Pyridine-hydrazone-based charge-transfer probe for detecting Cu²⁺ and Co²⁺ ions in aqueous solutions

In the field of environmental monitoring, there remain considerable challenges regarding the development of selective chemosensors with high sensitivity for detecting transition metal ions in aqueous media. In this study, we prepared and investigated 1,3-bis((2-((E)-(2-(pyridin-2-yl)hydrazineylidene)methyl)-1H-pyrrol-1-yl)methyl) benzene as a pyridine-hydrazone-based probe (receptor A) for the selective detection of metal ions. Upon interacting with Cu²⁺ and Co²⁺ ions, the probe responded with significant optical changes, thereby facilitating simple ion detection. The ultraviolet-visible absorption maximum of the receptor A underwent a remarkable hypsochromic shift to 291 nm upon the addition of Cu²⁺ solution, while the addition of Co²⁺ solution led to a bathochromic shift to 426 nm. Receptor A was capable of selectively detecting Cu²⁺ and Co²⁺ in aqueous solutions without any marked interference from other metal ions, with respective limits of detection of 2.12 × 10^-6 and 3.47 × 10^-8 M, which are significantly lower than the WHO guidelines. The ability of receptor A to detect Cu²⁺ and Co²⁺ in real water samples was also demonstrated. These findings highlight the potential utility of pyridine-hydrazones as an effective probe for real-time monitoring of Cu²⁺ and Co²⁺ ions in environmental samples.