A Thieno[3,2- <i>b</i> ]indole Platform for Conjugated Polymers via Direct Arylation Self-Polycondensation: Design, Synthesis, and Electrochromic Exploration

The lack of a versatile molecular platform compatible with atom-economical synthesis has hindered the development of new donor–acceptor (D–A) conjugated polymers. This work addresses this challenge by introducing thieno[3,2- b ]indole (TI) as a modular core for a direct arylation self-polycondensation (DASP)-driven strategy. Through systematic “longitudinal” derivatization, we constructed a series of new fused-ring monomers ( M1 – M4 ) with built-in D–A character by incorporating benzothiadiazole, benzoselenadiazole, quinoxaline, and fluorinated benzene acceptor units. DASP proved universally effective for this system, efficiently producing high-molecular-weight polymers ( PTI-1 to PTI-4, up to 103.8 kDa) and establishing its utility beyond simple systems. This molecular platform enabled a clear understanding of the roles of heavy-atom effects (Se vs S), acceptor strength, and noncovalent interactions (e.g., F···H), which collectively govern the optical band gaps (1.48–2.15 eV), energy levels, and solid-state order. Based on these insights, PTI-4 was identified as a high-performance electrochromic material, enabling a flexible, patterned device that demonstrates a clear path from rational design to functional application.