Finally, a recent research effort -in part related to the development of molecular rotors -has focused on the incorporation of photoswitches into framework materials, to achieve stimuliresponsive photoswitchable materials. The interest in this direction comes from the possibility to expose photoswitches to the porosity of the materials and letting them interact with guest molecules. Sheng et al. reported in 2023 the construction of a porous and flexible aromatic framework, built from assembly of a bistable overcrowded alkene-based photoswitch. While the photoswitch molecule itself is a two-state system, the 3D porous framework exhibits three possible states (see Figure ), which can be interconverted by the application of external stimuli: presence of solvent or irradiation at different UV-visible wavelengths. The contraction of the framework's mesopores can be triggered by optical stimulation, and recovered by solvent-induced swelling. Moreover, in the contracted phase, a fully reversible light-induced solid-state photoisomerization is possible. This paved the way to the design of a new class of light-responsive materials, and indeed in a 2024 work by some of the same authors, Sheng et al. reported another example of multi-stimuli responsive porous frameworks. These spiropyran-grafted porous aromatic frameworks are dynamic materials that undergo reversible transformation of spiropyran to zwitterionic merocyanine, by either chemical and physical stimulation. Such a material could be used for a variety of application, including pH active control, photocontrolled gas uptake and release, and others.