Azadihomocorannulene as a Heptagon-Embedded Diradicaloid.

Polycyclic aromatic diradical(oid) molecules are attracting significant attention because of their unique electronic and magnetic properties as well as their applications as functional materials. While diradical(oid) molecules bearing five-membered rings have been extensively investigated, those bearing seven-membered rings are relatively fewer. Herein, we report the synthesis of azapentabenzodihomocorannulene dication and diradical molecules. The synthesis was achieved through a mechanochemical C(sp)-H/C(sp)-H coupling in the presence of sodium as a key reaction. Electron spin resonance studies revealed that the neutral azapentabenzodihomocorannulene adopts a singlet diradical (diradicaloid) ground state with a small singlet-triplet energy gap of 2.1 kcal/mol. The electronic and optical properties were investigated both experimentally and theoretically to elucidate their aromatic character.