A multifunctional Schiff-base as chromogenic chemosensor for Mn2+ and fluorescent chemosensor for Zn2+ in semi-aqueous environment

Abstract

In this communication, a new multifunctional Schiff-base (S) obtained by reacting hydrazine with 3,5-dichloro-salicylaldehyde. The sensing ability of S was studied with various metal ions by visual test, UV–Vis and spectrofluorometric techniques in THF:H2O (1:1, v/v) media. Accordingly, visual test was confirmed by changing initial colourless solution of S to yellow upon interaction with Mn2+ while for other ions, it did not respond in natural light. However, same solution composition when it was observed under UV light, it exhibits green fluorescent colour with Zn2+. In order to see more photo physical properties of S-Mn2+ and S-Zn2+ are studied through by spectrophotometric and spectrofluorometric methods respectively. Spectrophotometrically, neat S exhibits a strong absorption band at 365 nm upon interaction with Mn2+, it exhibits a new absorption band at 425 nm. Spectroflurometrically, a new emission peak was observed at 500 nm upon excitation of S-Zn2+ at 390 nm while other metal ions did not exhibit any emission properties. Further, the formation 3:2 binding stoichiometry between S with Mn2+ and Zn2+ were studied by using Job’s plot and association constant for were estimated by Benesi-Hilderbrand (BH) method. The detection limit of S for Mn2+ and Zn2+ were found to be 3.6 × 10−7 M and 9.2 × 10−8 M respectively, which is much lower than the WHO guidance of their metal ions in drinking water. The coordination behaviour of S with Mn2+ and Zn2+ are well supported by NMR and theoretical calculations.