“Turn–on” benzophenone based fluorescence and colorimetric sensor for the selective detection of Fe2+ in aqueous media: Validation of sensing mechanism by spectroscopic and computational studies

Abstract

A diaminobenzophenone Schiff base derived probe 1, was synthesized and structure elucidation was carried out by spectroscopic studies viz., FT–IR, UV–vis, 1H, and 13C NMR and mass spectrometry. The sensing phenomenon with different metal ions (Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+) was investigated by employing absorption and fluorescence titrations, which demonstrated that probe 1 exhibited selective fluorescent sensing behavior towards Fe2+ ion among various other metal ions. The porobes selceteclivity towards Fe2+ was also examined by colorimetric assay which revealed a change in the color from light yellow to brown upon addition of Fe2+ ion. A remarkable increase in the fluorescence intensity of probe 1 was observed towards Fe2+ ion, which was found to be associated with the inhibition of photoinduced electron–transfer (PET) and CN isomerization processes, respectively. The chemosensor exhibited an association constant value of 6.173 × 107 M−2 as determined by using non–linear least square fit data. Job’s plot calculated the binding stoichiometry, and the sensing phenomenon of Fe2+ towards the probe was further supported by Density Functional Theory (DFT) calculations and 1H NMR studies. The detection limit of probe 1 was found to be 0.0363 µM, which is below the permissible limits according to the WHO guideline (5 μM) for Fe2+ ions in the drinking water. Furthermore, the practical application of probe 1 was studied by analyzing the content of Fe2+ in different water samples.