Influence of Interpenetration in Diamondoid Metal-Organic Frameworks on the Photoreactivity and Sensing Properties

The degree of interpenetration is known to influence the gas sorption, catalytic, magnetic and nonlinear optical properties, chirality, and sensing of various molecules but not the solid-state [2 + 2] photocycloaddition reaction. In our previous studies of a solvothermal reaction using dimethylacetamide (DMA) as one of the solvents, a photoreactive 6-fold interpenetrated metal organic framework with dia topology, [Zn(bpeb)(bdc)] (1) [bpeb = 1,4-bis[2-(4'-pyridyl)ethenyl]benzene; bdc = 1,4-benzenecarboxylate], was isolated. Because of the slip-stacked alignment of a dipyridyl ligand with two conjugated olefin bonds, the [2 + 2] cycloaddition reaction occurs under UV light leading to the formation of an organic polymer ligand fused with a coordination polymer, 2. On the contrary, under similar conditions when diethylformamide was used instead of DMA, a 5-fold interpenetrated structure, 3, with the same dia topology was obtained in this work. This has been found to be photostable as also predicted from the analysis of the solid state structure. All the solids show interesting photoluminescence properties, and the emissions were preferentially quenched by curcumin to make these materials as potentially useful sensing agents.