Luminescent Coordination Polymer with Extreme-Sensitive MnO₄^- and Acid-Sensing Capacity

MnO₄^- and environmental acidification threaten human health, biodiversity, and ecosystem stability. This necessitates dual-function sensors to simultaneously monitor MnO₄^- and acid. Herein, the carbazole-containing ligand 2,7-di(pyridin-4-yl)-9H-carbazole (L) is first applied to construct coordination polymers, which gives rise to a new one-dimensional (1-D) luminescent coordination polymer (LCP) [Cd(L)I₂·DMAC]_n (1). 1 exhibits a zigzag-like chain architecture, which is hydrogen-bonded to DMAC molecules. The carbazole moieties from adjacent chains exhibit face-to-face stacking. 1 has good water, pH, and thermal stability, and exhibits dual-responsive sensing capability toward MnO₄^- (single-emission detection) and acid (ratiometric fluorescence detection). This dual-responsive sensor via both single-emission and ratiometric fluorescence signals is first found. Notably, 1 achieves the lowest limit of detection (2.85 nM) in all LCP-based "turn-off" MnO₄^- sensors; therefore, it demonstrates extreme-high MnO₄^- sensing sensitivity. Furthermore, 1 exhibits a ratiometric fluorescence response to inorganic acids (HCl, HNO₃, HF) and organic acids (TFA). This feature enables naked-eye discernible color changes. The detection sensitivity of 1 reaches 800% per pH, which surpasses those of the most reported ratiometric sensors. Finally, the sensing mechanisms of 1 toward MnO₄^- and acid are explained by experimental and theorical methods.