The electronic structure of poly(pyridine-2,5-diyl) investigated by soft x-ray absorption and emission spectroscopies

The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and nonresonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the {\pi} electron bands in line with symmetry selection and momentum conservation rules. The effect is most vizual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of {\sigma} symmetry and are less frequency dependent.Comment: 11 pages, 7 figures, 1 table, http://www.sciencedirect.com/science/article/pii/S030101049800262

Calculations of NEXAFS Spectra of Substituted Benzenes

We examine the role of substituent strengths and positions for NEXAFS spectra of substituted benzenes by means of static exchange calculations on aniline, phenol, fluorobenzene, and terephthalaldehyde. Chemical shifts and intensities of the 1s → π* excitations are found to be closely related to the electronegative character of the substituent group. The intensities for the unconnected ring carbons exhibit a significant site dependent, alternant, behaviour, while the chemical shifts in the energy positions are small. The terephthalaldehyde molecule shows a crucial positional dependence for double substitution and gives also a nice example of the building block principle for NEXAFS. New assignments are given for the building blocks in the terephthalaldehyde spectrum and for all salient features in the discrete parts of the monosubstituted benzene spectra