Desymmetrized pillar[8]arenes: High-yield synthesis, functionalization, and host-guest chemistry

The preparation, functionalization, and investigations in host-guest properties of high-level pillararene macrocycles have long been a big challenge because of the lack of efficient synthetic methods. Herein, a novel type of pillararene derivative, namely desymmetrized pillar[8]arene (DP[8]A), has been successfully synthesized via a facile two-step strategy with high yield. Compared with its pillar[8]arene counterpart, DP[8]A is composed of four alkoxy-substituted benzene units and four bare benzene rings. Single crystal analysis has been performed in order to unveil the molecular conformation and packing mode of DP[8]A, which indicated that DP[8]A possesses a unique chair-like structure and much smaller steric hindrance. Density functional theory (DFT) calculations and electrostatic potential map suggested the inhomogeneous electronic distribution in the DP[8]A cavity. Water-soluble carboxylate-modified DP[8]A, that is, CDP[8]A, was also prepared to investigate the host-guest properties in aqueous solution with methyl viologen (MV), where the binding constant and morphologies of the formed host-guest complexes have been studied. In all, this new version of eight-membered pillararene derivative might potentially serve as a powerful macrocycle candidate for further applications in supramolecular chemistry.