Alkan, Fahri2016-01-082016-01-082009http://hdl.handle.net/11693/14967Ankara : The Department of Chemistry and the Institute of Engineering and Sciences of Bilkent University., 2009.Thesis (Master's) -- Bilkent University, 2009.Includes bibliographical references leaves 65-73.Due to their unique electro-optical properties, there has been a great deal of scientific interest in electronic structure of conjugated systems. In order to reveal the complete map of their electronic structure, several experimental investigations are done using UV-Vis and ultraviolet photoelectron spectroscopy (UPS). The experimental findings are usually interpreted by the results of quantum chemical calculations. In this study, we present the theoretical simulations of UV-Vis and UP spectra of conjugated systems by using density functional theory (DFT). In UV-Vis simulations, we investigated the excited states of oligothiophene anions and cations and almost identical UV spectra were obtained for these systems. This similarity in excitation energies are explained by the resemblance in energy levels and nature of excited states in anions and cations. In UPS simulations, the energy levels of conjugated systems were calculated by using ∆SCF/TDDFT and DFT orbital eigenvalues. It is shown that there is a good agreement between ∆SCF/TDDFT and experiment, especially for the investigated oligomers. In contrast, DFT orbital energies are considerably lower than the experiment. However, spacing of energy levels is consistent with both experiment and ∆SCF/TDDFT.xii, 73 leaves, illustrationsEnglishinfo:eu-repo/semantics/openAccessConjugated systemsDensity functional theory (DFT)UV-Vis spectroscopy Ultraviolet photoelectron spectroscopy (UPS)thiophenepyrrole furanQD381.9.E38 A44 2009Polymers--Electric properties.Polymers--Optical properties.Conjugated polymers.Photoelectron spectroscopy.ThesisB120067