Elucidating the structure of donor-acceptor conjugated polymer aggregates in liquid solution.

High-spin donor-acceptor conjugated polymers are extensively studied for their potential applications in magnetic and spintronic devices. Inter-chain charge transfer among these high-spin polymers mainly depends on the nature of the local structure of the thin film and π-stacking between the polymer chains. However, the microscopic structural details of high-spin polymeric materials are rarely studied with an atomistic force field, and the molecular-level local structure in the liquid phase remains ambiguous. Here, we have examined the effects of oligomer chain length, side chain, and processing temperature on the organization of the high-spin cyclopentadithiophene-benzobisthiadiazole donor-acceptor conjugated polymer in chloroform solvent. We find that the oligomers display ordered aggregates whose structure depends on their chain length, with an average π-stacking distance of 3.38 ± 0.03 Å (at T = 298 K) in good agreement with the experiment. Also, the oligomers with longer alkyl side chains show better solvation and a shorter π-stacking distance. Furthermore, the clusters grow faster at higher temperature with more ordered aggregation between the oligomer chains.