2020, Intorp, S.N., Hodecker, M., Müller, M., Tverskoy, O., Rosenkranz, M., Dmitrieva, E., Popov, A.A., Rominger, F., Freudenberg, J., Dreuw, A., Bunz, U.H.F.

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low-energy gap ΔEST′ of 0.58 to 1.0 kcal mol−1. The species are persistent in solution (half-life≈14–21 h) and in the solid state they are stable for weeks.