Layered Hydrogen-Bonded Organic Frameworks as Highly Crystalline Porous Materials

Abstract

Porous molecular crystals (PMCs) with well-defined, self-standing pores have been attracted much attention due to significant functionality provided by selective and reversible inclusion of certain chemical species into the pores. PMCs constructed through preorganized hydrogen bonds (H-bonds) are specifically called as hydrogen-bonded organic frameworks (HOFs). For recent two decades, HOFs have been intensively explored. HOFs are frequently obtained as single crystals, which is convenient to reveal the structure–property relationship. Their regenerable and reusable features are also appealing. However, HOFs are relatively fragile, and their designing strategy needs to be more considered compared with other porous frameworks because of weakness of H-bonds. Regarding this, we have demonstrated that C3-symmetric π-conjugated molecules (C3PIs) possessing o-bis(4-carboxyphenyl)benzene moieties in their periphery give layered frameworks composed of isostructural H-bonded hexagonal networks (H-HexNets) and that the frameworks can effectively provide stable, robust, multifunctional HOFs with permanent porosity. The frameworks also can work as a platform to achieve very unique alignment of functional molecules such as C60. Our strategy for constructing functional HOFs contributes to developing a new field of porous organic materials.