Chemical Patterning in Single Crystals of Metal-Organic Frameworks by [2+2] Cycloaddition Reaction

Conventional chemical patterning involves films of polymeric materials. Herein, we demonstrate that the presence or absence of guest solvents in the crystal voids modulates the patterning of the cyclobutane rings in highly strained metal-organic frameworks (MOFs) under UV light. The olefin pairs of the spacer ligands, which resemble a ladder-like structure, in the MOF, undergo a [2+2] cycloaddition reaction in a single-crystal-to-single-crystal manner. For instance, a partial photoreaction in the MOFs in the absence of a guest solvent as well as with dimethylacetamide in the voids generated two different patterns of the cyclobutane rings. Surprisingly, the MOF with the lattice dimethylformamide undergoes 100 % photoreaction, but the photoproduct contains broken chains. Such chemical patterning at the molecular level represents a next step in crystal engineering.