Pores in COFs are the functional regions and we calculated that the inclined and serrated arrangements account for an increase in the surface area by 6%, estimated for the interaction with He, or 3% for the interaction with N2, compared with eclipsed stacking. Moreover, the polarity of pores increases for the two stackings, because both oxygen and boron atoms are exposed to the pore surface. After our report on the stacking structure of COFs, the proposed stacking arrangements, especially the serrated one, were commonly adapted in the community. In 2017, Fan et al. have demonstrated for the first time inclined stacking of layers in 2D COFs by introduction of steric substituents between the layers. PXRD patterns of all the stacking arrangements. (d-g) (Top) structures and (bottom) electronic band structures (lowest two panels show zoom-ins of conduction band maximum (CBM) and valence band minimum (VBM)) of (a) monolayer (1L), (b) eclipsed (AAAA), (c) inclined (AA'A''A'''), and (d) serrated (AA'AA') stackings of COF-5. Single layer COF-5 has fairly flat bands close to the Fermi level (blue dashed horizontal lines). Prominent dispersion of bands in the direction perpendicular to the layers can be observed upon stacking single layer to multilayer COF-5, the strongest in case of AAAA (eclipsed) stacking. Calculations performed on the optimized structures from Ref. [63] at the DFT/PBE level of theory with TZP basis set as implemented in AMS/BAND software. Figure adapted from Ref. [63]. Pictures of structures made with VESTA. We have simulated the electronic band structure of single layer of COF-5, as an exemplary 2D COF structure, and compared it to these of bulk COF-5 with different stackings: eclipsed, inclined, and serrated (see Figure bottom panels for full band structure and zoom-ins of conduction and valence bands. The band structure of the single layer of COF-5 exhibits almost flat bands when compared to the 3D stackings. However, close examination of the valence and conduction bands in the vicinity of the Fermi level of the COF-5 single layer reveals a typical signature of the so-called (Archimedean) kagome lattice (see Figure CBM zoom). In the valence band (see Figure VBM zoom), these are two bands of linear dispersion, crossing at the K point, similar to graphene. These bands are also sandwiched between two flat bands, forming so-called ruby bands. Thus, the top of valence band is very flat throughout the Brillouin zone. The conduction bands are a bit more disperse, with minimum at the  point. The single layer of COF-5 is, thus, a direct-gap semiconductor with a band gap of about 2.7 eV. Our results are in good agreement with previously reported theoretical work of Liu et al., who obtained a band gap of 2.5 eV at a similar level of theory.