To isolate the biradical species and confirm the reversibility of redox interconversion, chemical reduction and subsequent oxidation of 2 2+ (BF 4 -) 2 were performed. As shown in Scheme 2, upon twoelectron reduction of cyclophane-type dicationic salts 2a 2+ (BF 4 -) 2 , 2b 2+ (BF 4 -) 2 , and 2c 2+ (BF 4 -) 2 with two equivalents of cobaltocene in dry MeCN, biradical species 2a ). Very weak signals assignable to the species with open-shell characters were observed, indicating that the singlet state is more stable for these biradicals. Therefore, for 2 •• , although there is a marginal contribution from the thermally excited triplet species in solution, the singlet state can be stabilized by a spin-spin interaction in the cyclophane-type structure. This study demonstrates that the cyclophane structure composed of planar -conjugated cations is an effective way not only to modulate physical properties such as absorption and redox properties but also to stabilize the corresponding reduced species including a biradical state.