Search

We have studied the sensitized fluorescence of coumarin 30 incorporated into nanoparticles from complexes of p-phenylbenzoyltrifluoroacetone and 1,10-phenanthroline with Y, La, Lu, Gd, Al, and Sc ions in 10% alcoholic-aqueous solutions. We have shown that, upon formation of nanoparticles from complexes of Y(III) and Ln(III) ions, coumarin 30 molecules are completely incorporated from the solution into nanoparticles from complexes up to dye concentrations in the solution comparable with the concentration complexes. For the nanoparticles under study, in the whole range of the examined dye concentrations, concentration quenching of the coumarin 30 cofluorescence has not been observed. Our results show that coumarin 30 is incorporated into lanthanide and yttrium complexes as a synergistic bidentate ligand. The possibility of creating brightly luminescent markers that absorb not only in the range of 360-370 nm, but also in the range of 440-450 nm, and have a narrow fluorescence spectrum with λ = 520 nm has been demonstrated. [ABSTRACT FROM AUTHOR]

We study the sensitization of fluorescence of Nile red in nanoparticles formed in aqueous solutions of complexes of Al, In, Sc, and Lu with DBM, DBM, and phen and of complexes of In with MBTA and phen. We show that, at concentrations of Nile red of 2-50 nM and complexes of 10-30 μM, the fluorescence intensity of Nile red in aqueous solutions increases by 1.5-2 orders of magnitude compared to its fluorescence in HO. We find that, at these concentrations of Nile red in solutions of complexes Al, the dye is completely contained in nanoparticles from these complexes. We show that Nile red molecules are inhomogeneously distributed in nanoparticles from complexes and, upon the completion of the formation of nanoparticles, dye molecules tend to be localized in regions of nanoparticles formed from diketonate complexes M(diketone)phen (M is Lu or In) and Al(DBM). Upon the localization of Nile red in these regions, the maximum of its fluorescence spectrum shifts toward ∼600 nm and, upon the penetration of Nile red into nanoparticles from Sc complexes, the shift of the maximum of its fluorescence spectrum compared to the spectrum in water does not exceed 10 nm. The shifts of the spectra are collated with the ability of ions to form diketonate and hydroxy diketonate complexes. We demonstrate that the fluorescence of Nile red is efficiently sensitized, not only upon its penetration into nanoparticles formed from complexes, but also upon its adsorption on the nanoparticle surface when Nile red molecules are introduced in solutions of already formed nanoparticles. [ABSTRACT FROM AUTHOR]

The monitoring of variations in the luminescence intensity ( Ilum) of nanostructures of Eu(MBTA)3phen (MBTA is p-methoxybenzoyl trifluoroacetonate) complexes formed in aqueous solutions upon the introduction of anions is proposed as a method of analyzing the composition of Eu(III), Gd(III) and Lu(III) phosphate complexes in solutions with [PO] < [Ln]. It is found that low-lability binuclear complexes, which rearrange within an hour or longer, are formed in these solutions. It is shown that the lability of Ln(III) carbonate complexes exceeds the lability of Ln(III) complexes with PO. An analysis of the dependence of Ilum of the solution on the concentration of Eu(III) ions and on the time from the instant of the solution preparation shows that, in aqueous solutions where the concentration of anions is higher than the concentration of Ln(III) ions, nanostructures of Eu(III) phosphate and carbonate salts are formed in the range of Ln(III) concentrations 0.5–5 μM at concentrations of anions on the order of 10 μM and at concentrations of exceeding 100 μM. The rearrangement of these nanostructures to nanostructures of Eu(MBTA)3phen complexes is studied. [ABSTRACT FROM AUTHOR]

The effects of the concentration of a number of dyes in an aqueous solution and of the method of formation of mixed nanostructures of dyes and Eu(MBTA)3phen (MBTA is p-methoxybenzoyltrifluoroacetone; phen is 1,10-phenanthroline) complexes that form these structures on the luminescence decay kinetics of Eu(III) ions are studied. It is shown that, in the concentration range 5–50 nM of Nile blue, the concentration dependences of the luminescence decay and of the decrease in τ lum of Eu(III) nearly coincide and are nearly linear. The dependence of the ratio of I lum of Eu(III) to the intensity of the sensitized delayed fluorescence of Nile blue on the delay time of the probe pulse is analyzed; it is found that the majority of dye molecules incorporated in nanostructures of Eu(MBTA)3phen complexes emit sensitized delayed fluorescence with times 1–50 μs. Analysis of the effect of the structure of nanostructures on the quenching of I lum of Eu(III) by the dye at different concentrations of Eu(III) shows that nanostructures of Eu(MBTA)3phen and Eu(NTA)3phen (NTA is 2-naphthoyltrifluoroacetone) complexes appear in the aqueous solution at a concentration of Eu(III) of 0.1 μM (the MBTA or NTA concentration is 50 μM, and the concentration of phen is 17 μM) and exist in the solution at the Eu(III) concentrations up to ∼5 μM. This confirms the conclusion on the occurrence range of nanostructures of Ln complexes previously made based on the analysis of columinescence in these structures. [ABSTRACT FROM AUTHOR]

The luminescence intensity of Eu(III) ions ( I Eu) in 3: 1 aqueous solutions of thenoyltrifluoroacetone, n-methoxybenzoylacetone, and dibenzoylmethane with 1,10-phenanthroline is studied in the presence and the absence of La(III), Gd(III), and Nd(III) ions. It is found that, in binary solutions of Eu(III) with La and Gd, the intensity I Eu, as well as the influence of chelates of La and Gd on I Eu, is considerably greater if these ions are introduced into the solutions of β-diketones and 1,10-phenanthroline simultaneously and homogeneously than when they are introduced into these solutions successively. This result is explained by the difference in the distribution of different Ln chelates over nanostructures. The average size of the structures arising is estimated. [ABSTRACT FROM AUTHOR]

We studied the luminescence intensity ( I lum) of the ions Eu(III) and Sm(III) in relation to the concentrations of ions Ln(III) and Al(III) in water at pH 7 at an excess of such beta-diketones as p-methoxybenzoyltrifluoroacetone (MBTA), dibenzoylmethane (DBM), and tenoyltrifluoroacetone (TTA) and in the presence of 1,10-phenanthroline (phen) used as a synergistic agent. Both the enhancement of I lum (Eu(III)) upon addition of Gd(III) (co-luminescence) and the effect of the third ion are found to depend on the order of addition of the ions to the solution and, therefore, on the sequence of formation of nanostructures of complexes of these ions in the solution, in which the transfer of the triplet energy of the organic part of complexes takes place, leading to an enhancement in I lum (Eu(III)). The intensity I lum (Eu(III)) is shown to increase equally rapidly upon addition of either Gd(III) or Al(III) to solutions with DBM + phen. In solutions of all the three beta-diketones studied, the Eu(III) ions incorporate better into nanostructures of triply charged ions whose radius is similar to or smaller than the radius of the Eu(III) ions. Our study of the effect that the replacement of H2O with D2O exerts of I lum of 5 × 10−8 M Eu(III) at different concentrations of ligands shows that, at [Ln(III)] < [OH−] and at a concentration of beta-diketones smaller than 3 × 10−5 M, the deuteration affects I lum(Eu(III)) and, therefore, the first coordination sphere of Eu(III) contains OH groups. It is shown that, in aqueous solutions with 3 × 10−5 M TTA + 10−5 M phen, the increase in I lum(Eu(III)) caused by the introduction of Gd(III) ions results from two processes occurring in the nanostructures of these complexes: the energy transfer from Gd(III) complexes to Eu(III) complexes and the increase of I lum of Eu(III) itself under the conditions in the solution where the total concentration [Ln] ≫ [OH−] and both the photochemical deactivation of Eu(III) and the exchange of its excitation energy for vibrations of the OH groups are suppressed. The reliability of the size estimation of nanostructures of metal complexes is discussed in terms of the effect of these nanostructures on I lum of chelates of Eu(III). [ABSTRACT FROM AUTHOR]

This study continues the experimental testing of the validity of the inductive resonance theory of dipole–dipole energy transfer from the T1 → S0 transition dipole to stretching vibrations of intramolecular CH bonds of naphthalene and its hydroxy derivatives. To this end, in the series of compounds under study, the range of variation of the geometrical parameter [Φ(CH)]2 of the Förster theory, which accounts for the mutual orientation of the energy donor and acceptor, is estimated. Preliminarily, the angles between the transition dipole moments of the radiative and absorptive electronic transitions (T1 → S0 and S0 → S1; T1 → S0 and S0 → S2; S1 → S0 and S0 → S1; and S1 → S0 and S0 → S2) are measured at 77 K by the method of polarization photoselection. From the polarization measurements, the angles between the phosphorescence transition dipole moment and the plane of a molecule are determined. It was found that, upon passage from naphthalene to its β derivatives, the orientation of the dipole moment of the radiative T1 → S0 transition relative to the plane of a molecule markedly changes, with the in-plane component of the dipole moment being increased by an order of magnitude. The experimentally determined rate constants of nonradiative deactivation of the T1 state averaged over the CH groups of the naphthalene ring system, knr(CH), are compared with the rate constants [Φ(CH)]2 of the inductive resonance energy transfer from the dipole of the T1 → S0 transition to the dipole of the CH vibrations polarized in the plane of a molecule, calculated with regard to the orientational factor [Φ(CH)]2. This comparison showed that, in the series of compounds under study, a change in the orientation of the dipole moment of the radiative T1 → S0 transition relative to the plane of a molecule does not affect the rate of the nonradiative T1 [functional_relationship] S0 transition. This inference is confirmed by the absence of a correlation between the rate constants kdd(CH) calculated by us (with regard to [Φ(CH)]2) and the well-known rate constants knr(CH) of individual sublevels of the T1 state measured at T ≤ 1.35 K for a number of organic molecules. The possible sources of discrepancy between the experimental data that knr(CH) is independent of [Φ(CH)]2 and the predictions of the theory are considered. A conclusion is made that the electronic–vibrational energy transfer between electric dipoles is the most probable mechanism of the T1 [functional_relationship] S0 transitions, but the rate constant of the dipole–dipole energy transfer upon interaction of the electronic and vibrational dipoles in a molecule does not depend on their orientations. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D[sub 2]O and d[sub 6]-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I[sub lum] and lifetime τ[sub lum] of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2[sup ′]-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10[sup –2]–10[sup –1] M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10[sup –6]–10[sup –3] M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ[sub lum] decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2[sup ′]-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III). © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Review: 104 refs. [ABSTRACT FROM AUTHOR]