Abstract
Molecular motors change conformation under the influence of light and
when attached to host molecules they may find applications as sensors
and switchable catalysts. Here we present a porphyrin macrocyclic host
functionalized with two motor appendages for future catalytic
applications. The compound is formed as a mixture of six stereoisomers
(three sets of enantiomers), which have been separated by (chiral)
chromatography. 1H NMR and chiral spectroscopy revealed that in one set
of diastereomers the two motors interact with the cavity of the host
(bound-bound), whereas in a second set one interacts and the other one
does not (bound-loose). In the third set both motors do not interact
with the host compound (loose-loose). The motorized hosts bind guest
molecules in the order: (loose-loose) > (bound-loose)
> (bound-bound). They can be switched with light to
pseudo-identical diastereomers, leading to orthogonal behavior in the
light-gated binding of guest molecules. Whereas the photo-isomerization
of the diastereomer set loose-loose significantly lowers the binding
affinity for viologen guests, the opposite is true for the diastereomer
set bound-bound, i.e. the binding affinity increases. For the
diastereomer set bound-loose no influence on guest binding is observed
as the effect of photoisomerization on the motors is cancelled out.