Dual‐Channel Gas‐Sensitive Fluorescent Switch: Realizing a Reversible Fluorescent Response to HCl and NH 3

Abstract Luminescent metal–organic frameworks (LMOFs) provide exceptional advantages over conventional materials in detecting harmful gases. However, challenges remain, such as limited stability, unclear fluorescence signal changes and insufficient mechanistic understanding. In this study, we developed two types of lanthanide metal–organic frameworks (Ln‐MOFs) exhibiting rapid (<5 s) and reversible fluorescence “turn‐on” responses to vapor exposure. Specifically, Ln‐TCPE demonstrates a swift response to HCl vapor via a unique dual‐channel mechanism: highly dipolar HCl molecules stabilize the conformation of tetraphenylethylene ligands through weak intermolecular interactions, causing a 780% increase in fluorescence intensity. Simultaneously, HCl coordination with Ln 3+ triggers a pronounced 45 nm redshift in fluorescence by altering the MOFs' overall energy and electron transfer dynamics. The combination of these two signals greatly amplifies the fluorescence transition. Outstanding stability allows the sample's initial fluorescence to be fully restored through simple thermal desorption, enabling recyclability. With fewer open metal sites, Ln‐ETTB achieves fluorescence “turn‐on” detection of NH 3 vapor solely via benzene ring locking, and it can likewise be recycled. This study presents the first report of such dual‐channel gas‐responsive LMOFs. We thoroughly elucidated the underlying mechanisms through experimental work and DFT calculations, paving the way for new advancements in LMOFs‐based gas sensing.