First Row Transition Metals Intercalation of Covalent-Organic Frameworks: A Promising Route to Tune the Material Structure and Electronic Properties

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. A new form of nanoporous material, transition metal intercalated COFs is proposed and its electronic properties are revealed. Using first-principles dispersion-corrected hybrid density functional theory (DFT-D), we have designed 31 new COF materials in-silico by intercalating all of the first row transition metals (TMs) with boroxine-linked and triazine-linked COFs. This is a significant addition considering that only 187 experimentally COFs structures has been reported and characterized so far. We have investigated their frameworks properties as well as material properties. Specifically, we predict that COF's band gap and density of states (DOSs) can be fine tuned by intercalating first row transition metal atoms (TM: Sc - Zn). The present DFT-D calculations showed that the d-subshell electron density of the TMs plays an important role in determining the material properties of the COFs.

The implications of controllable electronic structure and properties of intercalated COF materials for future device applications are discussed. Thus intercalated-COFs provide a new strategy to create semi-conducting and conducting materials within a rigid porous network in a highly controlled and predictable manner. This work opens up new avenues for the efficient production of TM-intercalated materials with promising future applications in nanoporous material science, electronics and chemical sensors.