Advanced design and application for viologen‐based redox devices with customizable functionalities

Abstract Viologens have garnered significant attention as versatile stimuli‐responsive materials due to their tunable coloration, exceptional redox reversibility, and rapid electron transfer kinetics. While several reviews have extensively surveyed the applications of viologens, a comprehensive analysis focusing on tailored functional design—specifically how intended device functionalities dictate the requisite physicochemical properties of viologen derivatives‐remains scarce. Oriented toward high‐performance applications, this review systematically summarizes recent advancements in the structural modification of viologens, with a particular emphasis on harnessing their redox‐mediated optical and electronic transitions. We critically evaluate four primary modification strategies that significantly influence device performance: side‐chain substitution, functionalization of the bipyridinium core, macromolecular polymerization, and the development of viologen‐based composites. The review elucidates the fundamental structure‐property‐performance relationships that underpin these chemical modifications. Furthermore, we highlight the progress in customizable devices enabled by these engineered materials, showcasing their applications in electrochromic (EC)‐fluorescence dual‐functional systems, photothermal regulation, multicolor displays, energy storage, and multi‐stimuli‐responsive architectures. Finally, we address current challenges and outline future research trends to inspire the design of next‐generation, task‐specific viologen‐based redox devices.