電子施體/受體共軛高分子系統之理論計算及特性應用

Theoretical Analysis and Applications of Donor-Acceptor Conjugated Polymer Systems

白佳靈(Chia-Ling Pai)

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(2005年)

https://doi.org/10.6342/NTU.2005.00444

摘要

電子施體/受體共軛高分子系統具有調控電子與光電特性的潛力，本文將探討兩組電子施體/受體共軛高分子系統之電子與光電性質，分別為：(1)以3,4-ethylenedioxythiophene (EDOT)和thiophene (T)為主電子施體/受體交替共軛高分子幾何結構與電子特性之理論計算；(2)以fluorene為主電子施體/受體共軛高分子混摻之光物理性質研究。

在以EDOT和T為主電子施體/受體交替共軛高分子之理論分析部份，電子特性與扭轉角度、分子內電荷轉移、施體/受體間鍵長以及鍵長改變量的關聯性將被探討。我們發現環的大小以及分子內電荷轉移對結構有很大的影響，而小分子的HOMO、LUMO和能隙受到電子受體強度所控制，然而，高分子的電子特性與其構成分子卻有明顯不同的趨勢，這主要是由於分子結構的轉變，如小分子EDOT-TP以及T-TP因分子內電荷轉移，使其高分子結構由aromatic轉變成quinoid；而EDOT-BPP因其鍵長改變量小和良好的電子受體強度，使其能隙僅0.7個電子伏特。由理論分析結果可知，電子受體的強度以及穩定的幾何結構對電子施體/受體交替共軛高分子系統之電子特性有重大的影響。

在以fluorene為主電子施體/受體共軛高分子混摻之實驗研究部分，我們將經由紫外光及可見光光譜和螢光光譜的量測來探討六組混摻系統中的光物理性質。在系統(I)：F6PY和F6BT以及系統(II)：F6PY和F8T2混摻中，有效的能量轉移被觀察到，在系統(I)中加入5 wt%的F6BT於F6PY中螢光效率可以提升到31.1 %，而在系統(II)中加入10 wt%的F8T2於F6PY中螢光效率可以提升到15.6 %，和原來構成混摻的高分子相比，皆有明顯地提升，然而，在F6TP混摻系統(III) ~ (V)中，螢光隨著F6TP的加入而被抑制，與系統(I)和系統(II)有明顯的不同，這可能是因為F6TP結構中的重原子，如硫和氮，抑制了螢光的發生。此外，白光材料可經由三成份混摻系統(VI)，由PFH (95.5 ~ 96.5 wt%)、F6BT (0.5 wt%)以及F6TP (3.0 ~ 4.0 wt%)的混摻而得，螢光效率約為8 %。

由理論分析與實驗研究的結果可知，電子施體/受體共軛高分子系統可提供電子與光電元件應用基礎上的嶄新理解。

關鍵字

共軛高分子 ； 電子施體/受體 ； DFT ； 賽吩 ； fluorene ； 高分子混摻 ； F&ouml ； rster能量轉移

並列摘要

Donor-acceptor conjugated polymer systems are potential used to tune the electronic and optoelectronic properties. In this thesis, the electronic and optoelectronic properties of two donor-acceptor conjugated polymer systems are explored: (1) theoretical analysis on the geometries and electronic properties of donor-acceptor alternating conjugated polymers based on 3,4-ethylenedioxythiophene (EDOT) and thiophene (T). (2) photophysical properties of fluorene based donor-acceptor conjugated polymer blends.

In the theoretical analysis on EDOT and T based donor-acceptor alternating conjugated polymers, the torsional angle, intramolecular charge transfer, bridge length, and bond length alternation were analyzed and correlated with the electronic properties. It was found that the geometries of the studied materials were significantly affected by the ring size and intramolecular charge transfer. The HOMO level, LUMO level, and band gap of the studied model compounds were well controlled by the acceptor strength. However, the electronic properties of the studied polymer showed a significant different trend with the acceptor strength due to the geometrical transformation. The model compound of EDOT-TP and T-TP has the aromatic geometry but is transformed to the quinoid geometry for large intramolecular charge transfer. The small bond length alternation and large acceptor strength in the EDOT-BDP polymer also results in the smallest Eg of 0.7 eV among the studied polymers. The theoretical results suggest that both the acceptor strength and the stable geometry contribute significantly to the electronic properties of donor-acceptor alternating conjugated polymers.

In the fluorene based conjugated polymer blends, photophysical properties of six blend systems were studied through UV-Vis absorption and photoluminescence spectra. Efficient energy transfer has been observed in blend system (I): F6PY and F6BT, and system (II): F6PY and F8T2. PL efficiencies could reach as high as 31.1 % and 15.6 % by adding only 5 wt% of F6BT or 10 wt% of F8T2 into F6PY, respectively. It suggests that the blend approach has the potential in enhancing the luminescence efficiency from the homopolymer. However, the PL emission of the F6TP blend system (III) ~ (V) did not show an enhancement as the systems (I) and (II). The PL quenching due to the heavy atom effects of sulfur or n→

並列關鍵字

conjugated polymer ； Donor-Acceptor ； DFT ； thiophene ； fluorene ； polymer blends ； F&ouml ； rster energy transfer

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