Stair-like narrow N-doped nanographene with unusual diradical character at the topological interface

The π-magnetism of finite-sized nanoribbons occurring on the topological molecular interfaces remains largely unexplored due to limited experimental examples. Herein, we report a rational design, solution synthesis, and systematical characterization of a novel type of stair-like aza-nanographene (ANG) ANG-a/b with precise N-doping on the interfacial cove edges. Within the same molecular π-backbone, ANG-a had a closed-shell structure due to the electronic perturbation of cove-edge substitution, while ANG-b hosted a spin-polarized interface state, and its open-shell singlet diradicaloid structure produced a combined optoelectronic, magnetic, and physicochemical characteristic. Besides, dicationic ANG-b was also synthesized and characterized as a ground-state diradicaloid, again closely associated with the interfacial spin polarization in the charged π-system. Our studies might provide insights into future structural engineering of topological open-shell materials with robust yet exotic spin-polarized interface states.