Two ‘turn-off’ Schiff base fluorescence sensors based on phenanthro[9,10-d]imidazole-coumarin derivatives for Fe3+ in aqueous solution
Two isomeric Schiff bases fluorescence sensors (PIC1 and PIC2) based on phenanthro[9,10-d]imidazole-coumarin derivatives were designed, synthesized and characterized, which both represented the selective ‘turn-off’ fluorescence phenomenon caused by paramagnetic quenching effect of Fe3+ with the formation of 1:1 sensor-Fe complexes in DMF/HEPES aqueous buffer (7:3, v/v, 10 mM, pH = 7.4). Although free PIC1 and PIC2 exhibited distinctive pH responses, they could be applied to detect Fe3+ in most biological systems. Furthermore, the detection limits of PIC1 and PIC2 for Fe3+ were calculated by the fluorescence titration to be 4.28 μM and 0.83 μM, respectively, and the determination of Fe3+ concentration in the real sample waters had been applied successfully. The possible mechanism of the fluorescence detection of Fe3+ had been proposed according to the analysis of Job’s plot, 1H NMR, and ESI-MS.