Role of the Chain Structure and Conformation of Conjugated Polymers on Aggregation Behavior

Abstract

The aggregation behavior and solid-state microstructures of conjugated polymers play an important role in optoelectronic properties and device performances. Adaption of classical polymer theory and phenomenological discussion of the structure were commonly applied to unravel the nature of aggregation. However, the broadened molecular weight distribution and the discrepancy in interactions between polymer backbones and alkyl chains increase the difficulty in pinpointing the nature of the aggregation mechanism and behavior. Here, four conjugated polymers were developed to construct the relationship between the polymer conformation and the aggregation behavior. The effect of the interunit torsion and the flexibility differences of the conjugated chains on the aggregation behaviors in solutions was investigated in detail. On this basis, a model combined with supramolecular polymerization and classical polymer theory brought a new perspective of thermodynamics to unravel the aggregation process in solution. The aggregation equilibrium inclined toward short-range/long-range π-stacks with planar/torsional units, and the disaggregated species inclined toward dispersed chains/coils with a rigid/flexible backbone. Furthermore, the aggregation structures were inherited to the solid phase, resulting in excellent electronic properties for the planar and rigid polymers and strong domain-regulation ability for the torsional and flexible polymers. Our investigation pioneers the introduction of supramolecular aggregation theory into the study of the aggregation behavior of conjugated polymers in solution, which sheds light on the nature of the aggregation of conjugated polymers from a thermodynamic perspective, constructs a landscape for the aggregation process, and also provides guidance for the structure design and the selection of modulation methods matching the structure and performance requirements.