Influence of polarity of medium on fluorescence characteristics of alkylaminobenzophenones

A study has been made of the instantaneous fluorescence spectra of 4,4′-bis-dimethylaminobenzophenone (Michler’s ketone, MK), 4,4′-bis-diethylaminobenzophenone (DEAB), and 4-dimethylaminobenzophenone (DMAB) in various solvents, at room temperature. It has been shown that an increase of the solvent polarity leads to an increase of fluorescence intensity and a shift of the fluorescence band maximum toward longer wavelengths. The presence of traces of water in the solutions increases the fluorescence intensity and gives a red shift of the maximum. From the relationships found between the position of the fluorescence maximum and the polarity of the solvent, estimates have been made of the dipole moment of the luminescent state, which is 1.6·10⁻²⁷ C·m for the MK, 2.1·10⁻²⁷ C·m for the DEAB, and 0.8·10⁻²⁷ C·m for the DMAB. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 36–40, January–February, 1997.     

Reactive intermediates in laser photolysis of guanosine

The photochemical reactions of aqueous solution guanosine with acetone as photosensitizer have been investigated by laser flash photolysis. From detailed kinetic analysis, the reaction mechanism has been derived: dehydrogenated guanosine radical G(-H)* and triplet guanosine ³G* were produced via electron transfer and triplet-triplet energy transfer respectively. The half-life time of ³G* has been determined to be 7.4 μs, and the quenching rate constant of Mn²⁺ on it was obtained to be 1.9 × 10⁸ M^-1 s^-1. Based on pH titration, the pKa value of ³G* was also obtained to be 8.7.     

Laser flash photolysis formation and direct kinetic studies of manganese(V)-oxo porphyrin intermediates

Irradiation of porphyrin-manganese(III) perchlorate complexes in acetonitrile with 355 nm laser light gave MnV-oxo intermediates that were characterized by their UV-vis spectra and reactivities. The MnV-oxo species of tetrakis(pentafluorophenyl)porphyrin (2), tetraphenylporphyrin (4), and tetra-(4-(N-methylpyridiniumyl))porphyrin (6) were generated. Second-order rate constants for reactions of 2 with substrates were as follows: 6.1 x 105 M-1 s-1 (cis-stilbene), 1.3 x 105 M-1 s-1 (diphenylmethane), 1.3 x 105 M-1 s-1 (ethylbenzene), and 0.55 x 105 M-1 s-1 (ethylbenzene-d10). In oxidations of cis-stilbene and diphenylmethane, the order of reactivity of the MnV-oxo species was 2 > 6 > 4.     

Influence of the reaction medium on platinum surface formation

The effect of an organic reaction medium on the Pt-black surface formation has been studied. It has been shown that under the action of the reaction medium an irreversible change of the catalyst surface occurs.

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Pt-. , .

     

Flash photolysis of s-trinitrobenzene solutions

Flash photolysis of s-trinitrobenzene (TNB) aerated solutions in alcohols generates a transient species with absorption maxima at 430 and 510 nm. The yield of the transient is a function of oxygen concentration, and its rate of formation is viscosity dependent. In deaerated solutions instead of the transient, a brown permanent product, identified as a charge transfer (CT) complex with absorption maxima at 470 and 550 nm, is produced. These species are formed only in polar solvents with relatively high proton affinity. The data suggest an intermolecular proton transfer, from electronically excited TNB to the solvent forming the anion The anion thereby produced interacts with oxygen in aerated alcohols to form the transient attributed to CT complex while in deaerated alcohols the anion reacts with the solvent to produce RO^?, which leads to the CT complex RO…^?TNB. This mechanism is supported by detailed kinetic and spectroscopic studies.     

Carbonyl sulfides as possible intermediates in the photolysis of oxathiiranes

Diphenyl oxathiirane, formed by irradiation of thiobenzophenone S-oxide at 77 K, is photochemically converted into a blue, thermally unstable compound which decomposes at ca 100–110 K (λ_max 550 nm, (? ca 11,000). Lack of change in magnetic susceptibility during the light induced conversion of sulfine to ketone via the oxathiirane and the subsequent blue intermediate implies the absence of triplet and biradical singlet transients. The unknown carbonyl sulfide functionality, R₂COS, thereby emerges as a strong candidate for producing the visible absorption.Comparison of the wave functions for CH₂SO and CH₂OS arising from MNDO limited CI geometry optimizations leads to the conclusion that the carbonyl sulfide structure is best described as a zwitterion rather than as a singlet biradical. The failure to observe cycloaddition products between the blue species and several dipolarophiles is rationlized in terms of a labile carbonyl suffide intermediate capable of facile sulfur extrusion from a long, weak O-S bond. Finally, the electronic absorption spectra of a series of para-substituted benzaldehyde O-sulfide model system have been calculated with CNDO/S-CI and correlated with the λ_max's of the corresponding series of diaryl blue substrates.The sum of the available experimental and theoretical data is consistent with the existence of closed shell carbonyl sulfides as observable, though labile, intermediates from the photolysis of oxathinanes.     

Influence of the polarity of the medium on the rate of oxidation of unsaturated compounds

Russian Chemical Bulletin -     

Evidence of the hydroxyl radical formation upon the photolysis of an iron-rich clay in aqueous solutions

With the use of laser flash photolysis, the formation of hydroxyl radicals upon the photolysis of an iron-rich clay (montmorillonite KSF) was demonstrated. The ^•OH radical was shown to be formed by the photolysis of the Fe(OH)_aq ²⁺ complex that escaped from the clay into the solution bulk.     

A spectroscopic study on medium polarity in fluorous alcohol

The paper describes the polarities of three fluorous (F) aliphatic alcohols: perfluorinated tert-butanol (F-t-BuOH), n-butanol (F-n-BuOH), and n-heptanol (F-n-HepOH). For the purpose, we conducted absorption and fluorescence spectroscopies of coumarin 153 (C153) and 102 (C102) in three F and 13 non-fluorous (non-F) alcohols and determined their maximum energies: ν^a (absorption) and ν^f (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., (ν^a − ν^f)) and a medium polarity parameter for 13 non-F alcohols, f(x): f(x) = [(D_s − 1)/(2D_s + 1) − (n² − 1)/(2n² + 1)], where D_s and n were the dielectric constant and refractive index of a solvent, respectively. By comparing the Stokes shifts of the dyes in three F alcohols with those in 13 non-F alcohols (i.e., (ν^a − ν^f) vs. f(x) plot), the D_s values in F-t-BuOH, F-n-BuOH, and F-n-HepOH were evaluated to be 2.7-3.9, 4.3-5.1, and 4.0-5.2, respectively, while those in the relevant non-F alcohols were 12.5, 17.5, and 12.9, respectively. Thus, the present experiments demonstrated that the polarities of these F alcohols were much lower than those of the relevant non-F alcohols.     

Regularities of formation of emboli of liquid polymer solutions in aqueous medium

Work on creating the basis for embolic compositions for the treatment of a wide range of pathologies of various organs was conducted. This basis is a solution of a biocompatible water-insoluble polymer in a biocompatible water-soluble solvent. Formation of the embolus in such an aqueous medium takes place in the transition of the solvent into the aqueous phase and the formation of a solid polymer clot occluding a blood vessel. Criteria for selection of the polymer and the solvent for the basis were formulated, and a number of polymers and solvents that meet these criteria were selected for further research. Research on the solubility of the selected polymers in solvents was carried out, and the rheoviscometric characteristics of polymer solutions, as well as parameters of solid emboli formation of polymer solutions in aqueous media, were found. The solution of cellulose acetate plasticized with OPADRY CA 500F190000 polyethylene glycol in dimethylsulfoxide with concentration of no less than 60 g/L was recognized as optimal for further studies.     

Effect of temperature on hydrogen peroxide photolysis in aqueous solutions

The photolysis of hydrogen peroxide in dilute aqueous solution (1 × 10⁻⁴ M) at various temperatures (15–85°C) and pH (ph 2.5–7) was studied by flash photolysis. The rate of oxygen production under continuous photolysis conditions was measured at room temperature. The rate constants and activation parameters are reported. Evidence for the formation of complexes between hydrogen peroxide and intermediate radicals is presented. The liquid phase data are discussed and compared with those available for the gas phase.     

Flash photolysis of solutions of sodium in ethers

Flash photolysis of ethereal solutions of sodium results in the almost complete disappearance of the original absorption band at 15000 cm⁻¹ and in the formation of solvated electrons. After the flash an intermediate with an absorption maximum at 12000 cm⁻¹ is formed. This absorption is assigned to a species which has the stoichiometric composition of a sodium atom. Although it may be described as a metal “monomer” we propose as an alternative model the concept of an “ion pair” of a solvated electron and a sodium cation. In analogy to the 12000 cm⁻¹ transient we propose that the blue species can be described as an associate of a sodium cation with two solvated electrons.     

Pulse photolysis of PbCl4 in non-aqueous solutions

Lead(IV) chloride solutions in CCl₄, CHCl₃, cyclohexane, benzene, toluene, chlorobenzene, N,N-dimethylformamide and pyridine have been irradiated with an approximatelyy 1.5 kJ pulse of UV radiation lasting 0.5 ms. The course of the photochemical processes has been followed by measuring the loss of PbCl₄, the changes of Cl₂ concentration and by identifiction of chlorination products. In a similar way, chlorine solutions in cyclohexane and benzene have been investigated. Primary processes are discussed in detail. The most probable process in solvents that do not form complexes with PbCl₄ is predissociation of the Pb-Cl bond

whereas in those forming complexes with PbCl₄ electron transfer takes place:

The results are compared with those obtained earlier under steady irradiation. This allows us to determine new pathways of secondary processes that are unobservable with the continuous illumination technique. The pathways include processes photoinduced by the phase of fresh finely dispersed PbCl₂ crystals:

     

Investigation of lead thiosulfate photolysis in aqueous solutions

A model of photolysis of PbS₂O₃ aqueous solutions has been proposed on the basis of identified photolysis products and semiempirical quantum-chemical calculations. The degradation of PbS₂O₃ starts with the dissociation of the sulfur-sulfur bond in the thiosulfate group via photochemical excitation and transition of the system a whole to the activated state, which is decomposed by the solvent. The interaction of the primary photolysis products with PbS₂O₃ results in the formation of final products.     

Pulse photolysis of PbCl4 in non-aqueous solutions

Lead(IV) chloride solutions in CCl₄, CHCl₃, cyclohexane, benzene, toluene, chlorobenzene, N,N-dimethylformamide and pyridine have been irradiated with an approximately 1.5 kJ pulse of UV radiation lasting 0.5 ms. The course of the photochemical processes has been followed by measuring the loss of PbCl₄, the changes of Cl₂ concentration and by identification of chlorination products. In a similar way, chlorine solutions in cyclohexane and benzene have been investigated. Primary processes are discussed in detail. The most probable process in solvents that do not form complexes with PbCl₄ is predissociation of the PbCl bond

whereas in those forming complexes with PbCl₄ electron transfer takes place:

The results are compared with those obtained earlier under steady irradiation. This allows us to determine new pathways of secondary processes that are unobservable with the continuous illumination technique. The pathways include processes photoinduced by the phase of fresh finely dispersed PbCl₂ crystals:

     

Reactive intermediates in the photolysis and thermolysis of 3-chloro-3-benzyldiazirine

The photochemical and thermal decomposition of 3-chloro-3-benzyldiazirine have been studied in different reaction conditions. The decomposition gives rise to benzylchlorocarbene which can rearrange to E and Z chlorostyrene and/or react with the environment. In the presence of acetic acid the main product is 1-chloro-2-phenylethyl acetate. Experiments with acetic acid-d₄ showed that some of the chlorostyrene is formed from the carbocation; other experiments conducted with tetramethylethylene as a carbene trapping agent show that the carbene is formed even in the presence of acetic acid.     

Bicyclic aziridines as intermediates in the photolysis of polycyclic aromatic azides.

According to the subsequent treatment, azepines $\text{16}$, $\text{17}$, $\text{19}$ or 1,2-dihydro derivatives $\text{18}$ and $\text{20}$ are obtained in the photolysis in basic medium of β-anthracenic azides $\text{7b}$ and $\text{7c}$ and provide strong evidence for the intermediate formation of bicyclic aziridines.     

The polarity of solutions of electrolytes

The polarity of solutions of LiClO₄ in acetic acid has been investigated. However, polarity scales based on light absorption, e.g. the π*₁-scale, are interfered by aggregation phenomena of the used solvatochromic dyes, whereas solvatochromic fluorescent dyes give proper results.     

Influence of medium polarity on the photosensitizing properties of hematoporphyrin and hematoporphyrin derivative (Photofrin II)

The influence of the polarity of the medium on the efficiency of Type I and Type II photosensitization as carried out by hematoporphyrin and its derivative Photofrin II was studied by EPR techniques. Our results suggest that porphyrin aggregates do not participate as such in the photosensitized processes. Thus, the solvent-induced breakdown of the aggregated components of Photofrin II appears to determine the photosensitizing efficiency of this porphyrin.