A combined spectroscopic and ab initio investigation of phenylacetylene-methylamine complex. Observation of σ and π type hydrogen-bonded configurations and fluorescence quenching by weak C-H···N hydrogen bonding

J Phys Chem A. 2010 Oct 28;114(42):11347-52. doi: 10.1021/jp105439y.


Two distinct isomers for the binary complex between phenylacetylene and methylamine were observed. The first complex is characterized by the presence of a C-H···N hydrogen bond between the acetylenic C-H group and the N atom of methylamine. In the second complex the N-H group of methylamine interacts with the π electron density of the benzene ring accompanied by a peripheral interaction between the methyl C-H group and the π electron density of the C≡C bond. Stabilization energies and Gibbs free energies at the complete basis set (CBS) limit of the coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)] suggest that while the C-H···N hydrogen bonded complex is the global minimum, the N-H···π hydrogen bonded complex is a high energy local minimum. The formation of the N-H···π complex could be related to kinetic trapping or higher accessibility. Comparison of the laser induced fluorescence (LIF) excitation and the one-color-resonant two-photon ionization (1C-R2PI) spectra suggests that formation of C-H···N hydrogen bonding leads to fluorescence quenching in phenylacetylene, most probably due to dipolar coupling in the excited state. The binary complex between the phenylacetylene and methylamine shows interesting isomer-dependent fluorescent properties.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylene / analogs & derivatives*
  • Acetylene / chemistry
  • Fluorescence*
  • Hydrogen Bonding
  • Methylamines / chemistry*
  • Molecular Dynamics Simulation*
  • Quantum Theory*
  • Spectrophotometry, Infrared
  • Spectrum Analysis
  • Ultraviolet Rays


  • Methylamines
  • phenylacetylene
  • methylamine
  • Acetylene