Multicolored and near-infrared electrochromic polyimide and polyamide functionalized with triphenylamine star-shaped architecture

Triphenylamine (TPA)-based polymers have emerged as an appealing family of electrochromic materials due to their colorless neutral state, intriguing electrochromic properties, and ease of processing. However, the limited long-term stability of these materials has been a significant barrier to their practical application. A novel TPA-based starburst diamine monomer has been successfully synthesized, and electroactive polyamide (PA) Ia and polyimide (PI) Ib with TPA star-shaped architecture were prepared by polycondensation reactions of this new diamine monomer with 4,4’-oxydibenzoic acid and 4,4’-biphthalic anhydride, respectively. Polymers Ia and Ib with four electroactive TPA centers in their repeat units demonstrated multi-colored electrochromism, high optical contrast, remarkable enhancement in electrochromic stability. Compared to other TPA-based polymers, the present PA Ia with starburst TPA side chains exhibited enhanced electrochromic stability (only 1.6 % and 3.9 % decay of its coloration efficiency (CE) at 1251 nm and 439 nm, respectively, after 20000 switching cycles) at the first oxidation stage. Notably, PI Ib also revealed excellent electrochromic stability (only 9.8 % and 6.2 % decay of its coloration efficiency (CE) at 1240 nm and 411 nm, respectively, after 8000 switching cycles) at the first oxidation stage. The record-high electrochromic stability of Ia and Ib can be attributed to the ability to stabilize the polaron, which originates from dispersing the charge of the cation radical on four electroactive centers via resonance. Polymers Ia and Ib also showed a broad and rather intense absorption in the near-infrared (NIR) region upon oxidation, and this is highly beneficial for applications such as smart windows and energy-efficient building technologies. Importantly, different multicolor of high electrochromic stability of polymers, which allow for multicolor tunability by adjusting the substituents, can be developed from the specifically designed structures with four electroactive centers in the side chains.