Design of viologen-based 2D cationic covalent organic polymer for multi-colored electrochromic devices with tuneable redox potential

Abstract Viologen-based ionic covalent organic polymers (V-iCOP) with higher dimensionality is promising for their various characteristics (porosity, redox potential, and color) owing to the tunability of their composition. In this work, 3 different viologen-based 2D cationic covalent organic polymer thin films (V-iCOP1, V-iCOP2, V-iCOP3) were synthesized by Zincke reaction with linkers of varying electron affinity: tris(4-aminophenyl)amine (TAPA), 1,3,5-tris(4-aminophenyl)benzene (TAPB), 1,3,5-tris-(4-aminophenyl)triazine (TAPT). The structural and electronic effects of the different linkers on the electrochromic device performances were investigated and compared with theoretical DFT calculations. Due to the cationic nature of the polymer thin film that promotes fast ionic diffusion, they overall show superior electrochromic performance in aqueous conditions. This is reflected from the rapid switching speed (