Enhancing nonlinear optical responses via Methoxy Positional Isomerism in Chalcone-Based Materials

Abstract

The functional moieties present in chalcone derivatives play a pivotal role in finely adjusting the thermal, optical, structural, and nonlinear optical (NLO) characteristics of the chalcone material. This paper details the synthesis of chalcone derivatives where three distinct trimethoxy substituents are integrated into the benzoyl moiety through carboxyl bonding with 2-acetyl pyridine. The synthesis employs the Schmidt condensation method, and the resultant samples are subject to scrutiny through FTIR and FT-Raman techniques to ascertain phase purity. The outcomes reveal substantial alterations in the structural, thermal, optical, and NLO attributes of the samples. The electron-donating property of the trimethoxy groups augments electron density within the chalcone molecule, thereby effecting multiple shifts in the material's characteristics. Interestingly, a methoxy group located at positions 2, 4, and 5 forms crystals with centrosymmetric properties. Conversely, relocating the methoxy groups to positions 3, 4, 5, and 2, 4, 6 induces a transformation from centrosymmetric to non-centrosymmetric crystal structures, resulting in a remarkable enhancement of NLO properties, encompassing second and third harmonic generation. Notably, the compound featuring trimethoxy substitution at positions 3, 4, and 5 demonstrates a 27-fold increase in second harmonic generation compared to the urea crystal. The detailed discussion encompasses the intricate relationship between the molecular structure and nonlinear properties, encompassing third harmonic generation.