| Summary: | Reactions of ZnSO<sub>4</sub>∙7H<sub>2</sub>O, <i>N</i>-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H<sub>2</sub>bdc) afforded a luminescent coordination polymer, [Zn(Br-1,3-bdc)(NI-mbpy-34)]<i><sub>n</sub></i> (<b>1</b>), under hydro(solvo)thermal conditions. Single-crystal X-ray structure analysis revealed that <b>1</b> features a three-dimensional (3-D) 2-fold interpenetrating <b>cds</b> (or CdSO<sub>4</sub>) net topology with the point symbol of (6<sup>5</sup>·8), where the Zn(II) centers are considered as 4-connected square-planar nodes. X-ray powder diffraction (XRPD) patterns and thermogravimetric (TG) analysis confirmed that <b>1</b> shows high chemical and thermal stabilities. Notably, <b>1</b> displayed solvent dependent photoluminescence properties; the fluorescence intensity and emission maximum of <b>1</b> in different solvent suspensions varied when a solvent was changed. Furthermore, the H<sub>2</sub>O suspension of <b>1</b> exhibited blue fluorescence emission and thus can be treated as a selective and sensitive fluorescent probe for turn-on detection of Cr<sup>3+</sup> cations through absorbance caused enhancement (ACE) mechanism and turn-off detection of Cr<sub>2</sub>O<sub>7</sub><sup>2−</sup>/CrO<sub>4</sub><sup>2−</sup> anions through collaboration of the absorption competition and energy transfer process, with limit of detection (LOD) as low as μM scale.
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