I. The nature of fluorine-mediated intermolecular interactions. II. The fluorophobic effect as a force for molecular recognition and self-assembly

The introduction of fluorine into a molecule can deeply affect its physicochemical properties. While even one fluorine atom can influence the hydrogen bonding properties and the lipophilicity of a molecule, several fluorine atoms tend to generate a new behavior, performance and potential for separation.;Fluoromethane was chosen as an example of a small molecule containing organic fluorine and its interactions with a variety of hydrogen donors and cations were calculated using ab initio methods. These results demonstrate that a single fluorine atom attached to an aliphatic carbon is able to engage in classical hydrogen bonds characterized by a binding energy approximately 70% of the energy involved in a sp3-oxygen-mediated hydrogen bond. The comparison of interaction energies among the different fluorinated methanes demonstrated that the further addition of fluorine atoms on the same carbon atom dramatically reduces the participation of fluorine in intermolecular interactions. Thus, a fluoromethyl group can engage in hydrogen bonds, while a trifluoromethyl functionality cannot. This explains the observed inability of perfluorinated and highly fluorinated molecules to engage in electrostatic and polarizability-mediated intermolecular interactions.;To study the properties of highly fluorinated molecules, a new series of calix[4]arene-based amphiphilic molecules was designed and synthesized. These semi-fluorinated derivatives are composed of a calix[4]arene scaffold functionalized with linear fluorinated chains at the upper rim and hydrophilic groups at the lower rim. These molecules form microscopic fluorous domains that drive the formation of polarity dependent self-assembly patterns. These semi-fluorinated calix[4]arene materials also respond to external stimuli, such as changes in the polarity of the solvent or pH. The unique combination of the rigid calix[4]arene core and the bulky and stiff perfluorooctyl chains results in liquid crystalline-like character. The calix[4]arene tetraamine was analyzed by temperature modulated differential scanning calorimetry and was found to exhibit a glass transition, indicating that this material is a glassy liquid crystal. This research contributes to establishing the properties of novel materials based on semi-fluorinated surfactants and amphiphilic calix[4]arenes.