A theoretical investigation of second-order nonlinear optical properties in push–pull π-conjugated compounds, including phenoxazine-based systems

This computational study analyzes how second-order nonlinear optical (NLO) properties can be enhanced in push–pull π-conjugated compounds of the type A-π-D, where the donor is based on an organic phenoxazine dye. Both the derivative and sum-over-states (SOS) methods were used to compare the molecular components of the known JK-201 species and POZ, as well as derivatives of the latter molecule with different electron-withdrawing substituents (POZ-F, POZ-CF3, and POZ-CN), to explore how molecular design affects the NLO response. Hyper-Rayleigh scattering (β_HRS) is evaluated in both static and dynamic conditions with incident wavelengths of 1064 and 1907 nm, respectively. This provides insights into both the scattering efficiency and electronic transitions. The first hyperpolarizability β is visualized by unit sphere representation, with precise β₀ calculations compared with the SOS model. Additionally, harmonic light intensity is calculated, and the predicted two-dimensional NLO spectra are examined, focusing on the dominant β_XXX component.