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 (12+), biphenyl group (22+) and [2,2]­paracyclophane (32+) have been successfully isolated. The electronic structures of 12+ – 32+ show bridge dependence. Magnetic studies and DFT calculations show that dications 12+ – 32+ possess an open-shell singlet ground state with a thermally excited triplet state. Dication 32+ has rather small singlet–triplet energy gap and could basically be regarded as a nearly pure diradical. Diradical dications 12+ – 32+ represent rare examples of diradicaloids with intramolecular long-range π-conjugation or π–π coupling interaction.