A novel benzidine based Schiff base “turn-on” fluorescent chemosensor for selective recognition of Zn^sup 2

A novel chemo-sensor based on diaminobenzidine (H2L) was synthesized and characterized. The chemo-sensor shows selective “turn-on” fluorescence response to Zn2+ ion over a variety of other competing metal ions such as Al3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Cd2+. The strong fluorescent emission can be observed even at ppm level concentration of the probe in the presence of Zn2+ with over 54 fold intensity enhancement at 509 nm. Similar fluorescence behaviour is also observed in a variety of solvents and solvent mixtures in the presence of zinc(II). The fluorescent emission is also detected when the H2L sample solution containing Zn2+ is exposed to UV radiation. The sensitive nature of fluorescent response of the probe to Zn2+ is gauged from the very low detection limit of 8.6 × 10−9 M. The chemo-sensor H2L binds to zinc(II) in 1:1 stoichiometry as determined by Job's plot and the binding constant is calculated as 7.8 × 104 M−1.