A multifaceted ferrocene-benzobisimidazole derivative: fluorogenic probe for Pb2+ and Zn2+ cations and unconventional fluorescence behaviour towards Cu2+ metal cations

Abstract

The ferrocene-benzobisimidazole derivative 1 shows high affinity for Pb²⁺ and Zn²⁺ metal cations over a range of other metal cations examined. In the presence of Pb²⁺ the emission spectrum is red-shifted by 13 nm with an important chelation-enhanced fluorescence effect (CHEF) CHEF = 55. The presence of Zn²⁺ cations also induced a perturbation of the emission spectrum although to a lesser extent than that found for Pb²⁺ cations (CHEF = 37). Upon complexation with Cu²⁺ cations, not only is the emission band red-shifted (Δλ = 67 nm) with a noticeable CHEF = 20, but also the maximum of such fluorescence emission exhibits a concomitant shift towards higher wavelengths when the excitation wavelength is gradually shifted to the red-edge of the absorption band (red-edge effect).