Assembly of a Highly Stable Luminescent Zn 5 Cluster and Application to Bio‐Imaging

The assembly sequence of the coordination cluster [Zn 5 (H 2 L n ) 6 ](NO 3 ) 4 ]⋅8 H 2 O⋅2 CH 3 OH ( Zn 5 , H 3 L n =(1,2‐bis(benzo[d]imidazol‐2‐yl)‐ethenol) involves in situ dehydration of 1,2‐bis(benzo[d]imidazol‐2‐yl)‐1,2‐ethanediol (H 4 L) through the formation of the [Zn(H 3 L) 2 ] + monomer, dimerization to [Zn 2 (H 3 L) 2 ] + , dehydration of the ligand to [Zn 2 (H 2 L n ) 2 ] + , and the final formation of the pentanuclear cluster. The cluster has the following special characteristics: 1) high stability in both refluxing 37 % HCl and 27 % NH 3 , 2) low cytotoxicity, and 3) pH‐sensitive fluorescence in the visible‐to‐near‐infrared (Vis/NIR) region in the solid state and in solution. We have applied it as a fluorescent probe both in vivo and in vitro. Its H‐bonding ability is the key to its affinity and selectivity for imaging lysosomes in HeLa cells and tumors in male BALB/C mice. It provides a new type of sensitive and biocompatible fluorescent probe for detecting small tumors (13.5 mm 3 ).