Studies of bipyridinium ionic liquids and deep eutectic solvents as electrolytes for electrochromic devices

In this work, two bipyridinium di-cations based on [(allyl)₂bpy]²⁺ and [(C₁₀)₂bpy]²⁺ combined with halogenate (I or Br), bistriflimide ([NTf₂]) and dicyanamide [DCA] anions have been prepared and electrochemical characterized. These salts were studied using a conventional electrolyte (TBAP in acetonitrile) and alternative electrolyte based DES (LiTfO:6EG) for 3- and 2- electrodes configuration devices. In the 2-configuration device, [(allyl)₂bpy][DCA]₂ and [(C₁₀)₂bpy][DCA]₂ showed different radical cation colorations particularly green and blue colors with different recovery times to original ones. In the case of [(C₁₀)₂bpy]I₂ a blue and a red-violet colorations attributed to the electrogenerated radical cation and the dimer respectively was obtained in agreement with previous literature. In parallel, bipyridinium based DES by suitable combination between [(C₁₀)₂bpy]X₂ and [(allyl)₂bpy]X₂ (X = Br, NTf₂, DCA) with several hydrogen bond donors in 2-electrode configuration devices have been also studied. DES based on [(allyl)₂bpy][NTf₂]₂:PEG200 and [(allyl)₂bpy][DCA]₂:PEG200 presented different coloration grades from pale brown to green taking longer times to recover the original color. The selected DES as alternative electrolytes or based bipyridinium derivatives can be promissory materials for efficient electrochromic devices.