Vol 50, No 5 (2016)

The problem of standardless molecular spectral analysis of multicomponent mixtures with allowance for photochemical reactions of their molecules has been formulated and its formal procedure has been developed. The case when the time dependence of the spectrum of the mixture is determined only by the change in the concentrations of the components with time and the spectra of the individual components remain constant has been considered. The corresponding requirements for the physicochemical properties of the molecules have been identified and shown to be met for quite a wide range of polyatomic molecules and their reactions. The exception is molecules with metastable excited electronic states. A large set of model calculations relevant to the actual molecular entities and their experimentally observed photochemical transformations have shown the practicability of the approach. The solution of the problem converges to exact values and is resistant to uncertainty in setting the initial spectral data due to the peculiarities of the experimental procedure, the choice of theoretical models, and other factors. The resulting theoretical values of the concentrations meet the least squares test and their errors are measured by the variance per unit weight. The variance makes it possible to evaluate the noise level of the spectral data used in the analysis and reliability of the result and can serve as a criterion for the correctness of the initial hypotheses about the qualitative composition of a multicomponent mixture.

It has been shown that the addition of molecular bromine to the monomer acrylamide (AA) results in the spontaneous formation of radicals. During heating the AA + Br₂ mixture, the radicals initiate polymerization and bromination reactions. Beginning well below the melting point of bromine, both the reactions proceed at a noticeable rate at its melting temperature.

The topologically diblock structure of a tetrafluoroethylene—hexafluoropropylene copolymer with a total weight fraction of crystalline structures of 0.07 is transformed into a fully amorphous matrix with a pseudo-network structure after irradiation with 1—4 MeV protons. Instead of crystalline branching points (as in the unirradiated copolymer), cluster structures have appeared in the matrix. Oxidative degradation processes that occur during the bombardment result in significant functionalization of the copolymer and a substantial increase in the surface free energy, its acid—base component, and surface polarity.

The kinetics of photolysis of a styrylquinoline (SQ) derivative as the photochromic ligand in organic—inorganic hybrid nanosystems (HNSs) with the core composed of CdS quantum dots (QDs) has been studied for the first time as a function of the number of ligand molecules in the HNS shell, which varied from 1 to 10. The hybrid nanosystems have been synthesized in the microwave-assisted mode according to the single-step injection-free procedure. It has been shown that high quantum yields of photoisomerization of the SQ ligand are conserved in the HNS. In the early stages of the photolysis, regardless of the number of SQ ligand molecules in the HNS shell, the kinetics obeys the equation for the photolysis of the monomolecular system (model SQ photochrome) with allowance for the absorption due to QDs as an inert shutter. During the course of long-term photolysis, the quantum dots undergo photodegradation to be completely decomposed. According to the principal component analysis data, several photoproducts with different absorption spectra are formed at the intermediate times of the HNS photolysis.

It has been established that the photoinduced process observed in EPR and in optical absorption spectra for 1,4-dithiane radical cations in the CF₃CCl₃ matrix at 77 K can be ascribed to a “boat”—“twist boat” conformational transition.

Cationic dye 3,3-diethylthiacarbocyanine (TCC) in a phosphate buffer solution (pH 6.86) in the presence of cucurbit[7]uril (CB7) occurs in the form of monomeric TCC@CB7 and dimeric (TCC@CB7)₂ complexes. The TCC@CB7 and (TCC@CB7)₂ complexes display fast (conventional) and delayed (thermally activated, of type E) fluorescence, as well as free TCC. The relative yield of fast fluorescence of TCC@CB7 is six times that of free TCC. The delayed fluorescence lifetimes τ_dfl of TCC@CB7 and (TCC@CB7)₂ are 0.5 and 1.6 ms, respectively. In the presence of p-nitroacetophenone (electron acceptor), the delayed fluorescence of (TCC@CB7)₂ is quenched dynamically with the rate constant of 7 × 10⁸ L mol^—1s^—1.

The graft copolymers of chitosan and oligo(D,L-lactide) obtained by solid-phase synthesis have been used as the basis of photosensitive compositions for the fabrication of three-dimensional microstructures by laser-induced stereolithography. The electronic absorption spectra of the copolymers are close to the sum of the spectra of native chitosan and polylactide, which has been chosen as a model of grafted oligolactide chains. The fundamental absorption bands of the copolymers lie in a range to 500 nm, and their contribution to the absorption intensity of a photosensitive composition based on the copolymers at second harmonic laser frequency is insignificant. Depending on the macromolecular characteristics of the copolymers, the three-dimensional crosslinking of photosensitive compositions on their basis in the course of microstructuring occurs with different efficiency.

The structure of compounds with the perovskite structure ABX₃ (A and B are cations, X are anions O^2—, F^—, Cl^—, Br^—, and I^—), which are widely used in engineering due to unique electrical, optical, and photovoltaic properties, has been considered. Hybrid organic—inorganic halide perovskites important for photovoltaics of a new generation are worth mentioning; they contain cations of organic nitrogen bases as monovalent cations. A molecular dynamics (MD) study of the CaTiO₃ base structure (Ca²⁺, Ti⁴⁺, and O^2—) has been performed in order to develop the methodology of computer simulation and optimization of the shape and parameters of atomic potentials for perovskite systems.

Yields of the products of the microwave plasmoid treatment of liquid n-hexane, n-heptane, or chloroform and their mixtures have been measured using the gas chromatography—mass spectrometry technique.

A variational method based on the determination of rotation as a state with a constant angular momentum has been proposed for calculating rovibrational energy levels of a polyatomic molecule. By using this method, energy level values can be determined for any vibrational state with arbitrary values of vibrational quantum numbers. This makes it possible to calculate the rovibrational energy levels of the “hot” molecules.