Solvothermal Synthesis and Growth of Covalent Organic Framework Electrochromic Film with Triphenylamine Active Unit

Covalent organic frameworks (COFs) with reversible redox units and a conjugated molecular skeleton possess novel photoelectrochemical properties. In this work, tris(4-aminophenyl)amine and 4,4-biphenyldiformaldehyde were chosen to synthesize TABP-COF electrochromic film with triphenylamine (TPA) active unit by a solvothermal method in a Teflon-lined reactor. The growth process and reaction time optimization of the TABP-COF were studied. TABP-COF shows a self-assembly growth process from an array of nanosheets to nanospheres. Owing to the redox characteristics of TPA, the TABP-COF film exhibits reversible electrochromic behavior. With a solvothermal reaction time of 72 h, the TABP-COF-3 film exhibits the best electrochromic properties, including contrast of 0.483 and response time of 7.3 s/13.6 s. Considering the abundance of redox-active units that can be chosen, COF materials with different redox units and color changes can be designed for a variety of applications in the field of electrochromic materials.