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

Abstract

Designing donor-acceptor (D-A) conjugated polymers (CPs) with exceptional electrical conductivity (sigma) 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 (AuCl3) 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 sigma up to 2044.5 S cm-1 and PF of 1061.2 & micro;W 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.