Dual responsive pyridoxal-AHMT based fluorescent sensor towards zinc() and mercury() ions and its bioimaging application

A novel dual responsive probe based on the pyridoxal-AHMT moiety was designed for fluorescence detection of Zn 2+ and Hg 2+ ions in HEPES buffer (pH = 8.0) (DMSO : water (1 : 1, v/v)) medium. The existence of the enol-thione tautomeric form of the probe was elucidated by single crystal XRD analysis. The excited state intramolecular proton transfer (ESIPT) mechanism and weak π-π interactions between aromatic rings in the probe may collectively contribute to the highly yellow fluorescence characteristic in solid state ( λ em = 540 nm). The fluorescence selectivity and sensitivity studies showed that the probe is highly responsive towards Zn 2+ and Hg 2+ ions over other studied metal ions. The fluorescence lifetime analysis was performed in solid and solution state for understanding the emission properties. The quantum chemical (DFT/TD-DFT) studies also supported the binding modes of Zn 2+ /Hg 2+ with the probe as interpreted by 1 H NMR titration. These studies were also performed to predict the proposed sensing mechanism. Further, the efficiency of the probe in sensing both Zn 2+ and Hg 2+ ions was also evaluated in the A549 cell line. In this current investigation, pyridoxal-AHMT based probe ( L ) was designed to detect Zn(II) and Hg(II) in solid/solution medium, and intracellular Hg(II) ions in A549 cell lines.