All macrocyclic dications exhibit strong absorptions in the visible region [ max /nm (log ): 420 (5.00) for 2a , respectively], a blue shift and an increase in full width at half-maximum (FWHM) of the absorption band at around 420 nm were observed for cyclophane-type dications 2 2+ (Figure ). This means that there is a contribution from H-type aggregates, and thus, even in solution, cation units in dication 2 2+ have a stacking geometry similar to those in the single crystal. Furthermore, the absorption maxima of the first band for these cations drastically changes depending on the donating ability of the substituent on the aryl group due to the significant change in the HOMO level. To gain insight into the stabilization energy by the stacking of cation units for cyclophane-type dications 2 2+ , the relative energies among the conformers was investigated using DFT calculations at the B97X-D/6-31G* level. As shown in Figures and-S21, the relative energies for the semi-open form and the open form are much higher than that for the closed form with the stacked geometry, which is calculated to be the most stable structure for all dications (semi-open form: E rel = 6.79 kcal mol -1 for 2a 2+ , 15.11 kcal mol -1 for 2b 2+ , and 6.68 kcal mol -1 for 2c 2+ and open form: E rel = 19.55 kcal mol -1 for 2a 2+ , 20.68 kcal mol -1 for 2b 2+ , and 18.77 kcal mol -1 for 2c 2+ ). This result indicates that the stacking of cationic units has a stabilization effect, which is greater than the electrostatic repulsion. Indeed, the noncovalent interaction (NCI) plots of 2 2+ at the B97X-D/6-31G* level show that, due to the delocalization of a positive charge that efficiently reduces electrostatic repulsion, the cation units facing each other of 2 2+ exert attractive rather than repulsive effects (Figures and). and -0.34 for 1c + ) when there is no interaction between the cation units, the stepwise reduction processes indicate that the cation units are close enough to interact with each other even in solution. In addition, unlike with monocations 1 + which exhibit an irreversible process, reversible redox waves were observed for dications 2 2+ , indicating that the cyclophane structure can stabilize both radical cation and biradical species. Although the closed-shell species might be obtained by the bond formation between the two radicals upon the 2e-reduction of 2 2+ , the reversible waves show that the -bond was not formed.