Structures, Properties, and Host−Guest Chemistry of P(O)-Bridged Pillar[<i>n</i>]arenes: A DFT Study

The structural construction and application development of pillararenes have been hot topics in supramolecular chemistry. To enrich the pillararene chemistry, this work proposed a new type of heteroatom-bridged pillararene molecules: phosphorus- (P-) and phosphoryl- (PO-) bridged pillararenes. Density functional theory (DFT) calculations were used to systematically predict and analyze the structures, properties, and host-guest complexes of P(O)-bridged pillar[<i>n</i>]arenes (P<i>n</i>P and P<i>n</i>PO, <i>n</i> = 4-7). Medium-sized P<i>n</i>P and P<i>n</i>PO maintained a prismatic molecular skeleton containing an ordered network of H-bonds. Compared with the parent pillar[<i>n</i>]arene, the substitution of P(O) groups significantly increased their cavity size and reduced the energy levels of HOMO and LUMO orbitals due to elongated P-C bonds and σ*-π* conjugation effects. The change of bridging groups affected the position of the maximum absorption peak of pillar[<i>n</i>]arenes; the absorption spectrum had a significant redshift, and the solvation effect in polar solvents had also been improved. P<i>n</i>P and P<i>n</i>PO preferred to form host-guest complexes with electron-deficient guests. Due to the electron-withdrawing property of phosphoryl groups, the inclusion capacity of P<i>n</i>PO toward neutral molecules was obviously stronger than that of P<i>n</i>P. These properties were expected to provide new ideas for expanding the pillararene chemistry.