Spin and Structural Dynamics of Persistent π-Mer and π-Dimer of a Tethered S,C,C-Bridged Triphenylamine Dimer

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.