A highly selective Schiff base fluorescent sensor for Zn2+, Cd2+and Hg2+based on 2,4-dinitrophenylhydrazine derivative

In pharmacological, environmental, biological, and material research, the design and synthesis of new fluorescence chemosensors based on Schiff base derivatives are crucial. To assess its selective detection of Zn2+, Cd2+ and Hg2+ ions, respectively, a novel 2,4-dinitrophenyl hydrazine-based Schiff base (L) was designed and characterized. In DMSO-H2O (10:90, v/v), the probe L envisages a very weak fluorescence emission due to isomerization of the C--N bond and the photoinduced electron transfer (PET) processes. Intriguingly, upon the addition of Zn2+, Cd2+ and Hg2+ ions to the solution of L, enhancement of fluorescence emission is observed. However, the probe remains silent in the presence of other ions. As a result, probe L serves as a unique chemosensor for the ions Zn2+, Cd2+ and Hg2+. The receptor L acts as a ratiometric pH sensor due to the different pH response and the dramatic change in emission color in presence of Zn2+, Cd2+ and Hg2+ ions from pH-2 to pH-10. The responses were observed in naked eye and also observed in UV-vis lamp at 365 nm. The binding stoichiometry for the L: Zn2+, Cd2+ and Hg2+ complexes were determined using the Benesi-Hildebrand plot and was discovered to be 1:1 ratio. The binding stoichiometry was validated using DFT and TD-DFT. The binding constant and detection limits are 1.10 x 107 M-1 and 1.66 x 10-8 M for Zn2+ complexes, 2.62 x 107 M-1 and 7.56 x 10-8 M for Cd2+ complexes and 3.34 x 107 M-1 and 2.11 x 10- 7 M for Hg2+ complexes, respectively. This provides a very efficient and simple method of determining the levels of Zn2+, Cd2+, and Hg2+ in real samples and living organisms. These sensing abilities were used for imaging living cells and as test strips for detecting Zn2+, Cd2+, and Hg2+.