Ligand-tuning of the Excitation Wavelength of a Solid State E/Z Isomerization: [Zn(TA)₂(2,2́-bipyridyl)] in a Supramolecular Framework

The single-crystal-to-single-crystal (SCSC) E→Z photoisomerization of TA in the supramolecular solid CECR-[Zn(TA)₂(bpy)]-H₂ (CECR = C-ethylcalixresorcinarene, HTA= tiglic acid, andbpy = 2,2́bipyridine, is induced by 458 nm light, indicating a red-shift of the photo-active wavelength on introduction of the aromatic bpy ligand compared with the previously studied reaction of CECR-[Zn(TA)₂(H ₂O)₂]4H₂O. Theoretical calculations show that the initial excitation involves the bipyridyl ligand, which acts as an intramolecular photosensitizer for the isomerization process. The reaction is topotactic and illustrated by photodifference maps.