By building an anion receptor with a gap that can be widened or narrowed by shining light on it, you can specifically control which anion binds, Leiden researchers write in Chemical Communications.

Imitating nature is one of the specialities of chemists. Anion receptors are no exception. Making them yourself has obvious applications in sensing and transport. One popular synthetic anion receptor is calix[4]pyrrole, because of its strong affinity for halogen ions. Researchers in Sander Wezenberg’s group at Leiden University have created a light-activated variant: one isomer allows all kinds of halogens to enter, while the other keeps larger ions at bay.