Colorless‐to‐Black/Gray Electrochromic Devices Based on Single 1‐Alkyl‐1′‐Aryl Asymmetric Viologen‐Modified Monolayered Electrodes

In the rising tendency of electrochromics and incipient development of multicolor systems, big attention is recently being paid to the colorless‐to‐black or gray electrochromic (EC) materials, since they can extend the applicability of the EC technology. However, the achievement of high performance EC materials which intrinsically provide colorless‐to‐gray/black electrochromism remains a strategic challenge. The present study reports on colorless‐to‐black/gray EC devices (ECDs) based on new 1‐alkyl‐1′‐aryl asymmetric viologens assembled in a nanostructured device configuration with poly(vinyl alcohol) (PVA)–borax gel electrolyte (conducting glass/viologen‐modified‐TiO₂/PVA–borax gel electrolyte/conducting glass). The asymmetric viologens reported herein have been conveniently functionalized with anchoring groups in both alkyl and aryl substituents, ensuring rapid anchoring process (≈1 min) and strong binding affinity toward TiO₂ monolayered working electrode. It is demonstrated herein that these ECDs based on a single asymmetric viologen provide not only gray but also real black electrochromism (a* and b* ≤ |5|) with great variation of the level of coloration (ΔL* = 53) and transmittance change (Δ%T ≥ 60), along with satisfactory switching times (5–10 s), transparent colorless‐off state, and good cyclability (≈10 000 cycles). Furthermore, these asymmetric viologens have also been tested in light‐scattering electrodes to prove their compatibility with them, extending their field of application.