Crystalline Diradical Dianions of Pyrene-Fused Azaacenes.

Although diradicals and azaacenes have been greatly attractive in fundamental chemistry and functional materials, the isolable diradical dianions of azaacenes are still unknown. Here we describe the first isolation of azaacene diradical dianion salts [(18-c-6)K(THF) 2 ] + [(18-c-6)K] + * 1 2-** and [(18-c-6)K(THF)] 2+ * 2 2-** by reduction of the neutral pyrene-fused azaacene derivatives 1 and 2 with excess potassium graphite in THF in the presence of 18-crown-6. Their electronic structures were investigated by various experiments, in conjunction with theoretical calculations. It was found that they are open-shell singlets in the ground state and their triplet states are thermally readily accessible due to the small singlet-triplet energy gap. This work provides two first examples of crystalline diradical dianions of azaacenes with considerable diradical character.