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

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.