Covalent organic frameworks (COFs) have emerged as a promising class of crystalline porous materials owing to their well-defined structures, tunable pore environments, and versatile functionalities. Among the diverse COF architectures, Vio-COFs represent a particularly promising class due to their unique combination of permanent positive charges, reversible redox activity, and extended π-conjugated frameworks. The synergistic integration of these features enables precise control over charge distribution, electron-transfer pathways, ion transport, and host–guest interactions, opening new opportunities for the development of advanced functional materials. Despite rapid progress, the fabrication of highly crystalline, stable, and multifunctional Vio-COFs remains challenging due to the limited availability of viologen-based monomers, electrostatic repulsion during framework formation, charge–porosity trade-offs, and the difficulty of maintaining redox stability under practical conditions. Therefore, the development of rational design strategies is essential to fully unlock the potential of Vio-COFs for advanced practical applications.
The integration of viologen units into COF backbones imparts distinctive electronic and ionic properties, significantly broadening the functional scope of conventional neutral COFs. The reversible redox transformation of viologen moieties (V²⁺/V•⁺/V⁰) enables dynamic electron storage and charge transfer, while their intrinsic cationic nature supports anion exchange, ionic conduction, and electrostatic interactions with guest molecules. Diverse engineering strategies have been explored to maximize the performance of Vio-COFs, including (i) the molecular design of viologen linkers to optimize electronic structures and redox properties, (ii) framework modulation to improve crystallinity, porosity, and the accessibility of active sites, (iii) the incorporation of catalytic centers to improve catalytic performance and selectivity, (iv) the regulation of charge-transfer pathways to facilitate efficient charge transport and photocatalysis, and (v) post-synthetic modification to introduce multifunctional responsive and catalytic functionalities.
The viologen-mediated construction strategy provides an effective approach for developing multifunctional COFs by synergistically integrating ionic frameworks, redox-active centers, and highly ordered porous architectures. The exceptional performance of Vio-COFs can be attributed to several key features: (i) permanent cationic frameworks that facilitate selective adsorption and ion transport; (ii) reversible redox activity that supports dynamic electron transfer and catalytic transformations; (iii) extended π-conjugated networks that facilitate charge transport and electronic communication; (iv) tunable pore structures that provide efficient molecular diffusion pathways and expose abundant active sites; and (v) the synergistic integration of viologen moieties with functional components, which broadens their applications in energy conversion, catalysis, sensing, adsorption, and optoelectronics.
Despite the remarkable progress made to date, several key challenges remain to be addressed before Vio-COFs can be widely implemented in practical applications. These challenges include scalable synthesis, improved long-term structural and redox stability, precise regulation of charge distribution, improved electrical conductivity, and a comprehensive understanding of structure–property–performance relationships. Future research should emphasize sustainable synthesis, advanced experimental characterization coupled with theoretical simulations to unravel charge-transfer mechanisms, and the rational development of application-driven Vio-COFs with optimized multifunctional performance.
This review provides a comprehensive overview of the design strategies, structural features, redox behavior, and functional applications of Vio-COFs. Through a systematic analysis of the relationships between viologen-derived ionic and electronic properties and material performance, it offers valuable insights for the rational design of next-generation charged and redox-active porous materials for advanced technological applications.
Citation: Qamar-un-Nisa Tariq, Siyu Deng, Yanling Yao, Chuntian Qiu, Qitao Zhang, Xiang Ling. Viologen-Linked Covalent Organic Frameworks: A Charged and Redox-Active Platform for Functional Materials[J]. Materials Futures . DOI: 10.1088/2752-5724/ae8fef
Materials Futures
Viologen-Linked Covalent Organic Frameworks: A Charged and Redox-Active Platform for Functional Materials
8-Sep-2026