Researchers of Karlsruhe Institute of Technology (KIT) and Uni-versität Hannover developed novel membranes, whose selectivity can be switched dynamically with the help of light. For this pur-pose, azobenzene molecules were integrated into membranes made of metal-organic frameworks (MOFs). Depending on the irradiation wavelength, these azobenzene units in the MOFs adopt a stretched or angular form. In this way, it is possible to dynamically adjust the permeability of the membrane and the separation factor of gases or liquids. The results are reported in Nature Communications.