Acidochromic Behavior of Dibenzylidene Cyclohexanone-Based Bischalcone: Experimental and Theoretical Study

Synthesis and characterization of substituted 2,6-dibenzylidene cyclohexanone-based bischalcone derivatives and their optimized geometries were investigated by density functional theory. The synthesized compounds were identified through ultraviolet–visible, Fourier transform infrared, and 1H nuclear magnetic resonance spectroscopies and elemental analysis. Significant acidochromic behavior was observed for 2,6-bis­(4-dimethylamino-benzylidene)-cyclohexanone 1e. This result is owing to the preferential protonation of the chromophoric N,N-dimethylamino group, that is, quaternary salt formation and deactivation of the resonance system. The result was consistent with computational studies where the protonation was favored by 211 kcal/mol in the gas phase. The compounds also showed solvatochromic behavior. The geometries of the synthesized compounds were optimized with B3LYP/6-311G+(d,p) and APFD/6-311+G­(d,p) basis sets. The single point energy indicated that APFD/6-311+G­(d,p) basis set gave the lowest energy of 445–655 kcal/mol for the studied bischalcone derivatives. Quantum chemical parameters were also calculated.