Title

運用第一原理計算研究影響二噻吩類型分子共平面性之因素

Translated Titles

A First-Principles Study on the Factors Influencing the Coplanarity of Bithiophene-based Molecules

DOI

10.6342/NTU.2014.01375

Authors

李奕鋐

Key Words

共平面性 ; 二噻吩 ; 第一原理計算 ; coplanarity ; bithiophene ; first principle calculation

PublicationName

臺灣大學化學工程學研究所學位論文

Volume or Term/Year and Month of Publication

2014年

Academic Degree Category

碩士

Advisor

林祥泰

Content Language

英文

Chinese Abstract

於此次的研究中,我們運用了第一原理計算來探討以二噻吩為主鏈的分子中,改變其共平面性的機制。我們在二噻吩不同位置導入具不同推拉電子能力的官能基團,研究其對共平面性的改變,以及其能階位置的影響。我們研究的官能基團包含甲基(弱的推電子基團) 、氰基及甲氧基(強推電子基),以及胺基(拉電子基)等。再研究方法上,我們先探討了不同的函數和基底函數的組合以確認計算方法的準確性,再進行分子結構的優化以及單點能量掃描。從結果的分析發現,影響二噻吩為主鏈之分子的共平面性之原因主要有三:二噻吩的共振效應、官能基團與噻吩間的排斥(立體障礙)與吸引。當引入的官能基為電子供給者時,會對增強二噻吩的共振的效應,增加平面性。若引入的官能基為電子為接受者時,則對二噻吩的共振效果沒有影響。另外,官能基與噻吩間的排斥作用,會破壞共平面性,吸引作用則會降低二噻吩二面角能障,通常會讓共平面性變好。而最後我們亦針對這些分子對光電性質的影響進行討論,我們發現共平面性以及官能基的性質可對分子的能隙產生影響,其中共平面性可改變分子的能隙寬度;官能基的性質則可改變最高分子佔領軌域及最低未佔領分子軌域的位置。

English 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.

Topic Category 工學院 > 化學工程學研究所
工程學 > 化學工業
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