Effective guest uptake and release using an azobenzene-embedded molecular cage

Designing cages with switchable cavities towards guests is the key for effective drug loading and controlled release. For this purpose, a new asymmetrical molecular cage containing two aza-vertices and three linkers-one azobenzene group and two diphenyl ether units—was synthesized. After complexing with two copper ions onto the vertices, the formed di-metallic cage shows a strong binding affinity (Ka = 1.58 × 107 M−1) towards a rhodamine dicarboxylate anion and can capture 79% of the guest in CH3OH/H2O solution even at extremely low concentrations of both 1.0 × 10−6 M. Furthermore, owing to high E→Z photoisomerization efficiency of the embedded azobenzene unit, 84% of the loaded rhodamine guest would be released from the cage cavity by UV light irradiation.