Intercalation of first row transition metals inside covalent-organic frameworks (COFs): a strategy to fine tune the electronic properties of porous crystalline materials.

Covalent-organic frameworks (COFs) have emerged as an important class of nano-porous crystalline materials with many potential applications. They are intriguing platforms for the design of porous skeletons with special functionality at the molecular level. However, despite their extraordinary structural tunability, it is difficult to control their electronic properties, thus hindering the potential implementation in electronic devices. A new family of nanoporous materials, COFs intercalated with first row transition metals, is proposed to address this fundamental drawback - the lack of electronic tunability. Using first-principles calculations, we designed 31 new COF materials in silico by intercalating all of the first row transition metals (TMs) with boroxine-linked and triazine-linked COFs: COF-TM-x (where TM = Sc-Zn and x = 3-5). We investigated their structure and electronic properties. Specifically, we predict that the band gap and density of states (DOS) of COFs can be controlled by intercalating first row transition metal atoms (TM: Sc-Zn) and fine tuned by the concentration of TMs. We also found that the d-subshell electron density of the TMs plays a main role in determining the electronic properties of the COFs. Thus intercalated-COFs provide a new strategy to control the electronic properties of materials within a porous network. This work opens up new avenues for the design of TM-intercalated materials with promising future applications in nanoporous electronic devices, where a high surface area coupled with fine-tuned electronic properties is desired.