Organofluorine compounds represented by perfluoroalkyl (Rf) compounds involving polytetrafluoroethylene (PTFE) attract keen interest for various practical chemistry fields such as material science and pharmaceutical science. Research of organofluorine compounds, however, has long been oriented to organic synthesis, and physicochemical background is still weak to fully understand the material property on the primary chemical structure. Recently, the Stratified Dipole-Arrays (SDA) theory [Chem. Rec. 2017, 17, 903.] has been published, which comprehensively explains various Rf compound-specific properties for both macroscopic and microscopic properties. On this theory, quantitative analysis of the molecular aggregation and orientation is being developed by using infrared and Raman spectroscopy. Multiple-angle incidence resolution spectrometry (MAIRS) coupled with FT-IR readily reveals the perfectly perpendicular orientation of a compound having an Rf chain with a length of (CF2)7 or longer in the two-dimensional molecular aggregate, i.e., a thin film. On the SDA theory, each molecular aggregate should be consisted of one of the right- or left-handed helical Rf chains. This means that the molecular domain of an Rf compound should exhibit Raman optical activity (ROA) even if the compound has no chiral center. In fact, our measurements of ROA on a single crystal of a Rf compound apparent ROA signal [J. Phys. Chem. 2019, 123, 3985.]. In this manner, vibrational spectroscopy works as a powerful tool to reveal the fine chemical structure of molecular aggregation of Rf compounds. For the full understanding, however, a conventional concept for hydrocarbons must be changed, since the relative mass of fluorine to carbon is overturned to the case of hydrogen to carbon. In the talk, fundamental details of vibrational spectroscopy on the SDA theory are presented in a comprehensive manner.
Takeshi Hasegawa (Kyoto University)