Furthermore, by modifying the electron-donating ability of the substituent on the aryl group, the color tone of the dications can be modulated without changing the LUMO level. Such a stacking structure observed in 2 2+ can also stabilize their radical cation and biradical species, and thus cyclophane-type dications 2 2+ exhibit clean electrochromic behavior via an intermediary radical cation and biradical. In addition, biradical species 2a •• -2c •• were successfully isolated upon two-electron reduction of cyclophane-type dicationic salts 2a 2+ (BF 4 -) 2 -2c 2+ (BF 4 -) 2 . Therefore, the cation-stacking approach can be a versatile method for developing stimuli-responsive molecules and stabilizing intrinsically unstable open-shell species.