Studies on the Bridge Dependence of Bis(triarylamine) Diradical Dications: Long-Range π‑Conjugation and π–π Coupling Systems

Three bis­(triarylamine) dications bridged with 2,2′-bithienyl group (<b>1</b>²⁺), biphenyl group (<b>2</b>²⁺) and [2,2]­paracyclophane (<b>3</b>²⁺) have been successfully isolated. The electronic structures of <b>1</b>²⁺ – <b>3</b>²⁺ show bridge dependence. Magnetic studies and DFT calculations show that dications <b>1</b>²⁺ – <b>3</b>²⁺ possess an open-shell singlet ground state with a thermally excited triplet state. Dication <b>3</b>²⁺ has rather small singlet–triplet energy gap and could basically be regarded as a nearly pure diradical. Diradical dications <b>1</b>²⁺ – <b>3</b>²⁺ represent rare examples of diradicaloids with intramolecular long-range π-conjugation or π–π coupling interaction