A DFT Investigation of Halogen-Substituted Indeno[1,2-b]quinoxaline–Oxazole Derivatives: Insights into Electronic Structure and Reactivity

Density functional theory calculations were used to investigate the structural and electronic properties of three halogen-substituted indeno[1,2-b]quinoxaline–oxazole derivatives: (E)-5-(4-bromophenyl)-2-[2-(7,8-dimethyl-11H-indeno[1,2-b]quinoxalin-11-ylidene)hydrazinyl]oxazole, (E)-5-(4-chlorophenyl)-2-[2-(7,8-dimethyl-11H-indeno[1,2-b]quinoxalin-11-ylidene)hydrazinyl]oxazole, and (E)-2-[2-(7,8-dimethyl-11H-indeno[1,2-b]quinoxalin-11-ylidene)hydrazinyl]-5-(4-fluorophenyl)oxazole. Stable molecular structures for all the three compounds were confirmed through geometry optimization at the RB3LYP/3-21G level of theory. Electronic structure analysis revealed that the frontier molecular orbital energy gaps are strongly influenced by the halogen substituent: ΔE_gap 3.44 eV (Br), 1.79 eV (Cl), and 1.75 eV (F). These variations indicate differences in molecular reactivity, charge transfer properties, and optoelectronic potential. Electrostatic potential (ESP) mapping further elucidated charge distribution patterns, highlighting electrophilic and nucleophilic regions. The findings provide valuable insights into the electronic modulation of the studied quinoxaline–oxazole derivatives, making them promising candidates for optoelectronic and material science applications.