Directly Grown Polyimide Covalent Organic Framework Films with High Electrochromic and Energy-Storage Performance

Two dimensional covalent organic framework (2D COF) films based on triphenylamine are considered to be promising electrochromic and energy-storage materials owing to their interlayer π-π electron delocalization, one-dimensional (1D) nanopores, and stable chemical structures. Triphenylamine-based 2D COF electrochromic films, nevertheless, rarely exhibit transparency and high optical contrast, which severely limited the scope of their application. In this work, two directly grown triphenylamine-based polyimide 2D COF films, TAPA-PMDA and TAPA-NTCDA PI COF, were prepared through solvothermal technology. Their morphologies were assembled into hierarchical nanoporous structures in the form of strips and gravel-like nanograins, respectively. Both the TAPA-PMDA and TAPA-NTCDA PI COF films exhibited a transparent bleached state and high optical contrast. Their optical contrasts were 77.6% at 752 nm and 60.4% at 708 nm, respectively. Interestingly, the TAPA-NTCDA PI COF film could exhibit multicolors (transparent, red-gray, and blue-gray) through regulating the contributions of the electron transition from HOMO to SOMO and HOMO-1 to SOMO of TPA^+•. In addition, the TAPA-PMDA and TAPA-NTCDA PI COF films also displayed fast switching and colored/bleached times of 7.3/2.7 and 5.3/8.1 s, respectively. Remarkably, the TAPA-PMDA PI COF film also demonstrated large specific capacitance and excellent charge-discharge rate capabilities. The directly grown polyimide 2D COF films are enormously promising for high-performance electrochromic and energy-storage materials.