DFT Study of the Influence of Cationic and Anionic Fragments on the Linear Optical Properties, First Hyperpolarizability, and Two-Photon Absorption of Benzoxazole Derivatives: A Perspective for OLEDs and Solar Cells Applications

This theoretical study presents the linear optical properties of absorption and fluorescence, as well as the nonlinear properties of first hyperpolarizability and two-photon absorption (TPA), in pi-conjugated organic compounds. Four pi-conjugated organic compounds derived from Benzoxazole were examined in the gas phase, in methanol, and in toluene, within the framework of Computational Quantum Chemistry, employing Density Functional Theory (DFT) with the CAM-B3LYP functional and the 6-311 + + G(d,p) basis set. The results reveal notable variations in the absorption and fluorescence spectra of organic compounds in the gas phase and in solvents such as methanol and toluene. In the gas phase, UV-violet peaks are observed, whereas in solvents, these peaks shift towards longer wavelengths, highlighting the influence of the chemical environment. Toluene intensifies absorption peaks, while methanol enhances fluorescence peaks, especially in compounds with a push-pull effect, such as Compound 4. Additionally, a significant increase in dipole moment, polarizability, and static and dynamic first hyperpolarizability for 1064 nm is evidenced in solvents, suggesting a greater nonlinear optical response capability of the compounds. The compounds exhibit maximum two-photon absorption (2PA) cross-sections that increase in solvents, especially in methanol, where Compound 4 reaches approximately 150 GM. Finally, Compound 4 in methanol and toluene offers better optical characteristics for use in OLED devices.