Visible-Light-Driven Rotation of Molecular Motors in a Dual-Function Metal–Organic Framework Enabled by Energy Transfer

The visible-light-driven rotation
of an overcrowded alkene-based
molecular motor strut in a dual-function metal–organic framework
(MOF) is reported. Two types of functional linkers, a palladium–porphyrin
photosensitizer and a bispyridine-derived molecular motor, were used
to construct the framework capable of harvesting low-energy green
light to power the rotary motion. The molecular motor was introduced
in the framework using the postsynthetic solvent-assisted linker exchange
(SALE) method, and the structure of the material was confirmed by
powder (PXRD) and single-crystal X-ray (SC-XRD) diffraction. The large
decrease in the phosphorescence lifetime and intensity of the porphyrin
in the MOFs upon introduction of the molecular motor pillars confirms
efficient triplet-to-triplet energy transfer between the porphyrin
linkers and the molecular motor. Near-infrared Raman spectroscopy
revealed that the visible light-driven rotation of the molecular motor
proceeds in the solid state at rates similar to those observed in
solution.