Improving the response of 2D COFs to the surface doping strategies through rational design of their chemical structure

The chemical structure of covalent organic frameworks (COFs) plays a key role in their response to the surface doping strategy used for tuning their electronic character, but it is still not fully understood. To explore a rational design proposal for their chemical structure, the electronic properties of three n-doped typical COFs, including boron-containing (COF-1), triazine-based (CTF), and C–C bond-linked (GCOF) COFs, were investigated theoretically in this work. As expected, the chemical doping effects are different for these COFs. The dispersion of the frontier bands, the nuclear-independent chemical shift (NICS) aromaticity index results, distribution of the electron localization function (ELF), and Hirshfeld charge population plots show that part of the transferred electron from dopants will be offset by the intralayer charge transfer of COFs. Thus, chemical doping effects are more significant if the electron distribution in the COFs is more localized. This means the response of COFs to the surface doping strategy should be dominated by the conjugation degree of their chemical structure. Our results prove that the intrinsic conjugation degree of COFs plays a key role in such doping functionalization strategies, which are expected to provide more useful information for the initial structure design of COF materials and facilitate their practical applications as active electronic transport materials in nanoscale devices.