Light-Powered Reversible Guest Release and Uptake from Zn₄L₄ Capsules

Abstract

A strategy for light-powered guest release from a tetrahedral capsule has been developed by incorporating azobenzene units at its vertices. A new Zn₄L₄ 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 <i>trans</i> configuration to the <i>cis</i> 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 <i>trans</i> form, resulting in guest re-uptake. A detailed ¹⁹F NMR study elucidated how switching led to guest release: each metal vertex tolerated only one <i>cis</i>-azobenzene moiety, with further isomerization leading to cage disassembly.