Three dimensional fluorene-based polyamides facile to transfer ion designed for near-infrared electrochromic application and detection for explosive

Near-infrared electrochromic (NIR EC) functional materials are attracting increasing attention owing to their great potential for applications in smart window. However, obtaining high performance NIR EC material with high optical transmittance contrast, fast redox switching and long-term cyclic stability is still a challenge. Introducing four triphenylamine (TPA) units into one planar fluorene core to build robust three dimensional (3D) framework which not only makes ion and electron move freely but also provides sufficient space and storage sites for hosting ions will meet the requirement. Here, three kinds of new polyamides (PAs) based on conjugated fluorene as the bridge unit were designed and polycondensized by a new diamine N, N'-(9,9-bis(4-(diphenylamino)phenyl)-9H-fluorene-2,7-diyl)-bis(N-(4-methoxyphenyl) benzene-1,4-diamine), with three kinds of dicarboxylic acids to form TPAF-6F, TPAF-CA and TPAF-OA. The obtained new PAs exhibit impressive solution-processability and excellent thermal stability. Cyclic voltammograms (CV) and differential pulse voltammograms (DPV) of the PAs imply strong electronic coupling within molecule. Furthermore, the TPAF-OA film exhibits excellent EC performance with multi-coloured EC behaviour, high optical contrast (92%), high coloration efficiency (203 cm² C⁻¹) and outstanding cycle stability (optical contrast remains 90% over 1400 cycles) in the NIR range. TPAF-CA also shows impressive fluorescence (PL) quantum efficiency which could be used as sensor for explosive and nonvolatile flash memory properties. The strategy of introducing 3D framework block into polymer will pave a way for fabricating high performance optoelectronic devices.