Schiff Base Derived from 4,4'-methylenedianiline and p-anisaldehyde: Colorimetric Sensor for Cu²⁺, Paper Strip Sensor...

The condensation product (L) of 4,4'-methylenedianiline and p-anisaldehyde acts as colorimetric sensor for Cu²⁺ and Pb²⁺ ions. On interaction with Cu²⁺, ethanolic solution of L changes its color to brown while it becomes light pink on interaction with Pb²⁺. Interaction of Al³⁺ with L coated paper strip emits bright blue fluorescence. Metal ions like Mg²⁺, Cu²⁺, Li⁺, K⁺, Na⁺, Mn²⁺, Al³⁺, Hg²⁺, Co²⁺, Pb²⁺, Ni²⁺, Cd²⁺, Zn²⁺, Fe³⁺ do not interfere the paper strip sensor. The fluorescent intensity of L in ethanol is quenched 25 times by Pb²⁺ ion. The interaction between L and Pb²⁺ is reversible and the detection limit of Pb²⁺ is 10^-6 M. The binding constant and stoichiometry of binding between L and Pb²⁺ was calculated to be 10^4.8 and 1:2. Theoretical calculations show that the binding of the metal ions to L are favorable and the fluorescence of L is due to π → π* transition.