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

Abstract

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 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 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 ¹H 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.