title: 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.
abstract: 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.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 India.
authors.forename: Surajit
authors.initials: S
authors.lastname: Maity
authors.forename: Arghya
authors.initials: A
authors.lastname: Dey
authors.forename: G Naresh
authors.initials: GN
authors.lastname: Patwari
authors.forename: S
authors.initials: S
authors.lastname: Karthikeyan
authors.forename: Kwang S
authors.initials: KS
authors.lastname: Kim
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D005453:Fluorescence; D006860:Hydrogen Bonding; D008744:Methylamines / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
chemical_list: D008744:Methylamines; C044736:phenylacetylene; C027451:methylamine; D000114:Acetylene