s in English

The monomer-dimer equilibrium for polymethine dyes, thiacarbocyanine (1) and its meso-substituted derivatives [9-ethyl- (2) and 9-methylsubstituted (3)], was investigated by absorption spectra in aqueous solutions at 15-40 degrees C. The formation of dimers is accompanied by the appearance of the absorption band shifted by 35-45 nm to shorter wavelengths with respect to the absorption band of the monomers. Changes in fluorescence and fluorescence excitation spectra of the dyes with increasing their concentration show the formation of nonfluorescing dimers. The values of the dimerization constants for dyes 3, 1, and 2 at 20 degrees C were found to be 4.4 x 10(3), 3.8 x 10(4), and 2.8 x 10(5) l/mol, respectively For 1 and 2, the dimerization enthalpies were determined to be -44.0 and -72.3 kJ/mol, respectively, and the dimerization entropies were calculated to be -62.5 and -142.3 J mol(-1) K-1, respectively.

Spectroscopic properties and kinetic behavior of dye positive holes originating From imida-, oxa- and thiacarbocyanines adsorbed to AgBr grains were studied by flash photolysis. Dye positive holes produced on flash irradiation of dyed emulsions within both the absorption band of a dye in the visible and intrinsic absorption of AgBr in the UV region are mostly accompanied by the reversible bleaching of the dye ground absorption and by the appearance of a new absorption in the visible which is partly transient in character. The observed spectral changes are due to the production of both, silver aggregates Ag-n(0), and dye positive holes. The ability of sensitizing dyes in the excited state for the electron transfer as well as the pathways of dye positive hole trapping are discussed.

The luminescence lifetime of uranyl ions is strongly increased by complex formation with fluoride ions in neutral aqueous solution. A monoexponential luminescence decay with a lifetime of 160 ± 2 μs is observed in the presence of 0.5 M NaF. The *[UO2F4]2− species oxidizes carboxylate anions by an outer-sphere mechanism. For anions with oxidation potentials higher than 2 V, the logarithms of the quenching rate constants (log kq) are linearly dependent on the oxidation potentials of the anions (Eox). This allows for the estimation of such potentials from kinetic data. The oxidation potentials of carboxylates RCOO− are only slightly dependent on R. The difference between these observations and earlier results may be interpreted in terms of two different pathways for the one-electron oxidation of carboxylates, depending on the balance between the driving force of the electron transfer reaction and the reorganization energies of the redox couples involved.

Electron transfer is the principal mechanism for quenching of the triplet state of eosin and Bengal rose by cyanide complexes of W(IV), Mo(IV), Fe(II), and Fe(III).

A scheme of primary reactions in photooxidation of pigments was considered assuming that electron transfer processes can occur via singlet excited as well as triplet states. The results of analysis are compared with the experimental data on relative yield values of chlorophylls a, b, and pheophytin a cation-radicals, as well as with the data on fluorescence quenching. A conclusion has been drawn that photooxidation of pigments proceeds exclusively via the triplet state. The dependence of rate constant quenching values of chlorophyll a triplet state by certain electron acceptors on values of half cell potentials was given.

The general pattern chlorophyll photooxidation is considered. The conclusion is made that the reaction of photooxidation occurs exclusively via the chlorophyll triplet state.

A method for studying the nature of electronic excited state under photooxidation is proposed. It is shown by an example of the oxidation of chlorophyll a with p-benzoquinone that the formation of cation-radicals of pigments proceeds only through the triplet state. On the basis of experimental data the values of the rate constants of formation of chlorophyll cation-radicals through the singlet-excited state (K2(1)--10(7) M-1 s-1) and triplet state (Kr=10(9) M-1 s-1) of the pigment are evaluated.

Nitriding of niobium and its alloys increases the ultimate strength by 50–100% at room temperature.

It was established that niobium is substantially strengthened as the result of cold plastic deformation with reduction exceeding 70%. The strength at room temperature is 25–30% higher in the cold-worked sheets than in the annealed sheets.