Some new compounds based on bis-benzimidazole moieties have been synthesized and characterized by IR and NMR spectroscopies. The ability of 3a in transition metal cation sensing such as Co2+, Ni2+, Zn2+, Mn2+, Fe2+ and Cu2+ have been investigated by UV-Vis and fluorescence spectroscopy in methanol solvent. The complexation constants and complex stoichiometry of Cu2+ have been determined. The experimental result shows that 3a exhibits high selectivity toward Cu2+ cation in a 1:1 complex stoichiometry. The absorption bond and the fluorescence intensity have been increased by addition of successive amount of Cu2+ solution in methanol. Therefore, these results demonstrate that, the compound can be used as a sensor to detect Cu2+ cation via absorption and emission spectroscopy.

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