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

A novel dual responsive probe based on the pyridoxal-AHMT moiety was designed for fluorescence detection of Zn2+ and Hg2+ 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 pi-pi interactions between aromatic rings in the probe may collectively contribute to the highly yellow fluorescence characteristic in solid state (lambda(em) = 540 nm). The fluorescence selectivity and sensitivity studies showed that the probe is highly responsive towards Zn2+ and Hg2+ 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 Zn2+/Hg2+ with the probe as interpreted by H-1 NMR titration. These studies were also performed to predict the proposed sensing mechanism. Further, the efficiency of the probe in sensing both Zn2+ and Hg2+ ions was also evaluated in the A549 cell line.