Chalcone-based Turn-Off Chemosensor for Selective and Susceptible Detection of Fe(2+) Ions: Spectroscopic and DFT Investigations.

Herein, in this report we are introducing newly synthesized chalcone derivative, "(E)-1-phenyl-3-(4-((5-(((Z)-thiophen-2-ylmethylene)amino)-1,3,4-thiadiazol-2-yl)thio)phenyl)prop-2-en-1-one" (5), as a chemosensor to detect Fe metal ions in HEPES buffer solution of pH 7.5. Spectroscopic techniques were used to confirm the synthesized sensor. To determine the chemical reactivity and molecular stability of the probe, a frontier molecular orbitals investigation was carried out. A molecular electrostatic potential map was investigated to know the binding site of 5 for metal ion coordination. The theoretical absorption and fluorescence emission properties were estimated and correlated with the experimental observations. The sensor showed excellent selectivity for Fe compared to all other studied metal ions. The fluorescence binding studies were carried out by adding different amounts of Fe ions for a fixed concentration of probe 5. The inclusion of Fe ions resulted in a decrease in fluorescence intensity with a bathochromic shift of emission wavelength of 5 due to the 5-Fe complexation. The binding affinity value for the probe was found to be 576.2 M with the help of the Stern-Volmer plot. The Job's plot and mass spectra supported the 2:1 (5: Fe) stoichiometry of complex formation. The detection limit and limit of quantification of 5 for Fe were calculated to be 4.79 × 10 M and 14.54 × 10 M. Further, in addition to this, the photophysical parameters such as fluorescence lifetime of 5 and 5-Fe complex measured to be 0.1439 and 0.1574 ns. The quantum yield of 5 and 5-Fe was found to be 0.0398 and 0.0376. All these experimental findings revealed that probe 5 has excellent selectivity and sensitivity for Fe ions.