THE ABSORPTION FEATURE OF CONJUGATED COMPOUNDS CONTAINING THE NSN-CHROMOPHORE

Abstract

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 HOMO's or LUMO's 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.