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

A Kagome structure covalent organic framework (COF) film with three-state NIR electrochromic properties was designed and synthesized. The COF film is composed of hexagonal nanosheets with high crystallinity and has three reversible color states at different applied potentials. It has high absorption spectra changes in the NIR region, ascribed to the strong intervalence charge transfer (IVCT) interaction of the Class III mixed-valence systems of the conjugated triphenylamine species. The film showed sub-second response time (1.3 s for coloring and 0.7 s for bleaching at 1050 nm) and long retention time in the NIR region. COF film shows superior NIR electrochromic properties in term of response time and stability, attributed to the highly ordered porous structure and the π-π stacking structure of the COF architecture. The COF film was applied in mimicking a flip-flop logic gate with optical memory function.