A Novel Solubilizing Fully π-Conjugated Ladder Polymer and Its Thermoelectric Properties

Fully conjugated ladder polymers (CLPs) have emerged as promising candidates for next-generation organic electronics due to their extended π-conjugation pathways, intrinsic charge transport anisotropy, and exceptional chemical and thermal stability. However, insolubility remains a critical bottleneck, primarily stemming from side reactions that disrupt the linear structure. Herein, we report a soluble CLP, benzo[a]benzo[5,6][1,4]thiazino[3,2-c]phenothiazine ladder (NBBTL), via a stepwise strategy to preserve the linear structure of the polymer. The resulting polymer exhibits unprecedented solution processability while maintaining structural integrity, enabling the first reported thermoelectric generator fabrication. Thermoelectric performance evaluation revealed that FeCl₃-doped NBBTL achieved a conductivity of 3.18 ± 0.33 S cm^-1 and a power factor of 0.94 ± 0.09 μW m^-1 K^-2. Further analysis of the polymer chain orientation in films by grazing-incidence wide-angle X-ray scattering revealed that NBBTL exhibits a bimodal orientation with both face-on and edge-on. This study demonstrates that strategic molecular engineering can overcome long-standing insolubility issues in CLPs, potentially paving the way for their wider application in organic electronics and thermoelectric energy conversion.