The synthesis and
isolation of one of the few examples of a π-extended
diamagnetic phenazine dication have been achieved by oxidizing a phenanthrene-based
dihydrophenazine precursor. The resulting dication was isolated and
fully characterized, highlighting an aromatic distorted structure,
generated by the conformational change upon the oxidation of the dihydrophenazine
precursor, which is also correlated with a marked electrochromic change
in the UV–vis spectrum. The aromaticity of the dication has
also been investigated theoretically, proving that the species is
aromatic based on all major criteria (structural, magnetic, and energetic).
Moreover, the material presents an intriguing dual reactivity, resulting
in ring contraction to a π-extended triarylimidazolinium and
reduction to the dihydrophenazine precursor, depending on the nature
of the nucleophile involved. This result helps shed light on the yet
largely unexplored reactivity and properties of extended dicationic
polycyclic aromatic hydrocarbons (PAHs). In particular, the fact that
the molecule can undergo a reversible change in conformation upon
oxidation and reduction opens potential applications for this class
of derivatives as molecular switches and actuators.