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.