Browsing by Author "Beyene, Taye"

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    Computational Investigation of Conducting Polythiophenes and Substituted Polythiophenes
    (Addis Ababa Universty, 2007-06) Beyene, Taye; Mustefa, Ahmed (PhD)
    Thiophene oligomers up to eight thiophene units and 3-(2,5-dialkoxyphenyl) thiophenes have been investigated using HF/STO-3G, DFT/STO-3G, DFT/3-21G*, and DFT/6- 31G* computational levels. The structures are optimized to calculate the thermodynamic properties, UV-Vis absorption wavelength, and band gap of the oligomers. Increase in the number of thiophene rings increases the stability of both the doped and undoped states. The band gap decreases with increases in the number of thiophene rings. Up on oxidation, the band gap became further narrower compared with the neutral forms. Introducing dialkoxy phenyl-substituent at the 3-position of thiophene enhanced the stability and band gap of the oligomers. Longer alkoxy chains on the phenyl ring made the oligomers to be more stable and to have narrower band gap. Key words: Thiophenes, density functional theory, band gap, excitation energy, and thermodynamic properties