Copper-Linked Rotaxanes for the Building of Photoresponsive Metal Organic Frameworks with Controlled Cargo Delivery

We have prepared
a photoresponsive metal–organic framework
by using an amide-based [2]­rotaxane as linker and copper­(II) ions
as metal nodes. The interlocked linker was obtained by the hydrogen
bond-directed approach employing a fumaramide thread as template of
the macrocyclic component, this latter incorporating two carboxyl
groups. Single crystal X-ray diffraction analysis of the metal–organic
framework, prepared under solvothermal conditions, showed the formation
of stacked 2D rhombohedral grids forming channels decorated with the
interlocked alkenyl threads. A series of metal–organic frameworks
differing in the E/Z olefin ratio were prepared either
by the previous isomerization of the linker or by postirradiation
of the reticulated materials. By dynamic solid state 2H
NMR measurements, using deuterium-labeled materials, we proved that
the geometry of the olefinic axis of the interlocked struts determined
the obtention of materials with different independent local dynamics
as a result of the strength of the intercomponent noncovalent interactions.
Moreover, the usefulness of these novel copper-rotaxane materials
as molecular dosing containers has also been assayed by the diffusion
and photorelease of p-benzoquinone, evaluated in
different solvents and temperatures.