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 So 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 L-1(b) electronic excited state. We find that the O-H stretching frequency shifts follow a linear relationship with the solvent polarity function F-0 = (2 epsilon(0) - 2)/(2 epsilon(0) + 1), where eo is the static dielectric constant of the solvent. These changes are directly correlated with photoacklity trends determined by reported pK(a) values and with structural changes in the O center dot center dot center dot N and O-H hydrogen-bond distances induced by solvation or photoexcitation of the hydrogen-bonded complexes.