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.