Pore-Space-Partition Enabled Through-Space-Charge-Transfer in Metal–Organic Frameworks for Enhanced Sarin Simulant Recognition

Abstract

While through-space charge transfer (TSCT) is proven as an effective mechanism for achieving dynamic and environment-sensitive luminescence in rigid U-shaped small-molecule systems, the rational design of TSCT-based materials keeps challenging. Herein, the pore-space-partition (PSP) strategy is proposed to precisely arrange donor–acceptor units within magnesium-based MOFs (SNNU-265 to SNNU-267), constructed by co-assembling tris(4-(pyridin-4-yl)phenyl)amine (TPPA) with amino-functionalized biphenyl dicarboxylates. These dual-ligand MOFs exhibit confined donor–acceptor alignment in narrow channels, facilitating TSCT-based fluorescence and sensing. As expected, upon exposure to the sarin simulant diethyl chlorophosphate (DCP), protonation of amino groups in SNNU-266 and SNNU-267 forms localized ─NH3+ acceptor sites, triggering TSCT from the electron-rich TPPA donors to the carboxylate-based acceptors. This electron redistribution induces pronounced red-shifted fluorescence quenching in both solution and vapor phases. Specially, SNNU-266 and SNNU-267 exhibit ultralow detection limits (0.017–0.025 ppm in solution; 0.04–0.08 ppm in vapor), rapid response (<10 s), high selectivity, and full recyclability. The 1H NMR titration, in situ FT-IR spectroscopy, and DFT calculations confirm that this TSCT mechanism is protonation-induced and confined within the rigid MOF lattice. Overall, this work demonstrates a simple and universal strategy for rational control of through-space charge transfer in MOFs, which enables a super-real-time detection ability for nerve agent simulants.