Adjusting interlayer interactions and proton conduction pathways of 2D covalent organic frameworks through the rotaxane structures

Covalent organic frameworks (COFs) have great potential as a versatile platform for proton conduction. However, the commonly applied two-dimensional (2D) COFs that are easy to design and synthesize have only one-dimensional (1D) channels for proton conduction, limiting the formation of continuous hydrogen bonds due to the anisotropy between its crystalline grains. Herein, we report a strategy to construct three-dimensional (3D) channels in 2D COFs using rotaxane structures and eliminate the strong interlayer π-π interactions, facilitating the formation of smooth 3D proton transfer pathways during guest doping. The presence of interlocking CD molecules in rotaxane-based COF (RCOF, CD-TpAzo) significantly diminishes the stacking energy between 2D layers from 154.2 to 55.2 kJ mol−1, resulting in more easily H3PO4 doping into its 3D channels and interlayers. As a result, CD-TpAzo@H3PO4-10 exhibits eight times shorter H+ spin-lattice relaxation time than TpAzo@H3PO4-10. At 150°C, the anhydrous proton conductivity of CD-TpAzo@H3PO4-18 reaches 0.78 S cm−1, even higher than that for pure H3PO4 (0.47 S cm−1) under the same conditions.