Colorless Triphenylamine-Based Polymers for Multicolor Electrochromism and Energy Storage Devices

Electrochromic triphenylamine-based materials have emerged as promising candidates for smart windows and energy storage devices due to their reversible redox activity and color-switching properties. This study reported three triphenylamine-based monomers, namely, 4,4′-(1,2-bis(4-fluorophenyl)-1H-phenanthro[9,10-d]imidazole-6,9-diyl)bis(N,N-diphenylaniline) (FTPA), 4,4′-(1,2-diphenyl-1H-phenanthro[9,10-d]imidazole-6,9-diyl)bis(N,N-diphenylaniline) (PTPA), and 4,4′-(1,2-bis(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazole-6,9-diyl)bis(N,N-diphenyl aniline) (OTPA) and their electrochemical polymerization to prepare polymer thin films, namely, PFTPA, PPTPA, and POTPA for electrochromism and energy storage. The present polymers used as anodic electrochromic materials appeared colorless in the neutral state and exhibited multicolor electrochromism. Among them, POTPA exhibited the highest coloration efficiency (337.6 cm²/C) and rapid switching kinetics (0.31 s for coloring and 0.32 s for bleaching) at 765 nm, albeit with moderate cycling stability. PFTPA demonstrated balanced performance, retaining >90% optical contrast after 150 cycles. Moreover, electrochromic energy storage devices based on these polymer thin films were fabricated, which displayed synchronized color transitions and energy storage capabilities, and powered light emitting diodes (LEDs) effectively. The findings highlighted the critical role of molecular design in optimizing electrochromic performance and underscored the potential of triphenylamine polymers in multifunctional smart technologies.