Microscopic solvent shifts in the electronic spectra of large van der waals molecules

The experimental red-shifts of the electronic origins of a number of large non-polar van der Waals molecules are reported. A comparison with the theoretical red-shifts calculated by a formalism given by Longuet-Higgins and Pople yields a good correlation, reflecting the dominant role of dispersion interactions in these complexes.     

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines

A theoretical investigation of the fully optimized geometries and electronic structures of metallophthalocyanines FePc, CoPc, NiPc, CuPc and ZnPc has been conducted with the density functional theory (DFT) method. A comparison between the different molecules for the geometry, molecular orbital, and atomic charge is made. The simulated order of the sizes of the central hole is FePc>CoPc>NiPcNiPc>CuPc>ZnPc, and the atomic charges of the central metal (M=Fe, Co, Ni, Cu, Zn) ions vary in the same order, FePc>CoPc>NiPcCoPc>FePc>CuPc>ZnPc, and the corresponding peaks predicted at 894, 896, 898, 882 and 871 cm(-1), respectively, also exhibit the same order as above-mentioned. Moreover, the lines of fit through plots of the experimental IR and Ra frequencies versus the calculated ones show very good correlations.     

X-Ray spectra and electronic correlations of FeSe(1-x)Te(x)

Critical issues concerning emerging Fe-based superconductors include the degree of electron correlation and the origin of the superconductivity. X-Ray absorption spectra (XAS) and resonant inelastic X-ray scattering spectra (RIXS) of FeSe(1-x)Te(x) (x = 0-1) single crystals were obtained to study their electronic properties that relate to electron correlation and superconductivity. The linewidth of Fe L(2,3)-edges XAS of FeSe(1-x)Te(x) is narrower than that of Fe-pnictides, revealing the difference between their hybridization effects and localization character and those of other Fe-pnictides. While no significant differences exist between the Fe L-edge XAS and RIXS of FeSe(1-x)Te(x) and those of Fe-pnictides, Se K-edge and Te K-edge XAS exhibit substantial edge shift, suggesting that the superconductivity in an Fe-Se superconductor is strongly associated with the ligand states. A comparison of the Se K-edge and Te K-edge spectra reveals that the charge transfer may occur between Se and Te. Given the Coulomb interaction and the bandwidth, the spectral results indicate that FeSe(1-x)Te(x) is unlikely to be a weakly correlated system unlike the Fe-pnictides of the "1111" and "122" families. The spectral results further demonstrate that superconductivity in this class of Fe-based compounds is strongly associated with the ligand 4p hole state.     

Formal-mathematical analysis of electronic paramagnetic resonance spectra with a hyperfine structure

Conclusion We intend to apply the methods exposed above in calculations on actual spectra. The author acknowledges Ya. S. Lebedev for a discussion of the results and S. P. Koneva and A. M. Kogan for doing the computations.Translated from Zhurnal Strukturnoi Khimii, Vol. 6, No. 1, pp. 39–46, January–February, 1965     

Structure-property correlations of a series of antimalarial chloroquine derivatives

Summary As part of the development of our in-house molecular modelling package, COSMIC, the structure-property relationships of a series of 13 antimalarial chloroquine derivatives have been investigated using physicochemical properties calculated from molecular models. This has involved the use of various statistical techniques. The compounds were analysed using three different modelling approximations concerning assumptions about the invariant amino alkyl side chain. The first two sets of data were obtained from models with and without the side shain using a formal charge of 0.0. Analysis of these data using principal components resulted in plots of principal component scores in which activity categories were separated. In the third data set, the side chain was modelled with a charge of +1 and an examination of the molecular properties showed poorer clustering of activity categories. We have also investigated relationships between biological activity and physicochemical properties using multiple linear regression. Although significant equations were developed, the correlation coefficients were low and it was not felt that they would be useful for quantitative prediction. The identification of important variables, however, may give some clues to the mechanism of action of these compounds.

---

Beziehungen zwischen Strukturen und Eigenschaften einer Reihe von Chloroquinderivaten mit Antimalariawirkung

Zusammenfassung Die physikalisch-chemischen Eigenschaften von 13 Chloroquinderivaten mit Antimalariawirkung wurden mittels Molekülmodellrechnungen bestimmt und unter Anwendung verschiedener statistischer Analysenmethoden ausgewertet. Die Untersuchungen sind Teil der firmeneigenen Entwicklung eines Software-Paketes für Molecular Modelling mit Namen COSMIC. Die konstante Aminoalkylseitenkette der Verbindungen wurde in den Modellierungen mit drei verschiedenen Näherungsannahmen berücksichtigt. Für die beiden ersten Datensätze wurde mit ungeladener Seitenkette und ohne Seitenkette gerechnet. Hauptkomponentenzerlegung der Daten ergab in beiden Fällen klare Trennungen hinsichtlich der Aktivitätskategorien. Bei der Berechnung des dritten Datensatzes wurde die Seitenkette mit einer Ladung von +1 modelliert. Die Clusterung der molekularen Daten in Aktivitätskategorien war in diesem Fall wesentlich schwächer ausgeprägt als in den beiden anderen Fällen. Außerdem wurde die Beziehung zwischen der biologischen Aktivität und den physikalisch-chemischen Eigenschaften durch multiple lineare Regressionsanalyse untersucht. Ungeachtet der Möglichkeit einer Herleitung von signifikanten Gleichungen waren die Korrelationskoeffizienten so gering, daß man die Beziehungen als ungeeignet für eine quantitative Vorhersage ansehen muß. Die ldentifikation der wichtigen Variablen kann aber dessenungeachtet nützliche Hinweise auf die Wirkmechanismen dieser Substanzklasse geben.

     

新型非线性光学材料的分子设计: 系列螺旋共轭化合物的结构、光谱及二 阶非 线性光学性质的理论研究

采用AM1和ZINDO系列方法研究了螺旋共轭分子2,2'-螺二茚-1,1',3,3'-四酮及其腈基衍生物的几何构型,研究了各分子的稳定构型,并以稳定为基础,计算了这些分子的电子光谱,二阶非线性光学系数βμ,β0,及电荷转移,考察了取代基变化对βμ的影响,计算结果表明所设计分子兼具较大的二阶非线性光学系数和较高的透过率,有希望成为一类新型的二阶非线性光学材料。     

Infrared correlations in the bile acid series

The infrared spectra of a number of esters and free acids in the cholanic acid series have been examined with the aid of a special solvent system which overcomes the problem of solubility. Eleven absorption regions in the 9–12 μ region have been correlated with specific substitution on the steroid nucleus and side chain. In certain cases, perturbations were found when di- or tri-substitution occurred in rings A, B, andJor C.     

Far IR spectra of dithiocarbamate complexes correlations with structure parameters

The far IR spectra (32–500cm⁻¹) of N,N-disubstituted dithiocarbamate complexes, M(R₂dtc)_n (n = 3, M Mn, Fe, Co; n = 2, M  Ni, Cu, Zn, Cd, Hg, Pb; R  Et, n-Pr, i-Pr, n-Bu, i-Bu; R₂N  pyrrol, pyrrolidyl) have been studied with the purpose of locating the modes involving displacement of the central atom. The IR bands related to changes in R(MS) and SMS have been found by comparing the IR spectra with M  const and R  variable, and those related to internal ligand modes with R  const and Mvariable. The spectral assignment thus obtained have been found to produce correlations with a number of structural parameters (v_ivs CFSE, v²_ivs R(MS) and ∡ SMS). The correlations reveal that the modes involving displacement of the central atom are coupled to a large extent.     

Recalling the appropriate representation of electronic spectra

This paper presents a critical discussion on the representation of UV-vis-NIR light absorption and fluorescence emission spectra of polyatomic molecules in liquid solution. A general overview how to handle the experimental spectra in order to extract physical data from them is presented together with some simulations to show the errors that can arise from unfortunate manipulation.     

The electronic spectra of unsaturated hydrocarbons a VESCF-CI treatment

A modified Pariser-Parr method, which allows for the inductive effect of alkyl groups by a VESCF method, has been applied to the calculation of the electronic spectra of a number of hydrocarbons. All singly- and doubly-excited configurations are included in the configuration interaction treatment, except for large molecules for which the configuration interaction matrices are truncated to an order of 110. The red shifts which result from methylation of the polyenes are well calculated. For azulene, the shift to either the red or the blue, depending on the location of the substituent, is also well calculated. The largest deviation between the calculated and experimental transition energies for all of the compounds studied was 1.1 eV, while the standard deviation of all observed transitions for planar compounds was 0.24 eV. The ionization potentials and the singlet-triplet transitions of these compounds were also studied.

---

Zusammenfassung Die Spektren einer Reihe von Kohlenwasserstoffen wurden nach einer modifizierten Pariser-Parr-Methode, bei der der induktive Effekt von Alkylgruppen mittels eines VESCF-Verfahrens berücksichtigt wird, berechnet, wobei alle ein- und zweifach angeregten Konfigurationen eingeschlossen wurden außer bei sehr großen Molekülen, wo deren Zahl auf 110 begrenzt wurde. Dabei ergeben sich in schöner Weise die Rotverschiebungen, die bei Methylierung von Polyenen beobachtet werden, desgleichen die Rot- und Violettverschiebungen je nach Ort des Substituenten bei Azulen. Die größten Abweichungen zwischen berechneten und beobachteten Übergangsenergien ist 1,1 eV, die Standardabweichung bei planaren Verbindungen 0,24 eV. Ferner wurden Ionisationspotentiale sowie Sigulett-Triplett-Übergänge der behandelten Verbindungen untersucht.

---

Résumé Une méthode Pariser-Parr modifieé, qui tient compte de l'effet inductif des groupes alkyles dans le cadre VESCF, a été employeé pour calculer les spectres électroniques de quelques hydrocarbures. Toutes les configurations mono- et di-excitées sont comprises dans le traitement d'interaction de configurations, excepté pour les grosses molécules; pour ces dernières, l'ordre des matrices d'interaction de configuration a été réduit à 110. Les déplacements versle rouge, après methylation de polyènes, sont bien calculés. Pour l'azulène, les déplacements vers le rouge ou le bleu, suivant le lieu de substitution, sont également bien calculés. La plus grande déviation entre les énergies de transition calculée et expérimentale était de 1.1 eV pour tous les produits étudiés, alors que la déviation standard de toutes les transitions observeés était de 0,24 eV dans les composés planaires. Le potential d'ionisation et les transitions singulet-triplet ont aussi été étudiés.

     

Condensed heterocycles with a thiazole ring. 14 Nature of the electronic spectra of symmetrical polymethine dyes of the thiazolo[3,4-b][1,2,4]triazine series

Symmetrical mono-, tri-, and pentamethinecyanine dyes with a thiazolo[3,4-b][1,2,4]triazine ring were synthesized. The electron-density distributions in the dye molecules in the ground and first and second excited states were obtained by quantum-chemical calculations. It was established that the first two electron transitions are localized on the same atoms and that charge transfer to the triazine fragment of the molecule is realized in the case of excitation. The degree of participation of the heterocyclic ring in the first electron transition, which is responsible for the color of the dye, decreases with lengthening of the polymethine chain.See [1] for communication 13.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 24, No. 3, pp. 418–423, March, 1988.     

Molecular-orbital calculation of the electronic spectra of salicylalkylimines

MO methods in the Hückel approximation are used to derive the bond orders, electron-density distributions, dipole moments, and frequencies and strengths of the electronic transitions. The assignment of the absorption bands (on the basis of the energy and intensity results) leaves no doubt that the bands near 400 m, whose intensity is very much dependent on the solvent, are due to n transitions. The electron densities and bond orders for the ground state and for the first two excited states, as well as for the n₁ transition, show that the molecules have a tendency to adopt quinoid structures on excitation. The calculated dipole moment for salicylalmethylimine agrees well with measured values for this class of compound.     

Interpretation of the electronic spectra of four disilanes

Time-dependent density functional theory (TD-DFT/B3LYP(AC)/cc-pVTZ/cc-pVTZ/6-311G//MP2/cc-pVTZ/cc-pVTZ/6-31G**) has been used to compute vertical excitation energies and oscillator strengths of the six low-lying excited states of four peralkylated disilanes, hexamethyldisilane (1), hexa-tert-butyldisilane (2), 1,6-disila[4.4.4]propellane (3), and 1,7-disila[5.5.5]propellane (4). The results provide an accurate interpretation of the reported UV absorption spectra of 1-4 in solution, and for 1 also in the gas phase up to 62,000 cm(-1). The excellent agreement of the calculated with the available experimental energies and oscillator strengths, and with magnetic circular (MCD) and linear (LD) dichroism, gives us confidence that the method will be useful for dependable interpretation of the electronic spectra of longer oligosilanes. Although the disilane chromophore finds itself in quite different environments in 1-4, its fundamental characteristics remain the same, with one important exception. In all four compounds, the first valence excited state is due to an electron promotion from the sigma(1) HOMO to the pi(1)* orbital, and the second valence excited state to a promotion from the sigma(1) HOMO to the sigma(1)* orbital. Surprisingly, however, it is only in 2, which has an extraordinarily long SiSi bond, that the terminating sigma(1)* orbital is the sigma*(SiSi) antibond, as anticipated, and the sigma sigma* transition has the expected very high oscillator strength. In 1, 3, and 4, the sigma*(SiSi) antibonding orbital is high in energy and does not play any role in low-energy excitations. Instead, the terminating orbital of the sigma(1)sigma(1)* excitation is represented by Si-alkyl antibonds, combined symmetrically with respect to rotation around the SiSi axis and antisymmetrically with respect to operations that interchange the two Si atoms. The common assumption that the characteristic intense sigma sigma* transitions of longer peralkylated oligosilanes extrapolate to the lowest sigma sigma* transition in common peralkylated disilanes is incorrect, and only the weak sigma pi* transitions extrapolate simply.