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 correlation with high basis sets, 6-31G* and 6-31G* in gas phase in a bid to understand their structure-property relationship. The molecular properties like the FMOs energies, dipole moments (μ), polarizabilities (α), molecular first hyperpolarizabilities (β) were obtained. The results showed that the molecular properties were enhanced upon substitution with different groups. The β value is a measure of second order susceptibility of molecule; MMP has a β value of 2.44 x10-30 esu (B3LYP), 3.75 times of urea (0.65 x10-30 esu) and 2.61 x10-30(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 x10-30 esu, 4.35 over urea’s (94.9%) while BLYP is 3.11 x10-30 esu, 4.78 times that of urea (84.3%). However, both basis sets gave expected results in the right order for the molecules however, all modeled analogues increased β value, confirming that they are better candidates for NLO applications than MMP. The electronic transitions were calculated with CAM-B3LYP.