Molecular Aggregation of Perfluoroalkyl Groups Can Win the Hydrogen Bonding between Amides

Hydrogen bonding is, in general, recognized to have a much stronger molecular interactive force than the dipole–dipole interaction that is one of the van der Waals forces. The molecular interaction between perfluoroalkyl (Rf) chains is driven by a two-dimensional dipole–dipole interaction network because of a large dipole moment along the C–F bond and a helical conformation about the Rf chain axis, which generates the Rf-specific tight and closed molecular packing. The polarization of a molecular aggregate on a macroscopic scale comprehensively explains the Rf compound-specific properties represented by the high melting point. This cooperative interaction in the two-dimensional network gives us an impression that the dipole–dipole interaction can win the H-bonding in a molecular aggregate. In the present study, amphiphilic compounds having an Rf group and an amide group are prepared, and the molecular aggregation factor is investigated by means of surface chemistry and vibrational spectroscopic techniques. In fact, we show that the dipole–dipole interaction becomes the dominant factor of the molecular aggregation of the amide-containing compound.