Colorimetric probing and fluorescent chemosensor features of functionalized sulphonamide-azomethine derivatives

Abstract

In this work, we have experimentally synthesized bromosulfonamide-based azomethine compounds through the reaction of 4-bromobenzenesulfonamide with 2-hydroxy-5-iodobenzaldehyde, 2-hydroxy-5-nitrobenzaldehyde, and 2-hydroxy-1-naphthaldehyde. We have also characterized the molecular structure of the investigated compounds with MS, 1H NMR, FTIR and UV–vis spectra. Theoretically, using DFT and TD-DFT methods, we computed frontier molecular orbitals (FMOs) energies and UV–vis spectra as well. We have also obtained the electron localization function (ELF) maps to identify electrophilic substitution sites in the molecules and density of states (DOS) diagrams to show the composition of the fragment orbitals that contribute to the molecular orbitals. We have investigatedsteady-state absorption, emission features, and excited state dynamics to better understand the photophysical process of bromosulfonamide-based azomethines. It has been demonstrated that by adding a naphthalene unit, the absorption properties of azomethine into two branches. Besides, azomethine, including heavy iodo atoms, presents a slight decrement in the fluorescence intensity. According to thorough calculations of charge transfer dynamics using femtosecond transient absorption spectra, the bromosulfonamide-based azomethines with iodo atoms and incorporating naphthalene units exhibit an intersystem crossing mechanism following photoexcitation. The colorimetric response of the compounds in DMSO to the addition of the equivalent amount of anions (F−, Br−, I−, CN−, SCN−, ClO4−, HSO4−, AcO−, H2PO4−, N3− and OH−) was investigated. In this regard, while the addition of F−, CN−, AcO−, H2PO4− and OH− anions into the solution containing the compounds resulted in a significant color change, the addition of Br−, I−, SCN−, ClO4−, HSO4− and N3−anions resulted in no color change.