The effect of introducing of a halogen substituent into the structure of 2,2'-bipyridyl-6,6-dicarboxamide on the stability of their europium complexes has been studied. It is shown that, regardless of the size of the halogen atom, one complex particle is formed, and the metal-ligand stoichiometry of the complex is 1:1. The stability constants of europium complexes have been determined. A decrease in the size of the halogen atom leads to an increase in the stability of the complexes due to steric hindrance diminishing.
The influence of the introduction of chlorine atoms into the phenanthroline fragment of 2,9-phenanthrolinedicarboxamide on the stability constant of the europium complex has been studied. Only one complex particle is formed, and the stoichiometry of the metal-ligand complex is 1:1, regardless of the presence of acceptor substituent in the ligand structure. Presence of two chlorine substituents in the dicarboxamide leads to an increase in the stability constant of the europium complex by two orders of magnitude compared to the unsubstituted ligand.
The effect of a donor methyl groups in the structure of 6,6′-bis(di(3,5-R-phenylphosphinoyl)-2,2′-bipyridyl R = H or Me on the stability constants of lanthanum complexes was studied. Regardless of the presence of a donor substituent in phosphine oxide moiety, the stoichiometry of the complex with lanthanum was 1:1 metal to ligand. The values of the stability constant of the complexes were obtained. The insertion of methyl groups lead to increase in stability of the corresponding complexes with lanthanum which correlates well with enhance in extraction ability of the corresponding compounds towards europium.
In this work, the luminescence properties of three europium complexes with ligands based on 2,2’–bipyridyldicarboxylic acid with various counterions (TFA, NO3, Cl) were studied in the form of powders and acetonitrile solutions. Their luminescence spectra were recorded at room temperature and in liquid nitrogen. We obtained and calculated the following luminescence characteristics: luminescence lifetime, relative intensities of each luminescence peak, asymmetry coefficient, radiative lifetime, internal quantum yield, luminescence quantum yield, and the effectiveness of sensitization.
The influence of the structure of phosphonic acid esters on the stability of their terbium complexes was studied. It was shown that one complex particle was formed irrespective the nature of the side ester chain, and the metal-ligand stoichiometry of the complex was 1:1. The stability constants of the terbium complexes were determined. An increase in the size of the bulky substituent leads to an increase in the stability of the complexes.
For the first time we study the stability of the lanthanide complexes with polydentate hyterocyclic phosphine oxides. Here we report the influence of the structure of phenanthroline (PhenPPO) and 2,2’-bipyridine (DPPO) phosphine oxides on the stability of their lanthanide complexes. An increase in the flexibility of the phosphine oxide structure leads to an increase in the stability of the complexes. The maximum of stability of the complexes is observed on neodymium ion, regardless of the structure of the ligands DPPO and PhenPPO.
Here we report the investigation of complexation between lanthanide ions nitrates and 4,7-dichloro-1,10-phenanthroline- 2,9-dicarboxamide by spectrophoitometric titration technique. In all studied systems, one complex species is formed with a metal-ligand stoichiometry of 1:1. The stability of the corresponding complexes are strongly depends on the metal ion radius. All of the complexes under the study have high stability, Lu and Gd complexes possesses lgβ more than 6 and Ho and Eu – more than 7.
The luminescent properties of two water-soluble europium complexes and two organo-soluble terbium and europium complexes with ligands based on different N-heterocyclic ligands in various mixed solvents (light and heavy water, glycerol, methanol and ethanol) were studied in this work. The absorption, emission, and excitation luminescence spectra were obtained and analyzed. We calculated the asymmetry coefficient, the luminescence quantum yield, and the luminescence lifetime at various concentrations of mixed solvents. The luminescence quenching was found more noticeable in methanol than in ethanol for all studied complexes. We observed that the luminescence quantum yield in the water-containing solvents (methanol/water, methanol/heavy water, ethanol/heavy water) is almost independent of the water or heavy water concentration. We received that heavy water has less influence on luminescence quenching than water, since the vibrational frequencies of OH groups are higher than that of OD groups. Luminescence quenching by adding glycerol to the solvent is more effective for the studied organo-soluble complexes than for water-soluble ones. This effect can be explained by the fact that the ligand of organo-soluble complexes surrounds the rare earth ion more closely, thus preventing glycerol OH groups from entering the coordination zone of the ligand.
The influence of structure of the phosphine oxide ligands on stability of their complexes was studied by spectroscopic techniques. Surprising the electron donating methyl groups at phenyl rings of phosphine oxide groups lead to decrease of the stability of europium complex comparing with ubsubsituted one due to their sterical prevention of conjugation between phenyl rings and P=O-groups.. This unusual behavior was first time demonstrated by spectroscopic titration and Job’s plot analysis.
In this work, the luminescent properties of three europium salts with various counterions (trifluoroacetate, nitrate and chloride) are studied. Their luminescence excitation spectra at room temperature and in liquid nitrogen have been recorded and studied. Their luminescence lifetime is determined when excited in the UV and visible regions of the spectrum. The influence of counterions and the number of water molecules in the structure of europium salts on their luminescent characteristics is determined.
The influence of the water on the stability of complexes of 6,6′-Bis(diphenylphosphinoyl)-2,2′-bipyridyl with lanthanide ions was studied. An increase in the stability value of the complexes is observed with a decrease in the ionic radius of the metal. An increasing of the water content in acetonitrile leads to decrease the stability of the complexes. Moreover the stability of the complexes became independent on ionic radii of metals.
Investigation of proteins interactions with luminescent europium complex is interesting for the practical task of sensitive protein detection, as well as to study fundamental problems of peptide-lanthanide interplay. Presented work is devoted to examine the spectroscopic properties of europium complex (europium trinitrate (2,2'-bipyridyl-6,6'- dikarbonilazandiil)tetrakis (methylene) phosphonate) and to study its interaction with human serum albumin using various spectroscopic techniques. This complex has unique optical ability such as high values of the phosphorescence intensity in aqueous solutions, which exceeds the intensity of many other known coordination complexes of rare earth elements.
New types of europium complexes with 2,2’-bipyridyl-based ligands were synthesized and their photophysical properties were studied in detail. The influence of the amidic-group substituents on the stability of their complexes with lanthanides also investigated. The branching of the substituent at the amidic group decreases both the quantum yields and stability of complexes.
Imaging techniques in biology and medicine are crucial tools to obtain information on structural and functional properties of living cells and organisms. To fulfill the requirements associated with application of these techniques it appears necessary to design markers with specific characteristics. Luminescent complexes of trivalent lanthanide ions with chelating ligands are of increasing importance in biomedical applications because of their millisecond luminescence lifetime, narrow emission band, high signal-to-noise ratio and minimal photodamage to biological samples. In order to extend the available emission wavelength range the luminescent samarium chelates are highly desirable. In this study the ligands with diamides of 2,2’-bipyridin-6,6’-dicarboxylic acid were used to improve photophysical characteristics of samarium complexes. We report the luminescence characteristics of samarium complexes with novel ligands. All complexes exhibited the characteristic emission of Sm (III) ion with the lines at 565, 597, 605, 645 and 654 nm, the intensity strongly depended on the ligand. Absorption and luminescence excitation spectra of Sm (III) complexes showed main peaks in the UV range demonstrating lanthanide coordination to the ligand. The absolute lumenescence quantum yield was measured for solutions in acetonitrile with excitation at 350 nm. The largest luminescence quantum yield was found for the samarium complex Bipy 6MePy Sm (3%) being much higher that for samarium complexes reported in the literature earlier. These results prove as well that samarium chelates are potential markers for multiparametric imaging techniques.
The development of new complexes of rare earth elements (REE) with chelating organic ligands opens up the possibility of purposeful alteration in the composition and structure of the complexes, and therefore tuning their optical properties. New ligands possessing two pyridine rings in their structure were synthesized to improve coordination properties and photophysical characteristics of REE compounds. Complexes of trivalent europium with novel chelating ligands were investigated using luminescence and absorption spectroscopy, as well as atomic force microscopy. Luminescence properties of new compounds were studied both for solutions and films deposited on the solid support. All complexes exhibit the characteristic red luminescence of Eu (III) ion with the absolute lumenescence quantum yield in polar acetonitrile solution varying from 0.21 to 1.45 % and emission lifetime ranged from 0.1 to 1 ms. Excitation spectra of Eu coordination complexes correspond with absorption bands of chelating ligand. The energy levels of the triplet state of the new ligands were determined from the phosphorescence at 77 K of the corresponding Gd (III) complexes. The morphology of films of europium complexes with different substituents in the organic ligands was investigated by atomic force microscopy (AFM). It strongly depends both on the type of substituent in the organic ligand, and the rotation speed of the spin-coater. New europium complexes with chelating ligands containing additional pyridine fragments represent outstanding candidates for phosphors with improved luminescence properties.
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