Fully Conjugated [4]Chrysaorene. Redox-Coupled Anion Binding in a Tetraradicaloid Macrocycle

[4]­Chrysaorene,
a fully conjugated carbocyclic coronoid, is shown
to be a low-bandgap π-conjugated system with a distinct open-shell
character. The system shows good chemical stability and can be oxidized
to well-defined radical cation and dication states. The cavity of
[4]­chrysaorene acts as an anion receptor toward halide ions with a
particular selectivity toward iodides (Ka = 207 ± 6 M–1). The interplay between anion
binding and redox chemistry is demonstrated using a 1H
NMR analysis in solution. In particular, a well-resolved, paramagnetically
shifted spectrum of the [4]­chrysaorene radical cation is observed,
providing evidence for the inner binding of the iodide. The radical
cation–iodide adduct can be generated in thin solid films of
[4] chrysaorene by simple exposure to diiodine vapor.