Guest-Dependent Luminescent Gallium Metal–Organic Framework for Ultrasensitive Detection of Nerve Agent Simulant

Metal–organic frameworks (MOFs) offer a structurally tunable platform for luminescent sensing, where both the pore environment and ligand conformation may play key roles in governing photophysical behavior. Herein, we report a porous Ga-based MOF (SNNU-130) constructed from a conformationally flexible perylene diimide (PDI) derivative for ultrasensitive detection of the nerve agent simulant diethyl chlorophosphate (DCP). SNNU-130 exhibits pronounced solvent-dependent emission, with fluorescence decreasing with solvent polarity in aprotic media but increasing in protic solvents. This contrasting behavior gives rise to a rare polarity-regulated fluorescence “turn-on” response toward DCP, most notably in acetone, where the material achieves an ultralow detection limit of 0.98 ppb and an extrahigh apparent enhancement constant of 1.24 × 106 M–1. Mechanistic studies suggest that DCP most likely acts as a pore-confined functional guest, perturbing the local conformation and packing of the PDI linkers and thereby modulating the excited-state relaxation behavior of the framework, making fluorescence emission more favorable. These findings establish a guest-modulated conformation-driven sensing mechanism and provide a foundation for designing next-generation MOF-based fluorescent probes for nerve agent detection.