Electrochemical synthesis and properties of multicolor electrochromic triphenylamine-based polymer films

Four novel triphenylamine-based (TPA-based) conjugate polymer films (one homopolymer and three co-polymers) were electrochemically synthesized from N4,N4′-bis(4-((6-(1H-indol-1-yl)hexyl)oxy)phenyl)-N4,N4′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (TPY) and 3,4-ethylenedioxythiophene (EDOT) as monomers. The polymer structure was tuned by adjusting the monomer proportions. The homopolymer contains electrochromic TPA and indole groups in its backbone, while an additional electrochromic EDOT groups are present in the co-polymers. The electrochemical, optical, and electrochromic properties of the polymers were characterized along with film morphologies. Each polymer is multicolored, with electrochromic performance that depends heavily on its structure. The introduction of EDOT into the backbone significantly improved polymer-film-forming properties. In addition, the co-polymers exhibited excellent spectroelectrochemical performance and are visible–near-infrared electrochromic materials. In particular, the spectrum of oxidized PTPY–EDOT-2 covers the entire visible region, while oxidized PTPY–EDOT-3, which contains the highest amount of EDOT, strongly absorbs in the near-infrared region (> 800 nm) while absorbing fully across the visible region. Consequently, PTPY–EDOT-3 is a potential candidate for display and camouflage applications owing to its excellent properties. Double-layer electrochromic devices (ECDs) were fabricated using polymer films and WO₃ as active layers. The homo- and co-polymers exhibit particularly different electrochromic performance. The PTPY ECD performs best. It exhibited a maximum contrast of 36.7% at 720 nm in the absence of EDOT, with a coloration efficiency of 418 cm²/C recorded; moreover, it exhibited an obvious memory effect, with a memory time of 20 min recorded at 480 nm. Consequently, these polymers are potentially useful for optoelectronics applications.

Graphical abstract

Novel conjugate polymer films that contain triphenylamine, 3,4- ethylenedioxythiophene (EDOT) and indole groups were electrochemical polymerized. Introducing EDOT into the backbone could significantly improve polymer-film-forming properties. These films are multicolored. The electrochromic devices exhibited high coloration efficiency, high optical contrast and obvious memory effect