Fluorescent Zr(IV) Metal–Organic Frameworks Based on an Excited-State Intramolecular Proton Transfer-Type Ligand

We report here the preparation of a series of Zr(IV) Metal Organic Frameworks of the MIL-140 structure type incorporating a ligand exhibiting an intense Excited State Intramolecular Proton Transfer (ESIPT) fluorescence. These solids were obtained by systematically varying the substitution rate of 4,4'-biphenyldicarboxylate by 2,2'-bipyridine-3,3'-diol-5,5'-dicarboxylate, and thoroughly characterized by complementary techniques, including high resolution powder X-ray diffraction, solid state NMR spectroscopy, nitrogen sorption experiments and time-resolved fluorescence. We showed that the incorporation of the ESIPT-type ligand induces an increase of the hydrophilicity, leading ultimately to a higher sensitivity toward hydrolysis, a phenomenon rarely observed in this structure type considered as one of the most stable among the Zr carboxylate MOFs. Eventually, the optimization of the amount of fluorescent ligand within the structure allowed combining a decent microposity (SBET > 750 m 2 .g-1) and a high stability even in boiling water, together with a high fluorescence quantum yield (> 30%).