Development of Living Crystallization-Driven Self-Assembly and Precision C–H Activation Polymerization for π-Conjugated Polymers

Traditionally, polymers such as polyethylene, polypropylene, and polystyrene have been predominantly developed and utilized as structural or packaging materials, focusing on their mechanical robustness, chemical stability, and low cost. In contrast, π-conjugated polymers are a fundamentally different class of materials, in which the delocalized electronic structure enables semiconducting behavior and tunable optoelectronic functionality. Therefore, they have emerged as key semiconducting materials in organic electronic devices, such as organic field-effect transistors, photovoltaic cells, and light-emitting diodes. In such applications, device performances depend not only on the chemical structure of the repeat unit but also by the precision of polymer synthesis and even their supramolecular self-assembled structures. Consequently, the development of synthetic strategies that provide both molecular-level precision and controllable higher-order structures is a central challenge in the field of conjugated polymers. This doctoral thesis addresses this challenge through the development of precision polymerization and its application onto crystallization-driven self-assembly for π-conjugated polymers, particularly on donor–acceptor (D–A) conjugated polymers. The thesis is organized into two main parts. Part A focuses on self-assembly enabled by previously developed living polymerization method based on Suzuki–Miyaura reaction. On the other hand, Part B focuses on the development of direct arylation polymerization (DArP), as a sustainable route to low-defect and structurally well-defined conjugated polymers. In Part A, two projects were conducted to investigate how crystallinity and a precision polymerization can be translated into controlled one-dimensional nanostructures, by applying previously established living Suzuki–Miyaura catalyst-transfer polymerization (SCTP). First, a polymerization-induced crystallization-driven self-assembly (PI-CDSA) strategy is developed using a donor-type poly(3-propylthiophene) core within fully conjugated D–A block copolymers (BCPs) synthesized via SCTP. The limited solubility and high crystallinity of the donor core are the key to trigger spontaneous in situ donor core–acceptor shell nanofiber formation during polymerization. Furthermore, a simple precipitation step generates uniform seeds that enable living CDSA with precise length and width control. In the second project, this concept is extended from donor-type to acceptor-type crystalline cores. Two different acceptor polymers, including weak acceptor polybenzotriazole and strong acceptor polyquinoxaline, are shown to possess sufficient crystallinity to act as self-assembling cores, enabling the formation of acceptor core–donor shell nanofibers. These studies highlight the importance of rational design of BCPs and precision polymerization methods as key tools to expand the scope of CDSA in fully conjugated polymers with various electronic characters. In Part B, two projects address the development of novel synthetic methods to simultaneously enable precision and sustainability in conjugated polymer synthesis, through DArP based on C–H activation chemistry. First, a low-temperature Pd/Ag dual-catalytic DArP is presented, in which the synergistic action of Pd catalysis for cross-coupling and Ag catalysis for mild C–H activation leads to significantly lower temperatures than conventional DArP. This approach affords a broad library of D–A conjugated polymers with reduced structural defects, enhanced crystallinity. In addition, these characteristics improved the performances of organic electronic devices, including ambipolar field-effect transistors and complementary metal-oxide-semiconductor inverters. Building on this foundation, the final project explores the merge of C–H activation and chain-growth polymerization, termed “direct arylation catalyst-transfer polymerization (DArCTP)”, to prepare a D–A alternating copolymer. Through a rational monomer design, a D–A alternating copolymer is synthesized with controlled molecular weight and dispersity, demonstrating the feasibility and limitations of DArCTP. Overall, this thesis demonstrates new synthetic and structural toolbox for π-conjugated polymers, by advancing precision polymerization and its application on controlled self-assembly. By bridging molecular synthesis, nanoscale self-assembly, and device performances, the work contributes to the development of polymers into semiconducting materials, offering new opportunities for next-generation organic electronics.