Takayuki ISHIDA (石田 尚行)

One‐ and two‐electron‐oxidized species of two π‐conjugated systems that adopt close π‐stacking structures are referred to as π‐mers and π‐dimers, respectively. These cationic species exhibit intriguing physicochemical properties that are markedly distinct from those of their parent monomeric radical cations. In this study, we have achieved the chemical oxidation of a newly designed tethered dimer comprising two planar sulfur‐ and carbon‐bridged triphenylamine (SCBT) units linked by a 1,8‐naphthalene moiety to obtain the corresponding π‐mer and π‐dimer as crystalline materials. Single‐crystal X‐ray diffraction analyses revealed that these cationic species adopt almost perfectly overlapping face‐to‐face close π‐stacking structures. As the degree of oxidation increases from the neutral form to the monocation and the dication, the interatomic S–S distance decreases drastically from 5.35 to 3.03 Å. The injection of electron spins into the neutral species effectively induces covalent‐like bonding interactions between the sulfur atoms and changes the degree of structural freedom of the molecule. The salt of the π‐mer exhibited an electrical conductivity of 1.9 × 10−6 S cm−1 at room temperature. The injection of spins by chemical oxidation also dramatically changed the dielectric response by generating dipole moments that affect the symmetry of the molecule.