Azoniadibenzo[a,j]phenalenide: A Polycyclic Zwitterion with Singlet Biradical Character.

A polycyclic zwitterion, azoniadibenzo[a,j]phenalenide, having a singlet biradical character, was synthesized and isolated for the first time. The negative charge was found to be delocalized over the periphery of the main core of the zwitterion and the positive charge was localized near the nitrogen atom. Its singlet biradical character was confirmed by a small HOMO-LUMO energy gap with their spatial overlap, and observation of thermally excited triplet species together with DFT calculations.