Room-temperature superprotonic conductivity in COOH-functionalized multicomponent covalent organic frameworks

In solid materials, the development of hydrogen bonding (H-bonding) networks within pores is crucial for efficient proton conductance. In this study, a chemically stable carboxylic acid-functionalized, quinoline-linked 2D microporous covalent organic framework (COF) (Qy-COOH) was synthesized using the Doebner multicomponent reaction (MCR) and compared to a similar framework lacking the -COOH functionality (Qy-H), prepared via an MC Domino reaction. The proton conductivity of the -COOH-functionalized MCR-COF was significantly enhanced, reaching 10^-2 S cm^-1, attributed to strong H-bonding interactions between water molecules and the dangling -COOH groups within the COF pores. In contrast, the analogous Qy-H framework exhibited a much lower proton conductivity of 10^-5 S cm^-1, while an imine-based COF showed only 10^-6 S cm^-1. This work represents the first demonstration of a general strategy to achieve efficient proton conduction in a class of layered 2D -COOH-functionalized COFs, offering superprotonic conductivity without requiring additives at room temperature. The MCR-COF design approach provides a promising pathway for developing highly stable and high-performance proton-conducting materials.