Raman spectra of alkyl-substituted azaoxa[8]circulenes: DFT calculation and experiment

Raman lines in spectra of recently synthesized azaoxa[8]circulenes have been assigned in detail on the basis of obtained experimental data and B3LYP/6-31G(d) calculations. Particular features of the structure of three azaoxa[8]circulenes have been considered based on data of X-ray structural analysis and DFT calculations. Regularities in changes of the geometric parameters have been found for benzene, furan, pyrrole, and naphthalene rings that occur upon formation of the macroring in comparison with free molecules. Raman spectra of macrorings have been shown to contain a characteristic set of lines the frequencies of which differ from those of analogous lines in Raman spectra of benzene, pyrrole, furan, and naphthalene. Results of quantum-chemical calculations agree well with experimental data with respect to line frequencies and intensities due to recalculation of Raman activities of normal vibrations into intensities of Raman lines.     

A comparative study of the electronic structure and spectra of tetraoxa[8]circulene and octathio[8]circulene

The electronic structure and spectra of two highly symmetric molecules of circulenes, namely, tetraoxa[8]circulene and octathio[8]circulene, which belong to the symmetry point groups D _4h and D _8h , respectively, have been investigated by the density functional theory (DFT) method using the hybrid functional B3LYP in the 6–31G(d) basis set. The infrared (IR) spectra of these molecules in the ground and excited triplet states have been compared. The comparison of the electronic absorption spectra of both molecules has revealed that the first electronic transition is forbidden and determined by the electronic-vibrational interaction due to the degenerate e _u modes. The ability of the studied circulenes to fluoresce and phosphoresce has been analyzed, because these compounds are of interest as promising materials for organic light-emitting diodes.     

A study of the role played by the Hartree-Fock orbital exchange in the formation of the energy of the first singlet charge-transfer excited state by the example of JK-62 and JK-201 sensitizing dye molecules

Based on the time-dependent density functional theory with the use of the functionals B3LYP, B97-2, BHandHLYP, BMK, MPWB1K, PBE1W, PBE1PBE, τ-HCTHh, and TPSS in the 6–31G(d) basis set of atomic orbitals, we have performed a quantum-chemical investigation of electronic and spectral properties of JK-62 and JK-201 bis-dimethylfluorenyl dye sensitizers for Grätzel photoelectric converters. In terms of the Bader theory, we have done a complete analysis of the electron-density distribution function in the dye molecules under study, which proves the occurrence of intramolecular nonvalent interactions, which, in turn, stabilize a planar mutual arrangement of structural fragments of dye molecules. The role that the Hartree-Fock orbital exchange plays in the energy formation of the first and most intense electronic transition, which is responsible for the primary current generation in a solar cell, has been elucidated.     

Polar properties of nominally pure polarized TGS crystals

Using the method of dynamic pyroeffect, polar properties of surface layers of nominally pure triglycinesulfate (TGS) crystals prepolarized in an electrostatic field are experimentally investigated. The results on the pyrocoefficient distribution over the crystal thickness modeled using the experimental dependences are reported. The model relies on the solution to the first-order integral Fredholm equation by the method of Tikhonov’s regularization.     

Magnetic and dielectric studies of multiferroic CuO nanoparticles confined to porous glass

Dc magnetization and ac electric permittivity were measured for the CuO-porous glass nanocomposite made and for pressed powder CuO. Magnetization curves showed a bend between two linear segments for both the nanocomposite and bulk cupric oxide at 230 K evidencing that the temperature of the transition from the paramagnetic into multiferroic phase did not change noticeably under nanoconfinement. Results suggested also a reduction of the temperature of the second transition into the collinear antiferromagnetic phase. ZFC and FC magnetizations were found to bifurcate for the nanocomposite and bulk CuO. The bifurcation was accompanied with peaks on ZFC magnetization.     

Structure and intramolecular stabilization of geometric isomers of Bi- and trithiazolidine-4-ones and their methyl derivatives: A DFT and QTAIM study

At the DFT level with the B3LYP hybride functional the structure and relative stability of geometric isomers of bi- and trithiazolidine-4-ones are calculated. Based on Bader’s analysis of the electron density distribution the presence of intramolecular hydrogen bonds and van der Waals interactions is found in the studied isomers. Energies of these interactions are calculated. It is shown that the presence of a substituent in the thiazolidine ring affects the stabiliyty of the studied geometric isomers.     

Acoustic studies of melting and crystallization of sodium nitrite nanocrystals in the pores of mesoporous silicate matrices

A conventional phase-pulse acoustic method was used to study melting and crystallization of sodium nitrite embedded in the pores of mesoporous silicate matrices. The pore diameter was 20, 37, and 52 Å. The measurements were performed at a frequency of 3–8 MHz in the temperature interval 290–560 K. The temperature dependence of ultrasonic velocity was found to exhibit anomalies corresponding to phase transitions of sodium nitrite. The transitions were smeared in temperature and shifted to lower temperatures from the melting point T _b of bulk sodium nitrite; the shift in crystallization temperature was greater than that of the melting temperature. The irreversible character of melting was revealed. The size dependence of the melting temperature of sodium nitrite was obtained. Phenomena observed in the experiments were discussed with the use of different size effect models.     

Electret effect and electrotransport in disperse organic and inorganic systems

The electret properties and electrotransport of venous human blood of various groups and a disperse system based on fine-grained mica are studied. General laws are revealed in the thermally stimulated current spectra of these inorganic and organic systems. The nature of the current peaks and their relation to the physicochemical transformations and the interphase interactions in these systems are discussed. A set of numerical parameters is obtained to describe the electrophysical state of the biological system; it can be used to diagnose the functional and biochemical states of this system.     

Comparison of propagation of a shock wave in a decaying plasma in various gases

The effect of gas humidity and composition on shock wave splitting in the plasma of a decaying glow discharge is investigated in dried and moist air, nitrogen, and argon over various time periods after the discharge termination. The shapes of the signals reflecting the gas pressure distribution behind the shock wave in these media are approximately the same except for some values of decay time comparable to the characteristic time of decay of excited state concentration (including singlet oxygen) after the termination of the discharge (8 ms). The signals in the same four gases are compared quantitatively for different time periods after discharge termination by expanding the signal into a Fourier series. The free term and the second and third modes in the Fourier expansion are compared. Analysis is carried out for up to time periods of 60 ms.     

Efficiency of the generation and self-addition of laser line frequencies upon the diode pumping of Er:BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Features of the generation of laser lines upon the diode pumping of Er:BaY₂F₈ crystals are studied. Blue, violet, and UV laser lines are most efficiently generated via the nonlinear frequency self-addition of 541 and 553 nm lines of Er³⁺ radiation with the corresponding IR line of Er³⁺ for Er:BaY₂F₈ crystals pumped by a laser diode with a wavelength of 972 nm.