Estudo de propriedades ópticas não lineares de derivados de dibenzalacetona

Abstract

Materials with high nonlinear optical properties are of great interest for the field of photonics due to the potentiality of use in several applications, such as 3D micro-fabrication, optical limiting, electro-optical devices, biological probes, photodynamic therapy, etc. In the last years, organic materials with nonlinear optical responses have emerged as promising candidates for diverse photonic applications. One of the main reasons for this potential is relatively easy tailoring of the molecular structure of organic compounds, while compared with inorganic ones, due to the evolution of molecular engineering. These molecular changes induce different linear and nonlinear optical responses, which must be carefully studied to define in which type of photonic device these organic compounds could be applied. In this thesis, a careful study of the change of linear and nonlinear optical responses was carried out as a function of the molecular structure of five organic compounds derived from dibenzalacetone. The nonlinear optical responses investigated corresponding to the second- and third-order processes, namely the first molecular hyperpolarizability (βHRS) and the two-photon absorption cross-section (σA2F ), respectively. The experimental values of βHRS and σA2F were obtained by using hyper-Rayleigh scattering and Z-scan techniques, respectively. The obtained values of βHRS ranging from 24×10−30 cm4statvolt−1 to 42×10−30 cm4statvolt−1. The σA2F spectra were determined by using the Z-scan technique, and the maximum values obtained are between 17 GM and 40 GM. Also, the σA2F spectra were adjusted by the sum over the essential states approach, in which it was possible to extract some important spectroscopic parameters such as the magnitude of the transition dipole moments between the excited states. To increase the interpretation of the presented study, a theoretical study was carried out to the simulated the absorption spectra of one- and two-photons, as well as the first molecular hyperpolarizability. These results were obtained through quantum chemical calculations using the time-dependent density functional theory by using the Gaussian 09 program package. Moreover, two additional programs were used to post-process the values provided by the Gaussian 09 to achieve the final results of the theoretical optical responses. These results allowed to correlate the linear and nonlinear theoretical optical responses of the molecular structures with the experimental ones. The theoretical values obtained for the first molecular hyperpolarizability, spectral behavior of the simulated absorption spectra of oneand two-photons showed good agreement with the experimental ones, indicating that the calculated transitions were similar to those observed experimentally.