Harnessing Maxwell's demon to establish a macroscale concentration gradient.

Maxwell's demon describes a thought experiment in which a 'demon' regulates the flow of particles between two adjoining spaces, establishing a potential gradient without appearing to do work. This seeming paradox led to the understanding that sorting entails thermodynamic work, a foundational concept of information theory. In the past centuries, many systems analogous to Maxwell's demon have been introduced in the form of molecular information, molecular pumps and ratchets. Here we report a functional example of a Maxwell's demon that pumps material over centimetres, whereas previous examples operated on a molecular scale. In our system, this demon drives directional transport of o-fluoroazobenzene between the arms of a U-tube apparatus upon light irradiation, transiting through an aqueous membrane containing a coordination cage. The concentration gradient thus obtained is further harnessed to drive naphthalene transport in the opposite direction.