Indole-imidazole hybrid Schiff base for the selective detection of the explosive picric acid via fluorescence “turn-off” process: Experimental and theoretical DFT-D3 study

Abstract

A compound containing a heteroatom and Schiff base, 3-(4,5-Diphenyl-1H-imidazol-2-yl)-1H-indole (INBIL) has been synthesized through the one-pot condensation of indole-3-carbaldehyde with benzil in ethanol and characterized using various analytical parameters like FT-IR, NMR; its thermal and chemical stability also established. The synthesized INBIL showed a 'turn off' luminescent property that has been used to detect picric acid. This luminescent sensor has a broad emission band at 415 nm in acetonitrile due to the conjugation of its double bond. It is worth noting that INBIL can be recycled through TEA treatment. The chemosensor exhibited the highest sensitivity with Ksv = 1.51 × 10−6 M, and a detection limit of 2.91 × 10−7 M, with perfect linearity up to 22 µL. The binding stoichiometry ratio between INBIL and picric acid was predicted to be 1:1 using Job's plot, which was confirmed by 1H NMR analysis. Finally, DFT-D3 calculations were used to calculate the excited molecule's singlet and triplet energy states.