Molecular design of triphenylamine-based high-performance polymers with high electrochromic stability and optical contrast

ABSTRACT A novel triphenylamine (TPA)-based diamine monomer, named N,N’ -bis(4-methoxyphenyl)- N,N’ -bis(4-((4-aminophenyl-2,4-dimethoxyphenyl)amino)phenyl)- p -phenylenediamine, featuring four nitrogen centers and multiple methoxy substituents, was synthesized. Electroactive polyamide Ia and polyimide Ib , characterized by a main-chain TPA architecture, were prepared through polycondensation reactions of this new diamine monomer with 4,4’-oxydibenzoic acid and 4,4’-biphthalic anhydride, respectively. Compared to other TPA-based polymers, polyamide Ia exhibits enhanced electrochromic stability, with only 11% and 9.7% decay in coloration efficiency (CE) at 1370 nm and 442 nm, respectively, after 13,500 switching cycles in the first oxidation stage. Notably, Ia demonstrates high optical contrast (86%) and impressive cycling stability, with only a 9.3% decay in CE at 1370 nm after 10,000 switching cycles. It also shows broadband near-infrared (NIR) absorption in the visible to NIR II range (λ max ∼1370 nm) during the second oxidation stage. This underscores the advantages of the molecular design, particularly the main-chain TPA architecture with four electroactive nitrogen centers and para -methoxy or 2,4-dimethoxy substituents, in enhancing electrochromic performance. Additionally, polyimide Ib displayed excellent electrochromic stability, with only 8.3% and 9.9% decay in CE at 1275 nm and 439 nm, respectively, after 10,000 switching cycles in the first oxidation stage. The remarkable electrochromic stability of Ia and Ib can be attributed to their ability to stabilize polarons, which stems from the dispersion of charge in the cation radical across the four electroactive TPA cores through resonance, along with the electron-donating effects of the methoxy substituents. Both Ia and Ib exhibit high optical contrast, robust cycling stability, and broadband NIR absorption in the visible to NIR II range during both the first and second oxidation stages, demonstrating promising applications in smart windows and energy-efficient building technologies.