10.1021/acsami.6b11321.s001 Yolanda Alesanco Yolanda Alesanco Ana Viñuales Ana Viñuales Germán Cabañero Germán Cabañero Javier Rodriguez Javier Rodriguez Ramón Tena-Zaera Ramón Tena-Zaera Colorless to Neutral Color Electrochromic Devices Based on Asymmetric Viologens American Chemical Society 2016 PVA-borax gel polyelectrolytes i.e application easy-to-make neutral-grayish color ECDs electrochromic devices electrochromic technology neutral-grayish colorations neutral-colored state device architecture Neutral Color Electrochromic Devices viologen Asymmetric Viologens Electrochromic materials study reports 2016-10-11 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Colorless_to_Neutral_Color_Electrochromic_Devices_Based_on_Asymmetric_Viologens/4055583 Electrochromic materials have extensively been investigated because of their potential fields of application, with a significant growing interest in expanding the provided colorations. However, among all palette of colors, colorless electrochromic devices (ECDs) that provide neutral-grayish colorations with a simple configuration remain a key challenge. The present study reports on the synthesis of asymmetrically 1-alkyl-1′-aryl-substituted viologens and their incorporation in PVA-borax gel polyelectrolytes for ECDs that constitute the simplest device architecture (glass/TCO/EC gel/TCO/glass). We demonstrate herein that these EC gels based on single asymmetric viologens provide more neutral-colored state than their corresponding symmetric viologens (<i>a</i>* and <i>b</i>* ≤ |15|), while maintaining satisfactory colorless bleached state (%<i>T</i><sub>b</sub> > 70% in the whole visible range), transmittance changes (i.e., ∼60%) and cyclability (i.e., ∼15 000 cycles). Additionally, the effect of the solvent on the observed coloration has also been investigated. This easy-to-make neutral-grayish color ECDs may significantly extend the potential of the electrochromic technology, because they adapt better aesthetically to the surrounding environment, as they are easier to implement in different applications.