Experimental and theoretical studies of a colorimetric cu²⁺ chemosensor in aqueous solution

We have synthesized a new colorimetric chemosensor 3-(E)-4-(E)-phenyl imino methyl (pheny limino methyl) benzene-1,2-diol (1) based on a combination of 4-aminoazobenzene and 2,3-dihydroxybenzaldehyde. Receptor 1 showed a selective color change from colorless to yellow in the presence of Cu²⁺ in CH3CN/bis-tris buffer solution (v/v, 1:1), while other metal ions such as Al3+, Zn²⁺, Cd²⁺, Cu²⁺, Fe²⁺, Mg²⁺, Cr3+, Ag+, Co²⁺, Ni²⁺, Na+, K+, Ca²⁺, Mn²⁺ and Pb²⁺ had no influence. The detection limit (31 M) of 1 for Cu²⁺ was comparable to that (31 M) recommended by WHO in drinking water. The formation of 1-Cu²⁺ complex was proposed to be a 1:1 ratio, based on Job plot. Moreover, the sensing mechanism of Cu²⁺ by 1 was supported by theoretical calculations.