A First-Principles Study on the Factors Influencing the Coplanarity of Bithiophene-based Molecules
Date Issued
2014
Date
2014
Author(s)
Li, Yi-Hung
Abstract
In this work, we use the first principle calculation to investigate the mechanism for the coplanarity of bithiophene-based molecules. We introduce different types of functional groups (electron donating/withdrawing) at different positions on bithiophene to investigate the effects on the change of coplanarity and the positions of energy levels.
The functional groups that we investigate include CH3 (weak electron donating group), CN and OCH3 (strong electron donating group), and NH2 (electron withdrawing group).
For the computational methods, first we investigate the different functional/basis set settings to check the accuracy for the methods. Then the structure optimization and single point energy scan are carried out. From the analysis of results, we discover that three factors can influence the coplanarity of bithiophene-based molecules: the π-resonance effect of bithiophene, the expulsion (steric effect) and attraction between functional groups and thiophene. When introducing electron donating functional group, the π-resonance effect of bithiophene will be enhanced and improve the coplanarity. When introducing electron withdrawing functional group, it has no influence on π-resonance effect of bithiophene. In addition, the expulsion between functional groups and thiophene will destroy the coplanarity; the attraction, on the other hand, can lower the bond angle of bithiophene and enhance the coplanarity. Finally we discuss the effects on optoelectronic properties for these bithiophene-based molecules. We discover that the coplanarity and types of functional groups can affect the energy levels. The former can change the HOMO-LUMO gaps, and the latter can change the positions of HOMO and LUMO levels of the molecules.
The functional groups that we investigate include CH3 (weak electron donating group), CN and OCH3 (strong electron donating group), and NH2 (electron withdrawing group).
For the computational methods, first we investigate the different functional/basis set settings to check the accuracy for the methods. Then the structure optimization and single point energy scan are carried out. From the analysis of results, we discover that three factors can influence the coplanarity of bithiophene-based molecules: the π-resonance effect of bithiophene, the expulsion (steric effect) and attraction between functional groups and thiophene. When introducing electron donating functional group, the π-resonance effect of bithiophene will be enhanced and improve the coplanarity. When introducing electron withdrawing functional group, it has no influence on π-resonance effect of bithiophene. In addition, the expulsion between functional groups and thiophene will destroy the coplanarity; the attraction, on the other hand, can lower the bond angle of bithiophene and enhance the coplanarity. Finally we discuss the effects on optoelectronic properties for these bithiophene-based molecules. We discover that the coplanarity and types of functional groups can affect the energy levels. The former can change the HOMO-LUMO gaps, and the latter can change the positions of HOMO and LUMO levels of the molecules.
Subjects
共平面性
二噻吩
第一原理計算
Type
thesis
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