Pairwise selective formation of aromatic stacks in a coordination cage.

An asymmetric alignment of electron-donating (D) and accepting (A) aromatics is a formidable challenge in the self-assembly of aromatic stacks because self-assembled aromatic stacks usually give alternating aromatic arrays, D-A-D-A-.... Here, we show that appropriate D-A guest pairs settle down in an electron-deficient aromatic box to yield an asymmetric quadruple A-D-A-A stacking sequence quantitatively. The inner D-A guest pair rapidly swaps their positions to create a dynamic aromatic array, and the swift guest motion largely depends on the donor aromatics.