Recent advances in viologen-based polymers and their photocatalytic applications

Abstract

Recently, viologen-based polymers have attracted significant attention in photocatalysis with promising applications in cross-coupling reactions, hydrogen evolution reactions, cyclic carbonate synthesis, and other types of valuable product synthesis from CO₂, as well as wastewater treatment. The photocatalytic approach is primarily driven by the viologen radical cation (V˙⁺) via single electron transfer (SET) or charge transfer (CT) processes under light irradiation. Incorporation of viologens as building blocks into polymer architectures through covalent bonding, host–guest encapsulation, or electron/charge transfer interactions offers key advantages including (i) low driving voltage for efficient electron-transfer, (ii) tunable optical responses to redox processes based on bipyridinium nitrogen substituents, and (iii) relatively direct synthesis compared to other organic linkers. These features enable the design of numerous viologen-based polymers with well-defined architectures and tailored functionalities for industrial and environmental applications. This mini-review critically addresses recent advancements in viologen-based polymers for photocatalytic applications from 2019 to the present day, highlighting key mechanistic insights, current challenges, and emerging opportunities. It also proposes strategic directions for future materials design, addressing existing limitations, and offers perspectives to guide future research and innovation in this rapidly evolving field.