Substituent and solvent effects on electronic absorption spectra of some N-(substitutedphenyl)benzene sulphonamides

The effects of substituents and solvents have been studied through the absorption spectra of nearly 23 ortho- and para-N-(substitutedphenyl)benzene sulphonamides in the range of 200-400 nm. The effects of substituents on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.     

Optical properties of Dy3+ doped calibo glass on addition of lead oxide

The effects of PbO on optical properties of dysprosium doped calibo glass have been studied. The content of PbO in the glass has been varied from 0 to 60 mol%. The absorption and fluorescence spectra are analyzed in terms of the Judd-Ofelt theory. It is observed that the fluorescence yield is maximum for the glass containing 40 mol% PbO. The I-R absorption spectra of these glasses have also been recorded and interpreted in terms of changes in the structure of the glasses.     

Electronic spectra of carbazole,dibenzofuran and dibenzothiophene

The magnetic circular dichroism and electronic absorption spectra of carbazole, dibenzofuran and dibenzothiophene have been measured. The absorption bands of these compounds are interpreted by using these observed spectra and the results of molecular-orbital calculations.     

Electronic spectra of adenine and guanine: Assignments and effects of solution environment

The results obtained by us on the ultraviolet absorption and fluorescence spectra of adenine and guanine and partially those of 8-azaguanine and 8-bromoguanine have been discussed and interpreted with the help of molecular orbital calculations. Effects of oxygenation and nitrogenation on the spectra and possible tautomerisations of molecules induced by oxygen and UV irradiation have mainly been the subjects of interest. Oscillations observed in the absorption spectra of guanine in aqueous solutions under UV irradiation have been interpreted in terms of the tautomerisation of the molecule following its slow complexation with the dissolved oxygen. This complexation of oxygen with guanine in DNA may cause lethal damage to biological systems including carcinogenesis.     

Effect of pyridine on infrared absorption spectra of copper phthalocyanine

Infrared absorption spectra of copper phthalocyanine in KBr pellet and pyridine solution in 400-1625 and 2900-3200 cm(-1)regions are reported. In the IR spectra of solid sample, presence of weak bands, which are forbidden according to the selection rules of D4h point group, is explained on the basis of distortion in the copper phthalocyanine molecule caused by the crystal packing effects. Observation of a new band at 1511 cm(-1) and change in intensity of some other bands in pyridine are interpreted on the basis of coordination of the solvent molecule with the central copper ion.     

The electronic structure,solvatochromism, and electric dipole moments of new Schiff base derivatives using absorbance and fluorescence spectra

Structural Chemistry - The electronic structure and electronic transitions of four new mono Schiff base derivatives are interpreted by using absorption and fluorescence spectra including 28...     

Spectral peculiarities of isomeric trans-styrylpyrazoles

The regularities in the electronic absorption spectra of trans-styrylpyrazoles were interpreted on the basis of quantum-chemical calculations by the Pariser-Parr-Pople configuration-interaction (PPP CI) method and data from the photoelectron spectra taking into account the peculiarities of the formation of the boundary molecular orbitals of pyrazole. The difference in the electronic effects of the isomeric pyrazolyl radicals determines the degree of polarization of the ethylene fragment and the C-C bonds of the pyrazole ring in the styrylpyrazole molecules; this is reflected in their IR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1061–1064, August, 1990.     

Electronic structure of the peptide linkage. II. A molecular orbital treatment of the electronic spectra of benzohydroxamic acids

The electronic absorption spectra of some benzohydroxamic acids have been analyzed and interpreted using the results of molecular-orbital calculations. Charge density distributions, dipole moments, and the extent of delocalization of the MOS were used to interpret the observed solvent effects. Comparison between the spectra of benzohydroxamic acids and that of simple amides led to conclusions regarding the structural differences between the two classes of compounds.     

External electric field effects on absorption, fluorescence, and phosphorescence spectra of diphenylpolyynes in a polymer film

External electric field effects on absorption, fluorescence, and phosphorescence spectra of a series of unsubstituted diphenylpolyynes have been examined in a PMMA film. The analysis of the electroabsorption spectra indicates that the shorter diphenylpolyynes exhibit only the change in molecular polarizability, whereas the longer ones exhibit the change both in dipole moment and in molecular polarizability following absorption. The finding of the change in dipole moment following absorption of centrosymmetric diphenylpolyynes is interpreted in terms of the symmetry distortion upon doping a polymer film. When the external electric field is applied, the fluorescence yield is reduced and enhanced, respectively, in diphenylacetylene and diphenyloctatetrayne, indicating that the rate of the nonradiative process from the fluorescence state is accelerated in diphenylacetylene and decelerated in diphenyloctatetrayne by an external electric field. All of the diphenylpolyynes used in the present study exhibit the change in molecular polarizability following the phosphorescence process.     

Infrared spectroscopy of small protonated water clusters at room temperature: an effective modes analysis

We perform infrared vibrational analysis on small protonated water clusters H(+)(H(2)O)(n), with n = 2, [ellipsis (horizontal)], 6, at room temperature. The absorption spectra are calculated based on classical trajectories obtained by the multistate empirical valence bond method. The analysis is carried out based on the effective modes analysis, which has been recently developed [Martinez et al., J. Chem. Phys. 125, 144106 (2006)] as generalization of the normal modes analysis. This technique enables us to decompose the full spectrum in maximally localized bands which are obtained by accounting for temperature and anharmonic effects. These effects are especially considered in the determination of the modes coupling. The spectra of the small clusters are interpreted by identifying the behavior of the excess charge, by understanding the role of hydrogen bonds, and by considering the effect of (micro-)solvation. Our results are presented by showing comparisons with other numerical methods and experimental measurements which are available in the literature.     

Inner-shell excitation spectroscopy and X-ray photoemission electron microscopy of adhesion promoters

The C 1s, Si 2p, Si 2s, and O 1s inner-shell excitation spectra of vinyltriethoxysilane, trimethylethoxysilane, and vinyltriacetoxysilane have been recorded by electron energy loss spectroscopy under scattering conditions dominated by electric dipole transitions. The spectra are converted to absolute optical oscillator strength scales and interpreted with the aid of ab initio calculations of the inner-shell excitation spectra of model compounds. Electron energy loss spectra recorded in a transmission electron microscope on partly cured adhesion promoter, atomic force micrographs, and images and X-ray absorption spectra from X-ray photoemission electron microscopy of as-spun and cured vinyltriacetoxysilane-based adhesion promoter films on silicon are presented. The use of these measurements in assisting chemistry studies of adhesion promoters for electronics applications is discussed.     

Tautomerism and the spectroscopic properties of some 4,6-disubstituted pyrimedines

Tautomerism of some 4,6-disubstituted pyrimidines (with the electron-donor groups such as OH, SH and NH₂) is discussed with regard to their electronic absorption spectra. The spectra of different tautomeric forms of the molecules are satisfactorily interpreted by means of the Pariser—Parr—Pople type of calculations.     

Effects of hydrogen bond and solvent polarity on the C=O stretching of bis(2-thienyl)ketone in solution

The optimized structural parameters, the absorption and the resonance Raman spectra have been investigated for the bis(2-thienyl)ketone in gas phase, in cyclohexane, methanol, and acetonitrile solvents by means of time dependent density functional theory calculations, the solvent electronic polarization effect on the solvation shift is examined and in well accordance with the calculation. The effect of increasing the polarity of the solvent is well represented by the polarizable continuum model, both for the absorption spectra and resonance Raman intensities. The Raman spectra of the C=O stretching mode, which is sensitive to the intermolecular interaction for bis(2-thienyl)ketone dissolved in solvents, were systematically studied. It was found that the hydrogen bond effect plays an important role in reducing the carbonyl stretching wavenumbers. The results of Raman shifts were interpreted through the dilution effect, solvation effects, and hydrogen bond-forming effects. Furthermore, the excitation profiles of several important Raman bands of bis(2-thienyl)ketone molecule in different solvents have been critically analyzed. The solvent effects on structural and symmetry properties of the molecule in S2 electronic state as well as the short-time photo relaxation dynamics have been discussed.     

Photoreduction of viologen-containing vinyl polymers by 2-propanol

In order to study the role of viologen-containing vinyl polymers in light energy conversion systems, the photoreduction of the polymer by 2-propanol and the properties of the reduced polymer were studied in comparison with methylviologen. There were marked polymer effects in the initial rate of photoreduction as well as in the absorption spectra of the photoreduced species. Both effects were interpreted in terms of the local concentration effect of viologen units in the photoreduction step. The spectral difference was found to be due to the dimeric association of the reduced viologen units on the polymer.     

Effect of polymer binding on the spectroscopic properties of stilbene-based fluorescent dyes

Studies utilizing absorption and emission spectrophotometry have been carried out to observe the effect of various polymer substrates on the spectral characteristics of several stilbene-based fluorescent dyes. Poly(vinyl alcohol), cellulose acetate, cellulose fiber, and bovine serum albumin were used as substrates for two common fluorescent whitening agents and for two model compounds. Binding of these molecules to polymers leads to a marked red shift in the absorption spectra and an increase in vibrational structure. These effects are attributed to an increase in molecular planarity induced by the polymer environment. For the case of bovine serum albumin, it is concluded that the dye molecules bind to the protein largely through electrostatic interaction involving the dye sulfonate groups. The spectral characteristics of the dye molecules on wool fibers are interpreted in light of these results.     

Substituent effects in the iron 2p and carbon 1s edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of ferrocene compounds

The iron 2p and carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of substituted ferrocene compounds (Fe(Cp-(CH3)5)2, Fe(Cp)(Cp-COOH), Fe(Cp-COOH)2, and Fe(Cp-COCH3)2) are reported and are interpreted with the aid of extended Hückel molecular orbital (EHMO) theory and density functional theory (DFT). Significant substituent effects are observed in both the Fe 2p and C 1s NEXAFS spectra. These effects can be related to the electron donating/withdrawing properties of the cyclopentadienyl ligands and their substituents as well as the presence of pi* conjugation between the cyclopentadienyl ligand and unsaturated substituents.     

Investigation of core-excited BK quantum yield spectra of amorphous and crystalline Fe40Ni40P14B6 alloys

X-ray quantum yield spectra from the BK edge in amorphous and crystalline Fe₄₀Ni₄₀P₁₄B₆ alloys are presented. ESCA core level binding energies were also measured. The quantum yield spectra are discussed together with calculated densities of states. A good coincidence between band structure calculations and experimental results is obtained. A small structure at absorption onset is interpreted as due to oxidation products at the sample surface. Crystallization effects after heating of the compound are discussed.     

Close correspondence between the Cs 4d spectra of molecular and crystalline CsCl

The Cs 4d absorption of molecular CsCl in the photon energy range from 70 eV to 180 eV has been determined for the first time. The absorption bands at the onset of the Cs 4d excitations are interpreted in terms of a simple ionic model. The close similarity of the spectrum of molecular and crystalline CsCl is discussed. The correspondence between these spectra and the 4d spectra of metallic and atomic Cs is pointed out.     

Experimental and theoretical investigation of the Li is spectra of molecular lithium halides

The Li 1s absorption spectra of molecular LiF and LiCl have been studied for the first time by experimental as well as by theoretical methods. The strong absorption bands at the onset of the Li 1s excitations can qualitatively be interpreted in terms of a simple ionic model. The spectra are analyzed and assigned in more detail on the basis of SCF and Cl calculations, and also within the framework of the Z + 1 core analogy model. The limitations of this model are discussed. Li 1s ionization potentials of LiF, Li₂F₂, LiCl, and Li₂Cl₂ are derived.     

Exciton dynamics of GaSe nanoparticle aggregates

Time-resolved and static spectroscopic results on GaSe nanoparticle aggregates are presented to elucidate the exciton relaxation and diffusion dynamics. These results are obtained in room-temperature TOP/TOPO solutions at various concentrations. The aggregate absorption spectra are interpreted in terms of electrostatic coupling and covalent interactions between particles. The spectra at various concentrations may then be interpreted in terms of aggregate distributions calculated from a simple equilibrium model. These distributions are used to interpret concentration-dependent emission anisotropy kinetics and time-dependent emission spectral shifts. The emission spectra are reconstructed from the static emission spectra and decay kinetics obtained at a range of wavelengths. The results indicate that the aggregate z axis persistence length is about 9 particles. The results also show that the one-dimensional exciton diffusion coefficient is excitation wavelength dependent and has a value of about 2 x 10(-5) cm(2)/s following 406 nm excitation. Although exciton diffusion results in very little energy relaxation, subsequent hopping of trapped electron/hole pairs occurs by a Forster mechanism and strongly red shifts the emission spectrum.