A robust spin-coupled tetraradical via nonalternant design.

A nonalternant, air-stable tetraradical with two fused 7-5-7 rings shows exceptional tetraradical character (y0 = 1.00, y1 = 0.89) and a strongly correlated singlet ground state.

• Why it matters: Polyradicals in open-shell polycyclic hydrocarbons are promising for spintronics and quantum technologies, but maintaining robust spin coherence while achieving strong spin-exchange coupling remains challenging.
• What they did: The authors synthesized and characterized the molecule using comprehensive electronic-structure and magnetic-response analyses, extracting spin-exchange parameters J1 = +321 K, J2 = -44 K, and J3 = -29 K.
• The result: The nonalternant design is linked to suppressed hyperfine and vibrational decoherence, yielding long spin relaxation and coherence time, alongside long ambient stability (t1/2 = 33 days).

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