Siegfried Bleisch

ELECTRONIC EXCITATION OF ORGANOSULFUR RADICALS

Abstract Transition energies of neutral and ionic sulfur containing heterocyclic radicals have been calculated by the method of Longuet-Higgins and Pople and compared with experimental excitation energies obtained by UV/VIS absorption and photoelectron spectroscopy. In most cases the calculated transition energies satisfactorily match the ones found experimentally. A few compounds behave exceptionally. Discrepancies between the two sets of experimental values are attributed to different molecular geometries of the radical species. According to the calculations, the UV/VIS absorption spectra of recently synthesized sulfur and nitrogen containing radicals are compatible with the 1,2,3-dithiazolyl structure.

THE ABSORPTION FEATURE OF CONJUGATED COMPOUNDS CONTAINING THE NSN-CHROMOPHORE

Abstract The NSN group absorbs at relatively long wavelengths in the uv region. Because of its capability to release or to accept electrons, adjacent groups can produce a pronounced red shift of the color band. Based on the more recently described PPP configuration analysis technique and the MIM-LCI method the color determining electronic transitions of organic sulfdiimides (Sulfurdiimines) has been accounted for in terms of their constituent parts. The calculations revealed that the position of the color band is mainly governed by frontier orbital interactions. Symmetrical junction of the NSN unit with conjugated fragments gives rise to deeply colored heterocyclic compounds, if either their HOMOs or LUMOs have the same symmetry and undergo an effective overlap. This condition is not fulfilled, in general, for compounds which are strongly stabilized in their electronic ground states.