Assembly of a Highly Stable Luminescent Zn5 Cluster and Application to Bio-Imaging

The assembly sequence of the coordination cluster [Zn-5(H2Ln)(6)](NO3)(4)]8H(2)O2CH(3)OH (Zn-5, H3Ln=(1,2-bis(benzo[d]imidazol-2-yl)-ethenol) involves insitu dehydration of 1,2-bis(benzo[d]imidazol-2-yl)-1,2-ethanediol (H4L) through the formation of the [Zn(H3L)(2)](+) monomer, dimerization to [Zn-2(H3L)(2)](+), dehydration of the ligand to [Zn-2(H2Ln)(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% NH3, 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 invitro. 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 (13.5mm(3)).