Os polímeros conjugados luminescentes são materiais com grande potencial tecnológico, mas apesar de estudados desde a década de 80, algumas de suas propriedades óticas ainda não foram totalmente entendidas. Por exemplo, ainda persistem dúvidas quanto à natureza das suas excitações primárias. Nesse sentido foi feito um estudo da fotoluminescência do poli[2-metoxy-5-(2-etil-hexiloxi)-1,4-fenileno vinileno] (MEH-PPV), polímero semicondutor luminescente cujas propriedades ópticas já foram muito investigadas. Além da banda de absorção principal na região visível do espectro, ele possui três bandas no ultravioleta. O objetivo deste trabalho é investigar a fotoluminescência do MEH-PPV quando excitado na região do ultravioleta. Após fotoexcitação no ultravioleta, observou-se apenas a fotoluminescência usual no visível. A intensidade da emissão depende fortemente da energia de excitação, da temperatura e da estrutura morfológica do sistema polimérico, determinada pelo método de preparação das amostras. Os resultados indicam que os estados excitados no ultravioleta relaxam rapidamente de forma não-radiativa até os estados de menor energia, de onde então ocorre a luminescência. Entretanto, a eficiência da fotoluminescência excitada no ultravioleta é consideravelmente reduzida, indicando que a excitação a altas energias abre novos canais de relaxação não-radiativos. / Luminescent semiconducting polymers are technological promising materials, but although studied since the 80’s some of their optical properties have not yet been fully understood. For instance, the nature of their primary excitations is still on debate. Therefore we proposed to study the photoluminescence following photoexcitation in the ultraviolet of the polymer poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV). It is a semiconducting luminescent polymer with a main absorption band in the visible part of the spectrum, but with three other absorption bands in the ultraviolet. After ultraviolet photoexcitation it was observed only the usual visible photoluminescence. The intensity of photoluminescence depends strongly on temperature, excitation wavelength and morphological structure of the polymer, determined by the method of sample preparation. The results show that by ultraviolet excitation the excited states relax rapidly non-radiatively to the lower energy states, from where luminescence results. However, the photoluminescence efficiency with ultraviolet photoexcitation is considerably reduced, implying that the highly excited states in the polymer have more non-radiative relaxation channels available.

Os polímeros conjugados luminescentes são materiais com grande potencial tecnológico, mas apesar de estudados desde a década de 80, algumas de suas propriedades óticas ainda não foram totalmente entendidas. Por exemplo, ainda persistem dúvidas quanto à natureza das suas excitações primárias. Nesse sentido foi feito um estudo da fotoluminescência do poli[2-metoxy-5-(2-etil-hexiloxi)-1,4-fenileno vinileno] (MEH-PPV), polímero semicondutor luminescente cujas propriedades ópticas já foram muito investigadas. Além da banda de absorção principal na região visível do espectro, ele possui três bandas no ultravioleta. O objetivo deste trabalho é investigar a fotoluminescência do MEH-PPV quando excitado na região do ultravioleta. Após fotoexcitação no ultravioleta, observou-se apenas a fotoluminescência usual no visível. A intensidade da emissão depende fortemente da energia de excitação, da temperatura e da estrutura morfológica do sistema polimérico, determinada pelo método de preparação das amostras. Os resultados indicam que os estados excitados no ultravioleta relaxam rapidamente de forma não-radiativa até os estados de menor energia, de onde então ocorre a luminescência. Entretanto, a eficiência da fotoluminescência excitada no ultravioleta é consideravelmente reduzida, indicando que a excitação a altas energias abre novos canais de relaxação não-radiativos. / Luminescent semiconducting polymers are technological promising materials, but although studied since the 80’s some of their optical properties have not yet been fully understood. For instance, the nature of their primary excitations is still on debate. Therefore we proposed to study the photoluminescence following photoexcitation in the ultraviolet of the polymer poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV). It is a semiconducting luminescent polymer with a main absorption band in the visible part of the spectrum, but with three other absorption bands in the ultraviolet. After ultraviolet photoexcitation it was observed only the usual visible photoluminescence. The intensity of photoluminescence depends strongly on temperature, excitation wavelength and morphological structure of the polymer, determined by the method of sample preparation. The results show that by ultraviolet excitation the excited states relax rapidly non-radiatively to the lower energy states, from where luminescence results. However, the photoluminescence efficiency with ultraviolet photoexcitation is considerably reduced, implying that the highly excited states in the polymer have more non-radiative relaxation channels available.

Conductive polymers are also known as "organic metals" due to their semiconducting properties. They are found in a wide range of applications in the field of organic electronics. However, the growing number of experimental works is not widely supported with theoretical calculations. Hence, the field of conductive polymers is experiencing lack of understanding of mechanisms occurring in the polymers. In this PhD thesis, the aim is to increase understanding of conductive polymers by performing theoretical calculations.        The polymers poly(3,4-ethylenedioxythiophene) (PEDOT) together with its selenium (PEDOS) and tellurium (PEDOTe) derivatives, poly(p-phenylene) (PPP) and naphthobischalcogenadiazoles (NXz) were studied. Several computational methods were applied for analysis of mentioned structures, including density functional theory (DFT), tight-binding modelling (TB), and Car-Parrinello molecular dynamics (CPMD) calculations. The combination of CPMD and DFT calculations was applied to investigate the PEDOT, PEDOS and PEDOTe. The polymers were studied using four different functionals in order to investigate the full picture of structural changes, electronic and optical properties. Temperature effects were studied using molecular dynamics simulations. Wide statistics for structural and molecular orbitals analysis were collected.         The TB method was employed for PPP. The formation and motion of the excitations, polarons and bipolarons, along the polymer backbone was investigated in presence of electric and magnetic fields. The influence of non-magnetic and magnetic impurities was determined.        The extended π-conjugated structures of NXz were computed using B3LYP and ωB97XD functionals in combination with the 6-31+G(d) basis set. Here, the structural changes caused by polaron formation were analyzed. The combined analysis of densities of states and absorption spectra was used for understanding of the charge transition. / <p>QC 20170928</p>