Martti Latva

Correlation between the lowest triplet state energy level of the ligand and lanthanide(III) luminescence quantum yield

Abstract The luminescence properties of 41 different Eu(III) and Tb(III) chelates that were synthesized with the purpose of developing new markers for chemical and biochemical applications were measured in aqueous solution and their suitability for labels in time-resolved immunoassays were evaluated. In spite of the influence of numerous factors on the luminescence quantum yields, a clear correlation was obtained between the energies of the lowest triplet state levels of the ligands and lanthanide (III) luminescence quantum yields of the respective chelates. Simultaneously Eu(III) and Tb(III) ions were observed to accept energy by their several different 5Dj, resonance levels depending on the energy of the lowest triplet state level of the ligand, and the Tb(III) luminescence quantum yields were observed to decrease due to the energy back transfer from excited Tb(III)∗ to the ligand when the energy difference between the 5D4 level of Tb(III) and the lowest triplet state energy level of the ligand is less than 1850 cm−1.

Hot electron-induced electrogenerated chemiluminescence of rare earth(III) chelates at oxide-covered aluminum electrodes

Aromatic Gd(III) and Y(III) chelates produce ligand-centered emissions during cathodic pulse polarization of oxide-covered aluminum electrodes, while the corresponding Tb(III) chelates produce metal-centered5D4 →7Fj emissions. It was observed that a redox-inert paramagnetic heavy lanthanoid ion, Gd(III), seems to enhance strongly intersystem crossing in the excited ligand and direct the deexcitation toward a triplet-state emission, while a lighter diamagnetic Y(III) ion directs the photophysical processes toward a singlet-state emission of the ligand. The luminescence lifetime of Y(III) chelates was too short to be measured with our apparatus, but the luminescence lifetime of Gd(III) chelates was between 20 and 70 μs. The mechanisms of the ECL processes are discussed in detail.

Solution structures of europium(III) complexes of ethylenediaminetetraacetic acid

Abstract Coordination of ethylenediaminetetraacetic acid (EDTA) with europium(III) has been studied at different concentrations in solution using 7F0 → 5D0 excitation spectroscopy and excited-state lifetime measurements. EDTA forms with Eu(III) ion three different species in equimolar solutions at room temperature. At low pH values EuEDTAH is formed and at higher pH values than 1.5 two EuEDTA− complexes, which differ from each other with one water molecule in the first coordination sphere of the Eu(III) ion, total coordination number and coordination geometry, are also formed. When the concentration of EDTA is higher than the concentration of Eu(III), an EuEDTA(EDTAH)4- species where the second EDTA is weakly coordinated to EuEDTA−, is formed. If the concentration of Eu(III) ion is higher than EDTA, the extra Eu(III) ions associate with EuEDTA− and link to one of the carboxylate groups of EDTA thus causing a shortening of the excited-state lifetime of the EuEDTA− complex.

X-ray irradiated sodium chloride as an excitation source for the sensitized terbium(III)-specific chemiluminescence of aromatic Tb(III) chelates in aqueous solutions

Abstract The viability of X-ray irradiated sodium chloride as the excitation source to generate the radiative 5 D 4 → 7 F j transitions of chelated terbium(III) is demonstrated. The dissolution of X-ray irradiated sodium chloride in an aqueous solution produces a dynamic solid/solution interface containing hydrated electrons and dissolution-uncovered holes as strong one-electron reducing and oxidizing intermediates, respectively, which provides the energetic basis to initiate the sensitized Tb(UI)-specific extrinsic lyoluminescence of X-ray irradiated sodium chloride by the ligand-oxidation-initiated reductive and/or ligand-reduction-initiated oxidative excitation pathways. Redox luminescence mechanisms of Tb(III) chelates containing phenol, aniline or hydroxybenzophenone derivatives as their chemical energy-accepting aromatic moieties are discussed in detail.

Time-resolved luminescence detection of europium(III) chelates in capillary electrophoresis

An instrumentally simple on-column time-resolved luminescence capillary electrophoresis (CE) detector for determining and characterizing migrated europium(III) chelates on the basis of their long-lived 5D0→7F-multiplet transitions has been constructed. In addition to the background fluorescence arising from the cell walls, this time-resolved luminescence method of measurement also allows an efficient discrimination of the analyte emission against the short-lived background fluorescence caused by possible fluorescent impurities in the electrophoresis buffer; this should provide a feasible means of constructing a CE detector for the trace analysis of europium(III) chelates and also of samples of biological interest labelled with europium(III) chelates. If supplied additionally with a device for determining the excited-state lifetimes of separated europium(III) chelates, this time-resolved luminescence detector should make possible the peak identification of migrated europium(III) chelates.

Near-infrared electrogenerated chemiluminescence of ytterbium(III) chelates in aqueous electrolytes

Abstract The near-infrared electrogenerated chemiluminescence (IR ECL) of Yb(III) chelates at a pulse-polarized oxide-covered aluminium cathode is described for the first time. The observed 2 F 5/2 → 2 F 7/2 radiative transition of Yb(III) is the lowest-energy ECL in aqueous solution reported to date. Also, a proposed explanation for the excitation and emission processes of this near-IR ECL of Yb(III) chelates has been given. The phenomenon offers many new application possibilities for analytical purposes, for example, a new point of view for wavelength discrimination.

Evaluation of solution structures of highly luminescent europium(III) chelates by using laser induced excitation of the 7F0 → 5D0 transition

Solution structures of 13 Eu(III) chelates were examined by using laser induced excitation of the 7F0 → 5D0 transition. Remarkable variations in the 7F0 → 5D0 excitation spectra of 2,2′,2″,2″−{[aryl]bis(methylenenitrilo}tetrakis(acetic acid) complexes of Eu(III) are observed depending on the denticity of the ligand and the number and character of the coordinated nitrogen atoms. The evaluation of the structures is made on the basis of the energy of the 7F0 → 5Do excitation transition of Eu(III) because the 7F0 → 5D0 transition energy is dependent on the number and type of coordinating atoms in the first coordination sphere of Eu(III). Additional information about the structures is obtained by measuring the excited-state lifetimes of the Eu(III) chelates. The 7F0 → 5D0 transition energy shifts always an equal amount to lower energies due to the coordination of a certain group or atom. The energies of the 7F0 → 5D0 excitation transitions are also used to calculate these ‘nephelauxetic’ shift parameters for coordinated nitrogen heteroatoms iin the 2,2′,2″,2″−{[4-phenylethynyl)pyridine-2,6-diyl]bis (methylenenurido)}tetrakis(acetic acid) (3). 2,2′,2″,2″-[(2,2′-bipyridine-6,6′-diyl)bis-(methylenenitrilo)] tetrakis (acetic acid) (4). 2,2′,2″,2″-[(2,2′:6,2″-terpyridine-6,6″-terpyridine-6.6″-diyl)bis(methylenenitrilo)]tetrakis(acetic acid) (5), 2,2′,2″,2″- (pyrazole-1,3-diyl)-bis(pyridine)-2,2′-diyl]bis(methylenenitrilo)]tetrakis(acetic acid) (7). 2,2′,2″,2″-([thizole-2,4-diyl)bis(pyridine)- 2,2′-diyl]-bis(methylenenitrilo(]tetrakis(acetic acid) (8) and 2,2′,2″,2″-([2,2,′-pyridine-2,6-diyl)bis(thiazole)-4,4′-diyl]bis-(methylenenitrilo)]-tetrakis(acetic acid) (9) complexes. The variation in the shift parameters of the nitrogen heteroatoms is suggested to be due to the different distances between the nitrogen heteroatoms and Eu(III) ions.

Enhanced EuIII ion luminescence and efficient energy transfer between lanthanide chelates within the polymeric structure in aqueous solutions

Four new binucleating symmetric bis(4-pyridine-2,6-dicarboxylic acids) have been synthesized and luminescence enhancement of their EuIII complexes by YIII ions observed. The results indicate that the mechanism of enhancement is based on the formation of a polymeric structure where EuIII ions and YIII ions are linked together by the ligands with the consequent transfer of absorbed energy along the polymer chain through several ligands toward the EuIII ion. The mechanism of energy transfer is probably different from the previously reported micellar co-luminescence where energy transfer occurs via the Forster dipole–dipole mechanism.

Sonoluminescence of chelated terbium(III) in aqueous solution

TbIII chelates containing aromatic moieties show sonoluminescence in aqueous solutions during the sonolysis of water. The observed 5D4→7FJ transitions of TbIII are due to the excitation of ligand, followed by an intramolecular energy transfer from the ligand to the central ion, which finally emits. No sonoluminescence of hydrated or EDTA-chelated TbIII ion could be observed. Ligand excitation can be based either on an energy transfer from the intrinsic emission centres of the sonolysis of water to the aromatic ligand, or on redox reactions between the ligand and hydroxyl radicals and hydrogen atoms produced by the sonolysis of water. Experimental results give greater support to the latter, chemiluminescent, excitation pathway.

Solution structures of luminescent chelates of europium (III) with 2,6-bis[N,N-bis(carboxymethyl) aminomethyl]-4-benzoylphenol

Abstract 2,6-Bis[N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol forms with europium(III) three structurally different luminescent chelates in aqueous sample solutions. Only the chelate with a dimeric structure, where two Eu(III) cations are encapsulated into the chelating cage consisting of two deprotonated phenolic hydroxyl groups and four 2,2′-(methylenenitrilo)bis(acetic acid) moieties having strong interactions with the deprotonated hydroxyl groups, is capable of initiating the sensitized 5 D 0 → 7 F j transitions of Eu (III) with an exceptionally long lifetime of 0.97 ms.