Manganese(II) complexes with diethylamine in aqueous solutions

Interaction between MnCl₂ and diethylamine (DEA) in aqueous solutions has been studied by UV, IR, and EPR spectroscopy as part of the design and research program on models of natural photosystems. The composition of the precipitate for comparable concentrations of reagents and solute oxygen has been investigated. Mn(II) was found to be oxidized with oxygen to give MnO₂·H₂O as a precipitate. In the solution over the precipitate, Mn(III) complexes with DEA are formed; the complex molecule has four and six amine molecules in the coordination sphere.     

Photochemistry of iron(iii)-lactic acid complex in aqueous solutions

Photochemistry of a 1: 1 Fe^III-lactic acid complex, [Fe(Lact)]⁺, in aqueous solutions was studied by stationary photolysis, nanosecond laser flash photolysis (355 nm, 6 ns), and femtosecond pump-probe spectroscopy (400 nm, 200 fs). The quantum yield of photolysis of [Fe(Lact)]⁺ upon excitation at 355 nm is 0.4 and 0.22 in the deoxygenated and air-saturated solutions, respectively. Weak transient absorption in the range 500–750 nm was observed in the nanosecond experiments. It was assigned to a [Fe^II...-O-CH(Me)-COO^·]⁺ radical complex. The spectral properties of the ligand-to-metal charge transfer excited state and the characteristic time of formation of the radical complex (1.5 ps) were determined in the femtosecond spectroscopy experiments. A reaction mechanism was proposed, which involves inner-sphere electron transfer in the excited complex with the formation of a radical complex [Fe^II...-O-CH(Me)-COO^·]⁺ and its subsequent transformation to the end product of the photochemical reaction.     

Two-quantum photochemistry of the complex <Emphasis Type="Italic">cis</Emphasis>,<Emphasis Type="Italic">trans</Emphasis>-[Pt<Superscript>IV</Superscript>(en)(I)<Subscript>2</Subscript>(CH<Subscript>3</Subscript>COO)<Subscript>2</Subscript>]

The two-quantum photochemistry of aqueous solutions of cis,trans-[Pt^IV(en)(I)₂(CH₃COO)₂] (complex 1) has been studied by laser flash photolysis using an irradiation wavelength of 355 nm. This compound can be considered as a model representative of the mixed-ligand Pt(IV) complexes tested for use in photodynamic therapy. The appearance of transient absorption, presumably due to two consecutively produced Pt(III) complexes, has been revealed. The spectral and kinetic characteristics of the intermediates have been determined. A mechanism of two-quantum photolysis of complex 1 is proposed on the basis of the data obtained.     

Photochromic properties of phenanthroline-annulated spirooxazine in the solid state

Photochromic transformations of phenanthroline-annulated spirooxazine were observed in polycrystalline powders and solid-phase films obtained from solutions by solvent evaporation. The spectral and kinetic properties of the solid-phase films were studied by stationary absorption spectroscopy and laser flash photolysis. The mechanism of photoinitiated reactions of solid-phase samples of phenanthroline-annulated spirooxazine includes mutual transformations of different transoid isomers of the merocyanine form.     

Photochemistry of <Emphasis Type="Italic">N</Emphasis>-substituted salicylic acid amides

The products of photolysis of N-substituted salicylic acid amides, viz., 2-hydroxy-3-tert-butyl-5-ethylbenzoic acid N-(4-hydroxy-3,5-di-tert-butylphenyl)amide (1) and 2-hydroxybenzoic acid N-[3-(4-hydroxy-3,5-di-tert-butylphenyl)prop-1-yl]amide (2), in heptane were studied by optical spectroscopy and stationary and nanosecond laser photolysis (Nd: YAG laser, 355 nm). It was shown by the method of partial deuteration of amides 1 and 2 that they exist in both the unbound state and as complexes with intraand intermolecular hydrogen bond. Amides 1 and 2 are subjected to photolysis, which results in the formation of a triplet state and phenoxyl radicals RO? presumably due to the absorption of the second photon by the excited singlet state. The formation of radical products due to N–H bond ionization was not observed. The main channel of decay of the triplet state and radicals RO? is triplet–triplet annihilation and recombination (k _r ≈ 2.3?10⁸ L mol^–1 s^–1), respectively. The UV irradiation of compounds 1 and 2 leads to the excitation of the amide groups, and no formation of radical products due to N–H bond ionization was observed.     

Primary photophysical and photochemical processes for Pt(SCN)<Subscript>6</Subscript><Superscript>2–</Superscript> complex

Photosolvation of a Pt^IV hexathiocyanate complex Pt(SCN)₆ ^2– in water and ethanol was studied by steady-state photolysis, nanosecond laser flash photolysis, and ultrafast kinetic spectroscopy. Complexes Pt(SCN)₅(H₂O)^– and Pt(SCN)₅(C₂H₅OH)^– were found to be the only reaction products. The quantum yields of photosolvation are independent of the excitation wavelength, being equal to 0.25 and 0.5 for the solutions of the complex in water and ethanol, respectively. Photosolvation proceeds by the mechanism of heterolytic metal—ligand bond dissociation without involvement of redox processes. The characteristic time of formation of the end products for both solvents is about 10 ps. Three successive intermediates detected on the picosecond time scale were interpreted as Pt^IV complexes. The nature of the intermediates and possible mechanisms of photosolvation are discussed.     

Photochemistry of dithiocarbamate Cu(II) complex in CCl4

Laser pulse photolysis was used to study the nature and reactions of intermediates in the photochemistry of the flat dithiocarbamate complex Cu(Et(2)dtc)(2) in CCl(4). A nanosecond laser pulse (355 nm) is shown to induce intermediate absorption bands of bivalent copper complex whose coordination sphere contains a dithiocarbamate radical Et(2)dtc(?) and a chloride ion at the axial position ([(Et(2)dtc)Cu(Et(2)dtc(?))Cl(a)]). At room temperature during some microseconds after the laser pulse, this intermediate interacts with the initial complex to form presumably a dimer [Cu(2)(Et(2)dtc)(3)(Et(2)dtc(?))Cl]. The latter vanishes in the second-order reaction. Analysis of kinetic and spectral features gives the arguments for the formation of a cluster [Cu(2)(Et(2)dtc)(3)Cl-tds-Cu(2)(Et(2)dtc)(3)Cl], which produces a new absorption band at 345 nm. The cluster decomposes in ～5 ms into final products, a binuclear complex [Cu(2)(Et(2)dtc)(3)Cl] and tetraethylthiuramdisulfide (Et(4)tds).     

A point pulsed light source

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 1, pp. 160–162, January, 1988.     

Photoinduced electron transfer via nonbuttressed metal-metal bonds. The photochemical study of binuclear complexes with platinum-thallium bonds

The photochemistry of binuclear metal-metal bonded complexes [(NC) 5Pt-Tl(solv) x ] (solv is water or dimethylsulfoxide) has been studied in aqueous and dimethylsulfoxide solutions. Both stationary and nanosecond laser flash photolysis have been carried out on the species. The metal-metal bonded complexes have been photolyzed by irradiation into the corresponding intense MMCT absorption bands. Photoexcitation results in the cleavage of the platinum-thallium bond and the formation of a solvated thallous ion and a cyano complex of platinum(IV), [Pt(CN) 5(solv)] (-), in both cases. The species have been characterized by multinuclear NMR and optical spectroscopy. The products of the photoreaction indicate a complementary two-electron transfer occurring between platinum and thallium ions in the binuclear Pt-Tl species. Quantum yield values for the photodecomposition of the species have been determined. The intermediates of the photoinduced metal-to-metal electron transfer have been detected and characterized by optical spectroscopy. The kinetics of transient formation and decomposition have been studied, and mechanisms of the photoactivated redox reaction have been suggested.     

Photophysics and photochemistry of uranyl ions in aqueous solutions: Refining of quantitative characteristics

The photochemistry and photophysics of aqueous solutions of uranyl nitrate have been investigated by nanosecond laser photolysis with excitation at 266 and 355 nm and by time-resolved fluorescence spectroscopy. The quantum yield has been determined for (UO₂²⁺)* formation under excitation with λ = 266 and 355 nm light (φ = 0.35). The quantum yield of uranyl luminescence under the same conditions is 1 × 10^–2 and 1.2 × 10^–3, respectively, while the quantum yield of luminescence in the solid state is unity, irrespective of the excitation wavelength. The decay of (UO₂²⁺)* in the presence of ethanol is biexponential. The rate constants of this process at pH 3.4 are k₁ = (2.7 ± 0.2) × 10⁷ L mol^–1 s^–1 and k₂ = (5.4 ± 0.2) × 10⁶ L mol^–1 s^–1. This biexponential behavior is explained by the existence of different complex uranyl ion species in the solution. The addition of colloidal TiO₂ to the solution exerts no effect on the quantum yield of (UO₂²⁺)* formation or on the rate of the reaction between (UO₂²⁺)* and ethanol. The results of this study have been compared with data available from the literature.