Estrutura eletronica de polimeros conjugados : a influencia da desordem

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

The present work is dedicated to the theoretical study of effects observed in organic conjugated polymers in which disorder plays an important role. The following problems have been chosen for study: (1) Chemical reaction of polyanilines in acidic solutions. It is well known that protonation doping leads to insulator-to-metal transition in some forms of polyanilines. We have been able to show that, for the random protonation of imine sites of polyaniline, modifications occur on the electronic structure that are consistent with the phase transition; (2) Effects of polymerization defects on the electronic structure of polythiophene. The occurrence of mislinks of a-b type is very common in the polymerization of heterocycles such as thiophene. The electronic structure of a long thiophene chain containing a variable number of randomly distributed a-b mislinks has been investigated. It is shown that those defects lead to loss of conjugation of the chain and consequently the optical abortion spectrum and conduction properties are affected; (3) Order-disorder phase transition in alkyl-substituted polythiophenes. Poly (alkylthiophenes) are soluble derivatives of polythiophenes that present, among others, the property of changing its color due to an increase in temperature (thermochromism). A model was built to relate thermochromism with a temperature-induced conformational disorder process (rotation of thiophenes out of the conjugation plane). Several features observed during heating-cooling cycles of these polymers have been elucidated within the present model. The electronic structure of disordered systems has been obtained by the combination of several quantum chemical and solid state techniques. A model Hamiltonian appropriate for a given problem has been chosen and the Negative Factor Counting (NFC) technique, which allows the calculation of the eigenvalue spectrum of an arbitrary matrix, was used to evaluate electronic properties

ASSUNTO(S)

polimeros - propriedades eletricas polimerização

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