Substituent Effects on the Structural and Nonlinear Optical Properties of 1-[4-({(E)- [4-(methylsulfanyl)phenyl]methylidene}amino)phenyl]ethanone and Some of its Substituted Derivatives- a Theoretical Method

This work investigates the structural and nonlinear optical properties of a D-A type 1-[4-({(E)-[4-(methylsulfanyl)phenyl]methylidene} amino)phenyl]ethanone, MMP, in which charge transfer occurs from -SCH3 donor to -COCH3 acceptor group through methylidene backbone, and some of its modeled analogues using quantum chemical calculations with pure BLYP and hybrid B3LYP correlations with high basis sets, 6-31G* and 6-31+G* in gas phase to understand their structure-property relationship. The molecular properties such as FMOs energies, dipole moments (μ), polarizabilities (α), and molecular first hyperpolarizabilities (β) were calculated. The results showed that the molecular properties are enhanced upon substitution with different groups. The β value is a measure of the second order susceptibility of molecule; MMP has a β value of 2.44  10-30 esu (B3LYP), 3.75 times of urea (0.65  10-30 esu) and 2.61  10-30(BLYP), 4.02 times that of urea. The experimental SHG efficiency of MMP is 4.13 times that of urea crystals of identical particle size, meaning that the BLYP correlation predicts the SHG efficiency and second order susceptibility more effectively than the B3LYP method. With 6- 31+G*, B3LYP gave 2.83  10-30 esu, 4.35 over urea’s (94.9%) while BLYP is 3.11  10-30 esu, 4.78 times that of urea (84.3%). Both basis sets gave expected results in the right order for the molecules, however, β value was increased for all analogous, confirming that they are better candidates for NLO applications than MMP. The electronic transitions were calculated with CAM-B3LYP.