The ability of modulating the properties of metal–organic frameworks (MOF) on demand by external light-stimuli is a most appealing pathway to enhance their performance in storage and separation and to render novel advanced applications. Photoswitchable linkers of different nature have been inserted in several MOF structures either as integral parts of their scaffolds or as guests in the pores. In this highlight we analyse the different strategies and expose some aspects that should be considered in the design of new generations of photoswitchable MOFs ... Read more

Three supramolecular isomers of lutetium metal-organic framework, {Lu₂(H₂O)₄(ATA)₃·4H₂O}_n (Lu-ATA@RT), {Lu₂(H₂O)₂(C₃H₇NO)₂(ATA)₃}_n (Lu-ATA@100), and {Lu₂(C₃H₇NO)(ATA)₃}_n (Lu-ATA@150), have been obtained from the reaction of Lu(NO₃)₃·6H₂O with 2-aminoterephthalic acid (ATA) at different temperatures. The resulting structures of Lu-ATA metal-organic frameworks depend on the temperature applied during the synthesis, revealing a temperature-susceptible supramolecular isomerism. Single-crystal X-ray diffraction analyses suggest that new compounds with formula {Lu₂(S)_x(ATA)₃}_n (S = solvent: H₂O, DMF) display different three-dimensional architectures which consist of dinuclear lutetium building units. The supramolecular isomer Lu-ATA@RT, formed at room temperature, has a pcu-net topology, while its double interpenetrated analogue Lu-ATA@100 assembles at 100 °C under hydrothermal conditions. Hydrothermal synthesis at 150 °C affords formation of the dense Lu-ATA@150 cage-like framework displaying a new hexagonal-packed net topology. All Lu-ATA isomeric phases are porous and display different gas-uptake behavior toward carbon dioxide as a function of polymeric network arrangement. The luminescent properties of Lu-ATA frameworks in the solid state as well as in suspension in the presence of different solvents reveal a solvent-dependent emission. ... Read more

Recently, MIL-125(Ti) and NH2-MIL-125(Ti), two titanium-based metal–organic frameworks, have attracted significant research attention in the field of photocatalysis for solar fuel generation. This work reveals that the differences between these structures are not only based on their light absorption range but also on the decay profile and topography of their excited states. In contrast to MIL-125(Ti), NH2-MIL-125(Ti) shows markedly longer lifetimes of the charge-separated state, which improves photoconversion by the suppression of competing decay mechanisms. We used spectroelectrochemistry and ultrafast spectroscopy to demonstrate that upon photoexcitation in NH2-MIL-125(Ti) the electron is located in the Ti-oxo clusters and the hole resides on the aminoterephthalate unit, specifically on the amino group. The results highlight the role of the amino group in NH2-MIL-125(Ti), the electron donation of which extends the lifetime of the photoexcited state substantially. ... Read more