Fine-tuning the backbone conformation of conjugated polymers and the influence on solution aggregation and optoelectronic properties

The backbone conformation plays a vital role in the solution aggregation behavior and photophysical and electrical properties of conjugated polymers. Previous studies indicated that the backbone conformation modification mainly relied on introducing various functional groups. However, regulating the molecular conformation through non-covalent interactions is highly susceptible to external factors such as solvents and temperature. Herein, four isoindigo-based polymers, IIDDP, IIDDP-C0, IIDDP-C1, and IIDDP-C2, are developed with distinct chain conformation. Covalent bonds are employed to fix the dihedral angle of the donor fragment and then control the main-chain conformation. Due to conformation-locking, it was observed that the planarization of the main chain from the solution to the thin film could not be achieved in the desired polymers with twisted backbones. Further investigations revealed that the relationship between the backbone conformation and the solution-state supramolecular structures play a critical role in controlling solid-state microstructures and optoelectronic performance of conjugated polymers.