Solvent-Free Synthesis of Chiral Substituted <i>N</i> -Benzylideneanilines Imines: X-ray Structure, and DFT Study

Solvent-free synthesis of five chiral-substituted <i>N</i>-benzylideneanilines (<b>I-V</b>) was reported in high yields, and all these imines were characterized by various physicochemical analysis techniques. Crystallographic analysis revealed that variations in crystal packing were primarily influenced by steric effects rather than halogen substituents. The contribution of halogen bonding to the chromic properties of these compounds was systematically evaluated. Their electronic and optical properties were also investigated theoretically using density functional theory (DFT) calculations at the B3LYP and M06-2X levels of theory with the 6-311+G-(d,p) basis set, which reproduced the experimental structures with good accuracy. Using frontier molecular orbital analysis, two regimes were identified: imines <b>I</b>, <b>II</b>, and <b>IV</b> have localized HOMOs on the imine moiety that lead to larger HOMO-LUMO gaps and higher chemical hardness, while imines <b>III</b> and <b>V</b> have orbitals that are delocalized over extended π-systems with smaller gaps, lower softness, and higher polarizability. Trends were corroborated by global reactivity parameters which indicated that the charge-transfer ability of <b>III</b> and <b>V</b> is enhanced and TD-DFT calculations reproduced the experimental ultraviolet-visible (UV-vis) with red-shifted absorptions. ECD spectra showed stronger Cotton effects in <b>III</b> and <b>V</b> being attributed to their electronic delocalization and lower hardness. NBO analysis revealed stabilization via π-(C-C) → π*-(N-C) and n-(O/Cl) → π*-(C-C) interactions; NCI plots highlighted dispersive and C-H···π contacts. Complementary QTAIM analysis identified two weak Cl···Cl interactions in imine <b>IV</b>, indicating the effect of halogen contacts on supramolecular packing. This integrated experimental-theoretical study showed that substituents regulate electronic structure, charge-transfer capacity, and chiroptical activity, guiding future designs of imine-based optoelectronic and functional chiral materials.