Journal of Physical Chemistry A, Vol.116, No.5, 1368-1374, 2012
pi-Hydrogen Bonding Wins over Conventional Hydrogen Bonding Interaction: A Jet-Cooled Study of Indole center dot center dot center dot Furan Heterodimer
In this study, we have explored the conformational landscape of the indole center dot center dot center dot furan dimer in a supersonic jet by using resonant two-photon ionization (R2PI) and IR-UV double-resonance spectroscopic techniques combined with dispersion-corrected density functional theory (DFT) calculations. Only one conformer of the dimer has been observed in the experiment. DFT/B97-D level calculation shows that N-H center dot center dot center dot pi hydrogen-bonded conformer CO is energetically more stable than the N-H center dot center dot center dot O hydrogen-bonded conformer (HB). Natural bond orbital (NBO) calculation also shows that the hydrogen-bonding interaction in the HB conformer is very weak. Finally, the structure of the observed dimer has been determined to be tilted T-shaped N-H center dot center dot center dot pi hydrogen-bonded (T') from very excellent agreement between experimental and theoretical N-H stretch frequency. The most significant finding of this study is the first-time observation of a N-H center dot center dot center dot pi bound conformer of a dimer, which wins over a conventional hydrogen-bonded conformer of the dimer.