Synthesis and\nCharacterization of n‑Doped Poly(benzodifurandione)\n(<b>n‑PBDF</b>) Derivatives via Aromatic Substitution

n-Doped poly(benzodifurandione) (<b>n-PBDF</b>)\nis an n-type\nconducting polymer with characteristics such as high electrical conductivity,\nsolution processability, and weathering stability. Here, we systematically\ninvestigate the structure property relationship on the impact of structural\nmodifications through aromatic substitution on the photophysical,\nelectrical, and structural properties of <b>n-PBDF</b> and its\noligomeric derivatives. We demonstrated that an electron donation\ngroup (methyl) raised the highest occupied molecular orbital energy\nlevel (+0.15 eV), while electron-withdrawing halogens (Br and Cl)\ndecreased the lowest unoccupied molecular orbital energy level (−0.12\nand −0.13 eV, respectively) in the polymers. Additionally,\nin both the undoped and doped oligomeric systems, these substitutions\nintroduce large torsion angles (θ > 17°), causing the\nmaterial\nto twist significantly. Moreover, the methyl-substituted polymer, <b>n-PBDF-Me</b>, was evaluated for its potential as a transparent\norganic conductor, due to its high optical transmittance (<i>T</i><sub>550</sub> > 93%). However, <b>n-PBDF-Me</b> films\nhave significantly lower conductivity than <b>n-PBDF</b> (0.40\nvs 1330 S/cm) at similar thickness.