Estrutura eletrÃnica e propriedades espectroscÃpicas de compÃsitos polianilina/ouro: uma investigaÃÃo ab initio

AUTOR(ES)

Marcus Vinicius Almeida Fernandes de FigueirÃdo

DATA DE PUBLICAÇÃO

2009

RESUMO

In this dissertation we use ab initio quantum chemistry theoretical methods to examine possible effects that the presence of a small number of attached gold atoms could have upon the spectra of polyaniline (PANI) oligomers. We have investigated in special the theoretical fluorescence spectra of the gold-polyaniline composites, by using the Hartree-Fock approximation to optimize the molecular geometry corresponding to the ground state and then applying the CIS (configuration of interaction singles) method to optimize the first excited state. We have considered different oxidation states of the polyaniline and varied the size of the gold cluster (1, 3 and 5 gold atoms) attached to each terminal side of the PANI oligomer, and determined the absorption and fluorescence spectra. We have also analyzed the diagram of energy levels and the behavior of the spatial localization of the molecular orbitals, when we established that the rules: a) relevant transitions always correspond to the interaction of occupied and unoccupied orbitals that are spatially localized in the same general region of the molecule, and b) transitions in the visible region are more likely to occur when the PANI oligomer interacts with gold electrodes (a fact in agreement with experimental results â see Appendix A). We have also examined the corresponding changes when planar and nonplanar configurations were considered for the oligomers. Finally, we found that even the presence of a single gold atom attached to each side of a PANI oligomer has a profound effect in the spectra, spatial localization of the frontier molecular orbitals and the corresponding energy levels, a fact that remains true when we double the size of the oligomers.

ASSUNTO(S)

ab initio localizaÃÃo dos orbitais moleculares fisica espectroscopia eletrÃnica ab initio spatial localization of molecular orbitals visible and fluorescence spectroscopy

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