Three-Dimensional Covalent Organic Frameworks with lil Topology

Abstract

The diversity of covalent organic frameworks (COFs) is continuously expanding, providing various materials with tailor-made structures and properties. However, the development of crystalline three-dimensional (3D) COFs with new topologies is an essential but arduous challenge. In this study, we first developed one kind of 3D COFs with the lil topological structure, which were assembled by D_4h- and C_2h-symmetric building blocks. The 3D COFs were determined in a space group of Imma, in which each D_4h-symmetric unit is connected with four C_2h-symmetric units, forming a noninterpenetrated network. The densely packed copper phthalocyanine and stable polyimide linkage render these COFs as a polymeric material with high dielectric constant and low dielectric loss at high frequencies (>1 kHz). Significantly, the dielectric constant was determined as high as 63, which constitutes a new record value among phthalocyanine-based and polyimide polymers. Therefore, this study not only provides important guidance for the design of 3D lil-net COFs but also supplies promising materials for application in high-energy-density and pulsed capacitors.