以苯并吡啶為主體具不同側鏈及主鏈之低能隙導電高分子合成及其特性研究

Abstract

本論文主要是探討二維電子施體、電子受體交替共聚高分子的光電特性，我們藉由Stille偶合反應及Yammamoto偶合反應合成PHQT、PFQT、PFQT2、PFQT3四種高分子。利用在側鏈引入不同基團 (茀或4-己基苯基)觀察側鏈與主鏈之間的交互作用，還有改變主鏈上電子施體 (噻吩)所佔之比例，研究主鏈上共軛長度對高分子光學、電化學性質的影響：紫外-可見光吸收光譜分成兩個區域，一個在300 nm~400 nm為單體π→π*的吸收範圍；另一個在500 nm~700 nm間是高分子鏈上分子內電荷轉移 (intramoleculars charge transfer)所造成的吸收，高分子能帶隙大約在1.75 eV~1.90 eV之間，其最高佔有分子軌域 (highest occupied molecular orbital, 簡稱HOMO)能階值大約在-5.27 eV~-5.13 eV之間。此系列高分子擁有不錯的熱穩定性，其熱裂解溫度大約都在400 ℃上下；利用廣角X光繞射測量高分子鏈在不同溫度下(100)結晶面間的距離，約為2.5 nm，隨著溫度升高，此距離亦隨之增加至2.8 nm。綜合以上所述，此系列高分子具有應用在光電元件活性層的可能性。

Two-dimensional donor-acceptor (D-A) structured conducting polymers, PHQT, PFQT, PFQT2, PFQT3, were designed and synthesized by introducing electron-deficient quinoxaline (acceptor) as core with electron-rich alky-fluorene or 4-hexylbenzene as its side chain and thiophene/oligo-thiophene (donor) in the main chain. Benefited from the D-A structures, the polymers possess low bandgaps with energies of 1.79 eV, 1.85 eV, 1.89 eV, and 1.76 eV for PHQT, PFQT, PFQT2, PFQT3, respectively, and show a broad absorption band in the visible region: the shoter wavelength absorption peak at ca. 300 nm~400 nm attributed mainly to the conjugated side chains and the longer wavelength absorption peak (charge transfer CT peak) between 500 nm and 700 nm ascribed to the absorption of the conjugated D-A main chains. The polymers are electrochemically active in oxidation and the corresponding cyclic voltammetry (CV) measurements show that the HOMO level of the polymers is ca. -5.31 eV~ -5.13 eV which is significantly lower than that of the conventional and most studied conducting polymer of poly 3-hexyl thiophene (P3HT). Powder X-ray diffraction analysis confirms that monodispersed PFQT shows a crystalline order plane of (100). The TGA analysis reveals that the temperature at which all polymers degrades was higher than 400 ℃. In summary, these polymers show potential for use as an active material in optoelectronic devices.