Covalent Organic Framework Film for Three-State Near-Infrared Electrochromism and Molecular Logic Gate.

A Kagome structure covalent organic framework (COF) film with three-state near-infrared (NIR) electrochromic properties was designed and synthesized. The morphology and structure characterization revealed that the COFTPDA-PDA film was composed of hexagonal nanosheets with high crystallinity. The COFTPDA-PDA film exhibit three reversible color states at different applied potentials, and high absorption spectra changes in the NIR region, which can be ascribed to the strong intervalence charge transfer (IVCT) interaction of the Class III mixed-valence systems of the conjugated triphenylamine species. The COFTPDA-PDA film showed the sub-second response time (1.3 s for coloring and 0.7 s for bleaching at 1050 nm) and the long retention time in the NIR region. In comparison with the amorphous film with the same monomers, COFTPDA-PDA film show superior NIR electrochromic properties in term of response time and stability, which could be attributed to the highly ordered porous structure and the π-π stacking structure of the COFTPDA-PDA architecture. Furthermore, the COFTPDA-PDA film was successfully applied in mimicking flip-flop logic gate with optical memory functions.