Conformational analysis and electronic transition of carbazole-based oligomers as explained by density functional theory

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• 作者：Songwut Suramitr ; Supa Hannongbua ; Peter Wolschann
• 关键词：Conducting polymer ; TD-DFT ; Carbazole ; Copolymer ; Excitation HOMO– ; LUMO energy ; Conformational analysis
• 刊名：Journal of Molecular Structure ; THEOCHEM
• 出版年：2007
• 期刊代码：63_01661280
• 类别：ch
• 出版时间：1 April 2007
• 卷：807
• 期：1-3
• 页码：109-119
• 文件大小：1162 K

摘要

The conformational analysis and vertical excitation energies of carbazole-based molecules were carried out by B3LYP calculations with three basis sets: 6-31G, 6-31G(d) and 6-311G(d,p). Carbazole-based molecules were separated into two types, carbazole combined with five-membered (Cz-co-Thiophene (Cz-co-Th)_<i>Ni> and Cz-co-Furan (Cz-co-F)_<i>Ni>) and six-membered (Cz-co-Fluorene (Cz-co-Fl)_<i>Ni> and Cz-co-Phenyl (Cz-co-P)_<i>Ni>) aromatic rings. The analyses of potential energy surfaces and torsional angles for carbazole-based oligomers reveal that these copolymerized with five-membered aromatic rings are more planar than those copolymerized with six-membered ring. The obtained results indicate that TD-PBE1PBE and TD-B3LYP methods predict the excitation energies with the 6-311++G(2d,2p) basis set based on B3LYP/6-311G(d,p) optimized geometries for (Cz)_<i>Ni>, (Cz-co-Fl)_<i>Ni> and (Cz-co-Th)_<i>Ni> in good agreement with experimental data. An analysis of the vertical singlet–singlet transition was also performed and the results indicated that for (Cz)_<i>Ni>, (Cz-co-Fl)_<i>Ni>, (Cz-co-P)_<i>Ni>, (Cz-co-F)_<i>Ni> and (Cz-co-Th)_<i>Ni> oligomers, S₁transition plays an important role. Excitation to the S₀ → S₁ state corresponds almost exclusively to the promotion of an electron from the HOMO to the LUMO. The electronic transition derived by TD-DFT method gives useful structural and electronic information for designing novel conducting polymer materials.