The propargylbenzene dimer: C-H···π assisted π-π stacking.

The propargylbenzene dimer was investigated using mass selected electronic and infrared spectroscopy in combination with quantum chemical calculations. The IR spectrum in the acetylenic C-H stretching region indicates that the two propargylbenzene units in the dimer are in an almost identical environment. The stabilization energies calculated at various levels of theory predict that the anti-parallel structure is the most stable isomer. The observed spectra are assigned to pi-stacked structures which incorporate C-H center dot center dot center dot pi interaction. The symmetry-adapted perturbation theory (SAPT) based energy decomposition analysis reveals that electrostatics contributes around 35% while the rest is due to dispersion. Comparison with the phenylacetylene and toluene dimers indicates that the higher stabilization energy of the PrBz dimer can be attributed to the synergy between the pi-pi stacking and C-H center dot center dot center dot pi interactions.