A DFT characterization of the structures and UV/vis absorption spectra of mauveine dyes

The equilibrium structure of the mauveines has been studied with the density functional theory. The molecular framework consists of a planar diaminophenazine with a centrally appended perpendicular phenyl ring and a laterally bound twisted aminophenyl group. Of the three aromatic fragments, it is only the aminophenyl part that exhibits a conformational flexibility around the C(phenazine)–N–C(phenyl) bonds. The electronic absorption spectra have been examined using hybrid time-dependent density functional theory. The π → π∗ excitations, mainly occurring in the phenazine moiety, are the major contributors to the strong absorption bands. Intramolecular π-charge transfer from the appended phenyl rings to the phenazine nucleus give rise to weakly-allowed transitions.