Understanding the Solvent-Regulated Assembly of Conjugated Polymers via Nanoscale Visualization

The multilevel assembly of conjugated polymers critically determines their electronic performance. However, establishing a direct correlation from molecular-level interactions to macroscopic morphology and charge transport properties remains challenging. In this work, advanced characterization techniques were employed to identify and visualize two distinct assembly processes of a representative n-type conjugated polymer, F4BDOPV-2T, in both solution and thin film states, allowing for a structural correlation between solvent affinities and assembly structures. In 1-chloronaphthalene, strong solvation of the conjugated backbones promoted sidechain-dominated growth of nanoscale assemblies and ordered lamellar packing, resulting in compact 3D cluster aggregates in solution and well-oriented, large-scale ordered crystalline grains in the solid state. Conversely, toluene favored sidechain solvation, leading to backbone-dominated assembly growth that formed fiber networks and interconnected crystalline grains. The superior grain connectivity during backbone-dominated growth outweighed the effect of smaller grain size, yielding a three-fold enhancement in electron mobility (μe = 2.05 cm2 V–1 s–1). Through real-space electron microscopy visualization, this work bridges intermolecular interactions with multilevel assembly structures of conjugated polymers, providing fundamental insights into rational solvent regulation and morphological control for high-performance organic electronics.