Exploration of solvent responsive Cr 3+ -Schiff base conjugates formonitoring Cr 3+ ions and organophosphates: Fabrication of spot-testingdevices.

Herein, we report 2-((2-hydroxybenzylidene)hydrazono)(phenyl)methyl)-5-methoxyphenol (SB) synthesized by Schiff base condensation and characterized by spectroscopic techniques, elemental analysis and X-ray crystallography. In solution phase, it interacts with Cr3+ ions and exhibits a prominent fluorimetric switch due to the formation of SB·Cr3+ conjugate. The dual behavior of SB·Cr3+ conjugates i.e. self-aggregation in high water fraction (fw  > 50%) and dissolution in low water fraction (fw  < 50%) proves this conjugation excellent tool for monitoring Cr3+ ions. The SB·Cr3+ conjugate in methanol-water (70:30 v/v) allows quantification of Cr3+ ions with limit of detection 0.44 μM and its self-aggregation in high water fraction facilitates extraction of Cr3+ ions with 95% extraction efficiency. Although SB interacts with Zn2+ ions which causes inference in the determination of Cr3+ ions however the interferent can be easily masked with SCN- ions. Besides, the SB·Cr3+ conjugates are also able to quantify organophosphate neurotoxins; i.e. diethyl chlorophosphate (with LOD 4.1 nM) and diethyl cyanophosphonate (with LOD 3.3 nM) from aqueous solutions. Moreover, SB and SB·Cr3+ conjugates can be coated on solid surfaces to fabricate portable devices for the on-spot detection of targets from real samples. Hence, the conjugation of Schiff base and Cr3+ ions can be explored for the recognition, quantification and extraction of Cr3+ ions and detection of organophosphates.