title: Ultrafast excited-state proton-transfer reaction of 1-naphthol-3,6-disulfonate and several 5-substituted 1-naphthol derivatives.
abstract: The 1-naphthol molecule has been the subject of intense research activity for the past 60 years due to its complex behavior as a photoacid upon optical excitation. We have utilized femtosecond mid-infrared spectroscopy and time-resolved fluorescence spectroscopy to investigate the excited-state proton-transfer reaction of 1-naphthol-3,6-disulfonate (1N-3,6diS) and several 5-substituted 1-naphthol derivatives. The proton dissociation rate constant of 1N-3,6-diS was found to be about 3 times faster and the pKa* about 2 pKa units more acidic than the values previously reported in the literature. A Marcus (free-energy) plot of excited-state proton dissociation rate constants vs the excited-state equilibrium constant of the photoacids, Ka*, was constructed using the C-5 series of 1-naphthol derivatives. The newly measured values for the ESPT rate constant and pKa* of 1N-3,6diS was found to fit well with the Marcus correlation. We discuss our findings in the context of the photoacidity phenomenon in general, and the photoacidity of 1-naphthol and its derivatives in particular.
authors.affiliation: Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2 A, D-12489 Berlin, Germany.
authors.forename: Mirabelle
authors.initials: M
authors.lastname: Prémont-Schwarz
authors.forename: Tamar
authors.initials: T
authors.lastname: Barak
authors.forename: Dina
authors.initials: D
authors.lastname: Pines
authors.forename: Erik T J
authors.initials: ET
authors.lastname: Nibbering
authors.forename: Ehud
authors.initials: E
authors.lastname: Pines