Molecular structures for three oxidation forms (anion, radical, and cation) of terbium(III) bis(porphyrinato) double-decker complexes have been systematically studied. We found that the redox state controls the azimuthal rotation angle (φ) between the two porphyrin macrocycles. For [Tb (tpp) ] (tpp: tetraphenylporphyrinato, n=-1, 0, and +1), φ decreases at each stage of the oxidation process. The decrease in φ is due to the higher steric repulsion between the phenyl rings on the porphyrin macrocycle and the β hydrogen atoms on the other porphyrin macrocycle, which results from the shorter interfacial distance between the two porphyrin macrocycles. Conversely, φ=45° for both [Tb (oep) ] and [Tb (oep) ] (oep: octaethylporphyrinato), but φ=36° for [Tb (oep) ] . Theoretical calculations suggest that the smaller azimuthal rotation angle of the cation form is due to the electronic interaction in the doubly oxidized ligand system.

Metal bis(porphyrinato) double‐decker complexes have been used for the construction of functional molecules such as molecular machines and single‐molecule magnets. Here, switching of the azimuthal rotation angle of terbium double‐decker complexes by redox stimulation is presented. This could contribute not only to a better understanding of their structure–property relationship but also to the design of redox‐driven molecular machines such as those similar to a Ferris wheel. More information can be found in the Full Paper by Ken‐ichi Yamashita, Takuji Ogawa et al. on page 1692 in Issue 13, 2018 (DOI: 10.1002/asia.201800324).