Tie-molecule-mediated co-assembly pathways in hierarchical conjugated block copolymer nanowires visualized by in-situ LP-TEM

Abstract

The performance of organic electronic materials is fundamentally governed by the hierarchical organization of pi-conjugated polymers (CPs) in solution. Unlike conventional polymer aggregation, crystalline CPs undergo a highly regulated seed-and-growth stepwise assembly via crystallization-driven self-assembly (CDSA), enabling the precise control of molecular alignment into sophisticated multi-compartment micelles. Controlling these crystallization pathways is essential not only for facilitating intramolecular charge transport (ICT) and charge transfer complex (CTC) formation through directed stacking but also for maintaining the requisite amorphous domains that ensure mechanical robustness in solution-processed films. In this study, we utilize in situ liquid-phase transmission electron microscopy (LP-TEM) to directly visualize the real-time evolution of conjugated nanowire bundles formed via a strategic co-assembly of diblock and triblock copolymers. We elucidate the critical role of triblock copolymers acting as "tie molecules," which bridge highly crystalline domains to align nanowires into hierarchical bundles. By capturing the nascent structural formation, we successfully decouple the intrinsic assembly kinetics from drying-induced artifacts, revealing how tie-molecule infiltration and interfacial crystallization enable the preservation of maximized crystallinity within individual nanowires while precisely governing the pi-conjugation orientation. These in situ observations provide a fundamental structural perspective on tie molecules, indicating that their spatial distribution is a key factor in modulating long-range alignment and CTC efficiency. Our findings demonstrate that utilizing tie molecules to establish robust charge transport pathways between crystalline domains provides a unique pathway to overcome the intrinsic conflict between crystalline intrachain transport and macroscopic mechanical toughness. By establishing a direct link between nanoscale assembly dynamics and macroscopic functions, this work proposes a rational framework for designing high-performance organic semiconductors, bridging the gap between solution-phase assembly dynamics and the morphological robustness of next-generation organic electronics.