Nonlinear optical properties of chalcone derivatives using hybrid experimental and density functional theory methods

The donor-acceptor arrangement of chalcone molecules is a crucial factor influencing their optical properties. Variations in this arrangement directly impact the molecular electronic structure, resulting in differences in electrostatic potential, dipole moment, molecular orbitals, electron density distribution, and (hyper)polarizability. These properties are closely related to the intramolecular charge transfer (ICT) pathway and its overall efficiency, making the arrangement an important aspect of the nonlinear optical behaviour. In this study, two novel fluoro-methoxy chalcone derivatives with different push-pull systems-D-pi-A-pi-D in compound I and D-pi-A-pi-A in compound II-were synthesized and characterized. The linear and third-order nonlinear optical properties were examined using UV-Vis spectroscopy and Z-scan experiment. Subsequently, density functional theory (DFT) was employed to investigate the difference in charge transfer mechanism. A higher chemical reactivity of compound I is suggested on its lower optical energy gap (E-g) and HOMO-LUMO energy gap. However, compound II is found to demonstrate superior reverse saturable absorption (RSA) response, 35 times greater than that of compound I, and better overall third-order optical nonlinearity. Compound II with D-pi-A-pi-A configuration is found to exhibit higher molecular planarity, a stronger push-pull effect, and greater local polarity and dipole moment. The experimental third-order nonlinear optical (NLO) susceptibility (chi((3))) is determined to be 6.01 x 10(-8) esu for compound I and 7.84 x 10(-8) esu for compound II, while the optical limiting threshold (F-OL) is determined to be 10.41 kJ cm(-2) for compound I and 5.67 kJ cm(-2) for compound II.