Density functional theory has been performed on the free host and its halide anion complexes of calix[4]pyrrole and halide substituted calix[4]pyrroles. The calculated result implied that the conformation feature of host is mainly due to pyrrole unit dipole moment. The result also indicated that β-halo substitution would enhance the interaction between calix[4]pyrrole and halide anion, and the interaction was the strongest for β-chloro substitution. It has also been described that effect of β-halo substitution on host-guest interaction from frequency analyses, NBO charge population, frontier orbital of interaction, dipole moment of activated conformation and Mulliken bonding population.

Key words: calix[4]pyrrole, anion recognition, β-halo substitution, host-guest interaction