Directly Grown Polyimide Covalent Organic Framework Films with High Electrochromic and Energy-Storage Performance
Haolin Xie, Qingqing Qiu, Huan Li, Ping Liu, Putrakumar Balla, Xiaopeng Qi, Tongxiang Liang, Jinming Zeng
Abstract
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.