Ligand-Driven Structural Control in Rare Earth-TNDI MOFs: Topological Diversity and Mixed Matrix Membranes for Real-Time Amine Detection

Rare-earth (RE) MOFs are notable for their structural tunability and diverse connectivity, making them promising for applications in gas separation, storage, and sensing. This work reports two new isostructural RE-based MOFs, Y-TNDI and Eu-TNDI, synthesized by using a rigid tetracarboxylate linker bearing a naphthalenediimide (TNDI) core. Unlike their Zr-TNDI counterpart, which features a single 4-c hexanuclear cluster and structural interpenetration, the RE-TNDI MOFs possess dual molecular building blocks: an 8-c hexanuclear cluster (RE6) and a 4-c mononuclear RE center. This discovery challenges the notion that dual-cluster formation arises solely from a linker asymmetry, showing that a symmetric rigid TNDI linker can also give rise to such structural heterogeneity. Building on this structural ingenuity, we investigated the Eu-TNDI MOF for the rapid and visual detection of volatile organic amines, chemicals with well-documented health hazards. The MOF displayed an almost 100% quenching efficiency. Interestingly, the MOF exhibits photochromic behavior upon exposure to visible light due to the formation of radicals, as confirmed by EPR. When embedded in a mixed-matrix membrane, this MOF exhibits remarkable colorimetric changes upon exposure to amines, transforming molecular design into an effective strategy for real-time detection. This work underscores the crucial role of metal and ligand selection as well as the structural characteristics of RE MOFs in driving advancements in both materials science and environmental monitoring.