What is the Assembly Pathway of Conjugated Polymers from Solution to the Solid State?

The hierarchical assembly of conjugated polymers has gained much attention due to its critical role in determining the optical/electrical/mechanical properties. The complex morphology in the solid state is fully determined by the polymer assembly pathway in the solution state, which in turn is sensitively modulated by molecular structure and processing conditions. However, molecular pictures of polymer assembly pathways remain elusive, due to the lack of detailed structural characterizations in the solution state and lack of understanding on how various factors impact the assembly pathways. In this talk, we discuss pre-aggregation and liquid-crystal mediated assembly pathways and their relationship. We develop SAXS models for in-depth analysis of the complex solution state structure of conjugated polymers complemented by imaging and spectroscopy. Further we discover a chiral, helical liquid crystal mediated assembly pathways from achiral conjugated polymers. We elucidate a hierarchical helical structure spanning the molecular scale to micron scale. We further trace the molecular origin of chiral liquid crystal assembly pathways. These studies change the way we perceive structure of conjugated polymers and may bring forth exciting new optoelectronic properties not imagined before.