The Self-Assembly of Bio-inspired π-Conjugated Polymers and Their Applications for Organic Electronics

• Main Authors: Lin, Yen-Ting, 林彥廷
• Other Authors: Ko, Fu-Hsiang
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/2wv548

博士 === 國立交通大學 === 材料科學與工程學系奈米科技碩博士班 === 105 === 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.