Porous Hydrogen-bonded Organic Frameworks (HOFs): Status and Challenges

Abstract

Hydrogen-bonded organic frameworks (HOFs), usually self-assembled by organic or metal-organic building blocks via intermolecular H-bonding interactions, have become a unique type of crystalline porous material. Although the weak and flexible nature of hydrogen bonds makes most HOFs fragile, the high stability and permanent porosity could be realized by the judicious selection of rigid building blocks with special spatial configuration as well as the introduction of framework interpenetration and/or other intermolecular interactions like π-π stacking and electrostatic interactions, etc. Compared with other crystalline porous materials like metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), HOFs feature mild preparation condition, high crystallinity, permissible solution processability, easy healing and regeneration, etc. These distinguishing merits make HOFs capable to be used as unique multifunctional porous materials. Herein, we first review the basic rules to design and synthesize stable and porous HOFs, and then systematically summarize the representative supramolecular synthons and backbones that have been used to build stable and porous HOFs. Emphasis is put on the potential applications of HOFs in gas adsorption and separation, proton conduction, heterogeneous catalysis, luminescence and sensing, biological applications, enantiomeric resolution and aromatic compounds separation, pollutants removal, and structure determination, etc.