Redox-Dependent Transformation of a Hydrazinobuckybowl between Curved and Planar Geometries

A red‐fluorescent heterobuckybowl with an embedded hydrazine structure was synthesized from a cyclobiphenothiazine derivative via a strained cyclobicarbazole. The hydrazinobuckybowl was found to possess bowl and twist structures in the neutral state, a shallow bowl structure in the monocation state, and a planar structure in the dication state by means of X‐ray crystallographic analysis, DFT calculations, and a comparison of experimental and calculated 13C NMR chemical shifts. The hydrazinobuckybowl is the first buckybowl that changes its geometry between curved bowl/twist structures and a planar structure depending on the oxidation state. The drastic geometrical change was possible as a result of the presence of two heteroatoms in the bowl skeleton and the multiple reversible redox reactions of the compound. Owing to the two kinds of bowl and twist conformations, the bowl‐inversion dynamics of the hydrazinobuckybowl were found to follow a triple‐well potential model. Behavior to bowl you over: A red‐fluorescent heterobuckybowl—a heteroatom‐containing partial bowl structure of fullerene—was synthesized that had bowl and twist structures in the neutral state, a shallow bowl structure in the monocation state, and a planar structure in the dication state. A reversible transformation from the curved bowl/twist shape to the planar shape was found to occur upon two‐electron oxidation (see picture).