Bis(bipyridinium) Salts as Multicolored Electrochromic Devices

Area of Science:

• Materials Science
• Electrochemistry
• Supramolecular Chemistry

Background:

• Bipyridinium scaffolds are explored for advanced materials.
• Ionic liquids offer unique properties for electrochemical applications.
• Electrochromic devices require stable and efficient materials.

Purpose of the Study:

• Synthesize novel oxobis(bipyridinium) salts with varied anions and linkers.
• Investigate the properties of these salts as room-temperature ionic liquids (RTILs).
• Evaluate their performance in multicolored electrochromic devices.

Main Methods:

• Preparation and characterization of symmetrical and nonsymmetrical oxobis(bipyridinium) cations with iodide and bistriflimide anions.
• Differential scanning calorimetry to determine glass transition temperatures.
• Cyclic voltammetry and detailed electrochromic performance analysis.

Main Results:

• Two novel RTILs, [(C3O)bpy(C4O)bpy(C3O)][NTf2]4 and [(C10)bpy(C4O)bpy(C3O)][NTf2]4, exhibited higher glass transition temperatures than previously reported dicationic scaffolds.
• A salt containing [(C10)bpy(C4O)bpy(C10)][NTf2] formed an ionic liquid crystal structure.
• The oxobis(bipyridinium) salts demonstrated efficient and reversible multicolored electrochromic properties.
• Tetracations showed higher chromatic contrast but lower coloration efficiency compared to dications.
• Anion exchange from iodide to bistriflimide improved transition times and coloration efficiencies.
• The electrochromic device based on [(C3O)bpy(C4O)bpyC3O]I4 showed good cycling stability, retaining 23% of initial color after 8640 redox cycles.

Conclusions:

• Novel oxobis(bipyridinium) salts can be designed as high-performance RTILs and electrochromic materials.
• The choice of linker and anion significantly influences the thermal and electrochromic properties.
• These materials hold promise for stable, multicolored electrochromic applications.