Red–blue light switch pushes equilibrium both ways

A molecular trap that exploits Le Chatelier’s principle, driving chemical reactions to overcome thermodynamic equilibrium, has been made by researchers in Germany. The trap is embedded in a reaction cycle in which different coloured light switches on different parts, so it can run forwards and backwards.

Left to their own devices, some reversible reactions (like esterifications or imine formations) reach equilibrium and never go to completion. These reactions can be driven forwards by physically removing one of the products – for example water using a Dean–Stark apparatus. Le Chatelier’s principle says that such a disturbed system will respond by moving towards a new equilibrium state, thereby producing more of the desired product

This system works in a similar way, but using light-driven photochemical reactions to remove molecules from one side or other of the equilibrium balance, pushing the reaction further in that direction. Similar dynamic reactions could be used to make self-healing polymers.