I.V. Khmelinski

Bio: I.V. Khmelinski is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Flash photolysis & Photodissociation. The author has an hindex of 5, co-authored 7 publications receiving 164 citations.

Photochemistry of the PtCl62− complex in methanol solution

Abstract: In the laser flash photolysis of PtCl 6 2− in methanol, a non-linear dependence of the yields of the trivalent platinum intermediates PtCl 6 3− and PtCl 5 2− on laser pulse intensity is observed. The non-linearity is due to the absorption of photons by PtCl 6 3− which is a primary product resulting from the electron transfer from a methanol molecule to excited PtCl 6 2− . Photodissociation of PtCl 6 3− yields PtCl 5 2− . However, PtCl 6 3− in the ground state also dissociates into PtCl 5 2− and Cl − . This monomolecular process proceeds with an activation energy of 29.7 kJ mol −1 and a rate constant of 1.05 × 10 6 s −1 at 300 K. The parameters of the reverse reaction between Cl − and PtCl 5 2− which yields PtCl 6 3− have also been measured (activation energy, −9.6 kJ mol −1 ; rate constant at 300 K, 7.6 × 10 6 M −1 s −1 ). When free Cl − is present in methanol at a concentration of more than 0.1 – 0.2 M, electron transfer from Cl − to excited PtCl 6 2− is also possible. The chlorine atom formed reacts with Cl − yielding the radical ion Cl 2 − which is detected by an intense absorption band with a maximum at 340 nm.

Intermediates in the photoreduction of PtCl62− in methanol

Abstract: Electron transfer from the solvent molecules to the excited complex is the primary process in the photoreduction of the PtCl 6 2− complex in methanol The CH 2 OH radical and the trivalent platinum complex PtCl 6 3− form the radical complex PtCl 6 3− …R which can disappear via several reactions At low temperatures of the solid matrix (77 – 160 K), the second electron is transferred from the radical to the Pt III ion to form the final product PtCl 4 2− In liquid methanol ( T > 170 K), this process competes with the dissociation of the radical complex into the free radical R and the complex PtCl 6 3− With oxygen present in the solution, another concurrent reaction is possible: the transformation of the complex PtCl 6 3− …R into the new radical complex PtCl 6 3− …RO 2 which exhibits an optical absorption spectrum in the range 330 – 450 nm

Pulsed laser photolysis of the PtCl62−—creatinine system in methanol

Abstract: The pulsed laser photolysis (excimer laser, XeCl; 308 nm) of the PtCl 6 2− —creatinine—methanol system was studied. The formation of an intermediate Pt III species (PtCl 5 2− cr, where cr = creatinine) was demonstrated and its decay kinetics were examined. Some kinetic and thermodynamic data of the photoinduced reaction were determined. The photolysis of the same system using stationary irradiation was also investigated allowing the end product of the reaction to be determined.

Primary photochemical processes of the PtCl62− complex in alcohols

Abstract: Laser flash photolysis was used to verify whether or not the primary photolysis mechanism of the PtCl 6 2− complex in ethanol and isopropanol was the same as that found previously in methanol (V. P. Grivin, J. Photochem. Photobiol. A: Chem., 51 (1990) 167, 371, 379). The primary process is the electron transfer from an alcohol molecule to the excited complex. The trivalent platinum complex and the solvent radical form the primary radical complex PtCl 6 3− …Ṙ. At room temperature, this radical complex dissociates yielding PtCl 6 3− , which further dissociates either photochemically after absorption of a photon or thermally, yielding PtCl 6 2− and Cl − . The high quantum efficiency of photodissociation results in a non-linear of PtCl 6 3− and PtCl 6 2− yield vs. laser pulse intensity. At low temperatures, the PtCl 6 3− …Ṙ radical complex either decays during the second electron transfer from the radical to the platinum ion yielding the final complex PtCl 4 2− or forms, in the presence of oxygen, a new radical complex PtCl 6 3− …RȮ 2 .

Laser pulse photolysis study of the reaction of the intermediate platinum(III) complex PtCl2−5 and 4-(2-p-dimethylaminophenyl ethynil)-6,6-dimethyl-3-cyano-5,6-dihydro-2(1H)-pyridone

Abstract: Laser flash photolysis was used to investigate the fast reaction of 4-(2- p -dimethylaminophenyl ethynil)-6,6-dimethyl-3-cyano-5,6-dihydro-2(1H)-pyridone (DHP) with the intermediate complex of platinum(III), PtCl 2− 5 , appearing in the photoreduction of PtCl 2− 6 in methanol. Kinetic and spectroscopic parameters of the new-formed complex PtCl 2− 5 |DHP were determined. DHP in this complex is coordinated by an −N(CH 3 ) 2 group nitrogen atom since a similar molecule with this group substituted by −O(CH 3 ) does not react with PtCl 2− 5 . Steady-state photolysis has shown that the transformation Pt(III) a Pt(II) involves escape of DHP from the coordination sphere since the final complex Pt(II)|DHP is not formed.

Light as a construction tool of metal nanoparticles : Synthesis and mechanism

Abstract: The photo-induced synthesis of metal nanoparticles (NPs) was reviewed with a closer look at those based on photochemistry. Recent developments in metal NPs research, photochemistry, and photoprocessing techniques have allowed researchers to devise various photo-induced synthetic strategies to obtain metal NPs under a variety of conditions. We begin by outlining the classical method. The photochemical synthesis of metal NPs including direct photoreduction and photosensitization has been developed to achieve decent yields. We focused on stabilization and functionalization method of NPs in photochemical synthesis, which has enabled us to fabricate a variety of metal nanostructures and composite materials. In addition, we mention an alternative approach, that is, laser ablation at the solid–liquid interface. Some of the most innovative studies dealing with the three-dimensional fabrication of metal NPs are highlighted, together with new directions such as potential applications for a light-driven actuator, bioimaging, and three-dimensional processing. This review is concluded with the future perspectives for the photo-induced synthesis of metal NPs.

Phthalocyanine fluorescence at high concentration: dimers or reabsorption effect?

Abstract: — For tetrasulfonated aluminum phthalocyanine (AlPcS4), dimer formation is characterized in the absorption spectrum by a broadening of the Q-band and the appearance of a new band at the red edge of the spectrum. The high concentrations required to produce dimers, however, often leads to anomalous observations in fluorescence spectroscopy. In the present study, we have examined the photophysical characteristics of two dye systems; AlPcS4 in a 66% ethanol/water mixture and disulfonated aluminum phthalocyanine in methanol. Using absorption spectroscopy, the formation of dimers is shown to be prevalent only in the case of AlPcS4. The fluorescence emission spectra in both cases, however, exhibit similar spectral changes with increasing dye concentration. The measured fluorescence decay profiles for both dyes also show similar trends: They are monoexponential, invariant with emission wavelength and have decay times that increase with dye concentration. These distortions are sometimes incorrectly attributed to dimer fluorescence. We find no evidence for the existence of dimer fluorescence and demonstrate that these data can be readily explained, by taking into consideration the effects of reabsorption of fluorescence.

Oxidative Decomposition of Rhodamine B Dye in the Presence of VO2+ and/or Pt(IV) under Visible Light Irradiation: N-Deethylation, Chromophore Cleavage, and Mineralization

Abstract: In order to make clear the roles of dissolved O2 in the photocatalytic decomposition of organic pollutants and to discriminate different degradation pathways (N-deethylation, chromophore cleavage, and mineralization) during the degradation of dye, the photodegradation of rhodamine B (RhB) has been investigated using vanadate and/or platinum species as electron acceptors in the presence or absence of O2 under visible light irradiation. It was found that with VO2+ as electron acceptor, RhB underwent efficient N-deethylation under visible light irradiation and O2 was found to slow down this process significantly. Little mineralization has been observed in the presence and absence of O2 in VO2+ systems. By contrast, Pt(IV) resulted in the cleavage of conjugated chromophore structure (bleaching) of RhB dye under the otherwise identical conditions. In this case, the presence of O2 did not affect the bleaching rate of the dye, but enhanced greatly the mineralization. Both cleavage of conjugated chromophore structure and N-deethylation occurred simultaneously upon the coaction of VO2+ and Pt(IV) under visible light irradiation. The mineralization yield of the combined system was evidently higher than the expected summation of separate ones. TOC, XPS, and ESR results indicate that in the VO2+ and Pt(IV) combined system VO2+ not only oxidized RhB leading to deethylation but also oxidized the reduced Pt(II) to regenerate Pt(IV) leading to the further cleavage of chromophore structure of RhB, which behaved quite different from the separate ones. A mechanism was also proposed to interpret the different pathways for the oxidative photodecomposition of RhB under visible irradiation.

Photobleaching of protoporphyrin IX in cells incubated with 5-aminolevulinic acid.

Abstract: Protoporphyrin IX (Pp IX) is the main photosensitizer in photochemotherapy with 5-aminolevulinic acid (ALA). Pp IX is photolabile and the present work shows that 70-95% of Pp IX in cells is degraded by clinically relevant light exposures (40-200 J cm(-2) at 630 nm). During light exposure a small yield of photoprotoporphyrin, which is also photolabile, is formed. A substantial fraction of Pp IX in cells incubated with ALA is bound to proteins. During light exposure these binding sites are destroyed, those close to tryptophan residues being the most sensitive. The rate of photodegradation of Pp IX in the cells is dependent on the initial concentration of Pp IX. The degradation mechanisms are therefore not only first order processes. Different degradation rates appear to be related to different types of binding sites. During light exposure, Pp IX molecules appear to move to different binding sites, evidently sites that are more vital for cell survival. Thus, the yield of photoinactivation of the cells, as measured per emitted photon of Pp IX fluorescence, increased during light exposure.

The Hexachlorocerate(III) Anion: A Potent, Benchtop Stable, and Readily Available Ultraviolet A Photosensitizer for Aryl Chlorides

Abstract: The hexachlorocerate(III) anion, [CeIIICl6]3–, was found to be a potent photoreductant in acetonitrile solution with an estimated excited-state reduction potential of −3.45 V versus Cp2Fe0/+. Despite a short lifetime of 22.1(1) ns, the anion exhibited a photoluminescence quantum yield of 0.61(4) and fast quenching kinetics toward organohalogens allowing for its application in the photocatalytic reduction of aryl chloride substrates.