A Novel Rhodamine-Benzimidazole Conjugate as a Highly Selective Turn-on Fluorescent Probe for Fe 3+

In this manuscript, a novel probe RHBI based on the rhodamine-benzimidazole conjugate was designed and synthesized. RHBI showed an extreme selectivity for Fe 3+ over other metal ions such as Pb 2+ , Ni 2+ , Co 2+ , Mn 2+ , Zn 2+ , Hg 2+ , Cd 2+ , Ag + , Mg 2+ , Ca 2+ , Ba 2+ , Na + and K + in acetonitrile. Upon the addition of 10 equiv. of Fe 3+ , a 1098-fold fluorescence intensity enhancement was observed at the maximum emission wavelength of 582 nm. Both the Job’s plot and ESI-MS showed that RHBI coordinated with Fe 3+ in a 1:1 stoichomitry and the calculated binding constant was 1.01 × 10 4 M −1 . The competition experiment for Fe 3+ ions mixed with other metal ions exhibited no obvious change except Cu 2+ that could induce a mild fluorescence quenching. Moreover, the fluorescence emission increased linearly with the Fe 3+ concentration in the range of 6 × 10 −6 –4 × 10 −5 M and the detection limit was 1.5 × 10 −8 M.