Hierarchical supramolecular assembly based on metal coordination of asymmetric ligand pairs and host–guest recognition

Abstract

Three distinct monomers were synthesized, namely CD2, E2, and F2. Monomer CD2 is composed of a crown ether group (B21C7) and two terpyridine (tpy) groups, monomer E2 contains two 6,6′′-di(2,6-dimethoxylphenyl)-substituted terpyridine (tmy) groups, and the homoditopic F2 comprises two ammonium salts (DAS). By combining monomer CD2 with Zn(OTf)₂, a supramolecular linear polymer (SLP1) was successfully obtained through metal coordination based on terpyridyl units. Upon introducing monomer E2 into the solution containing SLP1, a novel supramolecular linear polymer (SLP2) was formed in the solution via complementary metal coordination. Furthermore, by adding another monomer F2 to the solution of SLP2, we observed a further structural transformation of SLP2 into a supramolecular crosslinked polymer (SCP3). This transformation was facilitated by double noncovalent interactions involving both complementary metal coordination and host–guest recognition. Notably, all resulting supramolecular polymers, SLP1, SLP2, and SCP3, exhibited remarkable sensitivity towards OH⁻ along with noticeable changes in their fluorescence emission properties. Moreover, at high concentrations, SCP3 demonstrated the ability to form a supramolecular gel while also exhibiting excellent self-healing properties.