生物啟發共軛高分子自組裝研究 並應用於有機半導體元件

Abstract

生物啟發型共軛高分子自組裝科學在奈米結構材料領域取得重要進展。其中，氫鍵作用力與堆疊作用力是超分子識別和自組裝中最重要的一種分子間相互作用。藉由操控這些非共價鍵作用力進行分子自組裝進而實現不同尺度上的規則結構，使共軛高分子材料在有機電子元件領域有廣泛的應用。 本論文主要研究生物啟發型共軛高分子複合材料，利用側鏈帶有腺嘌呤的聚噻吩，以超分子作用力方式製備多維度奈米複合材料。首先將側鏈帶有腺嘌呤的聚噻吩與富勒烯混摻形成的高分子微胞因具有有機材料的記憶效應可應用於硬板/軟板有機記憶體元件。然後藉由堆疊作用力控制奈米碳管陣列排列規則，以氫鍵作用力提升奈米碳管的分散性。最後憑藉選擇性氫鍵作用力控制此生物啟發型共軛高分子腺嘌呤聚噻吩的表面形貌，有效提升有機薄膜電晶體架構中的半導體主動層載子遷移效能。 (1) 首先我們導入一個新的概念並成功地藉生物鹼基對互補性超分子作用力有效提升π共軛聚（3-己基噻吩）的特性。所製備出的生物啟發型共軛聚（3-己基噻吩）高分子是藉由側鏈導入腺嘌呤方式來控制其氫鍵作用力，接著我們混摻此生物啟發型共軛聚合物與(6,6)-苯基-C61-丁酸甲酯，成為一個全新的異質體接面微胞結構的高分子複合材料。我們在該混摻系統[共軛聚（3-腺嘌呤己基噻吩） / (6,6)-苯基-C61-丁酸甲酯]中使用不同極性的溶劑來控制其高分子微胞的形成。透過穿透式電子顯微鏡，高解析電子能譜儀和原子力顯微鏡分析，我們驚奇地發現在二甲基亞碸溶劑會形成(6,6)-苯基-C61-丁酸甲酯在內共軛聚（3-腺嘌呤己基噻吩）在外的高分子型微胞；在四氯乙烯溶劑則形成相反之共軛聚（3-腺嘌呤己基噻吩）在內(6,6)-苯基-C61-丁酸甲酯在外之高分子型逆微胞結構。通過使用循環伏安法，我們發現共軛聚（3-腺嘌呤己基噻吩）的最低未佔分子軌域比商業化共軛聚（3-己基噻吩）更高，它能夠擴大供體 - 受體對的能階之間的能量差距;因此，共軛聚（3-腺嘌呤己基噻吩）有更好的防止電子倒流的特性。而在高分子型逆微胞系統顯示出具有更大的VOC = 0.54伏特導電性，電流ISC = 229皮安培，相較於(6,6)-苯基-C61-丁酸甲酯有5倍導電性能增強。在此研究最後我們也成功地將此高分子型微胞系統應用於以全聚合物為材料的軟性記憶體元件中。 (2) 在第二部分，我們藉由將脲嘧啶以化學修飾方式接枝在奈米碳管上。成功地藉由X-光繞射觀察到接枝在奈米碳管上脲嘧啶－脲嘧啶特有的二聚物堆疊作用力，我們通過原子力顯微鏡和差示掃描量熱法發現這種脲嘧啶－脲嘧啶堆疊相互作用力是具有方向性與可逆性，並且能夠穩定脲嘧啶－奈米碳管陣列。我們使用了幾個實驗技術來觀察脲嘧啶－奈米碳管穩定分散在共軛聚（3-腺嘌呤己基噻吩）二甲基亞碸溶液的情況；從分散系統照片證明此混摻系統確實存在特殊的非共價鍵作用力。在掃描式電子顯微鏡和穿透式電子顯微鏡圖像中發現脲嘧啶－奈米碳管上和共軛聚（3-腺嘌呤己基噻吩）之間具有特異性的氫鍵作用力效應。為了進一步了解材料的自組裝機制，我們通過螢光能量轉移實驗發現脲嘧啶－奈米碳管在共軛聚（3-腺嘌呤己基噻吩）二甲基亞碸溶液裡能夠有效地將能量從共軛聚（3-腺嘌呤己基噻吩）轉移至脲嘧啶－奈米碳管，也就是說藉由能量轉移的機制使脲嘧啶－奈米碳管穩定在生物啟發型共軛高分子溶液中。在未來，我們可以透過這樣的分散系統，來生產高品質薄膜或是其他奈米複合材料的應用。 (3) 最後我們巧妙地設計側鏈誘導分子自組裝的方法來製備井然有序的有機薄膜電晶體半導體主動層。為了獲得具有氫鍵選擇性的半導體主動層，我們混摻側鏈導入腺嘌呤官能化的共軛聚（3-腺嘌呤己基噻吩）與三磷酸腺苷。通過該方法，能夠藉由共軛聚（3-腺嘌呤己基噻吩）側鏈誘導分子自組裝方式控制聚合物的形態，不需要經由額外的有機化學合成處理。側鏈誘導自組裝可藉由超分子之間的相互作用來理解，側鏈誘導分子自組裝能夠有效提高高分子結晶規則的一致性，進而提高了鏈間電荷輸送能力;當共軛聚（3-腺嘌呤己基噻吩）中的平面π電子系統因導入三磷酸腺苷，為釋放出立體障礙所承受的應力;側鏈會進行重排，偏向產生具有選擇性的腺嘌呤－腺嘌呤高分子對小分子氫鍵作用力，進一步使高分子鏈間因堆疊作用力的關係形成更緊密的距離，促進共軛聚（3-腺嘌呤己基噻吩）從原本非晶系的球狀結構變成纖維狀結構，進而提升載子流遷移率。該方法具有分子間相互作用的選擇性，未來在有機薄膜電晶體半導體主動層製備的應用具有一定的潛力。

The selfassembly of bioinspired conjugated polymer in solution and in solid state has attracted intense attentions; they are promising candidates with a variety of potential applications for nanostructural materials. Typically, synthetic macromolecules differ with respect to their biological counterparts, for example of nucleic acid, where the selfassemblies usually involved direct hydrogen bonding and stacking interaction. Bioinspired conjugated polymer displays interesting selfassembly phenomenon that allows the creation of hybrid materials for organic electronic devices especially for the generation of upcoming flexible application. In this dissertation, we focus on employing the concept of supramolecular to manipulate morphology of existed πconjugated polymers by noncovalent interaction. A new adeninegrafted poly(3hexylthiophene) (PAT) polymer has been prepared and investigated, which exhibits high thermal stability, good solvent resistance, excellent optical and electrochemical properties in the solution state and solid state owing to the adenine induced physical crosslinking. (1) We develop a new concept to construct and enhance the properties of existing functional polymers through biocomplementary interaction has been exploited. The new DNA-mimeticπconjugated poly(3hexylthiophene) (P3HT) has been synthesized as adenine-grafted poly(3adeninehexyl thiophene) (PAT) followed by blending with [6,6]phenylC61butyric acid methyl ester (PC61BM) as a new bulky heterojunction (BHJ) structure material. We use diverse polarity solvents in this blending system (PAT/PC61BM) and surprisingly found the formation of polymeric micelles in dimethyl sulfoxide (DMSO) solvent, and reversed hybrid micelles in trichloroethylene (TCE) solvent based on dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) analyses. By using cyclic voltammetry (CV), we found that the lowest unoccupied molecular orbital (LUMO) of PAT is higher than commercial P3HT and that it enlarges the energy gaps between the LUMOs of the donor-acceptor pair; hence, PAT has a better ability to prevent the electrons from flowing back. The reversed hybrid system shows a greater conductivity with Voc= 0.54 V, Isc= 229 pA and 5-fold enhanced performance compared to the initial PC61BM. The polymeric micelle system is successfully employed in a fully polymerbased memory device. (2) In this section, we report the first observation, through Xray diffraction, of noncovalent uracil–uracil (U–U) dimericπstacking interactions in carbon nanotube (CNT)–based supramolecular assemblies. The directionally oriented morphology determined using atomic force microscopy revealed highly organized behavior through πstacking of U moieties in a Ufunctionalized CNT derivative (CNTU). We developed a dispersion system to investigate the bio-inspired interactions between an adenine (A)terminated poly(3adeninehexyl thiophene) (PAT) and CNTU. These hybrid CNTU/PAT materials interacted through stacking and multiple hydrogen bonding between the U moieties of CNTU and the A moieties of PAT. Most importantly, the U•••A multiple hydrogen bonding interactions between CNTU and PAT enhanced the dispersion of CNTU in a high-polarity solvent (DMSO). The morphology of these hybrids, determined using transmission electron microscopy, featured grapelike PAT bundles wrapped around the CNTU surface; this tight connection was responsible for the enhanced dispersion of CNTU in DMSO. (3) In the final section, we have developed a strategy for modifying the channel layer of organic thin film transistors (OTFTs) through side-chain induced selforganization into a well-ordered film. To obtain selectively self-patterned layers, we treated an adenine-functionalized poly(3hexylthiophene) (PAT) with adenosine triphosphate (ATP). Using this strategy, interchain charge transport resulting from πconjugation was selected to control the polymer morphology, without the need of additional chemical synthetic processing. The side chain–induced self-organization can be understood in terms of supramolecular interactions. The πelectrons were delocalized among the thiophene rings, thereby improving the interchain charge transport ability; the resulting planar πelectron system in PAT:ATP resulted in closer intermolecular ππ distances, facilitating enhanced charge carrier mobility within a fibrillar structure. The PAT:ATPbased OTFT device exhibited moderate to improved electronic characteristics, with an average field mobility of 1.6  10–4 cm2 V–1 s–1 at –30 V and a threshold voltage (Vth) of 5 V, and an on/off current ratio of 106. This method has great potential for inducing selective intermolecular interactions in fully solution processed electronic devices.