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 x 107 M-1) towards a rhodamine dicarboxylate anion and can capture 79% of the guest in CH3CN/H2O solution even at extremely low concentrations of both 1.0 x 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.