Iminothiophenol Schiff base-based fluorescent probe for dual detection of Hg2+ and Cr3+ ions and its application in real sample analysis

Abstract

A new diphenylimidazole based fluorescent probe bearing the 2-aminothiophenol moiety (5) was designed and synthesised, which is showing dual-sensing behaviour for Hg2+ and Cr3+ ions in semi-aqueous CH3CN-H2O (8:2, v/v) solution and was successfully utilised to detect both analytes in environmental water samples. In addition, fluorescence bio-imaging in E-coli bacteria was also done. Upon addition of Hg2+ and Cr3+ ions, probe 5 showed 59 nm blue shift in fluorescence emission (from 494 to 435 nm). The analytical limit of detection was estimated to be 6 nM for Hg2+ and 1.96 nM for Cr3+, respectively. The detection of Hg2+ and Cr3+ by probe 5 is due to ion-induced complex formation with imine nitrogen (–CHN)). Moreover, thiol (-SH) moiety of 5 is also helping in the complex formation and the binding mode was proposed as 1:1 stoichiometric between Hg2+/Cr3+ ions and probe 5. Most importantly, compound 5 is a pH-independent fluorescent probe in the wide pH range of 6.0 to 12.0, and it can be used as a probe for dual sensing of Hg2+ and Cr3+ ions in primary conditions. These results imply new possibilities for constructing a new colorimetric and ratiometric response with a blue-shift in absorption and emission spectra of sensor 5.