Effect of cycloalkanone ring size on second and third order nonlinear optical properties of bischalcones

With the objective of establishing the effect of cycloalkanone ring size on the NLO properties of bischalcones para-substituted diarylideneacetone and substituted diarylidenecycloalkanone derivatives were synthesized by the Claisen-Schmidt condensation reaction and characterized by using UV-Vis, FT-IR, 1H NMR, 13C NMR and mass spectrometry. The second harmonic generation (SHG) efficiencies and third-order nonlinear optical (NLO) properties of the synthesized compounds were studied using the Kurtz-Perry method and the Degenerate Four Wave Mixing (DFWM) technique respectively. Among all the synthesized compounds that we have reported here, 2,6-bis-(4-methoxydibenzylidene) acetone showed the highest SHG efficiency (12.96 times that of urea) and 2, 6-bis-(4-methylthiobenzylidene) cyclopentanone showed the highest third order NLO property with chi (3) value of 2.650 +/- 0.023 x 10-13 esu. Though diarylideneacetones exhibited the highest SHG efficiency, among the diarylidenecycloalkanones SHG efficiency decreased with an increase in the cycloalkanone ring size. Diarylidenecyclopentanone series showed better third order NLO activity followed by diarylideneacetone, diarylidenecycloheptanone and diarylidenecyclohexanone series. The results indicate that the cycloalkanone ring size as well as the presence of substituents on the aryl rings affect the NLO properties. The experimental findings correlated well with the results of in silico studies with a correlation factor, R2 = 0.9285.