Visible spectrum of naphthazarin investigated through Time-Dependent Density Functional Theory

Using an ab initio approach taking into account environmental effects, we investigate the first absorption band of an important quinoidic dye, namely naphthazarin (5,8-dihydroxy-1,4-naphthoquinone). Several aspects have been considered in order to unravel the origin of the specific shape of this band: multiple absorptions, aggregation, presence of a tautomers, and vibronic couplings. It turns out that Time-Dependent Density Functional Theory (TD-DFT) is able to reproduce accurately the shape of the absorption spectra of naphthazarin if the latter effect is considered. The relative performances of a global, PBE0, and a range-separated, CAM-B3LYP, hybrids are also discussed in this framework.