Synthesis of Conducting Two-dimensional Polymers and Their Applications

Abstract

This thesis explores a burgeoning field of two-dimensional (2D) polymers, examining their definition, inherent characteristics, and the synthetic methodologies leading to their potential applications. Among 2D polymers, conducting 2D polymers (C2Ps), topologically planar polymers with π-conjugation, are the main theme of the thesis, including the theoretical and electronic properties of C2Ps, addressing the issues of their synthesis and integration into advanced electrochemical applications. This thesis represents a thorough investigation in the search for the 'Holy Grail' of post-graphene research. Chapter 1 provides a broad introduction to the field of 2D polymers, offering a background from their initial definitions to the detailed discussion of their properties, synthetic methods, and the potential they hold for future applications. It emphasizes their unique 2D topology derived from monomer design and the versatility afforded by organic synthesis. This foundation parallels that of linear polymers, enabling a myriad of variants through monomer engineering and modification, which is critical to research advancement and developing real-world applications. Chapter 2 transitions into a meticulous investigation of the challenges associated with crystallinity and solubility in C2Ps, significant hurdles in their incorporation into electronic devices via solution processing. The chapter presents triphenylene-based building blocks that, through a sequence of reversible and irreversible reactions, lead to the formation of crystalline C2P, C2P-5. The internal order of C2P-5 and their unprecedented hole mobility are revealed. The elucidated long-range order within the polymer films and the enhanced hole mobility represent a substantial advancement towards the development of high- performance optoelectronic devices. Chapter 3 discovers the intriguing frontiers in electronic properties of C2Ps. It reports a C2P, C2P-9, embedded with bulky pendant groups designed to suppress interlayer stacking and enhance the solubility of growth intermediates. The monomer design allows higher degree of polymerization by enhanced solubility, resulting in the outstanding electrical conductivity after doping. Through cutting-edge magnetotransport measurements, a stark contrast is unveiled between electronic states near the Fermi level. Upon p-type doping, finite n-type transport was observed with exceptionally high mobility and coherence lengths. This chapter underscores the profound impact of bulky pendant groups on solubility, electronic band structure, and the conduction pathways, offering insights into the sophisticated design of C2Ps. Chapter 4 describes metal-free hydrogen peroxide (H2O2) production using C2Ps as photoelectrocatalyts, focusing on pendant modification strategy that enables energy level modulation and catalytic activity enhancement. This chapter presents C2P-9N, synthesized from pendant modification of C2P-9, showing the record-high activity and selectivity for 2 electron oxygen reduction reaction (ORR). Furthermore, when coupled with 2 electron water oxidation reaction (WOR), C2P-9N works as a bifunctional electrode for ORR//WOR coupled cell with outstanding performance. Theoretical calculations revealed that modified pendant groups can effectively stabilize the intermediates, thus facilitating the rate- determining step in photocatalytic synthesis. This chapter serves as a key example of how modifying pendant groups in C2Ps can dramatically improve their band structure and catalytic properties.