Hydrogen Bonding Regulated\nFlexibility and Disorder\nin Hydrazone-Linked Covalent Organic Frameworks

Abstract

Covalent organic framework (COF) chemistry is experiencing\nunprecedented\ndevelopment in recent decades. The current studies on COF chemistry\nare mainly focused on the discovery of novel covalent linkages, new\ntopological structures, synthetic methodologies, and potential applications.\nHowever, despite the fact that noncovalent interactions are ubiquitous\nin COF chemistry, relatively little attention has been given to the\nrole of noncovalent bonds on COF structures and their properties.\nIn this work, a series of hydrazone-linked COFs involving noncovalent\nhydrogen bonds have been constructed, where the hydrogen-bonding interaction\nplays critical roles in the COF crystallinity and structures. The\nregulation of structural flexibility, the reversible transition between\norder and disorder, and the variety of host–guest interactions\nhave been demonstrated in succession for the first time in COFs. The\nresults obtained by the hydrogen-bonding-regulated strategy may also\nbe extendable to other noncovalent interactions, such as π–π\ninteractions, metal coordination interactions, Lewis acid–base\ninteractions, etc. These findings will inspire future developments\nin the design, synthesis, structural regulation, and applications\nof COFs by manipulating noncovalent interactions.