A Water‐Soluble Polyoxometalate−Organic Cage as a Cargo Carrier for Hydrophobic Dyes

Poor water solubility has been a long‐standing barrier that keeps many promising candidates of small‐molecule drugs and fluorescent probes from clinical applications. Here we present a water‐soluble, hydrolysis‐resistant polyoxometalate–organic cage ( 3 ) with a large cavity (1848 Å 3 ) capable of hosting hydrophobic drugs and fluorophores. Remarkably, it can bind four oversized molecules of tetrakis(4‐carboxyphenyl)porphyrin by threading their hydrophobic branches into the cage cavity. Fluorescence imaging results show that the anionic cage allows water‐insoluble aloe emodin cargoes to be brought into human embryonic kidney and mouse hepatic cell environments and exhibits low cytotoxicity thanks to its good stability, paving the way for its use in live cell imaging, drug delivery, and photodynamic therapy.