Investigation of the influence of the central ion on nonlinear optical
Transcrição
Investigation of the influence of the central ion on nonlinear optical
XVI Simpósio Brasileiro de Química Teórica – SBQT 2011 Ouro Preto – MG, 20-23 Novembro de 2011 30 Anos SBQT “Investigation of the influence of the central ion on nonlinear optical properties of a porphyrin derivative through the use of quantum mechanical methods” Eufrásia de Souza Pereira1(IC), Newton Martins Barbosa Neto2(PQ), Leonardo Tsuyoshi Ueno3(PQ), Diesley Martins da Silva Araújo1(PG), Weverson Rodrigues Gomes1(PG), Rodrigo De Paula4(PQ), Antonio Eduardo da Hora Machado1(PQ) 1 Universidade Federal de Uberlândia, Instituto de Química, P. O. Box 593; 38400-902 Uberlândia, MG 2 3 4 Universidade Federal de Uberlândia, Instituto de Física, Uberlândia, MG Universidade Federal de Uberlândia, Faculdade de Ciências do Pontal, Ituiutaba, MG Universidade Federal do Recôncavo da Bahia, Centro de Formação de Professores, Amargosa, Ba. Key-words: Nonlinear optics, metal porphyrins, DFT and TD-DFT, first hyperpolarizability, PM6. The study of nonlinear optical properties (NLO) of organometallic compounds has attracted considerable attention due to the enormous range of technological applications and future perspectives. The main advantages presented by such materials are: 1) great values for the magnitude of nonlinearities; 2) fast response times; and 3) easy structural manipulation that is used to tune the wished property aiming a specific application. It is known that a necessary pre-condition for the observation of NLO properties in this kind of material is the presence of conjugated structure with an efficient electron delocalization, which is responsible for high values of hyperpolarizabilities in such compounds, and a fast charge redistribution caused by the interaction with intense electromagnetic fields. Our studies have focused on organometallic compounds, particularly metal porphyrins and metal phthalocyanines. In this communication we employed the Density Functional Theory (DFT) and its Time Dependent analogous (TD-DFT) in order to investigate the influence of the central ion (Zn2+, Al3+, Fe3+ e Mn3+) on the photophysical and nonlinear optical properties of a cationic porphyrin derivative (meso-tetrakis-(1,3-dimethylimidazolium-2-yl)porphyrin tetraiodide). The ground state geometries and vibrational frequencies for the studied species were obtained using B3LYP/TZVP methodology. The excitation energies, oscillator strengths, etc. were calculated using TD-DFT method with the same functional and atomic basis set. These calculations were made with the use of Gaussian 09 computational package. The first hyperpolarizabilities (TOTAL), were estimated using the PM6 semi-empiric method (AMPAC 9), with solvated system simulated with the dielectric continuum model COSMO. Through the evaluation of the frontier molecular orbital, it is possible to verify that Mn3+ and Fe3+ exert a higher influence on the macrocycle electron density, through electron transfer, leading to a distortion of the orbital symmetry between HOMO and LUMO. As a consequence, nonlinear optical properties of these compounds are favored, which can be determined by the estimated values of TOTAL. For the derivative containing Zn2+, for example, for which an experimentally estimated value of HRS is available, the discrepancy between the experimental value in DMSO and the theoretical one is 18%. Support: FAPEMIG, CNPq, CAPES.