Enhanced Proton Conductivity of Imidazole Doped Thiophene Based Covalent Organic Frameworks via Subtle Hydrogen Bonding Modulation.

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 framework is a promising solution. However, the influence of the hydrogen donor ability of imine functional groups in covalent organic frameworks on the proton conduction has largely been unexplored. Herein, a series of iso-reticular thiophene based covalent organic frameworks has been synthesized with similar pore structure and surface area. Different amounts of imidazole were infiltrated to the covalent organic frameworks 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 covalent organic frameworks by one order of magnitude. The formation of hydrogen bonding between the imine group and imidazole was demonstrated by the Fourier transform infrared spectroscopy and density functional theory calculation.