Selective and sensitive sensing of Hg2+ and furazolidone antibiotic using flexible anthracene based sensor

A new fluorescent anthracene based probe, 9,10-bis((pyridine-2-ylthio)methyl)anthracene (ANSN) with 2-mercaptopyridine as receptor at 9 and 10 positions has been synthesized. ANSN selectively and sensitively detects the presence of toxic Hg²⁺ ion and furazolidone (FZD) antibiotic in water via turn off mechanism with detection limits of 0.80 μM and 0.12 μM, respectively. The sensor was characterised by ¹H NMR, ¹³C NMR and single crystal X-ray diffraction techniques. The ANSN crystallizes in monoclinic crystal system with C2/c space group and the pyridine-2-ylthio group adopts the anti-conformation with reference to the plane of anthracene unit. The removal of Hg²⁺ is very important as it is one of the toxic heavy metal presents on the earth that occurs in three forms-elemental, organic and inorganic. The stoichiometry and the interaction of Hg²⁺ with ANSN was examined by job plot and FT-IR spectroscopy, stating that the complex exists in 1:2 stoichiometric ratios. The lowering of stretching band of imine bond (C=N) at 1647 cm⁻¹ in free ANSN to 1609 cm⁻¹ in Hg²⁺ complex clearly demonstrated that the ligand interacts with Hg²⁺ by nitrogen atom. Moreover, the stability of the complex was inferred by DFT calculations. The fluorescence quenching of ANSN by FZD was explained by photoinduced electron transfer (PET). The anti-interference experiments suggested that present probe has good selectivity for both the quenchers. This study concludes that ANSN can be easily and widely used as a promising sensor for sensitive and selective detection of FZD and Hg²⁺ ion in water samples.