Multicolored near-infrared electrochromic polyimides: Synthesis, electrochemical, and electrochromic properties

•The polymer films showed reversible electrochemical oxidation, high coloration efficiency (CE), low switching time.•The polyimides revealed multielectrochromic characteristic.•The polyimides were the near-infrared (NIR)-absorbing electrochromic materials.

A novel series of multicolored near-infrared electrochromic aromatic polyimides have been synthesized by a conventional two-step polymerization process. All polymers displayed outstanding thermal stability, i.e. 20 wt% loss in excess of 593 °C in nitrogen and high char yields (higher than 68% at 750 °C). In addition, the polymer films showed reversible electrochemical oxidation, high coloration efficiency, low switching time, and anodic green electrochromic behaviors. The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels of these polymers were determined in the range of −4.759 to −4.801 and −1.758 to −2.002 eV (vs the vacuum level) by cyclic voltammetry method consisting with the results of quantum chemical calculation well, respectively. The polymer films revealed excellent stability of electrochromic characteristics for the radical cations generated, changing color from original yellowish to green and blue, with the absorption changing from ultraviolet to near-infrared.

Graphical abstractElectrochromic behavior of PI thin film. The inset shows the photographic images of the film at indicated applied voltages. Figure optionsDownload full-size imageDownload as PowerPoint slide