Mastering Fluorescence through a Rare-Earth Ion Functional Switch in Isostructural Bimetallic MOFs

The fluorescence properties of metal–organic frameworks (MOFs) are traditionally influenced by organic ligands, making the role of metal nodes, especially rare-earth centers in isostructural MOFs variants, a relatively understudied area. Herein, this study reports two isostructural bimetallic MOFs with identical organic ligand components but distinct rare-earth centers (La3+ and Eu3+). Photophysical analyses reveal that the choice of rare-earth ion dictates divergent fluorescent behaviors, including distinct quenching pathways and emission intensities. Significantly, these differences enable selective sensing: in the presence of norfloxacin, complex 1 exhibits a fluorescence turn-on response, while complex 2 demonstrates turn-off quenching. These findings confirm that rare-earth centers can act as a critical “functional switch” to modulate MOF fluorescence, offering a targeted strategy for the design of advanced fluorescent materials.