Dual fluorescence of 2-naphthalenecarboxylic acid in water-organic solvent mixtures

In water-ethanol, water-1,4-dioxane, and water-acetonitrile mixtures, neutral 2-naphthalenecarboxylic acid (2NCA) has been found to exhibit dual fluorescence. The two fluorescence bands have been assignable to the locally excited (LE) fluorescence and the intramolecular charge transfer (ICT) fluorescence, respectively. The solvation of 2NCA provided by water molecules seems to induce the ICT fluorescence of 2NCA. Fluorescence decay curves of neutral 2NCA in water and ethanol can be analyzed as a sum of two exponential decays.