S. S. Ostakhov

Chemiluminescence during thermal degradation of sodium persulfate in the presence of terbium sulfate: 2. The effect of water of crystallization

An abnormally strong influence of water of crystallization on the intensity of chemiluminescence (CL) in the thermal degradation reaction of sodium persulfate in the presence of terbium(III) sulfate was revealed. As the water is driven off terbium sulfate Tb2(SO4)3 · nH2O (n= 8–0), the luminescence intensity and light sum increase. The maximum CL intensity for the completely dehydrated sample is 20 times higher and the light sum is two orders of magnitude greater than those of the crystal hydrate containing eight water molecules. It was found that the rise in the CL yield is due to an increase in the yield of excitation of the emitter *Tb(III), rather than the yield of its emission, with a change in the coordination environment.

The influence of excitation of the 4f-orbital of Eu(fod)3 on complex formation with adamantanone and anomalous enhancement of Eu3+ luminescence under the action of H2O and D2O molecules in toluene

The influence of excitation of the 4f-orbital of, β-diketonate Eu(fod)3 (fod is heptafluorodimethyloctanedione) on the formation of the coordination bond with adamantanone (1) was studied by the nonradiative energy transfer technique. The kinetic parameters of fluorescence (FL) and the lifetime (τ) of the Eu3+ ion in toluene solutions were studied. The increase in the stability of the Eu(fod)3·1 complex when f—f-transitions of the Eu3+ ion are excited is related to an increase in the acceptor capability of Eu(fod)3 due to the increasing fraction of the covalent component determined by the participation of 4f-orbitals. An unexpected effect of enhancement of the Eu(fod)3 fluorescence under the action of H2O (D2O) molecules in toluene solutions was observed. The effect is assumed to be caused by an increase in the negative inductive effect when outer-sphere associates with the fluorinated radical of β-diketonate are formed. The mechanisms of the influence of electron-donating inner-sphere ligands and outer-sphere associates on the quantum yield of fluorescence of Eu(fod)3 are discussed.

Mechanically induced chemiluminescence in the dispiro(adamantane-1,2-dioxetane)—Eu(fod)3 system

Luminescence accompanying an impact mechanical treatment of solid particles of the complex of Eu(fod)3 (fod is 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione) with dispiro(adamantane-1,2-dioxetane) (1) was discovered and studied. The luminescence has a complex structure, and its spectrum belongs to the excited EuIII ions. The emission of light is observed only in a mechanical mixture of the Eu(fod)3 with dioxetane1 and in their cocrystallized form, but not in the case of the components taken separately. The mechanism by which the impacts cause the luminescence is considered. It was shown that the luminescence is not triboluminescence, but is chemiluminescence induced by the decomposition of compound1.

Photoinduced electron transfer from higher excited singlet states of tryprophan: 1. Effects of the excitation wavelength, pH, and temperature on quenching of Tryptophan fluorescence by europium(III) ions

Effects of the excitation energy, temperature, and pH on the quantum yield and the Stern-Volmer quenching constant for tryptophan fluorescence quenching by europium(III) chloride were studied. Competition between intracomplex reversible photoinduced electron transfer from tryptophan to Eu(III) ions and the processes of internal conversion and vibrational relaxation of higher excited singlet states Sn(n > 1) of tryptophan was revealed.

Fluorescence of the diterpenoid alkaloids lappaconitine andN-deacetyllappaconitine in acetonitrile

The absorption, excitation, and fluorescence spectra of the diterpenoid alkaloids, lappaconitine andN-deacetyllappaconitine, in acetonitrile were studied. On the basis of the coincidence of the spectra with the analogous spectra of model compounds, methyl esters of anthranilic andN-acetylanthranilic acids, the conclusion was drawn that the—OOC(Ph)NRH groups are fluorochromes in the alkaloids studied. The high quantum yield of fluorescence and the bathofluoric shift in the luminescence and absorption spectra ofN-deacetyllappaconitine were explained by an increase in the electron-releasing ability of the —NRH group in the deacetylation of lappaconitine.

Fluorescent study of the keto-enol equilibrium of 5-fluorouracil tautomers in aqueous solutions

A spectral-luminescent study of the keto-enol tautomerism of 5-fluorouracil (FU) has been performed. A discrepancy between the absorption and fluorescence (FL) excitation spectra of aqueous FU solutions (pH 7) has been established. Photoexcitation at the long-wavelength band (340 nm) of the FU excitation spectrum made it possible to detect the fluorescence of its dienol tautomer (λmax = 440 nm). The quenching of tryptophan fluorescence (K = 15 × 103 l/mol) and blood fluorescence by 5-fluorouracil has been investigated.

Recombination luminescence of poly(arylene phthalide) films: 1. Electronic and optical features of poly(arylene phthalide)s

Features of the luminescence and absorption spectra of poly(biphenylene phthalide), poly(fluorenylene phthalide), and poly(terphenylene phthalide) films were analyzed. Experimental results obtained for these films by optical methods and thermally stimulated current spectroscopy were compared. Long-lasting afterglow emission from the films after photoexcitation was observed. Possible explanations for the observed optical and thermally stimulated processes in the poly(arylene phthalide)s were suggested in terms of reversible electronic phase transitions induced by external factors in unconjugated polymers.

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) initiated by Ce(CIO4)3 in the excited state

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) (1) to adamantanone (2) initiated by Ce(ClO4)3 in the excited state in the MeCN−CHCl3 (2∶1) mixture was studied. The bimolecular rate constants of quenchingkq were determined from the kinetics of quenching of Ce3+* by dioxetane at different temperatures. The Arrhenius parameters of the quenching were calculated from the temperature dependence ofkq:Ea=3.2±0.3 kcal mol−1 and logA=11.6±6. The quantum yields of photolysis of 1 depending on its concentration and the rate constant of the chemical reaction of Ce3+* with 1 were determined. The latter coincides withkq:kch=(2.6±0.3)·109 L mol−1 s−1 (T=298 K). The fact that the maximum quantum yield of decomposition of dioxetane is equal to 1 indicates the absence of physical quenching of Ce3+* with 1. Nonradiative deactivation of Ce3+* in solutions of MeCN and in MeCN−CHCl3 mixtures was studied. It is caused by the replacement of H2O molecules in the nearest coordination surroundings of Ce3+ by solvent molecules and reversible transfer of an electron to the ligand. The activation parameters of the nonradiative deactivation of Ce+* were determined.

Fluorescence of 5-fluorouracil upon the transition from the second singlet excited state S2 to the ground state

Effect of the wavelength of excitation light (λex) on the fluorescence excitation and emission spectra of 5-fluorouracil in acidic solution (pH 2.5) was studied upon excitation at the S2 ← S0-transition absorption band. It has been found that direct excitation at the second or the shorter wavelength absorption band results in 5-fluorouracil fluorescence that originates not only from the first excited state S1 but is also due the transition from the second excited state S2 to the ground state.

The intracomplex radical-cation chain oxidation of tryptophan photosensitized by uranyl ion

AbstractPhotooxidation of tryptophan (Trp) in complexes with the uranyl ion upon selective excitation was studied, and the quantum yields of amino acid oxidation (ϕ(O2)) were determined. It was shown that the photosensitized oxidation of Trp by the uranyl ion involves the chain reaction of Trp·+ radical cations with O2, rather than follows the commonly accepted mechanism of interaction of the substrate radical cation with the superoxide ion