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.