Novel viologen derivatives for electrochromic ion gels showing a green-colored state with improved stability

We successfully synthesized a novel viologen derivative (1,1'-bis(3-fluoro-4-(trifluoromethyl) phenyl)-4,4'-bipyridinium bis(trifluoromethylsulfonyl) imide, TFMFPhV(TFSI) 2) exhibiting a green-colored state. We selected cyanophenyl viologen (CNPhV2+), a conventional electrochromic (EC) chromophore with a green color indication, to compare EC performance. Ion gels consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMI][TFSI]) were employed as a solid-state electrolyte for EC devices (ECDs). In comparison to CNPhV2+-containing devices, the ECDs with TFMFPhV2+ showed higher transmittance contrast, larger coloration efficiency, faster coloration and bleaching responses, and better coloration/bleaching operational stability. Cyclic voltammetry revealed that the more stable redox behavior of TFMFPhV2+ is the origin of the outstanding ECD performance.