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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. [ABSTRACT FROM AUTHOR]

Electrochromic symmetric and non-symmetric disubstituted oxo-bipyridinium ionic liquids are developed in high purities and yields. Detailed spectroscopic (NMR, FTIR and elemental analysis), thermal (DSC for melting point and glass transition temperatures, Tg determination) and electrochemical (cyclic and square wave voltammetry for determination of redox potential and evaluation of reversibility behaviour) analyses are performed. The most promising electrochromic oxo-bipyridinium ionic liquids in combination with transparent electrolytes are tested as reversible electrochromic devices. More efficient and sustainable electrochromic devices inspired by bipyridinium ionic liquids can be conceived for industrial applications such as electrochromic car rear-view mirrors and smart windows. [ABSTRACT FROM AUTHOR]

Low-cost electrochromic devices presenting fast switching continue to have an enormous interest for industrial applications; however the durability of the devices is a parameter of critical importance. The present work describes the preparation and characterization of ITO free electrochromic devices, being the use of hybrid electrodes for low-cost electrochromic devices the main focus. It was used silver grids (silver ink) as electrically conductive electrodes. These grids were screen-printed on polyethylene terephthalate (PET), using two different patterns and different line widths. The printing of a conductive polymer film on top of the grids for electrochemical protection of the metal was evaluated. These grids were characterized in terms of equivalent resistance and light transmission, considering each pattern, as well as electrochemical stability. The resulting electrochromic devices were tested using cyclic voltammetry, spectroelectrochemistry and colorimetry. The durability of the devices was characterized through the analysis of color contrast over time during continuous operation conditions using a cycling program. These experiments displayed electrochromic devices performing 100 cycles before degradation with switching times of 4.5 s and a color contrast (Δ E ) of 27 or a variation in transmittance of 50% between redox states. [ABSTRACT FROM AUTHOR]