Disequilibrating azobenzenes by visible-light sensitization under confinement

The ability to photoswitch azobenzenes from their stable E isomer to the metastable Z state is the basis of numerous applications of these molecules. However, this reaction typically requires UV light, which limits the applicability, particularly in biological settings. Here we introduce DisEquilibration by Sensitization under Confinement (DESC), a biomimetic approach to switch various azobenzenes using visible light of desired color, including red. DESC relies on a combination of a macrocyclic host and a photosensitizer, which act together to bind and selectively sensitize E-azobenzenes. After switching to the Z isomer, the azobenzene loses its affinity to—and is expelled from—the host, which can convert additional copies of E into Z. In this way, the host/photosensitizer complex acts as a light-driven supramolecular machine, converting photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed via direct photoexcitation.