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Anhydrous proton-conductive materials have attracted great attention in recent years. Doping imidazole as a proton carrier in porous materials, especially pure organic crystalline covalent organic frameworks (COFs), is a promising solution. However, the influence of the hydrogen donor ability of imine functional groups in COFs on the proton conduction has largely been unexplored. Herein, a series of iso-reticular thiophene-based COFs has been synthesized with a similar pore structure and surface area. Different amounts of imidazole were infiltrated to the COFs by vapor diffusion in a highly controlled manner. The introduction of thiophene rings increases the hydrogen bonding donation ability of the imine linker, which resulted in an enhanced proton conductivity of the imidazole-doped COFs by one order of magnitude. The formation of hydrogen bonding between the imine group and imidazole was demonstrated by Fourier transform infrared spectroscopy and density functional theory calculations.
Li et al. (Wed,) studied this question.