Air/Liquid Interfacial Nanoassembly of Molecular Building Blocks into Preferentially Oriented Porous Organic Nanosheet Crystals via Hydrogen Bonding

Nanosheets with highly regulated nanopores are ultimately thin functional materials for diverse applications including molecular separation and detection, catalysis, and energy conversion and storage. However, their availability has hitherto been restricted to layered parent materials, covalently bonded sheets, which are layered via relatively weak electrostatic interactions. Here, we report a rational bottom-up methodology that enables nanosheet creation beyond the layered systems. We employ the air/liquid interface to assemble a triphenylbenzene derivative into perfectly oriented highly crystalline noncovalent-bonded organic nanosheets under ambient conditions. Each molecular building unit connects laterally by hydrogen bonding, endowing the nanosheets with size- and position-regulated permanent nanoporosity, as established by in situ synchrotron X-ray surface crystallography and gas sorption measurements. Notably, the nanosheets are constructed specifically by interfacial synthesis, which suppresses the intrinsic complex interpenetrated structure of the bulk crystal. Moreover, they possess exceptional long-term and thermal stability and are easily transferrable to numerous substrates without loss of structural integrity. Our work shows the power of interfacial synthesis using a suitably chosen molecular component to create two-dimensional (2D) nanoassemblies not accessible by conventional bulk crystal exfoliation techniques.