Effects of connecting sequences of building blocks on reticular synthesis of covalent organic frameworks

The principle of reticular chemistry has been widely used to guide the design of crystalline porous materials such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs). While in the early strategies only the symmetries of the building blocks were considered for reticular synthesis of COFs, recently a few researches on COFs with hierarchical porosities indicate that connecting sequence of building blocks also plays a crucial role in determining crystalline structures of COFs. However, this important phenomenon has not been systematically investigated yet. In this article, a model system has been established to demonstrate how different connecting sequences of two C_2V-symmetric building blocks lead to the formation of four two-dimensional (2D) COFs with distinct framework structures. To verify this concept, target synthesis was conducted to produce three COFs, whose structures were confirmed by powder X-ray diffraction and pore size distribution analysis.