FIGURE 3 Isomerization pathways of: (A) molecular motor 7 , (B) the different isomers of double-motorized porphyrin cage Zn3 . For clarity, only the pathways of the (+)-Sp isomers of the porphyrin cage compounds are depicted; the same mutual relationships are valid for the corresponding enantiomers with the (−)-Rp cage configuration.
pseudo-identical isomers. In the isomers of double-motorized cage compound Zn3 , even more stereochemical elements are present than in 7 (Figure 3B). The planar chirality of the cage compound (R p orS p),26 as well as the point chiralities at the stereogenic centers, (R ) or (S ), of the motor substituents are fixed. The only stereochemical element that can be isomerized is the helicity of the molecular motor (M orP ), which is subject to photochemical inversion. Since the metastable isomer of a molecular motor is pseudo-identical to the stable isomer of the enantiomer of the same motor (Figure 3A), all the possible metastable isomers of any diastereomer of Zn3 are pseudo-identical to the stable isomers of one of its other diastereomers. In Figure 3B all stable and metastable isomers ofZn3 with the same color-code are considered to be pseudo-identical. In this more complex case, we call two isomers pseudo-identical if they possess identical motor helicities (M orP ) and identical planar chiralities (R p orS p).
TABLE 2 Photochemical and thermal properties of single- and double-motorized porphyrin cages. UV-vis experiments were conducted in CHCl3/CH3CN (1:1, v/v) and NMR experiments in CDCl3/CD3CN (1:1, v/v). Values for Zn2a and Zn2b were taken from reference 25.