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

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.