Controllable Transformation Between the Kinetically and Thermodynamically Stable Aggregates in a Solution of Conjugated Polymers

The aggregation behaviors of conjugated polymers significantly influence their performance in solution-processed optoelectrical devices. Traditionally, the formation of aggregates from the self-assembly of conjugated polymers is considered as a thermodynamic equilibrium process. The abundant degree of conformation freedom of conjugated polymers might lead to complex aggregation behaviors in solution. However, the energy landscape of conjugated polymers during aggregation has rarely been studied before, which would provide the energetic and structural information about different aggregates. Our work tried to unravel the energy landscape of conjugated polymers during aggregation and investigate the energetic and structural information of the thermodynamically and kinetically stable aggregates in solution. Herein, kinetically and thermodynamically stable aggregates of naphthalene diimide (NDI)-based polymers are obtained through rational molecular design and thermodynamic control. Investigation of the theoretical calculation, photophysical properties, and morphologies of the conjugated polymers demonstrates the formation of and differences between kinetically and thermodynamically stable aggregates. The energetic and structural analysis of kinetically and thermodynamically stable aggregates here provide insight into the relations among the structure, morphology, and properties of conjugated polymers at the molecular level. This work demonstrates the energy landscape of conjugated polymers during aggregation and further extends our understanding of the aggregation mechanisms.