Morphological adaptability through structural alterations in an AIE active novel chemosensor with Al(iii), Fe(iii), and gas phase/aqueous phase TNP recognition ability

Abstract

Aggregation-induced emission (AIE) active compounds have attracted tremendous interest due to their unique properties of restriction of intramolecular rotations, which leads to the generation of luminescence in these compounds. Here we have successfully developed a novel AIE active fluorescent probe H₂L [(E)-2,4-dibromo-6-(((5-chloropyridin-2-yl)imino)methyl)phenol] with Al(III), Fe(III), and aqueous and gas phase picric acid detection ability. UV, fluorescence, and DLS studies are implemented to give solid proof of the AIE active behavior of the probe. Optical, SEM, and TEM images clearly prove the morphological adaptability of the probe through structural alterations with the variation of water percentage. It shows AIE active behavior in DMSO–H₂O (3 : 7 v/v) solutions. One remarkable and noteworthy observation is that the ligand's morphology and emission intensity are altered by the presence of water with varying percentages (10–70%) when the AIE activity is taken into account. This results in the appearance of two distinct optical color changes and emission intensity changes within the 10–70% water percentage range. The probe becomes emissive in the solid state due to the intermolecular H-bonding and keto–enol tautomerism. Interestingly in 9 : 1 (v/v) DMSO–H₂O solvent H₂L can selectively detect Al(III) through turn-on fluorescence. In the AIE active medium, it can selectively detect Fe(III) and picric acid by turning off fluorescence. The ESIPT process in the solid state leads to molecular aggregation, resulting in the generation of strong luminescence in the probe, and impressively the solid state fluorescence is used to detect picric acid in the vapor phase. The LOD values are determined as 6.02 × 10⁻⁹ (M) for Al(III), 7.5 × 10⁻⁹ (M) for Fe(III) and 6 × 10⁻⁸ (M) for picric acid. During Al(III) sensing the ESIPT off and “CHEF” on mechanisms jointly operate leading to emission enhancement, whereas during Fe(III) sensing and picric acid sensing the destruction of the aggregation state is mainly responsible for the reduction of emission intensity of the probe. Impressively the probe can detect picric acid in the solid state also. The Job plot analysis of the UV spectral data and the mass spectral analysis support the 1 : 1 stoichiometry complexation between the probe and the analytes. Moreover, the proposed analytical system with its clear AIEE mechanism demonstrates a promising prospect for on-site practical applications. Finally, the probe's ability to detect and quantify Al(III) in the market-available drug samples has been checked.