Dimers. With this analysis of (benzene) 2 serving as a backdrop and a baseline, we next consider the porous systems: (annulene) 2 , (porphyrin) 2 , and (COF1) 2 . Figure presents one-dimension energy component profiles for the [18]annulene dimer, in a similar manner to what was presented for benzene dimer, starting in an eclipsed-cofacial configuration and sliding one annulene monomer across the other at 3.2 Å face-toface separation, corresponding to the minimum-energy separation in the offset-stacked structure. At this separation, a local minimum in E int is observed at a parallel displacement of 3.5 Å relative to the eclipsed-cofacial structure.