SOLVENT STRUCTURAL EFFECTS ON PROTON DISSOCIATION

Lifetime and quantum yield measurements are performed on the excited states of 1-naphthol-2-sulfonic acid potassium salt and its associated anion in aqueous solutions. In comparison to 1-naphthol, the intramolecular hydrogen bonding in the sulfonate derivative sterically reduces the extramolecular proton dissociation kdis and recombination krec rates. Despite the large differences between excited state rates in 1-naphthol-2-sulfonic acid and those in 1-and 2-naphthol, proton dissociation in all these molecules is controlled by reorientational motions of the adjacent water and requires a common (H2O)4±1 cluster as the proton acceptor. It is indeed found that kdis-1 and krec-1. at different temperatures are scaled to the Debye orientation time td. These findings further support the Robinson-Lee-Moore hydration model for endothermically produced protons in aqueous environments. © 1990, American Chemical Society. All rights reserved.