Bis(bipyridinium) Salts as Multicolored Electrochromic Devices

Abstract

Symmetrical and nonsymmetrical oxobis(bipyridinium) cations combined with iodide and bistriflimide anions were prepared. In the case of the bistriflimide‐based bis(bipyridinium) salts, two room‐temperature ionic liquids (RTILs) with a combination of linkers and terminal ethers, [(C3O)bpy(C4O)bpy(C3O)][NTf2]4 and [(C10)bpy(C4O)bpy(C3O)][NTf2]4, were obtained, with glass transition temperatures (between −6.9 and 6.0 °C) higher than those reported previously for salts of dication bipyridinium scaffolds (−17.5 to −30.0 °C). The prepared salt containing [(C10)bpy(C4O)bpy(C10)][NTf2] can form an ionic liquid crystal structure. The most promising salts were tested as efficient and reversible multicolored electrochromic devices through cyclic voltammetry studies and detailed characterizations of their electrochromic performances. In general, tetracations based on oxobis(bipyridinium) salts show higher chromatic contrast and lower coloration efficiency than similar dication salts. Exchange of the anion from iodide to [NTf2] increases the transition times and coloration efficiencies for all the prepared di‐ and tetracation salts. The electrochromic device stability of [(C3O)bpy(C4O)bpyC3O]I4 was tested by on/off cycling; this device loses around 23 % of the initial color after 8640 redox cycles and shows very good cycling stability compared with previously reported diiodide salts.

Redox of Viologen for Powering and Coloring

“…Since then, several approaches have been reported to obtain lower mp than 100 °C. For example, Saielli's group and Branco's group attached alkyl chains of different lengths at bipyridilyum‐nitrogen atoms and synthesized their bis(trifluoromethanesulfonyl)imide salts [72–75] . Those VILs still had mp higher than room temperature, making the use of them without dilution challenging.…”

Photochromic Room Temperature Ionic Liquids Based on Anionic Diarylethene Derivatives

“…[6] In this context, the incorporation of task-specific functionality into ILs, where the desired functional group is covalently tethered to the cation, anion or both became a very attractive approach. [7] Different research groups, including our group already reported several functionalized ILs, containing magnetic, [8][9][10][11] photochromic, [12] electrochromic, [13][14][15] luminescent, [16][17][18][19][20] photo-rheological [21] and energetic properties, [22,23] among others.…”

Influence of Cation Size and Polarity on Charge Transport in Ionic Liquid Based Electrolytes

“…Ionic liquids have attracted considerable attention as electrolyte components in various electrochemical systems such as supercapacitors, [1][2][3] lithium ion batteries, [4,5] electrochromic devices [6] and dye sensitized solar cells (DSSCs) [7,8] because of their favourable properties such as high thermal and electrochemical stability, low volatility and high conductivity. [9][10][11] The most attractive property of ILs is the possibility of fine tuning of their physical and electrochemical properties by changing the chemical composition.…”