Donor‐Unit‐Dependent Polymer Chain Packing Dictates Site‐Selective Doping and Charge Transport in High‐Performance Naphthyridinedione‐Based Organic Thermoelectric Conjugated Polymers

Designing donor–acceptor (D–A) conjugated polymers (CPs) with exceptional electrical conductivity (σ) and high power factor (PF) is critical for organic thermoelectric (OTE) applications, yet structure–property correlations are often obscured by the coupled effects of electronic properties and CP chain packing. Here, we report a series of high‐performance CPs based on a 1,5‐naphthyridine‐2,6‐dione (NTD) acceptor core, systematically varying the comonomer donor unit among thiophene, selenophene, and bithiophene to probe these relationships. Structural analysis shows that donor length dictates packing, switching from a bimodal, face‐on dominant orientation in mono‐donor CPs to a well‐defined edge‐on orientation in bithiophene‐based CPs. After gold(III) chloride (AuCl 3 ) doping, spectroscopy, electrical measurements, and theory reveal sterically controlled, donor‐selective charge localization on the electron‐rich bithiophene units, overriding the thermodynamic preference for the NTD core and enabling dopant intercalation into the lamellar spacing. This design delivers state‐of‐the‐art performance, with the bithiophene‐containing polymer (PNTDT‐BT) reaching σ up to 2044.5 S cm −1 and PF of 1061.2 µW m −1 K −2 . These results establish NTD as a potent OTE building block and highlight donor‐unit extension as a key strategy for sustaining high carrier densities.