A one-dimensional covalent organic framework film for near-infrared electrochromism

Covalent organic frameworks (COFs) are appealing for electrochromic (EC) application due to their designable redox-active building blocks, ordered porous structure, and well-developed π-π stacking structure, which greatly enhance the generation and transportation of carriers for EC switching. However, such EC COFs are rare and still dominated by two-dimensional network topology till now. Herein, a bis(triphenylamine)-based one-dimensional (1D) COF, termed as TAPD-TDA COF, was reported and the EC performance of the COF film directly grown on indium tin oxide (ITO) coated glass was systematically studied. Theoretical and experimental results indicated that TAPD-TDA COF possessed 1D covalent and π-π stacking structure, with comparatively high crystallinity and Brunauer-Emmett-Teller surface area. Furthermore, the characterization of the oriented COF film demonstrated that the film on ITO glass was uniform and exhibited reversible color transition between bright yellow and light grey during the applied cyclic potentials. Significantly, in the redox process, it displays remarkable absorption spectral changes in the near-infrared region, which is ascribed to the active degree of intervalence charge transfer (IVCT) effect between bis(triphenylamine) cation radicals within the COF skeleton. The absorption wavelength of the COF film linearly shifts between 1060 and 940 nm with the applied potentials. Undoubtedly, this work on a novel 1D COF might shed light on further exploration/application in smart optoelectronic materials.