Ultrafast Excited-State Proton-Transfer Reaction of 1‑Naphthol-3,6-Disulfonate and Several 5‑Substituted 1‑Naphthol Derivatives

• Published in: The journal of physical chemistry. B Vol. 117; no. 16; pp. 4594 - 4603
• Main Authors: Prémont-Schwarz, Mirabelle, Barak, Tamar, Pines, Dina, Nibbering, Erik T. J, Pines, Ehud
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 25.04.2013
• Subjects: 1-naphthol; Atomic and molecular physics; Derivatives; dissociation; Exact sciences and technology; Excitation; Excitation spectra; Femtosecond; Fluorescence; fluorescence emission spectroscopy; Molecular properties and interactions with photons; Molecular spectra; Physical chemistry; Physics; Rate constants; Spectroscopy; Energy levels; Proton transfer; Fluorescence; Naphthol derivatives; Mid infrared radiation; Infrared spectra; Excited states; Time resolved spectra; Ultrafast process
• ISSN: 1520-6106; 1520-5207; 1520-5207
• DOI: 10.1021/jp308746x

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 pK a* about 2 pK a 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, K a*, was constructed using the C-5 series of 1-naphthol derivatives. The newly measured values for the ESPT rate constant and pK a* 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.