Introduction to photoswitches and photopharmacology

Light-control has become an essential element in biomedical research and chemical biology, since photons offer the possibility of precisely confining biological activity in space and time. Employing light-responsive molecules that undergo a structural change upon irradiation, researchers have been able to engineer pharmacophores whose bioactivity can be modulated by suitable illumination. On the one hand, these molecules can be used to generate precise starting and end points in timesensitive experiments providing a clear advantage compared to uptake or diffusion-controlled systems. Rapid changes between active and inactive forms of a molecule can be used to trigger periodic signals in ion channels, for example. On the other hand, lightcontrol can be used to limit the activity of a photopharmacophore to a defined area, which is a highly sought-after property in drugs for medical applications. For drugs that cause side-effects due to their lack of specificity (e.g. anticancer agents), and those that cause resistance when accumulating in the environment (such as many antibiotics), photochemical modulation offers significant advantages, with the first molecules having entered clinical studies.