Having absolute control of the activity of a molecule in an organism, or deciding when, where and how a drug is activated—these are some of the goals possible with so-called photoswitchable molecules, compounds that change their properties in the presence of certain light waves. The results of a study led by the Institute for Bioengineering of Catalonia (IBEC) together with the Universitat Autònoma de Barcelona (UAB), bring objective this one step closer.