Construction and Electrochromic Properties of Two-Dimensional Covalent Organic Frameworks with Donor-Acceptor Structures of Triphenylamine and Bipyridine

The stacking between layers of a two-dimensional covalent organic framework (COF) leads to overlapping π orbitals, which enables charge carriers to be transported quickly through these pre-designed π orbitals. The two-dimensional COF featuring donor-acceptor interactions represents a straightforward approach for fabricating a high-performance organic electrochromic device. In this paper, N, N, N', N'-tetrad(4-aminophenyl)-1,4-phenylenediamine (TPDA) with electron-rich structure and 2,2'-bipyridine-5,5'-dialdehyde (BPDA) with strong electron absorption ability were used as the construction unit. COFTPDA-BPDA electrochromic materials with donor-acceptor structure were synthesized by Schiff base reaction, which can achieve reversible switching from red to dark gray. The color/fade time of the film at 474 nm wavelength is 6.8 s/11.9 s. The contrast retention rate of the film can reach 97.6% after 20 potential cycles, the memory time is as long as 4278 s. The present study demonstrates that constructing a donor-acceptor (D-A) structural unit with conjugated triphenylamine as the electron donor linked to bipyridine electron-withdrawing groups enhances charge transfer and redox reactions. With the success of this design strategy, the construction of the D-A structure is an important methodology for improving the electrochromic properties of materials.