Solvothermal synthesis of donor-acceptor covalent organic framework/coal-based polyaniline composites for three-state electrochromic materials

Conjugated covalent organic frameworks (COFs) with redox activity can be designed for photoelectric materials application. In this paper, COF based electrochromic films were synthesized by solvothermal method in a Teflon-lined reactor, with thieno [3,2-b]thiophene-2,5-dicarbaldehyde (TTDA) as electron donor unit (D) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) as electron acceptor unit (A) (COFTT). Coal-based polyaniline (CPANI) was used as COFTT growth substrate and conductive enhancing agent to improve the photoelectric performance of COFTT. The addition of CPANI results in the morphology transformation of COFTT from nanosheet to nanofiber. Meanwhile, the impedance of COFTT is reduced and the optical contrast is improved. The color of COFTT-CPANI-1 can vary from yellow to dark orange and brown under a voltage window of −3 V–2.2 V. Stability tests show that the contrast retention rate of the electrochromic device is 90.6% after 1600 s switching. Considering the rich selectivity of COF construction units and the designability of topological structure, the development of COF-based electrochromic materials with rich colors and excellent properties has a broad prospect.