二維共軛結構噻吩衍生高分子之合成與應用

Abstract

本研究主要以具有2-octyldodecyl碳鏈之三噻吩作為共軛側鏈，並於主鏈導入雙噻吩或含氮雜環之拉電子基團，2,1,3-benzothiadiazole (BTD)及新型π-expanded DPP (eDPP)雙噻吩，成功地合成出一系列高溶解度之二維共軛高分子，分別命名為OCP01、OCP02和OCP03，並分析探討它們的結晶性、光學和電化學性質與分子結構的相關性。紫外可見光譜及循環伏安法測量顯示，引入BTD與eDPP單元至分子主鏈，皆能促使吸收光譜有效地紅位移，並降低能隙，尤其是新型的eDPP單體，其特殊的六稠環烴(fused ring)結構，使得OCP03展現寬廣吸收與最小能隙。當主鏈存在BTD單元時，可增強450~650 nm的吸收區域，OCP02光學能隙下降為1.65 eV；而當主鏈引入eDPP單元時，可增加600~800 nm的吸收範圍，OCP03展現1.45 eV的窄能隙。XRD實驗證實，將BTD插入主鏈中，導致結晶性略微下降，然而具高平面性的eDPP則可有效增加分子鏈的有序堆疊，而且熱退火處理皆可進一步幫助側鏈與主鏈的規則性排列，有效提升結晶性質。另外，我們將含2,3-didecylthienyl側鏈之benzodithiophene (BDT)單元作為推電子基團，透過Sille coupling方法與eDPP進行共聚合，生成二維共軛高分子OCP04，其在長波長600~900 nm有寬廣吸收，光學能隙為1.52 eV。 此外，本研究將所合成之二維共軛高分子，OCP01、OCP02、OCP03和OCP04，初步應用在光催化二氧化碳還原反應中，各別以1%的高分子混摻於氧化石墨烯(graphene oxide, GO)形成光催化劑系統。結果顯示加入二維共軛高分子作為有機敏化劑，皆能有效提升二氧化碳還原為乙醛與甲醇的產量，特別是1% OCP04/GO系統，其乙醛生成量比起單純的GO系統要高出約5倍。

In this study, a series of highly soluble two-dimensional conjugated copolymers with 2-octyldodecyl-bearing terthiophene-vinylene group as conjugated side chains were designed and synthesized successfully. All intermediates and the resulting copolymers were structurally characterized by nuclear magnetic resonance (NMR) spectroscopy, elemental analysis (EA) and mass spectrometry. Moreover, gel permeation chromatography (GPC), ultraviolet-visible spectrometer (UV-vis), X-ray diffractometer (XRD), photoelectron spectroscopy in air (PESA) and cyclic voltammetry (CV) were employed to determine their molecular weight characteristics, light absorption properties, crystallinity and energy levels, respectively. As expected, the introduction of electron-deficient nitrogen-containing heterocyclic rings, 2,1,3-benzothiadiazole (BTD) and newπ-expanded DPP (eDPP), into the polymer backbone effectively broadens the absorption spectrum and lowers both the HOMO and LUMO levels, leading to narrow bandgaps. More importantly, this novel eDPP fused ring considerably enhances the crystallinity of the copolymers. In addition, these new two-dimensional conjugated polymers were blended with graphene oxide (GO) to generate catalytic systems for CO2 photo-reduction. The incorporation of 1 wt% of these polymers into GO as sensitizer substantially increases the reaction rate of the photocatalytic reduction of CO2 into methanol and acetaldehyde. Especially, the production rate of acetaldehyde of the OCP04/GO system is determined to be about 5 times higher than that of the pristine GO system.