Electronic structure insights into 3-(2-carboxyethyl)-1-methyl-1H-imidazol-3-ium bromide ionic liquid (AFIL): A detailed DFT and topological study

Imidazolium-based ionic liquids are gaining significant attention because of their adjustable electronic structure and various applications. This work explores the electronic structure and reactivity of 3-(2-carboxyethyl)-1-methyl-1H-imidazol-3-ium bromide (AFIL) through a combination of experimental tests and density functional theory calculations. Geometry optimization and vibrational analysis confirm a stable ion-pair framework that closely matches experimental IR and NMR data. Frontier molecular orbital analysis shows a moderate HOMO-LUMO energy gap. This suggests electronic stability while still allowing enough reactivity for catalytic and biological uses. Molecular electrostatic potential mapping identifies strong electrophilic regions around the –NH and –COOH hydrogens. It also highlights a strong nucleophilic character on the bromide anion and carbonyl oxygen atoms, pointing out the preferred sites for intermolecular interactions. Natural Bond Orbital analysis highlights strong interactions between lone pairs and antibonding donor-acceptor pairs, especially involving nitrogen and oxygen centres. This leads to significant electronic delocalization and stabilization. Topological analyses, including ELF, LOL, and RDG, confirm that hydrogen bonding, van der Waals forces, and electrostatic interactions primarily stabilize the molecular structure. TD-DFT calculations indicate clear electronic transitions that depend on the solvent, with increased stabilization in polar environments. Overall, these findings establish a direct relationship between structure, properties, and reactivity for AFIL. They also suggest its potential use in green catalysis and biologically relevant situations. • DFT reveals intrinsic bonding and electronic features of an acidic imidazolium ionic liquid. • ELF/LOL and RDG analyses clarify noncovalent interactions and cation–anion organization. • Gas-phase conceptual DFT descriptors are linked to MEP and NBO charge distributions. • TD-DFT explains solvent-dependent excitation behaviour via frontier orbital interactions.