Structural Insights into Luminescent Zn(II) Materials for Picric Acid Detection

One luminescent octanuclear porous Zn(II) complex, C1, and another luminescent Zn(II) coordination polymer, C2, have been synthesized by using a salen-type Schiff base ligand H₂L and terephthalic acid (H₂BDC). C1 exhibits a unique single-molecule porous structure, comprising eight Zn(II) centers in a distorted square-shaped architecture. In contrast, C2 features two Zn(II) centers with distinct geometries, adding diversity to its structure. This difference in geometry creates an intriguing structural feature in the complex. Both complexes demonstrate exceptional sensing capabilities, enabling swift and selective detection of picric acid (PA) in aqueous and vapor phases. The detection mechanism involves fluorescence quenching, with a nanomolar detection limit. The quenching process occurs through a joint operation of photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), intermolecular charge transfer (ICT), and the inner filter effect (IFE) mechanism.