Structural characterization of the self-assembly pathways. Visual inspections of the 40 self-assembly pathways of Octacid4•xylene at 298 K revealed that all pathways comprised three common steps (Fig. and Movies S1-S6). In Step 1, xylene entered the cavity portal exterior space that was confined by two aromatic linkers of the host; as apparent from the representative movies, there were substantial collisions between xylene and the equatorial portal in the linker region of Octacid4 that led to the portal expansion for guest ingress. In Step 2, xylene passed one methyl group through the equatorial portal, then the phenyl group through the portal with the phenyl plane perpendicular to the axial axis (viz., the axis passing two axial portals in the bowl-shaped region), and lastly the other methyl group through the equatorial portal. In Step 3, xylene rotated ~90° to keep its phenyl plane parallel to the axial axis. This rotation caused the equatorial portal contraction and impeded guest egress, according to the reported structural analyses of apo Octacid4 and the Octacid4•xylene complex using time series of radius of gyration of the Octacid4 cavity derived from MD simulations .