Intramolecular versus intermolecular hydrogen bonds in a novel conjugated dimethylamino-benzylidene-amino-2-naphthoic acid Schiff base.

A new compound based on the D-π-A concept, where D = dimethylamino-phenyl and A = naphthoic acid, separated by an imine motif, was designed, synthesized and characterized. The spectral, energetics, and structural characteristics of the compound were studied thoroughly theoretically by density functional theory (DFT) in the gas and aqueous phases and experimentally (steady-state absorption) in aqueous media with various degrees of polarity and hydrogen bonding ability. This compound shows high sensitivity to the polarity, basicity and proton affinity of the environment. Based on DFT, TD-DFT and NBO analysis, the compound exists in the ground-state with both intermolecular and intramolecular hydrogen bond conformations in association with the -COOH, with latter isomer calculated to be more stable. Furthermore, structural changes via intermolecular solute-solvent interactions, dictate electronic modifications and spectral changes. Graphical abstract Acidic and basic sites in DMAMN involved in protonation/deprotonation.