Recognizing Through-Bond and Through-Space Self-Exchange Charge/Spin Transfer Pathways in Bis(triarylamine) Radical Cations with Similar Geometrical Arrangements

Radical cations of bis(triarylamine)s, 3 and 4, in which the triarylamine redox centers are bridged by an ortho-phenylene and ortho-carborane cluster, respectively, have been prepared to elucidate the difference in intramolecular charge/spin-transfer (ICT/IST) pathway owing to the two different bridging units affording similar geometrical arrangements between the redox centers. Electrochemistry, absorption spectroscopy, VT-ESR spectroscopy, and DFT calculations reveal that 3^.+ and 4^.+ are classified into class II and class I mixed-valence systems, respectively, and therefore, through-bond and through-space mechanisms are dominant for the ICT/IST phenomena in 3^.+ and 4^.+ , respectively. Moreover, SQUID measurements for dicationic species provide the fact that virtually no spin-exchange interaction is observed for spins in 4²⁺ , while the antiferromagnetic interaction for spins in 3²⁺ , in accordance with the existence of a conjugation pathway for the ortho-phenylene bridge.