Curator's Take
This article shows that triangulene‑based organic diradicals can achieve spin‑triplet ground states with coherence times approaching a few hundred microseconds—comparable to solid‑state defects such as nitrogen‑vacancy centers—while also offering optically addressable transitions. By combining first‑principles predictions of phonon‑limited T₂ and spin‑selective intersystem crossing, the work provides a concrete chemical blueprint for molecular qubits that could operate at or near room temperature, opening a pathway to scalable, chemically tunable quantum hardware. The results also highlight that further engineering of low‑energy vibrations and isotopic purification are needed to reach the theoretical T₁ limits, underscoring both the promise and the practical challenges ahead.
— Mark Eatherly
Summary
The identification of molecules that combine long spin coherence times and efficient spin-optical interfaces, ideally at room temperature, is pivotal towards the development of molecular quantum technology. By means of advanced first-principles methods, we here unravel the electronic structure for triangulene (1), its aza-cation derivative (2), and the crystal of 2,6,10-tri-tert-butyl-4,8,12-trimesityl-triangulene (3), and show that these organic diradicals possess a triplet ground state well separated from the first singlet excited state approaching 0.5 eV, closely resembling solid-state defects like nitrogen vacancy centers. In addition, we compute spin decoherence times due to the interaction with phonons and surrounding nuclear spins, showing that a deuterated molecule of 3 in a nuclear spin-free environment would support $T_2 = 0.21$ ms at 10 K. Importantly, we show that the engineering of specific low-energy vibrations could significantly improve $T_2$ toward the limit imposed by the molecular core spin relaxation, here estimated to be as long as $T_1=27$ ms at 300 K for 2. Finally, we compute two-phonon contributions to inter-system crossing at 300 K for2 as a luminescent prototype, and find that it is highly spin-selective, supporting the possibility to engineer optical read out and spin initialization. These results advance a unified first-principles theoretical foundation of spin decoherence and spin-selective excited-state processes and point to novel chemical design strategies for optically addressable, highly coherent molecular qubits.