Development of ferrocene‐appended benzimidazopyridine and pyrroloquinoxaline probes for structure regulated distinct signalling of Fe3+ in aqueous media and HeLa cells

Abstract Two ferrocenyl (Fc) derivatives Fc‐benzimidazopyridine ( 5 ) and Fc‐pyrroloquinoxaline ( 6 ) have been synthesized through an inexpensive and metal‐free approach and via tailoring the reaction conditions. X‐ray single crystal analysis revealed that same reactants in the presence of different reagents and reaction condition afforded structurally distinct products 5 and 6 . Markedly, 5 and 6 act as fluorescent probes for Fe 3+ through discrete signalling with high selectivity and ppb level sensitivity. Based on the fluorescence changes, Job's plot, 1 H NMR titration and mass spectral studies, it has been proposed that the probe‐metal binding stoichiometry and nitrogen atoms present at different positions in 5 and 6 lead to the distinct fluorescent signalling ( turn‐on for 5 and turn‐off for 6 ). Further, it has been observed that position of donor atom plays major role in fluorescence signalling and probe‐cation stoichiometry. This work reports deeper insights and straightforward comparison between 5 and 6 in terms of exactly opposite fluorescence detection behaviour towards Fe 3+ in aqueous media as well as cell lines to the best of our knowledge.