Dual-Band Electrochromic Poly(Amide-Imide)s with Redox-Stable N,N,N’,N’-Tetraphenyl-1,4-Phenylenediamine Segments

Two amide-preformed aromatic diamine monomers, <i>N</i>,<i>N</i>-bis(4-(3-aminobenzamido)phenyl)-<i>N</i>',<i>N</i>'-bis(4-methoxyphenyl)-1,4-phenylenediamine (<i>m</i>-<b>6</b>) and <i>N</i>,<i>N</i>-bis(4-(4-aminobenzamido)phenyl)-<i>N</i>',<i>N</i>'-bis(4-methoxyphenyl)-1,4-phenylenediamine (<i>p</i>-<b>6</b>), were synthesized and utilized to prepare two series of electroactive poly(amide-imide)s (PAIs) through a two-step polycondensation reaction with commercially available aromatic tetracarboxylic dianhydrides. The obtained polymers exhibited solubility in various polar organic solvents, and most of them could form transparent, flexible films via solution casting. Thermal analysis indicated glass transition temperatures (<i>T</i>_g) ranging from 250 °C to 277 °C, as measured by DSC, with no significant weight loss observed before 400 °C in TGA tests. Cyclic voltammograms (CV) of the polymer films on ITO-coated glass substrates revealed two reversible oxidation redox pairs between 0.67 and 1.04 V vs. Ag/AgCl in an electrolyte-containing acetonitrile solution. The PAI films showed stable redox activity with high optical contrast both in the visible and near-infrared regions, transitioning from colorless in the neutral state to green and blue in the oxidized states. Furthermore, the polymer films retained good electrochemical and electrochromic stability even after more than 100 cyclic switching operations. The PAIs displayed outstanding electrochromic performance, including high optical contrast (up to 95%), rapid response times (below 4.6 s for coloring and 5.7 s for bleaching), high coloration efficiency (up to 240 cm²/C), and low decay in optical contrast (less than 5% after 100 switching cycles for most PAIs).