Overall, our DFT results explain why PM7 D1 and D2 exhibit short persistence lengths and are less likely to form large fiber-like aggregates in solution as compared to PM7. Firstly, we find that minimum-energy dihedral angles of PM7 D1 and D2 are larger than PM7 which lead to more non-planar and distorted backbone conformations, consistent with their shorter persistence lengths observed in solution. Secondly, dihedral angles of PM7 D1 and D2 require higher energies to planarize than dihedral angles of PM7, which is consistent with the longer backbone stacking distance observed in PM7 D1 and D2 solutions. Finally, PM7 D1 and D2 are more likely to switch between anti and syn conformations due to their low energy barriers, making their backbones more flexible than PM7. We attribute these observations of PM7 D1 and D2 to their planarity disrupting ester functionalized terthiophene acceptor moieties yielding flexible and non-planar conformations which prevent their tendency to form fibrillar aggregates in solution.