The project is aimed at the synthesis of a light-driven proton pump. The directed transport is driven by a photoactive molecule which undergoes a reversible rearrangement from a weak to a strong acid upon irradiation. The strong acid is able to protonate a transporter, e.g. the ring of a rotaxane, which carries the proton to the far end of the axis, releases the proton and returns to its starting position. Thus, pumping protons against a gradient ("uphill") should become feasible.