含噻吩環可溶性聚甲亞胺之合成、特性研究與理論電子結構

Soluble Thiophene Based Poly(azomethines): Synthesis, Properties, and Theoretical Electronic Structures

蔡馥娟(Fu-Chuan Tsai)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.01443

摘要

聚甲亞胺屬於高性能高分子，其光電特性及非線性光學研究在文獻中已有報導，然而它們的電子型態在理論上的分析尚未被發展。此外，原始的聚甲亞胺高分子在成膜時需要複雜的過程，需使用強質子酸或是路易士酸錯合物，因此，發展可溶於有機溶劑之聚甲亞胺高分子是必要的。本文中將以理論及實驗兩部分的研究來探討含噻吩環之可溶性聚甲亞胺高分子。

在理論分析部分中，我們探討不同的電子供體/電子受體之側鏈基取代或是主鍊上的取代，以及不同的連接鍊段對電子結構的影響。研究中發現PPV和PPN具有共平面的結構，然而PPI卻是非共平面的結構，這是因為在PPI中，亞胺基上的氫原子與氮-苯環上的氫原子過於靠近而產生排斥力，導致聚甲亞胺高分子有較大的能隙（2.35~2.66 eV）。當導入電子供體/電子受體的側鏈基時，其亞胺基與氮-苯環之間的扭轉角度皆會變大。此外，當主鍊上的苯環取代為具有拉電子能力的啶或是具有推電子能力的萘時，對電子結構並無太大影響，這是因為聚甲亞胺扭轉的結構所導致。

在實驗研究部分，我們合成四個含噻吩環可溶性的聚甲亞胺，並進行性質的鑑定。這些高分子在溶液中的能量頻帶邊緣吸收為2.36~2.44 eV，而在薄膜中為2.25~2.31 eV。此外，高分子薄膜在電化學測量中得到的能隙為2.23~2.29 eV，這四個高分子所測得之能隙都比母質PHTPI大一些，而導入不同的電子供體/電子受體之取代基並沒有太大的變化，反而比沒有取代基的聚甲亞胺來得大，然而不同的取代基對扭轉角度的影響則可用來說明能隙的趨勢。

此外，根據理論的結果我們可以提出全由噻吩環所組成且具有共平面結構的聚甲亞胺高分子。此非共平面的結構可藉由將主鍊上的苯環完全取代為塞吩環或是塞吩環的衍生物來改善，這樣一來，可以消除原本在芳香環所存在之氫原子間的排斥力，並且得到更小的能隙（PTTI: 1.42 eV; PEDOTI: 1.10 eV）。

關鍵字

電子結構 ； 聚甲亞胺 ； 高分子

並列摘要

Poly(azomethines) are a class of high performance polymers due to their interesting physical properties. The electronic, optical and nonlinear optical properties have been reported in the literature. However, the theoretical electronic structures of conjugated poly(azomethines) have not been investigated yet. Besides, the parent conjugated poly(azomethines) requires complicated processing solvent for processing into thin films, such as strong proton acid or Lewis Acid complexation. Hence, the development of new conjugated poly(azomethines) soluble in organic solvent is required. In this study, theoretical and experimental characterization on the soluble thiophene based conjugated poly(azomethines) were studied.

In the theoretical part, the effects of the linkage and donor/acceptor substituent or ring on the electronic properties of poly(azomethines) were studied. Poly(p-phenylene vinylene) (PPV) and poly(azine) (PAZ) show a coplanar conformation but poly(1,4-phenylene-methylidynenitrilo-1,4-phenylenenitrilomethylidene) (PPI) exhibits a twisted conformation. The nonplanar conformation in the PPI is attributed to the repulsion force between the adjacent hydrogen atoms on the C=N linkage and the N-phenylene. The bandgaps of the studied poly(azomethines) are in the range of 2.35~2.66 eV. All the substituted poly(azomethines) exhibit larger torsional angles than the parent material PTPI. Besides, there is no improvement on tuning the electronic structure due to twisted conformation if the phenylene on the backbone is replaced by the electron-accepting pyridine or the electron-donating naphthalene.

In the experimental part, four soluble thiophene based poly(azomethines) were synthesized and characterized. The absorption band edge of the polymer solution and that of the thin films was in the range 2.36~2.44 eV and 2.25~2.31 eV, respectively. The electrochemically determined HOMO-LUMO bandgap of polymer thin films was in the range of 2.23~2.29 eV. The bandgaps of the four prepared polymers are slightly larger than the parent material PHTPI. The bandgaps of the prepared polymers with various donor/acceptor substituents showed insignificant variation but slightly larger than that of the unsubstituted phenylene based poly(azomethine). The twisted conformation induced by the substitution might account for the trend of the bandgap.

Moreover, the nonplanar conformation in the poly(azomethines) system can be significantly improved if both the aromatic rings are thiophene rings or thiophene derivatives. In such case, the repulsion force between the adjacent hydrogen atoms on the C=N linkage and the N-phenylene that exists in the aromatic poly(azomethines) would be eliminated, leading to much smaller bandgaps of 1.42 eV and 1.10 eV for PTTI and PEDOTI, respectively.

並列關鍵字

electronic structure ； poly(azomethines) ； polymer

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