Abstract
Electrochromic (EC) materials with a dark-to-transmissive switch have great applications in optical communications, infrared wavelength detectors for spacecraft, and infrared camouflage coatings. However, such electroactive materials with high stability and cyclability are rare. Considering the advantages of the donor-acceptor approach (wide-range tuneable band position) and porous two-dimensional (2D) covalent organic framework (COF, well-ordered crystalline framework with stable structure and high surface area), in this work we constructed an extended delocalised π-electron layered dark purple EC-COF-1 by reacting the donor N,N,N′,N′-tetrakis(p-aminophenyl)-p-benzenediamine (TPBD) with the acceptor 2,1,3-benzothiadiazole-4,7-dicarboxaldehyde (BTDD). A sandwiched device made of EC-COF-1 exhibits the two-band bleaching (370 nm and 574 nm) in the visible region and becomes transparent under the applied potential with an induced absorption centring at 1400 nm. This discovery of a stable dark-to-transmissive switch in COF might open another door for their application in many EC devices for various purposes.
Highlights
Electrochromic (EC) materials with a dark-to-transmissive switch have great applications in optical communications, infrared wavelength detectors for spacecraft, and infrared camouflage coatings
Since our previous results have already demonstrated that triphenylamine units could realise wellordered frameworks with large crystal domains[25], the same strategy will be extended in the present research
We believe that the tuneable electron deficiency in aldehyde counterparts would produce the electronic transitions, with the varying degrees of charge transfer across the conjugated imine bond and decrease the energy gap to form the dark-coloured covalent organic framework (COF) (Supplementary Fig. 2)
Summary
Electrochromic (EC) materials with a dark-to-transmissive switch have great applications in optical communications, infrared wavelength detectors for spacecraft, and infrared camouflage coatings. A sandwiched device made of EC-COF-1 exhibits the two-band bleaching (370 nm and 574 nm) in the visible region and becomes transparent under the applied potential with an induced absorption centring at 1400 nm This discovery of a stable dark-to-transmissive switch in COF might open another door for their application in many EC devices for various purposes. To the best of our knowledge, black colour currently remains a big challenge due to the special demand for broadband absorption across the whole visible region Such gap strongly encourages us to develop COF with the ordered pores and the extended regular π–π stacking structures for potential application in electrochemistry and photoelectrochemistry fields.
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