A new selective chemosensor based on phenanthro[9,10-d] imidazole-coumarin with sequential “on-off-on” fluorescence response to Fe3+ and phosphate anions and its application in live cell

A phenanthro[9,10-d]imidazole-coumarin fluorescence sensor, N-(3-(1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetamide (PICA), has been synthesized and successfully achieved for the efficient detection for Fe3+ as a turn-off chemosensor in DMF/HEPES aqueous buffer (1:1, v/v, 10 mM, pH = 7.4). The detection of limit (LOD) for Fe3+ on fluorescence response of the sensor can be as low as 4.8 μM, which was successfully applied for the determination of the Fe3+ concentration in the real sample waters. The quenched 1:1 PICA–Fe3+ complex was found to subsequently act as a selective turn-on fluorescence sensor for phosphate anions against common anions and cations in the same condition with a displacement approach. The proposed mechanism of the “on-off-on” fluorescence response was further verified by 1H NMR and ESI-MS. Moreover, an imaging application of PICA for Fe3+ and phosphate anions in live cells was developed by fluorescence microscopy.