Covalent linker transformations in metal–organic
frameworks
(MOFs) enable their functionalization but often suffer from low conversions
or require harsh conditions, including heating, corrosive reactants
and solvents, or catalysts. In this work, using solvent-free mechanochemistry
for the first time for such conversions, we demonstrate the systematic
MOF pore modification with pendant hydroxyl groups and the resulting
effects on the network rigidity, its luminescent properties, as well
as adsorption of CO2and vapors of methanol, ethanol, isopropanol,
D2O, and H2O. A new zinc-based heterolinker
MOF (JUK-20) containing both protic luminescent units and reactive
tetrazine cores was used as a model and subjected to an inverse electron-demand
Diels–Alder (iEDDA) click reaction with a series of dienophiles
(x) of different lengths having OH groups. From the obtained series
of JUK-20(Zn)-x MOFs, a flexible material capable of luminescent humidity
sensing was identified, and the influence of water on the luminescence
of the material was explained by analogy with the excited-state intramolecular
proton transfer (ESIPT) model. In general, our results provide guidance
for designing and tuning MOFs for luminescence-based detection using
a stepwise synthetic approach.