Aspectroscopic/thermodynamic study of the rhodamine B lactone ->/<- zwitterion equilibrium

Article abstract of DOI:10.1016/0584-8539(88)80227-7

Temperature dependences of the visible absorption spectra of rhodamine B (RB) in water and 18 alcohol solvents have been examined and utilized to estimate thermodynamic parameters (ΔG⁰, ΔH⁰, ΔS⁰) for the RB lactone->/<- zwitterion (L ->/<- Z) equilibria in these solvents.From the L ->/<- Z equilibrium in the strong hydrogen-bonding solvent trifluoroethanol an intrinsic RB zwitterion molar absorptivity of ε = 1.30E5 dm³/mol*cm is estimated.The thermodynamic results suggest that the position of the RB L ->/<- Z equilibrium is strongly influenced by self-association of the solvent.The position of the equilibrium in aliphatic alcohols can be predicted from the simple features of the solvent molecules.Consequences of the results regarding calculation of the natural radiative lifetime of the fluorescent state from absorption spectrum are discussed.