title: Correlating photoacidity to hydrogen-bond structure by using the local O-H stretching probe in hydrogen-bonded complexes of aromatic alcohols.
abstract: To assess the potential use of O-H stretching modes of aromatic alcohols as ultrafast local probes of transient structures and photoacidity, we analyze the response of the O-H stretching mode in the 2-naphthol-acetonitrile (2N-CH3CN) 1:1 complex after UV photoexcitation. We combine femtosecond UV-infrared pump-probe spectroscopy and a theoretical treatment of vibrational solvatochromic effects based on the Pullin perturbative approach, parametrized at the density functional theory (DFT) level. We analyze the effect of hydrogen bonding on the vibrational properties of the photoacid-base complex in the S0 state, as compared to O-H stretching vibrations in a wide range of substituted phenols and naphthols covering the 3000-3650 cm(-1) frequency range. Ground state vibrational properties of these phenols and naphthols with various substituent functional groups are analyzed in solvents of different polarity and compared to the vibrational frequency shift of 2N induced by UV photoexcitation to the (1)Lb electronic excited state. We find that the O-H stretching frequency shifts follow a linear relationship with the solvent polarity function F0 = (2ε0 - 2)/(2ε0 + 1), where ε0 is the static dielectric constant of the solvent. These changes are directly correlated with photoacidity trends determined by reported pKa values and with structural changes in the O···N and O-H hydrogen-bond distances induced by solvation or photoexcitation of the hydrogen-bonded complexes.
authors: †Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States.
authors: Brian T
authors: BT
authors: Psciuk
authors: ‡Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
authors: Mirabelle
authors: M
authors: Prémont-Schwarz
authors: ‡Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
authors: Benjamin
authors: B
authors: Koeppe
authors: §Department of Chemistry, Ben-Gurion University of the Negev, P.O. Box 653, Be'er Sheva, 84105, Israel.
authors: Sharon
authors: S
authors: Keinan
authors: Dequan
authors: D
authors: Xiao
authors: ‡Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
authors: Erik T J
authors: ET
authors: Nibbering
authors: †Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States.
authors: Victor S
authors: VS
authors: Batista