Unlocking the secrets of color: Molecular engineering of triphenylamine-π-phenanthrimidazole polyamides for transparent-to-kaleidoscopic/black electrochromic switching

Electrochromic (EC) polymers represent potential applications in smart windows (SW), energy-efficient labels, digital displays and other fields, but large-scale development is limited by the unknown color modulation mechanism and the difficulty of realizing the transparent-to-black switching. Breakthrough, this study fills the gap for the mechanism of EC color modulation in polyamides (PAs) containing the electroactive group triphenylamine (TPA) through molecular engineering design and theoretical calculations. Specifically, we exploited the modification of TPA with bipolar phenanthroimidazole (PI) to successfully develop four PAs containing PI-π-TPA, which implemented the EC color-switching processes ranging from transparent to black, magenta, yellow and cyan, respectively. Notably, transparent-to-black switching color is the ultimate quest for EC field, PA-CP demonstrates a high transmittance change from colorless to black (∆T = 93%), fast switching time (coloring time t_c = 1.6 s, bleaching time t_b = 0.8 s) and extremely high coloration efficiency (η_CE = 914 cm²/C) as well as attenuation of 7.5% during 30,000 s cycling process. Significantly, ESW based on PA-CP (ESW-CP) assembly exhibits effective thermal modulation capability, and EnergyPlus simulations indicate more than 7% energy savings in 12 climate zones around the globe compared to standard commercial glass, which provides design strategy for achieving sustainable development.