Schiff Base Derived from 4,4'-methylenedianiline and p-anisaldehyde: Colorimetric Sensor for Cu2+, Paper Strip Sensor for Al3+ and Fluorescent Sensor for Pb2.

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 104.8 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.