The Vibronic Absorption Spectrum and Electronic States of Nile Red in Aqueous Solution

Abstract

AbstractThe TD‐DFT was applied to calculate the vibronic absorption spectrum of Nile red (NR) in an aqueous solution. Various hybrid functionals have been used. The O3LYP/6‐31G(d,p) theory level gave an excellent agreement with the experimental absorption spectrum both in the position of the maximum and in the shape. Extended basis sets with diffuse functions and showed the worst results compared to the compact 6‐31G(d,p) basis. The dipole moments and atomic charges of the ground and excited states of the NR molecule have been calculated. According to our calculations, the dipole moment of a molecule increases upon photoexcitation, which is consistent with the positive solvatochromism of NR. An insignificant photoinduced electron transfer from the aminodiethyl group to the center of the chromophore and carbonyl group was found. According to our calculations, vibronic coupling plays a significant role in the absorption spectrum of the NR.