A simple organic probe for ratiometric fluorescent detection of Zn(II), Cd(II) and Hg(II) ions in aqueous solution via varying emission colours to distinguish one another.

A bis (thiosemicarbazone) based probe has been synthesized and structurally characterized. The probe exhibits good selectivity towards Zn(II), Cd(II) and Hg(II) ions in an aqueous solution containing 95% water with ratiometric fluorescence changes. The modes of coordination of the probe with these metal ions and binding properties have been examined using different spectral techniques. The binding constants, determined using fluorescence titration data, are found to be 9.8 × 10, 1.39 × 10 and 2.03 × 10 M, respectively for Zn(II), Cd(II) and Hg(II) complexes. The high sensitivity of the probe has been demonstrated by the very low limit of detection i.e. 5.1, 3.4 and 0.51 μM for Zn(II), Cd(II) and Hg(II) ions, respectively. Different coordination mode of these metal ions with the probe has resulted in varying intra-ligand fluorescence (λ nm, Zn(II): 488, Cd(II): 470 and Hg(II): 578) among these metal complexes.