Vol 59, No 4 (2025)

The photophysical properties of biphotochromic dyads DoX and D10 containing two identical photochromes, 2-[2-(pyrene-1-yl)ethenyl]-quinoline (PEQ), linked by bridge groups of different lengths, as well as the corresponding dipyrenylcyclobutanes CBoX and CB10 formed from the dyads in the [2+2] photocycloaddition reaction (PCA) have been investigated by time-resolved emission spectroscopy (TRES). On the basis of TRES, the number of emitters was determined, their emission spectra, excited state lifetimes, and rate constants of competitive physical and chemical processes (emission, energy transfer, and reactions) were calculated. In dyads, the formation of excimers, possible intermediates of the PCA reaction, was detected by the appearance of emitters with lifetimes significantly increased compared to the model PEQ-photochrome. In cyclobutanes, a decrease in the lifetime of pyrene substituents as compared to 1-methylpyrene shows the energy transfer from substituents to the cyclobutane ring, which, according to the predissociation mechanism, initiates the ring-opening reaction (retro-PCA). In addition, CBoX shows the presence of non-emitting conformers. Quantum chemical calculations by DFT method confirmed the possibility of formation of different conformers of cyclobutane CBoX, differing in the relative position of pyrenyl substituents and the degree of their interaction with each other.

The use of ultraviolet irradiation in the practice of AOPs (Advanced Oxidation Processes) for the treatment of wastewater of various origins has been the subject of many studies. In recent years, the possibilities of using AOPs based on sulfate radicals, the main source of which is peroxodisulfuric acid, have been actively considered. In this paper, the effect of peroxydisulfuric acid additives on the process of photodegradation of fuchsin, bromocresol green and methyl red was studied. It was proven that the combination of UV radiation and H₂S₂O₈ has a synergistic effect and makes it possible to significantly increase the efficiency and rate of oxidation of dyes in comparison with individual photo- and reagent treatment. The maximum oxidation efficiency was 99.9% for bromocresol green, 93% for fuchsin and 76% for methyl red.

The spectral and kinetic characteristics of the dye Sbt ((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]thiazol-3-ium iodide) and its homodimers Dbt-5, Dbt-10 in chloroform and its binary mixtures with solvents of different polarity were studied. It was found that with an increase in the proportion of hexane in chloroform solutions of the studied dyes, non-fluorescent H-aggregates are formed. It was found that the spectral and photophysical parameters of the studied dyes depend on the polarity and viscosity of the solvents. Quantum-chemical calculations of the charge distribution and potential energy in the ground and excited states for the molecules of the studied compounds were carried out. Sbt and Dbt-10 dyes are characterized by higher values of quantum yields and lifetime of the excited state in a viscous medium, which is associated with the formation of the TICT (twisted intramolecular charge transfer) state. The transition of molecules to this state leads to effective quenching of fluorescence.

The radiolysis of the extractant N¹,N³-dimethyl-N¹,N³-dibutyltetradecylmalonamide and its 30% solution in n-tridecane under the action of 3 MeV electrons was studied. The key radiolytic processes are fragmentation of the extractant molecules. The decomposition is predominant along the bonds located in the β-position relative to the carbonyl group: N-Me, N-Bu, C-C₁₄H₂₉ and C-C(O). The C-C(O) bond is the weakest – its cleavage gives more than half of all the extractant degradation products. The observed yield of extractant degradation in solution is almost one and a half times higher than in the undiluted state. At the same time, a decrease in the yield of diluent degradation is observed in the solution. The observed effects indicate partial physical and chemical protection of the diluent by the dissolved extractant.

The structure and number of paramagnetic centers (PC) stabilized in papain γ-irradiated with a dose of 50 to 2300 kGy were studied using EPR spectroscopy. The radiation yield G≈6 PC/100 eV during radiolysis at 77 K is six times greater than the PC yield in the samples irradiated at 300 K. During radiolysis at 300 K, the maximum concentration of PC is achieved at doses of 200 kGy at a level of 8 × 10¹⁸ PC/g, whereas in papain radiolyzed at 77 K they accumulate up to 2300 kGy and reach 2.2 × 10²⁰ PC/g. During papain radiolysis at 77 K, the cleavage of the peptide bond prevails over the cleavage of bonds in the molecular groups of amino acid residues, including sulfur-containing ones. As a result, $-\text{C}\left(=0\right)-\stackrel{•}{\text{C}}\text{H}-{\text{CH}}_{\text{2}}\text{R}$ radicals are mainly recorded in the EPR spectra. In the multicomponent spectrum of papain irradiated at 300 K, a doublet with splittings of 1.77 mT is distinguished, attributed to the $-\text{C}\left(=0\right)-\stackrel{•}{\text{C}}\text{H}-\text{NH}-$ radical formed by the abstraction of hydrogen from the glycine residue. Peroxide radicals formed during radiation oxidation at 300 K are not retained in the matrix of irradiated papain as stabilized radicals and, most likely, participate in secondary radiation-chemical processes with the formation of oxygen-containing products. A tendency for the antiradical and antioxidant activity of papain to increase with increasing radiation dose is noted as a result of radiation destruction of the peptide bond with the formation of amino acid fragments that are donors of a hydrogen atom.

A mathematical model of radiation-induced transformations in vapor-gas mixtures containing hydrogen, nitrogen, oxygen and their compounds is presented. In accordance with the array of experimental data used in verification, the model adequately describes the directions and rates of processes in the temperature range from 0 to ~250°C, pressure from 1 kPa to 0.2 MPa (in some cases up to ~5 MPa) and absorbed dose rate up to 10³–10⁴ Gy/s over an unlimited time interval. The model can be used as a tool for performing fast calculations with wide sets of external parameters and initial conditions: when assessing the consequences of design and beyond design basis accidents at reactor facilities with water coolants, as well as when substantiating hydrogen explosion safety at facilities where there are sources of ionizing radiation.

The kinetics of radiation-induced telomerization of tetrafluoroethylene in dimethyl carbonate and dimethoxyethane was studied, new tetrafluoroethylene telomers were obtained. A detailed study of the IR spectra confirms the fact that fragments of solvent molecules are included in the composition of the obtained telomers. Selection of synthesis parameters (tetrafluoroethylene concentration, radiation dose) allows obtaining telomer solutions with the necessary characteristics for their further use as an additive in electrolytes for lithium-ion batteries.

The paper presents the results of PVDF film polarization in glow, barrier and corona discharges. Measurements of the piezoelectric coefficient d33 showed that the highest polarization efficiency under the selected process conditions is observed in the corona discharge. The study of samples by X-ray phase analysis and ATR-FTIR spectroscopy showed that after polarization, the proportion of piezoactive β-phase increases in the polymer, the highest content of which is observed after treatment in a corona discharge. It is noted that treatment in a discharge leads to a change in the wettability of the sample surface.

A DC discharge in a mixture of CO₂ and CH₄ at atmospheric pressure was studied at different ratios of CO₂ and CH₄ at the input and different polarities of the applied voltage. It was shown that when the cathode is located in the region of gas supply to the discharge at a gas flow rate ratio at the input of CO₂/CH₄ = 1, sparking of the discharge is observed in the discharge, which is associated with the intense formation of a solid phase from carbon-containing particles. The degree of decomposition of CH₄ is about 95%, and the degree of decomposition of CO₂ is within 85–95% and decreases with increasing concentration of CO₂ in the mixture. The ratio of concentrations of H₂ and CO at the discharge output can be controlled by the ratio of consumption of CO₂ and CH₄ at the discharge input.