Electronic and optical properties of pyrrole and thiophene oligomers: A density functional theory study |
| |
Authors: | Juan Chen Xingfeng Zhu Chenglin Luo Yafei Dai |
| |
Institution: | Department of Physics, School of Physics Science & Technology and Jiangsu Key Laboratory for NSLSCS, Nanjing Normal University, Nanjing, China |
| |
Abstract: | The conductive mechanism of pyrrole (Py) and thiophene (Th) oligomers is investigated in the framework of density functional theory. Geometric constructions and electronic structures of neutral n‐Py/n‐Th and oxidized n‐Pym+/n‐Thm+ oligomers (6 ≤ n ≤ 48, 2 ≤ m ≤ 18) are reported as a function of oligomer length. The charges in the oxidized oligomers have a localized distribution along the oxidized n‐Pym+/n‐Thm+ oligomers, and each set of two positive charges is localized in one area. Therefore, the charge carriers in oxidized n‐Pym+/n‐Thm+ oligomers are bipolarons. Furthermore, the nonlinear optical properties of the n‐Py/n‐Th oligomers are investigated, for which the static polarizability α, the first polarizability β, and the second polarizability γ are calculated. When the ratio of m/n is 1/3, the static polarizability <α> and the polarizability anisotropy Δα are maximized. In addition, neutral n‐Py/n‐Th oligomers have maximum <γ> values. The values of β were determined mainly by the dipole of the molecule, while the values of γ were closely related to the aromaticity of the oligomer. The stronger the aromaticity, the bigger the γ value. All calculations indicate that the polarizability and absorption spectrum can be tuned by controlling the oxidation level, making these oligomers applicable as good nonlinear optical materials. |
| |
Keywords: | conducting polymer density functional theory polarizability pyrrole thiophene |
|
|