Aethrene: A Stable Polycyclic Aromatic Hydrocarbon With a Triplet Ground State

Owing to their unique electronic structures and magnetic properties, high-spin radicals have garnered significant interest in the fields of organic electronics and spintronics. Nevertheless, the high reactivity of high-spin radicals renders efficient synthesis and selective isolation of the species a formidable challenge. An aethrene derivative 2 with an A-shaped geometric skeleton was designed with a Clar structure of allylic radicals embedded with aromatic benzenoid rings, and two bulky steric substituents were introduced at the zigzag edges to endow the compound with excellent stability. 2 exhibits a 15.5-day half-life under ambient and light conditions. The structure of 2 was unequivocally confirmed through x-ray crystallographic analysis. Aethrene 2 was demonstrated to possess a triplet ground state through DFT calculations and experimental methods, including continuous wave and pulsed electron paramagnetic resonance and superconducting quantum interference device measurements. Notably, its dication was successfully obtained by in-situ oxidation with NO·SbF₆ and exhibited a closed-shell ground state. This work shed new light on the design and synthesis of novel stable PAHs with high-spin multiplicity.