Two AIE-Ligand-Based 2-D Luminescent Metal–Organic Frameworks as Fe³⁺ Sensors

The design and synthesis of high-performance sensors are very important but remain great challenges. In this work, a new aggregation-induced-emission (AIE) molecule 4,4′-(((9H-fluoren-9-ylidene)methylene)bis(4,1-phenylene))dipyridine (L) was successfully synthesized and first developed as a functional ligand to construct two isomorphic metal–organic frameworks (MOFs) [M(L)(OBBA)]n [M2+ = Cd2+ (1), Co2+ (2); H2OBBA = 4,4′-oxybisbenzoic acid]. They adopt [M2(COO)4] flywheel clusters, OBBA2– bridges, and terminal L ligands as building units to form isomorphic 2-D networks with Lewis base active cites (uncoordinated pyridyl N). Both 1 and 2 exhibit excellent water, pH, and thermal stabilities and extremely efficient Fe3+ sensing abilities in the water environment. The quenching constants and detection limits reach the best levels reported so far. The sensing mechanism of 1 and 2 toward Fe3+ is studied in depth, and the difference in their sensing performance is also explained.