A direct experimental evidence for an aromatic C–H⋯O hydrogen bond by fluorescence-detected infrared spectroscopy

Formation of a weak aromatic C–H⋯O hydrogen bond has been discerned both experimentally and computationally in the 1,2,4,5-tetrafluorobenzene (TFB)–water system. The intermolecular structure of the isolated TFB–water cluster in a supersonic jet was characterized using fluorescence-detected infrared spectroscopy. The formation of a weak hydrogen bond in the cluster was directly evidenced by a low-frequency shift and intensity enhancement of the hydrogen-bonded aromatic C–H stretch in the TFB moiety. This is the first direct observation of an aromatic C–H⋯O hydrogen bond in isolated gas phase clusters.