Anion Receptors Based on Highly Fluorinated Aromatic Scaffolds

Abstract

Mono-, di-, and tri-pentafluorobenzyl-substituted hexafluorobenzene (HFB) scaffolds, viz., RI, RII, and RIII are proposed as promising receptors for molecules of chemical, biological, and environmental relevance, viz., N2, O3, H2O, H2O2, F–, Cl–, BF4–, NO3–, ClO–, ClO2–, ClO3–, ClO4–, and SO42–. The receptor–guest complexes modeled using M06L/6-311++G(d,p) DFT show a remarkable increase in the complexation energy (Eint) with an increase in the number of fluorinated aromatic moieties in the receptor. Electron density analysis shows that fluorinated aromatic moieties facilitate the formation of large number of lone pair−π interactions around the guest molecule. The lone pair strength of the guest molecules quantified in terms of the absolute minimum (Vmin) of molecular electrostatic potential show that Eint strongly depends on the electron deficient nature of the receptor as well as strength of lone pairs in the guest molecule. Compared to HFB, RI exhibits 1.1–2.5-fold, RII shows 1.6–3.6-fold, and the bowl-shaped RIII gives 1.8–4.7-fold increase in the magnitude of Eint. For instance, in the cases of HFB···F–, RI···F–, RII···F–, and RIII···F– the Eint values are −21.1, −33.7, −38.1, and −50.5 kcal/mol, respectively. The results strongly suggest that tuning lone pair−π interaction provides a powerful strategy to design receptors for small molecules and anions.