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

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.

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Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 India.


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.

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