Light-Powered Reversible Guest Release and Uptake from Zn 4 L 4 Capsules.

A strategy for light-powered guest release from a tetrahedral capsule has been developed by incorporating azobenzene units at its vertices. A new ZnL tetrahedral capsule bearing 12 diazo moieties at its metal-ion vertices was prepared from a phenyldiazenyl-functionalized subcomponent and a central trialdehyde panel. Ultraviolet irradiation caused isomerization of the peripheral diazo groups from the thermodynamically preferred configuration to the form, thereby generating steric clash and resulting in cage disassembly and concomitant guest release. Visible-light irradiation drove cage re-assembly following re-isomerization of the diazo groups to the form, resulting in guest re-uptake. A detailed F NMR study elucidated how switching led to guest release: each metal vertex tolerated only one -azobenzene moiety, with further isomerization leading to cage disassembly.