Enhancing Electrochromic Stability of Triphenylamine-Based Polymers via Monomer Ratio Optimization

In the pursuit of high-performance organic electrochromic (OEC) materials that transition from transparent to deep colors, we design and synthesize a series of copolymers─termed MeT_mPhF_n─composed of TPA and fluorene with triethylene glycol and ester groups incorporated. This is achieved through gradient tuning of monomer ratios via Suzuki copolymerization. Five of these polymers exhibit excellent film-forming properties, and their electrochromic devices demonstrate remarkable pale blue-to-reddish brown switching behavior. Notably, benefiting from the suitable continuity and moderate porosity of MeT_0.5PhF_0.5 film, the electrochromic device based on MeT_0.5PhF_0.5 showcases rapid reversible switching times of 2.5 s for coloring and 1.3 s for bleaching, highlighting its exceptional responsiveness. This device achieves the highest contrast of 58.7% at 465 nm, paired with impressive cycling stability, retaining 93.7% of its initial contrast ratio after 1440 cycles, and exhibits a high coloration efficiency of 619 cm² C^-1. This study presents an effective approach for designing and synthesizing high-performance electrochromic copolymers that effectively transition from colorless to vibrant hues, paving the way for advanced applications in smart windows and display technologies.