Acidochromic behavior of dibenzylidene cyclohexanone-based bischalcone: Experimental and theoretical study

Abstract

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.