Adjusting interlayer interactions and proton-conduction pathways of 2D covalent organic frameworks through the rotaxane structures
Jianjian Yang1, Weidong Fan1, Xiaofei Wei1
1Shandong Key Laboratory of Intelligent Energy Materials, State Key Laboratory of Heavy Oil Processing, School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
Abstract:
Covalent organic frameworks (COFs) have great potential as versatile platforms for proton conduction. However, the commonly applied 2D COFs that are easy to design and synthesize have only 1D channels for proton conduction, limiting the formation of continuous hydrogen bonds due to the anisotropy between their crystalline grains. Herein, we report a strategy to construct 3D channels in 2D COFs by 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 α-cyclodextrin (CD) molecules in a rotaxane-based COF (CD-TpAzo) significantly diminishes the stacking energy between the 2D layers from 154.2 to 55.2 kJ mol-1, resulting in easier H3PO4 doping into its 3D channels and interlayers. As a result, CD-TpAzo@H3PO4-10 exhibits an 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, which is even higher than that of pure H3PO4 (0.47 S cm-1) under the same conditions.
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