The electronic structures of 3-hydroxypyridines.

Chemical shifts are reported for 3-hydroxypyridine derivatives in acid, neutral, and alkaline media. The -charge distribution is reported (LCAO method, Huckel's approximation) for the neutral, anionic, cationic, and bipolar species. The results reveal the trends in the electron-density distribution in 3-hydroxypyridine derivatives.     

Theoretical investigations of the electronic states of porphyrins. III. Low-lying electronic states of porphinatoiron(II)

Ab initio configuration interaction calculations are reported on the lowest quintet, triplet, and singlet states of Fe^II(P). Due to the large number of states found, a catalog of the low-lying states is presented. Novel triplet and quintet charge-transfer states are reported as low as 1.3 eV. These states are d⁵ (S = 5/2) on the iron low-spin-coupled to the radical anion excited porphyrin ring (S = 1/2 or 3/2). Oscillator strengths originating from each of three low-energy triplet states are reported.     

Theoretical investigations of the electronic states of porphyrins. IV. Low-lying electronic states of bisammineporphinatoiron(II)

Ab initio CI calculations are reported on the lowest quintet, triplet, and singlet states of Fe^II(P) (NH₃)₂. The lowest singlet state has strong mixing between the configuration (d_xy² (d_π)⁴ and (d_xy)²(d_π)³e_gπ*. The lowest quintet is mixed between ⁶A_1g)d_π and (⁶A_1g)e_gπ*, where ⁶A_1g refers to the high-spin ferric configuration. We calculate many low-energy states as ³(π→π*) ring and metal triplet and quintet configurations [“triptriplets” and “tripquintets”]. The calculations also show low-energy charge-transfer configurations of ring anion excited quartets and ferric quartets and sextets [“quartquartets” and “quartsextets”]. The farthest red x,y-polarized bands of the experimental spectra of low-spin hemoproteins are identified as d_xy → e_gπ* or d_π → d mixed with d_π → d and the z-polarized bands are assigned as d_π → e_gπ*. The farthest red x,y-polarized bands of the high-spin hemoproteins are identified as excited quartsextet states. Picosecond transients observed in Fe^II(TPP) (pip)₂ are attributed to an initial ¹(d_π → e_gπ*) state, which inter-system crosses to high-spin states that lose one ligand.     

The electronic properties of conjugated ions. II

The calculations presented here demonstrate the relative importance of the excess charge effect for energy calculations, and its lack of importance for spin density calculations, in conjugated ions and radicals.Part 1 is considered to be Ref. [1].     

Line shapes in electronic absorption spectra. Phenanthrene

The 3000 Å, (¹B₂ ← ¹A₁), absorption system of phenanthrene in durene crystals at 4°K illustrates an electronic transition, which is subject to near-resonance vibronic perturbations whose effect is intermediate to both the small (sparse intermediate) and large molecule (statistical) limits. Both broad (300 cm^?1) and narrow (10 cm^?1) lines are evident. A model is proposed which incorporates both these features by fast allowing for a consideration of the interaction between a small number of discrete levels, those associated with the largest coupling, followed by a treatment of the broadening of these levels through interaction with the remaining near continuum of states of the lower electronic state. Thus, one and the same electronic state provides both a sparse and dense manifold of levels. An important result of the model is that in terms of absorption intensities all the lines emerge with the same heights but differ in widths. When the intensities are summed with respect to energies this aspect is obscured. This approach has been shown to satisfactorily reproduce many of the features of the ¹B₂ absorption spectra of phenanthrene and phenanthrene-d₁₀. The ¹B₂ absorption systems have also been measured in the vapour phase and fine structure attributable to vibronic coupling and sequence band development are discussed.     

Organic electronic devices and their functional interfaces.

A most appealing feature of the development of (opto)electronic devices based on conjugated organic materials is the highly visible link between fundamental research and technological advances. Improved understanding of organic material properties can often instantly be implemented in novel device architectures, which results in rapid progress in the performance and functionality of devices. An essential ingredient for this success is the strong interdisciplinary nature of the field of organic electronics, which brings together experts in chemistry, physics, and engineering, thus softening or even removing traditional boundaries between the disciplines. Naturally, a thorough comprehension of all properties of organic insulators, semiconductors, and conductors is the goal of current efforts. Furthermore, interfaces between dissimilar materials-organic/organic and organic/inorganic-are inherent in organic electronic devices. It has been recognized that these interfaces are a key for device function and efficiency, and detailed investigations of interface physics and chemistry are at the focus of research. Ultimately, a comprehensive understanding of phenomena at interfaces with organic materials will improve the rational design of highly functional organic electronic devices.     

Molecular geometry and excited electronic states : Part XIII. Conformational geometries of 9,10-diphenyl anthracene in different electronic states and its electronic spectral behaviour

The conformational geometries of 9,10-diphenyl anthracene in the S₀, S₁, and T₁ electronic states determined by means of the Warshel—Karplus method are presented. Based on the theoretical equilibrium geometries of the con- and dis-twisted conformations the calculated electronic transition energies and oscillator strengths are used for an interpretation of the electronic spectral behaviour in absorption and fluorescence. The corresponding theory-experiment comparison performed is satisfactory.     

The quasiparticle concept in vibrational–electronic problems in molecules. I. Partitioning of the vibrational–electronic Hamiltonian

The partitioning of the vibrational–electronic Hamiltonian is presented. This partitioning is based on a new quasiparticle transformation that is constructed in such a way that the adiabatic approximation is included into the unperturbed Hamiltonian; nonadiabacity, anharmonicity, and electron correlation are treated as perturbations. We also present the second quantization treatment for bosons. The many body perturbation theory expansion for the vibrational–electronic Hamiltonian is suggested. A comparison of this approach is made with gradient techniques.     

Ammonium eneselenolates: stereochemistry and electronic properties.

Ammonium eneselenolates were generated with high efficiency by reacting selenothioic acid S-esters with a THF solution of TBAF. The methylation of ammonium eneselenolates gave ketene selenothioacetals as stereoisomeric mixtures. The ratio of the two stereoisomers depended on the duration of the reaction before the addition of MeI. Ammonium eneselenolates were characterized by examining their (1)H, (13)C, and (77)Se NMR spectra, which indicated that ammonium eneselenolates were present almost exclusively as Z-isomers. These results suggested that ammonium eneselenolates are kinetically generated as stereoisomeric mixtures, and isomerization of E-isomers to Z-isomers then takes place to result in the exclusive formation of Z-isomers. During the methylation of Z-isomers of ammonium eneselenolates, the isomerization of Z-isomers to E-isomers occurs to give stereoisomeric mixtures of ketene selenothioacetals. NMR spectra of ammonium eneselenolates implied that the electrons at the selenium atom are somewhat delocalized to the carbon-carbon double bond and the carbon-selenium bond shows partial double-bond character.     

Molecular aniline clusters. II. The low-lying electronic excited states

The lowest electronically excited states of the aniline dimer and trimer related to the lowest π(?)←π transition of the monomer are investigated by applying time-dependent coupled cluster theory, primarily at the level of the (spin-component-scaled) CC2 model. Minimum energy structures in the vicinity of the Franck-Condon points were determined on the individual potential energy surfaces. For the dimer we find an excimer and a head-to-tail configuration (with the monomers substantially displaced relative to the ground state minimum) for the lowest (dark) and second lowest (bright) states, respectively. The excitation is delocalized on both chromophores for both of these states. For the trimer three distinct minima with quite different hydrogen-bonding arrangements are found for the three lowest states. In strong contrast to the dimer the excitation here is clearly localized on the individual aniline chromophores for each of these three states. One of the three geometries is rather similar to the ground state minimum, while the two others are rather different and thus have presumably quite small Franck-Condon factors. It can be expected that only the electronic origin of the first conformer can eventually be detected in the absorption spectrum of the trimer, provided that it is separated by high-enough barriers from other, energetically lower configurations.     

Vibronic coupling of electronic states. II. mathematical description of the model

A model of vibronic coupling of crude Born–Oppenheimer (CBO ) potentials within the scope of the linear variational procedure is presented. First numerical results testing the model are discussed.     

X-ray emission spectroscopy and electronic. Structure of heterocyclic compounds 2. Thiophene

The electronic structure of has been studied by X-ray spectroscopy. SK , SL _2,3- and CK _±-spectra were obtained. Theoretical spectra were constructed on the basis of ab initio and MNDO calculations and the experimental results were interpreted. The HOMO is an orbital in which the electron density is localized on the carbon atoms. Conclusions about the occupancy of the lowest 3d orbital were reached from the experimental results.For Communcation 1, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1188–1193, September, 1993.     

X-ray emission spectroscopy and electronic structure of heterocyclic compounds. 1. Furan

The electronic structure of the furan molecule was investigated by x-ray spectroscopy. A quantum-chemical calculation (ab initio) was undertaken, and the results were compared with the experimental data. The interpretation of the x-ray spectra of the molecule, the carbon atoms of which have a different energy position for the 1s levels, is discussed in detail. The electronic transitions from the MO to these core levels are clearly recorded in the carbon x-ray spectrum. It was shown experimentally that the HOMO is an orbital in which the electron density is localized at the carbon atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1631–1635, December, 1991.