Abstract:

Cyclobis(paraquat-p-anthracene) is a novel electron-deficient macrocyclic host. One of the most important applications of the host is molecular recognition. The binding energies of the host to several guest molecules like water, ammonia, alcohol, and heterocycles were investigated. The structures of the host-guest complexes were optimized using DFT (density functional theory) at B3LYP/3-21G level. The energies of the complexes were calculated at B3LYP/6-31G(d) level. The binding energies of the complexes were obtained after the correction of basis set superposition error. The 13C and 3He chemical shifts of the complexes were calculated by the gauge-including atomic orbital (GIAO) method at B3LYP/3-21G level. It indicates that the host can bind the guest molecules via hydrogen bonds between the heteroatoms in the guest and hydrogen atoms in the host. The binding energies of the complexes were mainly affected by the number and distance of the hydrogen bonds. The energy gaps for some of the complexes were increased owing to the formation of the hydrogen bonds. At the same time, the chemical shifts of the carbon atoms on the C—H bonds connected with the hydrogen bonds in the complexes relative to those of the same carbon atoms in the host were transferred downfield. The aromaticities of the complexes were relevant to the binding energies and ways. The aromaticity of the host was increased by the weak interaction between the host and guest molecules. The cyclic current of the host was decreased, thus the aromaticity was lowered owing to too strong host-guest interaction and incorporation of the guest molecules inside the cavity of the host.

Key words: Cyclobis(paraquat-p-anthracene), Molecular recognition, Chemical shift, Aromaticity