A Versatile Strategy for Light-Driven Active Transport of Ions

Transport across compartments is essential for biology to drive its vital processes. Chemists have developed synthetic transport systems, focusing mainly on passive transport, where cargo species move along a concentration gradient. However, active transport-moving substances against a concentration gradient-remains a challenge. Light is a promising energy source for driving active transport due to its precise spatiotemporal control, high selectivity, and operation without waste accumulation. Yet only a few examples of light-driven active transport have been reported: these systems rely on specific host-guest interactions, which enable the transport of one particular species in each case. Here, we present a general, robust strategy for light-driven active transport of charged cargos, based on light-controlled membrane permeability and charge complementarity. Positively charged azobenzene derivatives act as light-responsive carriers, and their photoisomerization is coupled to transport across a liquid membrane by a molecular ratchet mechanism. Notably, their transport drives active transport of negatively charged cargos by forming ion pairs. This system can transport various anions, which are simply added as salt, and it functions even in buffered solutions. This approach utilizing charge complementarity is compatible with active transport driven by other energy sources and holds potential for biomedical applications and smart materials.