Photoexcitation of Nile Blue Dye in Aqueous Solution: Td-DFT Study

Abstract

The vibronic absorption spectra of Nile blue (NB) oxazine dye in an aqueous solution using 13 hybrid functionals, the 6-31++G(d,p) basis set, and the IEFPCM solvent model were calculated. It turned out that the O3LYP functional provided the best agreement with the experiment. Various parameters of the NB cation in the ground and excited states (IR spectra, atomic charges, dipole moments, and transition moment) were obtained. Maps of the distribution of electron density and electrostatic potential have been built. The influence of four strong hydrogen bonds of the dye with water molecules on the absorption spectrum was analyzed. It has been shown that two from these bonds were strengthened upon NB excitation and two ones were weakened. It was found that explicit assignment of water molecules strongly bound to the dye leads to a redshift of the spectrum as a whole and worsened its shape.