Hydrogen Bonding and Intermolecular Vibrations of 7-Hydroxyquinoline·NH3 in the S0 and S1 States

Abstract

7-Hydroxyquinoline·(NH3)n microsolvent clusters have been shown to exhibit excited-state proton transfer (ESPT) in the S1 state for n ≥ 4 [Bach, A.; Leutwyler, S. J. Chem. Phys. 2000, 112, 560.]. We present a combined spectroscopic and ab initio theoretical investigation of the first member of this cluster series, the hydrogen-bonded 7-hydroxyquinoline·NH3 (7-HQ·NH3) complex. Mass- and rotamer-resolved S1 ↔ S0 vibronic spectra of supersonic jet-cooled 7-HQ·NH3 were obtained by two-color resonant two-photon ionization and dispersed fluorescence spectroscopy. Both the trans and cis rotamers are present in the jet, at a trans/cis ratio of 1:40. The H-bond vibrations σ (stretch), β1 and β2 (in-plane wagging), and τ (NH3 hindered internal rotation) were observed in the S0 and S1 states. Ab initio calculations using Hartree−Fock (SCF) and hybrid density functional (B3LYP) methods for the S0 state and the configuration interaction singles (CIS) method for the S1 state yield Cs symmetric equilibrium structures wi...