Donor–acceptor dichotomy in novel Schiff bases: comprehensive spectroscopic and DFT investigation of intramolecular hydrogen bonding and charge-transfer properties

(OH) = 13.5 ppm), and AIM electron densities establishes a robust link between computed hydrogen-bond strength and experimental resonance-assisted hydrogen bonding signatures. DFT geometries reveal that increasing Ar-C[double bond, length as m-dash]N-CH torsion (2.5-12.3°) enlarges the HOMO-LUMO gap (3.14-3.22 eV) and blue-shifts CT bands. Comparison with literature shows these values are typical, while the integrated multiparametric solvatochromism-NBO-AIM approach provides a quantitative, transferable framework for predicting CT behaviour in donor-acceptor Schiff bases.