Theoretical study on host-guest interaction between pillar[4]arene and molecules or ions

In order to systematically explore the general rule of the host-guest chemistry for pillararenes, this work investigates the weak interactions between pillar[4]arene and some typical guests (anions, cations, and dumbbell-shaped molecules) by using density functional theory (DFT) calculations at the ωB97XD/6-311G(d,p) level. The strong molecular recognition ability of pillar[4]arene has been discussed based on the geometry structure, electronic structure, and thermodynamic properties of the host-guest complexes. The results show that the equivalent lower and upper rims of the pillar[4]arene can be combined with both anion and cation, and its cavity can accommodate the alkyl part of the dumbbell-shaped molecule. The main host-guest interactions between pillar[4]arene and guests are hydrogen bond, cation-π, anion-π, and hydrophobic interaction by visualization of weak interactions using the Multiwfn program. Pillar[4]arene will form a more stable host-guest complex with the guest, which possesses conjugate structure and weak steric repulsion. This work intends to provide a theoretical basis for enriching the host-guest chemistry, understanding the supramolecular morphology, and expanding the applications of the pillararenes.