Luminescent Sm(III) complex bearing dynamic imine bonds as a multi-responsive fluorescent sensor for F and PO anions together with Zn cation in water samples.

We have designed and synthesized a new luminescent mononuclear samarium (III) complex Sm-2 based on the [1 + 1] Schiff-base macrocycle HL2, derived from the cyclocondensation reaction between dialdehyde and diamine precursors, and its exact architecture is determined to be [Sm(HL2) (NO)]. The sensing ability of complex Sm-2 is carefully evaluated for various common inorganic ions in solution. It is shown that complex Sm-2 is a multi-responsive fluorimetric sensor with high selectivity for F and PO anions together with Zn cation. The sensing process is rapid within 60 s for F and PO ions and 300 s for Zn ion. Further detailed responsive investigations suggest that its sensing behavior has excellent linear relationship between the fluorescence intensity (or absorption value) and ion concentration. The limit of detection (LOD) for sensing F, PO and Zn ions are as low as 2.61 μM (2.94 μM), 1.92 μM (1.64 μM) and 5.67 μM (3.53 μM), respectively, verified by fluorimetric (or colorimetric) titration experiments. ESI mass spectra prove that these efficient detections originate from the structure collapse of sensor Sm-2 because of the ion-induced imine bond breakage. Moreover, sensor Sm-2 shows excellent sensing performances for F, PO and Zn ions in real water samples, and we also have developed a convenient method to detect these three ions by use of the sensor impregnated test paper strips, providing rapid and distinguishable fluorimetric color changes. Therefore, the macrocyclic Sm(III) complex Sm-2 could be regarded as a valuable candidate for monitoring F, PO and Zn ions in practical applications.