Tautomeric Equilibrium of Fluorescein in Solution: Ab Initio Calculations

The tautomeric equilibrium of fluorescein was investigated by calculating the relative free energies of various tautomers at neutral, anionic, and dianionic states both in the gas phase and in solution (water or DMSO) using an ab initio quantum mechanical method (B3LYP/6-31++G**) in combination with the Poisson–Boltzmann continuum solvation approach.