Fusion of Cyclohepta[def]fluorene Units: Toward Synthesis of High‐Spin Non‐Benzenoid Nanographenes

Abstract

Non‐benzenoid diradicaloids possessing high‐spin ground states are attractive synthetic targets given their high potential for spintronics and quantum computing. Nevertheless, the synthesis of such compounds remains highly challenging due to their inherent instability. In this work, we present the synthetic attempt towards creating a non‐benzenoid diradicaloid (1) with a triplet ground state by fusing two cyclohepta[def]fluorene units onto a benzene ring. Our synthetic approach involves both oxidation and reduction pathways. In the oxidation path, we obtained the partially dehydrogenated products 1+H and 1+2H containing an indeno[1,2‐b]fluorene core from the tetrahydro precursor (2). However, further dehydrogenation to afford the target molecule (1) did not proceed. On the other hand, with the reduction pathway, a novel tetraketone precursor (9) with two pairs of pentagons and heptagons was successfully synthesized. The subsequent nucleophilic attack however was proved to be difficult probably due to the unselective nucleophilic addition on the zigzag nanographene ketones. Furthermore, UV‐vis absorption, cyclic voltammetry, and theoretical calculations were conducted to explore the optical, electrochemical properties, and aromaticity of all the obtained molecules (1+H, 1+2H and 9). Although the desired target 1 is not achieved, our work provides insight into designing novel high‐spin non‐benzenoid NGs based on nonalternant cyclohepta[def]fluorene system.