Investigation of the influence of the central ion on nonlinear optical

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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.