Understanding the nature of quinoidal and zwitterionic states in carbazole-based diradicals.

We report two carbazole-based diradicals, out of which the m-isomer shows a large diradical character y (0.89) and a small singlet-triplet energy gap ΔE (-0.98 kcal mol), whereas the p-isomer exhibits smaller y (0.79) but a much larger ΔE (-6.16 kcal mol). DFT calculations reveal that this tendency is also suitable for nitrogen and carbon-centered diradicals.