Spectroscopic, quantum chemical and topological calculations of 4-aryl quinolines using density functional theory

Density Functional Theory (DFT) calculations were performed with Gaussian 09 W to investigate the structural, electronic, and optical properties of several 4-aryl quinoline derivatives, with emphasis on dimethyl 6-chloro-4-phenylquinoline-2,3-dicarboxylate. Geometry optimizations were conducted using the M06-2×/6–311 + G(d,p) level of theory. Natural Bond Orbital (NBO) analysis elucidated charge distribution and intramolecular charge-transfer pathways, complemented by molecular electrostatic potential (MEP) mapping to identify electron-rich and electron-deficient regions. Frontier molecular orbitals (FMO), density of states (DOS), and reactivity descriptors were evaluated in aqueous conditions. Noncovalent interactions, including van der Waals forces and hydrogen bonding, were examined, and vibrational spectra were simulated for neutral and charged states to track frequency shifts. Time-dependent DFT (TD-DFT) calculations provided UV–Vis absorption characteristics, while topological analyses using the Electron Localization Function further clarified bonding and electron-density features. Together, these results offer a comprehensive understanding of the physicochemical behavior of the studied quinoline derivatives.