White-light powered autonomous molecular ratchet drives PdII capsules out of equilibrium

Abstract

Using an energy source to drive chemical reactions away from equilibrium is essential for life and remains a significant challenge in designing artificial out-of-equilibrium nanosystems and molecular machines. Achieving autonomous operation of such systems, as observed in nature, presents an even greater difficulty. Here, we report Pd^II-mediated coordination capsules based on ligand 1 embedding an azobispyrazole photoswitch. The more thermodynamically stable Ephotoisomer forms an equilibrium mixture of a Pd^II₃(E-1)₆ double-walled triangle and a Pd^II₂(E-1)₄ lantern in a 78:22 ratio. UV-light irradiation transforms both structures into a Pd^II₂(Z-1)₄ lantern, which then reverts solely to the out-of-equilibrium Pd^II₂(E-1)₄ lantern when exposed to visible light. The complete photoisomerisation proceeds through an information ratchet mechanism that can operate autonomously under continuous white light or sunlight exposure, selectively accumulating the out-of-equilibrium Pd^II₂(E-1)₄ structure. This work demonstrates how autonomous, light-driven processes can be harnessed to direct non-equilibrium behaviour in complex coordination assemblies.