Deprotonation‐Gated Multicolor Electrochromism in a Single‐Molecule Viologen

ABSTRACT Dynamic optical modulation serves as a cornerstone of modern optoelectronics, with electrochromic (EC) materials playing an indispensable role in diverse applications, including displays, smart windows, and adaptive mirrors. Among these, viologens have garnered significant interest owing to their reversible two‐state switching and low operating potentials. However, most viologen‐based systems remain confined to binary color transitions, which limits their functional versatility. To overcome this limitation, we have rationally designed an N‐salicylaldehyde viologen derivative, V‐SA , which achieves multistate electrochromism through the synergistic interplay between base‐induced deprotonation and applied bias voltage. Specifically, the electron‐withdrawing aldehyde substituent lowers the pKa of the hydroxyl group, enabling a highly sensitive color shift from pale yellow to deep blue upon base exposure. More importantly, by integrating this base‐responsive colorimetric behavior with reversible redox activity within a single molecular platform, V‐SA affords multiple well‐distinguished electrochromic states. Our findings demonstrate that the combination of targeted structural modification and orchestrated external stimuli offers a powerful and generalizable design strategy for developing multistate EC materials, paving the way toward advanced information processing and dynamic optical control.