Quinoidal Azaacenes: 99% Diradical Character

Quinoidal azaacenes with almost pure diradical character ( y = 0.95 to y = 0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR, NMR and SQUID measurements revealing thermally populated triplet states with an extremely low energy gap Delta E ST' of 0.28 to 0.42 kcal/mol. The species are persistent in solution (half-life ~ 14 - 21 h); in the solid-state they are stable for weeks.