Electronic structure and spectral characteristics of trinaphthodifuryls

It has been established that in pattern-free hydrated AlPO₄-5 crystals the water molecules are coordinated by more than half of the aluminum-oxygen tetrahedra. The fraction of the tetrahedra with different coordination of the aluminum atoms changes in the order Al_d>Al_t>Al_o, where Al_d is the fraction of the aluminum atoms that coordinate one water molecule, A1_o two water molecules, and Al_t is the fraction of the tetrahedrally coordinated aluminum.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 4, pp. 215–218, July–August, 1994.     

Electronic spectral characteristics of some phenolsulphonphthaleins

The visible electronic spectral characteristics of some phenolsulphonphthaleins were investigated in terms of medium and compound molecular structure effects. It was identified that in dilute solutions, the compounds studied exist in acid-base equilibria of the type HI⁻ = I⁻⁻ + H⁺. The recorded two visible absorption bands for dilute solutions of these compounds are assigned to transitions involving the whole molecule associated with charge delocalization which is liable to occur in the HI⁻ and I⁻⁻ forms. Effects of compound molecular structure, concentration and medium on the acid-base equilibrium are investigated and discussed. It is concluded that the solvent basicity as well as the possible stabilization of the dianion conjugate base I⁻⁻ by hydrogen-bond donation from the amphiprotic solvent play an important role in the extent of ionization of such compounds.     

Electronic structure and reduction processes in PtOx films

The electronic structure of various sputtered-deposited PtO films is probed using double-beam photoemission, optical absorption and electrical resistivity measurements: (i) Double-beam photoemission provides information on the density-of-states of the films in the vicinity of the Fermi level. (ii) Optical and resistivity measurements indicate that no intermediate PtO_x phase is seen during H₂ reduction of PtO₂ films.     

Electronic current and breakdown characteristics of tantalum oxide films

Steady electronic current data through extremely thick films in contact with aqueous electrolytes have been obtained. The effects of field strength, temperature of the bath, composition, concentration and resistivity of the contacting electrolyte have been studied. The data show that the same relation between electronic current and field holds irrespective of the film thickness. The data also indicate a direct relation between electronic current and breakdown voltage. The effect of electrolyte concentration on breakdown voltage can be explained in terms of Ikonopisov's electron injecting avalanche model. The major factor contributing to a decrease of breakdown voltage with an increase in the concentration of the electrolyte has been found to be due to the increase in primary electronic current.     

Electronic structure and polarographic characteristics of siloxaronaphthalenes and siloxarophenanthrenes

Theoretical and Experimental Chemistry -     

Uranyl compounds and complexes: Electronic structure,chemical bonding and spectral properties

The electronic structure of solid compounds -UO₃, Cs₂UO₂CL₄, UO₂F₄ and complexes UO ₂ ²⁺ and UO₂(NO₃)₂ · 2H₂O has been studied by the cluster discrete variational DV X method in Dirac-Slater and Hartree-Fock-Slater approximation. The analysis of relativistic effects in the electronic structure of uranyl compounds was based on the comparison of non-relativistic and relativistic DV results. The interpretation of X-ray photoelectron spectra of -UO₃ and Cs₂UO₂Cl₄ basing on the MO model is given. The various electronic states contributions to the chemical bonding in uranyl compounds are investigated.     

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

A comprehensive photophysical and spectroscopic study of a new class of p-phenylenevinylene oligomers (PPV-trimers) possessing different alkyl and alkyloxy sidechain substituents and different end groups (aldehyde, CC, phenylene and anthracene units) was undertaken in solution at room temperature (293 K), low temperature (77 K) and in thin films. The study comprises absorption, emission and triplet–triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion and singlet oxygen formation) and lifetimes. The data allow the determination of rate constants for all decay processes. From these, several conclusions could be drawn. Changing from alkyl to alkyloxy substituents does not change fluorescence and internal conversion yields but decreases the (already small) intersystem crossing yield. The introduction of anthracene at the terminal ends of the PPV-trimers leads to the lowest fluorescence yield reported in this study. Of particular importance is the fact that the fluorescence quantum yields in films are of the same order of magnitude as those in solution, which suggests the potential for use of these oligomers for light-emitting device applications. With one of the alkyloxy derivatives, a more detailed study of the early part of the fluorescence decay was made, and it was found that upon excitation a fast conformational relaxation process of the initially excited oligomer occurs, leading to a more planar conjugation segment.     

Electronic structure, physicochemical characteristics, and stability of polycyclobutadienes

The electron distributions, current distributions, enthalpies of formation, diamagnetic susceptibilities, electric polarizabilities, and the energies of the lowest singlet-singlet and singlet-triplet transitions for a series of polycyclobutadienes C_2n+2H₄ were calculated within the scope of the PPP method. It was shown that according to the energy and magnetic criteria the molecules of this series can be divided into three groups, the molecules of one of which are presumably stable. Donbass State Academy of Construction and Architecture. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 1–5, January–February, 1997.     

Electronic structure and electron transport characteristics of a cobalt complex

The molecular and electronic structures and electron transport characteristics of a Co complex are investigated using first principles calculations. The Co complex belongs to the D(2d) point group, and its two ligands are perpendicular to each other. The central atom Co forms a distorted octahedron with six donor N atoms. In a low oxidation state, the bond length between Co and pyrrole nitrogen, 1.849 A, is much shorter than the distance between Co and pyridine nitrogen, 2.168 A, while, in a high oxidation state, the bond length differences between Co and pyrrole nitrogen, 1.814 A, and between Co and pyridine nitrogen, 1.990 A, are not as large as those in the Co2+ complex. The HOMO energy of the low oxidation state is very close to the Fermi level of bulk Au, allowing hole creation in the molecule. On the other hand, the LUMO energy of the high oxidation state is close to the Au Fermi level, allowing a low barrier for electron injection from the Au cathode to the molecule. These structural characteristics make the Co complex a good hole-conduction molecule. The density of states, transmission probability, and I-V characteristics are evaluated using the Green function approach.     

Stoichiometric and structural analyses of thin high-Tc superconducting Bi-Sr-Ca-Cu-O films on silicon

Summary For the analyses of stoichiometry and structure of laser deposited Bi-Sr-Ca-Cu-O thin films and yttria stabilized zirconia buffer layers on silicon, the methods XRF, PIXE with low incidence energy, RBS and XRD were used. In the results a change of stoichiometry from target into the thin film was observed and the spatial intensity distribution of the laser plasma was measured. The degree of interdiffusion of thin film and substrate and the formation of the perovskite-structure during post annealing were determined. The Bi-Sr-Ca-Cu-O films are highly c-axis oriented perpendicular to the surface and mainly consist of the low-T_c phase with c=30.8 A.     

Electronic and vibrational spectral studies of substituted mercaptopyrimidines

The vibrational spectra (i.r., far i.r. and Raman) of 4,6-dimethyl-2-mercaptopyrimidine and 4,6-dihydroxy-2-methylmercaptopyrimidine have been reported along with their assignments. Hydrogen bonding and tautomeric behaviour are discussed. Electronic spectra in various solvents at different pH values are recorded. The effect of a change of solvent on the electronic transitions of both compounds is explained along with the bathochromic and hypsochromic shifts observed when the neutral form of the compound is changed to the anionic or cationic form.     

Synthesis, structure investigation, spectral characteristics and biological activities of some novel azodyes

Four novel azo compounds were synthesized; o-phenylazo- (C(14)H(13)N(3)O(2)) (I), p-bromo-o-phenylazo- (C(14)H(13)BrN(3)O(2)) (II), p-methoxy-o-phenaylazo- (C(15)H(16)N(3)O(3)) (III) and p-nitro-o-phenylazo-p-acetamidophenol (C(14)H(13)N(4)O(4)) (IV). These compounds were carefully investigated using elemental analyses, UV-vis, FT-IR, (1)H NMR and mass spectra. Also, the effects of p-substituents such as bromo, methoxy and nitro groups on the mass fragmentation pathways of these dyes were studied using Hammet's effects. This research aimed chiefly to threw lights on the structures-stability relationship of four novel newly prepared azo derivatives of p-acetoamidophenol. The data obtained referred to the variation of mass fragmentation pathways with the variation of p-substituent of these dyes which can be used in industry for various dyeing purposes. This variation is also correlated and verified by molecular orbital calculations which were done on ionic forms of these dyes using semi empirical PM3 program. The biological activities of these dyes were also investigated and its structure relationship was correlated.     

Electronic spectral detection in liquid chromatography

The use of absorbance and fluorescence spectrometers as liquid chromatography detectors is described. These detectors offer sensitive detection that can also identify the peaks in a chromatogram. Many examples, mainly from the separation of polycyclic aromatic hydrocarbons, are given that show the selectivity and usefulness of these detectors.     

Synthesis and spectral characteristics of vinyltetrazolinones

Several methods have been worked out to synthesize 1 - vinyl - 4 - substituted - Δ² - tetrazolin - 5 - ones. NMR spectra showed typical AMX-patterns for the vinyl protons with chemical shifts and coupling constants almost independent of the nature of the other N-substituent. From the shielding increments, it was concluded that the tetrazolinone group exercises a strong inductive electron-withdrawing effect, but only a small resonance effect on the vinyl group. This paper also describes the first cycloreversions of azide adducts, induced by electron impact. Other significant fragmentation patterns of several mono- and disubstituted tetrazolinones are discussed.