Excited state dipole moment of the fluorescein molecule estimated from electronic absorption spectra

Abstract

Abstract The solvatochromic study of fluorescein is performed in order to obtain information on both the interactions with solvents in which it is dissolved and the electro-optical parameters of the molecule in the first excited electronic state. The shifts of the visible absorption spectral band of fluorescein dissolved in several solvents were experimentally measured and correlated to solvent parameters such as the refractive index, electrical permittivity and the Kamlet-Taft parameters (hydrogen bond acidity and basicity, respectively). A quantum-mechanical study of the fluorescein molecule was additionally performed to determine some parameters of the fluorescein molecule in the ground electronic state. Following McRae s hypothesis, according to which the molecular polarizability does not change in the absorption process, the data obtained from the solvatochromic analysis and quantum-mechanical calculations were corroborated in order to estimate the dipole moment of fluorescein in its first excited electronic state.