Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling the structural unit of lignin. I. Molecular form

Quantum-chemical calculations of the electronic structure of molecules of model compounds of lignin in the ground and electronically excited states have been made by the CNDO/S method. The paper gives results on the energies and strengths of the oscillators of the electronic transitions and on the type of excited singlet and triplet states, shows the main configurations of the HOMOs and LUMOs participating in the transitions and their energies and statistical weights, and gives the distribution of charges and their redistribution on the passage of the molecules from the ground into the excited states. Donor-acceptor interactions in the molecules under investigation are discussed on the basis of the results obtained.Siberian Scientific-Research Institute of Pulp and Board, Bratsk. A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 265–274, March–April, 1988.     

Quantum-chemical investigation of the complex of Mg-porphin with tetracyanoquinodimethane

The potential hypersurface for the interaction of the molecules of Mg-porphin (P) and tetracyanoquinodimethane (TCQ) was investigated by the CNDO/2 method. The calculated energy minimum amounts to –8.95 eV and corresponds to a distance of 2.1 Å between the planes of the molecules with some displacement in relation to the central mutual arrangement. The results are regarded as tentative in view of the fact that the CNDO/2 method exaggerates the interaction. The electronic spectra of the P·TCQ complex are calculated by the CNDO/S-CI method for a series of arrangements of P and TCQ. Satisfactory agreement with experiment is obtained with a distance of about 3 Å between the planes of the molecules. It was shown that there are two transitions with charge transfer in the near IR region of the spectrum and also several transitions of the same type in the visible and near UV regions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 431–437, July–August, 1990.     

Electronic (vibronic) origin of configurational symmetry breaking in condensed media

We have attempted to describe all symmetry breaking (structural phase transformations) in condensed matter from a unified point of view as electronically-controlled through vibronic interactions. In this case, the mechanism for symmetry breaking involves vibronic mixing of different electronic states with nuclear displacements lowering the symmetry of the system (the Jahn-Teller effect and the pseudo-Jahn-Teller effect). Along with previously studied structural phase transitions in crystals and liquid-crystal transitions, we also discuss the case of the gas-liquid transition.Institute of Chemistry, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 3, pp. 262–269, May–June, 1991. Original article submitted February 14, 1991.     

Condensed heterocyclic compounds containing a thiazole ring. 12. Derivatives of thiazolo[3,4-b][1,2,4]triazine

Unsymmetrical monomethinecyanine dyes, containing a benzothiazole residue, were obtained from thiazolotriazine. To interpret the nature of the main absorption bands and localize the electronic transitions, the transition energies and electronic distribution of the first and second excited states of several model compounds were calculated by the self-consistent field method.For Communication 11, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1693–1697, December, 1986.     

Quantum-chemical analysis of the spectra of metal complexes of azaporphyrins by the INDO/S method

The electronic spectra of the complexes of tetraazaporphyrin and phthalocyanine with Cu, Ni, Co, Fe, and Mn have been calculated by the INDO/S method. Electron correlation has been taken into account by considering 210 singly excited configurations according to a method which permits the calculation of the spectra of complexes with singlet, doublet, and triplet ground states. Test calculations of the complexes of porphyrin with Fe and Co have been carried out, and the results have been compared with known results from nonempirical calculations. The energies of the orbitals of the ligand of the and types correlate with the corresponding peaks in the photoelectron spectra of azaporphyrins. The energies of the electronic transitions found are consistent with the experimental values.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 471–476, July–August, 1989.     

Classical and quantum properties of a simple autocatalytic mechanism — The Lotka-Volterra system

A method is proposed for construction of simple models describing chaotic regimes in chemical reactions. Using the Hamiltonian structure of the Lotka-Volterra system, a quantum analog of a model is described, which explains the observed and experimental transitions between discrete states for chaotic regimes in CSTR during external periodic perturbation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 49–56, January–February, 1993.     

Quantum-chemical calculations of the electronic structures of polymethylidyne dyes

The energies of the transitions of unsubstituted and substituted thia-, thiazolo-, and thienothiazolocarbocyanines, as well as quinocyanines and carbocyanines with a condensed thiophene, furan, selenophene, or pyridine ring, to the excited singlet states and their electronic structures were calculated by the MO LCAO method within the Pariser—Parr—Pople approximation. The nature of the long-wave and short-wave absorption bands in the spectra of these dyes and the peculiarities of the color of thieno-, furo-, and selenophenothiazolo- and -pyridocyanines, as well as the effect of substituents on their electronic characteristics as a function of the position in the heteroresidues and the nature of the latter, are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 626–633, May, 1978.     

Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling lignin. III. Quinones and quinone methides

An investigation has been made by the CNDO/S method with allowance for configurational interaction (the lowest six vacant and the highest eight occupied MMOs) of the electronic structure of a number of quinones and quinone methides forming component parts of the structural unit of lignin. The energies of the first singlet-singlet and singlet-triplet transitions and the redistribution of charges on excitation have been obtained, and the dependence of the energy of the transitions on the chromophores present in the molecule has been discussed. The change in the donor-acceptor properties of the fragments in excited states, leading to a change in the pathways in nucleophilic and electrophilic reactions has been shown.A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 858–865, November–December, 1988.     

A calculation of the rotatory strengths of the electron-transfer transitions of the Tris-(1,10-phenanthroline)iron(II) ion

The rotatory strengths of the metal-to-ligand transitions observed in the spectrum of the complex ion (–)-Fe(phen) ₃ ⁺² have been calculated theoretically. The excited electronic states were characterized using a coupled chromophore model. The calculated rotatory strengths are higher than the corresponding experimental values by a factor of about four.     

Nature of the excited states of dialkylamino derivatives of aromatic and heteroaromatic compounds with an annelated oxazole ring

On the basis of analysis of the electron density redistribution upon excitation, drawing on charge transfer numbers, we have considered the nature of the electronic transitions in the absorption spectra of analogs of 2,5-diphenyloxazole, in which the carbon atom at position 4 of the oxazole ring is bonded to the ortho position of the 5-phenyl fragment of the vinylene, azomethine, amide, and ester groups. We have shown that the differences in the electronic transitions of the basal molecule and the studied structural analogs are determined by the electron-donor effect of the bridging group and the degree of its conjugation with the extended -electron system of the original molecule. The dialkylamino derivatives of the studied compounds, on the other hand, display a high degree of similarity in the electronic structure of the excited states, and the characteristics of their long-wavelength transitions, such as in the case of substitution of the 2-phenyl fragment, do not depend on the nature of the bridging group of atoms. We give a theoretical explanation of the experimentally observed increase in the intensity of the long-wavelength transitions and the efficiency of luminescence upon introduction of dialkylamino groups into the 2- and 5-phenyl fragments.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 644–650, November–December, 1990.     

Quenching of luminescence of terbium(III) by platinum(IV) complexes

The rate constants (k_q) of the bimolecular energy-transfer reactions in systems consisting of the terbium(III) aquo complex and platinum(IV) complexes have been determined. The influence of the electronic and nuclear factors on the values of the rate constant of the reactions has been considered. It has been shown that the platinum(IV) complexes make up an adiabatic family of quenchers, while the energy-transfer reactions between terbium(III) aquo complexes are characterized by a high degree of nonadiabaticity x -10^–12). Estimates of the energies of the pure electronic transitions to electronically excited states of platinum(IV) complexes which are not observed spectroscopically have been obtained on the basis of the dependence of k_q on the change in the free energy of the energy-transfer process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 618–623, September–October, 1989.     

The Change in Coordination Mode of Malonodialdehyde Ligands in Be and Mg β-Diketonate Complexes

The process of torsion disclosure of the chelate ring in Be and Mg malonodialdehynates in the ground and excited states is studied with the aim to investigate photo- and thermodestruction of metal β-diketonates and the nature of the electron transitions in ab initio and density functional theory approximation. The change in the electronic structure parameters of the complexes under consideration with the changing coordination mode of a ligand is analyzed. The nature of the electron excited states and their role in stability of the studied compounds are established. The results of calculations obtained by different quantum-chemical methods are compared.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 6, 2005, pp. 415–422.Original Russian Text Copyright © 2005 by Lushchenko, L’vov, Vovna.     

Nature of electronic states and mechanism of photocoloration of oxaindanespironaphthopyrans

The nature of the electronic states was studied, and the mechanism of photocoloration is discussed for spironaphthopyrans of the oxaindane series. The life times of the T states, the quantum yields, the quenching rate constants, and the activation energies of the photocoloration are determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 495–499, July–August, 1989.The authors express their sincere gratitude to V. A. Lokshin for providing the spiropyrans.     

Potential energy surfaces of OsCO

Potential energy surfaces for the low-lying states of osmium carbon monoxide (OsCO) have been studied using the complete active space multi-configuration self-consistent field (CAS-MCSCF) followed by multireference singles+doubles configuration interaction (MRSDCI). Additionally, spin–orbit effects were included through the relativistic configuration interaction method. It is found that the ground state of OsCO is an 0⁺ spin–orbit state which is a mixture of ³Σ⁻ and ¹Σ⁺. Spin–orbit coupling not only splits the various electronic states of OsCO but also mixes different electronic states.     

Electronic structure,spectra, and classification of excited electronic states of the molecules MoCl4 and MoBr4

The absorption spectra of gaseous molybdenum tetrachloride and tetrabromide have been measured in the visible and UV regions. The SCF-X-SW method has been used to calculate the electronic structure, the spectra, and the system of first excited electronic states of these molecules. The results are compared with published data for the molecules CrCl₄ and CrBr₄.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 606–610, September–October, 1989.     

Nonadiabatic dissociation dynamics of ClHD van der Waals complex initiated by electron detachment of Cl–HD

Nuclear dynamics following the electron detachment of the Cl⁻–HD anion is investigated by a time-dependent wave packet propagation approach. Photodetachment of Cl⁻–HD promotes it to the van der Waals well region of the reactive ClHD potential energy surface. The latter is a manifold of three electronic states coupled by the electronic and (relativistic) spin-orbit coupling. Among the three surfaces, the electronic ground one is of ²Σ_1/2 type and yields products in their electronic ground state. The remaining two, ²Π_3/2 and ²Π_1/2, on the other hand, yield products in their excited electronic states. However, these two can yield products in their electronic ground state via nonadiabatic transitions to the ²Σ_1/2 state. The channel specific, HCl + D or DCl + H or Cl + HD, dissociation probabilities on this latter state are calculated both in the uncoupled and coupled surface situations. Separate initial transitions (via, photodetachment) to the ²Σ_1/2, ²Π_3/2 and ²Π_1/2 adiabatic electronic states of ClHD are considered in order to elucidate the nonadiabatic coupling effects on this important class of chemical reactions initiated by an electron detachment.     

Thermoluminescence of thin polymeric films obtained in a glow discharge plasma

The thermoluminescence and radiothermoluminescence were studied of thin polymeric films produced in a glow discharge plasma. It was shown that during the formation of polymeric films in the plasma, not only radical states but also ionic states are stabilized in them. Four luminescence maxima were detected on the radiothermoluminescence curves of the films. The possible assignment of the position of these maxima on a temperature scale to the relaxational transitions in the films is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 743–747, November–December, 1988.     

Tetradentate Schiff base oxovanadium(IV) complexes

Summary Eleven oxovanadium(IV) complexes of tetradentate Schiff bases, obtained by condensating two moles of an o-hydroxycarbonyl compound with a diamine, have been prepared and characterized by elemental analysis, m.p., and i.r. and electronic spectra. The i.r. and electronic spectra of the free ligand and the complexes are compared and discussed. The Gaussian analysis of the vis. spectra of the complexes, normally C₁ or C_s, in MeCN yielded four peaks at ca. 12000, 15000, 17700 and 20000–23000cm^–1, assigned to the four d-d transitions.     

Energy structures and electronic-transition wavelengths for trinuclear polymethine dyes

A study has been made on the energy structures and long-wave electronic transitions for linear trinuclear polymethine dyes by the method of additive generating functions. The necessary and sufficient conditions have been established for the occurrence of local levels related to the central nucleus. It is found that the bisvinylene shift is dependent on the structure of the central nucleus in this class of dyes. The relationship fits the available measurements, and it is predicted that there is a positive bridge effect, namely an increase in the bisvinylene shift in trinuclear dyes by comparison with binuclear ones.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 10–21, January–February, 1987.     

Electronic structure of titanium monoxide by the Xα-SW and CI methods

Parallel calculations of the spectrum of the low-lying electronic states of the TiO molecule have been performed by the nonempirical configuration-interaction method and the SCF-X method. The calculations were performed for the experimental value of the equilibrium internuclear distance in the ground electronic state. The electronic spectrum has been assigned on the basis of the results obtained, and the existence of a low-lying state of ³- symmetry has been confirmed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vo. 24, No. 2, pp. 212–215, March–April, 1988.