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The covalent organic frameworks (COFs) possess high designability, which provides a platform for synthesizing novel optoelectric materials, including electrochromic materials. In this work, N,N,N′,N′-tetra-(4-aminophenyl)-1,4-phenylenediamine (TPDA) with π-electron conjugate system and redox active centers was used as the main building block. The 4,4′-biphenyl diformaldehyde (BDA) and the 2,2′-thiophene-5,5′-diformaldehyde (TDA) were used as the aldehyde building units. Two imine-based COF electrochromic active materials (COF TPDA-BDA and COF TPDA-TDA) were prepared by Schiff base reaction. The test results reveal that COF TPDA-TDA has superior electrochromic properties than COF TPDA-BDA. Their contrasts are 0.46 and 0.40, and the coloring/fading times are 3.1/10.6 s and 10.9/14.3 s, respectively. The COF TPDA-TDA material possessing a bifunctional group structure was synthesized by replacing the biphenyl group with the bithiophene group with redox activity, which can enhance the optical properties and inter-layer π-π conjugation. Besides the electrochromic properties, the morphology and crystal lattice parameters are different. Therefore, it is expected to develop COFs-based electrochromic materials with rich colors, excellent performance, and wide application by introducing construction units with different redox active centers. [ABSTRACT FROM AUTHOR]

A NiO x film with varying crystallinity across film thickness has been prepared by reactive radio frequency magnetron sputtering. The main research achievement is that the electrochemical cycling stability of the NiO x film has been radically improved as compared with NiO x films deposited by the conventional technologies. At the same time, the optical modulation has been also improved, whereas other electrochromic parameters, such as the switching rate and high coloration efficiency have been preserved at the required level. [ABSTRACT FROM AUTHOR]