One of these fascinating avenues of research is the development of framework linkers and molecular rotors that can be driven by light as a stimulus. Danowski et al. first demonstrated in 2019 the possibility of incorporating a light-driven molecular motor into a crystalline zinc pillared-paddlewheel MOF, through post-synthetic solvent-assisted linker exchange (SALE). In these materials, termed "moto-MOFs" and depicted on Figure , the unhindered 360°unidirectional rotation of the motor units was retained in the framework and, importantly, the rotary speeds were similar to those observed in solution. In 2020, the Feringa group demonstrated in further work the general nature of this approach, studying the photoisomerization of the molecular motor pillars in a porphyrin Zn-paddlewheel MOF. In this approach, two types of ligands where used: a palladium-porphyrin photosensitizer and a bispyridine-derived molecular motor. The authors could show that the proximity induced by the framework leads to efficient triplet-to-triplet energy transfer between the porphyrin linkers and the molecular motor, and that photochemical isomerization of the molecular motor can be achieved with green light (530 nm). These works highlight the potential for external control, through noninvasive stimuli such as visible light, of intraframework dynamics -and therefore open many perspec- tives for future applications. We also note that such work is not restricted to MOFs, but has also been reported in some covalent organic frameworks. In a related direction of research, Zhu et al. reported the synthesis and characterization of a flexible silver-based MOF with methylene molecular rotor and [Ag 2 (CN 4 ) 2 ] coordination mode of the metal ions. This MOF demonstrated controllable molecular rotation driven by water sorption, and the authors were able to create soft double-layer structures in combination with polyvinylidene fluoride. These composites could act as actuators, bending in the presence of water vapor or CH 3 SH, and exhibiting guest-induced fluorescence quenching. This is an interesting step towards the application of MOFs with molecular rotors in sensing applications or as actuators. A few other such examples can be found in the literature, including the study by Li et al. of seven dynamic MOFs based on rare-earth metals and including molecular rotor linkers, exhibiting a highly sensitive photoresponse to the binding of low concentrations of metal ions in aqueous solutions.