The turn-off fluorescent sensors based on thioether-linked bisbenzamide for Fe 3+ and Hg 2+

Some dibenzamide derivatives with a thioether linker were designed, synthesized and characterized. The specific responses to Hg2+ and Fe3+ were investigated by fluorescence. According to fluorescence titration, the Job plot, 1H NMR, and ESI-mass analysis, the derivative with mono-hydroxyl substituent (1b) on the aromatic ring has high selectivity for Fe3+ ion with the formation of 1:1 1b-Fe3+ complexes. The specificity of 1c for Hg2+ could be switched by swapping the substituent from hydroxyl to amino, and a 1:2 (1c-Hg2+) complex was formed. Along with the obtained results, density functional theory (DFT) and natural bond orbital (NBO) analyses, Time-dependent (TD) DFT and natural transition orbital (NTO) analyses were employed to explore the geometric structures, properties and possible mechanisms.