Macrocyclic Polyradicaloids with Unusual Super-ring Structure and Global Aromaticity
Chunchen Liu, María Eugenia Sandoval-Salinas, Yongseok Hong, Tullimilli Y.Gopalakrishna, Hoa Phan, Naoki Aratani, Tun Seng Herng, Jun Ding, Hiroko Yamada, Dongho Kim, David Casanova, Jishan Wu
Organic opto-electronic and magnetic materials play an important role in future affordable electronics and clean energy, and aromaticity is one of the most important concepts that determine their physical and material properties. Over the past nine decades, Hückel's rule and Baird's rule have been developed to describe the (anti)aromaticity of monocyclic π-conjugated molecules. For polycyclic π-conjugated systems, localized aromaticity usually dominates, and there is almost no report of global aromaticity for benzenoid polycyclic hydrocarbons. In this work, we experimentally obtained two hydrocarbon-based macrocyclic polyradicaloids, which show a long-sought-after annulene-within-an-annulene super-ring structure and very unusual global aromaticity. Both Hückel's rule and Baird's rule can be followed for these polyradicaloids. Our study gives some new insight into the unique global aromaticity in polycyclic π-conjugated molecules.