Synthesis and Characterization of n-Doped Poly(benzodifurandione) (<b>n-PBDF</b>) Derivatives via Aromatic Substitution

n-Doped poly(benzodifurandione) (n-PBDF) is an n-type conducting polymer with characteristics such as high electrical conductivity, solution processability, and weathering stability. Here, we systematically investigate the structure property relationship on the impact of structural modifications through aromatic substitution on the photophysical, electrical, and structural properties of n-PBDF and its oligomeric derivatives. We demonstrated that an electron donation group (methyl) raised the highest occupied molecular orbital energy level (+0.15 eV), while electron-withdrawing halogens (Br and Cl) decreased the lowest unoccupied molecular orbital energy level (−0.12 and −0.13 eV, respectively) in the polymers. Additionally, in both the undoped and doped oligomeric systems, these substitutions introduce large torsion angles (θ > 17°), causing the material to twist significantly. Moreover, the methyl-substituted polymer, n-PBDF-Me, was evaluated for its potential as a transparent organic conductor, due to its high optical transmittance (T550 > 93%). However, n-PBDF-Me films have significantly lower conductivity than n-PBDF (0.40 vs 1330 S/cm) at similar thickness.