Investigation of the chemical and optical properties of halogen-substituted N-methyl-4-piperidone curcumin analogs by density functional theory calculations.

Halogen-substituted N-methyl-4-piperidone curcumin analog compounds were studied for their molecular structure, molecular vibration analysis, natural bond orbital, ultraviolet spectra, molecular reactivity analysis, and nonlinear optical properties. The molecules in interest were the (3E,5E)-3,5-dibenzylidene-1-methylpiperidin-4-one along with its substituted halogen (X = F- or Cl- or Br-) at the ortho, meta and para position in the phenyl ring. The calculated geometrical parameters at B3LYP/6-311++G(d,p) were in good agreement with the available experimental XRD data. Using the frequency calculations, the molecular vibrational modes have been analyzed. Meanwhile, the hyperconjugative stabilization energies have been calculated using NBO analysis to address the donor and acceptor in the hyperconjugation. The calculated UV spectra at TD-CAM-B3LYP/6-311++G(d,p) show strong absorption around 300 to 320 nm which corresponds to the absorption in the UV-A and UV-B region. From molecular electrostatic potential surface, CO moiety is one of the electronegative regions in the compounds where the CX moiety is the other electronegative region of the compounds. Fluoro-substituted compounds are the compounds with the most electronegativity while bromo-substituted compounds are the compounds with the least electronegativity. Calculations of average local ionization energy surfaces have been performed to obtain information related to the local reactivity of the molecules where the phenyl becomes less reactive after the substitution. The calculated first hyperpolarizability is 6 to 17 times larger than urea, the standard nonlinear optic material. These findings imply that all of the molecules considered have potential to be applied as active sunscreen material or nonlinear optic material.