Unidirectional threading of tadpole-looking guests into a symmetric pillar[5]arene through host–guest complexation

A mobilizable pseudo[2]rotaxane based on 1,4-diethoxypillar[5]arene (EtP5A) and phenazine derivative (G1) has been effectively prepared. The unidirectional threading of phenazine axle into the pillar[5]arene wheel was successfully realized. Due to the presence of some intermolecular forces such as π–π stacking, hydrophobic interactions, and C–H···π interactions, increasing EtP5A’s concentration in the solution of G1 and EtP5A can make the pillar[5]arene wheel gradually move away from the imidazole part to alkyl chains on G1. Another guest benzimidazole derivative G2 was introduced, which has less conjugate groups than G1, and we similarly found the unidirectional threading of G2 axle into the EtP5A wheel could be triggered by concentration. These changes of binding sites were monitored by NMR titration experiments and fluorescent methods. And the fluorescent nature introduced into pseudo[2]rotaxanes rendered it a good sensor for this threading process. Four types of novel pseudo[2]rotaxanes formed by EtP5A, G1 and G2 were obtained through the unidirectional threading.