Room‐Temperature Solid‐State Luminescence Switching via CO₂ Weak interaction in a Stable Europium Metal–Organic Framework

Luminescent metal‐organic frameworks (LMOFs) offer transformative potential for chemical sensing, yet their implementation faces challenges, including underexplored gas‐phase behavior and device integration difficulties. A robust europium‐based MOF is reported, {[Eu 2 (TBCM) 4 (CH 3 CO 2 H) 2 ]·8H 2 O·DMF} n denoted as INM‐EF‐1 ‐or simply 1·solv ‐, constructed from a tetrahedral carboxylate ligand (H 4 TBCM) that serves as both a structural scaffold and a sensitizing antenna for Eu 3 ⁺ emission. This framework exhibits permanent porosity, exceptional stability, and unique solid‐state photoluminescence modulation upon CO 2 interaction. Through single‐crystal‐to‐single‐crystal (SCSC) studies, in situ spectroscopy, and computational modelling, a physisorption‐driven mechanism is revealed where CO 2 increases the efficiency of ligand‐to‐metal energy transfer without framework degradation. To address practical limitations, a composite is engineered by embedding activated 1 in a polydimethylsiloxane (PDMS) matrix, achieving enhanced sensitivity and durability for CO 2 monitoring (>3000 ppm). Unlike reported LMOF reliant on solution‐phase detection or refractive index changes, our system operates via a reversible luminescence quenching/enhancement process at room temperature, demonstrating selectivity over common interferents (e.g., N 2 , O 2 ) and at ambient moisture. This work bridges critical gaps in LMOF development by elucidating structure‐property relationships in lanthanide‐responsive material and providing insights into host–guest interactions that govern its reactive luminescence.