mechanism of sensitization of Sb³⁺luminescence involving the low-lying state of the charge transfer was proposed.     

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with Gd^III, Eu^III, and Tb^III ions in aqueous solution. The ligand‐based luminescence is retained in the Gd^III cryptates, whereas this radiative deactivation is quenched in the Eu^III and Tb^III cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]³⁺ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb³⁺ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]³⁺, [Ln⊂ 2 ]³⁺ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]³⁺ do not match. The effects of H₂O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported.     

Preparation and examination of properties of lanthanide chloride salts with hexamethylenetetramine

Summary New complex salts of lanthanide chlorides with hexamethylenetramine of the general formulaLnCl₃·2HMTA·nH₂O [Ln=La, Pr, Nd, Sm, Dy, Er;HMTA-hexamethylenetetramine N₄(CH₂)₆;n=8, 10, 12] have been obtained. On the basis of IR IR spectra (4000-200cm^–1) and Raman spectra (3000-300 cm^–1), changes in the coordination sphere structure of the salts occurring in the course of thermal dehydration have been determined.

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Darstellung und Untersuchung der Eigenschaften von Komplexsalzen der Lanthanidchloride mit Hexamethylentetramin

Zusammenfassung Neue Komplexsalze der Lanthanidchloride mit Hexamethylentetramin mit der allgemeinen FormelLnCl₃·2HMTA·nH₂O [Ln=La, Pr, Nd, Sm, Dy, Er;HMTA — Hexamethylentetramin N₄(CH₂)₆;n=8, 10, 12] wurden dargestellt. Die Änderungen in der Struktur der Koordinationssphäre während der thermischen Dehydration der Salze wurden mittels Infrarot-(4 000–200 cm^–1) und Ramanspektroskopie (3 000–300 cm^–) bestimmt.

     

Fluorescent and photochemical properties of TbIII complexes with acrylic acid-based macromolecular ligands

The fluorescent and photochemical properties of Tb^III complexes with macromolecular ligands based on acrylic acid were studied. The photochemical behavior of the macromolecular Th^II complexes with acrylic acid-alkyl methacrylate copolymers differs considerably from those of Tb^III complexes with polyacrylic acid and of low-molecular-weight analogs; in the former case, the intensity of Tb³⁺ photoluminescence noticeably increases during photolysis rather than decreases. It was found that the increase in the length of the alkyl group in the alkyl methacrylate favors the enhancement of the luminescence during the photolysis. The higher efficiency of the enhancement of the Eu³⁺ fluorescence during the photolysis of similar complexes of Eu³⁺ compared to the complexers of Tb³⁺ is due to the nature of the electrodipole hypersensitive⁵D₀–⁷F₂ transition in Eu³⁺.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2007–2010, August, 1996.     

Geometry,Vibrational and NMR Spectra of Icosahedral 1-Methylazacloso-dodecaborane

Geometry, vibrational and NMR spectra of the icosahedral aza-closo-dodecaborane MeNB₁₁H₁₁ are calculated by ab initio methods. The results are compared with experimental data. They are in accord with local C_5v symmetry of the cluster unit and local C_3v symmetry of the methyl group. The boron atoms B7–B11 are coupled to B12 by the small constant ¹J (¹¹B, ¹¹B) = 12 Hz.     

Effect of Nonchromophoric Ligands on the Spectral Characteristics of Ruthenium(II) (2,2'-Bipyridine)diphosphine Complexes

The electronic absorption and luminescence spectra of the complexes cis-[Ru(bpy)(dppe)X₂] [bpy is 2,2'-bipyridine, dppe is 1,2-bis(diphenylphosphino)ethane] in 4 : 1 ethanol-methanol mixtures at 77 and 293 K were measured, and the luminescence decay times were determined. As the field strength of the nonchromophoric ligand X increases in the order I^- < Br^- < Cl^- < 1/2(CO₃ ^{2 -}) < NCS^- < NO₂ ^- < CN^-, the electronic transitions are blue-shifted, and the luminescence decay time becomes longer.     

Vibrational spectra of icosahedral (Ih and I) fullerenes

On the bases of the topological structures of the three big classes of icosahedral fullerenes: (1) C_n(I_h, n=60h²; h=1, 2,…), (2) C_n(I_h, n=20h²; h=1, 2,…), and (3) C_n(I, n=20(h²+hk+k²), h>k; h, k=1, 2,…), we derived formulas for the decomposition of their nuclear motions into irreducible representations. Hence, we obtained the infrared and Raman active modes for all of the icosahedral (I_h and I) fullerenes theoretically. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 113–117, 1998     

Praseodymium β-diketonates and luminescence properties of their solutions

The luminescence intensity of Pr(III) in a series of complexes with alkyl and thienyl fluoroacetylacetone derivatives has been shown to increase not only with an increase in the length of the fluoroalkyl radical but also with the introduction of an oxygen heteroatom into this radical. The luminescence intensity of Pr(III) increases by about two orders of magnitude when a donor ligand (an organic solvent) is introduced into the complex. In some cases, the triplet level of β-diketone become higher due to interligand energy transfer and the Pr(III) luminescence occurs from two emitting levels ¹ D ₂ (the ¹ D ₂ → ³ H ₄ transition, λ_lum = 605 nm) and ³ P ₀ (the ³ P ₀ → ³ H ₆ transition, λ = 612 nm). Heteroleptic Pr(III) β-diketonates have short lifetimes (τ); for example, the lifetime of the Pr(III) complex with thenoyltrifluoroacetone and diantipyrylmethane is shorter than 1 μs. Original Russian Text ? S.B. Meshkova, A.V. Kiriak, Z.M. Topilova, A.M. Andrianov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 4, pp. 614–619.